High-purity fiber raw material for free abrasive production

Abstract

A method for forming a high-purity granular material, such as silicon carbide powder, is disclosed. A precursor is added to a reactor, and at least a portion of the fibers are formed in the reactor from the precursor using chemical deposition that interacts with the precursor, and then the granular material is formed from the fibers. In one embodiment, the chemical deposition may include laser-induced chemical vapor deposition. The granular material may be formed by grinding or crushing the fibers into the granular material, for example, by ball milling the fibers. In one example, silicon carbide powder having greater than 90% beta crystalline phase purity and less than 0.25% oxygen contamination may be obtained.

Description

[Technical Field]

[0001] Cross-reference of related applications This application claims priority to U.S. serial number 62 / 966,157, filed on 27 January 2020, entitled “High-Purity Fiber Supply Material for Free Abrasive Production,” which is incorporated herein by reference in its entirety.Furthermore, this application relates to the following patent applications, each of which is incorporated herein by reference in whole: U.S. Patent Application Publication No. 2018 / 0370860, published on 27 December 2018, entitled “Functional High-Performance Fiber Structures”; U.S. Patent Application Publication No. 2015 / 0004393, published on 1 January 2015, entitled “High-Strength Ceramic Fibers and Methods for Manufacturing the Same”; and U.S. Patent No. 10,047,015, issued on 24 August 2018, both entitled “High-Strength Ceramic Fibers and Methods for Manufacturing the Same.” International Publication No. 2013 / 180764, published on December 5, 2013, titled "Additive Manufacturing Technology for the Manufacture and Characterization of Nuclear Reactor Fuel", U.S. Patent Application Publication No. 2017 / 0213604, published on July 27, 2017, titled "Additive Manufacturing Technology for the Manufacture and Characterization of Nuclear Reactor Fuel", International Publication No. 2015 / 200257, published on December 30, 2015, titled "Multilayer Functional Fiber and Method of Manufacturing", U.S. Patent Application Publication No. 2017 / 0331022, published on November 16, 2017, International Publication No. 2017 / 197105, published on November 16, 2017, entitled "Multilayer Functional Fibers and Method for Manufacturing the Same"; International Publication No. 2017 / 326838, published on November 16, 2017, entitled "Fiber Delivery Assembly and Method for Manufacturing the Same"; International Publication No. 2017 / 197082, published on November 16, 2017, entitled "Multilayer Functional Fibers and Method for Manufacturing the Same"; International Publication No. 2015 / 11, published on July 30, 2015, entitled "Continuously Blended Nanoscale Multiphase Fibers" International Publication No. 2935, entitled "Refractory Additive-Containing Composite Fiber and Method for Manufacturing the Same," published on April 5, 2018, International Publication No. 2018 / 064261, entitled "Elemental Additive-Containing Fiber and Method for Manufacturing the Same," published on June 7, 2018, and U.S. Patent Application No. 62 / 905,598, entitled "Microtrellis Nonwoven Fabric and Reinforced Composite or Hybrid Composite Material," filed on September 25, 2019, each of these is incorporated herein by reference in their entirety. [Background technology]

[0002] Technical Field The present invention generally relates to the field of materials, particularly particulate materials, for example in powder form, produced from high-purity fibers formed using laser chemical vapor deposition. Summary of the Invention Problem to be Solved by the Invention

[0003] Background Silicon carbide (SiC) is an artificial material used in a wide range of engineering applications due to its advantageous material properties, particularly fire resistance (high temperature compatibility), high hardness and high strength. Accordingly, there is a strong demand for high-purity SiC powders, granular materials for other applications, and methods for their efficient, scalable and controllable production.

[0004] Summary Disadvantages of the prior art are addressed and further advantages are provided by the present invention, wherein one aspect provides a method of forming a high-purity particulate material, comprising: providing a precursor in a reactor; forming at least a portion of fibers in the reactor from the precursor using chemical deposition interacting with the precursor; and forming the particulate material from the fibers. In one aspect, the chemical deposition may comprise laser-induced chemical vapor deposition. The particulate material may be formed by grinding or milling the fibers into a particulate material, for example, by ball milling the fibers.

[0005] In another aspect, the plurality of fibers may be formed in parallel using a single laser beam, or a plurality of laser beams with independent power control, or a plurality of laser beams without independent power control. At least one additive may be added during chemical deposition, which functions as a free oxygen getter to improve the oxidation resistance of the particulate material; and the particulate material may be specially shaped and / or coated.

