Volumetric plasma, systems and methods for generating same and uses thereof

Abstract

A volumetric plasma can be generated between a first electrode and a second electrode. The first and second electrodes can be separated from each other by a gap. The first electrode can include a first base layer and a plurality of first protruding portions extending along a first direction from the first base layer toward the second electrode. The first base layer can include a first conductive material. At least some of the first protruding portions can include a second conductive material. The melting temperature of the first conductive material and the melting temperature of the second conductive material can be at least 1000 K. During generation of the volumetric plasma, the temperature of the volumetric plasma between the first electrode and the second electrode can be within a range of 1000 to 8000 K, inclusive.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 378,215, filed October 3, 2022, entitled "Tip-Enhanced Volumetric Plasma and Its Production and Use," and U.S. Provisional Patent Application No. 63 / 513,567, filed July 13, 2023, entitled "Uniform Ultra-High Temperature Stable Plasma Operating at Atmospheric Pressure for the Synthesis of Extreme Materials," each of which is incorporated herein by reference in its entirety.

[0002] (Statement Regarding Federally Sponsored Research) This invention was made with government support under DESC0020233 awarded by the U.S. Department of Energy (DOE). The U.S. Government has certain rights in this invention.

[0003] (Technical field) The present disclosure relates generally to plasma systems and methods, and more particularly to the generation and use of volumetric plasma, for example, by applying an electric field between electrodes. [Background technology]

[0004] Plasma is formed when an electric field electronically and vibrationally excites molecules through an electron bombardment process. While plasma has been used for materials processing such as reactive ion etching and thin film deposition, it remains challenging to use conventionally generated plasmas in the fabrication of large-scale bulk materials, especially materials with high melting points. For such fabrication, large areas or volumes (e.g., >1 cm) are required. 2 ) may be preferred. Volumetric plasmas, such as glow discharges, have been demonstrated. However, flow discharges typically require low pressures (e.g., <150 Torr) and require high plasma neutral gas temperatures (T g ) is the electron temperature (T eAs a result of the low neutral gas temperature (e.g., <1000 K), the ability of glow discharge to process high temperature materials with particularly high yields is limited.

[0005] Arc discharges can be used to generate high-temperature plasmas (e.g., up to 10,000 K) at atmospheric pressure, but the generated plasma can have spatially nonuniform temperatures and be unstable. In particular, atmospheric arc discharges between conventional plate electrodes constrict into narrow, random arc channels (e.g., diameters of ~1 mm), and the resulting temperature distribution is highly nonuniform. Pin-to-pin electrodes can help avoid random discharges. For example, a high curvature of the electrode (e.g., a radius of several mm) can increase the local electric field strength and promote thermionic emission of secondary electrons. However, such pin structures can confine the arc plasma to a narrow channel with a limited plasma volume. The use of a rotating gliding arc can increase the discharge volume, but the plasma channel remains a narrow filament with nonuniform distributions of temperature and activated species. Summary of the Invention [Problem to be solved by the invention]

[0006] Embodiments of the disclosed subject matter may address, among other things, one or more of the problems and shortcomings set forth above. [Means for solving the problem]

[0007] Embodiments of the disclosed subject matter provide systems and methods for generating volumetric plasmas, as well as uses of such volumetric plasmas, for example, to expose a sample (e.g., precursor, reactant, or other material) to high temperatures over a relatively large area with improved temporal stability and / or spatial uniformity. In some embodiments, the volumetric plasma can be generated by applying a voltage between a pair of electrodes separated by a gap. The surface of at least one of the electrodes facing the gap can have a dense array of first protruding portions extending toward the other electrode. The array of first protruding portions can generate multiple concentrated electric fields that converge across the electrodes, which can accelerate Townsend breakdown to arc discharge transition and expand the initial spark discharge into volumetric plasma. In some embodiments, the surface of at least one of the electrodes facing the gap can have one or more longer protruding portions extending toward the other electrode farther than the first protruding portion so as to contact one or more portions of the other electrode or to be closely spaced from one or more portions of the other electrode. A longer protrusion can help initiate a plasma via a spark discharge at a lower breakdown voltage.

[0008] In one or more embodiments, a method can include generating a volumetric plasma between a first electrode and a second electrode separated from each other by a gap. The first electrode can include a first base layer and a plurality of first protruding portions extending from the first base layer toward the second electrode along a first direction. The first base layer can include a first conductive material. At least some of the first protruding portions can include a second conductive material. The melting temperature of the first conductive material and the melting temperature of the second conductive material can be at least 1000 K. During generation, the temperature of the volumetric plasma between the first electrode and the second electrode can be in the range of 1000 to 8000 K, inclusive.

[0009] In one or more embodiments, the system may include first and second electrodes, a power source, and a control system. The first electrode may include a first base layer and a plurality of first protruding portions. The first base layer may include a first conductive material. At least some of the first protruding portions may include a second conductive material. The melting temperature of the first conductive material and the melting temperature of the second conductive material may be at least 1000 K. The second electrode may be spaced apart from the first electrode by a gap. The plurality of first protruding portions may extend along a first direction from the first base layer toward the second electrode. A power source may be electrically coupled to the first and second electrodes. The control system may be operably coupled to the power source and configured to control operation of the power source. The control system may include one or more processors and a computer-readable storage medium storing instructions that, when executed by the one or more processors, cause the power source to apply a voltage between the first electrode and the second electrode such that a volumetric plasma is generated in or adjacent to the gap. The temperature of the bulk plasma may be in the range of 1000 to 8000 K inclusive.

[0010] Any of the various innovations of the present disclosure can be used in combination or separately. This Summary is provided to introduce a selection of concepts in a simplified form that are further described in the Detailed Description below. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. The foregoing and other objects, features, and advantages of the disclosed technology will become more apparent from the following Detailed Description, which proceeds with reference to the accompanying drawings. [Brief explanation of the drawings]

[0011] Embodiments will now be described with reference to the accompanying drawings, which are not necessarily drawn to scale. Where applicable, some elements may be simplified or otherwise not shown to help illustrate and explain the underlying features. Like reference numbers refer to like elements throughout the drawings. [Figure 1A] FIG. 1A is a simplified schematic diagram of a system having an electrode with a protruding portion for generating a volumetric plasma in accordance with one or more embodiments of the disclosed subject matter. [Figure 1B] FIG. 1B is a simplified schematic diagram of another system having a pair of electrodes with protruding portions for generating a volumetric plasma in accordance with one or more embodiments of the disclosed subject matter. [Figure 2A] FIG. 2A is a simplified perspective view of an electrode with a protruding portion, according to one or more embodiments of the disclosed subject matter. [Figure 2B] FIG. 2B is a simplified perspective view of a cloth electrode having fiber protruding portions, according to one or more embodiments of the disclosed subject matter. [Figure 2C] FIG. 2C shows a plan view of another cloth electrode with bundles of fiber protruding portions, in accordance with one or more embodiments of the disclosed subject matter. [Figure 2D] FIG. 2D shows an image of a carbon felt electrode with bundles of fiber protrusions, according to one or more embodiments of the disclosed subject matter. [Figure 2E] FIG. 2E shows a scanning electron microscope (SEM) image of the sharp distal tip of the fiber protruding portion of the carbon felt electrode, according to one or more embodiments of the disclosed subject matter. [Figure 2F-2G] 2F-2G are cross-sectional and plan views of an electrode having a protruding portion with a two-dimensional sharp distal tip, in accordance with one or more embodiments of the disclosed subject matter. [Figures 2H-2I] 2H-2I are cross-sectional and plan views of electrodes having protruding portions with blunt distal tips, in accordance with one or more embodiments of the disclosed subject matter. [Figure 3A]FIG. 3A is a simplified schematic diagram of a system having a pair of electrodes with short and long protrusions for generating a volumetric plasma in accordance with one or more embodiments of the disclosed subject matter. [Figure 3B] FIG. 3B is a SEMS image of a carbon felt electrode having short and long fiber protrusions, according to one or more embodiments of the disclosed subject matter. [Figure 3C] FIG. 3C illustrates an aspect of using protruding portions of short and long fibers to initiate and generate plasma, according to one or more embodiments of the disclosed subject matter. [Figure 3D] FIG. 3D is a graph showing current-voltage characteristics for initiating and generating a plasma using short and long fiber protrusions, in accordance with one or more embodiments of the disclosed subject matter. [Figures 3E-3F] 3E-3F are simplified schematic diagrams of a system using electrodes with short and long protrusions to generate volumetric plasma in accordance with one or more embodiments of the disclosed subject matter. [Figure 3G] FIG. 3G is a simplified schematic diagram of a system that uses an external trigger to initiate a volumetric plasma, in accordance with one or more embodiments of the disclosed subject matter. [Figure 3H] FIG. 3H illustrates an aspect of initiating and maintaining a volumetric plasma by varying the gap distance between the protruding portions of a pair of electrodes, according to one or more embodiments of the disclosed subject matter. [Figure 4A] FIG. 4A illustrates an aspect of treating a pellet using a generated volumetric plasma in accordance with one or more embodiments of the disclosed subject matter. [Figure 4B] FIG. 4B illustrates an aspect of treating one or more precursors using a generated volumetric plasma in accordance with one or more embodiments of the disclosed subject matter. [Figure 4C] FIG. 4C illustrates an aspect of using a generated volumetric plasma to treat one or more precursor particles carried by a gas flow, according to one or more embodiments of the disclosed subject matter. [Figure 4D]FIG. 4D illustrates an aspect of using a generated volumetric plasma to process one or more reactant streams into one or more products, according to one or more embodiments of the disclosed subject matter. [Figures 4E-4F] 4E-4F illustrate aspects of gravity-driven processing of one or more precursor particles using a generated volumetric plasma, according to one or more embodiments of the disclosed subject matter. [Figure 4G] FIG. 4G illustrates an aspect of using a generated volumetric plasma to process one or more precursor particles into a fine powder, according to one or more embodiments of the disclosed subject matter. [Figure 4H-4I] 4H-4I are perspective cross-sectional and plan views, respectively, of a coaxial electrode configuration for generating a volumetric plasma in accordance with one or more embodiments of the disclosed subject matter. [Figures 4J-4K] 4J-4K illustrate cross-sectional and plan views of another coaxial electrode configuration for generating a focused volumetric plasma in accordance with one or more embodiments of the disclosed subject matter. [Figure 5A] FIG. 5A is a simplified schematic diagram of a system for generating and scanning a volumetric plasma in accordance with one or more embodiments of the disclosed subject matter. [Figure 5B] FIG. 5B is a simplified perspective view of a power bed melting / sintering system using a volumetric plasma in accordance with one or more embodiments of the disclosed subject matter. [Figure 5C] FIG. 5C is a simplified schematic diagram illustrating aspects of a plasma sintering / fusion process using a focused volumetric plasma beam, in accordance with one or more embodiments of the disclosed subject matter. [Figure 5D-5E] 5D-5E are top and side views of a support electrode configuration for generating a volumetric plasma in accordance with one or more embodiments of the disclosed subject matter. [Figure 5F] FIG. 5F is a simplified cross-sectional view of a volumetric plasma system employing a support electrode configuration in accordance with one or more embodiments of the disclosed subject matter. [Figure 6A] FIG. 6A is a simplified process flow diagram of a method for generating and using a volumetric plasma in accordance with one or more embodiments of the disclosed subject matter. [Figure 6B] FIG. 6B depicts a generalized example of a computing environment in which the disclosed technology may be implemented. [Figure 7A] FIG. 7A is a graph showing the measured temperature profile of a plasma generated using a carbon felt electrode. [Figure 7B] Figure 7B is an image of the experimental setup that uses carbon felt electrodes to generate volumetric plasma. [Figure 7C] FIG. 7C shows an image of a pair of carbon felt electrodes with short and long fibers, as well as an SEM image of a short fiber on one of the carbon felt electrodes. [Figure 7D] FIG. 7D shows an SEM image of short fibers on a carbon felt electrode after plasma generation. [Figure 7E] FIG. 7E is a graph showing the temperature of the central region of a plasma generated using a pair of carbon felt electrodes as a function of input current. [Figure 8A] FIG. 8A is a graph of the applied voltage and measured electric field between carbon felt electrodes via electric field-induced second harmonic (E-FISH) generation. [Figure 8B] FIG. 8B is a graph of voltage-current versus time showing pulsed plasma operation of a pair of carbon felt electrodes. [Figure 9A] Figure 9A shows the X-ray diffraction analysis (XRD) pattern of Hf(C,N) synthesized using volume plasma generated by a pair of carbon felt electrodes. [Figure 9B] Figure 9B shows the XRD pattern of vitreous MgO synthesized using a volume plasma generated by a pair of carbon felt electrodes. [Figure 9C] FIG. 9C shows an image of the conversion of carbon black to carbon nanotubes using volumetric plasma. [Figure 10A] FIG. 10A is a cross-sectional SEM image of a tungsten sample synthesized using focused volume plasma in a powder bed fusion / sintering process. [Figure 10B]Figure 10B is a cross-sectional SEM image of a high-entropy diboride (HEB) coating on a Nb-10Hf-1Ti alloy substrate synthesized using volume plasma. [Figure 11] FIG. 11 shows the XRD patterns of the mixed powder precursor and atomized MoNbTaW alloy powder synthesized from the precursor using volume plasma. DETAILED DESCRIPTION OF THE INVENTION

[0012] ( General Considerations ) For purposes of this specification, certain aspects, advantages, and novel features of the disclosed embodiments are described herein. The disclosed methods and systems should not be construed as limiting in any way. Instead, the present disclosure covers all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and subcombinations with each other. The methods and systems are not limited to any particular aspect, feature, or combination thereof, and the disclosed embodiments do not require that any one or more particular advantages exist or problems be solved. Techniques from any embodiment or example can be combined with techniques described in any one or more of the other embodiments or examples. Given the many possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are illustrative only and should not be construed as limiting the scope of the disclosed technology.

[0013] Although some operations of the disclosed methods are described in a particular order for convenient presentation, it should be understood that this manner of description encompasses reordering unless a specific ordering is required by specific language described below. For example, operations described sequentially may in some cases be reordered or performed simultaneously. Moreover, for simplicity, the accompanying drawings may not show the various ways in which the disclosed methods may be used in conjunction with other methods. Furthermore, the description may use terms such as "provide" or "achieve" to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations corresponding to these terms may vary depending on the particular implementation and are readily discernible by those skilled in the art.

[0014] The disclosure of numerical ranges should be understood to refer to each discrete point within the range, including the endpoints, unless otherwise specified. Unless otherwise indicated, all numbers expressing amounts of ingredients, molecular weights, percentages, temperatures, times, etc. used in this specification or claims should be understood to be modified by the term "about." Thus, unless otherwise implicitly or explicitly indicated, or unless the context would be understood by one of ordinary skill in the art to have a clearer configuration, the numerical parameters described are approximations that may depend on the desired properties sought and / or the limits of detection under standard testing conditions / methods, as known to those skilled in the art. When directly and explicitly distinguishing an embodiment from the discussed prior art, an embodiment number is not an approximation unless the words "about," "substantially," or "approximately" are recited. Whenever "substantially," "approximately," "about," or similar language is expressly used in conjunction with a particular value, a variation of up to 10% of that value is intended, unless expressly stated otherwise.

[0015] Directions and other relative references may be used to facilitate explanation of the figures and principles herein but are not intended to be limiting. For example, terms such as "inner," "outer," "upper," "lower," "top," "bottom," "internal," "external," "left side," "right side," "front," "rear," "rear," etc. may be used. Such terms are used, where applicable, to provide some clarity of description, particularly when dealing with relative relationships with respect to the illustrated embodiments. However, such terms are not intended to imply absolute relationships, positions, and / or orientations. For example, with respect to an object, an "upper" portion can become a "lower" portion simply by rotating the object. Nevertheless, it is still the same portion, and the object remains the same.

[0016] As used herein, "comprising" means "including," and the singular forms "a" or "an" or "the" include plural references unless the context clearly dictates otherwise. The term "or" refers to a single element or a combination of two or more of the referenced alternative elements, unless the context clearly dictates otherwise.

[0017] Although there are alternatives for the various components, parameters, operating conditions, and the like described herein, these alternatives are not necessarily equivalent or will perform equally well. Nor is it intended to imply that the alternatives are listed in order of preference unless otherwise specified. Unless otherwise specified, any of the groups defined below may be substituted or unsubstituted.

[0018] Unless otherwise explained, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of this disclosure, suitable methods and materials are described below. The materials, methods, and examples are illustrative only and are not intended to be limiting. Features of the subject matter of this disclosure will become apparent from the following detailed description and the appended claims.

[0019] Terminology Overview The following is provided to facilitate a description of various aspects of the disclosed subject matter and to guide those of ordinary skill in the art in practicing the disclosed subject matter.

[0020] Volumetric plasma: A three-dimensional volume of electrons, ions, and / or excited molecules that is generated and / or maintained by applying an electric field between electrodes. In some embodiments, the plasma can be generated by applying a direct current (DC) voltage, an alternating current (AC) voltage (e.g., radio frequency (RF), e.g., in the range of 3 kHz to 300 GHz), or other waveform (e.g., pulsed voltage waveform) between the electrodes.

[0021] Cloth or felt: A structure formed of a plurality of fibers, e.g., woven together (e.g., to form a cloth) or otherwise bonded together (e.g., by matting, condensing, and / or compressing the fibers together to form a felt). In some embodiments, the cloth or felt may be formed from carbon or metal fibers (e.g., a refractory metal or refractory metal alloy). In some embodiments, carbon cloth or felt may be formed by carbonizing polyacrylonitrile (PAN) or rayon fibers (e.g., at a temperature of at least 1000 K).

[0022] Inert atmosphere: An atmosphere of one or more gases that do not undergo chemical reactions when exposed to the temperatures of the generated plasma. In some embodiments, each gas in the inert atmosphere is selected from the group consisting of nitrogen, argon, helium, neon, krypton, xenon, radon, and oganesson.

[0023] Refractory material: A material (e.g., an element or compound) having a melting point (e.g., at atmospheric pressure) of at least 1000 K, e.g., at least 1850 K (-1580°C). In some embodiments, refractory material is defined in ASTM C71-01, "Standard Terminology for Refractories," August 2017, which is incorporated herein by reference; in some embodiments, the refractory material can be carbon (e.g., graphite, carbon cloth, carbon felt, carbon nanotubes), a refractory metal, a refractory metal alloy, a refractory ceramic, or any combination thereof.

[0024] Refractory metal or refractory metal alloy: A metal or metal alloy having a melting point (e.g., at atmospheric pressure) of at least 1000 K, e.g., at least 2100 K (-1850°C). In some embodiments, the refractory metal can be niobium, molybdenum, tantalum, tungsten, rhenium, alloys thereof, or any combination thereof.

[0025] Refractory ceramic: An inorganic oxide, nitride, boride, or carbide material having a melting temperature (e.g., at atmospheric pressure) of at least 1000 K. In some embodiments, the ceramic is electrically conductive, e.g., at room temperature, at least 10 -2The ceramic has a conductivity of 0.1 S / cm. In some embodiments, the ceramic can be a metal carbide, a metal nitride, a metal diboride, silicon carbide, or any combination thereof. In some embodiments, the metal carbide can be tantalum carbide, hafnium carbide, zirconium carbide, niobium carbide, titanium carbide, or any combination thereof. In some embodiments, the metal nitride can be tantalum nitride, hafnium nitride, zirconium nitride, niobium nitride, titanium nitride, or any combination thereof. In some embodiments, the metal diboride can be tantalum diboride, hafnium diboride, zirconium diboride, niobium diboride, titanium diboride, or any combination thereof.

[0026] Refractory High Entropy Superalloy (RHEA): An alloy formed from five or more elements in substantially equal proportions, at least some of which are refractory metals.

