Method and system for producing multi-metal alloy nanoparticles

Abstract

The present disclosure relates to a method and system for producing multimetal alloy nanoparticles (MMA NPs), such as high-entropy alloy nanoparticles (HEA NPs). The method includes the steps of introducing a metal source containing multiple metals into a heat zone of a plasma torch to obtain a metal vapor containing multiple metals; substantially homogenizing the metal vapor by plasma expansion and turbulence; cooling the metal vapor to co-nucleate and co-condense MMA NPs; and collecting the MMA NPs. The system includes a reaction chamber configured to substantially homogenize the metal vapor by generating either plasma expansion or turbulence, or both; a plasma torch; a reactor including an inlet for introducing the multimetal source into the plasma torch and configured to cool the metal vapor to co-nucleate and co-condense MMA NPs; and a collector.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This disclosure claims the benefit of priority to U.S. Patent Application Publication No. 63 / 431,614, filed December 9, 2022, which is incorporated herein by reference in its entirety.

[0002] FIELD OF THE INVENTION The present disclosure relates to multimetal alloy nanoparticles (MMA NPs), such as high entropy alloy nanoparticles (HEA NPs). Additionally, the present disclosure relates to methods and systems for making multimetal alloy nanoparticles.

[0003] Introduction Multimetal alloy nanoparticles (MMA NPs) are useful in a wide range of applications, including catalysis, sensing, energy storage, and structural alloys. More specifically, nanosized particles have emerged as a new class of multifunctional materials in catalysis, plasmonics, nanoelectronics, chemical sensors, drug delivery, and more [Koo 2020]. However, in traditional alloy design, the compositional space has been limited to a maximum of three principal elements to avoid phase separation or the formation of harmful intermetallic phases. Multicomponent alloys containing five or more principal elements in near-equimolar ratios were first demonstrated in 2004 [Yeh 2004]. Despite the tendency of similar elements to separate or order, such alloys are stabilized by high configurational entropy and are called high-entropy alloys (HEAs) [Tsai 2014]. The homogeneous mixing of multiple elements in HEAs causes discontinuities in the internal structure, resulting in a unique combination of functional properties that are attractive for a wide range of applications, including catalysis, sensing, energy storage, and structural alloys [Wang 2021]. When particle sizes reach the nanoscale, the properties of HEAs can be further enhanced by the high surface area-to-volume ratio and quantum confinement effect, coupled with the four core effects proposed by Yeh [Tsai 2014].

[0004] Currently, most micron-sized MMA powders are produced by atomization or mechanical alloying techniques. However, both processes yield MMA powders with sizes on the order of tens of microns [Ding 2017]. Other synthesis methods for alloy nanoparticles include the co-reduction method, which involves supporting metal salts on a support and suppressing continuous particle growth and agglomeration through wet chemical synthesis. However, this method imposes additional constraints on the synthesis, such as ultrafast heating and cooling rates to avoid elemental segregation at the atomic scale, limiting the number of HEAs explored. The carbothermal shock (CTS) technique was used to produce MMA NPs with up to eight elements dispersed on a conductive carbon support [Yao 2018]. However, the CTS technique is limited to electrically conductive supports and operates in batch mode. Another method explored for the production of alloy NPs is vapor-solid (VS) conversion, which involves quenching a metal vapor containing multiple elements to form a crystalline solid. Direct current arc discharge [Mao 2019], oscillating spark discharge [Feng 2020], and laser ablation [Waag 2019] have been used as heat sources for metal vaporization in the production of alloy NPs using VS conversion. These VS conversion methods are limited to vaporizing pellets or targets and can only operate in batch mode. Therefore, VS conversion has not been utilized beyond lab-scale synthesis. Summary of the Invention

[0005] The successful development and commercialization of MMA NPs strongly depends on the widespread accessibility of various MMA NPs in different morphologies (bulk, thin films, powders). Although scalable and economically feasible synthesis methods for MMA NPs, especially HEA NPs, are of particular interest, the controlled incorporation of multiple elements into small particles (<100 nm) remains a major challenge due to the different atomic sizes and unfavorable valence electron configurations of the elements.

[0006] Thermodynamically driven phase separation can be avoided by controlling the diffusion rate of materials within the particles (e.g., by rapid heating followed by rapid cooling). This paper provides a continuous, high-temperature process based on thermal plasma jet technology that can be used to produce MMA NPs, such as HEA NPs containing multiple metals (e.g., five or more metals). Rapid cooling of a well-mixed vaporized metal source (e.g., about 10 3 Nanometer-sized MMA NPs can be continuously produced using a conventional process (cooling rates exceeding 1000 K / s). When five or more metals are used, HEA NPs can be produced. The uniformity of the produced MMA NPs can be further improved by separation and filtration, for example, using a cyclone separator and filter unit.

[0007] Thus, in one aspect, the present disclosure provides a method for producing multi-element metal alloy nanoparticles (MMA NPs), the method comprising: introducing a metal source comprising a plurality of metals into a thermal zone of a plasma torch under conditions that vaporize at least a portion of the metal source to obtain a metal vapor comprising the plurality of metals, wherein the temperature of the thermal zone of the plasma torch is greater than or equal to about 1000 K; substantially homogenizing the metal vapor by plasma expansion and turbulence; Metal vapor is about 10 3 K / sec ~ approx. 10 7 cooling at a rate of 1000 K / sec to co-nucleate and co-condense the MMA NPs; and and collecting the MMA NPs.

[0008] In some embodiments, the plurality of metals comprises at least two metals, at least four metals, at least five metals, at least seven metals, at least nine metals, about two to about ten metals, about two to about six metals, about five to about ten metals, two metals, three metals, four metals, five metals, seven metals, nine metals, or ten metals. In some embodiments, the plurality of metals comprises at least five metals. In some embodiments, the MMA NPs are high entropy alloy nanoparticles (HEA NPs).

[0009] In some embodiments, the plurality of metals is selected from metals in groups 1-15 of the periodic table of the elements. In some embodiments, the plurality of metals is selected from refractory metals, and optionally the refractory metal is selected from Nb, Mo, Ta, W, V, and mixtures thereof. In some embodiments, the plurality of metals is selected from Ni, Co, Cr, Fe, Mn, refractory metals, and mixtures thereof. In some embodiments, the plurality of metals is selected from Ni, Co, Cr, Fe, Mn, Mo, and mixtures thereof. In some embodiments, the plurality of metals includes Ni, Co, Cr, Fe, and Mo. In some embodiments, the plurality of metals includes Ni, Co, Cr, Fe, and Mn.

[0010] In some embodiments, the plasma torch is a DC plasma torch, a microwave plasma torch, an RF induction coupled plasma torch, or a hybrid thereof. In some embodiments, the plasma torch is an induction coupled plasma torch.

[0011] In some embodiments, the temperature of the heat zone of the plasma torch is about 3000K to about 10000K, about 5000K to about 10000K, about 3000K to about 9000K, about 3000K to about 8000K, about 3000K, about 4000K, about 5000K, about 6000K, about 7000K, or about 8000K.

[0012] In some embodiments, the temperature of the hot zone of the plasma torch is maintained by heating a plasma gas. In some embodiments, the plasma gas comprises argon and, optionally, at least one of hydrogen, helium, or mixtures thereof. In some embodiments, the plasma gas comprises argon and at least one of hydrogen, helium, or mixtures thereof.

[0013] In some embodiments, the plasma gas includes a center gas and a sheath gas. In some embodiments, the plasma gas is supplied at about 50 slpm to about 250 slpm, about 100 slpm to about 200 slpm, about 125 slpm to about 225 slpm, or about 150 slpm. In some embodiments, the center gas is supplied at about 20 slpm to about 50 slpm. In some embodiments, the sheath gas is supplied at about 30 slpm to about 230 slpm, about 100 slpm to about 150 slpm, or about 120 slpm.

[0014] In some embodiments, the metal source is introduced at a feed rate of about 0.5 g / min to about 3 g / min, about 1 g / min to about 2.5 g / min, or about 1.2 g / min to about 2 g / min.

