CA1274967A - Process for growing silicon carbide whiskers by undercooling - Google Patents
Process for growing silicon carbide whiskers by undercoolingInfo
- Publication number
- CA1274967A CA1274967A CA000531442A CA531442A CA1274967A CA 1274967 A CA1274967 A CA 1274967A CA 000531442 A CA000531442 A CA 000531442A CA 531442 A CA531442 A CA 531442A CA 1274967 A CA1274967 A CA 1274967A
- Authority
- CA
- Canada
- Prior art keywords
- growth
- temperature
- silicon carbide
- reaction system
- growth temperature
- 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
Links
Classifications
-
- 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
ABSTRACT OF THE DISCLOSURE
A method of growing silicon carbide whiskers, especially in the 8 form, uses a heating schedule wherein the temperature of the atmosphere in the growth zone of a furnace is first heated to or beyond the growth temperature and then is cooled to or below the growth temperature to induce nucleation of whiskers at catalyst sites at a desired point in time which results in the selection.
A method of growing silicon carbide whiskers, especially in the 8 form, uses a heating schedule wherein the temperature of the atmosphere in the growth zone of a furnace is first heated to or beyond the growth temperature and then is cooled to or below the growth temperature to induce nucleation of whiskers at catalyst sites at a desired point in time which results in the selection.
Description
PROCESS FOR GRQWING SILICON CARBIDE WHISKERS
sY UNDERCOOLING
BAC~GROUND OF THE INVENTION
The present invention relates generally ~o a method for manufacturing ~ silicon carbide whiskers according ~o a desired heating schedule and more particularly to a S heating schedule where the furnace atmosphere temperature is raised to at least the whisker growth temperature before being cooled ~o or below the growth temperature for a period to induce nucleation of silicon carbide crystals at the catalyst sites at a desired point in time which results in desirable mor~hologies for the crystals produced. This invention is the result of a contract with the Departmen~ of Energy (Con~ract No. W-7405-ENG-36).
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.
The whiskers have been used as a composite reinforcing material for metals, plastics, and ceramics. The most desirable whiskers are 3 silicon carbide single crystals which have a high length to diameter ratio.
Previous methods for. growing silicon carbide whiskers have generally heated the atmosphere of a growing zone inside a furnace until the growth temperature has been . ,~, ,....
reached. Temperatures could fluctuate up and down during the heating process, but no e~fort was made to deliberately reduce the atmosphere ~emperature after growth temperature was reached. In U. S. Patent 4,504,~53 05 issued to Tanaka et al., trays containing mat~rial~ for growing silicon carbide whiskers were moved from one temperature zone into the next higher temperature 20ne of a furnace partitioned into zones with varying temperatures. The trays were then held in the temperature zones for typically an hour or two. Again, no effort wa~
made to reduce the temperature of the growth materials after growth temperature was reached, but before the whiskers had completed growing.
In U.S. Patent 3,053,635 issued to Shockley, a method for growing silicon carbide crystals from a molten metal or alloy containing silicon and carbon in solution was described. A silicon carbide seed crystal was inserted into a molten bath which was at the saturation point for silicon carbide. The seed cooled a surrounding portion of the bath causing that portion to become supecsaturated and, as the seed was withdrawn from the solution, silicon carbide precipitated on the seed. However, no information was given as to how this process could be applied ~o a gaseous sys~em where the silicon and carbon components were not in a molten bath.
Overall, a need still existed for a method to more quickly and precisely (in time) induce nucleation at catalyst sites. Althouyh, heating the furnace atmosphere to the growth temperature and holding thereat promoted nucleation of silicon carbide whiskers at the catalyst sites, the time needed for nucleation to occur, especially at low partial pressures of the reactants, lengthened the time the furnace had ~o be maintained at growth temperature, and hence the amount of energy needed to grow a given quantity of silicon carbide whis~erR, It was necessary for the melted catalys~ particles to absorb sufficient silicon and ~arbon after reaching the growth 05 temperature to produce the su~ersaturation required for nucleation. Such supersa~uration can be achieved when a catalyst composi~ion progressively absorbs Si and C from the vapor phase, doing so isothermally at the growth temperature, until it reaches a compo-sition where the supersaturation is great enough that nuclea~ion will occur. Additionally, because i~ is difficult ~o regula~e the isothermal approach to nucleation, unwanted whisker - morphologies such as too fine or thicker bent growth may be produced in undesirable proportions. Silicon carbide whiskers with these morphologies are no~ suited to certain commercial uses.
SUMMARY OF THE INVENTION
The object of this invention is to provide a method for manufacturing ~ silicon carbide whiskers in a shorter length of time.
A further object of this invention is to provide a method for manufacturing ~ silicon carbide whiskers which requires less energy to induce nucleation of growing whiskers at the catalyst sites~
Yet another object of the present invention is to provide a method of manufacturing ~ silicon carbide whiskers with more desirable morphologies and sizes.
A final object of the present invention is to better control the time at which and the rate at which nucleation occurs to obtain desired morphologies of the crystals produced.
