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WO1994001363A1 - Fabrication de barbes de renforcement en carbure de silicium - Google Patents

Fabrication de barbes de renforcement en carbure de silicium Download PDF

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Publication number
WO1994001363A1
WO1994001363A1 PCT/SE1993/000329 SE9300329W WO9401363A1 WO 1994001363 A1 WO1994001363 A1 WO 1994001363A1 SE 9300329 W SE9300329 W SE 9300329W WO 9401363 A1 WO9401363 A1 WO 9401363A1
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Prior art keywords
component
εaid
mixture
boron
carbon
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Inventor
Dongxin Qui
Roy Tom Coyle
Richard D. Tait
Rick J. Orth
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Sandvik AB
Advanced Industrial Materials
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Sandvik AB
Advanced Industrial Materials
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
    • C30B25/005—Growth of whiskers or needles
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/36—Carbides

Definitions

  • This invention relates to a process for making silicon carbide whiskers and is particularly concerned with a process for providing relatively high yields of beta silicon carbide whiskers while controlling the size and shape of the whiskers.
  • Silicon carbide is a high strength ceramic material which has good chemical stability and excellent oxidation resistance to high temperatures due mainly to covalent bonding and a crystal structure related to that of diamond.
  • Silicon carbide whiskers are needle-shaped single crystals of silicon carbide having an aspect ratio, i.e., a length-to-diameter ratio, greater than about 3 and a typical diameter between about 0.1 and 10 microns.
  • the high aspect ratio of whiskers makes them a much more effective reinforcement in composites, especially ceramic matrix composites, than silicon carbide particulates.
  • whiskers exhibit much higher mechanical strength than silicon carbide fibers, which are either polycrystalline or amorphous forms of silicon carbide that typically have a diameter greater than 10 microns.
  • Silicon carbide whiskers are particularly suited for use in the reinforcement of all types of engineering ceramics including gas turbine ceramics, automotive ceramics and ceramic cutting tools. It is estimated that the market for the use of whiskers as reinforcements for engineering ceramics alone will be several hundred million dollars per year by the year 2000.
  • SUBSTITUTESHEET size and shape of the whiskers meet specified requirements. For example, in some instances it may be desirable that the diameter of the whiskers be less than one micron while in other cases whisker diameters of several microns are preferred. Also, straight whiskers are normally used to reinforce ceramic matrix composites because such reinforced composites have a higher fracture toughness than those reinforced with curly whiskers. On the other hand, curly whiskers may be more effective than straight whiskers for other reinforcing applications. For these and other reasons, it is desirable that the size and shape of the whiskers be controlled during synthesis.
  • the current dominant technology for producing silicon carbide whiskers is the carbother al reduction of silica by carbon in rice hulls.
  • Rice hulls are composed of about 15 to 20 percent ash that is primarily silica.
  • carbon in the rice hulls reacts with silica to form silicon carbide in accordance with the overall reaction of
  • the major problem with using rice hulls to synthesize silicon carbide whiskers is that the resultant product normally contains only between about 10 and 20 weight percent silicon carbide whiskers with the remainder being silicon carbide in the form of particulates, unreacted silica and unreacted carbon. Higher yields of silicon carbide whiskers are usually not possible because the chemical composition of the rice hulls and the degree of mixing of the carbon and silica therein are set by nature and cannot readily be varied. Thus, it is difficult to
  • SUBSTITUTESHEET obtain an intimate mixture of carbon and silica that is sufficiently porous to allow carbon monoxide gas to escape and thereby drive the overall reaction of carbon with silica to form silicon carbide to completion while allowing space for silicon carbide whiskers to grow. It can be seen from the above that future processes for producing silicon carbide whiskers should give a relatively high yield of whiskers having desired sizes and shapes which can be tailored according to the particular use desired for the whiskers.
  • silicon carbide whiskers can be obtained from mixtures of (1) a particulate form of carbon, (2) a silicon component selected from the group consisting of silica, hydrated silica and a source of silica, (3) a boron component, and (4) a seeding component comprising an element selected from the group consisting of the rare earths, Group IA, Group IB, Group VB, Group VIB, Group VIIB, and Group VIII of the Periodic Table of Elements, or a compound containing one or more of these elements.
  • a seeding component comprising an element selected from the group consisting of the rare earths, Group IA, Group IB, Group VB, Group VIB, Group VIIB, and Group VIII of the Periodic Table of Elements, or a compound containing one or more of these elements.
