JPS5939769A - Method of sintering silicon nitride - 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 (a) Background of the Technology The present invention relates to a method for sintering silicon nitride to obtain a silicon nitride burner having high high temperature strength and high density.

Recently, the development of ceramic materials, especially ceramics as heat-resistant materials, has been actively conducted, and covalent compounds, especially silicon nitride (SisN4), which are heat-resistant substances that are stable at high temperatures, are excellent materials. It is known that

Ceramics are generally used by molding and sintering raw ceramic powder, but in the case of Si3N4,
Unlike general oxide ceramics, it is a material that is difficult to sinter, so it is difficult to obtain a dense sintered body even if only a single composition, such as 5iBN4 powder, is sintered.

Therefore, in the case of 5iaN4 powder, MgOr kl
Sintering is carried out by adding oxide powder such as 201+ 1Y208 eceo2tBeo as a sintering aid.

However, the conventional method of press forming using 5isN+ powder containing a sintering aid and heating and sintering it in vacuum or normal pressure is not industrially useful due to its low sintering cost. However, since the micropores remain in the 5i3Na sintered body, it is difficult to obtain a high-density sintered body.

On the other hand, the hot press method, in which sintering is carried out under pressure at high temperatures, can produce a more dense sintered body, but it has the disadvantage that strength decreases at high temperatures and sintering costs are high. There are some difficulties.

This decrease in strength at high temperatures can be reduced by adding sintering aids.
This is thought to be due to the formation of a low melting point substance at the isN4 powder interface, which is unavoidable when a sintering aid is used.

Furthermore, the mixing ratio of the sintering aid may be reduced, or the powder may be sintered in a high-pressure gas atmosphere without the addition of a sintering aid, or the powder may be pulverized by instantaneously applying high pressure using explosive molding, etc., and then sintered. Methods such as sintering have been attempted, but all of these methods have the drawbacks of high sintering costs and a reduction in high-temperature strength, and have not been successful as industrial methods.

In view of the above points, the present inventors have developed a method for sintering 51gN4 powder to obtain a 5LaN4 sintered body with high temperature strength and high density while using a sintering aid.After press-forming 5isN4 powder, Maki, vacuum or This invention was achieved as a result of repeating tests by performing sintering under various atmospheres such as pressurization, and varying sintering conditions such as temperature.

(B) Disclosure of the Invention That is, the present invention provides that, when sintering a compact of 5iaNn powder to which a sintering aid has been added, the temperature raising process during sintering is carried out in the same sintering furnace (first step). A process of evaporating or decomposing oxygen or moisture adsorbed on the compact powder in a vacuum atmosphere or a reducing reduced pressure atmosphere (second stage). Step of sintering while removing the oxide film (8th step) Step of sintering in a pressurized atmosphere with N2 partial pressure of latm or more (4th step) N2 or Ar or Ar and N of 1000 atm or more
It is characterized by the process of further densification of the sintered compact in a pressurized atmosphere of a mixed gas of 11. This process results in a 51g product with high density, high strength, and little strength deterioration at high temperatures.
A N4 sintered body is obtained.

In the method of the present invention, the first step is to use 5is as a raw material.
Removes sintering inhibitors such as oxygen, moisture, or organic substances that are contained or adsorbed from N4 powder or sintering aid powder or during the powder processing process, or substances that remain in the sintered body and deteriorate the properties of the sintered body. It is intended to be carried out in a vacuum or in a reducing atmosphere. The treatment temperature range is preferably from room temperature to 1100° C. from the viewpoint of the effect of removing the above-mentioned harmful substances and preventing the 5isNa powder and the sintering aid powder from decomposing.

The second stage is a process in which sintering progresses while removing oxides on the surface of the 5iaN4 powder that constitutes the compact. In this process, a liquid phase is generated and densification begins, so the atmospheric pressure is The pressure must be reduced to prevent pores from remaining in the sintered body due to trapping of atmospheric gas or gas generated from the sintered body. As the atmospheric gas, N2 partial pressure is required to suppress the decomposition of the sintered body, and to enhance the effect of removing oxides from the powder surface.
It is effective to apply a partial pressure of N2 or CO gas.

The treatment temperature is preferably in the range of 800 to 1700°C. At temperatures below 800°C, no oxide removal effect can be expected. Further, a reduced pressure treatment at 1700° C. or higher is not preferable because it promotes decomposition of the 5isN4 powder.

The third stage is the original sintering process and 4. Therefore 5i3
latm to advance sintering while suppressing the decomposition of Ni.
A pressurized atmosphere with a partial pressure of N2 above is required.

Although the treatment temperature varies depending on the type of sintering aid used, it is generally in the range of 1500 to 2000°C.

The fourth stage is to remove pores remaining in the process up to the third stage and to densify the sintered body at a pressure of 1.000 atm or higher.
This is a step of applying hot static pressure at atmospheric pressure. Generally 1
Hot static pressure treatment under pressure of 1000at or more
However, in order to suppress the decomposition of 5iaN4, it is preferable to perform the treatment in an N2 atmosphere or a mixed gas atmosphere of N2 and Ar in the treatment of a 5isN4 sintered body. A temperature range of 1600 to 2000°C is effective.

As mentioned above, according to the present invention, in the same furnace body, continuously without taking it out into the air, (1) a step of removing harmful substances adsorbed to the compact powder, (2) an oxide film on the surface of the compact powder. The process of sintering while removing ■ 5i in a pressurized N2 atmosphere
It is possible to perform the process of proceeding with sintering while suppressing the decomposition of aN4, and the process of removing the pores contained in the sintered body in a high-pressure atmosphere and making the sintered body denser, resulting in high purity, high density, and A sintered body with high strength and little deterioration of strength characteristics at high temperatures can be obtained.

Example SisN489wt%, A120a 7%, Y2O34
% of the powder mixture was pressed into the shape of a test piece, and the sintered body was sintered under the following conditions. After grinding, the bending strength was measured. Table 1 shows the results.

Table 1

Claims (2)

[Claims] (1) When sintering a compact of silicon nitride powder to which a sintering aid has been added, in the same sintering furnace during the temperature raising process, (first step) molding in a vacuum atmosphere or reducing reduced pressure atmosphere. A process of evaporating or decomposing and removing oxygen or moisture adsorbed in the powder body (second stage) A process of sintering while removing an oxide film on the surface of the powder compact in a reduced pressure atmosphere with a N2 partial pressure of latm or less ( 3rd step) A step of proceeding with sintering in a pressurized atmosphere having a N2 partial pressure of latm or more (4th step) 1000 atm or more of N2 or Ar or Ar and N
2. A method for sintering silicon nitride, which is characterized by passing through four steps of further densification of the sintered body in a pressurized mixed gas atmosphere. (2) The first stage is carried out at a temperature ranging from room temperature to 1100°C, and the second stage
The temperature range is 800-1700°C, and the third stage is 15°C.
In the range of 00 to 2000 °C, the fourth stage is 1600 to 2
2. The method for sintering silicon nitride according to claim 1, wherein the sintering method is carried out at a temperature of 0.000°C.