JPS62108713A - Production of cubic boron nitride - Google Patents

Abstract

PURPOSE:To prolong the life of an apparatus and to obtain cubic boron nitride in a high yield by adding water, urea or an ammonium salt to pyrolytic boron nitride and holding them under conditions of high temp. and pressure within ranges in which cubic boron nitride is thermodynamically stable. CONSTITUTION:One or more kinds of compound selected among water, urea and ammonium salts are added as a catalyst to pyrolytic boron nitride and they are held under conditions of high temp. and pressure within ranges in which cubic boron nitride is thermodynamically stable to convert the pyrolytic boron nitride into polycrystalline cubic boron nitride. The pyrolytic boron nitride used is highly oriented boron nitride synthesized by a special production method called a chemical vapor deposition method (CVD method). It is necessary to add the catalyst by >=0.1mol% of the amount of the pyrlolytic boron nitride as starting material.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing cubic boron nitride. Cubic boron nitride is a substance that has attracted attention because it has properties suitable for use as a tool material such as cutting tool inserts and grinding abrasive grains.

(Prior art) Cubic boron nitride has a hardness close to that of diamond, and is superior to diamond in terms of chemical stability, for example, it can withstand high temperatures in an oxidizing atmosphere and is particularly reactive with iron group elements. It is in increasing demand as a useful material for cutting and grinding high-speed steel, nickel, and cobalt-based heat-resistant, high-strength materials with mechanical properties far superior to those of diamond. It's coming.

The conventional manufacturing method of cubic boron nitride is (a)
A method in which hexagonal boron nitride is treated under high temperature and pressure by adding an appropriate catalyst (temperature: about 1400℃ or more, pressure crab about 45K)
Over bar, Kagaku Kogyo (1982) September issue, 55-5
(page 8).

(b) A method of directly treating hexagonal boron nitride under high temperature and high pressure without adding a catalyst (temperature: 1600°C or higher, preferably 2000 to 3000°C, pressure crab 55 to 85kb)
ar.

Preferably 55 to 75 kbar; JP-A-167-1987
No. 110).

etc. are known.

(Problems to be Solved by the Invention) However, these methods have the following problems.

In method (a), cubic boron nitride can be produced under milder high-temperature and high-pressure conditions than in method (b), but the cubic boron nitride obtained is usually single-crystal particles. When such single-crystal grain cubic boron nitride is used as a grinding abrasive grain for difficult-to-cut materials, the grains tend to break due to the interstitial pillars peculiar to single-crystal grains, and it has been observed that the wear resistance of the grinding wheel is improved. do not have.

Polycrystalline cubic boron nitride may be produced by adjusting the amount of catalyst added, but in this case, the catalyst components remain as impurities in the cubic boron nitride, resulting in a decrease in strength.

In the method (b), since it is a direct conversion without using a catalyst, the resulting cubic boron nitride is polycrystalline, has no interstitial pillars, and has significantly improved fracture toughness compared to single crystal.
When used as abrasive grains, it exhibits higher wear resistance than cubic boron nitride obtained by method (a). However, very severe high temperature and high pressure processing conditions such as 2000 to 2300°C and 65 to 75 Kbar are required, which tends to damage expensive high temperature and high pressure equipment, and therefore method (b) is unsuitable for industrial production. be.

Furthermore, in both methods (a) and (b), hexagonal boron nitride is used as a raw material.

Usually commercially available hexagonal boron nitride is boron oxide (B2
It is manufactured by nitriding C13). For this reason, it is common to contain 5.000 to 10.000 ppm of oxygen as an impurity. Since the oxygen contained in such starting materials significantly inhibits the conversion of hexagonal boron nitride to cubic boron nitride, unreacted hexagonal boron nitride remains, which causes uneven cubic nitride. This causes the formation of boron and a decrease in the yield of cubic boron nitride. In order to prevent such a phenomenon, there is a drawback that a deoxidizing pretreatment step such as heating the raw material hexagonal boron nitride at 2000° C. for 2 hours or more in a nitrogen stream is required.

