Si-free reaction-bonded SiC

Abstract

To provide a method for manufacturing a ceramic component to solve one or more problems relating to cost, size and shape capability, purity, grain size, properties, and the like.SOLUTION: The present invention relates to a method for manufacturing a reaction-bonded silicon carbide (RB-SiC) material having low residual Si, including the steps of: fabricating an SiC+carbon preform containing diamond powder; infiltrating the preform with molten Si to fabricate an infiltrated preform; and maintaining the infiltrated preform in a furnace to allow a reaction from an Si+diamond to SiC to occur.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Cross - Reference to Related Applications / Incorporation by Reference

[0001] None applicable

[0002] Aspects of the present disclosure relate to reaction - bonded SiC ceramic components. More specifically, certain embodiments of the disclosure relate to reaction - bonded silicon carbide (RB - SiC) ceramic components made using diamond powder and having low residual Si.

Background Art

[0002]

[0003] Conventional techniques for fabricating ceramic components may have problems related to one or more of cost, size and shape capabilities, purity, grain size, properties, etc.

[0003]

[0004] Further limitations and disadvantages of conventional and traditional techniques will become apparent to those skilled in the art through comparison with some aspects of the present disclosure as described in the remainder of this application with reference to such systems and drawings.

Summary of the Invention

[0004]

[0005] A system and / or method for fabricating ceramic components using diamond powder, substantially as shown and / or described in relation to at least one of a plurality of figures, as more fully set forth in the claims.

[0005]

[0006] These and other advantages, aspects and novel features of the present disclosure, as well as details of the illustrated embodiments, will be more fully understood from the following description and the drawings.

Brief Description of the Drawings

[0006] [Figure 1]

[0007] A diagram of reaction - bonded silicon carbide (RB - SiC) according to an example embodiment of the disclosure. [Figure 2]

[0008] This is a diagram of an example RB-SiC microstructure according to an example embodiment of the disclosure. [Figure 3]

[0009] This is a diagram of the disclosed reaction bonding process using diamond powder in a preform, according to an embodiment of the disclosure. [Figure 4]

[0010] This is a table showing the properties of various forms of carbon, according to embodiments of the disclosure. [Figure 5]

[0011] This is a diagram of two "Si-free" RB-SiC samples according to an example embodiment of the disclosure. [Figure 6]

[0012] This figure illustrates a phase analysis using ImageJ for "Si-free" RB-SiC according to an example embodiment of the disclosure. [Figure 7]

[0013] This is a diagram of reaction-bonded boron carbide (RB-B4C) according to an embodiment of the disclosed example. [Figure 8]

[0014] This is a diagram of an example RB-B4C microstructure according to an embodiment of the disclosure. [Figure 9]

[0015] This is a diagram illustrating an example use of the RB-B4C according to an embodiment of the disclosure. [Modes for carrying out the invention]

[0007]

[0016] Reaction-bonded silicon carbide (RB-SiC) ceramic components are important in numerous industries. Examples of components include, but are not limited to, high-purity, corrosion-resistant semiconductor-treated components (e.g., chamber liners, furnace components, shower heads, focus rings); armor tiles; industrial wear and heat-resistant components; corrosion-resistant valves and structures for mining, petrochem, oil and natural gas exploration, etc.; and high-energy laser mirrors that can be directly polished.

[0008]

[0017] Traditional methods for forming "pure" SiC include sintering; hot pressing; and CVD. These methods are limited in many aspects, including cost, size and shape capability, purity, grain size, properties, etc. Reaction-bonded SiC (also known as SiSiC) has attractive size and shape capability, cost, purity, tailorability, etc. However, the presence of residual Si phase limits its use in areas such as high temperatures, corrosion, direct polishing, armor, wear, etc.

