JPH0365234A - Manufacturing of cubic system boron nitride - Google Patents

Abstract

PURPOSE:To obtain a highly pure cubic system boron nitride or its sintered product by incorporating a diamond-shaped boron nitride into a low-pressure phase boron nitride at the time of producing the cubic system boron nitride by subjecting the low pressure phase boron nitride to a static, noncatalytic treatment at an ultra-high pressure and temp. CONSTITUTION:The low pressure phase boron nitride (hBN and/or tBN) contg. a diamond-shaped boron nitride (rBN) is processed into a disk plate or powder. It is then filled in a belt type high temp. producing device and, after that, first pressure and then temp. is raised to attain the desired high temp. and pressure. At such high temp. and pressure, a treatment is performed for a predetermined time. After treatment, at first, the temp. and then the pressure is reduced back to room temp. and 1atm, respectively, and the cubic system boron nitride (cBN) produced by the high temp. and pressure treatment is removed from the device. When the low pressure phase boron nitride contg. rBN is treated at a high temp. and pressure, rBN is first converted into cBN in a short time by nondiffusing transition and hBN or tBN is then incorporated into the cBN particles as they grow and thereby converted into cBN. Thus, highly pure cBN particles are obtained.

Description

[Detailed description of the invention] (Industrial application field) Cubic boron nitride, which is a high-pressure phase of boron nitride,
CBN (denoted as J) has hardness and thermal conductivity second only to diamond, and is chemically stable, so it is being used as a tool for machining ferrous metals and as a heat dissipation substrate for semiconductor devices. There is.

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

(Prior art) In general, cBN is hexagonal BN, which is a low-pressure phase of boron nitride.
(hereinafter referred to as r hBN J) or turbostratic structure BN
(hereinafter referred to as r tBN J) is obtained by maintaining cBN under thermodynamically stable conditions. As a method for obtaining thermodynamic stability conditions for cBN, when static high pressure and high temperature treatment is used, the conversion pressure and temperature conditions are set to, for example, 65,000 atm.
Extremely strict conditions of 2100°C or higher are required. Therefore, industrially, a catalyst is used to set the conversion conditions to relatively mild conditions of 40,000 to 50,000 atm and about 1,500°C. By this method, single-crystal cBN particles are produced and are used as they are as abrasive grains for grinding tools such as whetstones.

On the other hand, if fine cBN particles are sintered under high pressure and high temperature, a sintered body for cutting tools can be obtained, but since cBN is difficult to sinter by itself, it is mixed with a bonding agent such as metal or ceramics and sintered. need to be tied. Currently used industrially c
Although BN is mostly produced by the methods described above, it has the disadvantage that the incorporation of catalysts and the presence of sintering aids reduce the inherent properties of cBN, and for this reason cBN is produced without the use of catalysts and sintering aids. Catalytic direct conversion method (hereinafter referred to as “direct method
) to produce cBN particles and sintered bodies,
It is hoped that this will be achieved under milder conditions. cBN produced by the direct method is a polycrystalline substance 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 a heat dissipation substrate. This is because it is expected.

The following literature is conventionally known as a method for producing cBN by a direct method.

Literature l) Materials Research Pluchin (Mate
Rials Research Bulletin).

7.999-1004 (1972) Document 2) JP-A-54-33510 Document 1)
It has been shown that "lump" J-shaped cBN was obtained by processing low-crystalline boron nitride as a starting material at temperatures above 1250 °C and pressures above 60 kbar. However, this example It was pointed out that HO may have acted as a catalyst (Osamu Fukunaga, "The base of cubic boron nitride and its applications", Ceramic Data Book °85.
431-436 (1985)), and there are no follow-up exam examples, so there are many unknown points.

Reference 2) describes a molded body of pyrolytic boron nitride heated at 1800°.
It is disclosed that an eBN sintered body is produced by high-temperature and high-pressure treatment at a temperature of 50 kbar or more and a pressure of 50 kbar or more.

In addition, cBN is produced by static high-temperature and high-pressure treatment without using a catalyst.
There are several reports on manufacturing 1s
It requires high-temperature, high-pressure treatment under severe conditions such as a temperature of 0.0''C or more and a pressure of 60 kbar or more, making it unsuitable for industrial production.

