CA1275088A - Prealloyed catalyst for growing silicon carbide whiskers - Google Patents
Prealloyed catalyst for growing silicon carbide whiskersInfo
- Publication number
- CA1275088A CA1275088A CA000524790A CA524790A CA1275088A CA 1275088 A CA1275088 A CA 1275088A CA 000524790 A CA000524790 A CA 000524790A CA 524790 A CA524790 A CA 524790A CA 1275088 A CA1275088 A CA 1275088A
- Authority
- CA
- Canada
- Prior art keywords
- silicon
- carbon
- catalyst
- weight percent
- gas
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/20—Carbon compounds
- B01J27/22—Carbides
- B01J27/224—Silicon carbide
-
- 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
Abstract
PREALLOYED CATALYST FOR GROWING
SILICON CARBIDE WHISKERS
ABSTRACT OF THE DISCLOSURE
A prealloyed metal catalyst is used to grow silicon carbide whiskers, especially in the .beta. form. Pretreating the metal particles to increase the weight percentages of carbon or silicon or both carbon and silicon allows whisker growth to begin immediately upon reaching growth temperature.
SILICON CARBIDE WHISKERS
ABSTRACT OF THE DISCLOSURE
A prealloyed metal catalyst is used to grow silicon carbide whiskers, especially in the .beta. form. Pretreating the metal particles to increase the weight percentages of carbon or silicon or both carbon and silicon allows whisker growth to begin immediately upon reaching growth temperature.
Description
,t~3.
PREALLOYED CATALYST FOR GROWING
SILICON CARBIDE WHISKERS
BACKGROUND OF THE INVENTION
The present invention relates generally to a prealloyed catalyst and the use of such a catalyst in manufacturing silicon carbide whiskers. More 05 particularly, the present invention relates to a prealloyed catalyst containing a sufficiently high percentage of carbon, silicon, or carbon and silicon to allow growth of silicon carbide whiskers to commence immediately upon reaching the growth temperature.
Silicon carbide whiskers are valued for their needle-like single crystal structure which leads to such excellent properties as high strength, high elastic modulus, heat resistance, chemical stability, and so on.
Tha whisXers have been used as a composite reinforcing material for metalsO plastics, and ceramics. The most desirable whiskers are ~ silicon carbide single crystals which have a high length to diameter ratio.
Various methods of using a catalyst to promote the growth of silicon carbide whiskers have been proposed. In U. S. Patent ~,500,504 issued ~o Yamamoto, a silica gel wi~h 6 to 25% by weight metal catalyst was mixed with furnace carbon black. The mixture t~en was placed in a non-oxidative atmosphere at a temperature of 1300 to 8~3 1700C to produce silicon carbide whiskers. The metal catalyst was selected from the group of iron, nickel, and cobalt. However, the metal was used as is, i.e., with no pretreatment. In U. S. Paten~ 3,622,272 issued to Shyne 05 et ~al., the use of powdered me~als such as iron, manganese, nickel, aluminum, and stainless ~teel was disclosed for its role as a surface nucleation site. The powdered metal coatings were applied to a substrate such as graphite for the growing of silicon carbide whiskers.
The only pretreatment disclosed for the me~al powders was to suspend them in a liquid carrier vehicle such that the metal powders could be applied to the surface of the grow~h substrate.
In the article "Growth of sic Whiskers in the System sio2 2 Nucleated by Iron," authored by J. A.
Bootsma et al., which appeared in J. Cryst. Growth 11, 297-309 (1971), the nucleation phenomenon of growing silicon carbide whiskers using iron particles as nucleating agents was studied. It was found that the iron par~icles first took up silicon and carbon from the vapor when ~he furnace temperature reached 1200C. After sufficient uptake, an Fe-Si-C alloy droplet was obtained from which the silicon carbide whisker grew. However, again there was no suggestion of pretreating the iron particle beore the furnace was heated up toward nucleation temperature.
U. S. Patent 3,721,732 issued ~o Knippenberg et al. on March 20, 1973, contained contradictory advice concerning the addition of silicon to iron catalyst par~icles. In Claim 4 as well as while discussing cubic growth, the patent speculated that admixing silicon to iron may facilitate cubic crystal growth. However, earlier in the patent text, it was s~ated that iron may without objection ~ Z'7~i~8~3 contain carbon and silicon or other elements, but improvement in the grow~h of crys~als, as a resul~, had no~ been found. At best, thîs patent lePt doubt abou~
wbe~her silicon addi~ion to iron catalys~ particles would 05 help~ in the overall growth of the silicon carbide whiskers. The role of specially treated catalyst particles in prompt initiation of nucleation at catalyst sites was not commented upon in this patent.
Overall, a need still existed for a me~hod to avoid 0 the delay in the growth of silicon carbide whiskers after reaching the growth temperature while the melted catalyst takes up from the surrounding furnace atmosphere the necessary percen~ages of carbon and silicon to ini~iate growth. When the catalyst particles were placed upon a carbon subs~rate, the particle interacted with the substrate in order to absorb carbon, which along with the accretion of silicon from the vapor results in an incubation time before growth can be initiated.
SUMMARY OF THE INVENTION
The object of this invention is to provide a catalyst and a method of using the catalyst to manufacture silicon carbide whiskers which yield whiskers with a desirable length to diameter ratio.
A ~ur~her object of the presen~ invention is to provide a catalyst and a method for using the catalyst to manufacture silicon carbide whiskers where whisker growth can immediately commence upon reaching the grow~h tempera~ure.