  • the seeding component usually contains an element or elements selected from the group consisting of lithium, potassium, sodium, rubidium, neodymium, niobium, vanadium, tantalum, chromium, molybdenum, manganese, iron, ruthenium, cobalt,
  • SUBSTITUTESHEET rhodium, nickel, palladium and copper Preferably, the seeding component is cobalt, nickel or iron, or compounds containing these metals.
  • the size and shape of the whiskers formed in the process of the invention are controlled by the size of the seeding component and the concentration of the boron component.
  • the use of seeds having a weight average particle size between about 0.1 and 3.0 microns results in the production of predominantly curly whiskers at relatively low concentrations of the boron component. As the concentration of the boron component increases, the amount of curly whiskers in the synthesis product decreases.
  • the use of seeds having a weight average particle size between about 3.0 and 200 microns tends to yield a high concentration of whiskers having a relatively straight shape when the boron component is present in sufficient quantity so that the mixture subjected to the high temperature synthesis step has a mole ratio of boron-to-silicon greater than about 0.20 and less than about 0.80.
  • the diameters of the whiskers can vary between 0.1 and 3.0 microns with a 1 micron diameter being somewhat typical.
  • Figure 1 in the drawing is a scanning electron photomicrograph, at 900 times magnification, of the product formed in Example 1 illustrating the formation of silicon carbide whiskers by heating in a nonoxidizing atmosphere a mixture of carbon black, fumed silica, cobalt metal having a weight average particle size of about 1.6 microns, and boron oxide powder in concentrations such that the mixture has a boron-to- silicon mole ratio of 0.11;
  • Figure 2 is a scanning electron photomicro ⁇ graph, at 1,000 times magnification, of the product formed in Example 2 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 1 but having a boron-to-silicon mole ratio of 0.22;
  • Figure 3 is a scanning electron photomicro ⁇ graph, at 1,000 times magnification, of the product formed in Example 3 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 1 but having a boron-to-silicon mole ratio of • 0.35;
  • Figure 4 is a scanning electron photomicro ⁇ graph, at 1,000 times magnification, of the product formed in Example 4 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 1 but having a boron-to-silicon mole ratio of 0.50;
  • Figure 5 is a scanning electron photomicro- graph, at 1,000 times magnification, of the product formed in Example 5 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 1 but having a boron-to-silicon mole ratio of 0.67;
  • SUBSTITUTESHEET Figure 6 is a scanning electron photomicro ⁇ graph, at 1,000 times magnification, of the product formed in Example 6 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 1 but having a boron-to-silicon mole ratio of 0.86;
  • Figure 7 is a scanning electron photomicro ⁇ graph, at 1,100 times magnification, of the product formed in Example 7 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 1 but having a boron-to-silicon mole ratio of 1.08;
  • Figure 8 is a scanning electron photomicro ⁇ graph, at 1,000 times magnification, of the product formed in Example 8 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 1 but having a boron-to-silicon mole ratio of 1.33;
  • Figure 9 is a scanning electron photomicro- graph, at 1,000 times magnification, of the product formed in Example 9 illustrating the formation of silicon carbide whiskers by heating in a nonoxidizing atmosphere a mixture of carbon black, fumed silica, cobalt metal having a weight average particle size between about 38 and 45 microns, and boron oxide powder in concentrations such that the mixture has boron-to-silicon mole ratio of 0.11;
  • Figure 10 is a scanning electron photomicro ⁇ graph, at 1,000 times magnification, of the product formed in Example 10 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 9 but having a boron-to-silicon mole ratio of 0.22;
  • Figure 11 is a scanning electron photomicro- graph, at 1,000 times magnification, of the product
  • Example 11 SUBSTITUTESHEET formed in Example 11 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 9 but having a boron-to-silicon mole ratio of 0.35
  • Figure 12 is a scanning electron photomicro ⁇ graph, at 1,000 times magnification, of the product formed in Example 12 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 9 but having a boron-to-silicon mole ratio of 0.50;
  • Figure 13 is a scanning electron photomicro ⁇ graph, at 1,000 times magnification, of the product formed in Example 13 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 9 but having a boron-to-silicon mole ratio of 0.67;
  • Figure 14 is a scanning electron photomicro ⁇ graph, at 1,000 times magnification, of the product formed in Example 14 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 9 but having a boron-to-silicon mole ratio of 0.86;
  • Figure 15 is a scanning electron photomicro ⁇ graph, at 1,000 times magnification, of the product formed in Example 15 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 9 but having a boron-to-silicon mole ratio of 1.08;
  • Figure 16 is a scanning electron photomicro- graph, at 1,000 times magnification, of the product formed in Example 16 illustrating the formation of silicon carbide whiskers by heating a mixture similar to that of Example 9 but having a boron-to-silicon mole ratio of 1.33.