[0015] In some embodiments, the plasma gas has a high thermal conductivity. In some embodiments, the plasma includes argon and hydrogen, or argon and helium. In some embodiments, the plasma gas includes about 5% to about 40% by volume, or about 10% to about 20% by volume of hydrogen. In some embodiments, the plasma gas includes about 5% to about 95% by volume, or about 50% to about 75% by volume of helium.

[0016] In some embodiments, the metal vapor is generated at a rate of about 10 per second. 3 K~about 10 6 K, or about 10 per second 5 K~about 10 6 In some embodiments, the metal vapor is maintained at a pressure substantially less than 2 atmospheres in the thermal zone. In some embodiments, the pressure is greater than 0.2 atmospheres.

[0017] In some embodiments, the metal source is introduced into a water-cooled reactor. In some embodiments, introducing the metal source comprises injecting the metal source.

[0018] In some embodiments, the metal source is solid, liquid, or gaseous, and optionally a metal powder. In some embodiments, the metal source comprises a substantially pure elemental metal, an alloy, and / or a metal salt. In some embodiments, the metal source is introduced with a carrier gas, and optionally, the carrier gas comprises argon.

[0019] In some embodiments, the method is sequential.

[0020] In some embodiments, the metals in the plurality of metals are substantially uniformly distributed within the MMA NP.

[0021] In some embodiments, the average diameter of the MMA NPs is less than about 1000 nm, less than about 800 nm, less than about 600 nm, less than about 400 nm, less than about 300 nm, less than about 200 nm, or less than about 100 nm. In some embodiments, the MMA NPs are greater than 2 nm, greater than 5 nm, greater than 10 nm, greater than 15 nm, or greater than 20 nm in diameter.

[0022] In some embodiments, homogenization is achieved by plasma expansion and / or turbulence.

[0023] In some embodiments, collecting the MMA NPs is performed using a cyclone separator. In some embodiments, collecting the MMA NPs includes separating the MMA NPs from an unvaporized metal source (if present). In some embodiments, collecting the MMA NPs includes separating the MMA NPs from impurities or by-products. In some embodiments, the impurities include an unvaporized metal source (if present). In some embodiments, separating the MMA NPs from an unvaporized metal source (if present) is performed using a cyclone separator.

[0024] In some embodiments, the method further comprises filtering the collected MMA NPs.

[0025] In another aspect, the present disclosure includes a system for producing multi-element metal alloy nanoparticles (MMA NPs), the system comprising: A reactor comprising: reaction chamber; a plasma torch coupled to the inlet end of the reaction chamber, the plasma torch configured to maintain a thermal zone having a temperature of about or greater than 1000K; an inlet configured to introduce a metal source containing a plurality of metals into a heat zone of the plasma torch; and a plasma gas inlet configured to receive plasma gas into a thermal region of the plasma torch; the plasma torch is configured to vaporize at least a portion of the metal source to obtain a metal vapor comprising a plurality of metals; the reaction chamber is configured to substantially homogenize the metal vapor by generating one or both of a plasma expansion or turbulence; Metal vapor is about 10 3 K / sec ~ approx. 10 7 configured to cool at a rate of 1000 K / sec to allow co-nucleation and co-condensation of MMA NPs; a reactor; and a collection device in communication with the outlet end of the reaction chamber, the collection device being configured to collect the MMA NPs; Includes.

[0026] In some embodiments, the collection device is a separator, optionally a cyclone separator, configured to separate the unvaporized metal source (if present) from the MMA NPs.

[0027] In some embodiments, the reaction chamber increases in diameter longitudinally from the inlet end to the outlet end of the reaction chamber, hi some embodiments, the reaction chamber has a diameter at the inlet end that is larger than the diameter of the plasma torch.

[0028] In some embodiments, the system further comprises a filter unit in fluid communication with the collection device, the filter unit configured to filter the collected MMA NPs.

[0029] In some embodiments, the reactor is water-cooled.

[0030] In some embodiments, the plasma torch is a DC plasma torch, a microwave plasma torch, an RF inductively coupled plasma torch, or a hybrid thereof.

[0031] In some embodiments, the hot zone of the plasma torch is maintained by heating a plasma gas. In some embodiments, the plasma gas comprises argon and, optionally, at least one of hydrogen, helium, or mixtures thereof. In some embodiments, the plasma gas comprises argon and at least one of hydrogen, helium, or mixtures thereof.

[0032] In some embodiments, the plasma gas has a high thermal conductivity. In some embodiments, the plasma includes argon and hydrogen, or argon and helium. In some embodiments, the plasma gas includes about 5% to about 40% by volume, or about 10% to about 20% by volume of hydrogen. In some embodiments, the plasma gas includes about 5% to about 95% by volume, or about 50% to about 75% by volume of helium.

[0033] In some embodiments, the plasma torch is configured to maintain the heat zone at a temperature of about 3000K to about 10000K, about 5000K to about 10000K, about 3000K to about 9000K, about 3000K to about 8000K, about 3000K, about 4000K, about 5000K, about 6000K, about 7000K, or about 8000K.

[0034] In some embodiments, the diameter of the outlet end of the reaction chamber is about 2 times, about 3 times, or about 4 times the diameter of the inlet end of the reaction chamber. In some embodiments, the diameter of the inlet end of the reaction chamber is about 2 times, about 3 times, or about 4 times the diameter of the plasma torch.

[0035] In some embodiments, the reactor is configured to pump metal vapor at a rate of about 10 per second. 3 K~about 10 6 K, or about 10 per second 5 K~about 10 6 It is designed to be cooled at a rate of 1000K.

[0036] In some embodiments, the inlet is an injection probe configured to inject a metal source into the thermal region.

[0037] In another aspect, the present disclosure includes multi-metal alloy nanoparticles (MMA NPs) made by the methods of the present disclosure. In another aspect, the present disclosure includes MMA NPs made using the systems of the present disclosure.