Additional objects, advantages and novel features of the invention will be set forth in part in the descrip~ion which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects '7~
4' and advantages of the inventi,on may be realized and attained by means of the instrumentalities and combinations particularly pointed ou-t in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present inven-tion, as embodied and broadly described herein, the method of this invention may comprise a method for manufacturing silicon carbide whiskers comprising: a. prea]loying a metallic catalyst with carbon silicon, or a mixture of carbon and silicon; b. applying the prealloyed catalyst to a carbon substrate; c. heating the substrate with applied prealloyed catalyst in a gaseous environment comprised of a reducing gas; d. introducing silicon containing gas and carbon containing gas in the gaseous environment; e~ maintaining the flow of the silicon containing gas while the temperature of the substrate is maintained above a minimum temperature above which silicon carbide whiskers will form; and f. cooling the silicon carbide whiskers after completion of whisker growth.
The prealloyed catalyst of carbon and silicon will contain 1 to 45 weight percent silicon.
In a further embodiment, the invention contemplates a method for manufacturing silicon carbide whiskers wherein manufacturing time is reduced which comprises providing a growth substrate having a coating comprised of metallic catalyst particles alloyed with silicon where the particles contain from about 1 to about 45 weight % silicon, heating the coated growth substrate in a gaseous environment comprised of a reducing gas, adding to the gaseous environment a gas comprised of silicon and a gas comprised of carbon, main-taining for a time period the coated growth substrate and gaseous environment at a temperature above a minimum tempera-ture at which silicon carbide whiskers will form, and removing the gas comprised of silicon and the gas comprised of carbon from the gaseous environment cooling the coated growth substrate and recovering silicon carbide whiskers from the coated growth substrate.
~3 ~ ;~'75~
4a The present invention may also comprise, in accordance with its objects and purposes, a catalyst for producing silicon carbide whiskers on a carbon substrate comprising a metal prealloyed with carbon and silicon before heating to the silicon carbide whisker '5 growth temperature.
An advantage of the present invention is the manufacturing of silicon carbide whiskers in the ~ form with adequate diameters to give desirable properties~
Yet another advantage of the present invention is the rapid initiation of growth of silicon carbide whiskers when the furnace atmosphere reaches the growth temperature BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are photomicrographs `` ~ 2~;~5~
and are incorporated in and form a part of the speci~ication, illustrate the embodiments of the present invention and, together with the description, serve to explain ~he principles o~ the invention. In the drawings:
05 ~FIGURE 1 is a photomicrograph at 80 times magnification for growth from a ferrosilicon catalyst growth wherein the ferrosilicon has not ]been carburized.
FIGURE 2 is a photomicrograph a~ 80 times magnification wherein a ferrosilicon catalyst particle has been car~urized.
FIGURE 3 is a photomicrograph at 240 times magnification where Alloy 62 catalyst particles have not been diluted with silicon.
FIGURE 4 is a photomicrograph at 2~0 times magnification wherein Alloy 62 catalyst particles have been diluted with silicon.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Untreated catalyst particles are available from many sources. For instance, stainless steel flakes are a~ailable from Novamet in Wykoff, New Jersey. Catalyst particles composed of a substance designated as Alloy 62 which has the following weight percent composition:
Mn 65, Co 19, Ni 20, Si 0.25, Ee 0.1, Cr 0.2. B 0.25, Zn 0.25, are available from Metallurgical Technology in ~inslow, New Jersey. Other catalysts such as Perrosilicon are commonly available from many sources. Before treatment the catalyst particles are sieved for size such that, as nearly as possible, no spherical particle is larger than 15 ~m or smaller 10 ~m or no flake particle upon melting would yield a sphere larger than 15 ~m or smaller than 10 ~m.
Various methods for pretreating the catalyst particles to increase the percentage of carbon or silicon or both ` ~75~`38~
are available. Silicon may be added by melting the catalyst particles and adding solid silicon to the melt.
The prealloyed substance is then pulverized into a desired size. Carbon may be added by this melting method also.
05 Carbon may also be added by carburizing the catalyst particles before they are placed in the silicon carbide whisker growth furnace. An addi~ional method for carburizing the catalyst particles is to allow a carbon rich ga5 to flow over the untreated catalys~ particles applied to growth surfaces in the furnace at a temperature below the growth temperature for silicon carbide whiskers. A colloidal carbon, such as dgf 123 produced by Miracle Power Products Co. of Cleveland, Ohio, can be sprayed over the catalyst before or after applying to the growth substrate which is put in the furnace.
Finally, a catalyst particle may be made from a mixture of elements chosen to resemble the weight percentage composition of various elements found in the cat~lyst ball present at the end of the silicon carbide whisker.
The percen~age of silicon or carbon or both silicon and carbon to be added to catalyst particles varies over a wide range. The catalyst can be composed of from 1 to about 45 ~eight percent silicon. The prealloyed catalyst can also contain from O.l to 5.0 weight percent carbon.
The metals which may serve as catalyst particles include one or more of the following metals: manganese, iron, nickel, cobalt, chromium, and niobium. One typical composition of a prealloyed catalyst is ~he following:
1.6 weight percent manganese, 23.4 weight percent cobalt, ZZ.g weight percent nicXel, 40.9 weigh~ percen~ silicon, 10.2 weight percent iron, and 1 weight-percent chromium.