[0006] The granular material may, in certain aspects, be silicon carbide powder having a beta-crystalline phase purity of over 90% and an oxygen contamination of less than 0.25%; or multi-element and multi-phase composition powder having an oxygen contamination of less than 0.25%; or nuclear fuel material.

[0007] Further features and advantages are realized by the technology of the present invention. Other embodiments and aspects of the present invention are described herein in detail and are considered to be part of the claimed invention.

[0008] Brief explanation of the drawing These and other features, embodiments, and advantages of the present invention will be better understood by reading the following detailed description with reference to the accompanying drawings, in which the same letters throughout the drawings represent the same parts. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram of a spinneret, a plate with a pattern of small holes into which a liquid precursor is supplied, and at the outlet, the flow pattern is gelled into filaments called "green fibers". [Figure 2] Figure 2 is a schematic diagram of an exemplary process for forming monofilament fibers. [Figure 3] Figure 3 is a schematic diagram showing how fiber LCVD is parallelized on a large scale by laser beam multiplexing according to the present invention. [Figure 4] Figure 4 shows parallel LCVD growth of carbon fibers using a module containing 64 individually controlled laser emitters according to the present invention. [Figure 5] Figure 5 shows a process for forming a rectangular array of fibers according to one or more embodiments of the present invention. [Figure 6A] Figure 6A is an elevated magnification SEM image of a large array of SiC fiber forests on an exemplary glassy carbon substrate according to one or more embodiments of the present invention. [Figure 6B]Figure 6B is an elevated magnification SEM image of a large array of SiC fiber forests on an exemplary glassy carbon substrate according to one or more embodiments of the present invention. [Figure 6C] Figure 6C is an elevated magnification SEM image of a large array of SiC fiber forests on an exemplary glassy carbon substrate according to one or more embodiments of the present invention. [Figure 7] Figure 7 shows a SiC fiber forest grown on HNS (High Nicalon-Type S) tow SiC fabric according to one or more embodiments of the present invention. [Figure 8A] Figure 8A shows SEM images of a SiC fiber and its high-magnification cross-section. [Figure 8B] Figure 8B shows SEM images of a SiC fiber and its high-magnification cross-section. [Figure 9A] Figure 9A is an SEM image of the SiC fiber from Figure 8A, showing its two distinct sections with different diameters. [Figure 9B] Figure 9B is an SEM image of the SiC fiber from Figure 8A, showing its two distinct sections with different diameters. [Figure 10A] Figure 10A is a schematic diagram of an exemplary ball mill that can be used to produce powder from fibers, according to one aspect of the present invention. [Figure 10B] Figure 10B is a schematic diagram of an exemplary ball mill that can be used to produce powder from fibers, according to one aspect of the present invention. [Figure 11] Figure 11 is an image of an exemplary batch of silicon carbide powder formed according to the principle of the present invention, drawn on a portion of a business card to show the scale. [Modes for carrying out the invention]

[0010] Detailed explanation Aspects of the present invention, and its particular features, advantages, and details, are described below in full with reference to the non-limiting examples (may be more) illustrated in the accompanying drawings. Descriptions of well-known systems, apparatus, manufacturing and processing techniques are omitted so as not to unnecessarily obscure the invention. However, it should be understood that the detailed descriptions and specific examples, while illustrating aspects of the invention, are given for illustrative purposes only and not to limit them. Various substitutions, modifications, additions, and / or arrangements within the spirit and / or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure. Furthermore, it should be noted that numerous inventive aspects and features are disclosed herein, and to the extent that they do not contradict each other, each disclosed aspect or feature can be combined with any other disclosed aspect or feature desired for a particular application, for example, to realize fibers using any of FLP, FFG, or any other fiber-forming techniques, and then to realize granular materials using any manufacturing technique.