[0009]

[0018] Reaction-bonded SiC (also known as RB-SiC or SiSiC) possesses many distinct characteristics. Compared to conventionally processed SiC (sintered, hot-pressed, CVD), reaction-bonded SiC can be fabricated in complex shapes (without shrinkage) and large sizes, its properties, grain size, and additional phases can be tailored to specific purposes, it can be produced in high purity, and it offers attractive process economics (e.g., relatively low process temperatures). However, RB-SiC often contains residual Si phase due to the fusion process used. The presence of Si phase limits its use in various applications, including semiconductor etching, high temperatures, corrosion, wear, armor, and directly polished mirrors.

[0010]

[0019] Existing methods for applications requiring "pure" ("Si-free") SiC involve using sintered, hot-pressed, or CVD forms of SiC. All of these processes have their problems. Sintered SiC has a 20% process shrinkage, which limits its size and shape capabilities. Furthermore, sintered SiC contains impurities (sintering aids). Finally, sintered SiC is processed at high temperatures (>2000°C compared to ~1500°C for RB), which leads to high costs. Hot-pressed SiC is formed by pressing SiC powder at high temperatures. This process is capital-intensive, expensive, and has very limited size and shape capabilities. CVD SiC is formed by converting MTS (methyltrichlorosilane) gas into SiC in a reactor and slowly growing the structure layer by layer. This process is slow, expensive, and extremely limited in terms of size and shape.

[0011]

[0020] A "Si-free" version of Si (e.g., with little to no residual Si phase) should have value in many markets where there is a need for attractive pricing, significant size and shape capabilities, and the properties provided by a pure SiC microstructure.

[0012]

[0021] RB-SiC must have a continuous network of Si to allow the fusion process to function. The minimum possible Si content is nominally 8-10%. This disclosure presents a method for producing RB-SiC ceramics with low or nominally zero residual Si by using a preform with SiC plus a small amount of diamond powder. In some embodiments, this is a two-step process: (1) fusion of a preform with molten Si under conditions where the Si+diamond reaction would be slow to produce a fused preform; (2) keeping the fused preform in a furnace to allow the Si+diamond → SiC reaction to occur, thus removing all Si from the microstructure. With respect to step (2), the rate of the reaction depends on the temperature and the size (surface area) of the diamond particles. The reaction time range may be less than 10 hours, less than 8 hours, or less than 5 hours, and in some embodiments, the reaction time is from about 3 to 5 hours. The reaction temperature range may be approximately 1400°C to 1600°C, and in some embodiments, the temperature range is approximately 1450°C to 1550°C, approximately 1480°C to 1550°C, or approximately 1500°C to 1550°C. The specific time at each temperature depends on the particle size. In some embodiments, a diamond particle size of less than 12 μm is required for reaction times of less than 10 hours. In other embodiments, a diamond particle size of less than 8 μm allows for both rapid reactions (less than 10 hours) and also allows all the diamond to react with SiC.

[0013]

[0022] Because diamond is a "high molecular weight" carbon, as diamond reacts with SiC, a large expansion occurs, allowing Si islands to be filled. Key advantages include one or more of the following: (1) attractive features of the RB process are maintained: size, shape, cost, low process temperature, tailorability, purity (no sintering aids), no process shrinkage, etc.; (2) Si-free microstructures are realized for critical applications: semiconductor etching, wear, directly polishable HEL mirrors, furnace liners, oil and natural gas, petrochem, corrosion, etc.; and / or (3) the microstructure may be tailored to meet the needs of the application (e.g., some residual diamond can be retained to increase hardness and / or thermal conductivity by starting with more than is needed to sufficiently react the Si phase with SiC).

[0014]

[0023] The disclosed method produces a preform of SiC and diamond powder. The preform may be a loose mixture of dry powders or a solidified object formed by casting, pressing, or other methods. In addition, the reaction bonding takes place under vacuum (the vacuum should remove all residual moisture such as all oxygen or room humidity, etc.). In other embodiments, the reaction may be carried out under an inert atmosphere and / or in a humidity-controlled environment.