This particular composition represents the element weight percentages found in a catalyst ball in the end of the ~r75~88 silicon carbide whisker after growth was initia~ed with an untreated Alloy 62 ca~alyst particle.
The ca~alyst after the prealloying treatment, is then deposited upon the growth substrate. Most often this 05 growt~h substrate is graphi~e. The ~wo most common methods for depositing the catalyst particles upon the substrate are painting and spraying. For both methods it i~
necessary to suspend the catalyst particles in some type of solution. For painting, i.e,, applying the catalyst particle suspension with a brush, a typical suspension Yehicle is made of a weight of Cabosil , which is a product o~ the Cabot Corporation, Boston, Massachusetts, equal to 4.5 parts by weight of catalyst particles ~hich is then further mixed with 50 parts each of a liquid acrylic resin and methyl ethyl ketone. Catalyst particles can also be suspended in a product of Micromeritics, Inc., of Atlanta, Georgia called 14A Sedisperse tapproximate composition: 0.1% phosphatidyl choline, 0.1%
phosphatidyl ethanolamine, 0.1% inositol phosphatides, 1.7g isopropyl myristate blended with alkyl polyoxyethylene ethanols, and 98~ base liquid.) Once the growth plates have been coated with catalyst particles, ~hey are placed in the growth zone of a furnace. The plates are typically graphite of 6 in. by 13 in. dimensions. The furnace can be a heated by SiC
resistance elements, and use a quartz muffle to contain the growth plates. Such furnaces allow the silicon carbide whisker growth to occur under a reducing at~osphere which is typically a hydrogen atmosphere. The furnace also allows for a flow of various gases ~hrough the growth zone. Typically these gases are SiO, SiC19, SiCH3C13, or silane. The growth ~emperature can be anywhere from 1200 to 1600 C, but preferably are 1350 ~ z7~38 to 1430C. After placing ~he coated growth substrates into the furnace, it is necessary to heat the furnace up.
Typically the grow~h period lasts for eight hour~. After reducing the temperature setting to 1000C, the growth 05 plates'are removed and cooled to room temperature. Then the silicon carbide whiskers are har~vested by careful scraping.
E~AMPLE 1 Figures 1 and 2 were produced by placing ferrosilicon catalyst particles on a solid carbon substrate in a Centorr Model 10-2.5 x 8 furnace. This electrically heated furnace was supplied with electrical power controlled by a Helmar Model TA-l power controller and used a 60 hertz current of 1000 amps at 10 vclts duriny the heat up time. The growth zone inside ~he furnace was monitored for temperature by means of thermocouples. The furnace allowed gases to flow through it during both heat up and growth periods. The predominan-t gas flowing through the furnace during both heat up and growth periods, after an argon purge, was hydrogen, a reducing gas. Figure 1 shows the result of heating ferrosilicon catalyst particles on a carbon substrate where the temperature was promptly lowered after reaching grvwth temperature. Yigure 1 also shows the result of not prealloying ~he catalyst particles with carbon. The ~low gases used during the heat up period did not contain a methane or other carbon containing component which would allow ~he catalyst particles during the hea~ up period to carburize.
~1.2'7~
.
TIMETEMPERATUR~
IN C
1:35 power on 1:~5 200 , 1~58 1100 05 2~04 1340
PREALLOYED CATALYST FOR GROWING
SILICON CARBIDE WHISKERS
BACKGROUND OF THE INVENTION
The present invention relates generally to a prealloyed catalyst and the use of such a catalyst in manufacturing silicon carbide whiskers. More 05 particularly, the present invention relates to a prealloyed catalyst containing a sufficiently high percentage of carbon, silicon, or carbon and silicon to allow growth of silicon carbide whiskers to commence immediately upon reaching the growth temperature.
Silicon carbide whiskers are valued for their needle-like single crystal structure which leads to such excellent properties as high strength, high elastic modulus, heat resistance, chemical stability, and so on.
Tha whisXers have been used as a composite reinforcing material for metalsO plastics, and ceramics. The most desirable whiskers are ~ silicon carbide single crystals which have a high length to diameter ratio.
Various methods of using a catalyst to promote the growth of silicon carbide whiskers have been proposed. In U. S. Patent ~,500,504 issued ~o Yamamoto, a silica gel wi~h 6 to 25% by weight metal catalyst was mixed with furnace carbon black. The mixture t~en was placed in a non-oxidative atmosphere at a temperature of 1300 to 8~3 1700C to produce silicon carbide whiskers. The metal catalyst was selected from the group of iron, nickel, and cobalt. However, the metal was used as is, i.e., with no pretreatment. In U. S. Paten~ 3,622,272 issued to Shyne 05 et ~al., the use of powdered me~als such as iron, manganese, nickel, aluminum, and stainless ~teel was disclosed for its role as a surface nucleation site. The powdered metal coatings were applied to a substrate such as graphite for the growing of silicon carbide whiskers.
The only pretreatment disclosed for the me~al powders was to suspend them in a liquid carrier vehicle such that the metal powders could be applied to the surface of the grow~h substrate.
In the article "Growth of sic Whiskers in the System sio2 2 Nucleated by Iron," authored by J. A.
Bootsma et al., which appeared in J. Cryst. Growth 11, 297-309 (1971), the nucleation phenomenon of growing silicon carbide whiskers using iron particles as nucleating agents was studied. It was found that the iron par~icles first took up silicon and carbon from the vapor when ~he furnace temperature reached 1200C. After sufficient uptake, an Fe-Si-C alloy droplet was obtained from which the silicon carbide whisker grew. However, again there was no suggestion of pretreating the iron particle beore the furnace was heated up toward nucleation temperature.
