JP2958449B2 - Method for producing cubic boron nitride particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for converting hexagonal boron nitride (hereinafter referred to as h-BN) to cubic boron nitride (hereinafter referred to as c -BN).

[0002]

2. Description of the Related Art Conventionally, c-BN is harder than diamond, does not react with iron, has high thermal conductivity, and is widely used for cutting and polishing steel materials and products. As a method for producing c-BN, h-
Although it has been obtained by converting crystals into c-BN using BN as a raw material and using a catalyst, c-BN obtained by this method has a catalyst component remaining in the grains because a catalyst is used. As a result, there is a disadvantage that the characteristics of c-BN may be impaired. Therefore, a method for directly converting the structure of h-BN to c-BN without using a catalyst (hereinafter, this method is referred to as a direct method) is desired.
In this case, very strict conditions of, for example, 1600 ° C. or more at 7.7 GPa were required, and the obtained product was a sintered body, and it was difficult to obtain a particulate material.

[0003]

DISCLOSURE OF THE INVENTION The present inventors have studied a method for obtaining c-BN particles under a milder condition using h-BN as a starting material by a direct method. First, a sample obtained by heating h-BN at a pressure of 7.7 GPa and a temperature of 1800 ° C. was observed with a high-resolution electron microscope.
Small crystal grains formed in the matrix of -BN,
It has been found that these crystal grains are composed of wurtzite-type boron nitride (hereinafter referred to as w-BN) and c-BN, and that there are many defects in w-BN. A high-resolution electron micrograph of the sample subjected to the heat treatment is shown in FIG.

As a result of studying this phenomenon, when h-BN is treated by a direct method without a catalyst, w-BN becomes c-B
Since it is understood that it is suggested to be formed prior to N, c-BN could be obtained more easily than before by promoting the production of w-BN.

Therefore, when the starting material h-BN is subjected to vibration milling, the crystal grains are finely divided parallel to the plate surface, and many amorphous regions are generated at the boundary, and many Defects were found to form, and it was found that heating them in the range of 6-8 GPa and 1250-1600 ° C. significantly accelerated the formation of c-BN. An object of the present invention is to provide a method for producing c-BN particles from h-BN by a direct method under milder conditions than before.

[0006]

The gist of the present invention is that a raw material powder of hexagonal boron nitride is subjected to vibration milling, and the obtained fine powder is subjected to a pressure of 6 to 8 GPa and a temperature of 1250 ° C. to 1600.
A method for producing cubic boron nitride particles, characterized by heating in a temperature range of ° C. That is, according to the present invention, when producing cubic boron nitride particles from hexagonal boron nitride by a direct method, vibration milling is applied to hexagonal boron nitride as a raw material powder, and the h-BN
After introducing a lot of defects into the inside, heat treatment under high pressure promotes the production of w-BM without a catalyst and converts h-BN to c-BN under conditions more relaxed than conventional conditions. is there.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail. As the hexagonal boron nitride raw material powder used in the present invention, an ordinary commercial product is used. Further, the vibration milling is performed by a normal commercially available apparatus, and the processing time is 5 minutes.
It is more than about a minute, and below it, the desired purpose cannot be achieved. The vibration milling process introduces many defects into the fine powder.

Next, the obtained fine powder is subjected to a pressure of 6 to 8 GPa,
The heat treatment is performed in a temperature range of 1250 ° C. to 1600 ° C. In this case, a pressure of 6 GPa or more is required, and below this pressure, conversion from h-BN to c-BN cannot be expected. Regarding temperature conditions, the effect is small at 1250 ° C. or less. A preferred temperature is 1350 ° C. The heat treatment time is about 15 minutes.

[0009]

Next, the present invention will be described more specifically with reference to examples. Example 1 An h-BN powder having an average particle size of about 10 μm was subjected to a milling treatment by a vibration mill for about 20 minutes, and the obtained powder was placed in a chamber at 1250 ° C. under a high pressure of 7.7 GPa.
Approximately 15 at each of 350 ° C, 1450 ° C and 1600 ° C
After holding for minutes, the mixture was cooled to room temperature. As a result of measuring an X-ray powder diffraction chart of the obtained powder, X-ray powder diffraction charts (A) of FIGS. 2A to 2D were obtained.

Comparative Example 1 The h-BN powder was heat-treated under the same conditions as in Example 1 except that no vibrating mill was used, and an X-ray powder diffraction chart of the obtained powder was measured. The X-ray powder diffraction chart (B) of FIG. 3 was obtained.

The above-described processing by the vibration mill shown in FIG. 2 was performed.
An X-ray powder diffraction chart obtained by high-pressure heat treatment at a temperature of 1250 ° C. to 1600 ° C. using h-BN, and FIG.
Using h-BN which is not treated by a vibrating mill,
When compared with the X-ray powder diffraction chart of the powder obtained by performing the high-pressure heat treatment under the temperature condition of 250 to 1600 ° C.,
It can be understood that the formation of -BN is remarkably promoted.

[0012]

As described above, the use of the h-BN powder which has been subjected to the vibration mill treatment allows the production of c-BN having a small amount of impurities and high hardness at a relatively low temperature by the direct method. The effect is brought. Therefore, the burden on the high-pressure synthesizer is small, and the economic efficiency is high. Since the obtained h-BN contains a large amount of defects (mainly twins), the hardness is higher than in the conventional method. Note that c-B
To obtain only N particles, use nitric acid + hydrogen fluoride solution (15
(0 ° C.) to dissolve the coexisting h-BN. Further, w-BN may be contained, but there is almost no decrease in hardness.

[Brief description of the drawings]

FIG. 1 is a high-resolution electron micrograph of w-BN + c-BN mixed particles generated in h-BN treated at a pressure of 7.7 GPa and a temperature of 1800 ° C.

FIG. 2 is an X-ray powder diffraction chart using h-BN subjected to a vibration mill treatment. (A) 1600 ° C, (b) 1
450 ° C., (c) 1350 ° C. and (d) 1250 ° C., where h: h-BN, c: c-BN, w: w-B
N.

FIG. 3 is an X-ray powder diffraction chart using h-BN not subjected to a vibration mill treatment. (A) 1600 ° C, (b) 14
In each case of 50 ° C., (c) 1350 ° C. and (d) 1250 ° C., h: h-BN, c: c-BN, w: w-BN
Is shown.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C01B 21/064 B01J 3/06

Claims (1)

(57) [Claims] A raw material powder of hexagonal boron nitride is subjected to vibration milling, and the obtained fine powder is subjected to a pressure of 6 to 8 GPa and a temperature of 1
A method for producing particles of cubic boron nitride, wherein the particles are heated in a temperature range of 250 ° C to 1600 ° C.