[0027] Powder: A plurality of particles, each having a maximum cross-sectional dimension (e.g., diameter when the particles are spherical) of about 1 mm or less. In some embodiments, the specified particle size represents the average particle size (e.g., average of the maximum cross-sectional dimensions) of all particles. In some embodiments, particle size can be measured according to one or more known standards, such as, but not limited to, ASTM B214-16, entitled "Standard Test Method for Sieve Analysis of Metal Powders," ASTM B330-20, entitled "Standard Test Method for Estimation of Mean Particle Size of Metal Powders and Related Compounds Using Air Permeability," ASTM B822-20, entitled "Standard Test Method for Particle Size Distribution of Metal Powders and Related Compounds by Light Scattering," and ASTM B922-20, entitled "Standard Test Method for Specific Surface Area of ​​Metal Powders by Physical Adsorption," which are incorporated herein by reference.

[0028] Nanoparticle: An engineered particle formed from one or more elements and having a maximum cross-sectional dimension (e.g., diameter when the particle is spherical) of about 1 μm or less, e.g., about 500 nm or less. In some embodiments, the nanomaterial has a maximum cross-sectional dimension of about 300 nm or less, e.g., in the range of 10-100 nm. In some embodiments, the nanomaterial is formed from at least two elements, e.g., three or more elements.

[0029] (Introduction) Disclosed herein are systems and methods for generating volumetric plasma and its uses, e.g., for material synthesis, manufacturing, and / or catalysis. In some embodiments, the generated volumetric plasma has a relatively large area (e.g., ≥ 1 cm). 2 ) can exhibit high temperatures (e.g., >1000 K, e.g., 3000-8000 K). In some embodiments, the generated volumetric plasma can exhibit improved temporal stability, improved spatial uniformity, or both. For example, the volumetric plasma can be substantially stable over time, with a peak temperature at a point within the volume, an average temperature across the volume, and / or a temperature at a point within the volume that varies by no more than 10% over at least 1 minute (e.g., ≥10 minutes). Alternatively or additionally, the volumetric plasma can have a substantially uniform temperature across its volume (or at least across its lateral region in a plane perpendicular to the gap thickness), e.g., the temperature at each point within the plasma is no more than 10% from the peak temperature or the average temperature across the plasma.

[0030] Volumetric plasma can be generated by applying a voltage between a pair of electrodes separated by a gap, with at least one surface of the electrode facing the gap having multiple protruding portions (e.g., pillars, fibers, tips, or other surface protrusions). The use of protruding portions can help reduce the voltage required for gas breakdown or allow for achieving uniform volumetric plasma at lower currents and powers. In particular, the protruding portions can create enhanced electric fields that converge across the surface of the electrodes, accelerating Townsend breakdown to arc transition, expanding plasma size and volume, and increasing plasma uniformity, unlike conventional arc discharges. Furthermore, the expansion can create a collective heating effect that can help stabilize the plasma.

[0031] For example, FIG. 1A shows a plasma generation system 100 having a first electrode 102, a second electrode 104, a power supply 108, and a controller 110. In the illustrated example, the first electrode 102 is separated from the second electrode 104 by a gap 106 of thickness g and has multiple 114 first protruding portions 116 extending toward the second electrode 104 (e.g., along the y-direction). In some embodiments, the thickness g of the gap 106 can be less than 10 cm, for example, in the range of 1 mm to 1 cm. A voltage (DC, AC, or other waveform, such as a pulsed voltage waveform) can be applied across the electrodes 102, 104 by the power supply 108 to form a volumetric plasma 118 within the gap 106. In some embodiments, the peak voltage applied between the electrodes 102, 104 during the volumetric plasma 118 may be 100 V or less (e.g., ≦50 V), and / or the peak current between the electrodes 102, 104 may be 100 A or less (e.g., ≦50 V).

[0032] In some embodiments, the volumetric plasma 118 can be generated at any pressure, e.g., in the range of 1 Torr to 10 atmospheres (atm), with or without the application of a magnetic field. For example, the volumetric plasma 118 can be generated at atmospheric pressure (e.g., about 1 atm). In some embodiments, the volumetric plasma 118 can exhibit a substantially uniform temperature across the lateral extent 120 of the plasma (e.g., in the xz plane). In some embodiments, the lateral extent 120 of the volumetric plasma 118 can be at least 1 mm, e.g., in the range of 1 mm to 100 cm. In some embodiments, the temperature at various points along the lateral extent 120 of the volumetric plasma 118 can be measured as a plasma temperature T P Within a narrow band 122 around, for example, 10% or less of the plasma temperature (e.g., T P = 1000 K, the band may be ±50 K). In some embodiments, the plasma temperature T P can be at least 1000 K, e.g., in the range of 3000-8000 K. Alternatively, in some embodiments, the volumetric plasma 118 can be a non-thermal or low-temperature plasma, e.g., where the temperature of electrons is above 1000 K (e.g., in the range of 3000-8000 K), while the temperature of heavier species (e.g., ions and neutrals) is below 1000 K (e.g., at or near room temperature). In some embodiments, the plasma temperature T P may be the average temperature over the lateral extent 120 of the volumetric plasma, or the temperature at the center of the lateral extent 120 of the plasma (e.g., in the xz plane).

[0033] In some embodiments, the plasma temperature T Pcan be varied by selecting or varying the power input from the power source 108 (e.g., with higher power corresponding to higher temperature), by selecting or varying the spacing of the gap 106 (e.g., with a smaller gap corresponding to higher temperature), and / or by selecting or varying the gas pressure between the two electrodes 102, 104 (e.g., with a higher pressure corresponding to higher temperature). In some embodiments, the volumetric plasma can be varied by, for example, varying the lateral extent 120 and / or the plasma temperature T P The temperature profile over the period may be stable in time, such that it remains approximately the same for any period of time, e.g., at least 1 minute (e.g., ≧10 minutes), for a substantially constant power input (e.g., power of a DC signal, power and frequency of an AC signal, power and frequency of a pulsed voltage waveform, etc.).

[0034] The controller 110 can control the operation of the power supply 108, e.g., the timing, application, and / or magnitude of the voltage, current, or power applied across the electrodes 102, 104, thereby controlling the characteristics (e.g., on / off, temperature, etc.) of the volumetric plasma. In the illustrated example, the controller 110 is operably coupled to the power supply 108. Alternatively or additionally, the controller 110 and the power supply 108 can be considered part of a single system, e.g., different modules of the control system 124. In some embodiments, the controller 110 can control other aspects of the system 100, e.g., the size of the gap 106 and / or the pressure between the electrodes 102, 104.

[0035] In the example shown in FIG. 1A , protruding portions extend from the base layer 112 of the first electrode 102. In some embodiments, the protruding portions may be disposed on or formed from a surface of the base layer 112, such as the pillars 116a of the plurality 114a in the top inset of FIG. 1A . Alternatively or additionally, in some embodiments, the protruding portions are exposed or truncated surface portions of the base layer 112, such as the fibers 116b, 114b in the bottom inset of FIG. 1A . In some embodiments, each protruding portion 116 can have a cross-sectional dimension (e.g., a maximum or minimum cross-sectional dimension in the x-z plane, e.g., a diameter) d of 500 μm or less. In some embodiments, the cross-sectional dimension d of the protruding portions 116 may be greater than 1 μm, for example, in the range of 1 to 100 μm. In some embodiments, the cross-sectional dimension d may represent the average of each of the protruding portions 116, with the cross-sectional dimensions of the protruding portions 116 being within 10% of the average.

[0036] In some embodiments, the spacing s between adjacent protruding portions 116 (e.g., along the x-direction, along the z-direction, and / or along the xz plane) can be 1 mm or less. In some embodiments, the spacing s can be about the same as or less than the cross-sectional dimension d, e.g., 100 μm or less (e.g., in the range of 1-50 μm). In some embodiments, the spacing s can represent an average spacing across the plurality 114. In some embodiments, the individual spacing between pairs of protruding portions 116 can be within 10% of the average. In some embodiments, the combination of the cross-sectional dimension d and the spacing s can result in a center-to-center spacing c of less than 1 mm, e.g., 1-100 μm. Alternatively or additionally, the plurality 114 of protruding portions can be spaced apart by more than 1 cm. 2 At least 10 per 4 10 protruding portions, e.g., about 10 5 pieces of protrusion / cm 2 The concentration of can be shown.

[0037] Alternatively or additionally, the spacing s may be greater than the Debye length (λ) of the system 100. D ) or may be approximately the same (e.g., within an order of magnitude) as the Debye length (λD ) represents the distance over which charges become increasingly electrically screened and the potential decreases exponentially by 1 / e, where e is the electron charge. The Debye length can be calculated by the following formula: TIFF2025535710000002.tif17166

[0038] where k B is Planck's constant (1.38e -23 J / K=8.617e -5 eV / K) and T e is the electron temperature (e.g., about 4000-8000 K), and n e is the electron density (e.g., about 10 -12 cm -3 ) and ε is the plasma dielectric constant (e.g., 55.26 e -2 / (eV μm)). In some embodiments, at spacings close to the Debye length, the electric fields generated by the protrusions can coalesce during the initial stages of plasma formation, which can aid in the formation of a uniform volumetric plasma. For example, T e = 8000K and n e =10 12 cm -3 Assuming that the Debye length (λ D ) can be estimated to be about 6.2 μm, and the spacing s can be in the range of 1 to 10 μm.

[0039] In some embodiments, the length h of the protruding portion 116 (e.g., along the y-direction from the surface of the base layer 112) can be greater than its cross-sectional dimension d. Alternatively or additionally, the length h of the protruding portion 116 can be less than the gap size g. In some embodiments, the length h of the protruding portion 116 can be greater than or equal to 100 μm and / or less than or equal to 1 cm, e.g., in the range of 200-500 μm. In some embodiments, the length h can represent an average length across the plurality of protruding portions 114. In some embodiments, the length of each protruding portion 116 can be within 10% of the average. In some embodiments, each protruding portion can be substantially straight and extend substantially parallel to the thickness of the gap (e.g., parallel to the y-direction), as shown, for example, by pillar 116a in FIG. 1A. Alternatively or additionally, in some embodiments, each protruding portion can deviate from being substantially straight along at least a portion of its length and / or can have a portion that is angled relative to the thickness of the gap (e.g., extending in the xz plane), as shown, for example, by fiber 116b in FIG. 1B, in which case the length h can be the distance that the protruding portion extends along the y direction.

[0040] In some embodiments, the first electrode 102 and the second electrode 104 can be formed of a conductive material that can withstand plasma temperatures, e.g., having a melting temperature (e.g., atmospheric pressure) that is at least 1000 K. For example, the first electrode 102 and / or the second electrode 104 can be formed of a refractory material (e.g., carbon, a refractory metal or alloy, and / or a refractory ceramic). In some embodiments, the base layer 112 of the first electrode 102 can be formed of a conductive material that is different from the conductive material of the plurality of protruding portions 114. For example, the base layer can be graphite, and the protruding portions can be a refractory metal (e.g., when the pillars 116a are formed on the base layer 112). Alternatively, in some embodiments, the base layer 112 and the protruding portions can be formed of the same conductive material (e.g., when the fibers 116b constitute both the plurality of protruding portions 114 and the base layer 112).

[0041] In the example shown in FIG. 1A , the second electrode 104 is provided as a planar electrode without any protruding portions. In some embodiments, the first electrode 102 with the protruding portions can operate as an anode, and the second electrode 104 without the protruding portions can operate as a cathode. However, in some embodiments, the second electrode 104 can have its own protruding portions. For example, FIG. 1B shows a plasma generation system 130 including a first electrode 102, a second electrode 134, a power supply 108, and a controller 110. Similar to the example of FIG. 1A , the first electrode 102 has a plurality 114 of protruding portions on the base layer 112 separated from the second electrode 134 by a gap 136 of thickness g. However, the second electrode 134 has another plurality 144 of protruding portions on the base layer 142, which can have the same or different configurations (e.g., shape, size, spacing, and / or material) as the plurality 114 of the first electrode 102.

[0042] In some embodiments, the volumetric plasma 118 may be used for material synthesis or processing (e.g., bulk materials, powders, nanoparticles, nanotubes, nanomaterials), chemical reactions (e.g., to convert one or more reactants into one or more products with or without a catalyst), sterilization (e.g., using low-temperature plasma to treat food or medical devices), or any other purpose for which application of plasma temperatures may be useful. In some embodiments, the plasma generating system may provide for rapid cooling (e.g., within 10 seconds) after application of high temperatures, for example, by removing the treated material from the volumetric plasma, reducing the temperature of the volumetric plasma, turning off the volumetric plasma, and / or providing active cooling modalities (e.g., airflow directed at the treated material, use of a heat exchanger, etc.). 3 ~10 5 Within the range of K / s, e.g., ≥ 10 2 K / s) can be provided.

[0043] Electrode configuration example In some embodiments, one or both electrodes in a plasma generation system can include an array of protruding portions. For example, FIG. 2A illustrates an electrode 200 configuration having a two-dimensional array (e.g., in the xz plane) of protruding portions 204 formed on a substantially planar base layer 202. In the example illustrated in FIG. 2A, the protruding portions 204 are shaped as rounded pillars or rods, although other shapes are possible according to one or more contemplated embodiments. In some embodiments, the base layer 202 and at least some of the protruding portions 204 can be constructed from a refractory material, such as a refractory metal.

[0044] In some embodiments, the protruding portions 204 can be formed by a three-dimensional printing modality, such as, but not limited to, laser-based direct energy deposition or laser powder bed fusion. Alternatively or additionally, in some embodiments, the array of protruding portions can be formed from an underlying base layer, for example, by cutting, sanding, and / or roughening the surface of a cloth or felt formed from refractory material fibers (e.g., carbon or metal fibers). For example, FIG. 2B shows a configuration of an electrode 210 having protruding portions 212 formed by fibers fragmented and / or exposed at the cut surface of a carbon cloth.

[0045] In some embodiments, the underlying base layer can include woven fibers, and the protruding portions can be arranged in bundles based on the weave pattern. For example, FIGS. 2C-2D show an electrode 220 configuration having bundles 222a-222c of cut fibers 224 held together but separated by laterally oriented fibers 226. Within each bundle 222a-222c, the cut fibers 224 can be separated from one another (e.g., along the xz plane) by an intra-bundle spacing s1 similar to the spacing s described above with respect to FIG. 1A. Between bundles (e.g., between bundles 222a and 222b in FIG. 2C), adjacent cut fibers 224 are spaced apart by a bundle spacing s that is greater than the intra-bundle spacing s1. b, for example, can be separated by 500 μm or less (e.g., 50-250 μm). In some embodiments, the transversely oriented fibers 226 can function as a base or support layer, and the cut fibers 224 extending beyond the transversely oriented fibers 226 (e.g., along the y-direction) function as protruding portions.

[0046] In some embodiments, the exposed end of the protruding portion (e.g., adjacent the gap) can have a narrowed or tapered shape, e.g., a one-dimensional tip. For example, FIG. 2E shows a configuration of an electrode 230 having a bundle 232 of cut fibers 234 sharpened to a conical tip 236, which can further reduce the arcing barrier. In some embodiments, the sharpening of the fiber tip can be the result of initial plasma generation. For example, after the initial plasma breakdown, the tip of a carbon fiber can gradually sharpen to a conical shape due to temperature and local electric fields. Other ways of sharpening the tip are also possible according to one or more contemplated embodiments. Alternatively or additionally, in some embodiments, the protruding portion can have a tip that is narrowed or tapered in only one dimension, e.g., forming a two-dimensional tip. For example, Figures 2F-2G show a configuration of an electrode 240 having elongated protruding portions 244 formed on a base layer 242, each of which can have a respective two-dimensional distal tip 246 (e.g., a knife edge).

[0047] Alternatively or additionally, in some embodiments, the protruding portions can be formed as protruding surface features of an underlying bulk component, e.g., a rounded or blunt distal tip. For example, FIGS. 2H-2I illustrate a configuration of an electrode 250 having multiple protruding portions formed by surface features 252a of an underlying base layer 252b. In the example shown in FIGS. 2H-2I, the protruding portions are rounded bumps 254 surrounded by concave portions 256. The bumps 254 can have a maximum cross-sectional dimension w (e.g., along the x-z plane) similar to the cross-sectional dimension d described above with respect to FIG. 1A, and / or the bumps 254 can be separated from adjacent bumps (e.g., along the x-z plane) by a center-to-center spacing c, similar to the spacing s described above with respect to FIG. 1A.

[0048] While the protruding portions in Figures 2A-2I are shown as having the same size and shape, in some embodiments, one, some, or all of the protruding portions can have a size and / or shape that is different from the size and / or shape of the other protruding portions. Furthermore, while Figures 2A-2I depict a regular array for the protruding portions, embodiments of the disclosed subject matter are not limited thereto. Rather, in some embodiments, the spacing, size, and / or shape of the protruding portions can vary across the face of the electrode (e.g., along the x-direction, along the z-direction, or both). For example, the array of protruding portions can have variable spacing or a random arrangement.

[0049] Examples of structures and configurations for volumetric plasma initiation In some embodiments, the apparatus for generating a volumetric plasma can include a means for initiating the plasma, for example, by providing a spacing smaller than the gap between the electrodes so that gas release occurs at a lower voltage than would otherwise occur. In some embodiments, the initiating means can be temporary, for example, the plasma can be removed or modified once initiated. In some embodiments, the initiating means can be reusable or reproducible, for example, to initiate a plasma between the electrodes more than once. Alternatively, in some embodiments, the initiating means can be a consumable item that is degraded or decomposed, for example, by the high temperature of the generated volumetric plasma.

[0050] In some embodiments, volumetric plasma can be generated by applying a voltage between electrodes separated by a first gap, where a surface of at least one of the electrodes facing the first gap can have a plurality of first protruding portions, and a surface of at least one of the electrodes facing the first gap can have a plurality of second protruding portions (e.g., pillar fibers, distal tips, or other surface protruding portions). In some embodiments, the first and second protruding portions can be on the same surface, where the second protruding portion is longer than the first protruding portion so as to extend into the first gap between the electrodes. In some embodiments, the second protruding portion forms a narrower second gap with the other electrode (e.g., the surface of the other electrode facing the gap, the first protruding portion extending from the surface of the other electrode, or the second protruding portion extending from the surface of the other electrode). In some embodiments, the narrower second gap can be at least one order of magnitude smaller than the first gap and / or can have a size within one order of magnitude of the cross-sectional dimension of the second protruding portion. In some embodiments, gas release can occur across the second gap at a voltage (or power) that is much lower than the voltage (or power) required to generate a gas discharge across the first gap, e.g., by at least an order of magnitude.

[0051] 3A shows a plasma generation system 300 having a first electrode 302, a second electrode 304, a power supply 108, and a controller 110. In the illustrated example, the first electrode 302 is separated from the second electrode 304 by a first gap 306 (e.g., having a thickness). In some embodiments, the gap 306 can be less than 10 cm, e.g., in the range of 1 mm to 1 cm. The first electrode 302 can have a plurality 114 of first protruding portions extending toward the second electrode 304 (e.g., along the y-direction), and the second electrode 304 can have a plurality 144 of second protruding portions extending toward the first electrode 302 (e.g., along the y-direction). Additionally, the first electrode 302 may have one or more second protruding portions 308 that extend farther (e.g., along the y-direction) than the first protruding portions of the plurality 114, and the second electrode 302 may have one or more second protruding portions 310 of its own that extend farther (e.g., along the y-direction) than the first protruding portions of the plurality 144. The second protruding portions 310 of the second electrode may have the same or different configuration (e.g., shape, size, spacing, and / or material) as the second protruding portions 308 of the first electrode 302.

[0052] In some embodiments, the second protruding portions 308, 310 may be disposed on or formed from the surface of the respective base layer 112, 142, e.g., similar to but longer than the pillars 116a in the top inset of FIG. 1A. Alternatively or additionally, in some embodiments, the second protruding portions 308, 310 are exposed or cut surface portions of the respective base layer 112, 142, e.g., similar to but longer than the fibers 116b in the bottom inset of FIG. 1A. In some embodiments, each second protruding portion 308, 310 can have a cross-sectional dimension (e.g., a maximum or minimum cross-sectional dimension in the x-z plane, e.g., a diameter) that is approximately the same as the cross-sectional dimension of the first protruding portions in the respective plurality 114, 144, e.g., 500 μm or less. In some embodiments, the cross-sectional dimension of second protruding portions 308, 310 may be greater than 1 μm, for example, in the range of 1 to 100 μm. In some embodiments, the cross-sectional dimension may represent an average for each of second protruding portions 308 or each of second protruding portions 310, and the cross-sectional dimensions of second protruding portions 308, 310 are within 10% of their respective averages.