U. S. Patent 3,721,732 issued ~o Knippenberg et al. on March 20, 1973, contained contradictory advice concerning the addition of silicon to iron catalyst par~icles. In Claim 4 as well as while discussing cubic growth, the patent speculated that admixing silicon to iron may facilitate cubic crystal growth. However, earlier in the patent text, it was s~ated that iron may without objection ~ Z'7~i~8~3 contain carbon and silicon or other elements, but improvement in the grow~h of crys~als, as a resul~, had no~ been found. At best, thîs patent lePt doubt abou~
wbe~her silicon addi~ion to iron catalys~ particles would 05 help~ in the overall growth of the silicon carbide whiskers. The role of specially treated catalyst particles in prompt initiation of nucleation at catalyst sites was not commented upon in this patent.
Overall, a need still existed for a me~hod to avoid 0 the delay in the growth of silicon carbide whiskers after reaching the growth temperature while the melted catalyst takes up from the surrounding furnace atmosphere the necessary percen~ages of carbon and silicon to ini~iate growth. When the catalyst particles were placed upon a carbon subs~rate, the particle interacted with the substrate in order to absorb carbon, which along with the accretion of silicon from the vapor results in an incubation time before growth can be initiated.
SUMMARY OF THE INVENTION
The object of this invention is to provide a catalyst and a method of using the catalyst to manufacture silicon carbide whiskers which yield whiskers with a desirable length to diameter ratio.
A ~ur~her object of the presen~ invention is to provide a catalyst and a method for using the catalyst to manufacture silicon carbide whiskers where whisker growth can immediately commence upon reaching the grow~h tempera~ure.
Additional objects, advantages and novel features of the invention will be set forth in part in the descrip~ion which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects '7~
4' and advantages of the inventi,on may be realized and attained by means of the instrumentalities and combinations particularly pointed ou-t in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present inven-tion, as embodied and broadly described herein, the method of this invention may comprise a method for manufacturing silicon carbide whiskers comprising: a. prea]loying a metallic catalyst with carbon silicon, or a mixture of carbon and silicon; b. applying the prealloyed catalyst to a carbon substrate; c. heating the substrate with applied prealloyed catalyst in a gaseous environment comprised of a reducing gas; d. introducing silicon containing gas and carbon containing gas in the gaseous environment; e~ maintaining the flow of the silicon containing gas while the temperature of the substrate is maintained above a minimum temperature above which silicon carbide whiskers will form; and f. cooling the silicon carbide whiskers after completion of whisker growth.
The prealloyed catalyst of carbon and silicon will contain 1 to 45 weight percent silicon.
In a further embodiment, the invention contemplates a method for manufacturing silicon carbide whiskers wherein manufacturing time is reduced which comprises providing a growth substrate having a coating comprised of metallic catalyst particles alloyed with silicon where the particles contain from about 1 to about 45 weight % silicon, heating the coated growth substrate in a gaseous environment comprised of a reducing gas, adding to the gaseous environment a gas comprised of silicon and a gas comprised of carbon, main-taining for a time period the coated growth substrate and gaseous environment at a temperature above a minimum tempera-ture at which silicon carbide whiskers will form, and removing the gas comprised of silicon and the gas comprised of carbon from the gaseous environment cooling the coated growth substrate and recovering silicon carbide whiskers from the coated growth substrate.
~3 ~ ;~'75~
4a The present invention may also comprise, in accordance with its objects and purposes, a catalyst for producing silicon carbide whiskers on a carbon substrate comprising a metal prealloyed with carbon and silicon before heating to the silicon carbide whisker '5 growth temperature.
An advantage of the present invention is the manufacturing of silicon carbide whiskers in the ~ form with adequate diameters to give desirable properties~
Yet another advantage of the present invention is the rapid initiation of growth of silicon carbide whiskers when the furnace atmosphere reaches the growth temperature BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are photomicrographs `` ~ 2~;~5~
and are incorporated in and form a part of the speci~ication, illustrate the embodiments of the present invention and, together with the description, serve to explain ~he principles o~ the invention. In the drawings:
05 ~FIGURE 1 is a photomicrograph at 80 times magnification for growth from a ferrosilicon catalyst growth wherein the ferrosilicon has not ]been carburized.
FIGURE 2 is a photomicrograph a~ 80 times magnification wherein a ferrosilicon catalyst particle has been car~urized.
FIGURE 3 is a photomicrograph at 240 times magnification where Alloy 62 catalyst particles have not been diluted with silicon.
FIGURE 4 is a photomicrograph at 2~0 times magnification wherein Alloy 62 catalyst particles have been diluted with silicon.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Untreated catalyst particles are available from many sources. For instance, stainless steel flakes are a~ailable from Novamet in Wykoff, New Jersey. Catalyst particles composed of a substance designated as Alloy 62 which has the following weight percent composition:
Mn 65, Co 19, Ni 20, Si 0.25, Ee 0.1, Cr 0.2. B 0.25, Zn 0.25, are available from Metallurgical Technology in ~inslow, New Jersey. Other catalysts such as Perrosilicon are commonly available from many sources. Before treatment the catalyst particles are sieved for size such that, as nearly as possible, no spherical particle is larger than 15 ~m or smaller 10 ~m or no flake particle upon melting would yield a sphere larger than 15 ~m or smaller than 10 ~m.