  • Silicon carbide whiskers of desired size and shape are produced in accordance with the process of the invention by combining a particulate form of carbon with a silicon component, a boron component and a seeding component to form a mixture, heating the resultant mixture in a nonoxidizing atmosphere at temperatures sufficiently above about 1300° C. to induce the reaction of carbon with silica to form silicon carbide whiskers and recovering a product containing the silicon carbide whiskers.
  • the particulate form of carbon used in the process of the invention can be any form of carbon that has a rather fine particle size and a relatively high specific surface area.
  • the weight average particle size of the carbon source is between about 1 and 1,000 nanometers, preferably between about 5 and 100 nanometers, while the surface area usually ranges between about 100 and 600, preferably between about 200 and 500, square meters per gram.
  • the particulate carbon can be in any form that gives the desired surface area and particle size.
  • the various forms of carbon black, such as furnace black and acetylene black are normally preferred since they usually have the requisite particle sizes and surface areas.
  • other forms of carbon such as activated carbon, graphite powder and even petroleum coke can be used if they have the appropriate physical properties.
  • an amorphous form of carbon is preferred over a crystalline form because amorphous carbon typically has a smaller particle size, a higher surface area and a higher reactivity.
  • the silicon component used to form the mixture which is converted at high temperatures into silicon carbide may be any crystalline or amorphous form of silica, a hydrated silica or a source of silica, i.e. a
  • silica SUBSTITUTE SHEET silicon-containing compound which decomposes into silica during the heating step.
  • the forms of silica have a surface area between about 50 and 500, preferably between 100 and 400, square meters per gram.
  • examples of different types of silica which may be used are high surface area materials such as fumed silica and silica glass powder.
  • the use of silica having a weight average particle size less than about 1.0 micron is preferred since smaller particles generally promote a more rapid reaction. In general, the weight average particle size of the silica is between about 1 and 100 nanometers, preferably between 5 and 50 nanometers.
  • Examples of hydrated silicas which may be used in the process of the invention include silicic acid, silica sols and silica gels while examples of the sources of silica that can be used include silicon alkoxides, such as tetraethoxy and tetramethoxy orthosilicate ⁇ , and other types of ⁇ ilanes.
  • the particulate carbon and silicon component are utilized in forming the mixture subjected to the high temperature silicon carbide synthesis step so that the carbon-to- silicon mole ratio in the mixture ranges between 2.0 and 6.0, preferably between 2.5 and 5.0, and most preferably between about 3.0 and 4.0. It is normally preferred that a stoichiometric excess of the particulate carbon be utilized.
  • the boron component used in the process of the invention is preferably boron oxide (B2O3) or an inorganic boron compound, such as boric acid (H3BO3), which decomposes to boron oxide at or below the silicon carbide synthesis temperatures utilized. Also, organoboron compounds which decompose to boron oxide may be used. It is believed that the boron component enhances whisker growth by forming a low temperature melt with silica, i.e., a borosilicate melt, during the high
  • SUBSTITUTESHEET temperature synthesis step which melt spreads or coats the surface of the carbon particles, thereby resulting in better contact of carbon and silica and thus better reaction kinetics. Also, the melt surrounding the carbon particles serves as a medium in which the whiskers can grow as opposed to prior art methods of making whiskers where there is no substantial liquid phase present, and whisker growth is inhibited by a solid environment.
  • organoboron compounds which may be used in the process of the invention include trimethyl borate [(CH3 ⁇ )3B], triethyl borate [(C2H 5 0)3B], triisopropyl borate [(C3H7 ⁇ )3B] and other boron alkoxides.
  • a sufficient amount of the boron component is used so that the mole ratio of boron-to-silicon in the mixture subjected to heating to form silicon carbide whiskers is between about 0.15 and 1.0, preferably between about 0.20 and 0.80.
  • the fourth and final component of the mixture which is heated to form silicon carbide whiskers in accordance with the process of the invention is a seeding component which, in essence, serves as a catalyst for the production of the silicon carbide whiskers.
  • the seeding component typically contains an element or elements selected from the group consisting of the rare earths, Group IA, Group IB, Group VB, Group VIB, Group VIIB, and Group VIII of the Periodic Table of Elements.