[0015]

[0024] Figure 1 is a diagram of a conventional reaction-bonded silicon carbide (RB-SiC, also called SiSiC). Referring to Figure 1, reaction-bonded SiC ceramics are fabricated by the reactive infiltration of molten Si into a SiC + carbon preform. In infiltration, the molten Si reacts with carbon to form additional SiC (Si + C → SiC), bonding the structure together. The final composite is composed of the original SiC, the SiC formed by the reaction, and residual Si. As discussed above, a minimum final Si content of 8-10 vol% is required for the process to function (i.e., a continuous network of interconnected Si is required for infiltration to proceed).

[0016]

[0025] In the creation of reaction-bonded silicon carbide (RB-SiC) ceramic materials as described herein, a preform is utilized. There are many different preform processes (casting, pressing, etc.). In one embodiment of this study, the preform is created using a slurry (SiC + C-based binder + deionized H2O), and the preform is formed into the desired shape including both an inner outer shape and an outer outer shape. The preform may be fabricated as a green part, and the green part is then reaction-bonded (infiltrated with Si) to end up as a finished ceramic part.

[0017]

[0026] Differences may be seen in the microstructure of the two example reaction-bonded SiC shown in Figure 2. In Example 1, the preform has a low carbon content, thus little Si + C → SiC reaction occurs, and the final Si content is high (30%). In Example 2, the preform has a high carbon content, thus a significant Si + C → SiC reaction occurs, and the final Si content is low (10%). The properties are listed in Table 1 below for both Example 1 and Example 2 (see Figure 2).

[0018]

Table 1

[0019]

[0027] This disclosure provides a method for producing reactive silicon carbide (RB-SiC) ceramic components having a low residual Si phase (e.g., nominally "Si-free") by utilizing diamond powder in a preform. Low residual Si content components are produced due to the very large expansion caused by the reaction of diamond to form SiC. In some embodiments, the Si content is 10% or less by weight of silicon, and in other embodiments, the Si content is 5% or less by weight of silicon, 3% or less by weight of silicon, 2% or less by weight of silicon, or 1% or less by weight of silicon. In some embodiments, low residual Si corresponds to the absence of detectable residual Si. Varying the processing time and temperature may yield different results.

[0020]

[0028] Applications for low-residual Si content materials include high-temperature, corrosive, and wearable applications (as a replacement for sintered SiC); process semiconductor applications (as a replacement for CVD SiC in focus rings and showerheads); and directly polishable HEL mirrors (typically, RB-SiC is difficult to optically polish due to the presence of a soft Si phase).

[0021]

[0029] Figure 3 is a diagram of a reaction bonding process, as disclosed herein, utilizing diamond powder in a preform. Referring to Figure 3, since diamond is a large molecular weight "carbon" (see Figure 4), the Si + diamond → SiC reaction is highly expansive (i.e., the SiC formed in the reaction can fill voids in the preform). Also, because diamond is a large molecular weight "carbon," the Si + diamond → SiC reaction is slow, thus allowing for the dissolution of the preform, followed by the reaction. If the initial diamond powder in the preform has a small particle size, it can react sufficiently during the process to form SiC, which creates "Si-free" reaction-bonded SiC. Figure 3 also shows that ceramic particles such as SiC and / or B4C may be used in the preform. See further discussion below.

[0022]

[0030] In some embodiments, the diamond particle size is in the range of about 5 μm to about 12 μm. At about ≤8 μm, all diamond may be reacted and removed, while at about 8 μm or larger, a "halo" is formed as discussed below. Particle size measurement may include measurement of particle diameter. Particle size measurement may be performed by laser scattering according to ASTM D4464.

[0023]

[0031] Figure 3 also shows diamond particles having a SiC coating ("halo") formed by the reaction. If the diamond particles are small enough, the coating ("halo") can surround the entire particle. Again, a small amount of diamond can result in a large amount of SiC due to volume expansion. In this disclosure, it is preferable that most, if not all, of the diamond reacts to form a monolithic structure. Monolithic structures are preferred because they facilitate machining, etc. If there is too much diamond, then an excess will remain, and the diamond-containing material will then be difficult to machine. Thus, in the disclosed material, both low Si and low residual diamond are preferred. However, in some embodiments, a slightly larger, controlled amount of diamond may be left in the material to give desired properties such as increased hardness.