Various methods for pretreating the catalyst particles to increase the percentage of carbon or silicon or both ` ~75~`38~
are available. Silicon may be added by melting the catalyst particles and adding solid silicon to the melt.
The prealloyed substance is then pulverized into a desired size. Carbon may be added by this melting method also.
05 Carbon may also be added by carburizing the catalyst particles before they are placed in the silicon carbide whisker growth furnace. An addi~ional method for carburizing the catalyst particles is to allow a carbon rich ga5 to flow over the untreated catalys~ particles applied to growth surfaces in the furnace at a temperature below the growth temperature for silicon carbide whiskers. A colloidal carbon, such as dgf 123 produced by Miracle Power Products Co. of Cleveland, Ohio, can be sprayed over the catalyst before or after applying to the growth substrate which is put in the furnace.
Finally, a catalyst particle may be made from a mixture of elements chosen to resemble the weight percentage composition of various elements found in the cat~lyst ball present at the end of the silicon carbide whisker.
The percen~age of silicon or carbon or both silicon and carbon to be added to catalyst particles varies over a wide range. The catalyst can be composed of from 1 to about 45 ~eight percent silicon. The prealloyed catalyst can also contain from O.l to 5.0 weight percent carbon.
The metals which may serve as catalyst particles include one or more of the following metals: manganese, iron, nickel, cobalt, chromium, and niobium. One typical composition of a prealloyed catalyst is ~he following:
1.6 weight percent manganese, 23.4 weight percent cobalt, ZZ.g weight percent nicXel, 40.9 weigh~ percen~ silicon, 10.2 weight percent iron, and 1 weight-percent chromium.
This particular composition represents the element weight percentages found in a catalyst ball in the end of the ~r75~88 silicon carbide whisker after growth was initia~ed with an untreated Alloy 62 ca~alyst particle.
The ca~alyst after the prealloying treatment, is then deposited upon the growth substrate. Most often this 05 growt~h substrate is graphi~e. The ~wo most common methods for depositing the catalyst particles upon the substrate are painting and spraying. For both methods it i~
necessary to suspend the catalyst particles in some type of solution. For painting, i.e,, applying the catalyst particle suspension with a brush, a typical suspension Yehicle is made of a weight of Cabosil , which is a product o~ the Cabot Corporation, Boston, Massachusetts, equal to 4.5 parts by weight of catalyst particles ~hich is then further mixed with 50 parts each of a liquid acrylic resin and methyl ethyl ketone. Catalyst particles can also be suspended in a product of Micromeritics, Inc., of Atlanta, Georgia called 14A Sedisperse tapproximate composition: 0.1% phosphatidyl choline, 0.1%
phosphatidyl ethanolamine, 0.1% inositol phosphatides, 1.7g isopropyl myristate blended with alkyl polyoxyethylene ethanols, and 98~ base liquid.) Once the growth plates have been coated with catalyst particles, ~hey are placed in the growth zone of a furnace. The plates are typically graphite of 6 in. by 13 in. dimensions. The furnace can be a heated by SiC
resistance elements, and use a quartz muffle to contain the growth plates. Such furnaces allow the silicon carbide whisker growth to occur under a reducing at~osphere which is typically a hydrogen atmosphere. The furnace also allows for a flow of various gases ~hrough the growth zone. Typically these gases are SiO, SiC19, SiCH3C13, or silane. The growth ~emperature can be anywhere from 1200 to 1600 C, but preferably are 1350 ~ z7~38 to 1430C. After placing ~he coated growth substrates into the furnace, it is necessary to heat the furnace up.
Typically the grow~h period lasts for eight hour~. After reducing the temperature setting to 1000C, the growth 05 plates'are removed and cooled to room temperature. Then the silicon carbide whiskers are har~vested by careful scraping.
E~AMPLE 1 Figures 1 and 2 were produced by placing ferrosilicon catalyst particles on a solid carbon substrate in a Centorr Model 10-2.5 x 8 furnace. This electrically heated furnace was supplied with electrical power controlled by a Helmar Model TA-l power controller and used a 60 hertz current of 1000 amps at 10 vclts duriny the heat up time. The growth zone inside ~he furnace was monitored for temperature by means of thermocouples. The furnace allowed gases to flow through it during both heat up and growth periods. The predominan-t gas flowing through the furnace during both heat up and growth periods, after an argon purge, was hydrogen, a reducing gas. Figure 1 shows the result of heating ferrosilicon catalyst particles on a carbon substrate where the temperature was promptly lowered after reaching grvwth temperature. Yigure 1 also shows the result of not prealloying ~he catalyst particles with carbon. The ~low gases used during the heat up period did not contain a methane or other carbon containing component which would allow ~he catalyst particles during the hea~ up period to carburize.
~1.2'7~
.
