JPS60186473A - Silicon nitride sintered body and manufacture - 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 [Field of Industrial Application] The present invention relates to a method for producing silicon nitride-based fine ceramics.

[Prior art]

Methods for producing silicon nitride sintered bodies can be classified into two types: reaction sintering and pressureless sintering. Compared to the pressureless sintering method, the reaction sintering method has the advantage of being able to easily produce large-sized objects, and the sintered bodies obtained by the reaction sintering method do not lose strength even at high temperatures. There are some excellent points. However, the current drawback is that it is not possible to obtain a dense and high-strength tissue, and it has lost its place as a high-strength member.

The main reason why densification cannot be achieved using the reaction sintering method is that almost no sintering shrinkage occurs at the time when the green body is transformed into a silicon nitride sintered body.

There is a two-step sintering method that improves this drawback of the reactive sintering method. In this two-step sintering method, a porous silicon nitride sintered body is first obtained by a reaction sintering method, and then AQ, Mg, and Y, which become sintering aids for silicon nitride, are added to the pores of the sintered body. In this method, the material is impregnated with a compound such as, and then sintered again to cause sintering shrinkage and densification.

However, like the sintered body obtained by pressureless sintering, the strength of the obtained sintered body significantly decreases at high temperatures of 1000°C or higher, and the strength of the sintered body obtained by the reaction sintering method is diminished. The drawback is that it disappears.

A method has also been proposed in which silicon powder is used as a starting material and the silicon is densified by shrinkage during sintering, but this method has not been successful in practice. The cause of this is silicon oxide (
This is because the silica film prevents the sintering of silicon together. One possible method for removing this silica film is to use H2 gas, but the reaction between H2 gas and the silica film does not occur unless it is at a high temperature of 1,200°C or higher. This method cannot be used because the sintering shrinkage progresses rapidly and is so large that the continuous pores necessary for the nitriding reaction inside the molded body are lost, and the nitriding reaction itself is inhibited.

The optimum temperature range for controlling sintering of silicon powders is around 1100'C, and it is necessary to remove the silica film on the surface of the silicon powder before reaching that temperature range.

[Purpose of the invention]

The purpose of the present invention is to solve this problem and provide a reaction sintering method for obtaining a silicon nitride sintered body as an inexpensive, high-quality, high-temperature, high-strength member by achieving high strength and high density. .

[Structure of the invention]

The present invention is characterized by the ability of H2 gas and CH4°c2H at high temperatures.
This method was developed based on the fact that immediately after decomposition, H ions and C ions generated from compounds that generate hydrocarbon gases such as 6 are in an activated state and have a very strong reducing effect.

As the compound, an organosilicon polymer compound having C and 81 as the main skeleton components or a compound such as phenol resin can be suitably used, and it can be thermally decomposed at a temperature of 500 "C or higher" to produce H2 gas, CH4, c2H , and other hydrocarbon gases. The compounds used in the present invention are not limited to organosilicon polymer compounds or phenolic resins, but also compounds that generate activated ■] ions and C ions that have the function of reducing silica membranes at around 1100°C. Of course, you can use it as you like. However, compounds that generate such pyrolysis gas at temperatures below 500°C.

For example, if polyvinyl butyral is used, it will react and lose its reducing properties before reaching the reaction temperature range of around 1100° C., making it difficult to maintain a reducing atmosphere at the reduction temperature of silica.

The above-mentioned pyrolysis gas is mixed by dispersing these compounds generated at 500 to 1100°C near the silicon powder in the green compact, and then heat-treated in an inert gas, and then heated to 1100°C for a predetermined time, e.g. By maintaining the temperature for 20 hours, a firing shrinkage rate of about 6% can be obtained.

The type of gas used for heat treatment in the first stage is N2
, a mixed gas of N2 and H2, a nitriding gas such as NH3, or an inert gas such as He, etc. can be used. However, if the temperature exceeds 1200°C, the molded body will rapidly undergo large sintering shrinkage, making it difficult to secure continuous holes in the molded body to cause the nitriding reaction.
Measurement at temperatures above 0°C.

The use of inert gases such as He is undesirable. On the other hand, in the nitriding gas, when the temperature exceeds 1200°C, the reaction between St and N2 proceeds, so the sintering shrinkage between St rapidly decreases, and at 1300°C, the sintering shrinkage completely disappears.

