JPH0818886B2 - Method for producing porous silicon carbide material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a porous silicon carbide based ceramic material.

2. Description of the Related Art Silicon carbide-based materials have been attracting attention in recent years as materials excellent in hardness, heat resistance, corrosion resistance, etc., and have come to be used in many fields such as sliding materials and high temperature mechanical materials.
However, this silicon carbide material is rarely used as a porous material. Porous silicon carbide materials are expected to show excellent performance when used in filters for treating high temperature or corrosive fluids. There are only heating elements and silicon carbide bricks. And since these are formed by molding silicon carbide particles using a glassy material such as clay particles as a binder, heat resistance and corrosion resistance are dominated by that of the binder part, and the original characteristics of silicon carbide are fully It wasn't possible. It is clear that if a porous material can be produced by a production method that does not use a vitreous binder, for example, a method of sintering silicon carbide particles, it will have better physical properties, but such a production method is not yet available. Not established.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Therefore, an object of the present invention is to provide a method for producing a porous silicon carbide based material by a method without using a vitreous binder, in order to obtain a porous material without the above-mentioned conventional defects. To provide.

Means for Solving the Problems In the method for producing a porous silicon carbide material according to the present invention which has succeeded in achieving the above object, an average particle diameter of 50 to 300 is included.
The surface of the silicon carbide particles of μm is coated with 3 to 15% by weight of a carbonaceous organic material in terms of carbide, and the powder composed of the coated silicon carbide particles has a bulk density of 1.7 to 2.1 g after the organic carbonization treatment described below. Molded under conditions such that / cm ³ , the resulting molded body is fired in a non-oxidizing atmosphere to carbonize the carbonizable organic matter in the molded body, and then the molded body after treatment is melted at 1450 ° C or higher with molten silicon. It is characterized in that the organic carbide in the molded body is reacted with silicon to be converted into silicon carbide by contacting the molded body with the silicon to penetrate the silicon into the molded body.

 Hereinafter, the manufacturing method of the present invention will be described in detail.

Silicon carbide particles having an average particle diameter of 50 to 300 μm are commercially available as an abrasive, and they can be used as they are as the raw material silicon carbide in the production method of the present invention. In general, the larger the particle size of silicon carbide, the larger the pore size of the product. Therefore, the particle size of silicon carbide to be used is appropriately selected according to the desired product pore size. The average particle size is 50
If it is smaller than μm, the voids between the silicon carbide particles in the molded product subjected to the silicon infiltration treatment become too small, and the voids are easily filled with silicon, making it impossible to secure the necessary pores. On the other hand, if the particle size exceeds 300 μm, the number of bonding points between the silicon carbide particles decreases, and only a product having insufficient strength can be obtained.

Carbonizing organic materials used for coating silicon carbide particles include those which dissolve in some solvent to form a coatable solution and which carbonize in high yield when fired in a non-oxidizing atmosphere, such as phenolic resins and furan. Thermosetting resin such as resin or pitch is used.

The coating can be carried out by thoroughly mixing the solution of the carbonizable organic substance and the silicon carbide powder with a stirrer, and subsequently heating and drying with stirring. It is also possible to use a fluidized bed coating method. The coated carbonizable organic matter is carbonized in the next firing step,
Since the formed carbide is the reaction target of molten silicon,
The suitable coating amount of the carbonizable organic material depends on the carbon yield of the carbonized organic material used. Therefore, it is appropriate to indicate the comprehensive suitable coating amount by the equivalent amount of carbide,
Its value is 3 to 15%, particularly preferably 5 to 12%, based on the weight of silicon carbide. Below 3%, the carbon coating formed on the silicon carbide particles cannot be a continuous phase, and therefore
Only low-strength products can be obtained in which the binding of silicon carbide particles with the silicon carbide formed in the reaction is insufficient. Further, if it exceeds 15%, it only reduces the porosity of the product, and is useless.

In the coating process, along with the carbonizable organic matter,
An auxiliary agent for improving moldability in the next molding step may be attached to the silicon carbide particles. As this auxiliary agent, those which cause thermal decomposition and scatter at a temperature below the carbonization temperature of the carbonizable organic matter, such as paraffin, wax, stearic acid, thermoplastic synthetic resin (eg acrylic resin, methacrylic resin), etc. are suitable. is there.