TIMETEMPERATUR~
IN C
1:35 power on 1:~5 200 , 1~58 1100 05 2~04 1340
2:07 l9oo 2:08:30 1403 temperature stabilized 2:09 gas on ~:10 1405 2~11:00 1404 2:12:00 1~02 b 2:13:30 1900 2:15:0~ 1396 2:18:00 1390 2.19:00 1389 gas off 2:19:10 power decreased to 1.5 2:38:00 1129 Figures 1 and 2 are photomicrographs taken at 80 ~imes magnification. Figure 2 is the result of using ferrosilicon catalyst particles on a solid carbon substrate, only this time the gas flow was initiated at a lower temperature and included a methane component. This methane component carburized the catalyst particles before they reached the growth temperature. The following table shows the heating schedule:
TIMETEMPERATURE
IN C
2:40 power on - setting 2.0 argon purge 2:99 150 power increase to ~.0 2~5~ 450 2:56 600 gas on
TIMETEMPERATURE
IN C
2:40 power on - setting 2.0 argon purge 2:99 150 power increase to ~.0 2~5~ 450 2:56 600 gas on
3:09:351340 power decreased to 2.18 3:111349 3:121393 3:1Z:451400 power decreased to 1.5 3:181338 3:271187 gas off argon on ``` ~.. ;~7~
.10 As can be seen from ~he figures, when the processed gas was introduced at a lower temperatur~ and included a carbon component, the growth of silicon carbide whiskers was greater than when there was no carburization of the 05 ferrosilicon ca~alyst particles. Figure 2 shows evidence of the growth of whiskers with the ca~alyst balls intact at the end of the whiskers when the growth period was terminated.
10The same furnace and procedures as used in Example 1 were used in Example 2. Figure 3 shows a photomicrograph at 240 times magnification of Alloy 62 catalyst particles after ten minutes a~ growth temperature, 1413 C. The catalyst was co~posed of the following weight percents:
566% Mn, 16~ Ni, 16% Co, 0.8% B, and 1.2% trace elements.
The heating schedule was as follows:
TIME TEMPERATURE
IN C
2:30 power on 2:50 1095 argon purge 3:01 1402 power backed off to 2.2 3:03 1409 gas on 3:05 1413 power backed off to ~.18 3:08 1414 3:10 1413 3:13 1412 gas off - power backed off to 1.5 As can be seen from Figure 3, the pho~omicrograph.
there was little nucleation at the catalyst par~icle sites and there was little growth of the silicon carbide whiskers where there had been any nucleation.
Figure 4 shows a photomicrograph at 2~0 times magnifica~ion for Alloy ~2 particles ~o which a substantial percentage of silicon has ~een added. The ll composition of the catalyst particles was as follows in weight percent: 25% Si, 50.0% Mn, 12.2% Ni, 12.2% Co, and 0.6% B. Again carbon substrats plates coated with catalyst particles were placed in the same furnace as in 05 Example 1. The heating schedule was as followso TXM~TEMPERATURE
IN C
9:56power on - setting 3 argon purye 10:04 700 10:08 1000 10:17 13~0 power backed off to 2.18 lOo1~ 1400 lO:l9:q5 1408 10:20:3~ 1~14 10:21 1~16 10:22 1420 10:23 gas on 10:24 1~26 10:25 1428 10:27 1430 10:33 1430 10:34 gas off flow off 10:34:30 power decreased to 1.5 10:45:30 1245 The difference between ~igure 3 and Figure 4 is striking.
~igure 3, which represents Alloy 62 without the addition of silicon after ten minutes at growth temperature, shows littls whisker growth with just a few whiskers and catalyst balls at their ends present. In contrast, Figure
.10 As can be seen from ~he figures, when the processed gas was introduced at a lower temperatur~ and included a carbon component, the growth of silicon carbide whiskers was greater than when there was no carburization of the 05 ferrosilicon ca~alyst particles. Figure 2 shows evidence of the growth of whiskers with the ca~alyst balls intact at the end of the whiskers when the growth period was terminated.
10The same furnace and procedures as used in Example 1 were used in Example 2. Figure 3 shows a photomicrograph at 240 times magnification of Alloy 62 catalyst particles after ten minutes a~ growth temperature, 1413 C. The catalyst was co~posed of the following weight percents:
566% Mn, 16~ Ni, 16% Co, 0.8% B, and 1.2% trace elements.
The heating schedule was as follows:
TIME TEMPERATURE
IN C
2:30 power on 2:50 1095 argon purge 3:01 1402 power backed off to 2.2 3:03 1409 gas on 3:05 1413 power backed off to ~.18 3:08 1414 3:10 1413 3:13 1412 gas off - power backed off to 1.5 As can be seen from Figure 3, the pho~omicrograph.
there was little nucleation at the catalyst par~icle sites and there was little growth of the silicon carbide whiskers where there had been any nucleation.
Figure 4 shows a photomicrograph at 2~0 times magnifica~ion for Alloy ~2 particles ~o which a substantial percentage of silicon has ~een added. The ll composition of the catalyst particles was as follows in weight percent: 25% Si, 50.0% Mn, 12.2% Ni, 12.2% Co, and 0.6% B. Again carbon substrats plates coated with catalyst particles were placed in the same furnace as in 05 Example 1. The heating schedule was as followso TXM~TEMPERATURE
IN C
9:56power on - setting 3 argon purye 10:04 700 10:08 1000 10:17 13~0 power backed off to 2.18 lOo1~ 1400 lO:l9:q5 1408 10:20:3~ 1~14 10:21 1~16 10:22 1420 10:23 gas on 10:24 1~26 10:25 1428 10:27 1430 10:33 1430 10:34 gas off flow off 10:34:30 power decreased to 1.5 10:45:30 1245 The difference between ~igure 3 and Figure 4 is striking.