[0038] Embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0039] [Figure 1] Panel (a) shows a flow chart illustrating an example of the disclosed method. Panels (b1) and (b2) of FIG. 1 show a schematic diagram of an example of the disclosed system. Panel (c) of FIG. 1 shows a schematic diagram of an example of the disclosed system. Panel (d) of FIG. 1 shows an exemplary configuration of the disclosed system. Panel (e) of FIG. 1 shows a schematic diagram of an example of the disclosed method compared to a conventional method for producing alloy NPs. [Figure 2] Photographs of HEA NPs made using the methods of the present disclosure are shown. The bottle on the left shows a sample of HEA NPs after filtration through a filter unit. The bottle on the right shows a sample of HEA NPs collected in a cyclone separator. [Figure 3]TEM images of CrFeCoNiMo HEA NPs made using the disclosed method, showing the size of the disclosed NPs at various magnifications. [Figure 4] Annular dark-field images of CrFeCoNiMo HEA NPs prepared using the method of the present invention in scanning TEM mode (ADF-STEM) at various magnifications, showing uniform ADF-STEM contrast within the particle. [Figure 5] High-resolution TEM (HR-TEM) image with local fast Fourier transform (FFT) pattern of CrFeCoNiMo HEA NPs prepared using the disclosed method, showing the crystallinity of the particles. [Figure 6] Electron Energy Loss Spectroscopy (EELS) and Energy Dispersive X-ray Spectroscopy (EDS) mapping of CrFeCoNiMo HEA NPs prepared using the disclosed method, showing the distribution of different metals within the particles. [Figure 7] 1A-1C are scanning electron microscope (SEM) images of MMA NPs (CrFeCoNiMo) prepared using the method of the present disclosure with different plasma gases: Ar-H (H: 8.3%) and Ar-He (He: 77.4%). [Figure 8] 1 is a graph showing the particle size distribution of MMA NPs (CrFeCoNiMo) produced using different plasma gases, Ar—H (H: 8.3%) and Ar—He (He: 77.4%), using the method of the present disclosure. [Figure 9] Panel (a) shows the X-ray diffraction (XRD) patterns of the feed mixture (Cr-Fe-Co-Ni-Mo) and MMA NPs (CrFeCoNiMo) produced using the disclosed method with different plasma gases: Ar-H (8.3% H) and Ar-He (77.4% He). The XRD patterns confirm the in situ alloying of pure elemental metals by the disclosed method. Panel (b) shows the XRD patterns of the feed mixture and various MMA NP samples taken from different locations in the cyclone separator and filter unit. [Figure 10] Transmission electron microscope (TEM) and high-angle annular dark-field scanning TEM (HAADF-STEM) images of MMA NPs (CrFeCoNiMo) prepared by the disclosed method using Ar-H (H: 8.3%) (panel (a)) or Ar-He (He: 77.4%) (panel (b)) as the plasma gas. The corresponding energy dispersive X-ray spectroscopy (EDS) elemental maps show the uniform distribution of the five metals in the particles. [Figure 11] Figure 1 shows the elemental composition of MMA NPs (CrFeCoNiMo) produced using different plasma gases (Ar-H (H: 8.3%) and Ar-He (He: 77.4%)). [Figure 12] Panel (a) shows an atomically resolved HAADF-STEM image and corresponding fast Fourier transform (FFT) analysis of MMA NPs (CrFeCoNiMo) produced by the disclosed method using Ar-H2 (H2: 8.3%) as the plasma gas, confirming its single face-centered cubic (FCC) structure. Panel (b) shows density functional theory (DFT) simulation phase stability calculations of MMA NPs (CrFeCoNiMo), demonstrating the higher stability of the FCC structure compared to the body-centered cubic (BCC) structure. [Figure 13] Figure 1 shows optical emission spectra (OES) measured at Z = 0.23 m from the bottom surface of the plasma torch during the synthesis of MMA NPs (CrFeCoNiMo) produced by the disclosed method using Ar-H2 (H2: 8.3%) (panel (a)) or Ar-He (77.4%) (panel (b)) as plasma gas, indicating that the plasma jet temperature was high enough to vaporize the injected metal powder. [Figure 14]Panel (a) shows a thermal-fluid simulation demonstrating the effect of reactor geometry (D reactor = D torch and D reactor = 3D torch) on turbulence intensity. Increased turbulence (D reactor = 3D torch) improves intermixing of the vapors generated from the vaporization of the feedstock mixture. Panel (b) shows the calculated temperature and thermal conductivity distributions for different plasma gases: Ar (100%), Ar-H2 (H2: 8.3%), and Ar-He (He: 77.4%). It demonstrates the enhanced cooling rate of the plasma jet in the presence of hydrogen or helium. Panels (c) and (d) show the calculated axial temperature profiles and local heating and cooling rates for different plasma gases: Ar-H2 (H2: 8.3%) (panel (c)) and Ar-He (He: 77.4%) (panel (d)). Local heating and cooling rates of up to 106 K / s are observed. [Figure 15] Figure 1 shows X-ray diffraction (XRD) patterns of the feedstock mixture (Cr--Mn-Fe-Co-Ni) and MMA NPs (CrMnFeCoNi) produced using the method of the present disclosure with different plasma gases (Ar-H (H: 8.3%) and Ar-He (He: 77.4%)). The XRD patterns confirm the in situ alloying of pure elemental metals by the method of the present disclosure. [Figure 16] High-angle annular dark-field scanning TEM (HAADF-STEM) images of MMA NPs (CrMnFeCoNi) produced by the disclosed method using Ar-H (H: 8.3%) (panel (a)) or Ar-He (He: 77.4%) (panel (b)) as the plasma gas. The corresponding energy dispersive X-ray spectroscopy (EDS) elemental maps show the uniform distribution of the five metals in the particles. [Figure 17] Energy dispersive X-ray spectroscopy (EDS) line scans along the black line across a single MMA NP (CrMnFeCoNi) produced using different plasma gases: Ar-H (H: 8.3%) (panel (a)) and Ar-He (He: 77.4%) (panel (b)). The scans show that the five metals are uniformly dispersed within the particle. [Figure 18]Figure 1 shows the elemental composition of MMA NPs (CrMnFeCoNi) produced using different plasma gases: Ar-H (H: 8.3%) (panel (a)) and Ar-He (He: 77.4%) (panel (b)). [Figure 19] Panel (a) shows a STEM image of Co-Mo binary nanoparticles (Co0.48Mo0.52) synthesized using the method of the present invention with Ar-H2 (H2: 8.3%), and the corresponding EDS elemental map in panel (b) shows the homogeneous mixture of the two elements within the particle. DETAILED DESCRIPTION OF THE INVENTION

[0040] Other features and advantages of the present disclosure will become apparent from the following detailed description, although the detailed description and specific examples, while indicating embodiments of the present disclosure, are given for purposes of illustration only, and the scope of the claims is not limited by these embodiments but should be accorded the broadest interpretation consistent with the description as a whole.

[0041] I. Definition Unless otherwise stated, the definitions and embodiments set forth herein and in other sections are intended to apply to all embodiments and aspects described in this disclosure, as would be understood by one of ordinary skill in the art.

[0042] As used herein, the term "and / or" means that the listed items are present or used either singly or in combination. In effect, the term means that "at least one" or "one or more" of the listed items are used or present.

[0043] As used in this disclosure, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. For example, an embodiment including "a compound" should be understood to refer to a particular aspect of one compound, or two or more additional compounds.

[0044] In embodiments that include an "additional" or "second" component, such as an additional or second compound, a second component, as used herein, is chemically distinct from the other or first component. A "third" component is distinct from the other, first, and second components, and further listed "additional" components are similarly distinct.

[0045] As used in this disclosure and the claims, "comprising" (and all forms of "comprising", e.g., "comprise" and "comprises"), "having" (and all forms of "having", e.g., "have" and "has"), "including" (and all forms of "including", e.g., "include" and "includes") or "containing" (and all forms of "containing", e.g., "contain" and "contains") are inclusive or open-ended and do not exclude additional, unrecited elements or process steps.

[0046] As used herein, "consisting" and its derivatives are intended as closed-form terms that specify the presence of stated features, elements, components, groups, integers, and / or steps and exclude the presence of other features, elements, components, groups, integers, and / or steps that are not stated.

[0047] The term "consisting essentially of" is used herein to specify the presence of stated features, elements, components, groups, integers, and / or steps and is intended to include those that do not materially affect the basic and novel characteristics of those features, elements, components, groups, integers, and / or steps.

[0048] Many chemical terms and abbreviations used herein are used by those of ordinary skill in the art. However, for clarity and consistency, definitions of selected terms are provided below.

[0049] As used herein, the terms "about," "substantially," and "approximately" refer to reasonable deviations of the modified term and refer to a range within which the result will not change substantially. These terms of degree should be interpreted as including a deviation of at least ±5% of the modified term, unless they negate the meaning of the word they modify or unless the context suggests otherwise to one skilled in the art.

[0050] As used herein, "high entropy alloy nanoparticle," "HEA NP," or similar term means an alloy containing five or more elements, each element in a concentration between 5 atomic percent and 35 atomic percent.

[0051] As used herein, the term "plasma expansion" refers to the phenomenon of plasma expanding due to changes in the available volume around it. For example, upon entering a reaction chamber, the plasma jet increases in volume due to changes in the diameter of the reaction chamber, and expands as the plasma jet moves through the reaction chamber.

[0052] As used herein, the term "turbulent flow" means the presence of recirculating vortices in the gas flow.

[0053] As used herein, "in communication with" means allowing the passage of matter, including in the form of a liquid, gas, solid, or a mixture thereof. For example, a component in communication with another component includes a component in fluid communication with the other component. For example, a component in communication with another component allows the passage of matter in a different form, such as a gas stream containing or carrying solid particles.

[0054] The term "homogenizing" as used herein means mixing multiple metals in a metal vapor to increase uniformity or increase uniformity of distribution, but does not necessarily require that the multiple metals in the metal vapor be in a completely uniform state or be completely uniformly distributed.

[0055] II. Methods and Systems of the Present Disclosure In one aspect, the present disclosure includes a method for producing multi-element metal alloy nanoparticles (MMA NPs), the method comprising: introducing a metal source comprising a plurality of metals into a thermal zone of a plasma torch under conditions that vaporize at least a portion of the metal source to obtain a metal vapor comprising the plurality of metals, wherein the temperature of the thermal zone of the plasma torch is greater than or equal to about 1000 K; substantially homogenizing the metal vapor by plasma expansion and turbulence; Metal vapor is about 10 3 K / sec ~ approx. 10 7 cooling at a rate of 1000 K / sec to co-nucleate and co-condense the MMA NPs; and collecting MMA NPs; Includes.

