JP2938500B2 - Method for producing raw material for cubic boron nitride sintered body - Google Patents

Description

The present invention relates to a method for producing a raw material for synthesizing a cubic boron nitride (cBN) sintered body suitable for a heat sink and a cutting tool, and in particular, to a method for producing a starting material. A method for efficiently producing a raw material obtained by diffusing and impregnating an alkaline earth metal boron nitride as a cBN conversion catalyst into a cracked boron nitride (P-BN) compact or a hexagonal boron nitride (hBN) sintered body Things.

[Conventional statement]

cBN is a material having hardness and thermal conductivity next to diamond, and its high-purity sintered body is expected to be applied particularly as a cutting tool and a heat sink for semiconductor elements.
As a method for producing a high-purity cBN sintered body, a P-BN molded body (JP-A-62-108772, JP-A-63-260865) or an hBN sintered body (JP-B-60-28782) ), The surface of each is diffused and impregnated with alkaline earth metal boron nitride, which is a cBN conversion catalyst, and sintered at high temperature and pressure under the thermodynamically stable conditions of cubic boron nitride. I have. By these methods, a high-purity sintered body in which cBN particles are directly bonded to each other can be produced. In particular, in the former method using a P-BN molded body as a starting material, a sintered body having high thermal conductivity can be obtained.

The method of diffusing and impregnating the alkaline earth metal boronitride is as follows: 1. Contact the P-BN molded body or hBN sintered body with the alkaline earth metal nitride and / or boronitride powder, Method of reacting and diffusing in an atmosphere (solid-phase method). 2. Put the hBN sintered body in a boron nitride crucible and make it not in contact with the alkaline earth metal nitride and / or boron nitride powder. Is known, but the above-mentioned method 1 (solid-phase method), in which diffusion conditions can be easily controlled, is generally used.

[Problems to be solved by the invention]

However, when producing a raw material for a cBN sintered body in which the alkaline earth metal boron nitride is diffused and impregnated by the solid phase method described above, the P-BN molded body or the hBN sintering is performed simultaneously with the heat treatment for the diffusion impregnation. The sintering of the alkaline earth metal nitride and / or boronitride powder contacted with the sintered body also proceeds at the same time,
The alkaline earth metal boronitride layer (catalyst layer) formed on the surface of the P-BN molded body or hBN sintered body adheres to the surrounding alkaline earth metal nitride and / or boronitride powder Phenomena often occur. For this reason, when recovering the P-BN formed body or the hBN sintered body (raw material for cBN sintered body) in which the catalyst is diffused and impregnated, the catalyst layer on the surface thereof is surrounded by a sintered alkaline earth metal nitride. And / or adhered to boron nitride and often fell off the surface of the raw material for the cBN sintered body, which was a major cause of lowering the yield.

In order to obtain a high-quality cBN sintered body, a raw material in which a catalyst layer is uniformly formed on a P-BN molded body or an hBN sintered body is considered. For this purpose, an alkaline earth metal nitride to be catalyzed and Preferably, the particle size of the boron nitride powder is small. However, powder having a fine particle size tends to be sintered and adhered. For this reason, it has been difficult to achieve both the synthesis of a high-quality raw material for a cBN sintered body having a uniform catalyst layer and the production of the raw material at a high yield.

An object of the present invention is to solve such a problem in the conventional solid phase method and to produce a raw material for a cBN sintered body at a high yield. That is, an object of the present invention is to provide a sintered P-BN molded product, which has been sintered during the heat treatment for diffusion impregnation, which has occurred in the conventional solid phase method, Alternatively, to provide a method for industrially producing a raw material for cBN sintered body with a high yield by eliminating the problem of sticking to the catalyst layer generated on the surface of the hBN sintered body and dropping the catalyst layer at the time of raw material recovery. It is in.

[Means for solving the problem]

The present inventors have proposed a P-BN molded article or hB
When diffusing and impregnating the alkaline earth metal boronitride into the N sintered body, the alkaline earth metal nitride and / or boronitride powder to be brought into contact with the P-BN molded body or the hBN sintered body is hBN powder. Is mixed, the sintering of the alkaline earth metal nitride and / or boronitride powder during the heat treatment for diffusion impregnation is suppressed, and the P-BN compact or the hBN sintered body adheres to the catalyst layer on the surface. Did not occur, which led to the present invention.

