JPH0593B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for synthesizing cubic boron nitride from hexagonal boron nitride, and more specifically, a method for synthesizing high-quality cubic boron nitride using impure hexagonal boron nitride. Regarding how to.

It is known that cubic boron nitride (hereinafter referred to as CBN) is a highly hard material with a diamond-like crystal structure. Although it is inferior to diamond in terms of hardness, its thermal and chemical properties are superior to those of diamond, so its use as a new polishing and cutting material for hardened steel, special steel, ceramics, etc. is being developed. Furthermore, by doping an appropriate element into its crystal lattice, it is possible to manufacture a P-type and N-type amphoteric semiconductor, and there are great expectations for its application as an electronic material by taking advantage of its excellent thermal conductivity. From this point of view, there is a demand for high-purity, high-quality CBN single crystals with desired grain size and crystal morphology.

Conventionally, a manufacturing method is known in which cubic boron nitride is converted into hexagonal boron nitride (hereinafter referred to as HBN) using a catalyst substance.

The catalytic materials mainly used are group a, a, and group elements in the periodic table of elements, and nitrides or alloys thereof. In addition, tin, lead, antimony alone or alloys, urea, ammonium salts, etc. are also known. However, when the above-mentioned metal catalyst is used, unstable borides and free boron are produced as by-products, and boron is mixed into the resulting CBN crystals, making the crystals black and opaque, and their particle strength significantly reduced. There are drawbacks. Furthermore, when nitride is used, unreacted nitride remains and the nitride is trapped in the resulting CBN crystal, making it impossible to obtain a high quality product.

On the other hand, when urea or ammonium salts are used, the particle size of the CBN obtained is extremely small, 0.1 to 0.5 microns, and in addition, the mechanism by which these catalysts convert HBN to CBN has not yet been elucidated. It was difficult to set the conditions to obtain the desired crystals.

The present inventors first added strontium boron nitride (Sr ₃ B ₂ N ₄ ) or barium boron nitride (Ba ₃ B ₂ N ₄ ) to HBN as a catalyst, thereby changing the temperature and pressure range of the reaction conditions. We have invented a method that allows easy production of large, high-purity, and high-quality single crystals of CBN, which has a wide tolerance range and easy control of grain growth rate.

However, in the above method, if the raw material HBN has a slightly large amount of impurities, these will be rolled up in the crystal and produce high-quality CBN.
However, there was a problem in that high purity HBN was required as a raw material.

Taking the above circumstances into consideration, the present inventors conducted intensive research on a method for synthesizing high-quality CBN using HBN containing impurities as a raw material.
Alkali metal or alkaline earth metal hydrides such as NaH, KH, CaH ₂ , MgH ₂ , SrH ₂ are used as raw materials.
It was discovered that HBN has a purifying effect on impurities contained in it.

The present invention was made based on the above discovery, and its gist is that CBN can be used at higher temperatures and under higher pressure than HBN.
In the method for synthesizing X ₃ B ₂ N ₄ as a catalyst
(where X is an alkaline earth metal) is a CBN synthesis method characterized by using an alkali metal or an alkaline earth metal hydride added thereto.

The method of the present invention will be explained below.

The method for producing X ₃ B ₂ N ₄ used as a catalyst in the present invention is, for example, when X is Sr, by mixing metal strontium or strontium nitride and HBN at a molar ratio of strontium to boron of 3:2, ₂ Obtained by heating at 950-1200°C in a stream of air for 2 hours or more. Other X ₃ B ₂ N ₄ are also Sr
It can be obtained in the same manner by using Be, Mg, Ca, and Ba instead of.