[0056] In another aspect, the present disclosure includes a system for producing multi-element metal alloy nanoparticles (MMA NPs), the system comprising: A reactor comprising: reaction chamber; a plasma torch coupled to the inlet end of the reaction chamber, the plasma torch configured to maintain a thermal zone having a temperature of about or greater than 1000K; an inlet configured to introduce a metal source containing a plurality of metals into a heat zone of the plasma torch; and a plasma gas inlet configured to receive plasma gas into a thermal zone of the plasma torch; The plasma torch is configured to vaporize at least a portion of the metal source to obtain a metal vapor comprising a plurality of metals; the reaction chamber is configured to substantially homogenize the metal vapor by generating one or both of plasma expansion or turbulence; Metal vapor is about 10 3 K / sec ~ approx. 10 7 configured to cool at a rate of 1000 K / sec to allow co-nucleation and co-condensation of MMA NPs; a reactor; and a collection device in communication with the outlet end of the reaction chamber, the collection device being configured to collect the MMA NPs; Includes.

[0057] 1(a), a flowchart of an example method 100 for producing MMA NPs is shown. As shown in FIG. 1(a), the method 100 for producing MMA NPs begins with step 102, in which a metal source is introduced into the heat zone of a plasma torch. The metal source can include multiple metals.

[0058] In step 102 of method 100, at least a portion of a metal source is vaporized in a plasma torch heat zone to obtain a metal vapor. It will be understood that if the metal source includes multiple metals, the metal vapor will include multiple metals. The temperature of the plasma torch heat zone can be about 1000 K or higher. The temperature of the plasma torch heat zone can be selected based on the properties of the metal of the metal source, as described below.

[0059] 1(a), in step 104, the metal vapor is substantially homogenized by plasma expansion and / or turbulence. The metal vapor may be substantially homogenized as described in detail below. The substantially homogenized metal vapor is then cooled in step 106, resulting in co-nucleation and co-condensation of MMA NPs. Cooling of the metal vapor is described in detail below. The substantially homogenized metal vapor may be cooled to approximately 10 3 K / sec ~ approx. 10 7The metal vapor can be cooled at a rate of 100 K / sec. The cooling of the metal vapor can be as described in more detail herein. The MMA NPs are collected in step 108 of method 100. In some embodiments, collecting the MMA NPs in step 108 includes separating the MMA NPs from impurities and by-products. For example, the impurities can include any unvaporized metal source (if present). It is contemplated that step 108 can be performed using a cyclone separator. The MMA NPs can be collected as described in more detail herein.

[0060] Referring to FIG. 1(b1), a schematic diagram illustrating an example of a system for producing MMA NPs according to the present disclosure is shown. The exemplary system 200 according to the present disclosure includes a reactor 210 and a collector 220. As shown in FIG. 1(b1), the reactor 210 can include a reaction chamber 216. The reactor 210 includes an inlet 212 and an outlet 218. The inlet 212 is for receiving a metal source (e.g., step 102 of method 100). The reactor 210 further includes a plasma gas inlet 213. The plasma gas inlet 213 is for receiving plasma gas for supplying to a plasma torch 214, as described below. The reaction chamber 216 is envisioned to have an inlet diameter larger than the diameter of the plasma torch 214 (as shown in FIG. 1(b1)). As shown, the plasma torch 214 can be coupled to the inlet end of the reaction chamber 216. The plasma torch 214 may function to generate and / or maintain a heat zone near the inlet 212 to vaporize at least a portion of the metal source within the reaction chamber 216 (e.g., step 102 of method 100). After vaporization, the metal vapor is substantially homogenized by plasma expansion and / or turbulence as it travels along the reaction chamber 216 (e.g., step 104 of method 100). The diameter of the inlet end of the reaction chamber 216 is larger than the diameter of the plasma torch 214 (see FIG. 1(b1)). This geometric design of the diameter difference between the plasma torch and the reaction chamber may increase plasma expansion and turbulence within the reaction chamber, improving homogenization of the metals in the metal vapor. It is also contemplated that the increased plasma expansion and / or turbulence may contribute to cooling of the metal vapor (e.g., step 106 of method 100). As shown in FIG. 1(b1), the reactor 210 is in communication with a collection device 220. Thus, the MMA NPs can exit the reactor 210 through an outlet 218 and be collected by a collector 220, which is further described below.

[0061] Referring to FIG. 1(b2), another embodiment of the system of the present disclosure is shown. The embodiment shown in FIG. 1(b2), system 200A, is similar to system 200 of FIG. 1(b1), except that the reaction chamber 216A increases in diameter longitudinally from the inlet end of the reaction chamber toward the outlet end of the reaction chamber. This reaction chamber geometric design increases the expansion and / or turbulence of the plasma within the reaction chamber, improving homogenization of the metals in the metal vapor. This feature, in combination with the difference in diameter between the plasma torch and the inlet end of the reaction chamber, can further improve homogenization.

[0062] Referring now to FIG. 1(c), a second exemplary system (300) for producing MMA NPs of the present disclosure is provided. The exemplary system 300 includes a reactor 300A, a collector 319 in communication with the reactor 300A, and a filter unit 320 in communication with the collector 319. As shown in FIG. 1(c), which illustrates the reactor 300A, a plasma torch 310 can be coupled to the reaction chamber 316 at its inlet end. The plasma torch can be a radio frequency (RF) inductively coupled plasma torch (ICP). The plasma torch 310 is provided with a plasma gas inlet 312 for introducing plasma gas into the plasma torch 310 to maintain a thermal zone of the plasma torch (or plasma jet) 311. The reactor 300A includes an inlet 314 configured to receive a feedstock metal source 313 within the thermal zone of the plasma torch 311. The metal source 313 is at least partially vaporized within the heat zone of the plasma torch 311 to produce a metal vapor 315 containing multiple metals. As the metal vapor 315 travels along the reaction chamber 316, it is mixed due to turbulence and / or plasma expansion. The reaction chamber 316 has a diameter that increases longitudinally from the inlet end to the outlet end of the reaction chamber, further increasing plasma expansion and turbulence. The reaction chamber 316 may have a diameter at the inlet end of the reaction chamber 316 that is larger than the diameter of the plasma torch 310 (see FIGS. 1(b) and 1(b)). The mixing substantially homogenizes the multiple metals in the metal vapor 315. The metal vapor 315 is cooled as it travels along the reaction chamber. The reactor 300A may be a water-cooled reactor, in which case the reactor 300A may include a water inlet 317a located near the outlet end of the reaction chamber and a water outlet 317b located near the inlet end of the reaction chamber. The reactor 300A may also include a spectroscopic measurement window (318), for example, for optical emission spectroscopy. The collector 319 may be a cyclone separator. The filter unit 320, if present, may include at least one filter 121. The filter may be a porous metal filter. The filter unit 320 may include a gas outlet 323 connected to a vacuum pump.The resulting MMA NPs exit reactor 300A through the outlet end of the reaction chamber and enter collector 319. The collected MMA NPs exit collector 319 and enter filter unit 320. MMA NPs 322 are deposited on at least one filter 321. The deposited MMA NPs are collected from at least one filter 321 to obtain product MMA NPs 324.

[0063] In some embodiments, the plurality of metals comprises at least two metals, at least four metals, at least five metals, at least seven metals, at least nine metals, about two to about ten metals, about two to about six metals, about five to about ten metals, two metals, three metals, four metals, five metals, seven metals, nine metals, or ten metals. In some embodiments, the plurality of metals comprises at least five metals. In some embodiments, the MMA NPs are high-entropy alloy nanoparticles (HEA NPs).

[0064] In some embodiments, the plurality of metals is selected from metals in groups 1-15 of the periodic table of the elements. In some embodiments, the plurality of metals is selected from refractory metals, and optionally the refractory metal is selected from Nb, Mo, Ta, W, V, and mixtures thereof. In some embodiments, the plurality of metals is selected from Ni, Co, Cr, Fe, Mn, refractory metals, and mixtures thereof. In some embodiments, the plurality of metals is selected from Ni, Co, Cr, Fe, Mn, Mo, and mixtures thereof. In some embodiments, the plurality of metals includes Ni, Co, Cr, Fe, and Mo. In some embodiments, the plurality of metals includes Ni, Co, Cr, Fe, and Mn.

