JPS5950617B2 - Method for producing silicon nitride-silicon carbide composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Since silicon nitride has superior heat resistance and spalling resistance compared to conventional semilac materials, it has attracted much interest as a structural material for engines, turbines, and the like.

The reason for this is that silicon nitride has a lower coefficient of expansion than other ceramic materials, but there is a desire for a material that has even better thermal shock resistance even in harsher usage environments.

In order to meet this demand, the present inventor conducted various studies in an attempt to improve the physical properties of silicon nitride sintered bodies.

According to the results, it appears that the spalling resistance of a sintered body can be further improved by adding silicon nitride to silicon carbide, which has high thermal conductivity. Even if a sintered body is produced by simply mechanically mixing, local uneven distribution of the components is unavoidable, and the constituent components of the sintered body become uneven, causing an imbalance in the structure, which is not preferable.

Therefore, the present inventor aimed to make the silicon carbide component uniformly exist in the silicon nitride ml fiber, and when heat-treating silica powder in the presence of carbon powder, carbon monoxide coexists in nitrogen to cause sintering. Various studies were conducted on the method.

Next, the experimental results will be explained.

Approximately 1 g of amorphous silica powder (average particle size 10 μm) mixed with 30% by weight of carbon black (average particle size 2 μm) inside was charged into a furnace and heated to 1500°C while being heated with nitrogen or nitrogen. The mixture was heated for 60 minutes while passing a mixed gas of carbon monoxide and carbon monoxide in the ratio shown in Table 1 at a rate of 450 ml/min to obtain the products shown in Table 1.

From the above results, it was confirmed that if a mixed gas of nitrogen and carbon monoxide (CO amount 2 to 8% by weight) is aerated, a product containing only silicon nitride and silicon carbide without containing silicon oxynitride or cristobalite can be obtained. It was done.

Next, in order to determine the physical properties of the products of experiment numbers 1.3.4 and 5 obtained in the above experiments, Al2O
3 was added in an amount of 5% by weight, molded under a molding pressure of 2000 kg/cm2, and then sintered at 1700°C to prepare a test sample.
These physical properties were measured and the results shown in Table 2 were obtained.

For comparison, Table 2 shows 85% by weight of silicon nitride powder (particle size: 5μ) and silicon carbide powder (particle size: 3μ).
) and 15% by weight were mechanically mixed and sintered under the same conditions as above, and the physical properties of a test sample were also shown as a comparative example.

Note (1) The * mark was determined at the temperature at which cracks were first observed in the sintered body when the heated sample was placed in water.

Note (2) When the sintered cut surface was observed using an optical microscope, it was found that silicon nitride and silicon carbide were evenly present in the samples of Experiment Nos. 3, 4, and 5 compared to those of the comparative example.

From the results in Table 2, a mixed gas of nitrogen and carbon monoxide (C
Experiment Nos. 3 and 4 in which a product consisting only of silicon nitride and silicon carbide obtained by aerating O (2 to 8% by weight) was sintered.
It was observed that the sintered product exhibited particularly excellent physical properties compared to the sintered product of Experiment No. 1, which was obtained by sintering a product containing 100% silicon nitride.

The present invention is based on these experimental results, and the mixture of silica powder and carbon powder is heated to 1350 to 1600°C.
A mixed gas of nitrogen and carbon monoxide (N2:C
This is a method for producing a silicon nitride-silicon carbide composition, which is characterized by aerating O at a weight ratio of 98 to 92:2 to 8).

In the present invention, as silica, naturally occurring high-purity silica stone, silica sand, or amorphous silica by-produced from various industries are used. Among these, it is preferable to use amorphous silica, and its particle size is The finer the details, the better the reactivity, but
It is usually preferable to use particles with an average particle size of 10 μm or less.

Further, as the carbon powder, powders of general carbon, graphite, etc. are used, but it is preferable to use carbon black from the viewpoint of high purity.

The mixing ratio of silica powder and carbon powder is preferably in the range of 28 to 35% by weight of the carbon powder inside.

In the present invention, a mixture of silica powder and carbon powder is heated at a high temperature while nitrogen is passed through it to produce less than half the amount of silicon nitride, and then a gas containing carbon monoxide mixed in nitrogen is passed through the mixture to form silicon nitride and It is also possible to simultaneously generate silicon carbide and create a homogeneous composition of silicon nitride and silicon carbide, but it is also possible to heat a mixture of silica powder and carbon powder at a high temperature and mix nitrogen and carbon monoxide in a specific ratio. A silicon nitride-silicon carbide composition can also be produced by passing the gas.

However, the latter method is preferred when producing a silicon nitride-silicon carbide composition of a specific ratio.

According to the present invention, a composition in which silicon nitride and silicon carbide are homogeneous and have a predetermined composition can be produced very easily from silica powder and carbon powder by high-temperature heating, and a sintered body of this composition is Since it has high thermal shock resistance, its industrial value is great.

Example 1 70g of amorphous silica powder with an average particle size of 8μ and an average particle size of 2μ
30 g of carbon black was wet mixed in a bottle mill for 20 minutes, formed into pellets with a diameter of 2 to 3 mm, and loaded into an electric furnace. 6 at 1500℃ with ventilation
Heating for 0 minutes gave 51 g of product.

The mineral composition of the product was examined by X-ray diffraction and found to be silicon nitride 8.
7% by weight, and 13% by weight of silicon carbide.

Example 2 The pellets were loaded into an electric furnace made in the same manner as in Example 1,
While heating to 1500°C, nitriding was carried out by flowing only nitrogen at a rate of 450 m1/min for the first 15 minutes, and after 15 minutes, the nitrogen aeration rate was increased to 420 m1/min, and carbon monoxide was mixed with this at 30 m1/min. The reaction was completed by aeration and subsequent heating for 45 minutes.

When the mineral composition of the obtained product was investigated by X-ray diffraction, it was found that
It had a uniform composition consisting of 79% by weight of silicon nitride and 21% by weight of silicon carbide.

Claims (1)

[Claims] 1. Mixture of silica powder and carbon powder at 1350~
A method for producing a silicon nitride-silicon carbide composition, which comprises heating to 1600° C. and passing a mixed gas of nitrogen and carbon monoxide (N2:CO weight ratio: 98-92:2-8).