JPH01167277A - Production of ceramic - Google Patents

Abstract

PURPOSE:To obtain ceramic having excellent flexural strength at high temperature and excellent dimensional accuracy, by reacting a molded article comprising carbon as an essential component with molten silicon and nitriding a remaining metal silicon. CONSTITUTION:A composition obtained by blending 5-50wt.% carbon component-containing material (e.g. graphite) with 50-95wt.% SiC powder, 0.1-20wt.% binder (e.g. PVA) and a filler (e.g. Al2O3) to give a composition, which is packed into a mold and molded to give a molded article. Then the molded article is immersed in molten silicon, reacted and sintered in vacuum or in an inert atmosphere at 1,450-1,800 deg.C to give a sintered material. Then the sintered material is heated under 1-10atm in a nitrogen atmosphere at 1,300-1,600 deg.C to nitride a remaining metal silicon in the sintered material.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing ceramics having excellent strength at high temperatures.

[Conventional technology]

Sintered bodies of silicon carbide are attracting attention as engineering materials because they have excellent strength at high temperatures, thermal shock resistance, corrosion resistance, chemical resistance, and abrasion resistance.

Known methods for producing such ceramics include (1) normal pressure sintering method, (2) hot press sintering method, and (2) reaction sintering method.

The pressureless sintering method (2) has the disadvantage that when producing a dense fired body, the dimensions of the resulting fired body are smaller than the shaped body. Therefore, in order to improve the dimensional accuracy of the product, it is necessary to control the shrinkage rate through sufficient management of raw materials, firing conditions, etc.

Furthermore, in order to obtain a high-density fired body, a sintering aid must be added to the raw materials. However, since the above-mentioned sintering aid is generally a substance that reduces the high-temperature properties of the fired product, it is difficult to obtain a dense fired product with excellent strength at high temperatures using the pressureless sintering method. . The bot press sintering method (2) does not require adding the above-mentioned sintering aid used in the pressureless sintering method (2) to the raw material, and can produce a relatively dense sintered body. However, due to manufacturing method reasons, only fired bodies with simple shapes can be manufactured.

In the past, in order to obtain a fired body with a complicated shape, it was necessary to go through a processing step after firing, which was unsuitable in terms of mass production and economy.

[Problem that the invention seeks to solve]

The reaction sintering method (ii) of the conventional manufacturing method is a method for obtaining a fired silicon carbide body by impregnating a molded body containing carbon as an essential component with molten silicon. This manufacturing method has excellent dimensional accuracy, with no difference in dimensions between the molded body before firing and the fired body. However, this manufacturing method has a problem in that metal silicon remains in the fired product, resulting in a reduction in the high-temperature properties of the resulting product.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing ceramics that has excellent strength at high temperatures and has little dimensional change before and after firing.

[Means for solving problems]

In order to achieve the above object, the method for producing ceramics of the present invention includes preparing a molded body containing carbon as an essential component, reacting this molded body with molten silicon, and then nitriding the remaining metallic silicon. Take.

[Effect]

That is, as a result of a series of studies to achieve the above object, the present inventors succeeded in producing a fired silicon carbide body using a normal reaction sintering method. The present inventors have discovered that by providing a nitriding reaction step to nitride the metallic silicon remaining in the fired body, it is possible to obtain ceramics that have excellent strength at high temperatures and have little dimensional change before and after firing.

The ceramic according to the present invention is obtained by using a carbon component, silicon carbide powder, a binder, etc. as raw materials, and further blending other raw materials as necessary to form a composition.

Examples of the carbon component include powders such as graphite, carbon black, and coke, and cool pitch. Further, it is also possible to use carbon generated when heat-treating in a non-oxidizing atmosphere using a large amount of the binder described below as the carbon component.

The above-mentioned silicon carbide powder includes α-type silicon carbide powder and β-type silicon carbide powder.
Examples include type silicon carbide powder, but α type silicon carbide powder is generally used.

The binder is polyhinyl alcohol.

Water-soluble resins such as hydroxypropyl cellulose, methyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose; thermosetting resins such as epoxy resins, phenol resins, urea resins and melamine resins; polyethylene and polypropylene.

Thermoplastic resins such as nylon, polyester, butyral and wax are used. These resins are appropriately selected depending on the molding method of the molded body (hereinafter referred to as "green body") before firing.

The blending amount of each of the above raw materials in the composition for obtaining ceramics is such that the carbon component content is 5 to 50% by weight (hereinafter referred to as "%").
(abbreviated as ), silicon carbide powder is 50-95%, and binder is 0.
However, from the viewpoint of effectiveness, it is preferable to set the carbon component content to 5 to 30%, the silicon carbide powder to 65 to 95%, and the binder to 0.3 to 10%.