[0065] In some embodiments, the plasma torch is a DC plasma torch, a microwave plasma torch, an RF induction coupled plasma torch, or a hybrid thereof. In some embodiments, the plasma torch is an induction coupled plasma torch.

[0066] In some embodiments, the temperature of the plasma torch thermal zone is about 3000 K to about 10,000 K, about 5,000 K to about 10,000 K, about 3,000 K to about 9,000 K, about 3,000 K to about 8,000 K, about 3,000 K, about 4,000 K, about 5,000 K, about 6,000 K, about 7,000 K, or about 8,000 K. In some embodiments, the temperature of the plasma torch thermal zone is at least about 1,000 K, at least about 2,000 K, at least about 3,000 K, or at least about 5,000 K. In some embodiments, the temperature of the plasma torch thermal zone is less than about 12,000 K, less than about 10,000 K, less than about 8,000 K, or less than about 7,000 K. The temperature of the plasma torch thermal zone can be selected depending on the metal source, and it is understood that the temperature is sufficient to vaporize at least a portion of the metal source. For example, a metal salt form of a metal element may have a lower vaporization temperature than the elemental form of that metal element. It is understood, for example, that different metal elements have different vaporization temperatures. Therefore, the temperature of the plasma torch's heat zone can be determined depending on the metal selected for inclusion in the desired MMA NPs. Conventional methods for preparing MMA NPs often use metal salts due to the technical difficulties of vaporizing elemental metals at high temperatures. While not intending to be bound by theory, the use of metal salts as a feedstock may affect the purity of the final MMA NP product due to the presence of counterions such as chloride in metal salts [Boulos 1994]. A thermal plasma jet is a partially ionized gas that can achieve high temperatures (e.g., >8000 K) and high velocities (e.g., up to the supersonic range) [Boulos 1994] and is capable of vaporizing high-temperature elemental metals in addition to low-temperature metal salts. The disclosed method and system use a thermal plasma jet, which can achieve high temperatures, enabling the use of pure elemental metals and higher-purity MMA NPs.

[0067] In some embodiments, the temperature of the hot zone of the plasma torch is maintained by heating a plasma gas. In some embodiments, the plasma gas comprises argon and, optionally, at least one of hydrogen, helium, or mixtures thereof. In some embodiments, the plasma gas comprises argon and at least one of hydrogen, helium, or mixtures thereof.

[0068] In some embodiments, the plasma gas includes a center gas and a sheath gas. In some embodiments, the plasma gas is supplied at about 50 slpm to about 250 slpm, about 100 slpm to about 200 slpm, about 125 slpm to about 225 slpm, or about 150 slpm. In some embodiments, the center gas is supplied at about 20 slpm to about 50 slpm. In some embodiments, the sheath gas is supplied at about 30 slpm to about 230 slpm, about 100 slpm to about 150 slpm, or about 120 slpm.

[0069] In some embodiments, the metal source is introduced at a feed rate of about 0.5 g / min to about 3 g / min, about 1 g / min to about 2.5 g / min, or about 1.2 g / min to about 2 g / min.

[0070] In some embodiments, the plasma gas has a high thermal conductivity. In some embodiments, the plasma includes argon and hydrogen, or argon and helium. In some embodiments, the plasma gas includes about 5% to about 40% by volume, or about 10% to about 20% by volume of hydrogen. In some embodiments, the plasma gas includes about 5% to about 95% by volume, or about 50% to about 75% by volume of helium.

[0071] In some embodiments, the metal vapor is generated at a rate of about 10 per second. 3 K~about 10 6 K, or about 10 per second 5 K~about 10 6 It cools at a rate of K.

[0072] In some embodiments, the metal vapor is maintained at a pressure substantially less than 2 atmospheres in the thermal zone. In some embodiments, the pressure is greater than 0.2 atmospheres.

[0073] In some embodiments, the metal source is introduced into a water-cooled reactor.

[0074] In some embodiments, introducing the metal source comprises injecting the metal source.

[0075] Without wishing to be bound by theory, the disclosed methods and systems can rapidly heat a metal source (e.g., feedstock) to create an atomic mixture of metal vapor and then rapidly cool the mixture at an ultrafast cooling rate to form solid solution particles. It is believed that the cooling of the metal vapor can be achieved by at least one of numerous design features of the disclosed methods or systems. One or more, or all, of the features of the disclosed methods or systems can contribute to the rapid cooling of the metal vapor. For example, the cooling of the metal vapor can be achieved at least in part by rapid and thorough mixing of the metal vapor due to plasma expansion and / or turbulent flow. In some embodiments, the plasma expansion and / or turbulent flow can be achieved by, for example, designing the reactor such that the diameter of the reaction chamber increases longitudinally from the inlet end to the outlet end of the reaction chamber. For example, the reaction chamber can be water-cooled. In some embodiments, the cooling of the metal vapor can be achieved at least in part by using a plasma gas with a high thermal conductivity such that the metal vapor is rapidly cooled by heat dissipation through the plasma gas as it passes through the reaction chamber. In some embodiments, a cooling gas can be introduced. For example, the reaction chamber can further include an inlet configured to introduce the cooling gas. In some embodiments, the cooling gas has a high thermal conductivity. In some embodiments, the cooling gas includes at least one of hydrogen or helium.

[0076] In some embodiments, the metal source is solid, liquid, or gaseous, and optionally a metal powder. In some embodiments, the metal source comprises a substantially pure elemental metal, an alloy, and / or a metal salt. In some embodiments, the metal source is introduced with a carrier gas, and optionally, the carrier gas comprises argon.

[0077] In some embodiments, the method is sequential.

[0078] In some embodiments, the metals in the plurality of metals are substantially uniformly distributed within the MMA NP.

[0079] In some embodiments, the average diameter of the MMA NPs is less than about 1000 nm, less than about 800 nm, less than about 600 nm, less than about 400 nm, less than about 300 nm, less than about 200 nm, or less than about 100 nm. In some embodiments, the MMA NPs are greater than 2 nm, greater than 5 nm, greater than 10 nm, greater than 15 nm, or greater than 20 nm in diameter.

[0080] In some embodiments, the homogenization is achieved by plasma expansion and / or turbulence. In some embodiments, after homogenization, the metal vapor is substantially homogenized. In some embodiments, following homogenization, the metal vapor is homogenized. In some embodiments, the multiple metals in the MMA NPs are substantially uniformly distributed. In some embodiments, the multiple metals in the MMA NPs are uniformly distributed.

[0081] In some embodiments, collecting the MMA NPs is performed using a cyclone separator. In some embodiments, collecting the MMA NPs includes separating the MMA NPs from an unvaporized metal source (if present). In some embodiments, collecting the MMA NPs includes separating the MMA NPs from impurities or by-products. In some embodiments, the impurities include an unvaporized metal source (if present). In some embodiments, separating the MMA NPs from an unvaporized metal source (if present) is performed using a cyclone separator.

[0082] In some embodiments, the method further comprises filtering the collected MMA NPs.

[0083] In some embodiments, the collection device is a separator, optionally a cyclone separator, configured to separate the unvaporized metal source (if present) from the MMA NPs.

[0084] In some embodiments, the reaction chamber increases in diameter longitudinally from the inlet end to the outlet end of the reaction chamber. In some embodiments, the diameter of the outlet end of the reaction chamber is about two times, about three times, or about four times the diameter of the inlet end of the reaction chamber. Without wishing to be bound by theory, a reaction chamber that increases in diameter longitudinally from the inlet end to the outlet end of the reaction chamber increases the expansion of the plasma and generates additional turbulence in the metal vapor as it passes through the reaction chamber from the inlet to the outlet. In some embodiments, the diameter of the inlet end of the reaction chamber is larger than the diameter of the plasma torch. In some embodiments, the diameter of the reaction chamber at the inlet end is about two times, about three times, or about four times the diameter of the plasma torch. Without wishing to be bound by theory, a reaction chamber that increases in diameter at the inlet end than the diameter of the plasma torch increases the expansion of the plasma and generates additional turbulence in the metal vapor as it enters the reaction chamber. The expansion and / or turbulence of the plasma mixes the multiple metals in the metal vapor and improves the homogeneity of the metal vapor during the co-nucleation and co-condensation stages, resulting in a more uniform distribution of the multiple metals in the resulting MMA NPs.