[0011] One of the most common formats for using SiC is in powder form, with particle sizes ranging from a few millimeters in diameter to less than 1 micron. The manufacturing method used for over 125 years is the Acheson process, which involves a reactor "bath" (or furnace) where silica (or sand) and powdered coke (carbon) raw materials are mixed together. A high-voltage current is supplied to the silica-coke mixture from electrodes, causing a carbonothermal reaction between the two components at temperatures exceeding 2000°C. The resulting reaction product is alpha-crystalline SiC material. Alpha-phase SiC has a two-dimensional, layered hexagonal crystalline structure, similar to graphite. Consequently, its hardness and strength properties are inferior to those found in beta-phase SiC, which has a three-dimensional face-centered cubic structure. Beta-shaped SiC is preferred due to its improved mechanical properties. To produce beta-SiC, the alpha-SiC feedstock material must undergo a conversion process in a high-temperature furnace capable of operating for extended periods at temperatures in the range of 1700-2000°C. Beta SiC powder manufacturers rely on this heat treatment method, which is subject to several constraints that affect the performance of the powder in its end application. These include: (i) the conversion rate from alpha to beta, which is usually in the 80% range but rarely exceeds 90%; (ii) oxygen contamination, which is desirable to be less than 1% to minimize the adverse effects of oxygen attack; and (iii) the consistency of production regarding (i) and (ii) and other considerations such as free carbon. These limitations arise from process variability inherent in the heat treatment conversion process, which includes variability in the quality of alpha feedstock and instability in furnace control parameters.

[0012] Even with such manufacturing challenges, beta SiC powder is a material demanded by various advanced technologies. Two examples of industrial applications of beta SiC powder are part of ceramic matrix composite (CMC) technology in the aviation / aerospace industry and the field of additive manufacturing (AM). Both applications may require beta SiC for improved mechanical behavior compared to the more readily available alpha SiC powder. In aerospace CMC manufacturing, beta SiC powder is added as a filler material during the matrix forming step for the purpose of filling volume and ultimately reducing porosity (unfilled space) in the cross-section of the finished part. AM processes use powder as the primary component material, supplied in manufacturer-specific slurry systems. Both of these high-tech applications are moving from laboratory and pilot-scale production to true industrial-scale volumes to meet increasing performance requirements.

[0013] In accordance with the above-incorporated U.S. and international patent applications, laser-driven chemical vapor deposition (LCVD) is a proven approach for forming high-performance fibers. The core concept is the introduction of a single laser beam, or in one embodiment a plurality of beam arrays, into a sealed chamber or reactor containing a desired mixture of precursor gases. The laser beam intersects a substrate surface or other seed material to initiate a gas-phase reaction, which produces a solid product (e.g., fiber) with the desired chemical properties and crystallinity. A fiber format can be manufactured by drawing the substrate away such that reaction products form continuously and additionally on the previously deposited material. The LCVD process provides a series of advantages, including: (i) high deposition rates on the order of hundreds of microns per second; (ii) very high purity of the deposited material free from undesirable contamination such as free oxygen; (iii) high crystalline phase purity; and (iv) the possibility of mass parallelization of fiber production using multiple laser beam LCVD, as disclosed in the above-incorporated patent applications.

[0014] According to one aspect of the present invention, SiC powder is produced by using an intermediate process in which SiC fibers are first produced, and then the fibers are processed into a granular form, for example, in the form of powder. The obtained powder retains all the advantages of LCVD-formed fibers, including but not limited to maintaining high chemical purity and phase purity, and low contamination. Furthermore, the high speed and scalability of LCVD production of multiple fibers in parallel can be utilized to increase the production rate and quantity of the produced powder.

[0015] Accordingly, in accordance with the present invention, all advantages apply to powder production based on the intermediate LCVD fiber manufacturing process, and several examples thereof (FLP and FFG) are first presented herein.

[0016] Example of LCVD - Fiber Laser Printer (trademark) (FLP)

[0017] FLP provides an extremely versatile approach for producing inorganic filaments. It is almost independent of the fiber material, which is a rare characteristic in manufacturing processes, and this is referred to as "Material-Agnostic". For example, FLP has been applied to the demonstration of filaments for which no other manufacturing methods are known, such as boron carbide, boron, tungsten carbide (with exceptional hardness of 27 to 29 GPa), Si-C-B ternary fibers (with exceptional tensile strength of 9 GPa). The assignee has demonstrated that it is possible to produce fibers of various compositions functionally graded along the axis. As a further demonstration of the material-agnostic nature of FLP, the assignee has demonstrated that it is possible to vary the radial distribution of fiber composition and microstructure. For example, it has been demonstrated that the microstructure distribution of SiCf can be customized from (i) deformation of elongated anisotropic grains in the fiber core to equiaxed fine grains at the fiber end to (ii) a uniform microstructure across the fiber. These unique characteristics contribute to the excellent material properties found in LCVD-produced fibers, such as the excellent creep resistance exhibited in the assignee's laser-printed SiCf.