[0024]

[0032] Generally, preforms with high carbon levels result in reaction-bonded ceramics with little residual Si phase because the Si + C → SiC reaction is expansive. Carbon can exist in several forms, including carbon black, graphite, and diamond. Diamond is a high-density form of carbon and, given a specific volume, contains more moles of carbon than other forms of carbon. Thus, the expansion (volume increase) in the Si + diamond → SiC reaction is large. The supply of silicon is in excess of what diamond can react with. Again, because of the high starting density of diamond, the conversion to SiC results in a very large volume expansion. This leads to a low Si content in reaction-bonded ceramics.

[0025]

[0033] Figure 4 is a table showing the properties of various forms of carbon. In some embodiments, diamond is a preferred form of carbon based on the expansive reaction profile described herein.

[0026]

[0034] In addition to the solid form of carbon (i.e., diamond powder), a solution of an organic material may be used to add additional carbon to the material before the reaction. The material used for adding the additional carbon may be a solution of food starch such as fructose. In addition to food starch, other sources of additional carbon include alcohols such as furfuryl alcohol and phenolic resins. Preferred organic materials are inexpensive, safe, and / or readily soluble in water. The additional carbon may also be added by immersing the preform in a solution of the organic material.

[0027]

[0035] Figure 5 shows two samples (A and B) of the creation of “Si-free” RB-SiC according to this disclosure. In sample A: The preform is 88 wt% SiC powder + 12 wt% 12 μm diamond powder. The reaction bonding process involves molten Si immersion holding in a furnace at 1500°C (holding for 3.3 hours compared to 1 hour standard). The resulting material has approximately 2 vol% residual Si and approximately 3 vol% residual diamond. (ImageJ is used for phase analysis). The material has a density of 3.19 g / cc and a Young's modulus of 433 GPa (compared to 3.21 and 450 for pure SiC). In sample B: The process is the same as in example A, except the preform is back-soaked in a 70% fructose solution prior to immersion to add additional carbon. The resulting material has approximately 1 vol% residual Si and approximately 4 vol% residual diamond (by ImageJ). The material has a density of 3.15 g / cc and a Young's modulus of 435 GPa.

[0028]

[0036] Figure 6 illustrates the phase analysis of "Si-free" RB-SiC, specifically for sample A described above, using ImageJ. Both the Si phase and the diamond phase are shown. ImageJ is open-source software that performs phase analysis using grayscale. Here, SEM images were taken, and the software was used to analyze the silicon and diamond grayscales to determine their respective volume percentages.

[0029]

[0037] Other ceramic materials may also be considered, including, but not limited to, RB-B4C as described herein, and may be low-Si versions of RB-B4C. This material may be 100% B4C (plus carbon) by weight, or a mixture of SiC and B4C (plus carbon). The amount of B4C in the SiC-B4C mixture may vary over a wide range of B4C, and the SiC preform ratios that may be used may contain SiC from about 0% to about 80% (or more) by weight. In some embodiments, percentages of SiC by weight of about 1% to about 80%, about 1% to about 70%, about 1% to about 50%, about 10% to about 80%, about 10% to about 70%, or about 10% to about 50% may be used. In further embodiments, large amounts of B4C may be used, including up to 100% and 100% by weight, such as up to 75%, up to 85%, or 90% by weight of B4C. As described herein with respect to RB-SiC, diamond powder may also be added to the RB-B4C system to make the RB-B4C system "Si-free". Figure 7 is a diagram of conventional reaction-bonded boron carbide (RB-B4C). Referring to Figure 7, reaction-bonded B4C ceramics are fabricated by reactive fusion of molten Si into a preform of ceramic particles + carbon (in this case, the ceramic particles may be B4C or B4C + SiC). During fusion, the molten Si reacts with the carbon to form additional SiC (Si + C → SiC) to bond the structure together. The final composition consists of ceramic particles, SiC formed by the reaction, and residual Si. Figure 3 (discussed above) shows a diagram of a reaction bonding process, as disclosed herein, which utilizes diamond powder in the preform and different ceramics such as SiC and / or B4C.