That is, the present invention relates to a method for producing a raw material for a cBN sintered body, which is obtained by diffusing and impregnating an alkaline earth metal boron nitride into a pyrolytic boron nitride molded body or a hexagonal boron nitride sintered body. In producing a raw material for a boron nitride sintered body, a pyrolytic boron nitride molded body or a hexagonal boron nitride crystal is mixed with 0.5 to 50% by weight of hexagonal boron nitride powder and 99.5 to 50% by weight of an alkali. Earth metal nitride and / or
Alternatively, it is characterized in that it is brought into contact with a mixed powder comprising boronitride powder and heated in a non-oxidizing atmosphere.

The content of hBN powder in the powder used for diffusion impregnation is
0.5 to 50% by weight is preferred. At 0.5% or less, the effect of adding the hBN powder is not exhibited, and the sintering of the powder during the diffusion impregnation process is not suppressed, so that the production yield of the raw material for the cBN sintered body is reduced. If it exceeds 50%, the concentration of the alkaline earth metal nitride and / or boronitride in contact with the P-BN molded body or the hBN sintered body decreases.
The diffusion speed of boron nitride into the hBN sintered body is low, and it takes a long time for diffusion and impregnation of the catalyst, which is not practical. The particle size of the powder is preferably 500 μm or less, more preferably 300 μm or less, in order to achieve uniform diffusion and impregnation.

The hBN powder used here is preferably a high-purity powder having an oxygen content of 1% or less, and a powder having a particle size of 100 μm or less is obtained by sintering alkaline earth metal nitride and / or boronitride powder. This is preferable for suppressing

Alkaline earth metals are group IIa of the periodic table, that is, Be, M
g, Ca, Sr, Ba, and Ra. Among them, in the method of the present invention, nitrides and / or boronitrides of Mg, Ca, Sr, and Ba, which are easy to handle, are usually used. The nitrides are Mg ₃ N ₂ , Ca ₃ N ₂ ,
Sr ₃ N ₂ (or Sr ₂ N + SrN) and Ba ₃ N ₂ are common, but the stoichiometric ratio of metal to nitrogen is also 2: 1, 11:
The existence of compounds such as 8, 3: 4, and 1: 6 is known, and any of these can achieve the object of the present invention. These nitrides can usually be produced by reacting each metal with nitrogen at a high temperature. Examples of industrially preferable nitriding reaction temperature and time conditions in which the reaction rate is moderately fast and thermal runaway of the nitridation reaction hardly occurs are Mg, Ca,
For Sr and Ba, 700-800 ° C, 850-950 ° C, respectively
Heating is performed at a temperature of 500 to 600 ° C and 450 to 550 ° C for 5 to 10 hours. In the case of Mg and Ca, since the metal is melted at the above-mentioned temperature, it is preferable to preliminarily preliminarily nitride the metal surface by heating at about 600 ° C. and about 750 ° C. for about 4 hours. Boron nitride is Me ₃ BN ₃ or Me
₃ B ₂ N ₄ (Me represents an alkaline earth metal), which can be produced by mixing a predetermined amount of each of the above nitrides with boron nitride and heating in nitrogen. . The conditions are 1100-13 for Mg, Ca, Sr, and Ba, respectively.
It is about 15 hours at temperatures of 00 ° C, 650-850 ° C, 500-800 ° C, and 700-1000 ° C.

The P-BN molded body or hBN sintered body to be brought into contact with this powder needs to be of high purity in order to obtain a cBN sintered body. Molded bodies are particularly preferred because of their very high purity,
Can be used without special pretreatment. On the other hand, the hBN sintered body is obtained by adding an oxide auxiliary to hBN powder and sintering it.Since oxygen inhibits conversion to cBN, when using this, Japanese Patent Publication No. 60-28782 is used. As shown in a gazette or the like, it is necessary to remove oxygen in advance by high-temperature treatment.

As a method of bringing the alkaline earth metal nitride and / or boronitride powder into contact with the P-BN molded body or the hBN sintered body, light embedding of the P-BN molded body or the hBN sintered body in the powder is performed. General.

