JPH01282149A - Composition for mullite sintered body and production of mullite sintered body utilizing the same - Google Patents

Abstract

PURPOSE:To obtain the composition for a mullite sintered body which is excellent in degree of sintering and mechanical strength by mixing specified mullite raw material powder with cerium oxide and thereafter calcining the mixture. CONSTITUTION:The aimed sintered body is obtained by uniformly mixing mullite raw material powder wherein alumina to silica is regulated to (65:35)-(80-20) (weight ratio) or 95-99.8wt.% mullite powder pulverized after calcining thin mullite raw material powder with 0.2-5wt.% cerium oxide powder or with salt or an organic compd. contg. 0.2-5wt.% cerium oxide and thereafter calcining the mixture. As the mullite raw material powder, when ratio of alumina to silica is deviated from the above-mentioned range, strength is deteriorated at high temp. and the aim cannot be achieved. Cerium oxide does not react with alumina and silica of the mullite raw material powder but exists as cerium oxide crystal, and softening is hardly caused by existence of cerium oxide crystal and deterioration of strength at high temp. is made small and also sintering temp. can be lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention has excellent sinterability, 1 mechanical strength, and 4! The present invention relates to a composition for a mullite sintered body that has good strength even at high temperatures, and a method for producing a mullite sintered body using the composition.

(Prior Art) Mullite sintered bodies have a high melting point, low expansion, and excellent heat resistance and creep resistance, so they have been used for high-temperature structural members.

Furthermore, the strength of high-purity mullite sintered bodies does not deteriorate even at high temperatures, as reported by Journal of American Ceramics and Society.
An Ceramic 5ociety) No. 7
0, No. 1, C-7-C8, published in 1987.

Many methods have been proposed for manufacturing such high-purity mullite sintered bodies using raw materials that have gone through a process of being made into a solution, such as high-purity metal alkoxides, colloidal silica, alumina sol, and water-soluble salts. .

(Problems to be solved by the invention) However, high-purity mullite sintered bodies have poor sinterability;
Even if a fine active raw material powder made through a solution process is used, it must be fired at a high temperature of 1650° C. or higher in order to produce a high-purity, high-strength mullite sintered body. Therefore equipment costs.

There is a problem in that fuel costs and the like increase, resulting in an increase in the cost of the mullite sintered body. Another problem is that it is expensive because fine, active raw material powder is produced through a process of making it into a solution. On the other hand, there is a method of producing a mullite sintered body by solid phase reaction using inexpensive oxide powder, kaolin, etc. However, this method has a problem in that the sinterability is poor and it is difficult to obtain sufficient strength even when fired at high temperatures.

In addition to the above method, as shown in Japanese Patent Publication No. 61-15532, there is a method for manufacturing a mullite substrate in which magnesia is added to lower the firing temperature to improve sinterability.

However, this method has problems in that creep resistance and strength decrease at high temperatures.

Therefore, when the present inventors added yttrium oxide powder to the mullite raw material powder, the sinterability improved, but the yttrium oxide powder reacted with the alumina and silica of the mullite raw material powder to form a glass phase.

When this glass phase is exposed to high temperatures, a problem arises in that the glass phase softens and the strength deteriorates.

The object of the present invention is to provide a composition for a mullite sintered body that does not have the above-mentioned problems, and a method for producing a mullite sintered body using the composition.

(Means for Solving the Problems) The present invention provides mullite raw powder or mullite powder 95~
A composition for a mullite sintered body containing 99.8% by weight of cerium oxide and 0.2 to 5% by weight of cerium oxide, and a mullite raw material powder or the mullite raw material having a weight ratio of alumina:silica of 65:35 to 80:20. 95 to 99.8% by weight of mullite powder obtained by firing and pulverizing the powder and 0.2 to 5% by weight of cerium oxide powder or 0.2% of cerium oxide
The present invention relates to a method for producing a mullite sintered body in which a salt or organic compound containing up to 5% by weight is uniformly mixed and then fired.

In the present invention, the mullite raw material powder has a 1 weight ratio of alumina:
Silica is in the range of 65:35 to 80:20,
Outside this range, the strength deteriorates at high temperatures, making it impossible to achieve the two objects of the present invention.

Mullite sintered bodies are produced by mixing alumina and silica, which serve as mullite raw material powder, with cerium oxide powder, a salt containing cerium oxide, or an organic compound at the same time.

It may then be fired to produce a mullite sintered body, or alumina and silica may be mixed, then fired and pulverized.
Mullite powder may be mixed with cerium oxide powder, a salt containing cerium oxide, or an organic compound, and then fired to form a mullite sintered body without any limitation.

The mullite in the mullite sintered body preferably contains 80% by weight or more of mullite crystals.

