Silicon nitride porous ceramics and its preparing method

Abstract

The porous silicon nitride ceramic is prepared with C and CO2 in 75-95 wt%, silicon nitride 1-10 wt%, and sintering assistant 2-20 wt%. The C / CO2 weight ratio is 0.4-0.6; and the sintering assistant is at least one the metal oxides Y2O3, Al2O3 and MgO. The preparation process includes the following steps: ball milling the materials, drying and sieving to obtain mixture powder; pressure forming in mold; and sintering in a nitrogen atmosphere furnace through raising temperature at the rate of 600deg.c / hr to 1500deg.c, further raising temperature at the rate of 180deg.c / hr to 1700-1800deg.c, and maintaining at nitrogen pressure of 6-10 atm for 2-8 hr to obtain the sintered body. The porous silicon nitride ceramic may be used as base filter material for separating gas in high temperature and corrosive atmosphere, heat resisting material and reinforcing material in gas turbine, engine, space shuttle, etc.

Description

Technical field [0001] The invention relates to a porous ceramic and a preparation method thereof, in particular to a silicon nitride porous ceramic and a preparation method thereof. Background technique [0002] Silicon nitride porous ceramics have good heat resistance, corrosion resistance, high strength, and high toughness due to the presence of rod-shaped particles in their microstructure. It is a gas separation filter under high temperature or corrosive atmosphere Or its base material and the reinforcing phase of metal matrix composites have been widely used. The existing preparation methods of silicon nitride porous ceramic materials mainly include the following: [0003] 1) Atmospheric sintering method, using silicon nitride particles or amorphous starting materials, heating the formed body in nitrogen to form a uniform fibrous silicon nitride-based porous ceramic, as proposed in Japanese Patent Laid-open Hei 10-67562 method. The formed body formed by the mixed powder cont...

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Problems solved by technology

However, these methods all use silicon nitride powder or amorphous powder. Since the price of silicon nitride powder is relatively high, the cost of silicon nitride porous ceramics obtained is relatively high.

[0004] 2) Direct nitriding method, using metal silicon powder to make a molded body first, and then placing it in nitrogen to directly react for nitriding to manufacture silicon nitride ceramics, but this method is difficult to obtain a dense sintered body, due to the nitriding of metal silicon The reaction formula is , in this reaction, there will be an increase in weight and volume relative to metal silicon, so it is also difficult to form a high porosity in the sintered body

Although this reaction can be used to produce silicon nitride powder, there are also certain problems, that is, the reaction temperature must be precisely controlled. If the temperature is above 1470 degrees, there is a danger of forming silicon carbide; when the temperature is below 1400 degrees, a large amount of silicon carbide containing Oxygen crystallization poor product

Utilize above-mentioned reaction to also attempt to make porous ceramics, as Japanese Patent Application Laid-Open 2001-206775 proposes the method that will contain silicon dioxide particle, the method for heat-treating the molded body of metal silicon particle below the average particle diameter 5um in nitrogen, But in this method, the total amount of silica and carbon in the shaped body is only 1-20% by weight, so the porosity in the sintered body is only 20-40%

In the attempt to make porous ceramics using the above reaction, there is also a silicon nitride porous ceramic obtained by heat-treating a molded body containing silicon dioxide, carbon and sintering aids in nitrogen. However, the obtained material has a low strength. not very good

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