JP2553371B2 - Method for producing composite of silicon nitride and carbon - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a composite of silicon nitride and carbon, in particular, by decomposing silicon carbide in silicon carbide powder, silicon carbide whiskers or silicon carbide fibers. The present invention relates to a method for producing a composite of silicon nitride and carbon by producing silicon nitride and carbon.

[Conventional technology]

Conventionally, there has been no proposal at all as a method for producing a composite of silicon nitride and carbon of this type, other than a method of coating the surface of silicon nitride fiber with carbon by chemical vapor deposition to form a composite.

[Problems to be Solved by the Invention]

However, this has the drawback that it is difficult to control the thickness of the carbon coating and is not suitable for mass production.
In addition, there is a drawback that powdery composites of silicon nitride and carbon or whisker composites cannot be produced at all, and by combining silicon nitride powders, silicon nitride whiskers or silicon carbide fibers, properties such as material strengthening ability cannot be improved. There was a flaw.

Therefore, the present invention provides a method for producing a composite of silicon nitride and carbon in order to solve these drawbacks.

[Means for solving the problem]

In order to solve the above problems, a method for producing a composite of silicon nitride and carbon according to the present invention is to decompose silicon nitride in a silicon carbide powder, a silicon carbide whisker or a silicon carbide fiber having a purity of 50% by weight or more to nitride the silicon carbide. It is characterized by including a decomposition step for producing silicon and carbon.

The decomposition step is preferably accomplished by heating to a temperature of 1200 ° C. or higher in an atmosphere having a nitrogen partial pressure of 100 atm or higher and performing a hot isostatic pressing process.

[Work]

The method for producing a composite of silicon nitride and carbon according to the present invention comprises a silicon carbide powder having a purity of 50% by weight or more, a silicon carbide whisker or silicon carbide in a silicon carbide fiber, which is decomposed in a decomposition step to obtain silicon nitride and Since carbon is produced, it has the function of directly compounding silicon nitride powder, silicon nitride whiskers or silicon nitride fibers with carbon, and in turn produces silicon nitride powder, silicon nitride whiskers or silicon nitride fibers in large quantities and at low cost. In addition, the size of the silicon carbide powder, the silicon carbide whiskers or the silicon carbide fibers is preselected so that the size of the composite of silicon nitride and carbon can be adjusted appropriately.

〔Example〕

Hereinafter, an example of a method for producing a composite of silicon nitride and carbon according to the present invention will be described in detail.

Silicon carbide powder, silicon carbide whiskers or silicon carbide fibers having a purity of 50% by weight or more are prepared as starting materials. The size of the silicon carbide powder, the silicon carbide whiskers or the silicon carbide fibers may be appropriately selected as desired depending on the size of the composite of silicon nitride and carbon.

Silicon carbide Si ₃ N ₄ and carbon C are produced by completely decomposing silicon carbide SiC in the silicon carbide powder, silicon carbide whiskers or silicon carbide fibers as a starting material in the decomposition step. That is, by heating to a temperature of 1200 ° C or higher in an atmosphere having a nitrogen partial pressure of 100 atm or more and performing hot isostatic pressing, 3SiC + 2N ₂ → Si ₃ N ₄ + 3C silicon carbide powder, carbonization All of the silicon carbide SiC in the silicon whiskers or silicon carbide fibers is decomposed to form silicon nitride Si ₃ N ₄ and carbon C to form a composite of silicon nitride and carbon.

In other words, by continuing the above-mentioned decomposition process for a predetermined time, the starting raw material, that is, silicon carbide powder, silicon carbide whiskers or silicon carbide SiC in the silicon carbide fibers.
Can all be decomposed into silicon nitride Si ₃ N ₄ and carbon C, and thus silicon nitride powder, silicon nitride whiskers or silicon nitride fibers can be formed into a composite of silicon nitride and carbon, respectively.

In addition, one embodiment of the method for producing a composite of silicon nitride and carbon according to the present invention will be described in detail with specific numerical values for better understanding.

Example 1 Silicon carbide SiC in a silicon carbide powder having a purity of 95% by weight or more and an average particle size of 0.9 μ is heated to a temperature of 1700 ° C. in an atmosphere having a nitrogen partial pressure of 100 atm or more. The hot isostatic pressing process was carried out for 2 hours.

As a result, as shown in Table 1, all of the silicon carbide SiC in the silicon carbide powder was decomposed into silicon nitride Si ₃ N ₄ and carbon C, and a powdery composite of silicon nitride and carbon was formed.

The powdery composite of silicon nitride and carbon had a black surface, but when it was oxidized by heating to a temperature of 800 ° C. for 0.5 hour in the atmosphere, it became white or white-green.