[0053] In some embodiments, the second protruding portions 308, 310 extend into and across the gap 306 so as to initially contact one another and form a high-resistance contact point and / or a narrow gap region 312 (e.g., on the order of their respective cross-sectional dimensions, e.g., ≦5 μm), which may facilitate initiation of a volumetric plasma at lower voltages. In some embodiments, each second protruding portion 308, 310 may extend from its respective base layer 112, 142 along the thickness of the gap 306 (e.g., along the y-direction) by a distance L. In some embodiments, the distance L may be 1 mm or greater, e.g., in the range of 10 to 100 mm. In some embodiments, the distance L may represent an average across each electrode 302, 304, and the distance each second protruding portion 308, 310 extends along the gap thickness may be within 10% of the average. In some embodiments, each second protruding portion 308, 310 can deviate from being straight along at least a portion of its length or can have a portion that is angled relative to the thickness of the gap (e.g., extending in the xz plane), for example, as shown in Figures 3A-3B, in which case distance L represents the distance the second protruding portion extends along the y direction. Alternatively or additionally, in some embodiments, each second protruding portion can be substantially straight, and distance L can extend substantially parallel to the thickness of the gap 306 (e.g., parallel to the y direction) to represent the length of the respective second protruding portion.

[0054] In some embodiments, the first electrode 302 and the second electrode 304 can be formed of a conductive material that can withstand plasma temperatures, e.g., having a melting temperature (e.g., at atmospheric pressure) that is at least 1000 K. For example, the first electrode 302 and / or the second electrode 304 can be formed of a refractory material (e.g., carbon, a refractory metal or alloy, and / or a refractory ceramic). In some embodiments, the base layer 112 of the first electrode 302 can be formed of a conductive material that is different from the conductive material of the plurality of first protruding portions 114 and / or different from the conductive material of the second protruding portion 308. Similarly, the base layer 142 of the second electrode 304 can be formed of a conductive material that is different from the conductive material of the plurality of first protruding portions 144 and / or different from the conductive material of the second protruding portion 310. Alternatively, in some embodiments, the base layer 112, the plurality of first protruding portions 114, and / or the second protruding portions 308 may be formed of the same conductive material, for example, when the fibers form the plurality of first protruding portions 114 (e.g., short fibers), the second protruding portions 308 (e.g., long fibers), and the base layer 112, as shown in FIG. 3B.

[0055] In some embodiments, the contact or narrowed gap region 312 of the second protruding portions 308, 310 can help initiate a volumetric plasma at a lower voltage than would otherwise be possible across the gap 306. Once initiated, the volumetric plasma can grow across and be sustained by the first protruding portions of the plurality 114 of first electrodes 302 and the first protruding portions of the plurality 144 of second electrodes 304. For example, FIGS. 3C-3D illustrate various aspects of plasma initiation and generation in the system 300. In an initial stage 320, a voltage can be applied across the gap 306 via the electrodes 302, 304, resulting in current flowing through the contacting second protruding portions and causing Joule heating thereof. Due to the current flow, the second protruding portions can begin to emit light despite the absence of plasma formation. Joule heating is intensified at the defect area or contact point of the second protruding portion where resistance is highest, thereby generating a localized ultra-high temperature (e.g., higher than the melting temperature of the second protruding portion, e.g., higher than 4000 K) that destroys the corresponding portion of the second protruding portion.

[0056] This self-termination creates an extremely narrow gap 314 between the second protrusions, e.g., close to the scale of the diameter of the second protrusions (~10 μm). The gap formation prevents current from flowing through the second protrusions, and the gap between the first and second electrodes remains dark even as the voltage in the second stage 322 increases. Further increase in the voltage in the third stage 324 begins to generate a gas discharge. In particular, the locally enhanced electric field at the tip of the second protrusions promotes a second electron emission that results in a spark discharge across the newly formed gap 314, which in turn generates a low breakdown voltage (e.g., V I≦100V, e.g., ∼40–45V), helps initiate the plasma. Once initiated, the plasma can then grow during the fourth stage 326, where the closely spaced, shorter first protrusions create a tip-enhanced electric field that converges across the surface of the electrode, accelerating the Townsend breakdown to arc transition, expanding the plasma size and volume, and increasing plasma uniformity, unlike conventional arc discharges. This expansion also creates a collective heating effect that helps stabilize the plasma. As the plasma expands, the voltage increases with the applied voltage V P Correspondingly, the plasma drops from the breakdown voltage (with a concomitant increase in current) until it reaches its stable volumetric form. By continuing to apply sufficient power (e.g., 400-800 W) between electrodes 302, 304, the volumetric plasma can continue and be stable for at least 1 minute (e.g., at least 10 minutes), or in some embodiments, depending in part on the plasma temperature and the materials used in the system.

[0057] In the example shown in FIG. 3A, the second electrode 304 is provided as a base layer 142 having first and second protruding portions. However, in some embodiments, the second electrode may have only a second protruding portion. For example, FIG. 3E illustrates a portion of a plasma generation system 340 having a first electrode 302 and a second electrode 344 separated from the first electrode 302 by a gap 346. Similar to the example of FIG. 3A, the first electrode 302 has a plurality of first protruding portions 114 and a plurality of second protruding portions 308. However, the second electrode 344 has only a second protruding portion 342, which may have the same or different configuration (e.g., shape, size, spacing, and / or material) as the second protruding portions 308 of the first electrode 302. Operation of the system 340 may otherwise be the same as the system 300, for example, as described above with respect to FIGS. 3C-3D.

[0058] Alternatively, in some embodiments, the second electrode may not have any protruding portions. For example, FIG. 3F shows a portion of a plasma generation system 350 having a first electrode 302 and a second electrode 352 separated from the first electrode 302 by a gap 356. Similar to the example of FIG. 3A, the first electrode 302 has a plurality of first protruding portions 114 and a plurality of second protruding portions 354. However, the second electrode 352 does not have any protruding portions. Instead, at least some of the second protruding portions 308 are long enough to initially contact the second electrode 352 and extend across the gap 356 to form a high-resistance contact point and / or a narrow gap region 358. Operation of the system 350 may otherwise be the same as the system 300, e.g., as described above with respect to FIGS. 3C-3D. In the example shown in FIG. 3F, the second electrode 352 is a bare electrode without a first protruding portion, however, according to one or more contemplated embodiments, the second electrode may have a first protruding portion (e.g., similar to the configuration of electrode 134 in FIG. 1B), and the second protruding portion 308 may contact or form a narrow gap region 358 with the first protruding portion of the second electrode.

[0059] Alternatively, in some embodiments, neither the first nor the second electrode may have a second protruding portion. Rather, a separate trigger (e.g., a wire) can be used to initiate the plasma at a lower voltage than using the electrodes alone. In some embodiments, after initiating the plasma, the separate member can be consumed by the plasma (e.g., has a melting temperature lower than that of the plasma) or removed from the plasma. For example, FIG. 3G shows a plasma generation system 360 having a first electrode 102, a second electrode 134, a power supply 108, a controller 110, and a trigger member 362 (e.g., a wire). The trigger member 362 can be positioned within the gap between the electrodes 102, 134, resulting in a narrower gap 364 (e.g., ≦10 μm) between the end of the trigger member 362 and one end of the first protruding portion of the first electrode 102. During operation, the gas discharge across the narrower gap 364 can help initiate a plasma at a lower voltage, which can then expand across the first and second electrodes 102, 134 and fill the gap between them.

[0060] 3G, the trigger member 362 is positioned to form a narrower gap with respect to a portion of the first electrode 102. Alternatively, in some embodiments, the trigger member 362 may be positioned such that a narrower gap is formed between the end of the trigger member and the end of one of the first protruding portions of the second electrode 134. In the illustrated example, the trigger member 362 forms a narrower gap 364 with one of the first protruding portions. Alternatively, in some embodiments, the narrower gap 364 may be formed with respect to more than one of the first protruding portions and / or with respect to a different portion of either electrode, such as with a longer second protruding portion if provided.

[0061] In some embodiments, instead of or in addition to providing a second protruding portion and / or a separate trigger, the gap thickness can be varied to facilitate plasma initiation. For example, FIG. 3H shows a portion of a plasma generation system 370 that uses a variable gap spacing between a first electrode and a second electrode. In the illustrated example, the first electrode has a base layer 112 with a plurality of first protruding portions 114, and the second electrode has a base layer 142 with a plurality of first protruding portions 144. However, other configurations for the first electrode and / or second electrode are also possible according to one or more contemplated embodiments. In the illustrated example, the first electrode is attached to or supported by a first translation stage 372a having a motor 374a, and the second electrode is attached to or supported by a second translation stage 372b having a motor 374b. The first and second translation stages 372 a, 372 b can be configured to move the first and second electrodes toward or away from each other to change the size of the gap between them. Other configurations for the first and second translation stages can also be used, according to one or more contemplated embodiments, such as having a translation stage for one electrode while the other electrode remains in a fixed position, mounting both electrodes on a common translation stage, using a translation stage that does not use a motor, or any other means for changing the size of the gap between the electrodes.

[0062] To initiate a plasma, a first electrode (e.g., having a base layer 112 and a plurality of first protruding portions 114) and a second electrode (e.g., having a base layer 142 and a plurality of first protruding portions 144) may be positioned to form a gap g1 of a first thickness, as shown at 380. When a voltage is applied to g1, a gas discharge 376 may be generated between a portion of the first protruding portion, which may grow into a volumetric plasma 378 through the remaining portions of the first protruding portions of the plurality 114, 144. Once the plasma 378 is generated, the first and second electrodes may be moved apart to form a gap g2 of a second thickness greater than the thickness of g1. As the electrodes move apart, the power applied to the electrodes may be controlled (e.g., by increasing the current and / or voltage) to maintain the plasma despite the increased size of the gap. Once the desired gap spacing is achieved, as shown at 382, ​​the volumetric plasma 378 may be used for a particular application. In some embodiments, a voltage can be applied between the electrodes while they are moving prior to plasma initiation. For example, a voltage can be applied and the gap between the electrodes gradually decreased until plasma is initiated. Once initiated, the gap between the electrodes can be maintained or gradually increased until the desired gap thickness is achieved.

[0063] Example of a configuration for using volumetric plasma As mentioned above, the generated volumetric plasma can be used for material synthesis or processing, or in chemical reactions, among other things. In addition to exposing materials to controllable high temperatures (e.g., in the range of 1000-8000 K), electromagnetic field changes in the volumetric plasma can produce synergistic effects in manufacturing or catalytic processes.

[0064] For example, FIG. 4A illustrates a plasma system configuration 400 for sintering or otherwise heating precursor pellets 402 (e.g., having a diameter of at least 10 mm, e.g., 15-30 mm) to form a bulk product. Instead of or in addition to pellets, the precursor can be in the form of particles. For example, FIG. 4B illustrates a plasma system configuration 410 for sintering or otherwise heating precursor particles 412 (e.g., powders, nanoparticles, elements or compounds supported on a substrate, etc.) to form a particulate product (e.g., powders or nanoparticles). The precursors 402, 412 can be disposed within the gap 306 between the first electrode 302 and the second electrode 304. For example, in some embodiments, the bulk product formed by subjecting the precursor 402 to a volumetric plasma can be a refractory ceramic (e.g., hafnium carbonitride (Hf—CN)), a refractory metal, or a refractory alloy (e.g., MoNbTaW alloy). For example, in some embodiments, the particular product formed by subjecting precursor 412 (e.g., biomass carbon or carbon black) to a volumetric plasma (e.g., at a temperature of 5000 K for 10 seconds) can be carbon nanotubes.

[0065] 4A-4B, the precursors 402, 412 are disposed directly on and supported by a portion of the first protruding portion of the plurality 114 of first electrodes 302. However, in some embodiments, the precursors 402, 412 may be supported in the gap 306 by, for example, a separate support member, to avoid contact with either of the electrodes 302, 304 or to contact only the second protruding portion. In some embodiments, the precursors 402, 412 may be provided in the gap 306 before initiation of the volumetric plasma. Alternatively, in some embodiments, the precursors 402, 412 may be introduced into the gap 306 once the volumetric plasma has already been initiated and / or stabilized.

[0066] In some embodiments, the system can be configured to convey precursors through the gap 306 (e.g., along a direction in the xz plane). For example, FIG. 4C shows a flow-through plasma system configuration 420 for sintering or otherwise heating precursor particles 424 (e.g., powders, nanoparticles, elements or compounds supported on a substrate, etc.) to form particulate product 426 (e.g., powders or nanoparticles). The precursor 424 can be conveyed into and through the gap between the first electrode 302 and the second electrode 304, and / or the product 426 can be conveyed out of the gap by a carrier gas flow 422, e.g., an inert gas.

[0067] In some embodiments, the flow-through configuration 420 can replace traditional arc discharge techniques for nanopowder synthesis. For example, an argon gas flow can carry precursors into and through a volumetric plasma, the temperature of which can be adjusted to obtain a desired nanopowder product. Such nanopowder products can include, but are not limited to, energy storage materials such as lithium-ion battery cathode powders (e.g., ternary cathode materials such as nickel-cobalt-manganese) and solid electrolyte powders (e.g., lithium-lanthanum-zirconium oxide). Alternatively or additionally, in some embodiments, the flow-through configuration 420 can be used for supported nanoparticle synthesis. For example, precursors can be pre-dispersed (e.g., coated) on a high-surface-area substrate (e.g., porous particles) that is carried through the plasma by a carrier gas 422. The precursors on the substrate can be converted to nanoparticles on the substrate by the plasma.

[0068] In some embodiments, the flow-through configuration of FIG. 4C can replace conventional methods (e.g., sol-gel processing, carbothermal reduction, mechano-chemical synthesis, etc.) in synthesizing ultra-high temperature ceramics (UHTCs) (e.g., having melting points above 3000 K), such as high-entropy (HE) UHTCs, e.g., HE carbides, HE borides, or HE nitrides. For example, precursor powders (e.g., carbon black, boron carbide, and / or MO (where M refers to a transition metal)) can be mixed and flowed via a carrier gas into a volumetric plasma at an ultra-high temperature (e.g., at least 3000 K). For HE-UHTCs, the precursor powder can include four or five powder components in substantially equal molar amounts. For example, HE-UHTC precursor powders can include, but are not limited to, carbides (e.g., hafnium carbide, tantalum carbide, zirconium carbide, niobium carbide, titanium carbide) and nitrides (e.g., hafnium nitride, tantalum nitride, zirconium nitride, niobium nitride, titanium nitride). In some embodiments, the composition of the carrier gas can vary depending on the chemical composition of the target UHTC powder, for example, from pure argon (or other inert gas) to combinations of argon with hydrogen, carbon monoxide, hydrogen, etc. The reaction temperature can be adjusted by the applied current, the gap distance between the electrodes, and / or the gas pressure. Premixed feedstock powders can be passed through an ultra-high temperature zone generated by a volumetric plasma, and the resulting powder can be collected after exiting the gap.

[0069] In the example shown in FIG. 4C, a carrier gas is used to transport the precursor through the gap between the electrode and the plasma therein. However, other means for transporting the precursor are contemplated according to one or more contemplated embodiments. In some embodiments, gravity can be used in addition to or instead of a carrier gas flow to transport the precursor through the plasma, for example, by orienting the thickness direction of the gap at a non-zero angle relative to gravity (e.g., so that the xz plane is not perpendicular to gravity). For example, FIG. 4E shows a gravity-fed plasma system configuration 440 for sintering or otherwise heating precursor particles 442 (e.g., powders, nanoparticles, elements or compounds supported on a substrate, etc.) to form a particulate product 444 (e.g., powder or nanoparticles). In the example shown in FIG. 4E, the gap extends substantially parallel to the direction of gravity, but in some embodiments, the lateral extension of the gap can be at an angle relative to gravity, as shown, for example, by configuration 450 in FIG. 4F. In either case, gravity can be used to move the precursor 442 into and through the gap between the first electrode 302 and the second electrode 304 and / or the product 444 from the gap.

[0070] In some embodiments, the gravity-feed configuration of FIG. 4E or FIG. 4F can replace conventional rotary kiln techniques for cement powder synthesis. For example, precursor powders (e.g., limestone, shale, sandstone or clay, and / or iron oxide) can be mixed and conveyed through a volumetric plasma between electrodes 302, 304. In some embodiments, the use of high-temperature plasma can remove impurities (e.g., fuel combustion residues) that would otherwise occur with conventional processing techniques. Furthermore, the plasma can generate ultra-high temperatures (e.g., ≥ 3000 K) that significantly exceed the temperatures of conventional rotary kilns (e.g., ∼ 1723 K), thereby allowing cement powder to form in a much shorter time (e.g., at least 30 minutes) than would be required by rotating a kiln to form large clinkers. In some embodiments, the time-limited high temperature exposure provided by the volumetric plasma can selectively convert only the faces of the limestone (e.g., to form 3CaO·SiO2, 2CaO·SiO2, and 3CaO·Al2O3), while the core of the limestone can still maintain CaCO3 (e.g., reducing CO2 emissions).

[0071] In some embodiments, the system can include a means for adjusting the size of the microparticles generated after exposure to the volumetric plasma. For example, FIG. 4G shows a gravity-fed plasma system configuration 460 for sintering or otherwise heating precursor particles 462 (e.g., fine powder or nanoparticles) to form a microparticle product 464. Similar to the previous example, gravity can be used to move the precursor 462 into and / or from the gap between the first electrode 302 and the second electrode 304 into and through the product 464. The system configuration 460 further includes a gas flow conduit 466 (e.g., a jet) that directs and / or focuses a gas flow (e.g., an inert gas) at the exit product 464, for example, to break up the product 464 (e.g., droplets that have not yet had a chance to solidify) into smaller-sized particles 468 (e.g., atomized).

[0072] In some embodiments, the gravity feed configuration of FIG. 4G can be used to synthesize micronized refractory high-entropy alloy (RHEA) powder from a fine refractory powder feed material. For example, the feedstock to the volumetric plasma can include a single-component, micro-sized mixed powder of refractory metals. The powder is melted and alloyed as it passes through the ultra-high temperature zone provided by the volumetric plasma. The molten, alloyed RHEA stream exiting the volumetric plasma is then exposed to a high-velocity gas jet (e.g., argon and / or helium), which breaks the stream into small droplets, the size of which can be tailored by gas composition, gas pressure, etc., to meet dimensional requirements for additive manufacturing, for example.

[0073] In the above examples, a volumetric plasma is used to convert a solid precursor into a solid product. However, embodiments of the disclosed subject matter are not limited thereto. Rather, the high temperatures provided by the volumetric plasma can be used, for example, to promote (e.g., catalyze) a chemical reaction of a gas with other material phases, without or with the provision of a separate catalyst (e.g., to help induce reaction selectivity). For example, FIG. 4D shows a plasma system configuration 430 for gas-phase processing, in which one or more reactants 432 are converted to one or more products 434 by exposing the reactants 432 to high temperatures (e.g., at least 1000 K) using a volumetric plasma between electrodes 302, 304.

[0074] In some embodiments, the gas-phase process configuration of FIG. 4D can be used to provide CO reduction, for example, to recycle CO from combustion product exhaust gases. For example, a mixture of CO and water vapor (HO) can be heated by a volumetric plasma to convert the mixture to a hydrocarbon fuel, such as methane or acetaldehyde. In some embodiments, the gas-phase process configuration of FIG. 4D can be used to synthesize ammonia (NH). For example, a mixture of nitrogen (N) and hydrogen (H) can be heated by a volumetric plasma to convert the mixture to ammonia. Alternatively, in some embodiments, the gas-phase processing configuration of FIG. 4D can be used to decompose ammonia, for example, to form nitrogen and hydrogen. Other synthesis and / or decomposition reactions are also possible in accordance with one or more contemplated embodiments.

