JPS60145965A - Manufacture of silicon nitride sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a silicon nitride sintered body.

Silicon nitride sintered bodies have excellent thermal and mechanical properties such as mechanical strength, creep resistance, heat resistance, thermal shock resistance, and corrosion resistance, so they have recently been used as high-temperature mechanical parts and high-temperature structural materials. It is expected to be used as wear-resistant materials and corrosion-resistant materials.

However, silicon nitride is a substance that is extremely difficult to sinter, and it is difficult to sinter it alone to form a high-density sintered body. Therefore, a method has been proposed in which a high-density sintered body is manufactured by adding oxide powder of various companies to silicon nitride powder and sintering the mixture. As the oxide powder, for example, oxides of magnesium, aluminum, yttrium, etc. are used.

Japanese Unexamined Patent Publication No. Sho 58-(i4279) discloses a method of adding magnesium oxide with a particle size of 500 Å or less to silicon nitride powder and sintering it. However, the silicon nitride sintered body obtained by this method Its strength is still far from sufficient for practical use.

The present inventors have discovered that by sintering a mixture of silicon nitride and magnesium oxide having a specific specific surface area and particle structure, a silicon nitride sintered body having excellent grain properties and a-nuclear properties can be obtained. The present invention was completed based on the discovery that this can be done.

That is, the present invention uses 1 to 30% by weight of magnesium oxide powder consisting of equiaxed primary particles with a specific surface area of 30rd/g or more.
and the remainder is granular silicon nitride powder with a specific surface area of 3 rd/g or more, which is sintered at a temperature of 1500 to 2000°C under a pressure of 50 to 1000 kg/-. This is the method for producing solids.

The magnesium oxide used in the present invention has a specific surface area of 3
0 rtr/g or more, and is a magnesium oxide powder consisting of equiaxed primary particles.

The above-mentioned magnesium oxide powder can be used, for example, in Japanese Patent Application No. 1988-88889 filed by the present applicant. ■It cannot be manufactured according to the method described in the book.

In the above method, magnesium vapor and oxygen-containing gas are mixed at a magnesium vapor partial pressure of 0.09 atm or less, an oxygen partial pressure of the oxygen-containing gas of 1/2 or more of the magnesium vapor partial pressure, and a reaction temperature of 800 to 16 oo C. This is a method of oxidizing magnesium by bringing them into contact with each other in parallel current conditions.

Magnesium oxide powder is usually produced by thermal decomposition of hydroxide, acetate, basic carbonate, oxalate, etc. However, it is known that the magnesillarum oxide powder synthesized by these salt separations has strong secondary agglomeration and also has a large secondary particle size. These aggregated particles are
It remains even after mixing with silicon nitride powder, has poor dispersibility at the secondary particle level, and is the cause of large silicate lumps or pores remaining at grain boundaries even after sintering. If such precipitated phases or pores are present at the grain boundaries, the locations become points of origin for fracture, making it impossible to obtain a high-strength sintered body.

On the other hand, the magnesium oxide powder obtained by the reaction of the above-mentioned magnesium vapor and oxygen-containing gas is
It is composed of equiaxed primary particles and has the advantage of almost no secondary aggregation. Therefore, when mixed with silicon nitride powder, uniform dispersion of primary particles can be easily achieved, and after sintering, a uniform structure in which silicon nitride particles are covered with a magnesium silicate layer several hundred thick is obtained. A sintered body with a fine structure can be obtained. It is known that a sintered body having such a uniform microstructure has high strength.

Thus, the magnesium oxide used in the present invention is
It is necessary to simultaneously satisfy the condition that the specific surface area is 30rd/g or more and the condition that the particle structure consists of equiaxed primary particles, and if either is not satisfied,
When mixed with silicon nitride, uniform dispersion at the secondary particle level cannot be achieved, resulting in a decrease in the strength of the resulting sintered body.

The silicon nitride used in the present invention has a specific surface area of 5rd/g
The above is a nitride-silicon powder whose particle structure is granular.

The silicon nitride powder can be produced, for example, by thermally decomposing silicon diimide or silicon tetraamide obtained by reacting silicon tetrachloride and ammonia in a liquid phase.

