Claims
- 1. A method for preparing a finely divided powder of silicon carbide which comprises pyrolyzing a vaporizable organosilicon compound having, in a molecule, two to four silicon atoms and at least one hydrogen atom directly bonded to at least one of said silicon atoms, said molecule having no oxygen or halogen atom directly bonded to said silicon atoms and said pyrolysis being carried out at a temperature of 750.degree. C. or higher in the vapor phase.
- 2. The method as claimed in claim 1 wherein the vaporizable organosilicon compound is an organopolysilane compound represented by the general formula R.sub.2n+2 Si.sub.n, in which R is a hydrogen atom or a monovalent hydrocarbon group, at least one but not all of the groups denoted by the symbol R being a hydrogen atom, and n is a positive integer of 2 to 4 inclusive.
- 3. The method as claimed in claim 1 wherein the vaporizable organosilicon compound is a silhydrocarbylene compound represented by the general formula R.sub.3 Si--R.sup.1 --SiR.sub.2).sub.m R, in which R is a hydrogen atom or a monovalent hydrocarbon group, R.sup.1 is a hydrocarbylene group and m is a positive integer of 1 or 2.
- 4. The method as claimed in claim 1 wherein the vaporizable organosilicon compound in the vapor phase is diluted with a reducing gas or an inert gas.
- 5. A method for preparing a finely divided powder of silicon carbide which comprises pyrolyzing a vaporizable liquid consisting essentially of an organosilicon compound having two to four silicon atoms and at least one hydrogen atom directly bonded to at least one of said silicon atoms, said silicon atoms being devoid of oxygen or halogen atoms directly bonded thereto, said pyrolysis being carried out at a temperature of 750.degree. C. or higher in the vapor phase.
- 6. The method as claimed in claim 5 wherein the vaporizable organosilicon compound is an organopolysilane compound represented by the general formula R.sub.2n+2 Si.sub.n, in which R is a hydrogen atom or a monovalent hydrocarbon group, at least one but not all of the groups denoted by the symbol R being a hydrogen atom, and n is a positive integer of 2 to 4 inclusive.
- 7. The method as claimed in claim 5 wherein the vaporizable organosilicon compound is a silhydrocarbylene compound represented by the general formula R.sub.3 Si--R.sup.1 --SiR.sub.2).sub.m R, in which R is a hydrogen atom or a monovalent hydrocarbon group, R.sup.1 is a hydrocarbylene group and m is a positive integer of 1 or 2.
- 8. The method as claimed in claim 5 wherein the vaporizable organosilicon compound in the vapor phase is diluted with a reducing gas or an inert gas.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 57-147342 |
Aug 1982 |
JPX |
|
BACKGROUND OF THE INVENTION
This is a continuation-in-part application from a copending U.S. application Ser. No. 525,290 filed Aug. 22, 1983 abandoned.
The present invention relates to a method for the preparation of a fine powder of silicon carbide or, more particularly, to a method for the preparation of a fine powder of silicon carbide by the vapor-phase pyrolysis of an organosilicon compound.
As is known, silicon carbide in a finely divided powdery form is a very promising material for the preparation of a sintered ceramic body highly resistant to heat and chemicals. It is essential that the silicon carbide powder has a purity as high as possible and a fine particle size distribution in the so-called submicron range in order that the sintered ceramic body thereof may have excellent performance as desired.
Several methods differing in principle have been proposed for the preparation of a silicon carbide powder suitable as a material for the sintered ceramic bodies of silicon carbide by satisfying the above mentioned requirements in the purity and particle size distribution including (1) a method in which so-called metallic silicon is reacted with carbon at a high temperature in an electric furnace and the thus obtained silicon carbide is finely pulverized, (2) a method of high-temperature vapor-phase pyrolysis of silane SiH.sub.4 or a chlorine-containing silane, e.g. an organochlorosilane or trichlorosilane SiHCl.sub.3, admixed, if necessary, with a hydrocarbon compound such as methane to deposit a fine powder of silicon carbide, (3) a method of pyrolyzing a high-polymeric polycarbosilane and (4) a method in which a powdery mixture of silicon dioxide SiO.sub.2 and carbon is heated at a high temperature.
Each of these methods has its own advantages and disadvantages and none of them is quite satisfactory when industrial production of such a silicon carbide powder is desired. For example, the first method of the pulverization of silicon carbide is, although this method is suitable for the preparation of a powder of .alpha.-SiC, industrially very disadvantageous due to the extreme hardness of silicon carbide which necessarily makes the process of pulverization very expensive in addition to the difficulties in obtaining a finely pulverized powder in the submicron range in a high yield without contamination. The second method is, even by setting aside the problem of the extremely high temperature for the pyrolysis, disadvantageous due to the relatively low yield of the powdery silicon carbide, which is crystallographically the .beta.-SiC. In addition, when the starting silane compound subjected to the pyrolysis is a chlorine-containing silane, the resultant silicon carbide powder always cannot be free from a trace amount of chlorine as an impurity which adversely affects the properties of the sintered body of silicon carbide. Disposal of the hydrogen chloride formed by the pyrolysis of the chlorine-containing silane as a byproduct is also a difficult matter. The silane SiH.sub.4 as an alternative starting compound in the second method is a very dangerous material and must be handled with utmost care to avoid hazardous explosion. Moreover, the quite large difference in the velocity of pyrolysis between this silane and the hydrocarbon compound admixed therewith may sometimes lead to the formation of a cluster-like mixture of elementary silicon and free carbon produced separately from the respective starting compounds. Further, the third method has a problem of the expensiveness of the polycarbosilane which is produced in a complicated process in addition to the relatively low purity and relatively coarse particle size distribution of the resultant silicon carbide necessitating troublesome and expensive post-treatment. The fourth method is disadvantageous due to the extremely high reaction temperature in addition to the problem of low purity of the product which may contain elementary silicon as a byproduct besides the unreacted starting materials also necessitating expensive post-treatment.
An object of the present invention is therefore to provide a novel and improved method for the preparation of a finely divided powder of silicon carbide free from the above described problems in the prior art methods.
The method for the preparation of a finely divided powder of silicon carbide provided by the present invention comprises pyrolyzing a vaporizable organosilicon compound having at least two silicon atoms in a molecule or, in particular, a polysilane compound represented by the general formula R.sub.2n+2 Si.sub.n, in which n is a positive integer of 2, 3 or 4 and each R is a hydrogen atom or a monovalent hydrocarbon group, at least one but not all of the groups denoted by R in a molecule being a hydrogen atom, at a temperature of 750.degree. C. or higher in the vapor phase. The above given general formula and definitions of the symbols prerequisitely exclude an oxygen or halogen atom directly bonded to the silicon atom.
US Referenced Citations (6)
Foreign Referenced Citations (3)
| Number |
Date |
Country |
| 592456 |
Feb 1960 |
CAX |
| 1047180 |
Dec 1958 |
DEX |
| 7900178 |
Apr 1979 |
WOX |
Continuation in Parts (1)
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Number |
Date |
Country |
| Parent |
525290 |
Aug 1983 |
|
Patent Grant
4676966