Additional objects, aAvantages and novel fea~ures of the invention will be set forth in part in the description ~ ~74~3~;7 which fo:l:lows, and :in part will become apparent to those skilled in the art upon examination of the EollowLrl~ or may be learned by practice of the lnvent:i.on. The objects and advanta~3es of -the invention may be realized and attained by means of the instrumen-talities and combinations particularly pointed ou-t in -the appended claims.
To achieve the foregoing and other objec-ts, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the invention contemplates a method of manufacturing ~ silicon carbide whiskers which comprises heating a reaction system consisting of a silicon source which is a silicon-containing gas or solid located within the reaction system, a carbon source which is a carbon-containing gas or solid located within the reaction system, and a catalyst in a reducing atmosphere, where the reaction system is first heated to a temperature which is equal to or above the whisker growth temperature, where the growth temperature is within a range of from about 1350C to about 1500C, and where the reaction system is cooled to a temperature which is equal to or below the growth temperature in order to induce nucleation at catalyst sites before the reaction system is held at the growth temperature for the growth period.
An advantage of the present invention is the shorter time period after a furnace has been heated to the growth temperature for inducing nucleation of silicon carbide whiskers at catalyst sites.
Another advantage of the present invention is reduction in energy required to initiate nucleation at catalyst sites of silicon carbide whiskers.
Yet another advantage of the present invention is the superior morphologies and size of the silicon carbide whiskers grown at the catalyst sites.
A final advantage of the present invention is better control of the time and the rate of nucleation by causing nucleation to occur at a certain time and rate by choosing ~ ~.
7~ 7 the time and amount of cooling of the reaction system to or below the growth temperature. This in turn alLows desired morphologies of the SiC whiskers to be produced.
BRIEF DESCRIPTION OF_THE DRAWINGS
05 ~he accompanying drawings, which are incorporated i~
and form a part of the s~ecification, illustrate the embodiment of the present invention and, together with the description, serve ~o explain the principles of the invention. In the drawings:
FIGURE l is a generalized phase diagram showing the pseudobinary phase relation for the growth of SiC whiskers by a VLS (vapor-liquid-solid) mechanism.
FIGURE 2 is a generalized graphical depiction of the nucleation rate dependence upon temperature.
FIGURE 3 shows a time-temperature diagram for the atmosphere in the reactor growth zone of Example l.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
To efficiently grow silicon carbide whiskers, especially in the ~ form, it is desirable to use a catalyst. After the catalyst has been applied to the growth substrate, and the growth substrate placed in a furnace, the furnace must be heated up to growth temperature. When growth temperature has been reached, the catalyst particles, especially when they are metal catalyst particles, must become supersa~urated with the silicon and carbon components that will go to make up silicon carbide whiskers in order to nucleate. Depending upon the initial composition of the catalyst particles, this supersa~uration at gro~th temperature takes generally 30-lSO minutes. Referring now to Figure l, the reason for supersaturating the , catalyst particles can be illustrated. The catalyst composition absorbs silicon and carbon from the furnace atmosphere at a temperature . , ~ . ~ , . .
~74~j7 ~ .
designed T~ until it reaches a liquidus composition shown at point TL, The catalyst particle is ~h2n cooled tthis cooling step giving the name undercooling to the invention) by an amount designated ~T expeditiously to a 05 temperature Tl to arrive at point ~, the nucleation point, on the phase diagram. At point ~ the catalyst particle is sufficiently supersaturated that nucleation occurs. Previous isothermal methods without undercooling are illustrated by the line at Tl which arrives at point N by merely increasing the portion of silicon carbide components in the catalyst particle.
Referring now to Figure 2, the generalized relationship between the nucleation rate and temperature is shown. As can be seen, the improvement in nucleation rate is ma~imized for a certain amount of undercooling.
8eyond that amount of temperature reduction, the nucleation rate begins to decrease from its maximum rate.
The TL tempera~ure is the equilibrium temperature of the liquid for particular compositions of silicon, earbon, and iron where the maximum amount of silicon and carbon has been absorbed without any precipitation of silicon carbide. After the temperature is decreased, precipitation of silicon carbide takes place at the nucleation sites. By controlling the amount as well as the time of undercooling, the nucleation rate, as well as the precise point in time, can be selected according to the relationship shown.in Figure 2.
The furnace used to grow silicon carbide whiskers must be of a type wherein a heated atmosphere can flow through a growth zone. One such ~urnace is a C.I. Hayes, Inc.
Model HG644. The Hayes furnace is heated by electrical resistance elements. It contains a sealed fused quartz muffle tube which allows the silicon carbide whisker ~ 7~ ~3~
growth to occur under a reducing atmosphere which 15 typically a hydro~en atmosphere containing l~s~er amounts of N2, CO and CH~. The actual whiskar growth takes place inside a secondary box enclosure called a reactor.
05 The ~urnace also allows for a flow of various reactant gases through the growth zone. Typically these gases are SiO, SiC14, SiCH3C13, or silane.
The furnace should also have a temperature range of from room temperature to 1500C. Heating of the furnace is done automatically by a MICRICON Model 823 programmer-controller. The reactor is warmed up to or beyond the growth temperature in typically 3 to 4 hours.