The silicon nitride used in the present invention has a specific surface area of 5rd/g
It is necessary to simultaneously satisfy the above condition and the condition that the particle structure is granular. If either of these conditions is not satisfied, the strength of the obtained sintered body will decrease.

The quantitative ratio of magnesium oxide I5) powder and silicon nitride powder is:
For the mixture of both, magnesium oxide powder 1+ powder is 7% by weight, preferably 1.5 to 0% by weight. If the amount of magnesium oxide powder used is more than 30% by weight, The high-temperature strength of the resulting sintered body decreases, and if the amount used is too small, the sintering promotion effect will not be observed and a high-density sintered body will not be obtained.

There are no particular restrictions on the method of mixing magnesium oxide powder and silicon nitride powder, and methods known per se may be used, for example, dry mixing of the two, or wet mixing of side stones in an organic solvent such as methanol or ethanol. A method of removing the organic solvent after mixing can be adopted.

In the present invention, a mixture of magnesium oxide powder and silicon nitride powder is sintered under pressure.

The sintering pressure is 50-1000 kg/c and the sintering temperature is 15
00-2000°C, preferably 1600-1800°C. If the sintering temperature is lower than the lower limit, a high-density sintered body cannot be obtained, and if the sintering temperature is higher than the upper limit, silicon nitride itself will decompose.

Sintering is performed in a non-oxidizing atmosphere such as nitrogen gas, argon gas, nitrogen/hydrogen mixed gas, nitrogen/carbon oxide mixed gas.

According to the present invention, which uses a mixture of magnesium oxide and silicon nitride having a specific specific surface area and particle structure, it can be seen from the results of the examples described below. 1- A silicon nitride sintered body with excellent physical properties can be produced.

Examples and comparative examples are shown below.

In the Examples and Comparative Examples, the t71 density of the sintered body was measured by the Archimedes method and expressed as a percentage of the theoretical density. The bending strength of the sintered body was determined by cutting out a 3 * 4 * 40 dragon rod-shaped test piece from the sintered body, grinding the surface in the axial direction with a diamond wheel, and then Span 30mm, crosshead speed 0.
It was measured by performing a three-point bending test at room temperature and 1200°C at a speed of 5 mm/min. The number of test pieces was 30 for room temperature and 10 for 1200°C, and the values are shown as their average values.

In the following description, all "%" indicates "% by weight".

Examples 1 to 4 By thermal decomposition of magnesium oxide powder consisting of equiaxed primary particles with a specific surface area of 63 m/g and silicon diimide synthesized according to the method described in Japanese Patent Application No. 1988-88889. The synthesized specific surface area is 12゜3n(/
g of granular silicon nitride powder were charged into an alumina ball mill in the proportions shown in Table 1, wet mixed in an Efnol, and dried to obtain an unmixed mixture.

150 g of the powder mixture was filled into a graphite die with a diameter of 100 mm, and hot pressed under the conditions listed in Table 1 in a mixed atmosphere of nitrogen/carbon oxide to perform molding and sintering at the same time. A quality sintered body was obtained.

The results are shown in Table 1.

Comparative Example 1 As magnesium oxide, magnesium oxide powder with a specific surface area of 15 m/g (manufactured by Kishida Chemical Co., Ltd., secondary particle size: 2.5 μ
The same method as in Example 1 was repeated except that m) was used.

The results are shown in Table 1.

Comparative Example 2 Same as Example 1 except that silicon nitride powder having a specific surface area of 10+n/g and a particle structure having a T1-like structure with a diameter of 0.2 μ and a length of 10 to 20 μ was used as the silicon nitride. The method was repeated.

The results are shown in Table 1.

Filled with hesitation

Claims (1)

[Claims] A mixture consisting of 1 to 30% by weight of magnesium oxide powder consisting of equiaxed =- missing particles with a specific surface area of 30rd/g or more, and the balance consisting of granular silicon nitride powder with a specific surface area of 5n(/g or more), 1-5 under pressure of 1000 kg/cd
A method for producing a silicon nitride sintered body, characterized by sintering at a temperature of 00 to 2000°C.