JPS5927726B2 - Manufacturing method of cubic boron nitride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing cubic boron nitride.

Cubic boron nitride has extremely high hardness and good thermal conductivity, so it is attracting attention as a cutting material, abrasive material, wear-resistant material, and heat sink material.

Conventionally, methods for producing cubic boron nitride include a catalytic method using a metal catalyst and a direct method that does not use a catalyst.

In the catalytic method, Ja, l[a, elements of group 17a and Sb
Synthesis was performed in the thermodynamically stable region of cubic boron nitride using metal elements such as , Sn, Pb, or nitrides thereof as a catalyst, mixed with hexagonal boron nitride as a raw material.

However, the cubic boron nitride powder synthesized by this method has a large particle size of 10μ to 500μ, making it difficult to use it as raw powder for producing a cubic boron nitride sintered body.

Furthermore, the metal elements used in the catalyst inevitably mix into the cubic boron nitride as impurities.

On the other hand, in the direct synthesis method without using a catalyst, 115 kbar
It requires a very high pressure of 1900°C or higher, and
, J. Chem, Phys., 38(5),
1144 (1963)], which had major drawbacks from the point of view of industrialization.

Furthermore, recently, as a direct synthesis method, 60 kbar +1
A method of synthesis under high pressure and high temperature of 200°C or higher was devised, but (Wakatsuki et at + Mat, Re
s.

Butt, 7,999 (1972)), in this case it is necessary to select and use hexagonal boron nitride, which is a fine powder of 1 μm or less and has poor crystallinity, as a raw material, and the synthesis conditions are also severe, at 60 kbar or more. Met.

On the other hand, according to Unexamined Patent Application Publication No. 50-21000, Wakatsuki et al. added a liquid substance with no catalytic action to hexagonal boron nitride raw material to produce cubic boron nitride with low crystallinity and fine particle size. A manufacturing method was reported.

Particularly when water or alcohol is added, the effect of facilitating the conversion of cubic boron nitride is said to be observed.

In this method, the lower limit of the pressure for synthesizing cubic boron nitride is often as high as 60 kbar, and even when water or alcohol is used, a high pressure of 55 kbar is required.

Based on the above background, the present inventors have developed a method for synthesizing fine powder cubic boron nitride under low pressure and temperature conditions, eliminating the shortcomings of the prior art. We have discovered a method using hexagonal boron nitride as a raw material to which ammonium oxide, ammonium iodide, and mixtures thereof are added.

The present invention is a synthesis method using hexagonal boron nitride as a raw material,
At least 30 kb of raw material mixed with the above catalyst material
It is characterized in that it is exposed to and reacted at a pressure of ar or more and a temperature of about 600° C. or more, which is in the thermodynamically stable region of cubic boron nitride.

The first effect of the present invention is that by adding hexagonal boron nitride, which is the catalytic material of the present invention, the pressure and temperature required for synthesizing cubic boron nitride can be significantly lowered than in the past.

This effect is due to the fact that the catalyst material of the present invention significantly increases the conversion rate of hexagonal boron nitride to cubic boron nitride.

A second advantage of the present invention is that the cubic boron nitride produced by the method of the present invention has a very small grain size of about 0.1 to 5 microns.

This particle size is so small that it cannot be obtained at all using conventional metal catalyst methods, and is a characteristic of the catalyst material of the present invention.

Since sintering becomes easier when the particle size is small, the cubic boron nitride produced by the method of the present invention is optimal as a raw material for sintering.

The third effect of the present invention is that by adding the catalyst of the present invention, cubic boron nitride can be synthesized regardless of the state of the raw material (crystallinity and particle size). is not limited to graphite-type boron nitride, but may also be wurtzite-type boron nitride.

Therefore, there is no need to use specially prepared fine particles of boron nitride as a raw material as in the past, and any raw material can be used.

The fourth effect of the present invention is that the ammonium fluoride, ammonium chloride, ammonium bromide, and ammonium iodide used in the present invention are composed of nitrogen, which is a constituent element of nitrogen nitride, halogen, and hydrogen; Unlike the synthesis method using a metal catalyst, there is no metal catalyst mixed in as an impurity, and the purity of the cubic boron nitride crystal is as high as or higher than the purity of the raw material.

Although a high-pressure and high-temperature generating device is required to carry out the present invention, the present invention is not limited by the method or device for generating high pressure and high temperature, but is capable of simultaneously generating the high pressure and high temperature necessary for synthesis. Any method and apparatus may be used.