After the desired growth temeerature has been reached or exceeded, the reactor atmosphere is cooled to or below the growth temperature. After the desired period of cooling, the reactor is brought to and maintained at the growth temperature desired. A thermocouple is placed in the center of the reactor growth zone to measure temperature.
Actual control of the reactor temperature is accomplished indirectly from a thermocouple on the outside of the muffle tube.
Substrates are placed in the growth zone of the reactor to serve as a basis for whisker growth. Typically these growth plates are made of graphite. Before being placed into the furnace, catalyst particles are placed upon the growth plates. One advantage of using a graphite plates as ~he grow~h subs~rates is that while the catalyst particles are still in contact with the graphite, they can absorb carbon from the plates after melting. Of course this absorption is cut off when the growing whiskers lift ~he catalyst particlas, which are now melted ineo a molten ball at the end of growing whiskers, away from the graphite substrates. Afterwards, the carbon source for .. , _ , . ._ _ . , . _ _. . , . _~ ... . _ .,. _ _ _ _ . ,. . . . _ _ . ._ the catalyst balls must be the gas mix~ure flowing through the growth zone. Thereore, the flowing atmosphere must contain a carbon source such as methane or a carbon atom in another more complicated gas. The silicon source for 05 ~he catalyst ball may ~e a siiicon-containing gas or a SiO2/C powder mixture.
The catalyst particles placed upon the growth plates to serve as nucleation sites for the beginning of whisker growth are typically metal particles. These metal particles may be comprised of one or more of the following metals: manganese, cobalt, nickel, iron, chromium, and silicon. These catalyst particles are available from many sources. For instance, stainless steel ~lakes are available from Novamet Company of Wykoff, New Jersey.
Flaked ferrosilicon can be obtained from many sources and should have an approximate particle size of 17 micrometers and a silicon content of approximately 22 weight percent.
~nother typical catalyst particle is composed of the substance designated as Alloy 62 which has the following weight percent composition: Mn 65, Co 14, Ni 20, Si 0.25, Fe 0.1, Cr 0.2, B 0.25, Zn 0.25; and is available from Metallurgical Technology in Winslow, New Jersey. The two most common methods for depositing the catalyst particles upon the substrate are painting and spraying. For both methods it is 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 vehicle is made of a weight of Cabosil~, which is a product of the Cabot Corporation, Boston, Massachusetts, equal to about half the 4.5 parts by weight of catalyst particles which is then fur~her mixed with 50 parts each of a liquid acrylic resin in methyl ethyl ketone. Similar fsuspension media are available for spraying.
. , _ . ., .... ... _ _ . . , ... _ _ .. _ ., .
~ ~d ~i) 4 ~
Referring now to Figure 3, a typical time-temperature profile for the temperature within the growth zone of a furnace, it is necessary to heat the atmosphere in the growth zone to the growth temperature. Growth 05 temperatures for the manufacture of silicon aarbide whiskers, especially in the ~ form, eypically are around 1400C but can vary from 1350 to 1500C.
Typically, to reach these growth tsmperatures, it takes 3-4 hours. Once the maximum temperature has been reached which can be from zero ~o 100C beyond the growth temperature, i~ is necessary to let the atmosphere ~emperature in the growth zone cool. This process, previously called undercooling, allows the temperature to fall to or below the growth temperature. Typically the undercooling is no more than 150 C when the growth temperature has not been exceeded during the heating up of the furnace. However, where the growth temperature has been exceeded by 100, undercooling may bring the temperature back down 250C to provide a temperature 150 below the growth temperature. After the minimum temperature has been reached during the under- cooling period, the atmosphere in the growth zone i6 returned to the growth temperature. Throughout this time period, both during the hea~ing up of the atmosphere temperature up to and beyond the growth temperature and during the undercooling, the silicon carbide growth gases are flowing through the growth zone.
After returning to the growth temperature following the undercooling period, th~ silicon carbide growth gases continue to flow throughout the entire growth period.
This typically lasts for a 18 hours. The furnace is then cooled to 1000C in 3-4 hours and the reactor removed from the furnace and allowed to cool. At room ., ~ ~
1, ~emperature, the silicon carbide whiækers grown are removed by careful scraping.
E~AMPLE 1 The C.I. Hayes, Inc. furnace Model HG644, previously 05 described, was fitted wi~h a 5-plate production type reactor whose box dimensions were 19 inches (48.3 cm) by 5.5 inches ~14 cm) by 5.5 inches (14 cm). The growth surface was brushed with Alloy 62 suspended in a vehicle of Cabosil and liquid acrylic resin. A gas mixture, flowing through the furnace at a rate of 41.5 l/min, was composed of the following volume percentage: H2 ~ 86.7, N2 ~ 7-9. C0 - 5.1, CH4 - 0.28, and sio - o. lo which were normalized over a 12 hour period. The ~iring cycle for the furnace is illustrated in Figure ~ when undercooling was initiated at 2.5 hours when the temperature was 1445 C. The temperature of the furnace fell to 1290C before being returned to the growth temperature of 1400C. The furnace temperature was allowed to fall after 21 hours and whisker growth ceased. Undercooling allowed precise control over the beginning of nucleation and produced 14.4 grams of long, uniform, smooth green SiC whis~sers of from 3 to 10 ~m in diameter. The whiskers produced were characterized as being in the 4 to 5 A category according to a table shown on page 1164 of the article John V. ~ilewski et al., "Growth of Beta-Silicon Carbide Whiskers by the ~LS
Process," J. Materials Science 20, 1160-1166 (1985).