[0085] In some embodiments, the system further comprises a filter unit in communication with the collection device, the filter unit configured to filter the collected MMA NPs.

[0086] In some embodiments, the reactor is water-cooled.

[0087] In some embodiments, the plasma torch is a DC plasma torch, a microwave plasma torch, an RF inductively coupled plasma torch, or a hybrid thereof.

[0088] In some embodiments, the hot zone of the plasma torch is maintained by heating a plasma gas. In some embodiments, the plasma gas comprises argon and, optionally, at least one of hydrogen, helium, or mixtures thereof. In some embodiments, the plasma gas comprises argon and at least one of hydrogen, helium, or mixtures thereof.

[0089] In some embodiments, the plasma gas has a high thermal conductivity. In some embodiments, the plasma includes argon and hydrogen, or argon and helium. In some embodiments, the plasma gas includes about 5% to about 40% by volume, or about 10% to about 20% by volume of hydrogen. In some embodiments, the plasma gas includes about 5% to about 95% by volume, or about 50% to about 75% by volume of helium.

[0090] In some embodiments, the plasma torch is configured to maintain the heat zone at a temperature of about 3000K to about 10000K, about 5000K to about 10000K, about 3000K to about 9000K, about 3000K to about 8000K, about 3000K, about 4000K, about 5000K, about 6000K, about 7000K, or about 8000K.

[0091] In some embodiments, the reactor is configured to pump metal vapor at a rate of about 10 per second. 3 K~about 10 6 K, or about 10 per second 5 K~about 10 6 It is designed to be cooled at a rate of 1000K.

[0092] In some embodiments, the inlet is an injection probe configured to inject a metal source into the thermal region.

[0093] In some embodiments, MMA NPs are produced at a rate of 50 g / h or more, 60 g / h or more, 70 g / h or more, 80 g / h or more, 90 g / h or more, or 100 g / h or more. In some embodiments, MMA NPs are produced at a rate of less than 3000 g / h, less than 2000 g / h, less than 1000 g / h, less than 900 g / h, less than 800 g / h, or less than 700 g / h.

[0094] The disclosed method and system offer many advantages over conventional methods for preparing MMA NPs: Unlike other methods that are limited by the life of a consumable electrode (e.g., arc discharge methods) or the type of feedstock (e.g., solid targets for laser ablation), the disclosed method can use various types of feedstock (e.g., solid, liquid, gas) and employs a virtually maintenance-free plasma torch that does not require a consumable electrode.

[0095] Conventional atomization methods require the formation of a metal pool from a metal mixture, but the achievable pool temperature is typically limited to less than 3,000°C. Therefore, some refractory metals with high melting points (e.g., Mo, Nb, W, Ta, and V) cannot be efficiently processed using atomization. In the disclosed method, plasma core temperatures can reach over 8,000 K or even 10,000 K, enabling the vaporization of any element in the periodic table. Conventional mechanical alloying methods can be performed at room temperature, but they present many challenges related to the high tendency for contamination and oxidation during high-energy ball milling. Conventional CTS and sol-gel combustion methods typically employ mixtures of metal salts or metal nitrides as feedstocks because the processing temperatures and energy content are not high enough to completely vaporize micron-sized pure metal powders. In these cases, chemical species other than the pure metals may be released from the feedstock, potentially becoming a source of contamination. Other high-temperature processes, such as arc discharge, oscillatory spark discharge, and laser ablation, are capable of melting and vaporizing pure metal powders, but these processes require the feedstock to be in the form of solid pellets or targets, significantly limiting process flexibility. The disclosed method allows for continuous vaporization of any type (e.g., pure metal, alloy, metal salt) and form (e.g., solid, liquid, or gas) of feedstock for efficient synthesis of MMA NPs. Therefore, the disclosed method and system can be used for the large-scale synthesis of high-purity MMA NPs, particularly HEA NPs.

[0096] In the disclosed method, rapid heating causes the injected metal source to vaporize within the plasma jet immediately after introduction, e.g., within tens of milliseconds. The resulting MMA NPs can be continuously collected in situ. Therefore, the production rate of the disclosed method is higher than that of other conventional processes. For example, a yield of approximately 35 g / h has been demonstrated. Other conventional methods disclosed in the literature operate in batch mode and exhibit significantly lower production rates, e.g., less than 1 g per batch [Yao 2018]. Conventional mechanical alloying methods are used for the mass production of HEA powders, but they require long processing times (over 10 hours) to complete the alloying process using mechanical energy and produce micron-sized particles.

[0097] Without wishing to be bound by theory, the fast cooling rate of the disclosed method can minimize the formation of phase separation or other intermetallic compounds during the cooling period. 3 K), thermal plasma jets can be achieved at temperatures up to 10 K due to the strong plasma jet expansion, high thermal conductivity of the plasma gas, and / or additional quenching or cooling gas injection. 5 ~10 6 K / sec cooling rate, which limits the diffusion of species within the grains during cooling and minimizes the formation of segregation or intermetallic phases.

[0098] Example The following non-limiting examples are intended to illustrate the present disclosure. Example 1 Preparation of five-element MMA NPs (HEA NPs) A system for producing MMA NPs was constructed. An example system is shown in Figure 1(d). This exemplary system included a reactor containing a 2-5 MHz radio frequency (RF) inductively coupled plasma torch (e.g., Tekna PL-50™ from Tekna Plasma Systems, Inc.) capable of generating a high-temperature thermal plasma jet, and a 1-m-long, water-cooled stainless steel reaction chamber. Stable plasma was maintained by heating a central inert plasma gas (e.g., argon, 30 slpm) to a high temperature (e.g., approximately 8000 K). Sheath gas was introduced into the plasma zone through the sheath gas inlet and helped stabilize the thermal plasma. The sheath gas included an inert gas (e.g., argon, 120 slpm) and / or a mixture of argon and hydrogen gas (e.g., 120 / 14 slpm) to prevent oxidation of HEA NPs by residual oxygen in the reaction chamber. Stable plasma was generated at a plate power of 45 kW, and the reactor pressure was maintained at 66.7 kPa, or atmospheric pressure. A mixture of five elemental metals (e.g., Ni, Co, Cr, Mo, and Fe) was continuously fed into the generated plasma jet. The powder mixture was released from a powder feeder and transported to the plasma torch by argon gas (5 slpm). The powder was injected into the plasma jet through an injection probe located at the top of the plasma torch. The feed rate was typically about 1.2–2.0 g / min. The final product was collected in a cyclone separator and / or a filter unit.

[0099] Characterization of five-element HEA NPs The resulting nanoparticles were characterized by transmission electron microscopy (TEM) (Figures 3-5), electron energy loss spectroscopy (EELS), and energy dispersive X-ray spectroscopy (EDS) mapping (Figure 6).

[0100] TEM images showed that the diameter of the obtained MMA NPs was less than 200 nm. It also showed that the MMA NPs of the present disclosure were crystalline (Figure 5). As shown in the EELS and EDS maps (Figure 6), the five elements (Ni, Fe, Mo, Co, and Cr) were uniformly distributed within the particles.

[0101] The ADF-STEM image (Figure 4) shows uniform contrast, indicating that the five elements (Ni, Fe, Mo, Co, and Cr) are uniformly distributed within the particle and not segregated.

[0102] Example 2 Preparation of quinary MMA NPs (CrFeCoNiMo) using argon-hydrogen plasma jet Chromium (Cr, <10 μm, 99.2%), iron (Fe, 6–10 μm, 99.5%), cobalt (Co, 1.6 μm, 99.8%), nickel (Ni, 3–7 μm, 99.9%), and molybdenum (Mo, 3–7 μm, 99.95%) powders were purchased from Alfa Aesar. The as-received elemental metal powders were mixed in equal amounts (1:1:1:1:1) and used in the synthesis experiments without further treatment.

[0103] MMA NPs were synthesized using RF thermal plasma. The synthesis system used included five parts: an induction plasma torch, a reaction chamber, a cyclone separator, a filtration chamber, and a feedstock delivery device.

[0104] A commercially available RF induction plasma torch (Tekna PS-50™, Tekna Systems, Inc.) consisting of a five-winding coil and a ceramic tube with an inner diameter of 50 mm was used for plasma generation.