It should be noted that although a certain effect can be recognized even if the amount of the catalyst substance added is small, it is practically 5% by weight or more.

Further, although there is no particular upper limit to the amount added, as the proportion of the catalyst substance increases, the proportion occupied by boron nitride in the sample decreases, and the amount of cubic boron nitride synthesized decreases.

Therefore, the proportion of the catalyst is practically preferably 5 to 70 weight percent.

A more detailed explanation will be given below with reference to Examples.

Example 1 As a raw material for boron nitride, 40w of ammonium fluoride was added to graphite-type hexagonal boron nitride with an average particle size of 0.05μ.
A mixture of t% was used.

Pressure is 40~60kbar, temperature is 800~1800℃
A synthesis experiment of cubic boron nitride was conducted under conditions of a reaction time of 30 minutes, and the particle size of the obtained cubic BN was measured.

The results are shown in Table 1. Note that pyrophyllite was used as the pressure medium.

Furthermore, the synthesized cubic BN was confirmed by X-rays, and its particle size was measured from an electron micrograph.

As is clear from the above examples, cubic boron nitride was synthesized under significantly lower pressure and temperature conditions than in the prior art, and the particle size of the synthesized cubic BN was determined by changes in the pressure and temperature of the synthesis conditions. The particle diameter was very small at 0.1 to 5μ, making it a desirable fine powder.

Example 2 A synthetic experiment similar to that in Example 1 was conducted except that ammonium fluoride was replaced with ammonium chloride, ammonium bromide, ammonium iodide, and a mixture of ammonium fluoride and ammonium chloride.

The average particle size of the synthesized cubic boron nitride is shown in Table 2.

From the above results, cubic boron nitride synthesized by adding a mixture of ammonium chloride, ammonium bromide, ammonium iodide, ammonium fluoride, and ammonium chloride is a very small fine powder with a particle size of 0.1 to 5μ. One thing is clear.

Example 3 In Example 2, the raw material hexagonal BN had an average particle size of about 5
A synthesis experiment similar to that in Example 2 was conducted except that graphite-type boron nitride and wurtzite-type boron nitride, which have good crystallinity of μ, were used.

The results are shown in Table 3.

From the above results, even if graphite-type boron nitride with good crystallinity with an average particle size of about 5 μm is used, ammonium fluoride, ammonium chloride,
It is clear that by mixing ammonium bromide and ammonium iodide, cubic boron nitride in the form of fine powder with a particle size of 0.1 to 5 μm can be synthesized.

Example 4 A similar synthesis experiment was conducted in Example 2 by changing the proportions of ammonium fluoride, ammonium chloride, ammonium bromide, and ammonium iodide.

Table 4 shows the synthesis yield of cubic boron nitride obtained at this time.

Example 5 A cubic boron nitride synthesis experiment was conducted in the same manner as in Example 1 except that the pressure was 30 kbar or higher and the temperature was 600° C. or higher.

The results are shown in Table 5.

As is clear from this example, cubic boron nitride is
Low pressures such as 40 kbar or from 600°C
The cubic BN was synthesized even at a low temperature of 800°C, and the obtained cubic BN was a fine powder.

As is clear from the table, when the additives of the present invention are not added, cubic boron nitride cannot be synthesized even at a high pressure of 60 kbar, but when 5 wt% or more of additives are added, the pressure is 45 kbar. Cubic boron nitride can be synthesized using

That is, it is clear that the addition of the catalyst of the present invention significantly increases the reaction rate in the synthesis of cubic boron nitride.

As is clear from the above examples, regardless of the grain size, crystallinity, crystal structure, etc. of the raw material boron nitride, ammonium fluoride, ammonium chloride, ammonium bromide, ammonium iodide, etc. Alternatively, by adding a mixture thereof, cubic boron nitride can be synthesized under significantly lower pressure and temperature conditions than conventional ones, and the particle size of the synthesized cubic BN is 0.1 to 5 μm.

Furthermore, as a manufacturing equipment, the temperature is 600℃ or higher and 3゜kbar.
Any device can be used as long as it can simultaneously generate the above high pressure and high temperature and maintain the pressure and temperature for the time required for the reaction.

Claims (1)

[Claims] 1. When high-pressure synthesis of cubic boron nitride is performed by adding a catalyst to macrogonal boron nitride, ammonium fluoride,
A method for producing cubic boron nitride, the method comprising using at least one of ammonium chloride, ammonium bromide, and ammonium iodide.