To synthesize CBN by the method of the present invention,
X ₃ B ₂ N ₄ , HBN, and LiH, NaH, KH,
Fine powders of alkali metal or alkaline earth metal hydrides such as CaH ₂ , MgH ₂ , SrH ₂ , etc. are mixed in a predetermined ratio and compacted under a surface pressure of 1.5 to 2.0 t/cm ² . A molded body of predetermined dimensions is formed. This was loaded into a well-known high-pressure, high-temperature reactor used for diamond synthesis, and the CBN stability range was 40-60Kbar, 1300-
It is held at 1600°C for a predetermined time to convert HBN to CBN. Or HBN powder or X ₃ B ₂ N ₄
A fine powder of alkali or alkaline earth metal hydride is added to the powder, each of these is compacted into a thin disk shape, the thin plates are stacked so that the above ingredients are in a predetermined ratio, and this is heated under high pressure and high temperature. It may be loaded into the reactor. Alternatively, HBN may be used in excess during the synthesis of X ₃ B ₂ N ₄ , and a product containing an excess amount of HBN may be used.

The mixing ratio of the above catalyst X ₃ B ₂ N ₄ and raw material HBN is:
X ₃ B ₂ N ₄ /HBN is preferably 5 to 50% by weight. Further, the hydride of alkali metal or alkaline earth metal is preferably in a range of 0.1 to 10% by weight of hydride/HBN. If it is less than 0.1% by weight, the purifying effect will not be very effective, and if it is more than 10% by weight, the yield of CBN will decrease.

Next, the effects of the present invention will be illustrated by Examples and Comparative Examples.

Example 1 HBN containing 0.8% by weight of oxygen and 0.2% by weight of metal impurities excluding alkali and alkaline earth metals, Sr ₃ B ₂ N ₄ and NaH at 150% each
Pulverized to a particle size of mesh or smaller, these were mixed at a weight ratio of 10:1:0.15, and a molding pressure of 1.5t/
It was made into a powder compact of 26 mmφ×32 mmH in cm ² . This was loaded into a high-pressure, high-temperature reactor and treated for 10 minutes at a pressure of 50 Kbar and a temperature of 1450°C to synthesize CBN. The produced CBN is dense and has good transparency.
Good quality euhedral grains, conversion rate to CBN is 42%
It was hot.

Example 2 Ba ₃ B ₂ N ₄ and NaH instead of Sr ₂ B ₂ N ₄ as catalysts
Using _CaH2 instead of _HBN : _{Ba3B2N4 : CaH2}
CBN was synthesized in the same manner as in Example 1, except that the weight ratio was 10:1.5:0.1. The generated CBN is
It was of good quality as in Example 1, and the conversion rate to CBN was 37%.

Comparative example 1 The weight ratio of HBN:Sr ₃ B ₂ N ₄ was changed without using NaH.
CBN was made the same as in Example 1 except that it was set to 10:1.
was synthesized. The CBN produced was opaque, had cavities inside, had low strength, and was easily disintegrated. The conversion rate to CBN was 43%.

Comparative Example 2 CBN was produced in the same manner as in Example 2 except that CaH ₂ was not used and the weight ratio of HBN:Ba ₃ B ₂ N ₄ was 10:1.5.
was synthesized. The produced CBN was not of good quality as in Comparative Example 1, and the conversion rate to CBN was 39%.

Comparative Example 3 The weight ratio _of HBC _{: Sr3B2N4} :NaH is 10:0.8:1.2
CBN was synthesized in the same manner as in Example 1, except that Although the CBN produced was of good quality,
The conversion rate to CBN was 21%.

As mentioned above, alkali metal or alkaline earth metal hydrides purify the impurities in the raw material HBN, so high quality CBN can be produced even if HBN contains some impurities.
The degree of freedom in selecting CBN as a raw material has been greatly expanded, and its economic effects are extremely large.

Claims (1)

[Claims] 1. As a catalyst in the method of synthesizing cubic boron nitride at higher temperature and pressure than hexagonal boron nitride.
A method for synthesizing cubic boron nitride, characterized in that X ₃ B ₂ N ₄ (where X is an alkaline earth metal) is added with an alkali metal or an alkaline earth metal hydride.