  • Periodic Table of Elements refers to the version commonly used in the United States and approved by Chemical Abstracts (CAS) . An example of such a table may be found on the inside front cover of the CRC Handbook of Chemistry and Phvsics, 69th edition, which was edited by R. C.
  • the seeding component contains lithium, potassium, sodium, rubidium, neodymium, niobium, vanadium, tantalum, chromium, molybdenum,
  • SUBSTITUTESHEET manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, copper and combination thereof.
  • the seeding component used is preferably in the form of a metal or mixture of metals, i.e. an alloy, but, if desired, a compound or a mixture of compounds containing the desired element or elements may be used. It has been found that the use of cobalt, nickel and iron metal as the seeding component or compounds containing cobalt, nickel or iron are particularly effective in producing a product containing high concentrations of silicon carbide whiskers.
  • the seeding component When the seeding component is a compound, it is typically in the form of an oxalate, a carbonate, a suicide, a carbide, a sulfide, a nitrate, a nitride, an oxide, a boride, a silicate, a sulfate, a phosphide, a phosphate or a halide with compounds in the form of an oxide, a carbonate or a nitrate being preferred.
  • a sufficient amount of the seeding component is used such that the mole ratio of the desired element in the seeding material to the silicon present in the mixture that is subjected to heating is between about 0.001 and 0.30, preferably between about 0.003 and 0.20, and more preferably between 0.01 and 0.15.
  • temperatures sufficiently high to cause silica to react with carbon in the mixture and thereby form silicon carbide via the carbothermal reduction of silica by carbon are typically above 1300° C. and usually range between about 1300° C. and 2000° C, preferably between about 1400° and 1900° C, and most preferably between about 1500° C. and 1800° C. The higher the temperature, the more rapid is the formation of silicon carbide. However, at temperatures above about
  • the mixture subjected to these high silicon carbide synthesis temperatures is normally formed by utilizing a commercial blender in order to obtain a thorough and intimate mixture of the four components.
  • the resultant bulk density of the mixture is usually relatively low, especially when carbon black is used as the particulate form of carbon and fumed silica as the silicon component, because of the relatively high surface areas of the particulate carbon and silica component.
  • this low bulk density provides an ideal environment for the growth of high quality silicon carbide whiskers, it also reduces the amount of feed that can be processed per unit of time.
  • the vacuum used is normally equivalent to between 25 and 29 inches of mercury applied for between 1 and 10 minutes.
  • the high temperature synthesis or carbothermal reduction step may be carried out in a batch-type or continuous operation normally in the presence of a substantially nonoxidizing atmosphere.
  • a flowing gas atmosphere is utilized to remove product carbon monoxide which, if present in high concentrations, would shift the reaction equilibrium away from the formation of silicon carbide.
  • this high temperature carbothermal reduction step is carried out at atmospheric pressure. If a batch-type operation is
  • the mixture may be heated inside a covered graphite container in an induction or resistance furnace.
  • the mixture may be passed through a rotary kiln or other high temperature heating device. In general, the heating takes place in a device which is devoid of trays and contains no substrate surface for whisker growth.
  • the product formed in the high temperature synthesis or carbothermal reduction step may, depending upon the initial concentration of the reactant ⁇ , contain silicon carbide particulates, unreacted seeding component, unreacted silica, borosilicate glass produced by the solidification of the residual borosilicate melt formed by the reaction of boron with silica at synthesis temperatures, and small amounts of the boride and suicide of the metal comprising the seeding component. Also, in some cases, unreacted carbon will be present.
  • This product is typically treated to separate the silicon carbide whiskers from these impurities. The actual treatment procedures utilized depends upon the purity of silicon carbide whiskers desired. In most cases, the raw product is subjected to air classification methods, such as elutriation, which are widely employed in the chemical processing industry for classifying solid particles.
  • This procedure will normally remove the larger particles of silicon carbide particulates and borosilicate glass along with any residual seeding component that remains. If the remaining silicon carbide whiskers are still not of the desired purity, a second step comprising a hydrofluoric acid and/or aqua regia wash can be used to dissolve residual silica, borosilicate glass and other impurities that could not be removed by air classification. Finally, if excess carbon is present in the product from the carbothermal reduction step, it can
  • SUBSTITUTE SHEET be combusted in an oxygen-containing atmosphere at moderate temperatures usually ranging between 500° and 700° C. to form gaseous products.
