JPS5815012A - Manufacture of cubic system boron nitride - Google Patents

Abstract

PURPOSE:To obtain cubic system BN having a large particle size and well developed crystal faces in a high yield by using a catalyst prepared by adding CaH2 to Li3BN2 when hexagonal system BN is converted into cubic system BN by holding it in the thermodynamically stable region. CONSTITUTION:CaH2 is added to Li3BN2 to prepare a catalyst, and the catalyst is mixed with hexagonal system BN. The pressure of the mixture is raised from about 47kb to about 51kb in about 13min while keeping the temp. at about 1,500 deg.C, and the temp. and pressure are dropped. The resulting cubic system BN is brown and has high transparency. The particle size is large, most of the particles have >=50mum size, and even particles having >=150mum size are contained. The yield is as high as about 40%. The preferred percentage of CaH2 added to Li3BN2 is about 1.5-35wt%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for converting hexagonal boron nitride to cubic boron nitride using a catalyst. The present invention relates to a method for obtaining large grain cubic boron nitride with particularly good crystallinity at a high yield.

Cubic boron nitride (hereinafter abbreviated as cBN) has a hardness second only to diamond, and has better thermal and chemical properties than diamond. It is a substance whose demand is increasing in the form of grains.

Various methods have been announced for producing cBN, but a well-known method is to produce cBN from hexagonal boron nitride (hereinafter abbreviated as hBN) in the presence of a catalyst.
This method uses alkali metals, alkaline earth metals, alloys containing them, nitrides, borides, etc. of these metals as catalysts when converting to cBN by maintaining the cBN within the thermodynamic stability region of cBN.

As catalyst materials, nitrides and borides have been well investigated, and KLi, N or Li1BN1 are said to be particularly effective. However, conventional cBN crystals obtained using these catalysts generally have fine particles of 50 μm or less and do not have good crystallinity, and have not been able to fully demonstrate their performance as grinding abrasive grains. Therefore, a technology for producing large grains of cBN with well-developed crystal planes has been desired.

The present invention provides a method for producing large-grained cBN with well-developed crystal planes at a high yield by improving the above-mentioned catalyst.

That is, in the method of the present invention, CaH is added to Li5BN*.

It is characterized in that cBN is obtained by using as a catalyst a catalyst containing hBN, coexisting with hBN, and maintaining the temperature and pressure within the thermodynamic stability range of cBN.

According to the inventors' experiments, only LtsBN* was mixed with hBN, and the pressure was slowly raised from about 47 kb to 51 kb over 13 minutes while maintaining the temperature at about 1,500 °C, and then the temperature was lowered. The cBN obtained by lowering the pressure was an opaque ocher color, and the particle size was mostly small, less than 50 μm. Furthermore, the yield is about 181
It was low. - Li, B according to the strength wood invention method
When 3.75 wtts of Ca H weight was added to N- as a catalyst and the other conditions were the same, the obtained CBN was brown in color and highly transparent. The particles are 50μ or more, and some of them are 1
Some particles exceeded 50μ. The yield was also as high as about 40 cm.

The advantage of using Li, BN= with CaHt added as a catalyst is that the particle size of cBN tends to increase and the yield increases. Other advantages include fewer cracks in the crystal, improved transparency, and easier development of crystal faces, making the crystal suitable for grinding abrasive grains.

According to experiments, CaH added to Li is B Nt,
The ratio by weight is preferably 1.5 to 35 inches. CaH.

If the amount is less than 1.5, the advantage of adding Ca does not appear, and the particle size is small and the yield is low, as in the case of only Li = BN. The ratio of CaH* is 1.5 to 35
In the range of 60%, the yield of cBN ranges from 20% to 50%, and a constant level of cBN can be obtained, and sometimes the yield can be as high as 60%. As the amount of CaH increases, the color of the crystal changes from yellowish brown to brownish brown, but if it is too much, the transparency may deteriorate and the particle size becomes slightly smaller. When the proportion of CaH* exceeds 35%, the grain size of the crystals becomes small to the same extent as when no additive is added, and the yield also becomes low.

Next, an example will be described.

Example L t s B Ng 200 “I, Ca
Ha 7.5"? and hHN60011 were mixed well and filled into a reaction vessel, and high temperature and pressure were applied. First, the pressure was increased to 4.
When the temperature reaches 7kb, keep the temperature at about 1.500℃,
The pressure was slowly increased by holding 47 kb for 5 minutes, 48 kb, 49 kb, 50 kb and 51 kb for 2 minutes each. When the temperature and pressure are lowered and the reactants are collected, brown, transparent, crystalline, well-developed cBN is obtained at 24
0■ obtained. Yield is 40 g. y chewed cBN
270 meshes, 140 meshes, under the name of Tyler.
The particle size was measured using a 100 Mesosie sieve and the results are shown in the table below. For comparison, the results when CaHt was not added are also shown.

Here, the pressure measurement is based on the change in the electrical resistance value of the metal used as the pressure detection element.
The T-row metastasis is 36.7 kb and is as follows.

The temperature was determined in advance by inserting a Pt-Pt 13%Rh thermocouple into the reaction vessel and determining the relationship between the temperature indicated by the thermocouple and the voltage, and in the actual synthesis, the temperature was estimated from the electric power value.

CaNt instead of CaH, L l * B Ng
When Li and BN were added to form a catalyst, the results were the same as when Li and BN were used alone.

CBN obtained even when using only CaH as a catalyst
Since the yield of is low and the crystal grain size is small, it is thought that the effect of the present invention is due to the combination of L i = B Ng and CaH.

Under the same temperature and pressure conditions as in the example, Ca5B was used as a catalyst.
*When a comparative experiment was conducted using a mixture of Ni and CaHa and a mixture of LtsBI'L and LiH, cBNt: could not be obtained in either case. Also Ca5lL
When we conducted a similar experiment using only N* as a catalyst, we found that
The cBNli particle size obtained was small, less than 30 tones in total, and the yield was low at 4123 tones.

The use of C'as Bt N4 was approved by Special Publication No. 55-60008.
According to its examples, 56,000 atmospheres,
It is said that it exhibits an effective catalytic function under conditions of 1,500°C, U60,000 atmospheric pressure, and 1,750°C. It is therefore clear that the catalyst according to the invention functions more effectively at lower pressures than the catalysts used in these comparative experiments.

Claims (1)

[Claims] Using lithium boron nitride to which calcium hydride gold is added as a catalyst, this catalyst is made to coexist with hexagonal boron nitride,
A method for producing cubic boron nitride, characterized in that cubic boron nitride is obtained by maintaining the cubic boron nitride within a thermodynamically stable region.