~igure 3, which represents Alloy 62 without the addition of silicon after ten minutes at growth temperature, shows littls whisker growth with just a few whiskers and catalyst balls at their ends present. In contrast, Figure
4, which represents Alloy 62 with silicon added, after ten minutes a~ growth temperature shows significant whisker development with ~he associated catalyst balls at the end 30 of the whiskers tha~ had nucleated at catalyst particle sites.
~5~
The foregoing description oP the preferred embodiments of the invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or ~o limit the invention to the precise form 05 disclosed~,and obviously many modifications and Yariations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others s~illed in the art to best utilize the invention in various embodiments and with ~arious modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
~5~
The foregoing description oP the preferred embodiments of the invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or ~o limit the invention to the precise form 05 disclosed~,and obviously many modifications and Yariations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others s~illed in the art to best utilize the invention in various embodiments and with ~arious modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
Claims (23)
1. A method for manufacturing silicon carbide whiskers comprising:
a. prealloying a metallic catalyst with carbon silicon, or a mixture of carbon and silicon;
b. applying said prealloyed catalyst to a carbon substrate;
c. heating said substrate with applied prealloyed catalyst in a gaseous environment comprised of a reducing gas;
d. introducing silicon containing gas and carbon containing gas in said gaseous environment;
e. maintaining the flow of said silicon containing gas while the temperature of said substrate is maintained above a minimum temperature above which silicon carbide whiskers will form; and f. cooling said silicon carbide whiskers after completion of whisker growth.
a. prealloying a metallic catalyst with carbon silicon, or a mixture of carbon and silicon;
b. applying said prealloyed catalyst to a carbon substrate;
c. heating said substrate with applied prealloyed catalyst in a gaseous environment comprised of a reducing gas;
d. introducing silicon containing gas and carbon containing gas in said gaseous environment;
e. maintaining the flow of said silicon containing gas while the temperature of said substrate is maintained above a minimum temperature above which silicon carbide whiskers will form; and f. cooling said silicon carbide whiskers after completion of whisker growth.
2. The method of Claim 1 wherein said prealloyed catalyst contains 1 to 45 weight percent silicon.
3. A method for manufacturing silicon carbide whiskers wherein manufacturing time is reduced comprising:
a. providing a growth substrate having a coating comprised of metallic catalyst particles alloyed with silicon where the particles contain from about 1 to about 45 weight %
silicon;
b. heating the coated growth substrate in a gaseous environment comprised of a reducing gas;
c. adding to the gaseous environment a gas comprised of silicon and a gas comprised of carbon;
d. maintaining for a time period the coated growth substrate and gaseous environment at a temperature above a minimum temperature at which silicon carbide whiskers will form; and e. removing the gas comprised of silicon and the gas comprised of carbon from the gaseous environment cooling the coated growth substrate and recovering silicon carbide whiskers from the coated growth substrate.
a. providing a growth substrate having a coating comprised of metallic catalyst particles alloyed with silicon where the particles contain from about 1 to about 45 weight %
silicon;
b. heating the coated growth substrate in a gaseous environment comprised of a reducing gas;
c. adding to the gaseous environment a gas comprised of silicon and a gas comprised of carbon;
d. maintaining for a time period the coated growth substrate and gaseous environment at a temperature above a minimum temperature at which silicon carbide whiskers will form; and e. removing the gas comprised of silicon and the gas comprised of carbon from the gaseous environment cooling the coated growth substrate and recovering silicon carbide whiskers from the coated growth substrate.
4. The method of Claim 1, wherein said minimum temperature is from 1200° to 1600°C.
5. The method of Claim 2, wherein said minimum temperature is from 1200° to 1600°C.
6. The method of Claim 3, wherein said minimum temperature is from 1200° to 1600°C.
7. The method of Claim 1, Claim 2 or Claim 3, wherein said prealloyed catalyst contains 0.1 to 5.0 weight percent carbon.
8. The method of Claim 4, Claim 5 or Claim 6, wherein said prealloyed catalyst contains 0.1 to 5.0 weight percent carbon.
9. The method of Claim 1, Claim 2 or Claim 3, wherein said metal catalyst contains one or more of the following metals:
manganese, iron, nickel, cobalt, chromium, and niobium.
manganese, iron, nickel, cobalt, chromium, and niobium.
10. The method of Claim 4, Claim S or Claim 6, wherein said metal catalyst contains one or more of the following metals:
manganese, iron, nickel, cobalt, chromium, and niobium.
manganese, iron, nickel, cobalt, chromium, and niobium.
11. The method of Claim 1, Claim 2 or Claim 3, wherein said prealloyed catalyst comprises 1.6 weight percent manganese, 23.4 weight percent cobalt, 22.9 weight percent nickel, 40.9 weight percent silicon, 10.2 weight percent iron, and 1 weight percent chromium.
12. The method of Claim 4, Claim 5 or Claim 6, wherein said prealloyed catalyst comprises 1.6 weight percent manganese, 23.4 weight percent cobalt, 22.9 weight percent nickel, 40.9 weight percent silicon, 10.2 weight percent iron, and 1 weight percent chromium.
13. The method of Claim 1, Claim 2 or Claim 3, wherein said prealloyed catalyst is applied to said carbon substrate as part of a methyl ethyl ketone and acrylic resin solution.
14. The method of Claim 4, Claim 5 or Claim 6, wherein said prealloyed catalyst is applied to said carbon substrate as part of a methyl ethyl ketone and acrylic resin solution.