[0018] The acquirer also demonstrated that fibers can be coated with FLP while they are being manufactured; this is an industry first. An interfacial layer of boron nitride or pyrolysis carbon (PyC) is deposited with an added SiC overcoat. It was shown that such a coating is feasible within a large dimensional window ranging from tens of nanometers (nm) to 10 μm. This is a valuable feature of FLP because (i) an interfacial layer coating is required for the material to exhibit composite behavior, and (ii) there is still no satisfactory solution for uniformly pre-coating fibers in tow and fabric. The current state of technology for commercially available SiCf tow (HNS, SA3) consists of depositing an interfacial layer immediately before matrix infiltration.

[0019] FLP also exhibits unparalleled flexibility in the geometric domain. As part of a DOE-funded experiment, the acquirer demonstrated that the diameter can be freely controlled during fiber growth, leading to the first demonstration of variable-diameter SiCf.

[0020] In most prior art, fiber formation is achieved by passing a liquid precursor through a spinneret. For example, Figure 1 is a schematic diagram of a spinneret, a plate with a pattern of small holes into which the liquid precursor is supplied. At the exit, the flow path pattern gels, forming a filament called a "green fiber." However, this prior art assumes that the fibrous material can exist in any form—a liquid, gel, or plastic—suitable for flowing through the small openings. Often, such a liquid or near-liquid state does not exist, especially with refractory materials. Therefore, the inventors concluded that when a spinneret is incompatible with the properties of the fibrous material, a better approach involves extracting the fiber from a laser focus at the location where the fiber is created from the surrounding fluid precursor, which is not possible using the spinneret of Figure 1. By focusing the laser on the fiber tip, the fiber is heated to a temperature at which the precursor dissociates and chemical vapor deposition (CVD) takes place. The fiber grows in the longitudinal direction and is drawn out of the reaction region at its growth rate, forming a monofilament fiber of any length. This process technology according to embodiments of the present invention is illustrated by Figure 2. Figure 2 is a schematic diagram of an exemplary process, including a reactor 10; an enlarged cutaway of the reactor chamber 20; and an enlarged view of the growth region 30. Self-seeded fibers 50 are grown toward an opposing coaxial laser 60 and removed via an extrusion microtube 40. The CVD precursor is injected into the reaction region from the extrusion microtube, which supplies growth and promotes convective growth by forming a small, high-concentration plume around the reaction region. This plume is embedded in a coaxial flow of inert gas that shields the reaction and carries away diluted byproducts. The reactor design is built upon an understanding of laser-induced chemical vapor deposition (LCVD) fiber growth. This reactor provides unique and valuable materials science research suitable for the rapid experimental development of specialized filaments. However, it may not be suitable for large-scale production.

[0021] In the microelectronics manufacturing industry, materials are mass-produced using optical (photolithography) methods, but large-scale replication of fiber growth is disclosed here. Pure optical parallelization for fiber growth is one approach to mass production of fibers. For example, parallelization of process technologies, as illustrated by Figure 2, can be pursued.

[0022] In one embodiment, the present invention may include the use of a large array of independently controlled lasers to grow a similarly large array of fibers 80 in parallel, demonstrating how fiber LCVD can be hyperparallelized from a filament grating 100 by doubling the laser beam 80 that guides plasma 90 around the tip of each fiber 80, as shown in Figure 3. In embodiments of the present invention, the large array of fibers 80 is directed toward a substrate to grow fibers standing upright in a large array directly on the substrate, and the environment at the laser tip is controlled to control and modify the material system of the fibers.

[0023] This was the first scientific instance of using a Computer to Plate (CtP) (e.g., Quantum Well Intermixing (QWI)) laser array in LCVD, as was the use of a shallow depth of focus. It yielded very beneficial results. Sample carbon fibers, as shown in Figure 4, were grown in parallel. Figure 4 shows parallel LCVD growth of carbon fibers using multiple lasers, e.g., a unit with 64 or more lasers. Left: Fibers during growth. Right: Resulting free-standing fibers with a diameter of 10–12 pm and a length of approximately 5 mm.

[0024] In all previous approaches, the beam was focused to a diffraction-limited spot over a long Rayleigh range. According to the present invention, the focus is not only strong enough to maintain CVD, but the depth of field means that fibers could only grow in small areas in front of and behind the image plane. This contradicts the generally accepted practice in LCVD where a long depth of field is preferred to maximize the growth area. The advantage of a shallow depth of field is significant because of the level of control it can provide. For example, if a fiber stops growing for some reason, the focus can be moved back to the tip of that fiber. All other growth will stop, and then resume once the lagging fiber is pulled back to the same level as the others.