The foregoing description of the preferred embodiments of the invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The ~'~74~
embodi.~ents were chosen and described in order to best explain the principles oE the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with 05 various modifications as are suited to the particular use contemplated. It is intended that the scope o~ the invention be defined by the claims appanded hereto.
.. . , . ,, . _ ~ . , .
sY UNDERCOOLING
BAC~GROUND OF THE INVENTION
The present invention relates generally ~o a method for manufacturing ~ silicon carbide whiskers according ~o a desired heating schedule and more particularly to a S heating schedule where the furnace atmosphere temperature is raised to at least the whisker growth temperature before being cooled ~o or below the growth temperature for a period to induce nucleation of silicon carbide crystals at the catalyst sites at a desired point in time which results in desirable mor~hologies for the crystals produced. This invention is the result of a contract with the Departmen~ of Energy (Con~ract No. W-7405-ENG-36).
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.
The whiskers have been used as a composite reinforcing material for metals, plastics, and ceramics. The most desirable whiskers are 3 silicon carbide single crystals which have a high length to diameter ratio.
Previous methods for. growing silicon carbide whiskers have generally heated the atmosphere of a growing zone inside a furnace until the growth temperature has been . ,~, ,....
reached. Temperatures could fluctuate up and down during the heating process, but no e~fort was made to deliberately reduce the atmosphere ~emperature after growth temperature was reached. In U. S. Patent 4,504,~53 05 issued to Tanaka et al., trays containing mat~rial~ for growing silicon carbide whiskers were moved from one temperature zone into the next higher temperature 20ne of a furnace partitioned into zones with varying temperatures. The trays were then held in the temperature zones for typically an hour or two. Again, no effort wa~
made to reduce the temperature of the growth materials after growth temperature was reached, but before the whiskers had completed growing.
In U.S. Patent 3,053,635 issued to Shockley, a method for growing silicon carbide crystals from a molten metal or alloy containing silicon and carbon in solution was described. A silicon carbide seed crystal was inserted into a molten bath which was at the saturation point for silicon carbide. The seed cooled a surrounding portion of the bath causing that portion to become supecsaturated and, as the seed was withdrawn from the solution, silicon carbide precipitated on the seed. However, no information was given as to how this process could be applied ~o a gaseous sys~em where the silicon and carbon components were not in a molten bath.
Overall, a need still existed for a method to more quickly and precisely (in time) induce nucleation at catalyst sites. Althouyh, heating the furnace atmosphere to the growth temperature and holding thereat promoted nucleation of silicon carbide whiskers at the catalyst sites, the time needed for nucleation to occur, especially at low partial pressures of the reactants, lengthened the time the furnace had ~o be maintained at growth temperature, and hence the amount of energy needed to grow a given quantity of silicon carbide whis~erR, It was necessary for the melted catalys~ particles to absorb sufficient silicon and ~arbon after reaching the growth 05 temperature to produce the su~ersaturation required for nucleation. Such supersa~uration can be achieved when a catalyst composi~ion progressively absorbs Si and C from the vapor phase, doing so isothermally at the growth temperature, until it reaches a compo-sition where the supersaturation is great enough that nuclea~ion will occur. Additionally, because i~ is difficult ~o regula~e the isothermal approach to nucleation, unwanted whisker - morphologies such as too fine or thicker bent growth may be produced in undesirable proportions. Silicon carbide whiskers with these morphologies are no~ suited to certain commercial uses.
SUMMARY OF THE INVENTION
The object of this invention is to provide a method for manufacturing ~ silicon carbide whiskers in a shorter length of time.
A further object of this invention is to provide a method for manufacturing ~ silicon carbide whiskers which requires less energy to induce nucleation of growing whiskers at the catalyst sites~
Yet another object of the present invention is to provide a method of manufacturing ~ silicon carbide whiskers with more desirable morphologies and sizes.
A final object of the present invention is to better control the time at which and the rate at which nucleation occurs to obtain desired morphologies of the crystals produced.
Additional objects, aAvantages and novel fea~ures of the invention will be set forth in part in the description ~ ~74~3~;7 which fo:l:lows, and :in part will become apparent to those skilled in the art upon examination of the EollowLrl~ or may be learned by practice of the lnvent:i.on. The objects and advanta~3es of -the invention may be realized and attained by means of the instrumen-talities and combinations particularly pointed ou-t in -the appended claims.