[0075] In the examples described above, the electrodes and the gap between them have generally planar geometries. However, other shapes and configurations are possible, according to one or more contemplated embodiments. Indeed, in addition to being an easy way to generate stable, large-area plasma, embodiments of the disclosed subject matter are scalable and easily adaptable to different manufacturing needs. In some embodiments, the electrodes can be arranged in a coaxial configuration, and the resulting gap can be non-planar. For example, FIGS. 4H-4I show a coaxial plasma system configuration 470 having an inner rod-shaped electrode 474 positioned within and coaxial with an outer annular electrode 472 (e.g., a tube), thereby forming an annular gap 476 therebetween. In the illustrated example, multiple protruding portions 479 477 cover the surfaces of both electrodes 472, 474, which can form a long, volumetric plasma channel. Due to the relatively closed environment (e.g., the gap is surrounded by the outer electrode except at the opposing axial end), this configuration may be particularly useful for gas phase reactions, alloying refractory metals, and / or various atomization processes, e.g., where a feedstock material enters gap 476 at one axial end, passes through a plasma channel to heat the material and / or subject it to the electric field effect of the plasma, and the resulting products exit gap 476 at the opposite axial end 478.

[0076] Alternatively or additionally, in some embodiments, the electrodes can be configured to confine the generated plasma to a small area, for example, to form a focused heating zone. For example, FIGS. 4J-4K show another coaxial plasma system configuration 480, but with a focused heating zone 488. In the illustrated example, the system configuration 480 includes an inner rod-shaped electrode 484 (e.g., a carbon felt rod) disposed within and coaxial with an outer electrode 482 (e.g., a graphite shell). The electrodes 482, 484 form a narrow annular gap 486 proximal to the focused heating zone 488, but away from the heating zone, the spacing (e.g., radial spacing) between the electrodes becomes large enough that plasma forms only proximal to the heating zone 488. Such a configuration can be useful for increasing the machining accuracy of the generated plasma, for example, for use in additive manufacturing (e.g., 3D printing on a substrate 490). In the illustrated example, a plurality of first protruding portions 492 (e.g., short carbon fibers) and a plurality of second protruding portions 494 (e.g., long carbon fibers) extend from the cover surface of the inner electrode 484, while the outer electrode 482 presents only a bare surface without any protruding portions. At least some of the second protruding portions 494 can contact the outer electrode 482, for example, to help initiate plasma formation.

[0077] In any of the disclosed embodiments, the system may include a rapid cooling (e.g., at least 10°C) in addition to exposure to ultra-high temperatures via the volumetric plasma. 2K / s). In some embodiments, cooling can be provided by turning off the volumetric plasma, for example, by providing insufficient power or at least a power level to the electrodes to support plasma generation. Alternatively or additionally, cooling can be provided by moving material from the volumetric plasma, for example, by using a carrier gas flow or gravity to transport the material from within the gap between the electrodes to outside the gap. Alternatively or additionally, cooling can be provided by moving the volumetric plasma away from the material, for example, by displacing one or both of the electrodes relative to the material and / or using a magnetic field to change the position of the generated plasma. Alternatively or additionally, active cooling modalities can be used, such as, but not limited to, directional airflow, heat exchangers, heat pumps, and thermoelectric modules. Other cooling techniques and modalities are also possible according to one or more contemplated embodiments.

[0078] Support electrode example In some embodiments, one or both of the electrodes may be supported so as to be movable relative to the other, for example, to enable processing of samples having dimensions larger than the dimensions of the volumetric plasma. In such an embodiment (or any other embodiment), one of the electrodes may have an area (e.g., of a surface facing the gap) smaller than the area (e.g., of a surface facing the gap) of the other electrode. In some embodiments, the smaller supporting electrode may be moved relative to the larger electrode, for example, to move the localized heating zone provided by the generated plasma across the surface of the larger electrode. For example, FIG. 5A shows a movably supported plasma generation system 500 capable of providing volumetric plasma 514 at different locations. In the illustrated example, the system 500 includes first and second electrodes, first and second translation stages 504a, 504b, a frame 502 supporting the first and second translation stages, a power supply 108, and a controller 110. The first electrode can have a first base layer 506 with a plurality of protruding portions 508 extending therefrom, and the second electrode can have a second base layer 510 with a plurality of protruding portions 512 therefrom. In the illustrated embodiment, the first base layer 506 can have an area A1 (e.g., in the xz plane) that is less than the area A2 (e.g., in the xz plane) of the second base layer 510, and the plurality of protruding portions 508, 512 can cover their respective areas.

[0079] The translation stages 504a, 504b may be mechanically coupled to the respective base layers 506, 510 and configured to move the respective electrodes in at least one dimension, for example, two dimensions (e.g., along the x-z plane). During operation, the translation stages 504a, 504b may therefore move the electrodes relative to one another to change the position of the generated volumetric plasma 514, for example, to scan a heating zone generated by the plasma across the surface of a sample on the base layer 510. Alternatively, in some embodiments, only one translation stage may be provided to move the electrode coupled to it, while the other electrode remains substantially stationary (e.g., supported in place by the frame 502). In some embodiments, one or both of the translation stages 504a, 504b may be configured to move the respective electrode along the y-direction and / or move in three dimensions, for example, to allow for changing the size of the gap between the electrodes.

[0080] In some embodiments, moving a volumetric plasma by moving one or both electrodes relative to the other can be used for additive manufacturing, for example, to achieve powder bed fusion or sintering. For example, FIG. 5B shows the configuration of a plasma system 520 for additive manufacturing. The system 520 includes a supporting electrode head 522 (e.g., having a 10 mm diameter carbon felt disk) and a base electrode strip 524. A powder bed 528 can be provided on and supported by the base electrode strip 524. In some embodiments, the powder bed 528 includes a pressed sample pellet derived from a conductive material, for example, a multi-element metal powder. By applying a voltage between the supporting electrode head 522 and the base electrode strip 524, a plasma beam 526 (e.g., having a column radius of ∼1 mm) can be generated. Either or both of the supported electrode head 522 and the base electrode strip 524 can be moved relative to the other (e.g., using a motorized platform) to scan the plasma 526 across the powder bed 528.

[0081] More details of the operation of system 520 are shown in FIG. 5C . During initial positioning stage 530, supported electrode head 522 moves over a portion of base electrode strip 524 exposed from powder bed 528, so that electrode first protruding portion array 534 and first protruding portion array 538 face each other. In the illustrated example, the electrodes also have respective second protruding portions 540, 542 that may be in contact 548 or at least closely spaced apart from each other at positioning stage 530. The voltage between the electrodes is then increased during plasma initiation stage 546, for example, to spark a gas discharge between second protruding portions 540, 542; the discharge then spreads and stabilizes into a columnar plasma 526 with the aid of first protruding portions 534, 538 during plasma stabilization stage 550. Once columnar plasma 526 is formed, one or both of the electrodes can be moved relative to the other to position a portion of powder bed 528 within plasma 526. During the sintering stage 554, the plasma 526 can be moved across the surface of the powder bed 528 to sinter or fuse different portions thereof.

[0082] In some embodiments, the support electrode configuration can include one or more holders for holding, shaping, increasing mechanical strength or rigidity, and / or providing electrical connection to the electrodes, for example, when the electrodes are formed from cloth or felt. For example, FIGS. 5D-5E show a support electrode configuration 560 in which electrodes 564a, 564b are spaced apart from one another by a gap 568. The surface portions of each of electrodes 564a, 564b facing gap 568 can have a plurality of protruding portions 566a, 566b, respectively, similar to the examples described above. The portion of electrode 564a opposite gap 568 can be inserted into and held by electrode holder 562a, and the portion of electrode 564b opposite gap 568 can be inserted into and held by electrode holder 562b. The electrode holders 562a, 562b can be electrically coupled to the power source 108 via respective electrical coupling members 572a, 572b (e.g., clamps secured to the outer surfaces of the holders).

[0083] In some embodiments, the holders 562a, 562b and the electrodes 564a, 564b can be formed from a conductive material having a melting temperature of 1000 K or greater. Alternatively, in some embodiments, the electrodes 564a, 564b can be formed from a conductive material having a melting temperature of 1000 K or greater, and the holders 562a, 562b can be formed from a conductive material having a melting temperature less than 1000 K. Power from the power source 108 can be supplied to the electrodes 564a, 564b to generate a plasma in the gap 568 through the electrode holders 562a, 562b and their respective coupling members 572a, 572b. In the illustrated example, each electrode holder 562a, 562b is a U-shaped member, although other shapes are possible according to one or more contemplated embodiments. In some embodiments, the electrodes 564a, 564b can be formed of a flexible or fluffy material, such as carbon felt or carbon cloth, and the electrode holders 562a, 562b can be formed of a more rigid material, such as machined graphite, 3D printed carbon, refractory metal, etc.

[0084] In the illustrated example, each electrode holder 562a, 562b also includes a respective base member 570a, 570b. In some embodiments, the base members 570a, 570b (e.g., legs) can be formed from an electrically insulating material (e.g., ceramic) and can be configured to support the electrode holder (and the electrode thereon) in a substantially vertical orientation (e.g., a gravity-fed configuration). In such embodiments, a region 574 of the gap 568 opposite the base members 570a, 570b can be considered an input region (e.g., for feeding precursors, reactants, or other materials to be processed by the plasma), and a region 576 of the gap 568 on the same side as the base members 570a, 570b can be considered an output region (e.g., where product or processed material exits the plasma). In some embodiments, one or more components can be provided in a capture zone 578 below or adjacent to the output region 576 to capture effluent products or processed materials.

[0085] Other configurations are also possible according to one or more contemplated embodiments. For example, in some embodiments, the input and output regions may be on opposite sides of gap 568 in the plan view of FIG. 5D rather than on opposite sides of gap 568 in the elevation view of FIG. 5E . Alternatively or additionally, in some embodiments, the input and output regions may be the same region, e.g., having material that leaves gap 568 along the same direction and through the same edge that they enter. Alternatively or additionally, in some embodiments, the output region may be along a direction orthogonal to the input region (e.g., input provided on the upper side of gap 568 and output exiting gap 568 via a side instead of (or in addition to) the lower side of gap 568).

[0086] FIG. 5F shows a further aspect of a plasma generation system 580 that uses electrode holders 562a, 562b, for example, to process precursors or particles delivered from an input hopper 592. In the illustrated example, the electrode holders 562a, 562b can have thickened bottom portions 586a, 586b, for example, to help increase the stability and / or rigidity of the stand-holders. The base members 570a, 570b of the electrode holders 562a, 562b can also be positioned within recesses 588 in an insulating holder 584 (e.g., formed of plastic or ceramic), for example, to help hold the holders in an upright position. In some embodiments, the entrance region 574 can have a different profile than the rest of the gap 568, for example, to deliver particles / reactants to the plasma and / or to avoid forming a plasma therein. For example, the electrodes 564a, 564b can include respective sloped surface portions 582a, 582b to form a tapered entrance region. Alternatively or additionally, in some embodiments, a collection member 590 (e.g., a substrate or hopper) may be supported on the base members 570a, 570b and positioned within the capture zone 578, for example, to collect processed material leaving the gap 568 and the plasma therein.

[0087] Exemplary Methods for Generating and Using Volumetric Plasmas FIG. 6A illustrates an embodiment of a method 600 for generating and using a volumetric plasma. The method 600 can begin with a process step 602, which can provide a pair of electrodes. In some embodiments, one or both of the provided electrodes can have a plurality of short protruding portions, e.g., any of the first protruding portions discussed herein with respect to any of FIGS. 1A-5F. In some embodiments, one or both of the provided electrodes can have at least one long protruding portion, e.g., any of the second protruding portions discussed herein with respect to any of FIGS. 3A-3F and 4A-5F. In some embodiments, providing the process step 602 can include fabricating the electrode or a portion thereof, e.g., forming the short and / or long protruding portions. For example, the short and / or long protruding portions can be manufactured by three-dimensional printing (e.g., laser-based direct energy deposition or laser powder bed fusion). Alternatively or additionally, in some embodiments, the short and / or long protruding portions can be manufactured by, for example, cutting a cloth or felt formed of a refractory material (e.g., carbon, a refractory metal, or a refractory metal alloy). Alternatively or additionally, in some embodiments, the short and / or long protrusions can be produced by sanding or roughening the surface of the fire-resistant material (e.g., cloth or felt).

[0088] Method 600 may proceed to decision step 604, where a plasma may be initiated between the electrodes. In some embodiments, when long protrusions are provided on one or both electrodes, plasma may be initiated via option 606a, where the long protrusions undergo Joule heating, creating a narrow gap between them, and then a spark discharge occurs across the narrow gap. For example, the use of long protrusions to initiate plasma via option 606a may be similar to that discussed herein with respect to any of FIGS. 3A-3F. Alternatively or additionally, in some embodiments, plasma may be initiated via option 606b, where the gap thickness may be reduced to allow a spark discharge between the electrodes, e.g., between short protrusions. For example, the use of a reduced gap thickness to initiate plasma via option 606b may be similar to that discussed herein with respect to any of FIGS. 3H and 5A-5C. Alternatively or additionally, in some embodiments, the plasma may be initiated via any other technique 606c, such as, but not limited to, applying a higher breakdown voltage, varying the gas pressure, and / or using a separate trigger (e.g., as discussed herein with respect to FIG. 3G).

[0089] Method 600 can proceed to treating step 608, where the volumetric plasma can be maintained. In some embodiments, treating step 608 can include growing an initiating plasma across the surface of the electrodes, e.g., via a short overhang, to form the volumetric plasma. In some embodiments, the volumetric plasma can be substantially spatially uniform and / or temporally stable. In some embodiments, treating step 608 can include applying a DC voltage, an AC voltage (e.g., RF), or a pulsed voltage waveform (e.g., a square wave) to the electrodes of sufficient power to sustain the plasma between the electrodes. In some embodiments, the plasma temperature and / or temperature profile of the volumetric plasma can be substantially constant for at least 1 minute, e.g., at least 10 minutes. In some embodiments, maintaining treating step 608 can include varying the power applied to the electrodes, varying the gap thickness between the electrodes, and / or varying the gas pressure between the electrodes, e.g., to change the plasma temperature. Alternatively or additionally, maintaining treating step 608 can include moving the volumetric plasma, e.g., to expose a material to the plasma (e.g., as discussed herein with respect to any of FIGS. 5A-5C).

[0090] Method 600 can proceed to step 610, where the volumetric plasma can be used in a manner similar to that discussed herein, e.g., with respect to any of Figures 4A-4K and 9A-11. For example, the volumetric plasma can be used to heat materials, such as, but not limited to, sintering pellets to form bulk materials, heating fixed or flow-through particles to form alloys, cements, or ceramics (e.g., nanopowders or supported nanoparticles), heating fixed or flow-through particles to form other particles (e.g., carbon nanotubes), heating fixed or flow-through particles to form surface layers (e.g., powder bed fusion), promoting thermochemical reactions (e.g., chemical synthesis or decomposition, with or without a catalyst), performing cryostabilization, or any other purpose.

[0091] While steps 602-610 of method 600 have been described as being performed once, in some embodiments, multiple iterations of a particular processing step may be used before proceeding to the next decision or processing step. Additionally, while steps 602-610 of method 600 are illustrated and described separately, in some embodiments, the processing steps may be combined and performed together (concurrently or sequentially). Furthermore, while FIG. 6A illustrates a particular order for steps 602-610, embodiments of the disclosed subject matter are not limited thereto. Indeed, in certain embodiments, steps may occur in a different order than illustrated or simultaneously with other steps. In some embodiments, method 600 may include steps or other aspects not specifically illustrated in FIG. 6A. Alternatively or additionally, in some embodiments, method 600 may comprise only some of steps 602-610 of FIG. 6A.

[0092] Computer implementation example 6B illustrates a generalized example of a suitable computing environment 631 in which the described innovations may be implemented, such as, but not limited to, power supply 108, controller 110, control system 124, a controller of conversion stage 372, and / or aspects of method 600. The computing environment 631 is not intended to suggest any limitation as to scope of use or functionality, as the innovations may be implemented in a variety of general-purpose or special-purpose computing systems. For example, the computing environment 631 may be any of a variety of computing devices (e.g., a desktop computer, a laptop computer, a server computer, a tablet computer, etc.).

[0093] Referring to FIG. 6B, a computing environment 631 includes one or more processing units 635, 637 and memory 639, 641. In FIG. 6B, this basic configuration 651 is included within the dashed line. The processing units 635, 637 execute computer-executable instructions. The processing units may be central processing units (CPUs), processors in an application-specific integrated circuit (ASIC), or any other type of processor (e.g., hardware processors, graphics processing units (GPUs), virtual processors, etc.). In a multi-processing system, multiple processing units execute computer-executable instructions to increase processing power. For example, FIG. 6B shows a central processing unit 635 and a graphics processing unit or co-processing unit 637. The tangible memory 639, 641 may be volatile memory (e.g., registers, cache, RAM), non-volatile memory (e.g., ROM, EEPROM, flash memory, etc.), or some combination of the two accessible by the processing units. The memories 639, 641 store software 633 in the form of computer-executable instructions suitable for execution by a processing unit(s) that implements one or more innovations described herein.

[0094] A computing system may have additional features. For example, computing environment 631 includes storage 661, one or more input devices 671, one or more output devices 681, and one or more communication connections 691. An interconnection mechanism (not shown), such as a bus, controller, or network, interconnects the components of computing environment 631. Typically, operating system software (not shown) provides an operating environment for other software executing in computing environment 631 and coordinates the activities of the components of computing environment 631.

[0095] Storage 661 may be removable or non-removable and includes magnetic disks, magnetic tapes or cassettes, CD-ROMs, DVDs, or any other medium that can be used to store information in a non-transitory manner and that can be accessed within computing environment 631. Storage 661 may store instructions for software 633 that implements one or more of the innovations described herein.

[0096] The input device(s) 671 may be a touch input device such as a keyboard, mouse, pen, or trackball, a voice input device, a scanning device, or another device that provides input to the computing environment 631. The output device(s) 681 may be a display, a printer, speakers, a CD-writer, or another device that provides output from the computing environment 631.

[0097] The communication connection(s) 691 enable communication over a communication medium to another computing entity. The communication medium conveys information such as computer-executable instructions, audio or video input or output, or other data in a modulated data signal. A modulated data signal is a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, the communication medium may be electrical, optical, radio frequency (RF), or another carrier.

[0098] Any of the disclosed methods can be implemented as computer-executable instructions stored on one or more computer-readable storage media (e.g., one or more optical media disks, volatile memory components (such as DRAM or SRAM), or non-volatile memory components (such as flash memory or a hard drive)) and executed on a computer (e.g., any commercially available computer, including a smartphone or other mobile device that includes computing hardware). The term computer-readable storage medium does not include communication connections such as signals and carrier waves. Any computer-executable instructions for implementing the disclosed technology, as well as any data created or used during the implementation of the disclosed embodiments, may be stored on one or more computer-readable storage media. The computer-executable instructions may be a dedicated software application or part of a software application accessed or downloaded, for example, via a web browser or other software application (such as a remote computing application). Such software may be executed, for example, on a single local computer (e.g., any suitable commercially available computer) or in a networked environment using one or more networked computers (e.g., via the Internet, a wide area network, a local area network, a client-server network (such as a cloud computing network), or any other such network).

[0099] For clarity, only selected aspects of software-based implementations are described. Other details well known in the art are omitted. For example, it should be understood that the disclosed technology is not limited to any particular computer language or program. For example, aspects of the disclosed technology can be implemented by software written in C++, Java™, Python™, and / or any other suitable computer language. Likewise, the disclosed technology is not limited to any particular computer or hardware type. Specific details of suitable computers and hardware are well known and need not be described in detail in this disclosure.

[0100] It should also be appreciated that any functionality described herein may be performed, at least in part, by one or more hardware logic components instead of software. For example, without limitation, exemplary types of hardware logic components that may be used include field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on a chip (SOCs), complex programmable logic devices (CPLDs), etc.