  • the process of the invention is based, at least in part, on the discovery that the use of both a boron component and a seeding component results in a very high yield of silicon carbide whiskers, typically greater than about 50 weight percent and usually greater than about 80 to 95 weight percent of the product. It has been unexpectedly discovered that the size and shape of the resultant whiskers can be controlled by the size of the seeding component utilized, and, in some cases, the concentration of the boron component. It has been found that curly whiskers normally result when the seeding component has a relatively small size and the boron concentration is relatively low whereas straight whiskers can be obtained by using a larger size seeding component and a broad range of boron concentrations.
  • the seeding component has a weight average particle size between about 0.10 and 3.0 microns, preferably between about 0.50 and 2.0 microns.
  • the weight average particle size of the seeding component normally ranges between about 3.0 and 200 microns, preferably between about 5.0 and 100 microns, and more preferably between 10 and 60 microns.
  • the effective concentrations ' of the boron component in the mixture subjected to the high temperature synthesis step of the process of the invention depends somewhat on the size of the seeding component used. Generally, a higher concentration of boron is required with larger seeding components while lower concentrations are satisfactory when the seeding component is smaller in size.
  • the boron-to-silicon mole ratio in the mixture subjected to high temperature silicon carbide synthesis will typically range from about 0.20 to 0.90, preferably between about 0.30 and 0.70.
  • the weight average particle size of the seeding component ranges between about 3.0 and 200 microns in size
  • the boron-to-silicon mole ratio in the mixture will typically range between about 0.35 and 1.0, preferably between about 0.50 and 0.80.
  • a seeding component having a weight average particle size less than 3.0 microns is used in the silicon carbide synthesis process, greater than about 50, usually between 60 and 70, weight percent of the whiskers in the synthesis product is curly in shape.
  • whiskers produced regardless of their shape, normally have a diameter ranging between about 0.1 and 3.0 microns with a typical diameter being about 1 micron.
  • the aspect ratio normally ranges between about 10 and 150, frequently between 20 and 60 and typically about 50. Most of the whiskers produced are reasonably smooth.
  • Examples 1 through 8 the seeding component utilized was cobalt metal having a weight average particle size of about 1.6 microns. Each of these eight examples was conducted at a different concentration of boron to illustrate the effect of increased boron concentration on the resultant whiskers. Examples 9 through 16 were also conducted
  • SUBSTITUTE SHEET utilizing cobalt metal as the seeding component but the cobalt used had a much larger weight average particle size, i.e., between about 35 and 45 microns, and was present in a higher concentration. Also, the concentration of carbon in the mixture subjected to whiskers synthesis was higher than that used in Examples 1 through 8.
  • Silicon carbide whiskers were synthesized by adding 50 grams of Aerosil 380 fumed silica powder supplied by Degussa Corporation to 33 grams of FW 200 channel carbon black also supplied by Degussa Corporation.
  • the fumed silica had a weight average particle size of about 7 nanometers and a specific surface area of about 380 square meters per gram.
  • the carbon black had a weight average particle size of about 13 nanometers, a specific surface area of about 460 square meters per gram, and contained about 21 weight percent volatiles.
  • the mixture of silica and carbon black was combined with 3.06 grams of boron oxide powder and 4.16 grams of elemental cobalt powder having a weight average particle size of about 1.6 microns.
  • the resultant combination of the four components was mixed in a Waring commercial blender for about five minutes.
  • the resultant powdery mixture was then subjected to a vacuum in the blender for five minutes to remove excess air and increase the bulk density of the mixture.
  • the carbon-to- silicon mole ratio, the boron-to-silicon mole ratio and the cobalt-to-silicon mole in the mixture were, respectively, 2.6, 0.11 and 0.08.
  • Approximately one-half of the material in the blender was then removed and placed in a 12-inch long graphite boat having a truncated circular cross section with an inside diameter of three inches. The boat was covered with a graphite lid having uniformly distributed holes to allow the escape of
  • the loaded graphite boat was placed into a horizontal graphite tube furnace which was roughly 180 inches long with a 48 inch hot zone followed by a water-cooled zone.
  • the furnace hot zone was preheated to 1650° C. while argon was passed through the furnace to create an argon atmosphere.
  • the boat was pushed 12 inches further into the furnace every 30 minutes. After the fourteenth push or seven hours, the boat was removed from the water- cooled zone of the furnace.
  • Example 2 The procedure of Example 1 was followed except that 6.44 grams of boron oxide powder were used, thereby giving a boron-to-silicon mole ratio in the mixture subjected to blending of 0.22.