To achieve the foregoing and other objec-ts, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the invention contemplates a method of manufacturing ~ silicon carbide whiskers which comprises heating a reaction system consisting of a silicon source which is a silicon-containing gas or solid located within the reaction system, a carbon source which is a carbon-containing gas or solid located within the reaction system, and a catalyst in a reducing atmosphere, where the reaction system is first heated to a temperature which is equal to or above the whisker growth temperature, where the growth temperature is within a range of from about 1350C to about 1500C, and where the reaction system is cooled to a temperature which is equal to or below the growth temperature in order to induce nucleation at catalyst sites before the reaction system is held at the growth temperature for the growth period.
An advantage of the present invention is the shorter time period after a furnace has been heated to the growth temperature for inducing nucleation of silicon carbide whiskers at catalyst sites.
Another advantage of the present invention is reduction in energy required to initiate nucleation at catalyst sites of silicon carbide whiskers.
Yet another advantage of the present invention is the superior morphologies and size of the silicon carbide whiskers grown at the catalyst sites.
A final advantage of the present invention is better control of the time and the rate of nucleation by causing nucleation to occur at a certain time and rate by choosing ~ ~.
7~ 7 the time and amount of cooling of the reaction system to or below the growth temperature. This in turn alLows desired morphologies of the SiC whiskers to be produced.
BRIEF DESCRIPTION OF_THE DRAWINGS
05 ~he accompanying drawings, which are incorporated i~
and form a part of the s~ecification, illustrate the embodiment of the present invention and, together with the description, serve ~o explain the principles of the invention. In the drawings:
FIGURE l is a generalized phase diagram showing the pseudobinary phase relation for the growth of SiC whiskers by a VLS (vapor-liquid-solid) mechanism.
FIGURE 2 is a generalized graphical depiction of the nucleation rate dependence upon temperature.
FIGURE 3 shows a time-temperature diagram for the atmosphere in the reactor growth zone of Example l.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
To efficiently grow silicon carbide whiskers, especially in the ~ form, it is desirable to use a catalyst. After the catalyst has been applied to the growth substrate, and the growth substrate placed in a furnace, the furnace must be heated up to growth temperature. When growth temperature has been reached, the catalyst particles, especially when they are metal catalyst particles, must become supersa~urated with the silicon and carbon components that will go to make up silicon carbide whiskers in order to nucleate. Depending upon the initial composition of the catalyst particles, this supersa~uration at gro~th temperature takes generally 30-lSO minutes. Referring now to Figure l, the reason for supersaturating the , catalyst particles can be illustrated. The catalyst composition absorbs silicon and carbon from the furnace atmosphere at a temperature . , ~ . ~ , . .
~74~j7 ~ .
designed T~ until it reaches a liquidus composition shown at point TL, The catalyst particle is ~h2n cooled tthis cooling step giving the name undercooling to the invention) by an amount designated ~T expeditiously to a 05 temperature Tl to arrive at point ~, the nucleation point, on the phase diagram. At point ~ the catalyst particle is sufficiently supersaturated that nucleation occurs. Previous isothermal methods without undercooling are illustrated by the line at Tl which arrives at point N by merely increasing the portion of silicon carbide components in the catalyst particle.
Referring now to Figure 2, the generalized relationship between the nucleation rate and temperature is shown. As can be seen, the improvement in nucleation rate is ma~imized for a certain amount of undercooling.
8eyond that amount of temperature reduction, the nucleation rate begins to decrease from its maximum rate.
The TL tempera~ure is the equilibrium temperature of the liquid for particular compositions of silicon, earbon, and iron where the maximum amount of silicon and carbon has been absorbed without any precipitation of silicon carbide. After the temperature is decreased, precipitation of silicon carbide takes place at the nucleation sites. By controlling the amount as well as the time of undercooling, the nucleation rate, as well as the precise point in time, can be selected according to the relationship shown.in Figure 2.
The furnace used to grow silicon carbide whiskers must be of a type wherein a heated atmosphere can flow through a growth zone. One such ~urnace is a C.I. Hayes, Inc.
Model HG644. The Hayes furnace is heated by electrical resistance elements. It contains a sealed fused quartz muffle tube which allows the silicon carbide whisker ~ 7~ ~3~
growth to occur under a reducing atmosphere which 15 typically a hydro~en atmosphere containing l~s~er amounts of N2, CO and CH~. The actual whiskar growth takes place inside a secondary box enclosure called a reactor.
05 The ~urnace also allows for a flow of various reactant gases through the growth zone. Typically these gases are SiO, SiC14, SiCH3C13, or silane.
The furnace should also have a temperature range of from room temperature to 1500C. Heating of the furnace is done automatically by a MICRICON Model 823 programmer-controller. The reactor is warmed up to or beyond the growth temperature in typically 3 to 4 hours.
After the desired growth temeerature has been reached or exceeded, the reactor atmosphere is cooled to or below the growth temperature. After the desired period of cooling, the reactor is brought to and maintained at the growth temperature desired. A thermocouple is placed in the center of the reactor growth zone to measure temperature.
Actual control of the reactor temperature is accomplished indirectly from a thermocouple on the outside of the muffle tube.