[0025] The effects of a shallow depth of focus according to several embodiments of the present invention are shown in Figure 4. The non-uniform interfocal power distribution of the diffraction grating, combined with the long depth of focus of the diffraction-limited optical system, prevents any control over the position of the growth front in the fiber array. A major advantage is evident in Figure 4: the fibers grow uniformly to the same height. This was an unexpected advantage of light source imaging beyond the diffraction-limited optical system, because the depth of focus is 5 to 30 times shallower (vertically and horizontally, respectively) than the Rayleigh range of a comparable diffraction-limited focus. This proves to be a significant advantage as fibers grow rapidly both in and out of the focus. This makes it possible to track fiber growth and even to retrieve fibers that have stopped growing without affecting other fibers that have already grown. This unique characteristic of the CtP laser bar is expected to represent a major advantage in controlling future parallel LCVD growth for fiber arrays.

[0026] Example of LCVD - Fiber Forest Manufacturing Equipment (FFG)

[0027] Using any of the embodiments described above, fibers can be grown on a substrate using LCVD. In fact, the fibers do not need to be continuous. Large arrays of short composite fibers can be derived by parallel deposition on a base wafer using the reactors described in detail above. Arrays of fibers, such as those illustrated in Figure 5, can be printed simultaneously in some embodiments, and in some cases directly, to model arrays of these fibers that can be mounted on fuel pellets.

[0028] Figure 5 shows a method of process steps on a square subsection of a circular wafer having an approximate diameter, which in some embodiments may include a diameter of 10 to 15 mm. For clarity, the length scale shown perpendicular to the wafer is reduced according to some embodiments. In step 501, a substrate is provided. The substrate may include a wafer substrate, which may be made of a refractory, oxidation-resistant material such as SiC, ZrC, or BeO, or it may include a glass ceramic such as BMAS, BSAS, or zirconium silicate. In some embodiments, the substrate may not be a flat surface but may include pre-formed fibers, which are not shown, according to embodiments described herein, or any solid surface. In some embodiments, in step 502, any array of pedestal fibers in one or more embodiments of a refractory material such as C or SiC is grown on the substrate. In step 503, a first set of short fibers is grown on the pedestal, or on the substrate if no pedestal is present. In step 504, long fibers are grown on the first set of short fibers.

[0029] FFG can be made analogous to FLP rotated perpendicular to the surface of the substrate. In doing so, according to one or more aspects of the present invention, arrays of short, free-standing fibers up to ~1 / 4 inch (~6.35 mm) in length are generated, as shown in Figures 6A-C, at increased magnification, which are SEM images of a large array of SiC fiber forests on a glassy carbon substrate. The fiber composition and microstructure are inherited from the FLP. Of particular interest to the present invention, the fiber forests are grown over a limited area of ​​the substrate. Figure 7 shows a rectangular array of SiC fibers grown on an HNS woven fabric. The inventors now believe that these processes can be used to grow fibers on a wide variety of substrates using a wide variety of precursors.

[0030] In summary, the present invention is built upon exemplary innovations discussed as a whole with respect to Figures 1-4 and 5-7, respectively. The first innovation—the fiber laser printer (FLP)—is the subject of the above-mentioned incorporated publication entitled "High-Strength Ceramic Fibers and Methods for Manufacturing Them." The second, more recent innovation is the fiber forest manufacturing apparatus (FFG), which is the subject of the above-mentioned incorporated publication entitled "Functional Polymer Fiber Structures." Both innovations rely on the same principle of fast laser-induced chemical vapor deposition (R-LCVD), which uses a laser beam for each fiber, although the use of a single laser and / or diffraction grating also falls within the scope of the present invention. In the example of the FLP, the fibers can be self-seeded, and the product is a continuous ribbon of identical straight filaments, parallel to one another. In the example of the FFG, the fibers are seeded on a flat substrate, resulting in a huge array of anchored, self-supporting short filaments, respectively, as seen in Figures 6A-C, which are SEM images of a large array of SiC fiber forests on a glassy carbon substrate, according to one or more aspects of the present invention.