  • a scanning electron photomicrograph of a portion of the resultant product at 1,000 times magnification is shown in Figure 2 and indicates that the silicon carbide particulate concentration has decreased with the increasing boron-to-silicon mole ratio while the concentration of
  • SUBSTITUTESHEET whiskers has increased. The concentration of curly whiskers remained high.
  • Example 3 The procedure of Example 1 was followed except that 10.24 grams of boron oxide powder were used, thereby giving a boron-to-silicon mole ratio in the mixture subjected to blending of 0.35.
  • a scanning electron photomicrograph of a portion of the resultant product at 1,000 times magnification is set forth in Figure 3 and shows that there is a much lower concentration of silicon carbide particulates and a higher concentration of whiskers in the product as compared to that obtained in Examples 1 and 2. Although a portion of the whiskers are still curly in shape, the concentration of these curly whiskers has decreased.
  • EXAMPLE 4 The procedure of Example 1 was followed except that 14.50 grams of boron oxide powder were used, thereby giving a boron-to-silicon mole ratio in the mixture subjected to blending of 0.50.
  • a scanning electron photomicrograph of a portion of the resultant product at 1,000 times magnification is set forth in Figure 4 and shows that, at this concentration of boron, there is a higher concentration of whiskers in the synthesized product as compared to that obtained in Examples 1 through 3. It also appears that the diameters of the whiskers are smaller than those of the whiskers made in the previous examples. The concentration of curly whiskers appears to have significantly decreased.
  • EXAMPLE 5 The procedure of Example 1 was followed except that 14.50 grams of boron oxide powder were used, thereby giving a boron-to-silicon mole ratio in the mixture subjected to blending of 0.50.
  • a scanning electron photomicrograph of a portion of the resultant product at 1,000 times magnification is set forth in Figure 4 and shows that, at this concentration of
  • Example 1 The procedure of Example 1 was followed except that 19.34 grams of boron oxide powder were used so that the mixture subjected to blending had a boron-to- ⁇ ilicon mole ratio of 0.67. A scanning electron photomicrograph of a portion of the re ⁇ ultant product at 1,000 times
  • SUBSTITUTE SHEET magnification is shown in Figure 5 and indicates the presence in the as-synthesized product of a low concentration of silicon carbide particulates and a high concentration of silicon carbide whiskers. As compared with the product obtained in Examples 1 through 4, the concentration of curly whisker ⁇ i ⁇ relatively low.
  • Example 6 The procedure of Example 1 was followed except that 24.86 grams of boron oxide powder were used so that the boron-to-silicon mole ratio in the mixture subjected to blending was 0.86.
  • a scanning electron photomicro ⁇ graph of a portion of the resultant product at 1,000 times magnification is set forth in Figure 6 and shows the presence of a few rather large particles of material which were determined to be borosilicate glass. Because of the presence of this material in the as- ⁇ ynthesized product, the concentration of ⁇ ilicon carbide whi ⁇ kers in the product decreased as compared to that in the product of Examples 4 and 5. Although the whi ⁇ kers formed appear to be primarily straight in shape, a few curly whisker ⁇ are ⁇ till pre ⁇ ent.
  • EXAMPLE 7 The procedure of Example 1 wa ⁇ followed except that 31.24 gra ⁇ of boron oxide powder wa ⁇ u ⁇ ed ⁇ o that the mole ratio of boron-to- ⁇ ilicon in the mixture subjected to blending wa ⁇ 1.08.
  • FIG. 1 A comparison of Figures 1 through 8 reveals several trends which were confirmed by the use of an optical microscope at various magnifications.
  • the concentration of curly shaped whisker ⁇ in the as- ⁇ ynthe ⁇ ized product tend ⁇ to decrease a ⁇ the boron concentration in the feed increases.
  • the concentration of silicon carbide whisker ⁇ in the a ⁇ -synthesized product is relatively low.
  • the concentration of whisker ⁇ (1) increases as the mole ratio of boron-to-silicon increases from 0.11 to 0.35, (2) remains relatively constant at a boron-to-silicon mole ratio ranging between 0.35 and 0.67, and (3) then begins to decrease at boron-to-silicon mole ratio ⁇ of 1.08 and higher becau ⁇ e of the pre ⁇ ence of ⁇ ignificant amount ⁇ of boro ⁇ ilicate gla ⁇ .
