JPS6356188B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing a boron nitride (hereinafter referred to as BN) molded body by an improved sintering method. Conventional technology To obtain a BN molded body, A) a method of sintering a reaction intermediate during the production of BN powder, B) a method of mixing boric anhydride with BN powder and sintering it, and C) a method of volatilizing boron chloride etc. Conventionally, a method has been used in which a boron compound and a raw material for forming titanium, such as ammonia, are co-thermally decomposed on a high-temperature heating element. Problems to be Solved by the Invention As shown in U.S. Pat. No. 2,808,314, method A) uses a reaction intermediate as a raw material, so the purity of the molded product is poor and the binder in the molded product is used as a raw material. There are drawbacks such as difficulty in controlling the amount of boric anhydride as a compound and inability to control the particle size of the molded product. Method B) is a method that improves the drawbacks of method A), but has the drawback that when the same amount of binder as in A) is used, the strength of the molded product is weaker than in A). To solve this problem, methods have been taken to add CaO, SiO ₂ , etc., but these have the disadvantage of deteriorating the properties of BN, such as impairing heat conductivity and changing electrical properties. . The method described in C) can obtain a molded product with high purity even without a binder and bring out the basic physical properties of BN, but it takes a long time to manufacture, is not suitable for mass production, and the molded product is expensive. There is a problem with becoming. Means for Solving the Problems The present invention aims to provide a high-purity, high-strength molded product that improves the drawbacks of the above-mentioned methods. This is a method for producing a boron nitride molded body, which is characterized in that the surface of the powder is oxidized and then sintered. This will be explained in detail below. All raw materials used in conventional methods can be used in this method, but those that have been highly purified and highly crystallized in the powder stage are preferred. of course,
This does not apply to binders added for the purpose of intentionally changing the physical properties of the molded product, such as thermal expansion characteristics and conductivity. In addition, it is preferable that the particle size of the BN powder is fine from the viewpoint of the strength of the molded product, but in practice it may be as long as it can be obtained by currently known methods, and It may be further pulverized using a pulverizer. The surface of the raw material powder is oxidized using high-temperature steam in air or an oxygen atmosphere, but air is preferred in order to strictly control the amount of oxidation. The oxidation temperature is in the range of 650 to 1200℃, but in order to strictly control the amount of oxidation, it is preferable to keep it as low as possible.
°C is appropriate. As a result, the surface of the BN powder is oxidized,
It is thought that B ₂ O ₃ and a BN precursor partially composed of B, N, and O are formed, and this is re-decomposed into BN and B ₂ O ₃ during sintering, thereby completing the sintering. The degree of this oxidation is 1 to 20% by weight in terms of the strength of the sintered body.
should be within the range of If it is less than 1% by weight, the strength will be insufficient, and if it exceeds 20% by weight, the thermal properties will deteriorate. Next, the present invention will be specifically explained with reference to Examples and Comparative Examples, but it goes without saying that the present invention is not limited thereto. Example 1 Average particle size 5 μm, specific surface area 6 m ² /g, BN purity
99.95% BN powder was heated at 820℃ in a Matsufuru furnace under air.
The material was oxidized for 20 hours to obtain a raw material containing 6.9% B ₂ O ₃ and hot pressed at 1800° C. and 110 kg/cm ² in a nitrogen atmosphere to produce a molded body. Example 2 Average particle size 2 μm, specific surface area 30 m ² /g, BN purity
99.95% BN powder was air oxidized in a Matsufuru furnace at 950°C for 60 minutes to obtain a raw material containing 5.7% B ₂ O ₃ . This was pressurized with cold water at a pressure of 4000Kg/ ^cm2 ,
Then, it was sintered at 1900°C under normal pressure nitrogen atmosphere to produce a molded body. Example 3 Average particle size 2.8 μm, specific surface area 15 m ² /g, BN purity
99.95% BN powder, 0.8% calcium oxide by weight
After mixing in a ball mill for 10 hours, the mixture was oxidized at 1100° C. for 5 minutes in a siliconite furnace equipped with an alumina furnace tube to obtain a powder containing 7.3% B ₂ O ₃ .
This was hot pressed at 1850° C. and 127 kg/cm ² in a nitrogen atmosphere to produce a molded product. Comparative Example 1 8% by weight of boric anhydride was added to the BN powder used in Example 1, mixed in a ball mill for 10 hours, and this powder was hot pressed at 1800° C. and 110 kg/cm ² . The physical properties of the molded product obtained were extremely poor in bending strength. Comparative Example 1' 887 g of boric acid and 500 g of calcium phosphate were mixed with 580 g of water, dried at 150°C, pulverized in a Raikai machine to pass through 7 meshes, and placed in a siliconite furnace with an alumina core tube in an NH ₃ atmosphere. The reaction was allowed to proceed at 950°C for 16 hours, and the reaction product was pulverized using a hammer mill until it passed through a screen with a hole diameter of 1 mm.
After leaving it for 120 minutes under stirring in 180°C for 120 minutes, it was filtered and washed with hot water repeatedly, and when the pH of the filtrated water reached 7, it was further washed with hot water at 20°C, dried at 180°C for 24 hours, and then heated to 1800°C.
It was hot pressed at 110Kg/cm ² in a nitrogen atmosphere.
The molded product obtained in this way has a high B ₂ O ₃ content of 22%,
It had extremely high heat resistance. Comparative Example 2 The BN powder used in Example 2 was mixed with 8% by weight of boric anhydride and mixed in a ball mill for 10 hours. This powder was then pressurized with cold water at a pressure of 4000 kg/cm ² and then
Sintered at 1900℃ under normal pressure nitrogen atmosphere. The sintered product had cracks in all directions and could not be formed into a molded product. Comparative Example 3 8% by weight of boric anhydride was added to the powder obtained in Example 3 in which calcium oxide was added and mixed, and the mixture was mixed in a ball mill for 10 hours, and hot pressed at 1850° C. in a 127 kg/cm ² nitrogen atmosphere. The resulting molded product had low strength. Table 1 shows the physical properties of the molded bodies obtained in the above Examples and Comparative Examples.

[Table] Effects of the Invention According to the method of the present invention, it is possible to use high-purity BN powder, which was conventionally difficult to use because it is difficult to sinter, and the amount of binder can be easily controlled. The molded product has high purity and high strength and is industrially useful.

Claims (1)

[Claims] 1. After oxidizing the surface of boron titanide powder,
A method for producing a boron titanide molded body, characterized by sintering. 2. The oxidation treatment is carried out at 650 to 1200°C in an oxidizing atmosphere,
2. A method according to claim 1, characterized in that the sintering is preferably carried out at a temperature of 750 DEG -950 DEG C. and then the sintering is carried out by hot pressing. 3. A method according to claim 1, characterized in that 1 to 20% by weight of the boron titanide is surface oxidized.