[0031] Examples of SiC powder formation

[0032] As one example of the present invention, for silicon carbide fibers, varying the gas precursor mixture can lead to a range of fiber chemistry from carbon-rich to silicon-rich. Under all conditions, SiC fibers can have a beta phase content greater than 90%. The inventors have discovered that stoichiometric SiC (Si:C 1:1 ratio) can be formed in a coarse fibrous form by appropriate precursor settings and LCVD deposition parameters. This is somewhat similar to bonding loose SiC "boulders" together, because the LCVD deposition process of silicon carbide is a region with a high nucleation rate and low growth rate, forming many nanocrystalline grain sites that do not grow rapidly. Therefore, the resulting SiC fibers can be a mechanically weak and easily shatterable material.

[0033] Figures 8A-B are SEM images of SiC fibers (with relatively large diameters - approximately 200-300 μm) and their high-magnification cross-sections, showing the coarse, brittle composition desirable for such fibers, resembling bonded pebbles. Figures 9A-B are SEM images of the SiC fiber from Figure 8A, showing two separate cross-sections with different diameters ranging from approximately 215 μm to approximately 326 μm.

[0034] According to the present invention, light grinding or crushing or similar procedures can quickly and efficiently convert the manufactured fibers into a coarser and / or ultimately finer granular form, such as a powder (depending on the level of processing applied).

[0035] As an example, Figures 10A and 10B are schematic diagrams of an exemplary ball mill that can be used to produce powder from fibers according to one aspect of the present invention. Such ball mills are commercially available. According to the present invention, fibers can be deposited in the body as feed material, ground to a suitable controllable size after the mill is started, and collected as a finished product after the grinding is complete. Other types of mechanical grinding or pulverization, such as jet grinding, may be employed according to the present invention.

[0036] Figure 11 is an image of an exemplary batch of silicon carbide powder formed according to the principle of the present invention, drawn on a portion of a business card to show scale.

[0037] Another important feature of LCVD is the ability to combine multiple gas precursor materials to supply multiple elements to the gas-phase reaction, resulting in unique compositions containing multiple phases of the material. For example, a combination of silane, ammonia, and boron trichloride gas in an LCVD reaction can yield a closely mixed combination of silicon nitride and boron nitride. According to the present invention, these composite compositions and their chemical properties are then carried over to the fiber-to-powder format. Whether in fiber or powder format, these multiphase materials offer a blend of previously unavailable material properties to address the requirements of high-tech applications. Thus, according to the present invention, any additional composition and / or chemical properties formed during the LCVD process will persist in the powder format.

[0038] Furthermore, specific chemical species can be introduced through careful gas precursor selection, with the intention of cultivating desired performance behavior in the deposited material, regardless of whether the format is fibrous or ultimately in powder form. The amount of species is nominally trace. For example, refractory metals with melting points above 2000°C could be added as in-situ getters to capture incoming free oxygen and improve the oxidation resistance of the material. Metals such as hafnium, zirconium, and titanium have a high affinity for oxygen and would be candidates for getters.

[0039] Furthermore, a fibrous core may be formed first, and the material of interest may be deposited thereon using LCVD (e.g., silicon carbide or other desired material). Before or after grinding, the core material may remain in the fibers or may be removed using any suitable removal process (i.e., heating, solvent, etc.).

[0040] Molding and coating addition

[0041] According to one aspect of the present invention, the formed grains may be specially molded and / or coated. The grains may be ground into a specific shape to maximize their fracture toughness with a high surface area-to-volume ratio. Optimizing this ratio increases the amount of fracture energy that can be absorbed. For example, a spherical shape can better dissipate fracture energy. In addition, coatings (e.g., interfacial layers - boron nitride, carbon, beryllium oxide) may be applied to the grains to further improve the fracture toughness behavior of the composite. Without coating, the grains may be prone to fracture by cracks propagating within the grain. The coating can absorb and / or deflect cracks, allowing the grains to maintain their mechanical integrity. Additional coatings, such as silicon carbide, can act as an environmental protection barrier for the grains.