On the other hand, as another method for producing cubic boron nitride,
No. 0-2245 discloses rhombohedral boron nitride (
A method of obtaining eBN using shock wave pressurization at room temperature using (rBN) is disclosed, but as stated in the text, it is necessary to add 80% by weight or more of metal powder as a heat dissipation material in order to suppress reverse conversion. Not only is the production efficiency very low, but it is also impossible to obtain a sintered body made of cBN as a single component.
This composition of heat dissipating material has the drawback of deteriorating the inherent properties of cBN. Further, in order to prevent wurtzite boron nitride from being produced as a by-product in cubic boron nitride, it is necessary to use low-pressure phase boron nitride consisting 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 with using low-pressure phase boron nitride consisting only of rBN. There was a point.

(Problem to be solved by the invention) It is possible to synthesize eBNO using a direct method under lower temperature and lower pressure conditions than synthesis, and to produce high-purity eBNO, which has been difficult to put into practical use due to low industrial productivity. It is an object of the present invention to obtain particles of eBN or sintered bodies thereof.

The inventors investigated various methods for producing cBN by a direct method, especially the relationship between the type of low-pressure phase boron nitride used as a raw material and the conditions for conversion to cBN. It has been unexpectedly discovered that by using cBN, conversion to cBN becomes possible under conditions of high temperature and high pressure that are significantly milder than conventional conditions, leading to the present invention.

(Means for Solving the Problem) That is, the present invention provides a method for producing cubic boron nitride by statically treating low-pressure phase boron nitride at ultra-high pressure and high temperature without using a catalyst. This is a method for producing cubic boron nitride, characterized in that it contains rhombohedral boron nitride.

The present invention will be explained in more detail below.

The low-pressure phase boron nitride containing rBN used as a raw material in the present invention is prepared, for example, by the following method.

1) A mixture of hsN and/or tBN particles with rRN particles 2) An rBN plate in contact with an hBN and/or tBN plate 3) Pyrolytic boron nitride is synthesized by CVD method etc. In this case, hBN and/or tBN and rBN are precipitated under carefully selected conditions.Here, hBN and tBN particles, plates, etc. are substances that are widely produced industrially and are easily available. .

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

The rBN plate can also be produced by pressure molding rBN particles.
Alternatively, as described in Japanese Patent Publication No. 64-3948, for example, it can be synthesized by a method in which a boron source gas and a nitrogen source gas are supplied onto a heated gas and deposited.

Pyrolytic boron nitride in which rBN is precipitated together with hBN and/or tBN can be synthesized, for example, by the method described in Example 2 of Japanese Patent Publication No. 64-3948. hBN in boron,
The mutual ratio of tBN and rBN can be adjusted by varying the surface temperature of the heated substrate to a range exceeding 1700''C, as stated in that publication.

The rBN content of the low-pressure boron nitride used in the present invention is 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 there is almost no effect, and as mentioned above, when the content is increased, it is less effective than other low-pressure boron nitrides. Since a large amount of rBN, which is difficult to obtain, is required, economical efficiency decreases.

The above-mentioned raw materials related to the method of the present invention are processed into disks or powder and filled into a belt-type high temperature generator. Thereafter, the pressure is first increased and then the temperature is increased, and the desired temperature and pressure are maintained for a certain period of time to perform high-temperature and high-pressure treatment. At this time, the holding temperature, pressure and time are preferably 17
00~2050″C15~65,000 atm and 5 minutes-3
It's time. After the treatment, first the temperature and then the pressure are returned to room temperature and 1 atm, respectively, and the cBN produced by the high temperature and high pressure treatment is taken out from inside the apparatus. The obtained cBN has the same excellent properties as cBN produced without using conventional catalysts, and the present invention allows it to exhibit excellent properties under mild high temperature and high pressure conditions with higher productivity than before. You can manufacture eBNs that you have.

(Function) Conventionally, low-pressure phase boron nitride, which has been used as a raw material for cBN, has been used as hBN and/or tB due to its ease of availability and price.
N was widely used. However, these conventional raw materials require severe high-temperature, high-pressure treatment at a temperature of 2100°C or higher and a pressure of 65 kbar or higher, as in the example in Document 2), making them unsuitable for industrial production. When using the raw material of the present invention containing a small amount of rBN by the method described above, for example, 1700 to 2050 °C and 5
It becomes possible to produce cBN without using a catalyst under temperature and pressure conditions with excellent productivity of ~65,000 atm.

