JPH08189B2 - Method for producing cubic boron nitride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) Cubic boron nitride (hereinafter referred to as “cBN”), which is a high-pressure phase of boron nitride, has hardness and thermal conductivity second only to diamond, and Since it is chemically stable, it is being used as a tool for machining iron-based metals and as a heat dissipation substrate for semiconductor devices.

The present invention relates to a production method for obtaining cBN from low pressure phase boron nitride by a static high temperature high pressure method without using a catalyst.

(Prior Art) Generally, cBN is hexagonal BN, which is a low-pressure phase of boron nitride.
(Hereinafter referred to as “hBN”) or turbostratic structure BN (hereinafter referred to as “tB”).
(Denoted by "N") is maintained under thermodynamically stable conditions for cBN. When using static high-pressure and high-temperature treatment as a method for obtaining the thermodynamic stability condition of cBN, very severe conditions such as conversion pressure and temperature conditions of 65 kbar and 2100 ° C or higher are required. Therefore, industrially, a catalyst is used to set the conversion conditions to 40 to 50 kbar and a relatively mild condition of about 1500 ° C. By this method, single crystal type cBN
Particles are generated and used as they are as abrasive grains for a grinding tool such as a grindstone.

On the other hand, when fine cBN particles are sintered under high pressure and high temperature, a sintered body for cutting tools can be obtained, but cBN is difficult to sinter alone, so it is mixed with a bonding aid such as metal or ceramics and sintered. There is a need. CBN currently used industrially
Where most of them are manufactured by the above method,
The disadvantage is that the incorporation of catalyst and the presence of sintering aid deteriorates the original properties of cBN. Therefore, the catalyst-free direct conversion method without using catalyst and sintering aid (hereinafter referred to as "direct method").
Therefore, it is desired to realize the production of cBN particles and sintered bodies under milder conditions. CBN produced by the direct method is a polycrystalline body composed of fine particles and has features such as high hardness, high purity, photothermal conductivity, and high toughness, so it is expected to exhibit excellent performance as a tool material and heat dissipation substrate. Because it is expected.

The following documents are conventionally known as methods for producing cBN by the direct method.

Reference 1) Materials Research Burchin (Material)
s Research Bulletin), 7,999-1004 (1972) Reference 2) JP-A-54-33510 Reference 1) uses low crystalline boron nitride as a starting material.
It has been shown that "lump" cBN was obtained by processing at temperatures above 1250 ° C and pressures above 60 kbar. However, in this example, it was pointed out that H ₂ O acted as a catalyst (Shun Fukunaga, "Synthesis and Application of Cubic Boron Nitride", Ceramic Data Book '85, 431-436 (1
985))), and there are no additional trials, and there are many unclear points.

Reference 2) describes that a molded body of pyrolytic boron nitride is subjected to high temperature and high pressure treatment at a temperature of 1800 ° C. or higher and a pressure of 50 kbar or higher,
It is disclosed to produce a cBN sintered body.

Besides this, cBN can be treated by static high temperature and high pressure treatment without using a catalyst.
There are several reports of manufacturing
It requires high temperature and high pressure treatment under severe conditions such as temperature above ℃ and pressure above 60 kbar, which is not suitable for industrial production.

On the other hand, as another method for producing cubic boron nitride, Japanese Patent Publication No. 60-2245 discloses a method for obtaining cBN by shock wave pressurization at room temperature using rhombohedral boron nitride (rBN) as a raw material. Although disclosed, as described in the text, it is necessary to add 80% by weight or more of metal powder as a heat radiating material in order to suppress the reverse conversion, and not only the production efficiency is very poor, but also cBN
It is not possible to obtain a sintered body consisting of a single component, and the compounding of this heat-dissipating material has the drawback of degrading the original properties of cBN. Further, in order to prevent wurtzite type boron nitride from being produced as a by-product in cBN, it is necessary to use low-pressure phase boron nitride composed only of rBN as a raw material. However, since rBN is a low-pressure phase boron nitride that can be synthesized only under special conditions, it is expensive and difficult to obtain, and there are many problems in using low-pressure phase boron nitride consisting only of rBN. was there.

(Problems to be solved by the invention) Since the synthesis of cBN by the direct method can be performed under the condition of lower temperature and lower pressure than the conventional method, it has been difficult to put it to practical use because of its low industrial productivity. It is an object of the present invention to obtain particles of cBN or a sintered body thereof.

The inventors have conducted various studies on the method for producing cBN by the direct method, particularly the relationship between the type of low-pressure phase boron nitride used as a raw material and the conversion conditions to cBN, and as a result, a small amount of rBN in the conventional raw material, hBN powder. However, by using the one added as an inducer / promoter for converting into cBN, it was unexpectedly found that the conversion into cBN is possible under a condition of mildly high temperature and high pressure, which led to the present invention. It is a thing.

(Means for Solving the Problems) That is, according to the present invention, low-pressure phase nitriding boron is used for producing cubic boron nitride by treating low-pressure phase-chambered boron at a static ultrahigh pressure and high temperature without using a catalyst. Of cubic boron nitride, characterized in that the element is a compact of a mixed powder of 99 to 60% by weight of hexagonal boron nitride (hBN) powder and 1 to 40% by weight of rhombohedral boron nitride (rBN) powder. It is a manufacturing method.

 The present invention will be described in more detail below.

The low-pressure phase boron nitride used as a raw material in the present invention is a compact obtained by adding and mixing rBN particles to hBN particles.

Here, hBN particles are industrially widely produced substances and can be easily obtained.