[0030]

[0038] The properties of the two materials are listed in Table 2 below.

[0031] [Table 2]

[0032]

[0039] Figure 8 shows the microstructure of the RB-B4C material. The difference is observed between the material labeled RBBC-751 in the figure prepared from a 100% B4C preform and the material labeled BSC-400 in the figure prepared from a preform containing a mixture of SiC and B4C (40 wt% SiC plus 60 wt% B4C). In the material labeled BSC-400, the lightly colored particles are B4C, and the darker, smaller particles are SiC.

[0033]

[0040] Examples of applications for RB-B4C materials are shown in Figure 9. In some embodiments, reaction-bonded B4C is used for neutron absorption applications. Low-Si RB-B4C, as described herein, is a convenient nuclear material and is valuable for neutron absorption applications (where B4C captures neutrons). The presence of Si in these types of materials offers little advantage due to Si swelling in the neutron flux. This problem is mitigated by removing Si through reaction with diamond, as described herein. Characteristics of these materials include, but are not limited to, high B4C content (e.g., 75% B4C, 10% SiC, 15% Si by weight); the ability to grow in large sizes and complex shapes; and conductivity for EDM machining. Applications include, but are not limited to, shielding / containment panels; components for nuclear laboratories; and neutron collimators.

[0034]

[0041] In some embodiments, a method is disclosed for producing RB-SiC ceramics in a nominally zero-residue Si (e.g., "Si-free") state by utilizing diamond powder having a particle size of ≤8 μm. The method steps include, but are not limited, adding a small amount of diamond to a SiC preform; fusing molten Si if the Si+-diamond reaction is too slow to produce a fusing preform; and holding the fusing preform at a furnace temperature after fusing to allow the Si+-diamond → SiC reaction to occur, thus removing the Si phase. In some embodiments, the diamond particles are small enough to react completely with SiC during the process and leave no residual diamond (good for applications where final machining is required). In further embodiments, the diamond particles are large enough to produce a halo effect after processing (e.g., a diamond core with a SiC coating). This is good for applications where ceramics with enhanced hardness are desired (armor, wear, etc.). The disclosed method results in a material that may be used as Si-free RB-SiC semiconductor process components (shower heads, focus rings, chamber liners); Si-free RB-SiC ware / fire-resistant / corrosion-resistant components (for use in mining, petrochem, oil and natural gas exploration, furnace liners, etc.); and / or as Si-free RB-SiC (or RB-B4C) for armor tile applications.

[0035]

[0042] The preform is prepared using a blend of ceramic particles (such as SiC and / or B4C). The preform may be prepared as a green part by various methods, such as using a loose mixture of dry powders, or by preparing a slurry that is formed in a mold (or cast into a brick-like form for later machining) using a water- and carbon-based binder. The slurry is frozen, dried, or both to remove the solvent and solidify the green part. A drying / carbonization procedure is then performed, which may be carried out under a nitrogen atmosphere. In some embodiments, the temperature range for this step is from about 260°C to about 371°C (from about 500°F to about 700°F). During the carbonization procedure, the carbon-based binder is decomposed (thermally decomposed).

[0036]

[0043] The diamond powder used may have a variety of particle sizes. In some embodiments, the particle size of the diamond powder is between approximately 3 μm and 15 μm; in other embodiments, the particle size of the diamond powder is between approximately 3 μm and 10 μm; approximately 3 μm and 9 μm; approximately 3 μm and 8 μm; approximately 3 μm and 7 μm; approximately 3 μm and 6 μm; or approximately 3 μm and 5 μm. In one embodiment, the particle size of the diamond powder is less than 15 μm; in another embodiment, the particle size of the diamond powder is between approximately 10 μm. As discussed above, the use of small particles (<8 μm) allows all the diamond to react sufficiently with SiC. Using larger diamond particles (>8 μm) results in the formation of a SiC halo, leaving some residual diamond. However, residual diamond can be advantageous depending on the application (e.g., higher hardness materials).