[0101] Additionally, any of the software-based embodiments (e.g., including computer-executable instructions for causing a computer to perform any of the disclosed methods) can be uploaded, downloaded, or remotely accessed via appropriate communications means. Such suitable communications means include, for example, the Internet, the World Wide Web, an intranet, a software application, cable (including fiber optic cable), magnetic communication, electromagnetic communication (including radio frequency, microwave, and infrared communication), electronic communication, or other such communications means. In any of the above examples and embodiments, the provision of requests (e.g., data requests), instructions (e.g., data signals), commands (e.g., control signals), or any other communications between systems, components, devices, etc. may be through the generation and transmission of appropriate electrical signals via wired or wireless connections.

[0102] Fabrication example and experimental results The plasma generation device 700 consisted of two carbon felt electrodes 706a, 706b connected to graphite holders 702a, 702b, as shown in Figure 7B. To fabricate the electrodes, a piece of carbon felt measuring 50 mm x 150 mm x 6.5 mm was punched into a 25.4 mm diameter disk and then cut ~1 mm away from the felt surface using a razor blade, thereby severing the carbon fibers that make up the felt and creating vertically oriented carbon fiber tips. Two circular graphite blocks measuring 50 mm x 50 mm x 25 mm were fabricated using a computer numerically controlled (CNC) machine to provide holders for the carbon felt electrodes. The graphite holders 702a, 702b were connected to the positive and negative tabs of a programmable power supply via copper wires 704a, 704b. The gap 708 between the two electrodes 706a, 706b was set to ~3 mm but can be adjusted for different applications. The complete electrode device 700 was housed in a glove box filled with pure argon gas at atmospheric pressure. In this configuration, multiple long carbon fibers (loosened by the electrode cutting process) extend from the carbon felt surface and form contact between the two electrodes, as shown in Figure 7C. In addition, cutting the carbon felt produces an electrode surface characterized by a high density of shorter, vertically aligned carbon fibers with blunt tips separated by uncut, horizontally aligned fibers with an inter-bundle distance of ~200 µm, as shown in Figures 7C-7D. The carbon fiber tip features a diameter of approximately 10 µm, which is much smaller than the micron-to-centimeter scale of metal pin electrodes conventionally used to generate arc plasma.

[0103] To initiate the plasma, the voltage was gradually increased (e.g., to ~33 V) between electrodes 706a and 706b. The longer fibers in contact with each other generated intense Joule heating, which caused the fibers to glow. Defective regions or contact points between fibers had higher resistance than the fibers themselves, resulting in localized heating at the fiber junctions. At higher currents, excessive Joule heating caused the fibers to break, resulting in extremely high temperatures that created small gaps between the long fibers, opening the circuit. These small gaps (e.g., ~ several μm) significantly reduced the gas breakdown voltage (e.g., ~42 V), increased plasma uniformity through enhanced electric fields, and increased secondary electron emission at the fiber tips. Once a spark formed and initiated the plasma, the gas discharge expanded between the electrodes, which can be attributed to the array of shorter, vertically aligned fiber bundles, which generated a concentrated electric field that converged across the electrode surface. Therefore, this unique tip-enhanced electrode design enabled a smooth transition to a volumetric arc discharge. The resulting plasma produced an extremely bright light, and a neutral density filter was required to clearly observe the plasma. Interestingly, the carbon fiber had a sharper tip after the plasma generation process, as shown in Figure 7D, which remained sharp even 10 minutes after plasma discharge. The carbon tip was likely sharpened by the concentrated electric field generated when a voltage was applied between the two electrodes. Such a sharp tip could also further increase the surrounding local electric field, facilitating the discharge process.

[0104] The continuous volumetric plasma (e.g., approximately 25 mm in diameter, limited only by the size of the electrode) exhibited highly controllable temperatures between 3000 and 8000 K, as well as uniform temperature distribution, as shown in Figure 7A. Compared to conventional arc jet or pin-to-pin arc plasma technologies, the device 700 can achieve plasma at relatively high temperatures uniformly over a large area at atmospheric pressure with a moderate current input (e.g., ~45 A). Notably, the carbon fiber tip remains stable even under these ultra-high temperature conditions due to the carbon electrode's low heat capacity, high thermal conductivity, and high emissivity. As a result, the volumetric plasma can maintain stable operation for more than 10 minutes with sustained power input.

[0105] The temperature of the plasma was determined using Rayleigh thermometry, a linear technique in which the Rayleigh scattering signal is proportional to the total number density of molecules in the plasma and inversely proportional to the temperature. As shown in Figure 7E, the plasma temperature was determined using a linear technique in which the current was 15 A-45 A (3 A / cm). 2 -9A / cm 2 When the current was increased to 20 A (equivalent to 4 A / cm²), the plasma temperature increased from ~4200 K to ~7700 K. This demonstrated the capability of the setup to generate an ultra-high temperature environment with precise control of temperature. 2 ) was measured by a line scan across the center of the plasma and found to be approximately 4700 K across the electrode surface, demonstrating the uniformity of the plasma. 2 Plasma temperatures were measured using gray body emission spectroscopy at intervals of approximately 3 mm, yielding an average temperature of approximately 4500 K. Despite these extremely high plasma temperatures, numerical simulations show that the carbon tip features a lower temperature distribution, reaching just 3000 K even when the plasma center is set to 7000 K. This may be due to the carbon tip's high thermal conductivity and emissivity, which help rapidly transfer heat away from the electrode. This may also explain how the carbon tip can remain stable in such an extremely high temperature environment required for continuous plasma operation.

[0106] To investigate the role of fibers in the plasma breakdown process, a control experiment was conducted using a pair of stainless steel electrodes without any fiber features. These plate electrodes required nearly 1500 V across a ~3 mm gap to achieve gas discharge breakdown, which is more than 30 times higher than the 42 V required using a carbon fiber tip-enhanced electrode across the same electrode gap distance. The significant reduction in the breakdown voltage of the disclosed device can be attributed to the presence of long carbon fibers, which provide a small gap distance through Joule heating breakdown, as well as the enhanced electric field at the shorter carbon fiber tips, which promotes Townsend breakdown. In addition, short fiber tips can enhance secondary electron emission to enable volumetric spark discharge formation with uniform temperature distribution. In contrast, stainless steel plate electrodes lack sharp fiber tips or short tips for enhanced electric fields to facilitate secondary electron emission, thus requiring much higher voltages to achieve gas discharge breakdown and making it difficult to generate uniform, volumetric plasma. Furthermore, when using fiberless stainless steel plate electrodes, the discharge location is very narrow and unpredictable, typically following a streamer path, making such a configuration unsatisfactory for material manufacturing. In contrast, the short fiber tip arrays of the disclosed device can enable volumetric plasma formation via localized tip-enhanced electric fields that converge gas discharges across the electrodes.

[0107] Control experiments were also conducted in the disclosed device to isolate the effects of long- and short-chain carbon fibers. In some cases, plasma breakdown could not be generated under the same conditions by removing the long fibers between the carbon felt electrodes and ensuring that no contact was formed. However, higher breakdown voltages and / or other plasma initiation techniques could be used in place of long carbon fibers. Furthermore, to investigate the role of short-fiber tip arrays, two graphite plate electrodes of the same dimensions were used, with only a bundle of long fibers glued between the electrodes. These control electrodes initially exhibited similar behavior to the carbon felt electrodes, with sparks forming after a period of darkness. However, as the voltage continued to increase, only spark discharges were observed; no continuous or expanding plasma formed. In contrast, the disclosed setup generated a stable volumetric plasma due to the presence of high-density, short carbon fibers decorating the surface of the electrodes.

[0108] Figure 3D shows the current-voltage (CV) characteristics of the disclosed plasma discharge process using a tip-enhanced carbon felt electrode. The plasma electric field strength between the electrodes was also simultaneously measured using an in situ electric field-induced second harmonic (E-FISH) method, and the results are shown in Figure 8A. Conceptually, E-FISH measures the electric field via the second harmonic signal of an excitation laser in the presence of an externally applied electric field. The second harmonic signal is quadratically proportional to the plasma field strength. To determine the final electric field, the E-FISH signal was calibrated by measuring the electric field generated before breakdown using a DC power source and corrected for the number density of molecules using Rayleigh scattering. The E-FISH measurements were characterized by a spatial resolution of approximately 3 mm along the laser beam propagation direction (estimated based on the confocal length of the laser beam).

[0109] Referring to FIG. 3D, as the top carbon felt (cathode) bias voltage was increased from zero to ~33 V (first stage 320), a bright filament was observed between the electrodes, which were long carbon fibers touching each other and therefore undergoing Joule heating due to the current passing through the electrodes. Thereafter, from ~33 V to ~42 V, no current signal was observed in the CV curve (second stage 322), and no light emission from the fibers was observed. This lack of current may be due to the high temperatures achieved by the Joule-heated fibers in the first stage 320, causing them to physically break down in areas of high resistance (e.g., interfiber junctions) and form narrow gaps between these long fibers. The gaps between the long fibers stop the Joule heating effect, causing the fibers to darken again.

[0110] As the voltage increased further to ~42-45 V (third stage 324), the electric field increased further, and a spark discharge was observed. This discharge occurred within the narrow gap between the broken fibers via the tip-enhanced field emission effect. This discharge process helped reduce the plasma breakdown voltage by promoting electron impact ionization via Townsend avalanche, thereby igniting the plasma (fourth stage 326). This transition to an arc discharge resulted in a current surge of up to 18 A (i.e., the arc discharge breakdown current), and a rapid drop in voltage to ~20 V was observed due to the increase in the electron number density and conductivity of the plasma gas (fifth stage 328). After breakdown, the electric field measured by E-FISH between the two electrodes was very low (~5 V / mm), indicating that only a low electric field was required to maintain the plasma. The arc discharge volume then began to rapidly expand between the electrodes.

[0111] When the current reached ~45 A (sixth stage 330), the plasma generated a temperature of ~7700 K. The current was then gradually reduced from 45 A (seventh stage 332). During this stage, the arc remained stable (albeit at a lower intensity) even when the current just reached ~7 A, below the gas discharge breakdown current (~18 A in the fifth stage 328). This significant hysteresis can be explained by the fact that once an arc is initiated, a high density of electrons exists between the electrodes, making it easier to maintain the arc state. In addition, the plasma temperature was still very high (>3000 K), which promoted thermionic emission of electrons from the short carbon fiber tip. However, when the current was reduced below 7 A (eighth stage 334), the plasma terminated with a voltage surge to 42 V, closing the hysteresis loop. In general, the breakdown voltage of the disclosed plasma device was significantly lower than previously reported plasma breakdown values ​​and was highly reproducible (~42 ± 2.6 V, based on 15 experiments).

[0112] Volumetric plasmas can also be rapidly turned on and off, for example, by simply modulating the applied voltage and current. As shown in Figure 8B, pulsed plasmas can be generated by using a programmable power supply to repeatedly set the applied voltage to 45 V for 0.5 seconds, then returning the voltage to 0 V for 0.5 seconds. This process increased the plasma's current to 35 A for 1 second. The plasma can be heated to 1000 K and 6000 K in less than 1 second. 3 The plasma was cycled at ramp / cooling rates of 1000 K / s. This excellent tunability was attributed to the low voltage barrier for arc-plasma transition made possible by the tip-enhanced electrode. The ability to pulse the plasma to briefly reach high temperatures and then quench back to low temperatures allows the disclosed device to control reaction pathways for various non-equilibrium syntheses where rapid temperature changes are required (e.g., rapid cooling).

[0113] This continuous, volumetric, uniform, and stable ultra-high-temperature plasma can be used to synthesize a variety of high-temperature materials. For example, the disclosed apparatus was used to synthesize and sinter hafnium carbonitride (Hf(C,N)), an ultra-high-temperature ceramic that has been difficult to prepare due to its high melting point (>4000 K). With the disclosed setup, the plasma can reach temperatures of several thousand K in less than one second, which prevents nitrogen dissociation and therefore enables the successful synthesis and sintering of Hf(C,N). To investigate the synthesis of Hf(C,N), pellets were prepared from a mixture of HfC and HfN precursor powders. Specifically, HfC (99% purity) and HfN (99.5% purity) powders were weighed in a nominal atomic ratio of Hf:C:N = 0.53:0.27:0.2, then mixed and ball-milled for 5 hours. The tungsten carbide ball-milling jar was sealed with tape in an argon environment to protect the powder from oxidation during milling. The ball-milled powder was then pressed into a 10 mm diameter pellet and placed on the surface of the lower electrode in the gap region between two tip-enhanced carbon felt electrodes 706a, 706b (Figure 7B). A programmable power supply was used to generate a plasma, and the pellet was heated for 10 seconds to plasma temperatures of 4400 K, 4500 K, 4800 K, and 5150 K, as measured by Rayleigh scattering. The sintered pellet was then cooled to room temperature for further characterization.

[0114] The temperature profile of the plasma generated at different currents using the HfC / HfN pellet on the bottom carbon felt electrode 706b was consistent with the temperature of the plasma without the pellet sample present. The sintered ceramic pellet obtained from the plasma structure was investigated for its phase and structure. Before sintering, the cross section of the precursor pellet showed a compacted powder structure. After a one-stage plasma sintering process at a plasma temperature of 5150 K for approximately 10 seconds, the cross section of the obtained ceramic pellet showed good density and uniformity. The X-ray diffraction (XRD) pattern of the obtained Hf(C,N) sample is shown in Figure 9A. After synthesis, the rock salt crystal structure A predominantly single-phase Hf(C,N) was successfully achieved. These results demonstrate that the ultra-high temperature of the plasma in the disclosed apparatus can rapidly synthesize and sinter predominantly single-phase Hf(C,N) in as little as 10 seconds.

[0115] The disclosed plasma setup also has a fast quenching capability, where the temperature can drop from 6000 K to 1000 K in less than one second. Such rapid quenching capability can be used to synthesize bulk extreme materials, such as, but not limited to, amorphous high-melting-point oxides, which typically require a rapid quenching process after melting to achieve the desired disordered state. Furthermore, most high-melting-point oxide materials are extremely difficult to convert to the amorphous state via conventional tools due to the simultaneous requirement of both high-temperature melting and rapid cooling. The amorphous phase of ultra-high-temperature oxides, such as magnesium oxide (MgO), is typically produced as a thin film by sputtering, not as a bulk material.

[0116] As a demonstration, the disclosed plasma heating and quenching method was applied to crystalline MgO powder. Specifically, MgO crystalline oxide powder (>99% purity) was compressed into an 8 mm diameter pellet. After plasma initiation, the pellet sample was inserted into the gap region between two carbon felt electrodes 706a, 706b and heated to ~6000 K for 20 seconds until the pellet melted. The plasma was then turned off, and the sample was quickly removed with a ceramic plate and cooled to room temperature in a few seconds via a strong airflow. The rapid cooling process helped maintain the spherical shape generated by surface tension in its previous molten state. Figure 9B shows the XRD pattern of the resulting MgO; no sharp peaks were detectable, indicating the formation of an amorphous MgO phase. Image analysis of the cross section of the MgO sample showed no obvious grain boundaries. The disclosed plasma heating and quenching method can also be applied to other oxides with high melting points (e.g., >3000 K). For example, similar results were obtained using zirconia (ZrO2) crystalline oxide powder (purity 99%) and yttria-stabilized zirconia (YSZ) crystalline oxide powder (TZ-3Y).

[0117] The disclosed plasma device can also be used to synthesize tungsten-based refractory alloys directly from elemental metal powders. For example, a W-1.5Nb-0.5Ti alloy was designed, in which tungsten (W) serves as the primary refractory metal, while low-melting niobium (Nb) and titanium (Ti) promote sintering. Specifically, tungsten (99.95% purity), niobium (99.85% purity), and titanium (99.98% purity) powders were mixed with a nominal composition of 98% W, 1.5% Nb, and 0.5% Ti by weight. The powder blend was further mixed in a tumbler mixer for 5 hours to achieve high homogeneity. The powder mixture was then printed into a 1 x 8 x 30 mm flat rectangular shape using a binder jetting method (ExOne™ Innvent+®, available from Desktop Metal, Burlington, Massachusetts, USA). A standard set of printing parameters for tungsten alloys was selected for the printing process (e.g., saturation: 60%; binder setting time: 5 seconds; drying time: 10 seconds; layer thickness: 50 μm; roughing roller: 300 rpm; smoothing roller: 400 rpm). A low-carbon binder was used to minimize carbon contamination during the printing process. After printing, the samples were cured in an oven at 200 °C for 8 hours to develop strength for subsequent de-dusting and handling processes. After removing excess powder with compressed air, the samples underwent a debinding step at 450 °C for 30 minutes to decompose and evaporate the binder into organic fumes, leaving a shaped powder mixture (e.g., pellet), which was then sintered using the disclosed plasma apparatus.

[0118] The pellet was placed on the surface of the lower electrode 706b, and a plasma was generated in the gap 708 using a programmable power supply. The generated plasma heated the pellet for 10 seconds to a plasma temperature of ~4700 K, as measured by Rayleigh scattering. The sintered pellet was then cooled to room temperature for further characterization. Images and energy dispersive X-ray spectroscopy (EDS) mapping results indicated that the applied plasma treatment formed a dense W-1.5Nb-0.5Ti alloy with a uniform distribution of W, Nb, and Ti elements. Furthermore, the elemental ratios of the synthesized samples matched those of the precursors, indicating that the rapid plasma heating process minimized (or at least reduced) elemental evaporation.

[0119] For comparison, specimens with the same composition, 98W-1.5Nb-0.5Ti (wt%), were synthesized using conventional arc melting. Specifically, raw materials in pure metallic form with purities of >99.99 wt% (W: 99.999 wt%, Nb: 99.999 wt%, Ti: 99.99 wt%) were washed and weighed before being placed in the chamber of an arc melting furnace. The chamber was pumped and purged with pure argon (Ar) until the chamber pressure reached 2 psi. The Ar gas flushing process was repeated four times to ensure an inert environment within the working chamber. The open-circuit voltage was 85 V, and the current was set at 350 A, which is the maximum recommended limit to avoid damage to the tungsten electrodes of the arc melting furnace. At the start of the arc melting process, the high-purity Zr (>99.99 wt%) specimens were completely melted to further remove residual oxygen in the chamber. Each melting lasted ~1 min, followed by 20 s of furnace cooling with cold tap water flowing through the copper crucible. The melting process was repeated three times to maximize alloy composition homogeneity. After melting, the samples were sliced ​​and polished for microstructural analysis. The resulting samples showed significant heterogeneity, as well as unmelted tungsten within the microstructure.

[0120] The disclosed plasma apparatus was also used to synthesize MoNbTaW (equimolar) refractory alloys with similar results, thereby suggesting the generality of the disclosed plasma setup for synthesis / sintering. In particular, transition metal element powders (all >99% purity) were used to synthesize Mo 0.25 Nb 0.25 Ta 0.25 W 0.25 The powders were weighed in the nominal ratio, then mixed and ball-milled for 5 hours. The tungsten carbide ball-milling jar was sealed with tape in an Ar environment to protect the powder from oxidation. The ball-milled powder was then pressed into a 10 mm diameter pellet. The sample was placed on the surface of the lower electrode 706b, and a plasma was generated in the gap 708 using a programmable power supply. The generated plasma heated the pellet to a plasma temperature of ~4700 K as measured by Rayleigh scattering for 10 seconds, after which the sintered pellet was cooled to room temperature.

[0121] The disclosed plasma device can also be used to produce high-value carbon materials, such as carbon nanotubes (CNTs), by simply heating biomass carbon or carbon black without a catalyst. Specifically, 50 mg of carbon black powder was spread on the surface of the lower tip enhancement electrode 706b, and a programmable power supply was used to generate a plasma with a gap 708. The generated plasma heated the powder to a plasma temperature of approximately 6600 K (40 A input current) for 10 seconds, as measured by Rayleigh scattering. The material was then cooled to room temperature for further characterization. After plasma treatment, imaging showed that the majority of the carbon black was converted to multi-walled CNTs, consisting of approximately 5 to 15 carbon layers, as shown in Figure 9C. The ends of the CNTs were also analyzed using transmission electron microscopy (TEM), but no metal nanoparticle catalysts were observed. These results suggest that the conversion of carbon black to CNTs is due to the high-temperature plasma treatment alone, rather than to potential metal contaminants in the starting material. Electron energy loss spectroscopy (EELS) analysis of the produced CNTs also shows typical characteristic carbon K-edge profiles that are consistent with CNT profiles in the literature. These results demonstrate the potential of the disclosed plasma device in producing value-added products such as CNTs from carbon black, a widely available and inexpensive by-product from the petroleum industry.