[0105] A 1 m long double-walled stainless steel reactor was used. Its diameter was designed to be at least three times the diameter of the plasma torch (e.g., 150 mm) to promote mixing of the metal vapors by increasing turbulence. The chamber walls were water-cooled to increase the cooling rate of the resulting MMA NPs.

[0106] A cyclone separator was employed at the bottom of the reactor to selectively remove unvaporized feed particles, and the nanosized final product was collected from four porous metal filter units (surface area = 20 × 50 cm, pore size 2.8 μm) in a filtration chamber connected to the end of the cyclone separator.

[0107] In the synthesis experiments, the plasma power was fixed at 45 kW with an RF frequency of approximately 3 MHz (Lepel Co.), and a mixture of argon and hydrogen was used as the plasma gas: carrier gas (Ar) 5 slpm, center gas (Ar) 30 slpm, and sheath gas (Ar / H2) 120 / 14 slpm.

[0108] The feedstock was continuously supplied by a vibrating powder feeder (PFR200 Feeder, Tekna Systems, Inc.) and delivered to an injection probe located above the plasma torch by argon carrier gas. The powder mixture feed rate was approximately 1.2–2.0 g / min. The reactor pressure was maintained constant at 66.7 kPa during synthesis. To confirm the formation of metal vapors due to the vaporization of the feedstock and to investigate their spatial variation, optical emission spectroscopy measurements were performed at Z = 0.23 m from the bottom of the plasma torch during synthesis (QMMJ-55-UVVIS-200 / 240-2PCBL-0.25, OZ Optics Ltd., core size 200 μm).

[0109] After 150 min of operation under these conditions, a total of approximately 200 g of powder was delivered. The reaction products were collected in the open environment from the cyclone separator (42 g) and the filter unit (84 g) and were characterized without further purification or treatment.

[0110] Example 3 Synthesis of quinary MMA NPs (CrFeCoNiMo) using an argon-helium plasma jet The exemplary method described in Example 2 was used, but the plasma gas was changed to a mixture of argon and helium (carrier gas (Ar) 5 slpm, center gas (Ar) 30 slpm, sheath gas (He) 120 slpm) to further improve the cooling rate of the plasma jet. This resulted in MMA NPs with smaller size (Ar-H: 60.8 nm, Ar-He: 39.7 nm) (Figures 7 and 8) and higher crystallinity (Figure 9). The characterization of the MMA NPs of Examples 2 and 3 is shown in FIGS.

[0111] Example 4 Synthesis of quinary MMA NPs (CrMnFeCoNi) using argon-hydrogen plasma jet Using the exemplary method described in Example 2, quinary MMA NPs were produced with the five elements uniformly mixed within the particle.

[0112] Chromium (Cr, <10 μm, 99.2%, Alfa Aesar), manganese (Mn, <10 μm, 99.6%, Thermo Fisher), iron (Fe, 6–10 μm, 99.5%, Alfa Aesar), cobalt (Co, 1.6 μm, 99.8%, Alfa Aesar), and nickel (Ni, 3–7 μm, 99.9%, Alfa Aesar) powders were purchased. The as-received elemental metal powders were mixed in equal amounts (1:1:1:1:1) and used in synthesis experiments without further treatment.

[0113] Example 5 Synthesis of quinary MMA NPs (CrMnFeCoNi) using an argon-helium plasma jet The exemplary method described in Example 4 was used, but the plasma gas was changed to an argon-helium mixture (carrier gas (Ar) 5 slpm, center gas (Ar) 30 slpm, sheath gas (He) 120 slpm), to further improve the cooling rate of the plasma jet. The results of the evaluation of the properties of the MMA NPs of Examples 4 and 5 are shown in FIGS.

[0114] Example 6 Synthesis of binary MMA NPs (CoMo) using an argon-hydrogen plasma jet Using the exemplary method described in Example 2, binary MMA NPs were produced with the two elements homogeneously mixed within the particle.

[0115] Cobalt (Co, 1.6 μm, 99.8%) and molybdenum (Mo, 3–7 μm, 99.95%) powders were selected as feedstocks (Alfa Aesar). The as-received elemental metal powders were mixed in equal amounts (1:1) and used in the synthesis experiments without further treatment.

[0116] In the synthesis experiments, the plasma power was fixed at 45 kW, the RF frequency was fixed at approximately 3 MHz (Lepel Co.), and a mixture of argon and hydrogen was used as the plasma gas: carrier gas (Ar) 5 slpm, center gas (Ar) 30 slpm, and sheath gas (Ar / H2) 120 / 14 slpm.

[0117] The EDS elemental map of the obtained MMA NMPs shows that the two elements are homogeneously mixed in the particles collected from the filtration chamber. The STEM image of the obtained MMA NPs is shown in Figure 19.

[0118] While the present disclosure has been described with reference to examples, it should be understood that the scope of the claims is not limited to the embodiments set forth in the examples, but is to be accorded the broadest interpretation consistent with the description as a whole.

[0119] All publications, patents, and patent applications are incorporated by reference in their entirety to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference in its entirety. Where a term in this disclosure is used with a different definition in a document incorporated by reference, the definition in this disclosure shall control for that term.

[0120] References 1.Yeh, J.-W., et al., Nanostructured high-entropy alloys with multiple principal elements.Adv.Eng.Mater.6,299(2004). 2.Tsai,M.H.,et al.,High-entropy alloys:a critical review.Mater.Res.Lett.2,107-123(2014). 3.Wang,X.et al.,High-entropy alloys:emerging materials for advanced functional applications.J.Mater.Chem.A 9,663-701(2021). 4.Ding,P.,et al.Preparation,characterization and properties of multicomponent AlCoCrFeNi2.1 powder by gas atomization method.J.Alloys Compd.721,609-614(2017). 5.Yao,Y.,et al.,Carbothermal shock synthesis of high-entropy-alloy nanoparticles,Science 359,1489(2018). 6.Mao,A.,et al.,Plasma arc discharge synthesis of multicomponent Co-Cr-Cu-Fe-Ni nanoparticles.J.Alloys Compd.775,1177-1183(2019). 7.Feng,J.,et al.,Unconventional alloys confined in nanoparticles:building blocks for new matter.Matter 3,1646-1663(2020). 8.Waag,F.,et al.,Kinetically-controlled laser-synthesis of colloidal high-entropy alloy nanoparticles.RSC adv.9,18547-18558(2019). 9.Koo,W.-T.,et al.,The design and science of polyelemental nanoparticles.ACS Nano 14,6407-6413(2020). 10.Boulos M.I.,et al.,Thermal Plasmas :Fundamentals and Applications(1994).

Claims

1. A method for producing multi-element metal alloy nanoparticles (MMA NPs), comprising: introducing a metal source comprising a plurality of metals into a thermal zone of a plasma torch under conditions to vaporize at least a portion of the metal source to obtain a metal vapor comprising the plurality of metals, wherein the temperature of the thermal zone of the plasma torch is about or greater than about 1000 K; substantially homogenizing the metal vapor by plasma expansion and turbulence; The metal vapor is heated to about 10 ３ K / sec ~ approx. 10 ７ cooling at a rate of 1000 K / sec to co-nucleate and co-condense the MMA NPs; and collecting the MMA NPs; A method comprising:

2. 10. The method of claim 1, wherein the plurality of metals comprises at least two metals, at least four metals, at least five metals, at least seven metals, at least nine metals, about two to about ten metals, about two to about six metals, about five to about ten metals, two metals, three metals, four metals, five metals, seven metals, nine metals, or ten metals.

3. The method of claim 1 or 2, wherein the plurality of metals comprises at least five different metals.

4. The method of claim 3 , wherein the MMA NPs are high entropy alloy nanoparticles (HEA NPs).

5. 5. The method of any one of claims 1 to 4, wherein the plurality of metals is selected from metals of groups 1 to 15 of the periodic table of the elements.

6. 6. The method of any one of claims 1 to 5, wherein the plurality of metals is selected from refractory metals, optionally wherein the refractory metals are selected from Nb, Mo, Ta, W, V, and mixtures thereof.