Substrates are placed in the growth zone of the reactor to serve as a basis for whisker growth. Typically these growth plates are made of graphite. Before being placed into the furnace, catalyst particles are placed upon the growth plates. One advantage of using a graphite plates as ~he grow~h subs~rates is that while the catalyst particles are still in contact with the graphite, they can absorb carbon from the plates after melting. Of course this absorption is cut off when the growing whiskers lift ~he catalyst particlas, which are now melted ineo a molten ball at the end of growing whiskers, away from the graphite substrates. Afterwards, the carbon source for .. , _ , . ._ _ . , . _ _. . , . _~ ... . _ .,. _ _ _ _ . ,. . . . _ _ . ._ the catalyst balls must be the gas mix~ure flowing through the growth zone. Thereore, the flowing atmosphere must contain a carbon source such as methane or a carbon atom in another more complicated gas. The silicon source for 05 ~he catalyst ball may ~e a siiicon-containing gas or a SiO2/C powder mixture.
The catalyst particles placed upon the growth plates to serve as nucleation sites for the beginning of whisker growth are typically metal particles. These metal particles may be comprised of one or more of the following metals: manganese, cobalt, nickel, iron, chromium, and silicon. These catalyst particles are available from many sources. For instance, stainless steel ~lakes are available from Novamet Company of Wykoff, New Jersey.
Flaked ferrosilicon can be obtained from many sources and should have an approximate particle size of 17 micrometers and a silicon content of approximately 22 weight percent.
~nother typical catalyst particle is composed of the substance designated as Alloy 62 which has the following weight percent composition: Mn 65, Co 14, Ni 20, Si 0.25, Fe 0.1, Cr 0.2, B 0.25, Zn 0.25; and is available from Metallurgical Technology in Winslow, New Jersey. The two most common methods for depositing the catalyst particles upon the substrate are painting and spraying. For both methods it is 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 vehicle is made of a weight of Cabosil~, which is a product of the Cabot Corporation, Boston, Massachusetts, equal to about half the 4.5 parts by weight of catalyst particles which is then fur~her mixed with 50 parts each of a liquid acrylic resin in methyl ethyl ketone. Similar fsuspension media are available for spraying.
. , _ . ., .... ... _ _ . . , ... _ _ .. _ ., .
~ ~d ~i) 4 ~
Referring now to Figure 3, a typical time-temperature profile for the temperature within the growth zone of a furnace, it is necessary to heat the atmosphere in the growth zone to the growth temperature. Growth 05 temperatures for the manufacture of silicon aarbide whiskers, especially in the ~ form, eypically are around 1400C but can vary from 1350 to 1500C.
Typically, to reach these growth tsmperatures, it takes 3-4 hours. Once the maximum temperature has been reached which can be from zero ~o 100C beyond the growth temperature, i~ is necessary to let the atmosphere ~emperature in the growth zone cool. This process, previously called undercooling, allows the temperature to fall to or below the growth temperature. Typically the undercooling is no more than 150 C when the growth temperature has not been exceeded during the heating up of the furnace. However, where the growth temperature has been exceeded by 100, undercooling may bring the temperature back down 250C to provide a temperature 150 below the growth temperature. After the minimum temperature has been reached during the under- cooling period, the atmosphere in the growth zone i6 returned to the growth temperature. Throughout this time period, both during the hea~ing up of the atmosphere temperature up to and beyond the growth temperature and during the undercooling, the silicon carbide growth gases are flowing through the growth zone.
After returning to the growth temperature following the undercooling period, th~ silicon carbide growth gases continue to flow throughout the entire growth period.
This typically lasts for a 18 hours. The furnace is then cooled to 1000C in 3-4 hours and the reactor removed from the furnace and allowed to cool. At room ., ~ ~
1, ~emperature, the silicon carbide whiækers grown are removed by careful scraping.
E~AMPLE 1 The C.I. Hayes, Inc. furnace Model HG644, previously 05 described, was fitted wi~h a 5-plate production type reactor whose box dimensions were 19 inches (48.3 cm) by 5.5 inches ~14 cm) by 5.5 inches (14 cm). The growth surface was brushed with Alloy 62 suspended in a vehicle of Cabosil and liquid acrylic resin. A gas mixture, flowing through the furnace at a rate of 41.5 l/min, was composed of the following volume percentage: H2 ~ 86.7, N2 ~ 7-9. C0 - 5.1, CH4 - 0.28, and sio - o. lo which were normalized over a 12 hour period. The ~iring cycle for the furnace is illustrated in Figure ~ when undercooling was initiated at 2.5 hours when the temperature was 1445 C. The temperature of the furnace fell to 1290C before being returned to the growth temperature of 1400C. The furnace temperature was allowed to fall after 21 hours and whisker growth ceased. Undercooling allowed precise control over the beginning of nucleation and produced 14.4 grams of long, uniform, smooth green SiC whis~sers of from 3 to 10 ~m in diameter. The whiskers produced were characterized as being in the 4 to 5 A category according to a table shown on page 1164 of the article John V. ~ilewski et al., "Growth of Beta-Silicon Carbide Whiskers by the ~LS
Process," J. Materials Science 20, 1160-1166 (1985).
