JPH0662348B2 - Porous ceramic composite material and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a porous ceramic composite material and a method for producing the same, and particularly to a porous ceramic composite material in which the surface of porous silicon carbide ceramics is coated with silicon nitride and the same. The present invention relates to a manufacturing method.

[Prior art and problems to be solved]

Generally, silicon carbide ceramics is known as a structural material having excellent heat resistance as a whole, but it is known that its durability against thermal changes due to rapid heating and cooling, that is, thermal shock resistance is somewhat difficult. There is.

Further, it is known that silicon nitride ceramics is a structural material excellent in the above thermal shock resistance.

And it is known that the porous silicon carbide ceramics in which fine continuous air holes are formed in the silicon carbide ceramics are produced by the method described in JP-A-62-297279. Similar to the above, carbon silicon ceramics also have some difficulty in thermal shock resistance, and are not sufficiently resistant as a structural material such as a filter for high-temperature gas where there is a large temperature change, and the temperature change is large. It has been desired to improve the thermal shock resistance so that it can be used even in places.

It is an object of the present invention to provide a porous ceramic composite material having excellent heat resistance as well as excellent thermal shock resistance and a method for producing the same.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the porous ceramic composite material of the present invention has a fine continuous air hole, and the surface layer portion including the inner surface of the continuous air hole is constituted by a silicon nitride material, and the silicon nitride material is 1 25% by volume, the remaining 7
5 to 99% by volume is made of a silicon carbide material, and the porosity of the continuous ventilation holes is 10 to 50% by volume.
Further, the method for producing a porous ceramic composite material of the present invention is a method in which the surface of silicon carbide particles having an average particle size of 50 to 300 μm is coated with 3 to 15% by weight of a carbonaceous equivalent of a carbonizing organic material, and the coated carbonization is performed. The powder of silicon particles is molded under the condition that the bulk density of the compact after carbonization of the organic matter is 1.7 to 2.1 g / cm ³ , and the compact obtained is fired in a non-oxidizing atmosphere. The carbonizable organic substance therein is carbonized, and then the carbonized molded product is brought into contact with molten silicon at 1450 ° C. or higher to allow silicon to penetrate into the molded product, and the organic compound carbide in the molded product is reacted with silicon to form silicon carbide. In addition, it has means for excessively supplying silicon to the surface of the molded body, and further for converting the silicon on the surface of the molded body into silicon nitride by reacting nitrogen or ammonia gas with the molded body having excessively supplied silicon. There.

[Action]

The present invention, by adopting the above configuration and means,
Porous ceramic composites composed of silicon carbide / silicon nitride have excellent thermal shock resistance, which is useful as a structural material in places with large temperature changes, and also have excellent overall heat resistance. The porous ceramic composite material made of silicon can be easily produced.

[Specific configuration of the invention]

Hereinafter, the porous ceramic composite material made of silicon carbide / silicon nitride according to the present invention will be described in detail.

Silicon carbide particles having an average particle size of 50 to 300 μm are commercially available as an abrasive, and the powder of silicon carbide particles as a raw material of the present invention can be used as it is.

Generally, the larger the particle size of silicon carbide, the larger the pore size of the product. Therefore, the particle size of silicon carbide used is appropriately selected according to the desired product pore size.

If the average particle size is less than 50 μm, the voids between the silicon carbide particles in the molded body that undergoes the silicon melting treatment become too small, and the voids are easily filled with silicon,
It becomes impossible to secure the required porosity.

On the other hand, if the particle size exceeds 300 μm, the number of bonding points between the silicon carbide particles decreases, so that the strength of the porous ceramic composite material becomes insufficient.

The carbonizing organic substance used for coating the silicon carbide particles described above is dissolved in some solvent to form a solution capable of coating the silicon carbide particles, and carbonizes in a high yield when fired in a non-oxidizing atmosphere. For example, a thermosetting resin such as phenol resin or furan resin, pitch, or the like can be used.

The coating step can be carried out by thoroughly mixing the solution of the carbonizable organic substance and the powder of silicon carbide particles with a stirrer, and subsequently heating and drying with stirring.

It is also possible to use a fluidized bed coating method.

The coated carbonized organic matter is carbonized in the subsequent firing step, and the formed carbide is the reaction target of the molten silicon. Therefore, the suitable coating amount of the carbonized organic matter varies depending on the carbon yield of the carbonized organic matter used.

Therefore, it is appropriate that the comprehensive coating amount of the above-mentioned carbonizable organic substance is indicated by the equivalent amount of carbide, and the value is 3 to 15%, particularly preferably 5 to 12% based on the weight of silicon carbide.
Is.

If it is less than 3%, the carbon coating formed on the silicon carbide particles cannot be a continuous phase, so that the bonding of the silicon carbide particles by the silicon carbide generated in the reaction is insufficient and only a product having low strength can be obtained.

Further, if it is 15% or more, it only reduces the porosity of the product and is useless.

In the coating step, an auxiliary agent for improving the moldability in the next molding step may be attached to the carbonized silicon particles together with the carbonizable organic material.

As this auxiliary agent, those which cause thermal decomposition and scatter at a temperature lower than the carbonization temperature of the carbonizable organic matter, for example, paraffin, wax, stearic acid, thermoplastic synthetic resin (eg acrylic resin, methacrylic resin, etc.) are suitable. Is.