[0037]

[0044] The amount of diamond powder is generally less than 20% by weight. In some embodiments, the amount is between 15-20% by weight; between about 10-15% by weight; between about 5-10% by weight; or less.

[0038]

[0045] As discussed above, both low-Si and low-residue diamond are preferred. However, low-Si offers the best performance, while low-residue diamond offers the best machinability. The balance between these two may be determined based on the desired application.

[0039]

[0046] In some embodiments, a large portion of the diamond powder in the preform is reacted. In some embodiments, more than 75% of the diamond is reacted; more than 85% of the diamond is reacted; more than 95% of the diamond is reacted.

[0040]

[0047] In the disclosed materials, the low final Si content (low residual Si phase) in the "Si-free" material corresponds to a lower limit of 0% Si (undetectable) and less than 10% by weight of residual Si. In some embodiments, less than 9% by weight of Si remains; less than 8% by weight of Si remains; less than 7% by weight of Si remains, less than 6% by weight of Si remains; less than 5% by weight of Si remains; less than 4% by weight of Si remains; less than 3% by weight of Si remains; less than 2% by weight of Si remains; less than 1% by weight of Si remains; less than 0.5% by weight of Si remains; or less than 0.1% by weight of Si remains. In some embodiments, no detectable Si is present (0% remains).

[0041]

[0048] As used herein, “and / or” means one or more of the items in the list connected by “and / or.” For example, “x and / or y” means any of the elements of the three-element set {(x), (y), (x,y)}. In other words, “x and / or y” means “one or both of x and y.” As another example, “x, y, and / or z” means any of the elements of the seven-element set {(x), (y), (z), (x,y), (x,z), (y,z), (x,y,z)}. In other words, “x, y and / or z” means “one or more of x, y, and z.” As used herein, the term “exemplary” means to serve as an unrestricted example, instance, or example. As used herein, the terms "etc.," "eg," and "for example" refer to one or more non-limiting examples, cases, or instances outside of a list.

[0042]

[0049] While the present invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various modifications may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt the teachings of the invention to specific circumstances or materials without departing from the scope of the invention. Therefore, it is intended that the invention will not be limited to the specific embodiments disclosed herein, but will include all embodiments that fall within the scope of the claims set forth herein.

Claims

1. A method for producing reaction-bonded silicon carbide (RB-SiC) material having low residual Si, A step of fabricating SiC and carbon preforms containing diamond powder, A step of immersing the preform with molten Si in order to produce a fused preform, A step of maintaining the fused preform in the furnace and allowing the Si and diamond to react to form SiC. Includes, The aforementioned low residual Si corresponds to 5% or less by weight of residual Si. method.

2. A method according to claim 1, wherein the majority of the diamond reacts.

3. A method according to claim 2, wherein 75% or more of the diamonds react.

4. A method according to claim 3, wherein 85% or more of the diamonds react.

5. A method according to claim 4, wherein 95% or more of the diamonds react.

6. A method according to claim 1, wherein the low residual Si corresponds to the absence of residual detectable Si.

7. A method according to claim 1, wherein the diamond powder has a particle size between about 3 μm and 15 μm.

8. A method according to claim 7, wherein the diamond powder has a particle size between about 3 μm and 10 μm.

9. A method according to claim 1, wherein an additional carbon is added to the preform before the reaction.

10. A method according to claim 9, wherein the additional carbon is added by immersing the preform in a solution of an organic material.

11. The method according to claim 1, wherein the preform is B ４ A method that also contains C.

12. A method according to claim 11, wherein B in the preform ４ The C:SiC ratio ranges from approximately 0% SiC to approximately 80% SiC by weight.

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