The foregoing description of the preferred embodiments of the invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The ~'~74~
embodi.~ents were chosen and described in order to best explain the principles oE the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with 05 various modifications as are suited to the particular use contemplated. It is intended that the scope o~ the invention be defined by the claims appanded hereto.
.. . , . ,, . _ ~ . , .
Claims (8)
1. A method of manufacturing .beta. silicon carbide whiskers which comprises heating a reaction system consisting of a silicon source which is a silicon-containing gas or solid located within said reaction system, a carbon source which is a carbon-containing gas or solid located within said reaction system, and a catalyst in a reducing atmosphere, where said reaction system is first heated to a temperature which is equal to or above the whisker growth temperature, where said growth temperature is within a range of from about 1350°C to about 1500°C, and where said reaction system is cooled to a temperature which is equal to or below said growth temperature, in order to induce nucleation at catalyst sites, before said reaction system is held at said growth temperature for the growth period.
2. The method of Claim 1 wherein said reducing atmosphere is a hydrogen atmosphere.
3. The method of Claim 1 wherein said carbon source before whisker growth includes a graphite substrate.
4. The method of Claim 1 wherein said silicon source is an SiO2 and carbon powder mixture.
5. The method of Claim 1 wherein said catalyst comprises one or more of the following metals: manganese, cobalt, nickel, iron, chromium and silicon.
6. The method of Claim 1 wherein said reaction system is cooled 150°C below the growth temperature, before the growth period.
7. The method of Claim 1 wherein said reaction system is heated up to 100°C beyond the growth temperature before the growth period.
8. The method of Claim 1 wherein said .beta. silicon carbide whiskers are grown by the vapor-liquid-solid mechanism.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/839,302 US4702901A (en) | 1986-03-12 | 1986-03-12 | Process for growing silicon carbide whiskers by undercooling |
| US839,302 | 1986-03-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1274967A true CA1274967A (en) | 1990-10-09 |
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ID=25279370
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000531442A Expired - Fee Related CA1274967A (en) | 1986-03-12 | 1987-03-06 | Process for growing silicon carbide whiskers by undercooling |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4702901A (en) |
| JP (1) | JPS62230700A (en) |
| CA (1) | CA1274967A (en) |
| DE (1) | DE3707832A1 (en) |
| FR (1) | FR2595720B1 (en) |
| GB (1) | GB2190908B (en) |
| IT (1) | IT1204918B (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH02137799A (en) * | 1988-11-18 | 1990-05-28 | Shin Etsu Chem Co Ltd | Production of silicon carbide whisker |
| US5037626A (en) * | 1988-11-22 | 1991-08-06 | Union Oil Company Of California | Process for producing silicon carbide whiskers using seeding agent |
| US5404836A (en) * | 1989-02-03 | 1995-04-11 | Milewski; John V. | Method and apparatus for continuous controlled production of single crystal whiskers |
| US5055276A (en) * | 1989-11-15 | 1991-10-08 | Huckins Harold A | Ceramic whisker growing system |
| AU5436596A (en) * | 1995-03-31 | 1996-10-16 | Hyperion Catalysis International, Inc. | Carbide nanofibrils and method of making same |
| KR100806999B1 (en) * | 2004-12-28 | 2008-02-25 | 마쯔시다덴기산교 가부시키가이샤 | METHOD FOR PRODUCING SILICON CARBIDESiC SINGLE CRYSTAL AND SILICON CARBIDESiC SINGLE CRYSTAL OBTAINED BY SUCH METHOD |
| KR101009373B1 (en) | 2009-06-04 | 2011-01-19 | 한국에너지기술연구원 | Preparation method of silicon carbide thick film and silicon carbide thick film prepared using the method |
| KR101897020B1 (en) * | 2011-12-26 | 2018-09-12 | 엘지이노텍 주식회사 | Silicon carbide powder, method for manufacturing the same and silicon carbide sintered body, method for manufacturing the same |
| DE102015100062A1 (en) * | 2015-01-06 | 2016-07-07 | Universität Paderborn | Apparatus and method for producing silicon carbide |
| CN106048728B (en) * | 2016-06-28 | 2018-06-26 | 山东天岳晶体材料有限公司 | A kind of method of growing high quality silicon carbide whisker |
| CN113564687B (en) * | 2021-08-24 | 2022-07-22 | 安徽工业大学 | Chromium-catalyzed silicon carbide whisker and preparation method thereof |
| CN115724689B (en) * | 2022-11-21 | 2023-05-26 | 景德镇陶瓷大学 | Low-temperature in-situ synthesis method of silicon carbide whisker coated surface modified cordierite honeycomb ceramic and product prepared by same |
