JPS589788B2 - Manufacturing method of silicon nitride sintered body - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a silicon nitride sintered body.

Conventionally, silicon nitride sintered bodies are not sintered by silicon nitride itself, so sintering aids such as MgO, Al2O3, SiO
2. It is manufactured by appropriately mixing Y2O3, CO2O3, La2O3, etc., and sintering the mixture.

The silicon nitride sintered body obtained by this method does not contain silicon nitride as a single phase, but when its microstructure is observed with a scanning electron microscope, it shows a glass phase formed by the sintering aid at the silicon nitride grain interface. Or a crystalline phase is present.

Therefore, the excellent high-temperature heat resistance of silicon nitride is significantly degraded by the glass phase or crystalline phase present at the grain interface.

The present invention relates to a new manufacturing method that solves this problem, and its purpose is to provide a method for manufacturing a new silicon nitride sintered body that does not have the conventional glass phase or crystalline phase. be.

As a result of intensive research to achieve the above object, the present inventors pressure-molded a mixture of silicon nitride powder and an imide compound containing polysilane or a Si atom, or both compounds, and produced nitrogen, ammonia, or a mixture thereof. gas or N2
It has been found that an excellent silicon nitride sintered body can be obtained by sintering in a +H2 atmosphere.

The present invention was completed based on this knowledge.

The silicon nitride sintered body obtained by the method of the present invention becomes silicon nitride when polysilane or an imide compound containing Si atoms is sintered in an atmosphere of nitrogen, ammonia, a mixed gas of both, or N2+H2. , a single phase of silicon nitride.

This is essentially completely different from sintering using conventional sintering aids.

That is, the silicon nitride sintered body obtained by the method of the present invention does not have any glass phase or crystalline phase that is produced by the conventional method, and has a completely uniform structure.

Therefore, it is possible to obtain a sintered body that can fully exhibit the excellent characteristics inherent to silicon nitride.

In addition, conventionally, a pressure sintering method has been adopted as a general method for obtaining a high-density silicon nitride sintered body, but the method of the present invention does not require a pressure sintering method. It has the advantage that it can be easily obtained at the same time as sintering.

Examples of the polysilane include hydrogen compounds having 20 or more Si atoms.

Imide compounds containing Si atoms include Si2(NH)N2, Si2N3H2Cl, Si(NH
)2, Si2(NH)3, S120(NH)3, Si4
Examples include O2N2H5Cl2, Si8N10H11Cl5, and the like.

The mixing ratio of silicon nitride powder and polysilane or an imide compound containing Si atoms (a mixture thereof may also be used) is 99.9 to 50% by weight of silicon nitride powder to 0.1 to 0.1 to 0.1 to 0.1 to 50% by weight of polysilane or imide compound containing Si atoms. It is 5.0% by weight.

When the proportion of silicon nitride is large, a high-density sintered body is obtained, and when the proportion of silicon nitride is small, a low-density sintered body is obtained.

That is, the density of the silicon nitride sintered body can be controlled by the mixing ratio of both.

Both mixtures are pressurized at about 0.1 to 10 t/cm2.

The density of the silicon nitride sintered body can be controlled by this degree of pressure.

For example, when trying to obtain a sintered body with a low density, 0.1 to
1 t/cm2, 1 to 1 when trying to obtain a medium density sintered body
5t/cm2, if you want to obtain a high density sintered body, 5t/cm2.
Pressure is applied to ~30t/cm2.

The sintering temperature is preferably 1000 to 2000°C.

Polysilane or imide compounds containing Si atoms do not undergo nitriding reaction at temperatures lower than 1000°C;
When the temperature is exceeded, silicon nitride thermally decomposes and separates into silicon and nitrogen.

The atmosphere during sintering requires the presence of N2, NH3, a mixed gas thereof, or a mixed gas of N2+H2.

This atmospheric gas easily nitrides polysilane or imide compounds containing Si atoms, producing silicon nitride at the grain interface of silicon nitride particles, resulting in a so-called single-phase uniform silicon nitride sintered body. .

The gas pressure of the atmosphere is preferably 1 to 200 atmospheres.

1 to 10 atm when trying to obtain a low density sintered body, 1 to 50 atm when trying to obtain a medium density sintered body, and 1 to 200 atm when trying to obtain a high density sintered body. is appropriate.