[0042] Examples of nuclear applications

[0043] The fibers and related manufacturing techniques discussed herein can achieve a multitude of structures and compositions in accordance with all of the incorporated patent applications mentioned above. It is noteworthy that any element that is compatible with the desired fiber formation process (e.g., LCVD) disclosed herein, and in granular or other processed form, falls within the scope of the present invention. For example, nuclear fuel formation as part of fibers and fiber-related structures is disclosed in the aforementioned patent applications titled “Additive Manufacturing Techniques for the Production and Characterization of Reactor Fuel”; “Functional Polymer Fiber Structures”; and “Microtrellis Nonwoven Fabrics and Reinforced Composite or Hybrid Composite Materials.” According to one aspect of the present invention, high-purity fibers can be formed from various nuclear fuel materials. In one aspect of the present invention, nuclear fuel material fibers can then be ground or pulverized into granular form for use where such fuel material is required. The fuel granules can then be formed into fuel pellets or other fuel structures. In this regard, nuclear fuel production can benefit from the scale and purity of the fiber formation and grain pulverization processes of the present invention. Exemplary nuclear fuel materials include, but are not limited to, uranium, plutonium, uranium dioxide, uranium nitride, uranium mononitride, uranium carbide, and / or uranium silicide.

[0044] In summary, the present invention is, in one aspect, a method for forming a high-purity granular material, comprising: providing a precursor in a reactor; forming at least a portion of the fibers in the reactor from the precursor using a chemical deposition that interacts with the precursor; and forming a granular material from the fibers. In one embodiment, the chemical deposition may include laser-induced chemical vapor deposition. The granular material may be formed by grinding or crushing fibers into granules, for example, by ball milling the fibers.

[0045] In another embodiment, multiple fibers may be formed in parallel using a single laser beam, multiple laser beams with independent power control, or multiple laser beams without independent power control. At least one element may be added during chemical deposition, which acts as a free oxygen getter to improve the oxidation resistance of the granular material, and the granular material may be shaped and / or coated.

[0046] The granular material may, in certain aspects, be silicon carbide powder having a beta-crystalline phase purity of over 90% and an oxygen content of less than 0.25%; or multi-element and multi-phase composition powder having an oxygen content of less than 0.25%; or nuclear fuel material.

[0047] The terms used herein are for the sole purpose of describing specific embodiments and are not intended to limit the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to also include the plural form unless the context clearly indicates otherwise. The terms “to equip” (and any form of “to equip,” such as “to equip (plural)” and “to equip”), “to have” (and any form of “to have,” such as “to have (singular)” and “having”), “to include” (and any form of “to include,” such as “to include (singular)” and “containing”), and “to contain” (and any form of “to contain,” such as “to contain (plural)” and “containing”) will be further understood to be modifiable verbs. As a result, a method or apparatus that “equips,” “has,” “includes,” or “contains” one or more steps or elements possesses, but is not limited to possessing only, those one or more steps or elements. Similarly, any step or element of a method or apparatus that “companies,” “has,” “includes,” or “contains” one or more features possesses, but is not limited to possessing only, one or more of those features. Furthermore, an apparatus or structure configured in a certain way is configured in at least that way, but may also be configured in a way not described.

[0048] All means or step-plus-function elements in the following claims are intended to include any structures, materials, or actions for performing a function in combination with any other elements of the claims specifically claimed, if any. The description of the invention is presented for illustrative and explanatory purposes, but is not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the invention. The embodiments have been selected and described to best illustrate the principles and practical applications of one or more aspects of the invention, and to enable others skilled in the art to understand one or more aspects of the invention in terms of various embodiments with various modifications to suit a particular intended use.

Claims

1. A method for forming a high-purity granular material, Provide the precursor into the reactor, Forming fibers in the reactor from the precursor, including using chemical deposition that interacts with the precursor, and This includes forming the granular material from the aforementioned fibers, The aforementioned chemical deposition includes laser-induced chemical vapor deposition. A method comprising the granular material containing silicon carbide powder.

2. The method according to claim 1, wherein forming the granular material includes grinding or crushing the fibers to form the granular material.

3. The method according to claim 2, wherein forming the granular material includes ball milling the fibers.

4. Multiple fibers are formed in parallel using a single laser beam, or multiple laser beams with independent power control, or multiple laser beams without independent power control, and The method according to claim 1, further comprising forming a granular material from a plurality of fibers.

5. The method according to claim 1, further comprising adding at least one element to the chemical deposition, which functions as a free oxygen getter to improve the oxidation resistance of the granular material.

6. The method according to claim 1, wherein the silicon carbide powder has a beta-crystalline phase purity of more than 90% and an oxygen content of less than 0.25%.

7. The method according to claim 1, wherein the granular material comprises a multi-element and multi-phase composition powder having an oxygen content of less than 0.25%.

8. The method according to claim 1, further comprising molding and / or coating the granular material.

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