In addition, inorganic fibers can also be added to the above composition in order to improve the strength, thermal shock resistance, and toughness of the obtained fired body. Inorganic fibers include whiskers such as silicon carbide and silicon nitride, aluminum oxide, aluminum silicate,
Examples include short fibers or long fibers of silicon oxide, zirconium oxide, silicon carbide, and carbon.

Furthermore, ceramic particles of oxides such as aluminum oxide, zirconium oxide, and silicon oxide, and non-oxides such as silicon nitride, aluminum nitride, boron nitride, sialon, and titanium carbide may be added as appropriate to the extent that the objects of the present invention are not hindered. You can.

When manufacturing ceramics using the above raw materials, it can be performed, for example, as follows. That is, the carbon component, silicon carbide powder, binder, and other additives exemplified above are appropriately blended, and this mixture (composition) is prepared.
We get a green body from . Note that the green body is molded by conventionally known methods such as a press molding method, a sheet molding method, an injection molding method, an extrusion molding method, and a casting molding method.

Next, the obtained green body is subjected to reaction sintering by (1) gradually immersing it in molten silicon, or (2) heating it together with metal silicon to impregnate it with molten silicon. This sintering temperature basically needs to be higher than the melting point of metal silicon, 1414°C, and the reaction sintering is usually carried out at a temperature of 1450 to 1800°C in a vacuum or an inert atmosphere.

Next, the residual metal silicon in the fired body thus obtained is nitrided at a temperature of 1300 to 1600° C. in a nitrogen atmosphere to obtain a ceramic body. Note that when performing the above nitriding treatment, the higher the gas pressure, the faster the reaction between the remaining metal silicon and nitrogen will be completed;
Zero atmosphere is preferred.

〔Effect of the invention〕

As described above, the present invention manufactures ceramics by further providing a step of nitriding the metal silicon remaining in the fired body following the steps of the conventional reaction sintering method. Therefore, in the obtained ceramic, almost no metallic silicon remains, and silicon nitride produced by the nitriding treatment is a ceramic material that has high-temperature properties along with silicon carbide, and contributes to improving the strength of the ceramic. In this way, the ceramics produced by this invention are
It has excellent strength even in high-temperature ranges, and has excellent dimensional accuracy after firing, with almost no change in dimensions before and after firing.

Next, examples will be described together with comparative examples.

〔Example〕

30 parts by weight of a graphite particle dispersion (Hitasol AB-1: manufactured by Hitachi Powdered Metals) (hereinafter abbreviated as "Part J").

α-type silicon carbide powder (UFP-1: manufactured by Shinano Electric Smelting Co., Ltd.) 7
0 parts of binder (Maxelon A: manufactured by Chukyo Yushi Co., Ltd.), 1 part of 2 parts of dispersing agent (Ceramo D114: manufactured by Dai-Kogyo Seiyaku Co., Ltd.), and 80 parts of distilled water were mixed and stirred to form a slurry composition. Obtained. The obtained slurry composition was cast into a plaster mold to produce a molded body using a cast molding method. Next, after drying the molded body,
A green body was obtained by cutting into a size of 5 x 10 x 50 mm. The obtained green body was immersed in molten silicon for 30 minutes at a vacuum level of 10-2 torr and a temperature of 1500°C, and then
It was pulled out from the molten silicon and left to stand for an additional 30 minutes to obtain a fired body. Next, this fired body was heated to 1 atm under a nitrogen atmosphere.
Nitriding treatment was carried out at 1400° C. for 3 hours and then at 9.5 atm and 1500° C. for 5 hours.

Powder X-ray diffraction of the nitrided fired body confirmed that the content of metallic silicon in the fired body was 1% or less, and that the main components were silicon carbide and silicon nitride. In addition, the bending strength measurement results at room temperature and 1400″C are as follows:
As shown in the table below, the results were good.

[Comparative example]

No nitriding treatment was performed. A fired body was obtained in the same manner as in Example 1 except for the above.

Powder X-ray diffraction of this fired body revealed that the content of metallic silicon in the fired body was 12%.

Further, the measurement results of bending strength at room temperature and 1350''C are shown in the table below.

From the table, it can be seen that the example products have better bending strength at high temperatures than the comparative example products.

Claims (4)

[Claims] (1) A method for producing ceramics, which comprises preparing a molded body containing a carbon component as an essential component, reacting this molded body with molten silicon, and then nitriding the remaining metallic silicon. (2) The method for producing ceramics according to claim 1, wherein the molded body is obtained by molding a composition comprising a carbon component-containing material and a filler using a mold. (3) Claim 2, in which the composition is a powder composition
Manufacturing method of ceramics described in section. (4) After reacting the molded body with molten silicon, the remaining metallic silicon is nitrided by impregnating the molded body with molten silicon and performing 1 step in either a vacuum or an inert atmosphere.
Claim 1, which is performed by firing in a temperature range of 450 to 1800°C, and firing the fired body in a temperature range of 1300 to 1600°C in at least one of a nitrogen atmosphere and an ammonia atmosphere. manufacturing method of ceramics.