The required amount of powder consisting of silicon carbide particles after coating is put in a mold and compression-molded using a uniaxial press or the like. As described above, the molding conditions in this case 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 . When 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 over 2.1 g / cm ³ ,
Along with that, silicon also enters the interparticle spaces that have become smaller, so that a porous 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 ° C in a non-oxidizing atmosphere.
The mixture is heated to ~ 1200 ° C to carbonize the carbonizable organic matter in the molded body (if a decomposable molding aid is used, decompose it before carbonizing the carbonizable organic matter). Since carbonization of a carbonizable organic substance is accompanied by liberation of volatile substances, the formed carbide has a large number of fine continuous air holes.

Then, the molded body is heated to 1450 ° C. or higher, which is the melting point of metallic silicon, preferably about 1450 ° C. or higher in a vacuum or an inert gas.
Heat to 1700 ° C. and contact with 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 molded and the temperature is raised in contact with the molded product.
At this time, the molten silicon infiltrates into the continuous air holes of the organic carbide portion of the molded body by a capillary phenomenon, and then reacts with carbon to generate silicon carbide. The amount of silicon required to convert all organic carbides to silicon carbide is typically around 2.5 times the weight of organic carbides. Since the above-described process is followed, silicon is not taken into the molded body without limitation without limiting the supply amount of molten silicon.
It does not make sense to prepare an amount of silicon that exceeds about three times the above required amount.

When the organic carbide portion is converted to silicon carbide as described above, the silicon carbide particles originally present in the molded body are integrated with the silicon carbide generated by this reaction and a small amount of silicon which remains unreacted. The voids between the silicon carbide particles existing in the molded body are too large for the molten silicon to permeate by the capillary phenomenon as long as the above-mentioned raw materials and molding conditions are selected, so that most of them remain as voids. By the above, a porous material consisting essentially of silicon carbide is formed.

EFFECTS OF THE INVENTION According to the production method of the present invention, a porous silicon carbide-based material that is substantially composed of silicon carbide and has continuous pores with a pore size of about 50 to 300 μm uniformly distributed about 20 to 40 vol% can be stably prepared. Can be manufactured. A particular advantage of the manufacturing method of the present invention is that, because a heterogeneous binder, such as a glassy binder in the conventional method, is not used, the product is inferior to the silicon carbide portion in terms of physical properties and corrosion resistance of the binder portion. It has excellent physical properties and durability without deterioration.

Example 900 g of silicon carbide particles having an average particle size of 100 μm were put in a mixer with a stirrer and mixed together with 100 g of a novolac type phenol resin dissolved in 500 ml of acetone, followed by heating with stirring to evaporate the acetone, thereby carbonizing. The silicon particles were coated with phenol resin.

Then, coated silicon carbide powder at 1 ton / c
A disk having a diameter of 70 mm and a thickness of 5 mm was formed under a pressure of m ² and the obtained formed body was fired. The molded body after firing has a weight of 35.4
g, bulk density 1.84 g / cm ³ , 94% by weight silicon carbide and 6
It consisted of wt% resin carbide.

This calcined compact was heated under vacuum in contact with 7.1 g of metallic silicon powder (330% of 2.12 g of carbon in the compact) and kept at 1500 ° C for 2 hours to obtain a large amount of molten silicon. The part was penetrated into the shaped body. The molded body obtained by allowing to cool after this infiltration treatment was 93.7% by weight or more of silicon carbide, and had a uniform porosity with a pore size of 70 to 160 μm and a porosity of 30 vol%. Also, the bending strength is 8.5 Kg / mm ² ,
The Young's modulus was 18,400 Kg / mm, which had sufficient physical properties for use as a filter.

Claims (1)

[Claims] 1. A surface of silicon carbide particles having an average particle diameter of 50 to 300 μm is coated with 3 to 15% by weight of a carbonaceous organic substance in terms of carbide, and a powder comprising the coated silicon carbide particles is treated with an organic substance described below. The bulk density of
Molded under conditions such that 1.7 ~ 2.1 g / cm ³ , the obtained molded body is fired in a non-oxidizing atmosphere to carbonize the carbonizable organic matter in the molded body, then the molded body after treatment at 1450 ° C A method for producing a porous silicon carbide-based material, characterized in that the organic carbide in the molded body is reacted with silicon to be converted into silicon carbide by bringing the silicon into contact with molten silicon and allowing the silicon to penetrate into the molded body.