JPS5823327B2 - Method for producing β-type silicon carbide powder - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for producing β-type silicon carbide powder.

Silicon carbide is attracting attention as a promising heat-resistant ceramic material due to its high high-temperature strength and excellent heat and corrosion resistance.

Since these silicon carbide sintered bodies are made by powder metallurgy, it is desirable that the silicon carbide powder used as a raw material be fine and highly active.

One method for synthesizing silicon carbide is to reduce silicon oxide with carbon and carbonize it.

β-type silicon carbide, which is generally produced at temperatures below 1600°C, is called a low-temperature type, and is more likely to be fine and active than α-type silicon carbide, which is produced at higher temperatures.

However, since the synthesis of these β-type silicon carbides is generally possible only at relatively low temperatures, it has not been possible to increase the yield sufficiently during production.

(Usually, β-type silicon carbide transforms to α-type at high temperatures of 1,600°C to 1,700°C or higher.

) With the aim of obtaining β-type silicon carbide in high yield, the present inventors conducted various investigations into the effects of various trace additives on silicon carbide synthesis, and as a result, completed the method of the present invention.

The feature of the present invention is that iron, cobalt or nickel or their oxides are added to silicon oxide in a non-oxidizing state by adding 0.5 mol% to 3 mol% of iron, cobalt and nickel to the silicon oxide mixture. 130 in atmosphere
According to the method of the present invention, which involves heating in a temperature range of 0°C to 1600°C, fine powder of β-type silicon carbide can be obtained in a high yield.

It is thought that these additives, even those added as oxides, are reduced to metals during carbonization.

Although the details of the behavior of these additives during the reaction are not clear, as will be described in detail in the Examples section below, there are no products to which iron, cobalt, nickel, or their oxides are added by the method of the present invention. The production rate of β-type silicon carbide was 2 to 3 times higher than that of the additive.

When adding 3 mol% or more, no effect is observed by increasing the amount of addition, and the amount of these additives is 3 mol% of iron, cobalt: or nickel relative to silicon oxide.
It has been found that the following is sufficient.

In the method of the present invention, the heating temperature is 1300°C to 1600°C.
℃ because, as is well known, above 1600°C, fine β-type silicon carbide cannot be obtained, and below 1300°C the yield of silicon carbide is not sufficient.

The method of the present invention will be explained in more detail below with reference to Examples.

Example 1 Reagent silicic acid anhydride powder and carbon black in a weight ratio of 1:1
After adding a predetermined amount of reagent ferric oxide powder, the mixture was mixed in a wet ball mill for 4 hours, and then dried.

Next, the mixture 41 was placed in a carbon tube, heated to 1500° C. in a vacuum furnace, and held for 2 hours to synthesize silicon carbide.

The product was cooled in the furnace to room temperature, then taken out and placed in air at 650°C.
After roasting for 2 hours to remove excess carbon, 35%
Repeated treatment with hydrofluoric acid to dissolve and remove unreacted silicon oxide and other impurities, and further
The mixture was roasted at ℃ for 2 hours to obtain silicon carbide powder.

For comparison, silicon carbide was synthesized using the same process without adding iron oxide.

All powders obtained as a result of X-ray diffraction were β-type silicon carbide.

FIG. 1 shows a photograph of the appearance of silicon carbide powder obtained when 1.7 mol % of ferric oxide was added to silicon oxide as iron.

The resulting powder has a fine and irregular shape.

Next, the production rate of silicon carbide was calculated from the weight of the obtained powder.

Note that the production rate is expressed as the amount of silicon carbide after carbonization relative to silicon oxide before carbonization, expressed as a molar ratio.

The results are shown by white circles in FIG.

The horizontal axis in FIG. 2 is the amount of iron, cobalt, or nickel added to silicon oxide, and the vertical axis is the production rate of silicon carbide.

As is clear from FIG. 2, the production rate of silicon carbide is greatly improved by adding 0.5 molar or more iron to silicon oxide.

It is also clear that addition of iron in an amount of 3 mol or more does not have the effect of adding a large amount, and that addition of iron of 3 mol or less is sufficient.

Example 2 Reagent silicic acid anhydride powder and carbon black in a weight ratio of 1:
After adding a predetermined amount of nickel oxide powder obtained by thermally decomposing the reagent nickel hydroxide, the mixture was treated in the same manner as in Example 1 to synthesize silicon carbide.

FIG. 3 shows the X-ray diffraction pattern of the obtained powder.

All of the obtained powders were β-type silicon carbide.

FIG. 4 shows a photograph of the appearance of silicon carbide powder obtained by adding 2.2 mol% of nickel to silicon oxide.

The powder is fine and some whisker-like crystals are observed.

The relationship between the amount added and the production rate is shown in FIG. 2 by the hatched circle.

The product to which nickel was added showed a production rate 2 to 3 times higher than that without the addition of nickel.

Example 3 Test silicic acid anhydride powder and carbon black in a weight ratio of 1:
After adding cobalt oxide powder obtained by thermally decomposing cobalt carbonate to a ratio of 3 molar cobalt to silicon oxide, the same treatment as in Example 1 was carried out to obtain silicon carbide. performed the synthesis.

The obtained powder was β-type silicon carbide as shown in FIG.

FIG. 5 shows a photograph of the appearance of the obtained powder.

The production rate of silicon carbide is shown by the black circle in Figure 2.

The product to which cobalt was added showed a production rate more than three times higher than that without the addition of cobalt.

As is clear from the Examples above, according to the method of the present invention, β-type silicon carbide can be synthesized easily and in high yield.

Further, the effects of iron, cobalt, and nickel on the silicon carbide production rate were all approximately the same.

In carrying out the present invention, silicate minerals that already contain the above-mentioned additive metal in their natural state can also be used as silicon raw materials.

[Brief explanation of drawings]

1 to 5 show graphs, powder appearance photographs, or X-ray diffraction patterns showing the results of Examples 1 to 3.

Claims (1)

[Claims] 1. Iron, cobalt or nickel or their oxides are added to a mixture of silicon oxide and carbon at 0.5 mol% as iron, cobalt and nickel, respectively, to 3 mol% silicon oxide, and non-oxidized In a sexual atmosphere. 1. A method for producing β-type silicon carbide powder, which comprises heating in a temperature range of 1300°C to 1600°C.