On the other hand, rBN particles can be synthesized by the reaction of a boron compound containing oxygen and cyan gas as described in, for example, Japanese Patent Publication No. 60-2244.

The low-pressure boron nitride used in the present invention has an rBN content of 1 to 40.
% Is appropriate. If the content of rBN is less than 1%, it takes a long time to convert the entire raw material into cBN, so that the effect is almost nonexistent, and if the content is increased, it can be obtained compared to other low-pressure boron nitride. Since it requires a large amount of rBN, which is difficult to achieve, economic efficiency is reduced.

The above raw materials according to the method of the present invention are processed into powder compacts and loaded into a belt type high temperature generator. After that, first, the pressure is subsequently raised, and the temperature and pressure are maintained at a desired temperature and pressure for a certain period of time to perform high temperature and high pressure processing. At this time, the temperature, pressure and time to be held are preferably 1700 to 20 respectively.
50 ° C., 50-65 kbar and 5 minutes-3 hours. After the treatment, first the temperature and then the pressure are returned to room temperature and 1 atm, respectively, and cBN produced by the high temperature and high pressure treatment is taken out of the apparatus. The obtained cBN has the same excellent properties as cBN produced without using a conventional catalyst, and the present invention provides excellent properties under mild high temperature and high pressure conditions with higher productivity than the conventional one. It is possible to manufacture the own cBN.

(Working) Conventionally, hBN and / or tBN has been widely used as the low-pressure phase boron nitride used as a raw material of cBN because of its availability and price. However, these conventional raw materials have a temperature of 2100 ° C. or higher and a pressure of 65 kb as in the example of Reference 2).
It is not suitable for industrial production because it requires severe high-temperature and high-pressure treatment as above. However, when the raw material of the present invention containing a small amount of rBN in the above-mentioned conventional raw material is used, for example, 1700 to 2050 ° C. and 50 to 65 kbar without using a catalyst under excellent temperature and pressure conditions for productivity. cBN can be manufactured.

The reason why the direct conversion to cBN is possible under such mild conditions is considered to be as follows.

The raw materials of the present invention are 99 to 60% by weight of hBN powder and 1 to 40 of rBN powder.
It consists of a compact of a powder mixture of weight%.

 Here, rBN has a different crystal structure from hBN.

In other words, hBN is a two-layer cycle in which the stacking period of hexagonal network layers formed by alternating bonding of boron and nitrogen is ABABAB ……, and rBN is a three-layer cycle in which the cycle is ABCABCABC ……. is there.

When viewed from the <111> direction, cBN has a three-layer cycle of ABCCABCABC ..., which is the same as rBN. Due to the similar crystal structure, the layers of the hexagonal network layer of rBN are compressed to form a hexagonal network. It is thought that it is possible to convert to the structure of cBN by moving the constituent atoms alternately a little from the plane.

This conversion is a so-called non-diffusion transition that occurs without changing the positions of BN constituent atoms.

On the other hand, if hBN is to be converted to cBN, a so-called diffusion transition process is required to break the two-layer periodic structure into a three-layer periodic structure.

Generally, the non-diffusion transition is considered to occur more easily and in a shorter time than the diffusion transition.

When the raw material of the present invention is subjected to high temperature and high pressure treatment under the conditions of 1,700 to 20,050 ° C. and 5 to 65,000 atm, it is considered that rBN is first converted to cBN by a non-diffusion transition within a short time. next,
Under the same conditions, hBN, which does not cause conversion by itself, has already converted, and it is taken into and converted into cBN as the cBN particles in contact therewith grow, and eventually the entire raw material changes to cBN. It seems to do.

(Example) Next, the present invention will be described more specifically based on Table 1 showing Examples and Comparative Examples.

Example 1-12 According to the method disclosed in Japanese Patent Publication No. 60-2244, hydrogen cyanide was reacted with vaporized boron oxide to synthesize acicular crystals of rBN having a thickness of about 1 micron. The rBN whiskers were crushed and mixed with a commercially available hBN powder in the ratio shown in Table 1.

These mixed powders were pressure-molded to obtain a disk, which was subjected to a high-temperature high-pressure treatment for a predetermined time under the temperature and pressure conditions shown in Table 1 using a belt-type high-temperature high-pressure generator.

Powder X-ray diffraction measurement was performed on the treated sample, and the weight% of cBN in the sample was determined from the calibration curve prepared in advance and is listed in Table 1.

Comparative Example 1-12 Example 1-12 was carried out under the same conditions as Example 1-12, except that a disk formed by molding powder consisting of only hBN was used as a raw material of cBN.

(Effect of the invention) According to the present invention, the synthesis of cBN by a direct method without a catalyst is prepared by using a mixed powder compact of 99-60 wt% hBN powder and 1-40 wt% rBN powder as a raw material. Since it can be realized under high temperature and high pressure conditions, which is significantly milder than before, by using as a raw material, high-purity cBN particles or a sintered body thereof that has not been put into practical use due to low industrial productivity up to now. There is an effect that can be obtained.

Continuation of the front page (56) References JP-A-61-31359 (JP, A) JP-A-1-184033 (JP, A) JP-B 64-3948 (JP, B2)

Claims (1)

[Claims] 1. A low-pressure phase boron nitride is a hexagonal boron nitride (hBN) when a low-pressure phase boron nitride is processed at a static ultrahigh pressure and high temperature without using a catalyst to produce cubic boron nitride. Powder 99-60% by weight and rhombohedral boron nitride (rBN) powder 1-40
A method for producing cubic boron nitride, which is a compact of a mixed powder of wt%.