After that, when the composition of the powdery composite of silicon nitride and carbon was analyzed, most of carbon C was oxidized and carbon dioxide CO
_It was removed as ₂ , and carbon C was reduced to 0.5% by weight. At this time, it is known that oxygen O ₂ in the atmosphere does not penetrate into the inside of the powdery composite of silicon nitride and carbon. Therefore, due to the change in the color of the surface, the oxidation of carbon C occurs on the surface. Therefore, it can be determined that carbon C was present near the surface.

Example 2 Example 1 was repeated except that the nitrogen partial pressure in the atmosphere in which the hot isostatic pressing was performed was 1000 atm and the temperature at that time was 1450 ° C.

The results at this time are shown in Table 1, and as in Example 1, all of the silicon carbide SiC in the silicon carbide powder was decomposed into silicon nitride Si ₃ N ₄ and carbon C. A powdered composite of carbon was produced.

Comparative Example 1 Example 1 was repeated except that the nitrogen partial pressure in the atmosphere in which the hot isostatic pressing was performed was 9 atm, the temperature at that time was 1770 ° C., and the time was 10 hours. Was repeated.

The results at this time are shown in Table 1, but unlike Example 1, silicon carbide SiC in the silicon carbide powder was not decomposed into silicon nitride Si ₃ N ₄ and carbon C at all.

Comparative Examples 2 and 3 The temperature in the atmosphere in which the hot isostatic pressing was performed was
1250 ° C and 1450 ° C, and time is 4 hours and 2
Example 1 was repeated, except at the times indicated.

The results at this time are shown in Table 1, but unlike in Example 1, silicon carbide SiC in the silicon carbide powder was hardly decomposed into silicon nitride Si ₃ N ₄ and carbon C at all.

Comparative Examples 4 and 5 The temperature in the atmosphere in which the hot isostatic pressing was performed was
1200 ° C and 1350 ° C, and time is 4 hours and 2
Example 2 was repeated in each case, except at the times indicated.

The results at this time are shown in Table 1, but unlike Example 2, the silicon carbide SiC in the silicon carbide powder was hardly decomposed into silicon nitride Si ₃ N ₄ and carbon C.

Example 3 Silicon carbide SiC in a silicon carbide whisker having a purity of 95% by weight or more and an average outer diameter and an average length of 0.5 μ and 20 μ, respectively, was subjected to 1700 in an atmosphere having a nitrogen partial pressure of 100 atm or more. Hot isostatic pressing was carried out for 2 hours with heating to a temperature of ° C.

As a result, all of the silicon carbide SiC in the silicon carbide whiskers was decomposed into silicon nitride Si ₃ N ₄ and carbon C, as shown in Table 2, and a whisker composite of silicon nitride and carbon was produced.

The silicon nitride and carbon whisker composite had a black surface, but when it was oxidized by heating to a temperature of 800 ° C. for 0.5 hours in the atmosphere, it became white or white-green.

After that, when the composition of the silicon nitride and carbon whisker composite was analyzed, most of the carbon C was oxidized and carbon dioxide was
It was removed as CO ₂ and carbon C was reduced to 0.5% by weight. At this time, it is known that oxygen O ₂ in the atmosphere does not penetrate into the inside of the whisker composite of silicon nitride and carbon. Therefore, due to the change in the color of the surface, oxidation of carbon C occurs on the surface. Therefore, it can be judged that carbon C was present near the surface.

Example 4 Example 3 was repeated except that the nitrogen partial pressure in the atmosphere in which the hot isostatic pressing was performed was 1000 atm and the temperature at that time was 1450 ° C.

The results at this time are shown in Table 2, and like Example 3, the silicon carbide SiC in the silicon carbide whiskers was all decomposed into silicon nitride Si ₃ N ₄ and carbon C, and thus silicon nitride and A carbon whisker composite was formed.

Comparative Example 6 Example 3 was repeated except that the nitrogen partial pressure in the atmosphere in which the hot isostatic pressing was performed was 9 atm, the temperature at that time was 1770 ° C., and the time was 10 hours. Was repeated.

The results at this time are shown in Table 2, and unlike Example 3, the silicon carbide SiC in the silicon carbide whiskers was not decomposed into silicon nitride Si ₃ N ₄ and carbon C at all.

Comparative Examples 7 and 8 The temperature in the atmosphere in which the hot isostatic pressing treatment was performed was
1250 ° C and 1450 ° C, and time is 4 hours and 2
Example 3 was repeated, except at the times indicated.

The results at this time are shown in Table 2, but unlike in Example 3, silicon carbide SiC in the silicon carbide whiskers was hardly decomposed into silicon nitride Si ₃ N ₄ and carbon C.