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

The raw material of the present invention contains rBN therein.

rBN has a different crystal structure than hBN and tBN.

In other words, in hBN, the period of stacking hexagonal network layers formed by alternately bonding boron and nitrogen is ABABAB-
--1 two-layer period, and while tBN has irregular layer stacking and no periodicity, rBN has a period of ABCABC in contrast to hBN or tBN.
ABC---one three-layer period.

When cBN is viewed from <llb direction, the stacking period is rBN
has the same three-layer period as ABCABCABC---1,
Due to this similarity in crystal structure, it is thought that it is possible to convert the structure of rBN to cBN by compressing the glabella of the hexagonal network layer and alternately moving the atoms that make up the hexagonal network a little from the plane.

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

On the other hand, in order to convert hBN or tBN to cBN, a so-called diffusion transition process is required to break down the two-layer periodic laminated structure and change it to a three-layer periodic laminated structure.

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

The raw materials of the present invention were heated to 1700-2050℃ and 5-6.5℃.
When treated at high temperature and high pressure under conditions of 10,000 atmospheric pressures, rBN is thought to convert into cBH within a short period of time through a non-diffusion transition.Secondly, under the same conditions, hBN or tBN, which do not undergo conversion on their own, have already been converted into cBH. As the cBN particles in contact with it convert and grow, cB is incorporated into them.
It is believed that the entire raw material is converted to N and finally to cBH.

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

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

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

Powder X-ray diffraction measurement was performed on the sample after treatment, and the weight percent of cBN in the sample was determined from a calibration curve prepared in advance.

Comparative Example 1-12 Comparative Example 1-12 was carried out under the same conditions as in Example 1-12, except that a disk formed from a powder made only of commercially available hBll was used as the raw material for cBN.

Example 13-16 BI
Spray J3 gas and ammonia gas onto the heated board,
A pyrolytic boron nitride plate was obtained by maintaining the surface temperature of the substrate at 1600° C. and the pressure at 5 torr. The product of the obtained sample was identified by X-ray diffraction measurement and was found to be composed of rBN.

This was cut into thin discs, and commercially available hBN and tB were used.
By alternately stacking thin disks of pyrolytic boron nitride made of N, disks with various weight percentages of rBN thin plates were produced as shown in Table 1.

This disk was used as a raw material for eBN, and was heated for a predetermined time under the temperature and pressure conditions shown in Table 1 using a belt-type high temperature and high pressure generator.
High temperature and high pressure treatment was performed.

Powder X-ray diffraction measurement was performed on the sample after treatment, and the weight percent of cBN in the sample was determined from a calibration curve prepared in advance.

Example 17-20 By the method of Example 2 of Japanese Patent Publication No. 64-3948, BC
Spray Is gas and ammonia gas onto the heated substrate,
By adjusting the surface temperature of the substrate, various r values shown in Table 1 can be achieved.
A pyrolytic boron nitride plate with BN content was obtained.

This was cut into disks, used as raw materials for cBN, and subjected to high temperature and high pressure treatment for a predetermined period of time under the temperature and pressure conditions shown in Table 1 using a belt type high temperature and high pressure generator.

Powder X-ray diffraction measurement was performed on the sample after treatment, and the weight percent of cBN in the sample was determined from a calibration curve prepared in advance.

Comparative Example 13-20 Example 13 except that commercially available pyrolytic boron nitride discs made only of hBN and tBN were used as raw materials for cBN.
It was carried out under the same conditions as -20.

(Effects of the Invention) According to the present invention, cBN can be synthesized by a direct method without using a catalyst by preparing a raw material obtained by adding a small amount of rBN to a conventional raw material and using this as a raw material. Since this process can also be carried out under extremely mild conditions of high temperature and high pressure, it is possible to obtain high-purity cBN particles or sintered bodies thereof, which have not been put to practical use due to low industrial productivity.

Claims (1)

[Claims] 1. In producing cubic boron nitride by processing low-pressure phase boron nitride at static ultra-high pressure and high temperature without using a catalyst, the low-pressure phase boron nitride is characterized in that it contains rhombohedral boron nitride. A method for producing cubic boron nitride.