  • the concentration of boron i ⁇ low, i.e. below a boron-to-silicon mole ratio of 0.22 the amount of silicon carbide particulates in the
  • EXAMPLE 9 The procedure of Example 1 wa ⁇ followed except that the mixture ⁇ ubjected to blending wa ⁇ formed by combining 61.2 grams of the fumed silica with 49.1 grams of carbon black, 6.1 gram ⁇ of elemental cobalt powder having a weight average particle ⁇ ize between about 38 and 45 micron ⁇ instead of 1.6 microns as used in Example ⁇ 1 through 8, and 3.75 grams of boron oxide powder.
  • the boron-to- ⁇ ilicon mole ratio, the carbon-to-silicon mole ratio and the cobalt-to-silicon mole ratio in the mixture subjected to blending were, respectively, 0.11, 3.2 and 0.10.
  • Example 1 Unlike in Example 1 where the as- ⁇ ynthe ⁇ ized product had a greeni ⁇ h color, the product of thi ⁇ example was yellowish, evidently because of the u ⁇ e of the larger ⁇ ize cobalt particle ⁇ .
  • a ⁇ canning electron photomicro ⁇ graph of a portion of the product at 1,000 time ⁇ magnification is shown in Figure 9. As can be seen from the figure, there is a very high concentration in the as- synthesized product of silicon carbide particulates and a relatively low concentration of whiskers, all of which appear to have a very small diameter. There appears to be few if any whiskers having a curly shape; the vast majority of the whiskers are straight.
  • SUBSTITUTESHEET concentration of the re ⁇ ultant whiskers are much ⁇ maller than tho ⁇ e of the whi ⁇ ker ⁇ produced in Example 1. Al ⁇ o, it appears that very few of the whi ⁇ ker ⁇ formed in this example have a curly shape while the majority of the whisker ⁇ formed in Example 1 are curly.
  • EXAMPLE 10 The procedure of Example 9 wa ⁇ followed except that 7.88 gram ⁇ of boron oxide powder were u ⁇ ed ⁇ o that the boron-to- ⁇ ilicon mole ratio in the mixture ⁇ ubjected to blending wa ⁇ 0.22.
  • a scanning electron photomicro ⁇ graph of a portion of the resultant ⁇ ilicon carbide- containing product at 1,000 time magnification is shown in Figure 10.
  • the concentration of ⁇ ilicon carbide whi ⁇ kers in the as- synthesized product has increased while the concentration of ⁇ ilicon carbide particulate ⁇ has decreased.
  • Example 9 The procedure of Example 9 was followed except that 12.53 grams of boron oxide powder were used so that the boron-to- ⁇ ilicon mole ratio in the mixture ⁇ ubjected to blending wa ⁇ 0.35.
  • Figure 11 A comparison of Figure 11 with
  • EXAMPLE 12 The procedure of Example 9 was followed except 17.75 grams of boron oxide powder were used so that the boron-to-silicon mole ratio in the mixture subjected to blending wa ⁇ 0.50.
  • Example 9 The procedure of Example 9 was followed except 23.67 grams of boron oxide powder were used so that the boron-to-silic ⁇ n mole ratio in the mixture ⁇ ubjected to blending was 0.67.
  • Figure 5 the photomicrograph of the product obtained at
  • Example 9 The procedure of Example 9 wa ⁇ repeated except 30.43 gram ⁇ of boron oxide powder were u ⁇ ed ⁇ o that the boron-to- ⁇ ilicon mole ratio in the mixture ⁇ ubjected to blending wa ⁇ 0.86.
  • SUBSTITUTE SHEET 15 and indicate ⁇ the presence of rather large diameter straight whiskers which, because of a large increase in the amount of residual borosilicate glass formed, are present in a concentration les ⁇ than that obtained in Example 14. Al ⁇ o, some of the whisker ⁇ appear to contain coating ⁇ of the boro ⁇ ilicate glass.
  • Figure 15 is compared with Figure 7, the photomicrograph of the product from Example 7 using the smaller particle cobalt seeding material at the same boron-to-silicon mole ratio, it is seen that there is little difference between the size, shape and concentration of whisker ⁇ .
  • EXAMPLE 16 The procedure of Example 9 was repeated except that 47.32 grams of boron oxide powder were used so that the boron-to- ⁇ ilicon mole ratio in the mixture ⁇ ubjected to blending wa ⁇ 1.33.
  • Example ⁇ 1 through 8 it would appear, when comparing the re ⁇ ult ⁇ of Example ⁇ 1 through 8 with those of Examples 9 through 16, that the ⁇ maller cobalt seeds used in Examples 1 through 8 tend to yield a greater concentration of whi ⁇ ker ⁇ at an identical boron- to- ⁇ ilicon mole ratio a ⁇ long a ⁇ the mole ratio i ⁇ below 0.86. Thi ⁇ i ⁇ evidently due to the pre ⁇ ence in the ⁇ maller ⁇ eed ⁇ of a larger number of nucleation ⁇ ite ⁇ for the growth of whi ⁇ ker ⁇ .