[0122] The disclosed plasma process was adapted to a three-dimensional fabrication device, specifically a powder bed melting / sintering system, by constructing a platform with a focused plasma beam (similar to the device shown in Figures 5B-5C). Specifically, a small cathode carbon felt electrode (8 mm diameter) was used for plasma generation, and the input current was carefully adjusted to focus the plasma beam into a filament with a column radius of approximately 1 mm. A carbon felt strip was used as the anode electrode to facilitate electron transfer. The carbon felt strip also supported the sample (a pressed pellet derived from a multi-element metal powder). The carbon felt strip was connected to a motor, allowing it to move along a preprogrammed path. For the sample, tungsten powder (99.9%) was pressed into a pellet and placed on the carbon felt strip. The plasma was turned on, and the carbon felt strip with the pellet on it was moved relative to the focused plasma. After scanning, the heated sample was gradually cooled to room temperature for further analysis. Figure 10A shows a cross-sectional SEM image of a tungsten sample obtained from this powder bed fusion / sintering process. Compared to the unprocessed pellet, a highly dense structure was achieved, demonstrating the excellent melting / sintering capabilities of this technique.

[0123] In addition to bulk samples, the disclosed plasma device can also be used for coating deposition. As a proof of concept, a platform with a focused plasma beam (similar to the configuration shown in Figures 5B-5C) was used to form ultra-high temperature ceramic (UHTC) coatings on, for example, metal alloys to improve their high temperature resistance. In particular, boron (>98%), molybdenum (99.9%), tantalum (99.98%), titanium (99%), tungsten (99.95%), and zirconium (99.5%) powders were deposited (Mo 0.2 Ta 0.2 Ti 0.2 W 0.2 Zr 0.2)B2 were weighed, mixed, and ball-milled for 3 hours. An 80 mol% excess of boron powder was added to compensate for the evaporative loss of boron oxide during HEB formation. The powder was further heated to 1800 °C by a carbon heater in an Ar-filled glove box to induce the self-propagation reaction. Toluene (45 wt%), fish oil (0.5 wt%), and powder (40 wt%) were mixed and milled for 3 hours. Polyvinyl butyral (6 wt%) and benzyl butyl phthalate (8.5 wt%) were then added and milled for an additional 6 hours to form a slurry. This slurry was cast to form a coating on the surface of a Nb-10Hf-1Ti alloy substrate, followed by calcination at 450 °C for 1 hour.

[0124] A cathode carbon felt electrode (25.4 mm diameter) was used for plasma generation, and the anode electrode was a carbon felt strip that supported the coated sample and facilitated electron transfer. The plasma was turned on, and the carbon felt strip moved the HEB-coated alloy sample relative to the plasma, ensuring uniform heating of the sample by the plasma. After scanning, the sample was gradually cooled to room temperature for further analysis. As shown in Figure 10B, the plasma-treated sample exhibited a high entropy diboride (HEB) coating on the surface of the C103 alloy (Nb-10Hf-1Ti), confirming good bonding with no gaps between the coating and the substrate.

[0125] The high heating / cooling rates of the disclosed plasma processes can be useful in the synthesis and processing of certain materials. For example, high cooling rates during high-temperature synthesis can provide several advantages, as the ability to rapidly cool a material after it has been processed at high temperatures can affect its microstructure, mechanical properties, and performance. Some of the key advantages of high cooling rates can include, but are not limited to: ● Fine microstructure: Rapid cooling can result in the formation of a fine and uniform microstructure in the material. A finer microstructure can improve mechanical properties such as strength, hardness, and wear resistance. Preservation of metastable phases and reduction of segregation and precipitation: Rapid cooling can help preserve metastable phases formed during high-temperature synthesis. Rapid cooling rates can minimize the segregation of alloying elements and the formation of undesirable precipitates, which can result in a more homogeneous material with improved mechanical properties and corrosion resistance. ● Improved productivity and energy efficiency: Faster cooling rates reduce overall processing times, improving productivity and reducing energy consumption. This can be particularly relevant in industries where high throughput and energy efficiency are important, such as electronics manufacturing and large-scale metal processing.

[0126] As mentioned above, the disclosed plasma process can achieve plasma temperatures between 1000K and 6000K in less than 1 second, with a temperature of ∼10 3 K / s total ramp / cooling rate (and ~10 5 The temperature can be cycled at high speeds (initial cooling rates can reach 1000 K / s). This excellent tunability is due to the low voltage barrier for arc-plasma transition made possible by the tip-enhanced electrode, as well as the fast power shutoff that can be used to synthesize glass-phase ceramic materials that cannot be easily achieved by conventional methods (such as spark plasma sintering).

[0127] High heating / cooling rates may also be useful for non-equilibrium synthesis, as described above for amorphous ceramics. To further demonstrate its utility for non-equilibrium synthesis, the disclosed plasma process was used to produce refractory high-entropy alloy (RHEA) particles and finely divided tungsten tetraboride (WB4) particles with ultrahard properties. Medium / high-entropy alloys are a relatively new class of materials containing multiple elements in approximately equal proportions. By finely dividing medium / high-entropy alloys and controlling their size, composition, and morphology, it is possible to tailor their properties, such as mechanical strength, ductility, and corrosion resistance. Finely divided medium / high-entropy refractory metal alloy powders can be widely used in additive manufacturing processes such as powder bed fusion or binder jetting, as well as in surface coatings.

[0128] To produce RHEA particles, elemental powders (e.g., Mo, Nb, Ta, and W) were fed into the plasma via gravity feed (e.g., using a setup similar to Figure 4G). The powders were heated and melted in the plasma region to form a high-entropy liquid, then rapidly cooled to form micronized particles, which were subsequently collected. The micronized powder size can be controlled by adjusting the temperature and powder flow rate. The micronization, spheroidization, and alloying processes of the RHEA synthesis process benefit not only from the extreme high temperatures (up to 8000 K) provided by the plasma generated by the tip-enhanced carbon electrodes, but also from the long reaction zone residence time provided by the uniform and stable plasma distribution within the gap between the carbon electrodes.

[0129] The resulting atomized MoNbTaW RHEA alloy powder is granular and silvery gray, in contrast to the black powder-like mixture of the single components. Images of the atomized MoNbTaW refractory metal powder show a high degree of sphericity, with no satellite particles observed adhering to the surface of larger particles. The average particle size was statistically determined to be 81.2 ± 13.4 μm. EDS mapping of the MoNbTaW powder sample showed a uniform distribution of the four elements within the particles. XRD patterns of the plasma-atomized RHEA powder and the corresponding precursor powders of the single-component mixture are shown in Figure 11, where the distinct peak shifts and disappearance of diffraction peaks from the single components shown for the MoNbTaW RHEA powder indicate alloying between the four components. The generality of this method for the synthesis of atomized RHEA powders was further verified by extending the refractory metal powder species involved to WNbTi and MoNbTaWCr, in particular, with similar results.

[0130] The alloying process, crystalline structure, and chemical composition of the refractory metal powder can be adjusted by the applied temperature, which can depend on the voltage between the electrodes, the current, the gap distance, and / or the gas pressure. The size of the atomized alloy powder can be adjusted by the atomizer design. The argon carrier gas can be optimized with respect to the introduction of the mixed refractory metal powder precursor into the plasma region (e.g., powder feed rate, feed amount, etc.) to further improve production efficiency.

[0131] Furthermore, the disclosed plasma process was used to synthesize atomized WB4 particles. The synthesis route was similar to that for the medium / high entropy alloy powders described above, except that tungsten and boron elemental powders were premixed and passed through the plasma zone. The ultra-high temperature plasma drives the reaction to form WB4 phase particles as they cool. Cross-sectional images of the resulting WB4 showed texture and morphology similar to that of bulk WB4, as reported in the literature. However, here, atomized powder was synthesized instead of bulk material. Such atomized WB4 powders may be useful for additive manufacturing.

[0132] Additional Examples of the Disclosed Technology In view of the above-described implementations of the disclosed subject matter, the present application discloses additional examples in the appendices listed below. It should be noted that any feature of an appendice alone, or two or more features of an appendice taken in combination, and optionally, any further examples combined with one or more features of one or more additional appendices, are also included within the scope of the present application's disclosure.

[0133] Appendix 1. generating a volumetric plasma between a first electrode and a second electrode spaced apart by a gap, the first electrode comprising a first base layer and a plurality of first protruding portions extending along a first direction from the first base layer toward the second electrode, the first protruding portions extending along the first direction from the first base layer toward the second electrode; the first base layer includes a first conductive material; At least some of the first protruding portions include a second conductive material; the melting temperature of the first conductive material and the melting temperature of the second conductive material are at least 1000 K; During the generation of the volumetric plasma, the temperature of the volumetric plasma between the first electrode and the second electrode is in the range of 1000 to 8000 K (inclusive). method.

[0134] Appendix 2. The method according to any of the sections or examples herein, particularly Appendix 1, comprising: each of the first protruding portions has a maximum cross-sectional dimension of 500 μm or less in a plane substantially perpendicular to the first direction; each of the first protruding portions has a length along the first direction of 1 cm or less; each of the first protruding portions is spaced apart from an adjacent one of the plurality of first protruding portions by 1 mm or less; or Any combination of the above method.

[0135] Appendix 3. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 1 and 2, comprising: a cross-sectional dimension of each of the first protruding portions is in the range of 1 to 100 μm (inclusive), for example, in the range of 1 to 50 μm (inclusive); The length of each of the first projecting portions is within the range of 200 to 500 μm (inclusive), The distance between adjacent first protruding portions is 100 μm or less, for example, 50 μm or less, The density of the first protruding portions is at least 10 4 portion / cm 2 or Any combination of the above method.

[0136] Appendix 4. The method described in any section or example of this specification, particularly any one of Appendices 1 to 3, wherein the distance between adjacent first protruding portions is within the range of 3 to 20 μm (inclusive).

[0137] Appendix 5. The method described in any section or example of this specification, particularly any one of Appendices 1 to 4, wherein the thickness of the gap along the first direction is in the range of 1 mm to 10 cm (inclusive), for example, in the range of 1 mm to 1 cm (inclusive).

[0138] Appendix 6. A method as described in any section or example of this specification, particularly any one of Appendices 1 to 5, wherein generating a volumetric plasma comprises applying a direct current (DC) voltage between a first electrode and a second electrode.

[0139] Appendix 7. A method as described in any section or example of this specification, particularly any one of Appendices 1 to 5, wherein generating a volumetric plasma comprises applying an alternating current (AC) voltage between a first electrode and a second electrode.

[0140] Appendix 8. The method described in any section or example of this specification, particularly any one of Appendices 1 to 5, wherein generating a volumetric plasma comprises applying a pulsed voltage waveform between the first electrode and the second electrode.

[0141] Appendix 9. A method according to any section or example of the present specification, particularly any one of Appendices 1 to 8, wherein the peak voltage applied between the first electrode and the second electrode during the generation of the volumetric plasma is 100 V or less, or the peak current between the first electrode and the second electrode during the generation of the volumetric plasma is 100 A or less.

[0142] Appendix 10. The method according to any of the sections or examples of this specification, particularly any one of Appendices 1 to 9, wherein generating the volumetric plasma comprises: initiating a volumetric plasma by applying a first direct current (DC) voltage, a first alternating current (AC) voltage, or a first pulsed voltage waveform between the first electrode and the second electrode; maintaining the volumetric plasma initiated by applying a second DC voltage, a second AC voltage, or a second pulsed voltage waveform between the first electrode and the second electrode; Including, wherein the absolute value of the peak voltage of the second DC voltage, the second AC voltage, or the second pulse voltage waveform is less than the absolute value of the peak voltage of the first DC voltage, the first AC voltage, or the first pulse voltage waveform.

[0143] Appendix 11. A method as described in any of the sections or examples herein, particularly in Appendix 10, comprising: The absolute value of the peak voltage of the first DC voltage, the first AC voltage, or the first pulse waveform is in the range of 10 to 100 V (inclusive), and / or the absolute value of the peak voltage of the second DC voltage, the second AC voltage, or the second pulse waveform is in the range of 10 to 50 V (inclusive).

[0144] Appendix 12. A method according to any section or example of the present specification, particularly any one of Appendices 10 to 11, wherein during initiation of the volumetric plasma, a first DC voltage, a first AC voltage, or a first pulsed voltage waveform is applied between the first electrode and the second electrode for at least 1 minute, or during maintenance of the initiated volumetric plasma, a second DC voltage, a second AC voltage, or a second pulsed voltage waveform is applied between the first electrode and the second electrode for at least 1 minute.

[0145] Appendix 13. The method according to any section or example of this specification, particularly any one of Appendices 1 to 12, wherein generating a volumetric plasma between the first electrode and the second electrode is carried out at about atmospheric pressure.

[0146] Appendix 14. A method according to any section or example of the present specification, particularly any one of Appendices 1 to 13, wherein the size of the generated plasma along the second direction is at least 1 mm, for example, in the range of 1 mm to 100 cm (inclusive), and the second direction lies in a plane substantially perpendicular to the first direction.

[0147] Appendix 15. The method according to any section or example of the present specification, particularly any one of Appendices 1 to 14, wherein generating plasma is carried out at a pressure in the range of 1 Torr to 10 atm, with or without the application of an external magnetic field.

[0148] Appendix 16. The method according to any section or example of the present specification, particularly any one of Appendices 1 to 15, wherein the first and second conductive materials are the same material.

[0149] Appendix 17. The method described in any section or example herein, particularly any one of Appendices 1 to 16, wherein the first conductive material, the second conductive material, or both, are formed from carbon or graphite.

[0150] Appendix 18. The method according to any section or example herein, particularly any one of Appendices 1 to 17, wherein the first conductive material, the second conductive material, or both, are formed from a refractory metal, a refractory metal alloy, or both.

[0151] Appendix 19. The method of any section or example herein, particularly any one of Appendices 1-18, wherein the first electrically conductive material, the second electrically conductive material, or both, are formed of a metal carbide, silicon carbide, a metal nitride, a metal diboride, or any combination thereof.

[0152] Appendix 20. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 1 to 19, comprising: the second electrode comprises a second base layer and a plurality of second protruding portions extending from the second base layer toward the first electrode along a first direction; the second base layer comprises a third conductive material; The method, wherein at least some of the second protruding portions include a fourth conductive material, and the melting temperature of the third conductive material and the melting temperature of the fourth conductive material are at least 1000K.

[0153] Appendix 21. The method according to any section or example herein, particularly any one of Appendix 1 to Appendix 20, wherein the first and second conductive materials are the same material, the third and fourth conductive materials are the same material, the second and fourth conductive materials are the same material, the first and third conductive materials are the same material, or any combination of the foregoing.

[0154] Appendix 22. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 1 to 21, comprising: prior to generating the volumetric plasma, an end of each of at least some of the first protruding portions has a first shape, and after generating, an end of each of at least some of the first protruding portions is sharpened to have a first conical shape different from the first shape; and / or A method, wherein before generating the volumetric plasma, an end of each of at least some of the second protruding portions has a second shape, and after generating, an end of each of at least some of the second protruding portions has a second conical shape that is different from the second shape.

[0155] Appendix 23. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 1 to 22, comprising: the first electrode further comprises a plurality of third protruding portions extending from the first base layer toward the second electrode along the first direction farther than the plurality of first protruding portions, at least some of the third protruding portions being formed of a fifth conductive material; the second electrode further comprises a plurality of fourth protruding portions extending from the second base layer toward the first electrode along the first direction farther than the plurality of second protruding portions, at least some of the fourth protruding portions being formed of a sixth conductive material; At least one of the third protruding portions contacts at least one of the fourth protruding portions in the gap or is separated from at least one of the fourth protruding portions by 25 μm or less, for example, 5 μm or less; The method, wherein the melting temperature of the fifth conductive material and the melting temperature of the sixth conductive material are at least 1000K.

[0156] Appendix 24. A method as described in any section or example of this specification, particularly Appendix 23, wherein generating the volumetric plasma includes initiating the volumetric plasma via a gas discharge between the third and fourth protruding portions, and maintaining the volumetric plasma via a gas discharge between the first and second protruding portions.

[0157] Appendix 25. A method according to any section or example of the present specification, particularly any one of Appendixes 23 to 24, comprising, before initiating the volumetric plasma, applying a first voltage between the first and second electrodes, thereby causing a current to flow through a contact portion of at least one of the third and fourth protruding portions, thereby causing Joule heating, wherein the Joule heating causes destruction of at least one of the third and / or fourth protruding portions, such that at least one of the third protruding portions is separated from at least one of the fourth protruding portions by a distance of 1 to 25 μm (inclusive), for example, 1 to 5 μm (inclusive).

[0158] Appendix 26. A method according to any section or example of the present specification, particularly any one of Supplementary Notes 23 to 25, wherein, before initiating the volumetric plasma, a first voltage is applied between the first and second electrodes, thereby causing a current to flow through a contact portion of at least one of the third and fourth protruding portions, resulting in Joule heating, and the Joule heating causing destruction of at least one of the third and / or fourth protruding portions, such that at least one of the third protruding portions is separated from at least one of the fourth protruding portions by a distance not greater than three times the cross-sectional dimension of the third or fourth protruding portion.

[0159] Appendix 27. The method according to any section or example of the present specification, particularly any one of Appendices 23 to 26, wherein the first and second conductive materials are the same material, the third and fourth conductive materials are the same material, the fifth and sixth conductive materials are the same material, the second and fourth conductive materials are the same material, the first and third conductive materials are the same material, the second and fifth conductive materials are the same material, the fourth and sixth conductive materials are the same material, or any combination of the above.

[0160] Appendix 28. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 23 to 27, comprising: The method, wherein one, some, or all of the first through sixth conductive materials are formed from or include: (i) carbon or graphite; (ii) a refractory metal, a refractory metal alloy, or both; (iii) a metal carbide, silicon carbide, a metal nitride, a metal diboride, or any combination thereof; or (iv) any combination of (i) through (iii).

[0161] Appendix 29. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 23 to 28, comprising: each of the third protruding portion and / or the fourth protruding portion has a cross-sectional dimension in a plane substantially perpendicular to the first direction of 1 mm or less, for example, 500 μm or less; the cross-sectional dimension of the third protruding portion and / or the fourth protruding portion is in the range of 1 to 100 μm (inclusive), for example, in the range of 1 to 50 μm (inclusive); wherein each of the third protruding portions and / or each of the fourth protruding portions has a length along the first direction that is greater than 1 mm, for example, a length in the range of 10 to 100 mm (inclusive), or any combination of the above.

[0162] Appendix 30. The method according to any of the clauses or examples herein, in particular any one of appendices 1 to 29, comprising, before generating the volumetric plasma: forming the first electrode by cutting a portion from a first cloth comprising a woven carbon or metal fiber fabric, the first base layer being the remaining portion of the first cloth after the cutting, and the plurality of first protruding portions and / or the plurality of third protruding portions being carbon or metal fibers exposed from the cut surface of the remaining portion of the first cloth; and / or forming the second electrode by cutting a portion from a second fabric comprising a woven carbon or metal fiber fabric, the second base layer being the remaining portion of the second fabric after the cutting, and the second base layer being the carbon or metal fibers exposed from the cut surface of the remaining portion of the second fabric; A method comprising:

[0163] Appendix 31. The method of any section or example herein, particularly Appendix 30, wherein the remainder of the first fabric and / or the remainder of the second fabric comprises a plurality of woven carbon or metal fibers extending along a second direction in a plane substantially perpendicular to the first direction.