The composition for a mullite sintered body according to the present invention contains 95 to 99.8% by weight of mullite raw powder or mullite powder obtained by firing and pulverizing mullite raw material powder, and 0.9% by weight of cerium oxide.
The content is in the range of 2 to 5% by weight, and mullite raw powder or mullite powder obtained by firing and pulverizing mullite raw powder is 99.9% by weight.
If the content exceeds 8% by weight and the content of cerium oxide is less than 0.2% by weight, the effect of improving sinterability will be insufficient, and if the content of mullite is less than 95% by weight and the content of cerium oxide exceeds 5% by weight. This causes the problem that the sintered body foams or its strength deteriorates at high temperatures.

In the present invention, examples of salts containing 0.2 to 5% by weight of cerium oxide include cerium nitrate and cerium acetate.

Cerium carbonate, cerium hydroxide, cerium sulfate, etc. are used, and the organic compound containing 0.2 to 5% by weight of cerium oxide is cerium methoxide.

There is no particular restriction on the method of mixing with the salt or organic compound containing lithium (it may be carried out by a conventionally known method). Further, the firing temperature is appropriately selected depending on the composition or blending ratio, and is not particularly limited.

(Function) In the present invention, cerium oxide does not react with the alumina and silica of the mullite raw material powder and exists as cerium oxide crystals. It is believed that the deterioration is reduced and the sintering temperature can be lowered.

(Example) The present invention will be explained in detail below.

Example 1 Aluminum oxide powder (manufactured by Showa Denko, trade name UA-510)
5, purity 99.99%) and silicon dioxide powder (manufactured by Koso Chemical, high purity reagent, purity 99.99%) were weighed in the proportions shown in Table 1, and dissolved by wet mixing in a ball mill for 6 hours. The grains were then spray dried. This was calcined at 1650° C. for 1 hour, cooled, and then ground to obtain a mullite powder. This mullite powder contained 900 parts by weight of mullite crystals.

Next, cerium oxide powder (manufactured by Nissan Kigenso, purity 99.991) and yttrium oxide powder (manufactured by Mitsubishi Chemical Industries, Ltd., purity 99.99) were added to the mullite powder obtained above in the proportions shown in Table 1. and wet-mix again using a ball mill until the average particle size is about 1 μm.

Shattered. To 100 parts by weight of the obtained slurry, 2 parts by weight of polyvinyl alcohol (Cran A, trade name Poval 110) and 2 parts by weight of wax (manufactured by Mopil Oil Co., Ltd., trade name Marlex 209) were added, and the mixture was spray-dried to form granules for molding. Obtained. The molding granules were then rubber press molded at a pressure of 12 tons/al and fired for 3 hours at the temperatures shown in Table 2 to obtain mullite sintered bodies.

The obtained mullite sintered body was cut into a size of 3w + x 4am x 40m, and the bending strength at room temperature and at 1200°C was measured by a three-point bending test based on JIS R1601-1981. The results are shown in Table 2.

Furthermore, the relationship between the firing temperature and the bulk density of the mullite sintered body is shown in FIG. In Table 2, since the mullite sintered body of No. 5 was foamed, the bending strength was not measured.

Table 1 Arrows indicate items not included in the present invention.

Table 2 Arrows indicate items not included in the present invention.

As is clear from Table 1, Table 2, and Figure 1, the firing temperature of the mullite sintered body according to the present invention is approximately 50 to 150°C lower than that of the high purity mullite sintered body with fragrance 1. Moreover, it has excellent bending strength at room temperature, and has a t.
It can be seen that the deterioration is small even at a high temperature of 0°C. On the other hand, it can be seen that the mullite sintered bodies with fragrances of 6°7 and 12 have a large deterioration in bending strength at high temperatures.

(Effects of the Invention) The mullite sintered body obtained by the present invention can be fired at a temperature 50 to 150°C lower than the conventional firing temperature, has excellent strength at room temperature, and does not deteriorate in strength even at high temperatures. This mullite sintered body is small and can be produced at low cost, making it extremely suitable industrially.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between firing temperature and bulk density of sintered mullite. Grilling mildness ('C) Fig. 1

Claims (2)

[Claims] 1. Mullite raw powder or mullite powder 95-99
．． A composition for a mullite sintered body comprising 8% by weight of cerium oxide and 0.2 to 5% by weight of cerium oxide. 2. Weight ratio of alumina:silica is 65:35 to 80:
20 mullite raw material powder or 95 to 99.8% by weight of mullite powder obtained by firing and pulverizing the mullite raw material powder and 0.2 to 5% by weight of cerium oxide powder or a salt containing 0.2 to 5% by weight of cerium oxide. Alternatively, a method for producing a mullite sintered body characterized by mixing an organic compound uniformly and then firing it.