Since the heat treatment for diffusion and impregnation is usually performed at a temperature of 1100 to 1300 ° C., in order to prevent oxidation of the P-BN molded body, hBN sintered body, alkaline earth metal nitride and / or boronitride, nitrogen, It is necessary to heat in a non-oxidizing atmosphere such as a rare gas.

The raw material produced by the method of the present invention is subsequently converted into a cBN sintered body by high-temperature and ultra-high pressure treatment. The condition is selected from a thermodynamically stable region of cBN at 1300 ° C. or higher and 40,000 atmospheres or higher. As a device for generating such high temperature and high pressure, a device of a belt type, a girdle type or the like is generally used.

〔Example〕

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Examples 1 to 9 and Comparative Examples 1 to 3 From a plate of pyrolytic boron nitride (Denka P-BN, trade name, manufactured by Denki Kagaku Kogyo KK) having a density of 2.16 g / cm ³ , a thickness of 1 m
A disk of m × 7 mm in diameter was punched out by an ultrasonic machine. Each of the 50 discs was a mixture of an alkaline earth metal nitride or boronitride powder and an hBN powder (grade GP, particle size 325 mesh or less, manufactured by Denki Kagaku Kogyo KK) as shown in Table 1. , And held at 1200 ° C. for 20 hours in a nitrogen atmosphere to diffuse and impregnate the alkaline earth metal boronitride catalyst on the surface of the P-BN disk, and to remove the impregnated alkaline earth metal nitride or boron nitride. The state of the mixed powder of the powder and the hBN powder, the amount of impregnated catalyst, and the percentage of impregnated P-BN disks that could be recovered without falling off of the catalyst layer (non-defective rate) were examined. Table 1 shows the results. The fact that the alkaline earth metal boron nitride was impregnated in the P-BN disc was confirmed by X-ray diffraction, respectively, and the catalyst impregnation amount was determined from the weight change of the P-BN disc before and after the heat treatment. Was.

Examples 10 to 14 and Comparative Examples 4 to 6 hBN sinter (grade N-1 manufactured by Denki Kagaku Kogyo KK) having a density of 1.9 g / cm ³ was treated in a nitrogen atmosphere at a temperature of 2100 ° C. for 2 hours. The oxygen content after the treatment was 0.1% by weight or less. From this plate, a disk having a thickness of 1 mm and a diameter of 7 mm was punched by an ultrasonic machine. Each 50 discs were buried in a mixed powder of Mg ₃ N ₂ powder and hBN powder (made by Denki Kagaku Kogyo KK, grade GP, particle size 325 mesh or less) shown in Table 2,
Holding at 1160 ° C. for 8 hours in a nitrogen atmosphere, the surface of the P-BN disk was diffused and impregnated with a magnesium boron nitride (Mg ₃ BN ₃ ) catalyst, and the impregnated Mg ₃ N ₂ powder and hBN powder were mixed. The state of the mixed powder, the amount of impregnated catalyst, and the ratio of impregnated hBN sintered bodies that could be recovered without falling off of the catalyst layer (yield rate) were examined. Table 2 shows the results. The impregnation with magnesium boronitride was confirmed by an X-ray diffraction method. The catalyst impregnation amount was determined from the weight change of the hBN sintered body disk before and after the heat treatment.

[Effects of the present invention] According to the present invention, a raw material for a cubic boron nitride sintered body having high purity and high thermal conductivity can be produced with a high yield.

Claims (1)

(57) [Claims] 1. A method for producing a raw material for a cubic boron nitride sintered body in which an alkaline earth metal boron nitride is diffused and impregnated into a thermally decomposed boron nitride molded body or a hexagonal boron nitride sintered body. A boron nitride compact or a hexagonal boron nitride sintered body is mixed with 0.5 to 50% by weight of hexagonal boron nitride powder and 99.5 to 5
A raw material for a cubic boron nitride sintered body, which is brought into contact with a mixed powder comprising 0% by weight of an alkaline earth metal nitride and / or boronitride powder and heated in a non-oxidizing atmosphere. The manufacturing method.