[0164] Appendix 32. The method according to any of the clauses or examples herein, in particular any one of appendices 1 to 29, comprising, before generating the volumetric plasma: The first electrode is formed by roughening the surface of a first cloth containing woven carbon or metal fibers, wherein the first base layer is a bulk portion of the first cloth, and the plurality of first protruding portions and / or the plurality of third protruding portions are carbon or metal fibers that are fragmented at or exposed from the surface of the bulk portion of the first cloth by the roughening; and / or The method includes forming the second electrode by roughening the surface of the second cloth, wherein the second base layer is a bulk portion of the second cloth, and the plurality of second protruding portions and / or the plurality of fourth protruding portions are carbon or metal fibers that are fragmented at or exposed from the surface of the bulk portion of the second cloth by the roughening.

[0165] Appendix 33. The method according to any of the clauses or examples herein, particularly Appendix 32, comprising: The method, wherein the bulk portion of the first fabric and / or the bulk portion of the second fabric comprises a plurality of woven carbon or metal fibers extending along a second direction in a plane substantially perpendicular to the first direction.

[0166] Appendix 34. The method according to any of the clauses or examples herein, in particular any one of appendices 1 to 29, comprising, before generating the volumetric plasma: forming a plurality of first protruding portions on a first base layer; forming a plurality of third protruding portions on the first base layer; forming a plurality of second protruding portions on the second base layer; forming a plurality of fourth protruding portions on the second base layer; or Any combination of the above, A method comprising:

[0167] Appendix 35. The method described in any section or example herein, particularly in Appendix 34, comprising: The method, wherein forming the plurality of first protruding portions, forming the plurality of second protruding portions, forming the plurality of third protruding portions, and / or forming the plurality of fourth protruding portions comprises three-dimensional printing.

[0168] Appendix 36. The method described in any section or example herein, particularly in Appendix 35, comprising: Three-dimensional printing methods include laser-based direct energy deposition or laser powder bed fusion.

[0169] Appendix 37. The method described in any section or example herein, particularly any one of Appendices 1 to 36, wherein the first electrode, the second electrode, or both, have a non-planar shape.

[0170] Appendix 38. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 1 to 37, comprising: the second electrode has a surface area facing the gap that is greater than a surface area of ​​the first electrode; The method further includes, during generation of the volumetric plasma, moving one of the first and second electrodes relative to the other to vary a position of the generated volumetric plasma.

[0171] Appendix 39. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 1 to 38, comprising: The method further includes, prior to or simultaneously with generating the volumetric plasma, disposing one or more precursors within or adjacent to the gap between the first electrode and the second electrode such that the volumetric plasma heats the one or more precursors to form one or more products.

[0172] Appendix 40. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 1 to 39, comprising: The method further includes flowing one or more gases and / or one or more precursors through the volumetric plasma during generation of the volumetric plasma, such that the volumetric plasma heats the one or more gases and / or one or more precursors to form one or more products.

[0173] Appendix 41. A method as described in any section or example herein, particularly in Appendix 40, comprising: The method, wherein the first and second electrodes are positioned such that a thickness of the gap along the first direction is at a non-zero angle with respect to the direction of gravity, such that gravity assists the flow of the one or more precursors through the gap.

[0174] Appendix 42. The method according to any of the sections or examples of the present specification, particularly any one of Appendices 40 to 41, The method, wherein the flow includes using a carrier gas and / or a substrate to support the one or more precursors within the volume plasma, flowing into the volume plasma, and / or flowing out of the volume plasma.

[0175] Appendix 43. A method as described in any of the sections or examples herein, particularly in Appendix 42, comprising: The method wherein the carrier gas comprises an inert gas.

[0176] Appendix 44. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 39 to 43, comprising: The method further comprising ceasing generation of the volumetric plasma, moving one or more product products out of the volumetric plasma, and / or moving the volumetric plasma away from the one or more product products.

[0177] Appendix 45. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 39 to 44, comprising: The method further comprising actively cooling the one or more products and / or exposing the one or more products to a gas stream to break up the one or more products into smaller size droplets.

[0178] Appendix 46. The method according to any of the sections or examples of this specification, particularly any one of appendices 1 to 45, wherein generating the volumetric plasma comprises: initiating a volumetric plasma by applying a voltage between first and second electrodes with a gap at a first distance; moving the first electrode away from the second electrode and / or moving the second electrode away from the first electrode; and maintaining the initiated volumetric plasma by applying a voltage between the first electrode and the second electrode with the gap being greater than the first distance; A method comprising:

[0179] Appendix 47. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 1 to 46, comprising: The method wherein generating the volumetric plasma is such that said volumetric plasma is maintained at the same volume for at least 10 minutes.

[0180] Appendix 48. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 1 to 47, comprising: A method wherein the temperature of the volumetric plasma is spatially uniform, eg, the temperature of the volumetric plasma across a second direction substantially perpendicular to the first direction varies by 10% or less.

[0181] Appendix 49. A method according to any of the sections or examples of the present specification, particularly any one of Appendices 1 to 48, comprising: one, some, or all of the first protruding portion, the second protruding portion, the third protruding portion, and the fourth protruding portion have a substantially one-dimensional sharp distal tip at an end thereof proximal to or within the gap; one, some, or all of the first protruding portion, the second protruding portion, the third protruding portion, and the fourth protruding portion have a substantially two-dimensional sharp distal tip at an end thereof proximal to or within the gap; one, some, or all of the first protruding portion, the second protruding portion, the third protruding portion, and the fourth protruding portion have a blunt distal tip at its end adjacent to or within the gap; or including any combination of the above method.

[0182] Appendix 50. A system configured to perform the method described in any one of appendices 1 to 49 as described in any section or example of this specification, in particular, for example, with respect to any of Figures 1A to 11.

[0183] Appendix 51. a first electrode including a first base layer and a plurality of first protruding portions, wherein the first base layer includes a first conductive material, at least some of the first protruding portions include a second conductive material, and a melting temperature of the first conductive material and a melting temperature of the second conductive material are at least 1000K; a second electrode spaced apart from the first electrode by a gap, the second electrode having a plurality of first protruding portions extending along a first direction from the first base layer toward the second electrode; a power source electrically coupled to the first and second electrodes; a control system operably coupled to the power supply and configured to control its operation, the control system comprising: one or more processors; and a computer-readable storage medium storing instructions that, when executed by the one or more processors, cause the power supply to apply a voltage between the first electrode and the second electrode such that a volumetric plasma is generated in or adjacent to the gap, and such that a temperature of the volumetric plasma is in the range of 1000 to 8000 K; Including, the system.

[0184] Appendix 52. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 51, each of the first protruding portions has a cross-sectional dimension in a plane substantially perpendicular to the first direction of 1 mm or less, e.g., 500 μm or less; Each of the first protruding portions has a length along the first direction of 1 cm or less, for example, 5 mm or less; each of the first protruding portions is spaced apart from an adjacent one of the plurality of first protruding portions by 1 mm or less; or Any combination of the above system.

[0185] Appendix 53. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 52, a cross-sectional dimension of each of the first protruding portions is in the range of 1 to 100 μm (inclusive), for example, in the range of 1 to 50 μm (inclusive); The length of each of the first protruding portions is within the range of 200 to 500 μm (inclusive), The spacing between adjacent first protruding portions is 100 μm or less, for example, 50 μm or less; The density of the first protruding portions is at least 10 4 portion / cm 2 or Any combination of the above system.

[0186] Appendix 54. A system described in any section or example of the present specification, particularly any one of appendices 50 to 53, wherein the spacing between adjacent first protruding portions is within the range of 3 to 20 μm.

[0187] Appendix 55. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 54, The system wherein the thickness of the gap along the first direction is in the range of 1 mm to 10 cm inclusive, for example, in the range of 1 mm to 1 cm inclusive.

[0188] Appendix 56. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 55, The system, wherein the power supply is configured to apply a direct current (DC) voltage, an alternating current (AC) voltage, or a pulsed voltage waveform between the first electrode and the second electrode.

[0189] Appendix 57. A system described in any section or example herein, particularly any one of Appendices 50-56, wherein the computer-readable storage medium stores additional instructions that, when executed by one or more processors, cause the power supply to apply a peak voltage of 100 V or less between the first electrode and the second electrode to generate volumetric plasma, and / or apply a peak current of 100 A or less between the first electrode and the second electrode to generate volumetric plasma.

[0190] Appendix 58. The system described in any section or example herein, particularly any one of appendices 50-57, wherein the computer-readable storage medium stores additional instructions that, when executed by one or more processors, further cause the power source to: initiating a volumetric plasma by applying a first direct current (DC) voltage, a first alternating current (AC) voltage, or a first pulsed voltage waveform between the first electrode and the second electrode; maintaining the initiated volumetric plasma by applying a second DC voltage, a second AC voltage, or a second pulsed voltage waveform between the first electrode and the second electrode; Here, the absolute value of the peak voltage of the second DC voltage, the second AC voltage, or the second pulse voltage waveform is smaller than the absolute value of the peak voltage of the first DC voltage, the first AC voltage, or the first pulse voltage waveform.

[0191] Appendix 59. A system as described in any of the sections or examples herein, particularly in Appendix 57, comprising: The absolute value of the peak voltage of the first DC voltage, the first AC voltage, or the first pulse waveform is within the range of 10 to 100 V (inclusive), or the absolute value of the peak voltage of the second DC voltage, the second AC voltage, or the second pulse waveform is within the range of 10 to 50 V (inclusive).

[0192] Appendix 60. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 59, The first and second electrodes are sized such that the size of the plasma generated along the second direction is at least 1 mm, e.g., in the range of 1 mm to 100 cm (inclusive), and the second direction is in a plane substantially perpendicular to the first direction, in the system.

[0193] Appendix 61. 1. A system as described in any section or example herein, particularly any one of Appendices 50-60, wherein the system is configured to generate a volumetric plasma at a pressure in the range of 1 Torr to 10 atm (inclusive), for example, at about 1 atm.

[0194] Appendix 62. The system described in any section or example herein, particularly any one of Appendices 50 to 61, wherein the first conductive material is the same as the second conductive material.

[0195] Appendix 63. 62. The system described in any section or example herein, particularly any one of Appendices 50-62, wherein the first conductive material, the second conductive material, or both, comprises a refractory metal, a refractory metal alloy, or both.

[0196] Appendix 64. The system according to any of the clauses or examples herein, particularly any one of appendices 50 to 63, The system, wherein the first conductive material, the second conductive material, or both, comprises a metal carbide, silicon carbide, a metal nitride, a metal diboride, or any combination thereof.

[0197] Appendix 65. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 64, the second electrode comprises a second base layer and a plurality of second protruding portions extending from the second base layer toward the first electrode along a first direction; the second base layer comprises a third conductive material; At least some of the second projecting portions include a fourth conductive material; The melting temperature of the third conductive material and the melting temperature of the fourth conductive material are at least 1000K.

[0198] Appendix 66. A system described in any section or example of this specification, particularly any one of Appendices 50 to 65, wherein at least one of the first to fourth conductive materials is the same as the other of the first to fourth conductive materials.

[0199] Appendix 67. A system described in any section or example herein, particularly any one of Appendices 50 to 66, wherein each end of at least some of the first protruding portions is conical, and / or each end of at least some of the second protruding portions is conical.

[0200] Appendix 68. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 67, the first electrode further comprises a plurality of third protruding portions extending from the first base layer toward the second electrode along the first direction farther than the plurality of first protruding portions, at least some of the third protruding portions being formed of a fifth conductive material; the second electrode includes a plurality of fourth protruding portions extending along the first direction from the second base layer toward the first electrode, at least some of the fourth protruding portions being formed of a sixth conductive material; At least one of the third protruding portions contacts at least one of the fourth protruding portions in the gap or is separated from at least one of the fourth protruding portions by 25 μm or less, for example, 5 μm or less; The melting temperature of the fifth conductive material and the melting temperature of the sixth conductive material are at least 1000K.

[0201] Appendix 69. A system as described in any section or example herein, particularly in Appendix 68, comprising: The computer-readable storage medium stores additional instructions that, when executed by the one or more processors, cause the power source to initiate a volumetric plasma via a gas discharge between the third protruding portion and the fourth protruding portion, and to maintain the initiated volumetric plasma via a gas discharge between the first protruding portion and the second protruding portion, in a system.

[0202] Appendix 70. A system according to any of the sections or examples of this specification, particularly any one of appendices 68-69, The computer-readable storage medium stores additional instructions, which when executed by the one or more processors, include applying a first voltage by a power source before initiating a volumetric plasma, applying the first voltage between the first electrode and the second electrode, causing a current to flow through a contact portion of at least one of the third and fourth protruding portions, causing Joule heating thereof, and the Joule heating causing destruction of at least one of the third and / or fourth protruding portions, such that at least one of the third protruding portions is separated from at least one of the fourth protruding portions by a distance of 10 μm or less, for example, 1 to 5 μm (inclusive).

[0203] Appendix 71. A system described in any section or example of this specification, particularly any one of Appendices 68 to 70, wherein at least one of the first to sixth conductive materials is the same as another of the first to sixth conductive materials.

[0204] Appendix 72. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 71, The system, wherein one, some, or all of the first through sixth conductive materials include (i) carbon or graphite, (ii) a refractory metal, a refractory metal alloy, or both, (iii) a metal carbide, silicon carbide, a metal nitride, a metal diboride, or any combination thereof, or (iv) any combination of (i) through (iii).

[0205] Appendix 73. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 72, each of the third protruding portion and / or the fourth protruding portion has a maximum cross-sectional dimension in a plane substantially perpendicular to the first direction of 1 mm or less, e.g., 500 μm or less; the maximum cross-sectional dimension of each of the third and / or fourth protruding portions is in the range of 1 to 100 μm (inclusive), for example, 1 to 50 μm (inclusive); Each of the third protruding portions and / or each of the fourth protruding portions has a length along the first direction that is greater than 1 mm, for example, a length in the range of 10 to 100 mm (inclusive), or Any combination of the above system.

[0206] Appendix 74. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 73, The system, wherein the first electrode, the second electrode, or both, comprise woven carbon fiber or metal fiber.

[0207] Appendix 75. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 74, The system, wherein the plurality of first protruding portions, the plurality of second protruding portions, the plurality of third protruding portions, and / or the plurality of fourth protruding portions comprise three-dimensionally printed pillars.

[0208] Appendix 76. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 75, The system, wherein the first electrode, the second electrode, or both have a non-planar shape.

[0209] Appendix 77. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 76, The system further includes a first translation stage configured to move the first electrode and / or a second translation stage configured to move the second electrode.

[0210] Appendix 78. A system as described in any section or example herein, particularly in Appendix 77, comprising: a control system operably coupled to the first translation stage and / or the second translation stage and configured to control operation thereof; The computer-readable storage medium stores additional instructions that, when executed by the one or more processors, cause the first translation stage and / or the second translation stage to move one of the first and second electrodes relative to the other of the first and second electrodes.

[0211] Appendix 79. A system according to any of the sections or examples of this specification, particularly any one of appendices 77-78, the second electrode has a surface area facing the gap that is greater than a surface area of ​​the first electrode; The computer-readable storage medium, when executed by one or more processors, causes a first translation stage and / or a second translation stage to change the position of a volumetric plasma in a system.

[0212] Appendix 80. The system described in any section or example herein, particularly any one of appendices 77-79, wherein the computer-readable storage medium stores instructions that, when executed by one or more processors, cause the system to: the first translation stage and / or the second translation stage positioning the first and second electrodes such that the gap is at a first distance; a power supply initiating a volumetric plasma by applying a voltage between the first and second electrodes with a gap at a first distance; the first translation stage and / or the second translation stage moving the first and second electrodes away from each other after initiation of the volumetric plasma; The power supply sustains the initiated volumetric plasma by applying a voltage between the first and second electrodes with the gap being greater than the first distance.

[0213] Appendix 81. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 80, The system, wherein the first and second electrodes are positioned such that the thickness of the gap along the first direction is at a non-zero angle with respect to the direction of gravity.

[0214] Appendix 82. A system according to any of the sections or examples of this specification, particularly any one of appendices 50 to 81, one, some, or all of the first protruding portion, the second protruding portion, the third protruding portion, and the fourth protruding portion have a substantially one-dimensional sharp distal tip at an end proximal or internal to the gap; one, some, or all of the first protruding portion, the second protruding portion, the third protruding portion, and the fourth protruding portion have a substantially two-dimensional sharp distal tip at an end proximal or internal to the gap; one, some, or all of the first protruding portion, the second protruding portion, the third protruding portion, and the fourth protruding portion have a blunt distal tip at its end adjacent to or within the gap; or any combination of the above, including system.

[0215] Appendix 83. A method for operating a system described in any section or example herein, particularly any one of Appendices 1 to 49, for example as described with respect to any of Figures 1A to 11.

[0216] Appendix 84. A method for generating and / or using plasma according to any of the embodiments disclosed herein, or combinations thereof, for example, as described in connection with any of Figures 1A-11.

[0217] conclusion Any of the features illustrated or described herein, for example, with respect to Figures 1A-11 and Supplements 1-84, can be combined with any other feature illustrated or described herein, for example, with respect to Figures 1A-11 and Supplements 1-84, to provide systems, devices, structures, methods, and embodiments not otherwise illustrated or specifically described herein. All features described herein are independent of one another and can be used in combination with any other feature described herein, except where structurally impossible. Given that the principles of the disclosed technology may be applied in many possible embodiments, it should be recognized that the illustrated embodiments are merely examples and should not be construed as limiting the scope of the disclosed technology. Rather, the scope is defined by the following claims. Accordingly, the inventors claim all that comes within the scope and spirit of these claims.

Claims

1. generating a volumetric plasma between a first electrode and a second electrode spaced apart by a gap, the first electrode comprising a first base layer and a plurality of first protruding portions extending along a first direction from the first base layer toward the second electrode, the first protruding portions extending along the first direction from the first base layer toward the second electrode; the first base layer includes a first conductive material; At least some of the first protruding portions include a second conductive material; the melting temperature of the first conductive material and the melting temperature of the second conductive material are at least 1000 K; During the generation of the volumetric plasma, the temperature of the volumetric plasma between the first electrode and the second electrode is in the range of 1000 to 8000 K (inclusive). method.

2. Each of the first protruding portions has a maximum cross-sectional dimension of 500 μm or less in a plane substantially perpendicular to the first direction, each of the first protruding portions has a length along the first direction of 1 cm or less; each of the first protruding portions is spaced apart from an adjacent one of the plurality of first protruding portions by 1 mm or less; or Any combination of the above The method of claim 1.

3. a maximum cross-sectional dimension of each of the first protruding portions is in the range of 1 to 100 μm; the length of each of the first protruding portions is in the range of 200 to 500 μm; the interval between adjacent first protruding portions is 100 μm or less; The density of the first protruding portions is at least 10 ４ Portion / cm ２ or Any combination of the above The method of claim 2.

4. The method of claim 3, wherein the spacing between the first protruding portions is between 1 μm and 50 μm inclusive.

5. The method of claim 1 , wherein the thickness of the gap along the first direction is between 1 mm and 1 cm, inclusive.

6. The method of claim 1 , wherein generating the volumetric plasma comprises applying a direct current (DC) voltage between the first electrode and the second electrode.

7. The method of claim 1 , wherein generating the volumetric plasma comprises applying an alternating current (AC) voltage between the first electrode and the second electrode.

8. The method of claim 1 , wherein generating the volumetric plasma comprises applying a pulsed voltage waveform between the first electrode and the second electrode.

9. a peak voltage applied between the first electrode and the second electrode during generation of the volumetric plasma is 100 V or less; a peak current between the first electrode and the second electrode during generation of the volumetric plasma is 100 A or less; or Both of the above, The method according to any one of claims 6 to 8.

10. generating the volumetric plasma includes: initiating the volumetric plasma by applying a first direct current (DC) voltage, a first alternating current (AC) voltage, or a first pulsed voltage waveform between the first electrode and the second electrode; maintaining the volumetric plasma initiated by applying a second DC voltage, a second AC voltage, or a second pulsed voltage waveform between the first electrode and the second electrode; Including, an absolute value of a peak voltage of the second DC voltage, the second AC voltage, or the second pulse voltage waveform is smaller than an absolute value of a peak voltage of the first DC voltage, the first AC voltage, or the first pulse voltage waveform; The method of claim 1.