Comparative Examples 9 and 10 The temperature in the atmosphere in which the hot isostatic pressing treatment was performed was
1350 ° C and 1450 ° C and time is 4 hours and 2
Example 4 was repeated, except at the times indicated.

The results at this time are shown in Table 2, but unlike in Example 4, silicon carbide SiC in the silicon carbide whiskers was hardly decomposed into silicon nitride Si ₃ N ₄ and carbon C.

Example 5 In a silicon carbide fiber having a purity of 50% by weight or more, an average outer diameter of 15 μ and an average length of 10 cm by cutting (silicon carbide fiber “Nicalon” manufactured by Nippon Carbon Co., Ltd.) The silicon carbide SiC is heated to a temperature of 1700 ° C. in an atmosphere having a partial pressure of nitrogen of 100 atm or more and subjected to hot isostatic pressing by 2
Ran over time.

As a result, all the silicon carbide SiC in the silicon carbide fiber was decomposed into silicon nitride Si ₃ N ₄ and carbon C, as shown in Table ₃ , to produce a fibrous composite of silicon nitride and carbon.

The silicon nitride and carbon fibrous composite had a black surface, but when it was oxidized by heating to a temperature of 800 ° C. for 0.5 hours in the atmosphere, it became white or white-green.

After that, when the composition of the fibrous composite of silicon nitride and carbon was analyzed, most of carbon C was oxidized and carbon dioxide CO
_It was removed as ₂ , and carbon C was reduced to 0.5% by weight. At this time, it is known that oxygen O ₂ in the atmosphere does not penetrate into the inside of the fibrous composite of silicon nitride and carbon, so the oxidation of carbon C occurs on the surface due to the change in the color of the surface. Therefore, it can be determined that carbon C was present near the surface.

Example 6 Example 5 was repeated except that the nitrogen partial pressure in the atmosphere in which the hot isostatic pressing was performed was 1000 atm and the temperature at that time was 1450 ° C.

The results at this time are shown in Table 3, and as in Example 5, the silicon carbide SiC in the silicon carbide fiber was entirely decomposed into silicon nitride Si ₃ N ₄ and carbon C, and thus silicon nitride and A fibrous composite of carbon was produced.

Comparative Example 11 Example 5 was repeated except that the nitrogen partial pressure in the atmosphere in which the hot isostatic pressing was performed was 9 atm, the temperature at that time was 1770 ° C., and the time was 10 hours. Was repeated.

The results at this time are shown in Table 3, and unlike Example 5, silicon carbide SiC in the silicon carbide fiber was not decomposed into silicon nitride Si ₃ N ₄ and carbon C at all.

Comparative Examples 12 and 13 The temperature in the atmosphere in which the hot isostatic pressing was performed was
1250 ° C and 1450 ° C, and time is 4 hours and 2
Example 5 was repeated, except at the times indicated.

The results at this time are shown in Table 3, and unlike Example 5, silicon carbide SiC in the silicon carbide fiber was hardly decomposed into silicon carbide Si ₃ N ₄ and carbon C.

Comparative Examples 14 and 15 The temperature in the atmosphere in which the hot isostatic pressing was performed was
1200 ° C and 1350 ° C, and time is 4 hours and 2
Example 6 was repeated, except at the times indicated.

The results at this time are shown in Table 3, but unlike in Example 6, the silicon carbide SiC in the silicon carbide fiber was hardly decomposed into silicon nitride Si ₃ N ₄ and carbon C.

〔The invention's effect〕

As is apparent from the above, the method for producing silicon nitride and carbon according to the present invention is to decompose silicon carbide in silicon carbide powder, silicon carbide whiskers or silicon carbide fibers having a purity of 50% by weight or more to decompose silicon nitride and carbon. Since it includes a decomposition step for producing (i), it has an effect of directly producing a composite of silicon nitride and carbon from silicon carbide powder, silicon carbide whiskers or silicon carbide fibers.
i) At the same time, it has the effect of inexpensively producing a large amount of a composite of silicon nitride and carbon, and at the same time, (iii) silicon carbide powder,
By selecting the size of the silicon carbide whisker or the silicon carbide fiber in advance, the size of the composite of silicon nitride and carbon can be adjusted appropriately.

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Claims (2)

(57) [Claims] 1. A silicon carbide powder having a purity of 50% by weight or more,
A method for producing a composite of silicon nitride and carbon, comprising a decomposition step of decomposing silicon carbide in silicon carbide whiskers or silicon carbide fibers to produce silicon nitride and carbon. 2. The decomposition step is accomplished by heating to a temperature of 1200 ° C. or higher in an atmosphere having a nitrogen partial pressure of 100 atm or higher and performing hot isostatic pressing. A method for producing a composite of silicon nitride and carbon according to claim 1.