7. The method of any one of claims 1 to 5, wherein the plurality of metals is selected from Ni, Co, Cr, Fe, Mn, refractory metals, and mixtures thereof.

8. The method of any one of claims 1 to 7, wherein the plasma torch is a DC plasma torch, a microwave plasma torch, an RF inductively coupled plasma torch, or a hybrid thereof.

9. 9. The method of claim 1, wherein the temperature of the heat zone of the plasma torch is about 3000K to about 10000K, about 5000K to about 10000K, about 3000K to about 9000K, about 3000K to about 8000K, about 3000K, about 4000K, about 5000K, about 6000K, about 7000K, or about 8000K.

10. The method of any one of claims 1 to 9, wherein the temperature of the hot zone of the plasma torch is maintained by heating a plasma gas.

11. The method according to any one of claims 1 to 10, wherein the plasma gas has a high thermal conductivity.

12. The method of claim 11 , wherein the plasma comprises argon and hydrogen or argon and helium.

13. The method of any one of claims 1 to 12, wherein the plasma gas comprises from about 5% to about 40% by volume, or from about 10% to about 20% by volume, of hydrogen.

14. The method of any one of claims 1 to 12, wherein the plasma gas comprises from about 5% to about 95% by volume, or from about 50% to about 75% by volume, of helium.

15. The metal vapor is about 10 ３ K / sec ~ approx. 10 ６ K / sec, or about 10 ５ K / sec ~ approx. 10 ６ 15. The method of claim 1, wherein the cooling is carried out at a rate of 100 K / sec.

16. The method of any one of claims 1 to 15, wherein the metal vapor is maintained substantially at a pressure of less than 2 atmospheres in the thermal zone.

17. 17. The method of claim 16, wherein the pressure is greater than 0.2 atmospheres.

18. The method according to any one of claims 1 to 17, wherein the introduction of the metal source is carried out in a water-cooled reactor.

19. The method of any one of claims 1 to 18, wherein introducing the metal source comprises injecting the metal source.

20. The method of any one of claims 1 to 19, wherein the metal source is a solid, liquid or gas, and optionally the metal source is a metal powder.

21. The method of any one of claims 1 to 20, wherein the metal source comprises a substantially pure elemental metal, an alloy and / or a metal salt.

22. A method according to any preceding claim, wherein the metal source is introduced with a carrier gas, the carrier gas optionally comprising argon.

23. The method of any one of claims 1 to 22, wherein the method is continuous.

24. The method according to any one of claims 1 to 23, wherein the metals in the plurality of metals are substantially uniformly distributed in the MMA NPs.

25. The method of any one of claims 1 to 24, wherein the MMA NPs have an average particle size of less than about 1000 nm, less than about 800 nm, less than about 600 nm, less than about 400 nm, less than about 300 nm, less than about 200 nm, or less than about 100 nm.

26. The method according to any one of claims 1 to 25, wherein the homogenization is achieved by plasma expansion and / or turbulence.

27. The method of any one of claims 1 to 26, wherein the collection of the MMA NPs is carried out using a cyclone separator.

28. 28. The method of any one of claims 1 to 27, wherein, if an unvaporized metal source is present, said collecting said MMA NPs comprises separating said MMA NPs from said unvaporized metal source.

29. The method of any one of claims 1 to 28, wherein the method further comprises filtering the collected MMA NPs.

30. A system for producing multi-element metal alloy nanoparticles (MMA NPs), comprising: A reactor comprising: reaction chamber; a plasma torch coupled to the inlet end of the reaction chamber, the plasma torch being configured to maintain a thermal zone having a temperature of about or greater than 1000 K; an inlet configured to introduce a metal source containing a plurality of metals into the heat zone of the plasma torch; and a plasma gas inlet configured to receive a plasma gas into the heat zone of the plasma torch; the plasma torch is configured to vaporize at least a portion of the metal source to obtain a metal vapor comprising a plurality of the metals; the reaction chamber is configured to generate one or both of plasma expansion and turbulence to substantially homogenize the metal vapor; The metal vapor is heated to about 10 ３ K / sec ~ approx. 10 ７ and cooling at a rate of 1000 K / sec to allow co-nucleation and co-condensation of the MMA NPs. a reactor; and a collection device in communication with the outlet end of the reaction chamber, the collection device being configured to collect the MMA NPs; Including, the system.

31. 31. The system of claim 30, wherein the collection device is a separator, optionally a cyclone separator, configured to separate any unvaporized metal source from the MMA NPs, if any.

32. 32. The system of claim 30 or 31, wherein the reaction chamber has a diameter that increases longitudinally from the inlet end to the outlet end of the reaction chamber.

33. The system of any one of claims 30 to 32, further comprising a filter unit in communication with the collection device, the filter unit configured to filter the collected MMA NPs.

34. The system of any one of claims 30 to 33, wherein the reactor is water-cooled.

35. The system of any one of claims 30 to 34, wherein the plasma torch is a DC plasma torch, a microwave plasma torch, an RF inductively coupled plasma torch, or a hybrid thereof.

36. The system of any one of claims 30 to 35, wherein the hot zone of the plasma torch is maintained by heating the plasma gas.

37. The system of any one of claims 30 to 36, wherein the plasma gas has a high thermal conductivity.

38. 38. The system of claim 37, wherein the plasma gas comprises argon and hydrogen or argon and helium.

39. 39. The system of any one of claims 30 to 38, wherein the plasma gas comprises about 5% to about 40% by volume hydrogen, or about 10% to about 20% by volume hydrogen.

40. 39. The system of any one of claims 30 to 38, wherein the plasma gas comprises about 5% to about 95% by volume, or about 50% to about 75% by volume, helium.

41. 41. The system of any one of claims 30-40, wherein the plasma torch is configured to maintain the heat zone at a temperature of about 3000K to about 10000K, about 5000K to about 10000K, about 3000K to about 9000K, about 3000K to about 8000K, about 3000K, about 4000K, about 5000K, about 6000K, about 7000K, or about 8000K.

42. The system of any one of claims 30 to 41, wherein the metal source is a solid, liquid, or gas.

43. The system of any one of claims 30 to 42, wherein the metal source is a metal powder.

44. The system of any one of claims 30 to 43, wherein the metal source comprises a substantially pure elemental metal, an alloy, and / or a metal salt.

45. 45. The system of any one of claims 30-44, wherein the plurality of metals comprises at least two metals, at least four metals, at least five metals, at least seven metals, at least nine metals, from about two to about ten metals, from about two to about six metals, from about five to about ten metals, two metals, three metals, four metals, five metals, seven metals, nine metals, or ten metals.

46. The system of any one of claims 30 to 45, wherein the plurality of metals comprises at least five different metals.

47. 47. The system of claim 46, wherein the MMA NPs are metal high entropy alloy nanoparticles (HEA NPs).

48. 47. The system of any one of claims 30 to 46, wherein the plurality of metals is selected from metals in groups 1 to 15 of the periodic table of the elements.

49. 48. The system of any one of claims 30 to 47, wherein the plurality of metals comprises a refractory metal, optionally wherein the refractory metal is selected from Nb, Mo, Ta, W, V, and mixtures thereof.

50. 48. The system of any one of claims 30-47, wherein the plurality of metals is selected from Ni, Co, Cr, Fe, Mn, refractory metals, and mixtures thereof, optionally wherein the plurality of metals is selected from Ni, Co, Cr, Fe, Mn, Mo, and mixtures thereof, optionally wherein the plurality of metals comprises Ni, Co, Cr, Fe, and Mo, optionally wherein the plurality of metals comprises Ni, Co, Cr, Fe, and Mn.

51. The system of any one of claims 30 to 50, wherein the injection probe is configured to inject the metal source in combination with a carrier gas.

52. 52. The system of any one of claims 30-51, wherein the diameter of the outlet end of the reaction chamber is about 2 times, about 3 times, or about 4 times the diameter of the inlet end of the reaction chamber.

53. The metal vapor is about 10 ３ K / sec ~ approx. 10 ６ K / sec, or about 10 ５ K / sec ~ approx. 10 ６ 53. The system of any one of claims 30 to 52, wherein the system is cooled at a rate of 1000 K / sec.

54. The system of any one of claims 30 to 53, wherein the inlet is an injection probe configured to inject the metal source into the thermal region.

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