  • the re ⁇ ult ⁇ of Example ⁇ 9 through 16 indicate that, when a larger ⁇ ize cobalt ⁇ eeding component i ⁇ used, the diameter of the whisker ⁇ produced increa ⁇ e ⁇ a ⁇ the concentration of boron increa ⁇ e ⁇ . Thi ⁇ i ⁇ in contra ⁇ t to the re ⁇ ult ⁇ obtained with the smaller seed ⁇ where the diameter decrea ⁇ e ⁇ and then increa ⁇ e ⁇ with increa ⁇ ing boron concentration ⁇ .
  • the concentration, ⁇ hape and ⁇ ize of ⁇ ilicon carbide whi ⁇ ker ⁇ obtained by the proce ⁇ of the invention can be controlled by adju ⁇ ting the concentration of boron and the ⁇ ize of the ⁇ eeding component u ⁇ ed in the feed. It appear ⁇ from the example ⁇ that the optimum concentration of primarily ⁇ traight whi ⁇ ker ⁇ i ⁇ obtained utilizing a boron-to- ⁇ ilicon mole ratio ranging between about 0.30 and 0.70 when the seeding component ha ⁇ a weight average particle ⁇ ize ranging between about 38 and 45 micron ⁇ .

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Abstract

L'invention concerne un procédé de fabrication de barbes de renforcement en carbure de silicium dans lequel une forme particulaire de carbone est combinée avec un composé de silicium, un composé de bore et un composé d'ensemencement, pour former un mélange qui est alors soumis à une température supérieure à 1300 °C environ dans une atmosphère non oxydante, de sorte que le carbone réagit avec la silice pour former des fibres de carbure de silicium. Le carbone particulaire, le composé de silicium, le composé de bore et le composé d'ensemencement préférés sont, respectivement, le noir de carbone, la silice fumée, l'oxyde de bore et le cobalt, le fer ou le nickel. La taille et la forme des barbes peuvent être modifiées en changeant la taille du composé d'ensemencement et la concentration du composé de bore.
PCT/SE1993/000329 1992-07-06 1993-04-20 Fabrication de barbes de renforcement en carbure de silicium Ceased WO1994001363A1 (fr)

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SE9202089A SE9202089D0 (sv) 1992-07-06 1992-07-06 Production of silicon carbide whiskers

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115724689A (zh) * 2022-11-21 2023-03-03 景德镇陶瓷大学 一种碳化硅晶须涂层表面改性堇青石蜂窝陶瓷的低温原位合成方法及其制得的产品

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0310265A1 (fr) * 1987-09-30 1989-04-05 The Standard Oil Company Formation de nitrure de silicium et de carbure de silicium en forme de fibres
US4873069A (en) * 1987-03-09 1989-10-10 American Matrix, Inc. Method for the preparation of silicon carbide whiskers
EP0434667A2 (fr) * 1985-04-04 1991-06-26 Nippon Steel Corporation Procédés de production de particules et d'un corps fritté de carbure de silicium
US5037626A (en) * 1988-11-22 1991-08-06 Union Oil Company Of California Process for producing silicon carbide whiskers using seeding agent

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0434667A2 (fr) * 1985-04-04 1991-06-26 Nippon Steel Corporation Procédés de production de particules et d'un corps fritté de carbure de silicium
US4873069A (en) * 1987-03-09 1989-10-10 American Matrix, Inc. Method for the preparation of silicon carbide whiskers
EP0310265A1 (fr) * 1987-09-30 1989-04-05 The Standard Oil Company Formation de nitrure de silicium et de carbure de silicium en forme de fibres
US5037626A (en) * 1988-11-22 1991-08-06 Union Oil Company Of California Process for producing silicon carbide whiskers using seeding agent

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115724689A (zh) * 2022-11-21 2023-03-03 景德镇陶瓷大学 一种碳化硅晶须涂层表面改性堇青石蜂窝陶瓷的低温原位合成方法及其制得的产品
CN115724689B (zh) * 2022-11-21 2023-05-26 景德镇陶瓷大学 一种碳化硅晶须涂层表面改性堇青石蜂窝陶瓷的低温原位合成方法及其制得的产品

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