The present invention utilizes the characteristics of these gases to control the amount of firing shrinkage of the molded body.

〔Example〕

Hereinafter, organic silicon polymers (P, C, S') and phenol resins were used as compounds that generate H2 gas and hydrocarbon gases such as CH4 and C2Ha at temperatures of 500°C to 1100°C as used in the present invention. The effects of this case will be described by way of examples.

Example 1 At a mixing ratio of 90% by weight of silicon powder of 44μ or less and 510% by weight of P, C, whose main skeleton components are C and Si, p,
A solution of c and s dissolved in hexane was mixed into silicon powder, and while stirring, the hexane was evaporated to prepare a molded body from the obtained powder.

This molded body was nitrided and synthesized under the heat treatment conditions shown in Table 1 up to 1300°C, and the results are shown in the same table.

As a comparative example, results are shown in which an alcohol solution of polyvinyl butyral (P, V, B) was used instead of p, c, s, all other conditions were the same, and the amount added was 5% by weight. Thermal decomposition properties of p, c, and s in a non-oxidizing atmosphere are approximately 15% in the range of 250°C to 500°C, and 15% in the range of 500°C to 1
At 200°C, approximately 30% hydrogen and methane gas evolution occurs. On the other hand, polyvinyl butyral almost completely decomposes at temperatures up to 500°C.

Example 2 A solution of phenol resin dissolved in alcohol was mixed with silicon powder at a mixing ratio of 90% by weight of silicon powder of 44μ or less and 10% by weight of phenol resin (P, H, R), and alcohol was added while stirring. After evaporating the
Using the obtained powder, a molded body was made according to the trial decision and Table 2
The results of nitriding synthesis under the conditions described in are shown in the same table. The thermal decomposition characteristics of phenol resin in a non-oxidizing atmosphere began to occur at around 450°C and almost ended at 1200°C, and the amount of hydrogen and methane gas generated in this range was about 50%. Similarly, p, c described in Example 1
, s, P, V, and B were also prepared under the same conditions as in Example 1. The amounts of p, c, s and P, V, and B added are all 10% by weight.

Table 2 P, 11. R: Phenol resin As shown in Examples 1 and 2, 500°C to 1200°C
In the range of , it releases reducing gases, H2 and CH4 gases. The effects of p, c, s and phenol resins are very large.

[Effect of the invention] Under the same temperature conditions, the sintering shrinkage rate of the conventional molded body is
It is about 0.1%, and it can be seen that the effect of the present invention is clearly significant compared to the conventional method.

The physical properties of the silicon nitride sintered body obtained by the present invention are that the bulk density is 2.92 and the bending strength at room temperature is 60 kg/112.1.
Bending strength at 400°C is 6314g/vna 2
These qualities are unprecedentedly high in quality obtained by the reaction sintering method, and the high strength at 1400° C. is the highest quality of ceramics currently reported.

The high-temperature strength members obtained by the novel reaction sintering method of the present invention have great prospects in the future, and are being reevaluated for applications that were previously considered impossible, such as ceramic engines, turbines, and blades.

Claims (1)

[Claims] 1. Molding by adding to silicon powder a compound that is decomposed by heating to generate hydrocarbon compounds such as N2 or CH4, C, H, etc. over a temperature range of 500°C or higher and 1200°C or lower. After making a body and heat-treating the molded body in an atmosphere of one of nitriding gases and inert gases or a mixture thereof, the silicon is chemically changed into silicon nitride at a temperature of 1200°C or higher in the nitriding gas. A method for producing a silicon nitride sintered body, characterized by: 2. The nitriding gas for heat treatment is N2. 2. The method for producing a silicon nitride sintered body according to claim 1, wherein the gas is mainly NH3 and the heat treatment temperature is 1300° C. or lower. 3. The method for manufacturing a silicon nitride sintered body according to claim 1, characterized in that the inert gas for the heat treatment is gas or He, and the heat treatment temperature is 1200° C. or less. 4. The silicon nitride sintered body according to claim 1, wherein the nitriding gas for chemically changing silicon into silicon nitride is N2 gas or a mixed gas of N2 gas and N2 gas. Production method.