The powder of the silicon carbide particles that have been coated is put in a required amount in a molding die and compression-molded using a single-screw press or the like. In this case, the molding conditions are such that the bulk density of the molded body after the organic substance carbonization treatment is 1.7 to 2.1 g / cm ³ .

If the bulk density is less than 1.7 g / cm ³ , it becomes difficult to obtain a product having the strength required for practical use.

On the other hand, if the density is higher than 2.1 g / cm ² , silicon will also enter the interparticle voids that have become smaller, and a porous ceramic material cannot be obtained.

The bulk density of the molded product can be set to a desired value by adjusting the molding pressure, the molding temperature and the like.

The obtained molded product is first about 500 to 500 in a non-oxidizing atmosphere.
It heats at 1200 degreeC and carbonizes the carbonizable organic substance in a molded object. (When a decomposable molding aid is used, it is decomposed prior to carbonizing organic matter.) Since carbonization of carbonizing organic matter is accompanied by liberation of volatile substances, the formed carbide has many fine open pores. Will have.

Thereafter, the molded body is heated in a vacuum or in an inert gas at a melting point of metallic silicon of 1450 ° C. or higher, preferably 1450 ° C.
Heat to ~ 1700 ° C to contact molten silicon.

As a method for this, a method of raising the temperature in a state where the molded body is embedded in powdered metal silicon, a method of applying a paste of metal silicon powder with an appropriate binder to the surface of the molded body and heating it There is a method in which a sheet of metal silicon powder is heated and the temperature is raised in contact with the molded product.

At this time, the molten silicon intrudes into the open pores together with the surface portion of the organic carbide portion of the molded body by a capillary phenomenon, and then reacts with carbon to form silicon carbide in the surface layer portion including the inner surface of the open pores.

The supply amount of silicon at this time is an amount necessary for converting all organic carbides to silicon carbide, and silicon nitride in the subsequent step of converting into silicon nitride is 1 to 25% by volume with respect to the entire ceramic composite material. Contact a certain amount.

When the organic carbide is converted into silicon carbide as described above, the silicon carbide particles in the porous silicon carbide ceramics composed of the silicon carbide particles as the base material are integrated with the silicon carbide generated by this reaction and unreacted silicon. Turn into.

The existing form of unreacted silicon is a network that covers the silicon carbide generated by the reaction.

Next, the porous ceramics compact having unreacted silicon on the surface is maintained at a temperature of 1250 to 1500 ° C. at which the unreacted silicon reacts with nitrogen gas, and nitrogen gas or ammonia gas is supplied to the compact. Then, the above-mentioned unreacted silicon is reacted with nitrogen gas or ammonia gas, and the silicon nitride of silicon nitride is formed so as to cover the surface of the porous ceramics formed body in which the silicon carbide produced by the reaction with the silicon carbide particles in the above step is formed. Form the layers.

The reaction time for forming the silicon nitride layer on the surface is 2
It is about 20 hours, and it is formed so as to be 1 to 25% by volume of the whole porous ceramics composite material.

On the other hand, silicon carbide accounts for 75 to 99% by volume of the entire porous ceramic composite material.

In addition, the porosity of the continuous ventilation holes of the porous ceramics composite material formed through the above manufacturing process is 10 to 50% by volume.

The porous ceramic composite material according to the present invention obtained as described above, the layer of silicon nitride formed in the surface layer portion including the surface in the continuous ventilation hole is excellent in thermal shock resistance as compared with silicon carbide, When a high-temperature gas passes through the continuous pores of the porous ceramics composite material, this gas does not come into direct contact with silicon carbide, but with silicon nitride that has excellent thermal shock resistance and covers the surface layer, so that heat resistance is improved. The impact resistance is greatly improved, and the heat resistance and mechanical strength of the silicon carbide as the base material are maintained as they are.

〔The invention's effect〕

Since the present invention is configured as described above, the heat resistance and mechanical strength of the silicon carbide ceramics that is the base material are maintained as they are, and the silicon nitride ceramics formed on the surface layer portion including the surface in the communicating holes are Since the layer has better thermal shock resistance than silicon carbide, the overall thermal shock resistance of the porous ceramic composite material is significantly improved, and the porous ceramics having these excellent properties are also improved. It has an excellent effect that a composite material can be manufactured by a simple process.

Claims (2)

[Claims] 1. A surface layer portion having fine air vents and including an inner surface of the air vents is made of a silicon nitride material,
This silicon nitride material is 1 to 25% by volume, and the remaining 75 to
99% by volume is made of a silicon carbide material, and the porosity of the continuous ventilation holes is 10 to 50% by volume. 2. The surface of silicon carbide particles having an average particle size of 50 to 300 μm is coated with 3 to 15% by weight of a carbonaceous organic substance in terms of carbide, and the powder of the coated silicon carbide particles after the carbonization treatment with an organic substance is performed. Molded product has a bulk density of 1.7-2.1 g / cm
Molded under conditions such that the resulting product becomes ³ , and the resulting molded product is fired in a non-oxidizing atmosphere to carbonize the carbonizable organic matter in the molded product, and the carbonized product is then treated with molten silicon at 1450 ° C or higher. Silicon is infiltrated into the compact by contacting it, and the organic carbide and silicon in the compact are reacted with each other to form silicon carbide, and silicon is excessively supplied to the surface of the compact, and further, this excessive silicon is supplied. A method for producing a porous ceramics composite material, which comprises reacting nitrogen or ammonia gas with a body to convert silicon on the surface of the compact into silicon nitride.