11. the absolute value of the peak voltage of the first DC voltage, the first AC voltage, or the first pulse voltage waveform is in the range of 10 to 100 V (inclusive); the absolute value of the peak voltage of the second DC voltage, the second AC voltage, or the second pulsed voltage waveform is in the range of 10 to 50 V (inclusive); or Both of the above, The method of claim 10.

12. During the initiation of the volumetric plasma, the first DC voltage, the first AC voltage, or the first pulsed voltage waveform is applied between the first electrode and the second electrode for at least 1 minute; While maintaining the initiated volumetric plasma, the second DC voltage, the second AC voltage, or the second pulsed voltage waveform is applied between the first electrode and the second electrode for at least 1 minute; or Both of the above, The method of claim 10.

13. The method of claim 1 , wherein generating the volumetric plasma between the first electrode and the second electrode occurs at atmospheric pressure.

14. 10. The method of claim 1, wherein a size of the generated volumetric plasma along the second direction is in the range of 1 mm to 100 cm, inclusive, and the second direction lies in a plane substantially perpendicular to the first direction.

15. 10. The method of claim 1, wherein generating the volumetric plasma occurs at a pressure ranging from 1 Torr to 10 atm, inclusive, with or without the application of an external magnetic field.

16. The method of claim 1 , wherein the first and second conductive materials are the same material.

17. The method of claim 1 , wherein the first conductive material, the second conductive material, or both, comprises carbon or graphite.

18. The method of claim 1 , wherein the first conductive material, the second conductive material, or both, comprises a refractory metal, a refractory metal alloy, or both.

19. 10. The method of claim 1, wherein the first conductive material, the second conductive material, or both, comprises a metal carbide, silicon carbide, a metal nitride, a metal diboride, or any combination thereof.

20. the second electrode includes a second base layer and a plurality of second protruding portions extending from the second base layer toward the first electrode along the first direction; the second base layer includes a third conductive material; At least some of the second projecting portions include a fourth conductive material; the melting temperature of the third conductive material and the melting temperature of the fourth conductive material are at least 1000 K; The method of claim 1.

21. the first and second conductive materials are the same material; the third and fourth conductive materials are the same material; the second and fourth conductive materials are the same material; the first and third conductive materials are the same material, or Any combination of the above 21. The method of claim 20.

22. prior to generating the volumetric plasma, an end of each of the at least some first protruding portions has a first shape, and after generating the volumetric plasma, an end of each of the at least some first protruding portions is pointed to have a first conical shape different from the first shape; before generating the volumetric plasma, an end of each of at least some of the second protruding portions has a second shape, and after generating the volumetric plasma, an end of each of at least some of the second protruding portions has a second conical shape different from the second shape; or Both of the above, 21. The method of claim 20.

23. the first electrode further includes a plurality of third protruding portions extending from the first base layer toward the second electrode along the first direction farther than the plurality of first protruding portions, at least some of the third protruding portions being formed of a fifth conductive material; the second electrode further includes a plurality of fourth protruding portions extending from the second base layer toward the first electrode along the first direction farther than the plurality of second protruding portions, at least some of the fourth protruding portions being formed of a sixth conductive material; At least one of the third protruding portions contacts at least one of the fourth protruding portions in the gap or is separated from at least one of the fourth protruding portions by 5 μm or less; the melting temperature of the fifth conductive material and the melting temperature of the sixth conductive material are at least 1000 K; 21. The method of claim 20.

24. generating the volumetric plasma includes: initiating the volume plasma via a gas discharge between the third and fourth protruding portions; maintaining the volume plasma via a gas discharge between the first and second protruding portions; 24. The method of claim 23, comprising:

25. and applying a first voltage between the first and second electrodes before initiating the volumetric plasma, such that a current flows through a contact portion of at least one of the third and fourth protruding portions to cause Joule heating; the Joule heating causes destruction of at least one of the third and / or fourth protruding portions, whereby the at least one of the third protruding portions is separated from the at least one of the fourth protruding portions by a distance of 1 to 5 μm, inclusive; 25. The method of claim 24.

26. the first and second conductive materials are the same material; the third and fourth conductive materials are the same material; the fifth and sixth conductive materials are the same material; the second and fourth conductive materials are the same material; the first and third conductive materials are the same material; the second and fifth conductive materials are the same material; the fourth and sixth conductive materials are the same material, or Any combination of the above 24. The method of claim 23.

27. One, some, or all of the first to sixth conductive materials are (i) carbon or graphite; (ii) a refractory metal, a refractory metal alloy, or both; (iii) a metal carbide, silicon carbide, metal nitride, metal diboride, or a combination thereof; (iv) any combination of (i) to (iii) above; 24. The method of claim 23, comprising:

28. each of the third protruding portion and / or the fourth protruding portion has a maximum cross-sectional dimension in a plane substantially perpendicular to the first direction of 500 μm or less; a maximum cross-sectional dimension of each of the third protruding portion and / or the fourth protruding portion is in the range of 1 to 100 μm (inclusive); each of the third protruding portions and / or each of the fourth protruding portions has a length along a first direction that is greater than 1 mm; the length of each of the third protruding portion and / or the fourth protruding portion is in the range of 10 to 100 mm (inclusive); or Any combination of the above 24. The method of claim 23.

29. before generating the volumetric plasma, forming the first electrode by cutting a portion from a first cloth comprising a woven carbon or metal fiber fabric, the first base layer being the remaining portion of the first cloth after the cutting, and the plurality of first protruding portions and / or the plurality of third protruding portions being carbon or metal fibers exposed from the cut surface of the remaining portion of the first cloth; and / or forming the second electrode by cutting a portion from a second fabric comprising a woven carbon or metal fiber fabric, the second base layer being the remaining portion of the second fabric after the cutting, and the second base layer being carbon or metal fibers exposed from the cut surface of the remaining portion of the second fabric; 24. The method of claim 23, comprising:

30. 30. The method of claim 29, wherein the remainder of the first fabric and / or the remainder of the second fabric comprises a plurality of woven carbon or metal fibers extending along a second direction in a plane substantially perpendicular to the first direction.

31. before generating the volumetric plasma, forming the first electrode by roughening a surface of a first fabric comprising woven carbon or metal fibers, wherein the first base layer is a bulk portion of the first fabric, and the plurality of first protruding portions and / or the plurality of third protruding portions are carbon or metal fibers fragmented at the surface of the bulk portion of the first fabric or exposed from the bulk portion by the roughening; and / or forming the second electrode by roughening a surface of the second cloth, wherein the second base layer is a bulk portion of the second cloth, and the plurality of second protruding portions and / or the plurality of fourth protruding portions are carbon or metal fibers fragmented at the surface of the bulk portion of the second cloth or exposed from the bulk portion by the roughening; 24. The method of claim 23, comprising:

32. 32. The method of claim 31 , wherein the bulk portion of the first fabric and / or the bulk portion of the second fabric comprises a plurality of woven carbon or metal fibers extending along a second direction in a plane substantially perpendicular to the first direction.

33. before generating the volumetric plasma, forming a plurality of first protruding portions on the first base layer; forming a plurality of third protruding portions on the first base layer; forming a plurality of second protruding portions on the second base layer; forming a plurality of fourth protruding portions on the second base layer; or Any combination of the above, 24. The method of claim 23, comprising:

34. 34. The method of claim 33, wherein forming the plurality of first protruding portions, forming the plurality of second protruding portions, forming the plurality of third protruding portions, and / or forming the plurality of fourth protruding portions comprises three dimensional printing.

35. 35. The method of claim 34, wherein the three dimensional printing comprises laser-based direct energy deposition or laser powder bed fusion.

36. The method of claim 1 , wherein the first electrode, the second electrode, or both, have a non-planar shape.

37. the second electrode has a surface area facing the gap that is greater than a surface area of ​​the first electrode; The method further includes, during generation of the volumetric plasma, moving one of the first and second electrodes relative to the other to vary the position of the generated volumetric plasma. The method of claim 1.

38. 10. The method of claim 1, further comprising disposing one or more precursors in or adjacent to the gap between the first electrode and the second electrode prior to or concurrently with generating the volumetric plasma, wherein the volumetric plasma heats the one or more precursors to form one or more product products.

39. 10. The method of claim 1, further comprising: during generation of the volumetric plasma, flowing one or more gases and / or one or more precursors through the volumetric plasma such that the volumetric plasma heats the one or more gases and / or the one or more precursors to form one or more products.

40. 40. The method of claim 39, wherein the first and second electrodes are positioned such that a thickness of the gap along the first direction is at a non-zero angle with respect to a direction of gravity, such that gravity assists the flow of the one or more precursors through the gap.

41. 40. The method of claim 39, wherein the flowing comprises using a carrier gas and / or a substrate to carry the one or more precursors into the volumetric plasma.

42. 42. The method of claim 41, wherein the carrier gas comprises an inert gas.

43. ceasing generation of said volumetric plasma; removing one or more product products from said volumetric plasma; moving the volume plasma away from one or more product products; or Any combination of the above, 43. The method of any one of claims 38 to 42, further comprising:

44. actively cooling the product; exposing the one or more products to a gas stream to break up the one or more products into smaller sized droplets; or Doing both of the above, 44. The method of claim 43, further comprising:

45. generating the volumetric plasma includes: initiating a volumetric plasma by applying a voltage between the first and second electrodes with a gap at a first distance; moving the first electrode away from the second electrode and / or moving the second electrode away from the first electrode; and maintaining the initiated volumetric plasma by applying a voltage between the first electrode and the second electrode with the gap greater than the first distance; The method of claim 1 , comprising:

46. The method of claim 1 , wherein generating the volumetric plasma comprises maintaining the volumetric plasma at the same volume for at least 10 minutes.

47. The method of claim 1 , wherein the temperature of the volumetric plasma is spatially uniform.

48. one, some, or all of the first protruding portion, the second protruding portion, the third protruding portion, and the fourth protruding portion have a substantially one-dimensional sharp distal tip at an end proximal or internal to the gap; one, some, or all of the first protruding portion, the second protruding portion, the third protruding portion, and the fourth protruding portion have a substantially two-dimensional sharp distal tip at an end proximal or internal to the gap; one, some, or all of the first protruding portion, the second protruding portion, the third protruding portion, and the fourth protruding portion have a blunt distal tip at an end proximal to or within the gap; or any combination of the above, including 24. The method of any one of claims 1, 20, and 23.

49. A system configured to carry out the method of any one of claims 1 to 48.

50. a first electrode including a first base layer and a plurality of first protruding portions, wherein the first base layer includes a first conductive material, at least some of the first protruding portions include a second conductive material, and a melting temperature of the first conductive material and a melting temperature of the second conductive material are at least 1000 K; a second electrode spaced apart from the first electrode by a gap, the second electrode having a plurality of first protruding portions extending from the first base layer toward the second electrode along a first direction; a power source electrically coupled to the first and second electrodes; a control system operatively coupled to the power supply and configured to control its operation, the control system comprising one or more processors and a computer-readable storage medium storing instructions that, when executed by the one or more processors, cause the power supply to apply a voltage between the first electrode and the second electrode such that a volumetric plasma is generated in or adjacent to the gap, and such that a temperature of the volumetric plasma is within a range of 1000 to 8000 K, inclusive; A system including:

51. each of the first protruding portions has a maximum cross-sectional dimension of 500 μm or less in a plane substantially perpendicular to the first direction; each of the first protruding portions has a length along the first direction of 1 cm or less; each of the first protruding portions is spaced apart from an adjacent first protruding portion of the plurality of first protruding portions by 1 mm or less; or Any combination of the above 51. The system of claim 50.

52. a maximum cross-sectional dimension of each of the first protruding portions is in the range of 1 to 100 μm, inclusive; the length of each of the first protruding portions is in the range of 200 to 500 μm (inclusive); the interval between adjacent first protruding portions is 100 μm or less; The density of the first protruding portions is at least 10 ４ Portion / cm ２ or Any combination of the above 51. The system of claim 50.

53. 53. The system of claim 52, wherein the spacing between adjacent first protruding portions is in the range of 1 to 50 μm, inclusive.

54. 51. The system of claim 50, wherein the thickness of the gap along the first direction is in the range of 1 mm to 1 cm, inclusive.

55. 51. The system of claim 50, wherein the power supply is configured to apply a direct current (DC) voltage, an alternating current (AC) voltage, or a pulsed voltage waveform between the first electrode and the second electrode.

56. 56. The system of claim 55, wherein the computer-readable storage medium stores additional instructions that, when executed by the one or more processors, cause the power source to: applying a peak voltage of 100 V or less between the first and second electrodes to generate the volumetric plasma; applying a peak current of 100 A or less between the first and second electrodes to generate the volumetric plasma; or Do both of the above.

57. 51. The system of claim 50, wherein the computer-readable storage medium stores additional instructions that, when executed by the one or more processors, further cause the power source to: initiating the volumetric plasma by applying a first direct current (DC) voltage, a first alternating current (AC) voltage, or a first pulsed voltage waveform between a first electrode and a second electrode; maintaining the initiated volumetric plasma by applying a second DC voltage, a second AC voltage, or a second pulsed voltage waveform between the first electrode and the second electrode; Here, the absolute value of the peak voltage of the second DC voltage, the second AC voltage, or the second pulse voltage waveform is smaller than the absolute value of the peak voltage of the first DC voltage, the first AC voltage, or the first pulse voltage waveform.

58. the absolute value of the peak voltage of the first DC voltage, the first AC voltage, or the first pulse voltage waveform is in the range of 10 to 100 V (inclusive); the absolute value of the peak voltage of the second DC voltage, the second AC voltage, or the second pulse voltage waveform is within the range of 10 to 50 V (inclusive), or both; 58. The system of claim 57.

59. 51. The system of claim 50, wherein the first and second electrodes are sized such that the size of the generated plasma along a second direction is in the range of 1 mm to 100 cm, inclusive, and the second direction is in a plane substantially perpendicular to the first direction.

60. 51. The system of claim 50, wherein the system is configured to generate the volumetric plasma at a pressure in the range of 1 Torr to 10 atm, inclusive.

61. 51. The system of claim 50, wherein the first conductive material is the same as the second conductive material.

62. 51. The system of claim 50, wherein the first conductive material, the second conductive material, or both, comprises a refractory metal, a refractory metal alloy, or both.

63. 51. The system of claim 50, wherein the first conductive material, the second conductive material, or both, comprises a metal carbide, silicon carbide, a metal nitride, a metal diboride, or any combination thereof.

64. the second electrode includes a second base layer and a plurality of second protruding portions extending from the second base layer toward the first electrode along the first direction; the second base layer includes a third conductive material; At least some of the second projecting portions include a fourth conductive material; the melting temperature of the third conductive material and the melting temperature of the fourth conductive material are at least 1000 K; 51. The system of claim 50.

65. 65. The system of claim 64, wherein at least some of the first through fourth conductive materials are the same as others of the first through fourth conductive materials.

66. an end of each of at least some of the first projecting portions is conical; an end of each of at least some of the second projecting portions is conical; or Both of the above, 65. The system of claim 64.

67. the first electrode further includes a plurality of third protruding portions extending from the first base layer toward the second electrode along the first direction farther than the plurality of first protruding portions, at least some of the third protruding portions being formed of a fifth conductive material; the second electrode includes a plurality of fourth protruding portions extending from the second base layer toward the first electrode along the first direction, at least some of the fourth protruding portions being formed of a sixth conductive material; At least one of the third protruding portions contacts at least one of the fourth protruding portions in the gap or is separated from at least one of the fourth protruding portions by 5 μm or less; the melting temperature of the fifth conductive material and the melting temperature of the sixth conductive material are at least 1000 K; 51. The system of claim 50.

68. 68. The system of claim 67, wherein the computer-readable storage medium stores additional instructions that, when executed by the one or more processors, further cause the power source to: initiating the volume plasma via a gas discharge between the third and fourth protruding portions; Maintaining the volume plasma initiated via a gas discharge between the first and second protruding portions.

69. The computer-readable storage medium stores additional instructions that, when executed by the one or more processors, apply a first voltage between the first electrode and the second electrode by the power source before initiating the volumetric plasma, causing a current to flow through a contact portion of at least one of the third protruding portion and the fourth protruding portion and causing Joule heating; the Joule heating causes destruction of at least one of the third protruding portion and the fourth protruding portion such that at least one of the third protruding portion and the fourth protruding portion is spaced apart from at least one of the fourth protruding portions by a distance of 1 to 5 μm; 69. The system of claim 68.

70. 68. The system of claim 67, wherein at least one of the first through sixth conductive materials is the same as others of the first through sixth conductive materials.

71. 68. The system of claim 67, wherein one, some, or all of the first through sixth conductive materials include: (i) carbon or graphite; (ii) refractory metals, refractory metal alloys, or both; (iii) a metal carbide, silicon carbide, metal nitride, metal diboride, or a combination thereof; (iv) Any combination of (i) to (iii) above.

72. each of the third protruding portion and / or the fourth protruding portion has a maximum cross-sectional dimension in a plane substantially perpendicular to the first direction of 500 μm or less; a maximum cross-sectional dimension of each of the third protruding portion and / or the fourth protruding portion is in the range of 1 to 100 μm (inclusive); each of the third protruding portions and / or each of the fourth protruding portions has a length greater than 1 mm along the first direction; the length of each of the third protruding portion and / or the fourth protruding portion is in the range of 10 to 100 mm (inclusive); or Any combination of the above 68. The system of claim 67.

73. 51. The system of claim 50, wherein the first electrode, the second electrode, or both, comprise woven carbon or metal fibers.

74. 68. The system of any one of claims 50, 64, and 67, wherein the plurality of first protruding portions, the plurality of second protruding portions, the plurality of third protruding portions, and / or the plurality of fourth protruding portions comprise three-dimensionally printed pillars.

75. 51. The system of claim 50, wherein the first electrode, the second electrode, or both, have a non-planar shape.

76. moreover, (i) a first translation stage configured to move the first electrode; (ii) a second translation stage configured to move the second electrode; (iii) both (i) and (ii); Including, the control system is operably coupled to the first translation stage and / or the second translation stage and configured to control operation thereof; the computer-readable storage medium storing additional instructions that, when executed by one or more processors, cause the first translation stage and / or the second translation stage to move one of the first and second electrodes relative to the other of the first and second electrodes; 51. The system of claim 50.

77. the second electrode has a surface area facing the gap that is greater than a surface area of ​​the first electrode; the computer-readable storage medium storing instructions that, when executed by one or more processors, cause the first translation stage and / or the second translation stage to move one of the first electrode and the second electrode relative to the other so as to change a position of the volumetric plasma; 77. The system of claim 76.

78. 77. The system of claim 76, wherein the computer-readable storage medium stores instructions that, when executed by the one or more processors, cause the system to: positioning the first and second electrodes by a first translation stage and / or a second translation stage so that a gap is at a first distance; initiating a volumetric plasma by applying a voltage between the first and second electrodes with a power source while the gap is at the first distance; After the volumetric plasma is initiated, the first translation stage and / or the second translation stage move the first and second electrodes away from each other, and maintain the initiated volumetric plasma by applying a voltage between the first and second electrodes with the power supply while the gap is greater than the first distance.

79. 51. The system of claim 50, wherein the first and second electrodes are positioned such that a thickness of the gap along the first direction is at a non-zero angle with respect to the direction of gravity.

80. one, some, or all of the first protruding portion, the second protruding portion, the third protruding portion, and the fourth protruding portion have a substantially one-dimensional sharp distal tip at an end proximal or internal to the gap; one, some, or all of the first protruding portion, the second protruding portion, the third protruding portion, and the fourth protruding portion have a substantially two-dimensional sharp distal tip at an end proximal or internal to the gap; one, some, or all of the first protruding portion, the second protruding portion, the third protruding portion, and the fourth protruding portion have a blunt tip at an end proximal to or within the gap; or Any combination of the above 68. The system of any one of claims 50, 64, and 67.

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