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|---|---|---|---|---|
| CA608032A (en) * | 1960-11-01 | L. Berry Kenneth | Process for preparing corundum | |
| US3011912A (en) * | 1959-12-22 | 1961-12-05 | Union Carbide Corp | Process for depositing beta silicon carbide |
| US3053635A (en) * | 1960-09-26 | 1962-09-11 | Clevite Corp | Method of growing silicon carbide crystals |
| US3246950A (en) * | 1961-01-03 | 1966-04-19 | Monsanto Co | Method of preparing fibrous silicon carbide |
| DE1187591B (en) * | 1961-09-08 | 1965-02-25 | Degussa | Process for the production of silicon carbide or mixtures containing it |
| US3161473A (en) * | 1962-06-06 | 1964-12-15 | Corning Glass Works | Method of making beta-silicon carbide fibers |
| US3230053A (en) * | 1962-09-05 | 1966-01-18 | Noel T Wakelyn | Apparatus for producing high purity silicon carbide crystals |
| US3236780A (en) * | 1962-12-19 | 1966-02-22 | Gen Electric | Luminescent silicon carbide and preparation thereof |
| US3346414A (en) * | 1964-01-28 | 1967-10-10 | Bell Telephone Labor Inc | Vapor-liquid-solid crystal growth technique |
| US3275415A (en) * | 1964-02-27 | 1966-09-27 | Westinghouse Electric Corp | Apparatus for and preparation of silicon carbide single crystals |
| GB1039748A (en) * | 1964-07-25 | 1966-08-24 | Ibm | Improvements relating to methods of growing silicon carbide crystals epitaxially |
| US3391681A (en) * | 1965-12-29 | 1968-07-09 | Du Pont | Preparation of aluminum and chromium sesquioxide fibers |
| US3653851A (en) * | 1966-04-04 | 1972-04-04 | Monsanto Co | High-strength metal-silicon carbide article |
| NL133589C (en) * | 1966-09-15 | 1900-01-01 | ||
| NL6615376A (en) * | 1966-11-01 | 1968-05-02 | ||
| US3493431A (en) * | 1966-11-25 | 1970-02-03 | Bell Telephone Labor Inc | Vapor-liquid-solid crystal growth technique |
| 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. |
| US3520740A (en) * | 1967-05-18 | 1970-07-14 | Gen Electric | Method of epitaxial growth of alpha silicon carbide by pyrolytic decomposition of a mixture of silane,propane and hydrogen at atmospheric pressure |
| US3622272A (en) * | 1968-04-01 | 1971-11-23 | Gen Technologies Corp | Method of growing silicon carbide whiskers |
| US3840647A (en) * | 1969-01-24 | 1974-10-08 | Suwa Seikosha Kk | Method for producing whiskers |
| GB1280506A (en) * | 1969-08-29 | 1972-07-05 | Laporte Industries Ltd | Refractory compounds |
| AU1903770A (en) * | 1969-08-29 | 1972-02-24 | Laporte Industries Limited | Refractory compounds |
| GB1280648A (en) * | 1969-08-29 | 1972-07-05 | Laporte Industries Ltd | Refractory compounds |
| SE377108B (en) * | 1970-03-27 | 1975-06-23 | Kanegafuchi Spinning Co Ltd | |
| JPS50115197A (en) * | 1974-02-21 | 1975-09-09 | ||
| US4100233A (en) * | 1975-04-25 | 1978-07-11 | The Research Institute For Iron, Steel And Other Metals Of The Tohoku University | Silicon carbide fibers having a high strength and a method for producing said fibers |
| US4349407A (en) * | 1979-05-09 | 1982-09-14 | The United States Of America As Represented By The United States Department Of Energy | Method of forming single crystals of beta silicon carbide using liquid lithium as a solvent |
| JPS6044280B2 (en) * | 1982-02-25 | 1985-10-02 | 東海カ−ボン株式会社 | Method for producing silicon carbide whiskers |
| JPS6052120B2 (en) * | 1982-06-04 | 1985-11-18 | タテホ化学工業株式会社 | Silicon carbide manufacturing method |
| US4513030A (en) * | 1982-06-18 | 1985-04-23 | The United States Of America As Represented By The United States Department Of Energy | Method of producing silicon carbide articles |
-
1986
- 1986-03-12 US US06/839,302 patent/US4702901A/en not_active Expired - Fee Related
-
1987
- 1987-03-05 GB GB8705101A patent/GB2190908B/en not_active Expired
- 1987-03-06 CA CA000531442A patent/CA1274967A/en not_active Expired - Fee Related
- 1987-03-11 DE DE19873707832 patent/DE3707832A1/en not_active Withdrawn
- 1987-03-11 FR FR8703332A patent/FR2595720B1/en not_active Expired - Fee Related
- 1987-03-12 JP JP62057896A patent/JPS62230700A/en active Pending
- 1987-03-12 IT IT19669/87A patent/IT1204918B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| IT8719669A0 (en) | 1987-03-12 |
| US4702901A (en) | 1987-10-27 |
| GB2190908B (en) | 1989-11-08 |
| FR2595720B1 (en) | 1993-02-12 |
| FR2595720A1 (en) | 1987-09-18 |
| DE3707832A1 (en) | 1987-09-17 |
| JPS62230700A (en) | 1987-10-09 |
| GB2190908A (en) | 1987-12-02 |
| IT1204918B (en) | 1989-03-10 |
| GB8705101D0 (en) | 1987-04-08 |
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