Further, during this sintering, it is preferable that a mixed powder of silicon nitride and silicon oxide or silicon nitride powder be present around the pressure-formed sample.

This allows uniform heating of the sample and nitriding using nitriding gas, promoting sufficient nitriding to the inside of the sample, and preventing direct contact between the sample support box and the sample, preventing contamination from the support box. can be obtained.

The silicon nitride sintered body of the present invention obtained as described above has higher strength than the conventional silicon nitride sintered body mixed with a sintering aid and sintered, and the strength decreases at high temperatures. It has excellent properties with extremely low

The bending strength of the silicon nitride sintered body obtained by the conventional method (when mixed with 05% Mg) and the silicon nitride sintered body obtained by the method of the present invention and its change with temperature are as follows.

As the results show, the product of the present invention has high bending strength;
Moreover, the strength of the conventional type rapidly decreases when the temperature exceeds 1000℃, but the strength of the present invention exceeds 1000℃.
Even at 200°C, the strength decreases only slightly.

Furthermore, the sintered body obtained by the method of the present invention has an extremely excellent property of being about three times as oxidation resistant at high temperatures.

Example 1 5% by weight of polysilane (the same applies to imide compounds containing Si atoms) was mixed with silicon nitride powder, and the mixture was press-molded at 1 t/cm2.

This was normal pressure sintered in silicon nitride powder at 1750° C. for 2 hours in a 10 atm N2 gas atmosphere.

The obtained silicon nitride sintered body has a single phase and has a bulk specific gravity of 30
2. Bending strength at 1200℃ is 115kg/mm2
Met.

Example 2 20% by weight of polysilane was mixed with silicon nitride powder, and 0.
Pressure molding was performed at 1t/cm2.

The molded product is mixed with silicon nitride powder and silicon oxide in a molar ratio of 1:1.
The powder mixed in 1 was sintered under normal pressure at 1800° C. for 2 hours in a mixed gas atmosphere of 1 atm N2+H2.

The obtained silicon nitride sintered body is single-phase and has a bulk specific gravity of 0.8
3. Thermal conductivity was 0.07 Kcal/m, hr, °C, and the bending strength was 32 kg/mm at 1200 °C.

It was suitable as a structural material for lightweight insulation, exhibited a closed cross-sectional layer, and had zero air permeability.

Example 3 0.5% by weight of polysilane was mixed with silicon nitride powder, and 2
Pressure molding was performed at 0t/cm2.

This molded product was placed in silicon nitride powder at 200 atm of N2.
Normal pressure sintering was performed at 1750° C. for 2 hours in a mixed gas atmosphere of +H2.

The obtained silicon nitride sintered body is single-phase, has a high specific gravity of 3.09, and has a bending strength of 135 kg/cm at 1200°C.
It was mm2.

Example 4 1.0 of an imide compound containing Si atoms was added to silicon nitride powder.
The weight percent was mixed and pressure molded at 10t/cm2.

This molded product was heated in 50 atm of N2+H in silicon nitride powder.
Normal pressure sintering was performed at 1750° C. for 2 hours in an atmosphere of a mixed gas of Step 2.

The obtained silicon nitride sintered body is single-phase, has a bulk specific gravity of 3.00, and a bending strength at 1200°C of 129 kg/
It was mm2.

Claims (1)

[Claims] 1. A mixture mainly consisting of silicon nitride powder and polysilane or an imide compound containing Si atoms, or a mixture thereof, is pressure-molded and then heated with nitrogen, ammonia, a mixture of both, or N2+H2. A method for producing a silicon nitride sintered body, characterized by sintering in an atmosphere of 1 to 200 atmospheres. 2 The amount of polysilane or imide compound containing Si atoms or a mixture thereof mixed with silicon nitride powder is 0.
The method for producing a silicon nitride sintered body according to claim 1, wherein the content is 1 to 50% by weight. 3. The method for producing a silicon nitride sintered body according to claim 1 or 2, wherein the pressure forming is performed at a pressure of 0.1 to 30 t/cm2. 4. The method for producing a silicon nitride sintered body according to claim 1, 2, or 3, wherein the sintering temperature is 1000 to 2000°C. 5. Claims 1, 2, and 3 in which silicon nitride powder or mixed powder of silicon nitride and silicon oxide is present around the pressure-molded mixture during sintering of the mixture.
4. A method for producing a silicon nitride sintered body according to item 4.