15. The method of Claim 1, Claim 2 or Claim 3, wherein the reducing gas is hydrogen.
16. The method of Claim 4, Claim 5 or Claim 6, wherein the reducing gas is hydrogen.
17. The method of Claim 1, Claim 2 or Claim 3, wherein the gas comprised of silicon is a gas chosen from a group containing SiO, SiC14, SiCH3C13, and silane.
18. The method of Claim 4, Claim 5 or Claim 6, wherein the gas comprised of silicon is a gas chosen from a group containing SiO, SiC14, SiCH3C13, and silane.
19. The method of Claim 1, Claim 2 or Claim 3, wherein the gas comprised of carbon is methane.
20. The method of Claim 4, Claim 5 or Claim 6, wherein the gas comprised of carbon is methane.
21. The method of Claim 1, Claim 2 or Claim 3, wherein said growth of silicon carbide whiskers is promptly initiated upon said reducing atmosphere reaching growth temperature.
22. The method of Claim 4, Claim 5 or Claim 6, wherein said growth of silicon carbide whiskers is promptly initiated upon said reducing atmosphere reaching growth temperature.
23. A catalyst for producing silicon carbide whiskers on a carbon substrate comprising a metal prealloyed with carbon, silicon, or a mixture of carbon and silicon before heating to the silicon carbide whisker growth temperature.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US81486685A | 1985-12-30 | 1985-12-30 | |
| US814,866 | 1985-12-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1275088A true CA1275088A (en) | 1990-10-09 |
Family
ID=25216204
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000524790A Expired - Fee Related CA1275088A (en) | 1985-12-30 | 1986-12-08 | Prealloyed catalyst for growing silicon carbide whiskers |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPH0791158B2 (en) |
| CA (1) | CA1275088A (en) |
| DE (1) | DE3644299C2 (en) |
| FR (1) | FR2592399B1 (en) |
| GB (1) | GB2186208B (en) |
| IT (1) | IT1198258B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4911781A (en) * | 1987-05-05 | 1990-03-27 | The Standard Oil Company | VLS Fiber growth process |
| EP0290258B1 (en) * | 1987-05-05 | 1992-09-16 | The Standard Oil Company | Vls fiber growth process |
| NL9300816A (en) * | 1993-05-12 | 1994-12-01 | Univ Delft Tech | Method of preparing a porous silicon carbide |
| US5383421A (en) * | 1993-05-19 | 1995-01-24 | The Dow Chemical Company | Method for forming beta-silicon carbide whiskers, singly or in a matrix, using an organotitanium coordination compound catalyst |
| CN113564687B (en) * | 2021-08-24 | 2022-07-22 | 安徽工业大学 | Chromium-catalyzed silicon carbide whisker and preparation method thereof |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1195729B (en) * | 1958-10-23 | 1965-07-01 | Siemens Ag | Process for producing bodies from high-purity silicon carbide |
| GB1077667A (en) * | 1963-10-08 | 1967-08-02 | Atomic Energy Authority Uk | Improvements in or relating to nuclear fuel material |
| NL143436B (en) * | 1966-12-14 | 1974-10-15 | Philips Nv | PROCESS FOR MANUFACTURING WIRE-SHAPED SILICON CARBIDE CRYSTALS AND ARTICLES WHOLLY OR PARTICULATED OF THESE CRYSTALS. |
| GB1242051A (en) * | 1967-05-08 | 1971-08-11 | Nat Res Dev | Improvements in the manufacture of silicon carbide |
| US3622272A (en) * | 1968-04-01 | 1971-11-23 | Gen Technologies Corp | Method of growing silicon carbide whiskers |
| GB1280648A (en) * | 1969-08-29 | 1972-07-05 | Laporte Industries Ltd | Refractory compounds |
| JPS5821578B2 (en) * | 1975-08-30 | 1983-05-02 | 松下電工株式会社 | insulation material |
| JPS57101000A (en) * | 1980-12-12 | 1982-06-23 | Sumitomo Electric Ind Ltd | Preparation of ceramic whisker |
| JPS599220A (en) * | 1982-06-30 | 1984-01-18 | Shin Etsu Chem Co Ltd | Production of silicon carbide whisker |
| JPS61291498A (en) * | 1985-06-17 | 1986-12-22 | Shin Etsu Chem Co Ltd | Production of silicon carbide whiskers |
-
1986
- 1986-12-08 CA CA000524790A patent/CA1275088A/en not_active Expired - Fee Related
- 1986-12-10 GB GB8629499A patent/GB2186208B/en not_active Expired
- 1986-12-23 JP JP61307608A patent/JPH0791158B2/en not_active Expired - Lifetime
- 1986-12-23 DE DE3644299A patent/DE3644299C2/en not_active Expired - Fee Related
- 1986-12-24 IT IT22872/86A patent/IT1198258B/en active
- 1986-12-29 FR FR8618275A patent/FR2592399B1/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| GB8629499D0 (en) | 1987-01-21 |
| FR2592399A1 (en) | 1987-07-03 |
| IT8622872A1 (en) | 1988-06-24 |
| GB2186208B (en) | 1989-10-25 |
| FR2592399B1 (en) | 1995-12-22 |
| JPS62158200A (en) | 1987-07-14 |
| DE3644299A1 (en) | 1987-07-02 |
| GB2186208A (en) | 1987-08-12 |
| IT8622872A0 (en) | 1986-12-24 |
| IT1198258B (en) | 1988-12-21 |
| DE3644299C2 (en) | 1995-09-21 |
| JPH0791158B2 (en) | 1995-10-04 |
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