(Means for Solving the Problems) The present inventors have conducted extensive research with the aim of solving the above-mentioned drawbacks of the conventional manufacturing method of cubic boron nitride, and have achieved We have discovered a method for producing polycrystalline cubic boron nitride in high yield, which has high fracture toughness, excellent wear resistance, and does not contain any residual catalyst under mild conditions of high temperature and high pressure.

The present invention involves adding one or more compounds selected from the group consisting of water, urea, and ammonium salts to pyrolyzed boron nitride as a catalyst, and adding this to pyrolytic boron nitride within the thermodynamic stability range of cubic boron nitride. This is a method for producing cubic boron nitride, characterized by converting pyrolytic boron nitride into polycrystalline cubic boron nitride by holding it under high temperature and high pressure conditions.

The pyrolytic boron nitride used in the present invention is produced by chemical vapor deposition (
It is highly oriented boron nitride synthesized by a special manufacturing method called CVD method. The synthesis of pyrolytic boron nitride by the C,VD method is described, for example, in U.S. Pat. No. 3.152.006.
As disclosed in the above issue, a boron halide such as boron trichloride and ammonia are used as gaseous raw materials, and a temperature of 1
This is achieved by precipitating nitrogen and boron from the gas phase on the surface of a suitable substrate under conditions of 450°C to 2300°C and a pressure of 50 Torr or less. Pyrolytic boron nitride is deposited as a plate with a thickness of several mm It is commercially available.

Such pyrolytic boron nitride does not require any oxygen or oxides in its manufacturing process, and can be produced with extremely high purity.Moreover, pyrolytic boron nitride itself is extremely stable in air. Since the surface oxidation phenomenon observed in commercially available hexagonal boron nitride powders can be ignored, it can always be considered as boron nitride with extremely low oxygen content even without special treatment and handling.

Commercially available pyrolytic boron nitride is a plate-shaped molded product, but it is highly flexible and can be easily crushed. The pyrolytic boron nitride powder is then mixed with a powder of one or more compounds selected from the group consisting of water, urea and ammonium salts as a catalyst.

The mixing ratio of the catalyst needs to be 0.1 mol % or more based on the pyrolytic boron nitride that is the raw material. If the amount is less than 0.1 mol %, the conversion to cubic boron nitride will not be complete. Further, it is sufficient to add the catalyst in an amount of 10 mol % or less, and no further effect is observed even if it is added more than that.

When the catalyst-containing pyrolytic boron nitride powder bundle thus obtained is used as a starting material to convert pyrolytic boron nitride to cubic boron nitride, it is possible to convert Various advantages can be obtained. First, unlike when normal hexagonal boron nitride is used as a raw material, polycrystalline cubic boron nitride is produced even in the presence of a catalyst. In this case, even if the amount of catalyst added is not strictly controlled, the cubic boron nitride produced is polycrystalline, and there is hardly any residual catalyst that could cause particle destruction. The reason for this is not clear, but the formation mechanism is different between ordinary hexagonal boron nitride and pyrolytic boron nitride, and the difference in microstructure caused by this is due to
This is thought to be reflected in the microstructure of cubic boron nitride after conversion. In addition, since the starting material contains a catalyst for converting cubic boron nitride, the high temperature and high pressure conditions required for conversion to cubic boron nitride can be changed to mild conditions in the thermodynamic stability range of cubic boron nitride, such as 1450 ~1500℃, 45
~50Kbar is sufficient. Therefore, in the method of the present invention, the conditions required when conventionally known hexagonal boron nitride is directly treated under high temperature and high pressure conditions without adding a catalyst, such as 2
Polycrystalline cubic boron nitride is produced under much milder conditions than 000-2300°C and 65-75 Kbar. Therefore, the high temperature and high pressure equipment is less likely to be damaged, the life of the equipment can be extended, and industrial productivity can be significantly improved. Furthermore, pyrolytic boron nitride, which is the starting material in the present invention, does not contain any oxygen or oxides during its manufacturing process, and pyrolytic boron nitride itself has excellent stability in air and oxidation resistance. Therefore, the oxygen content is extremely low, and the advantage is that cubic boron nitride can be obtained in high yield without the need for the deoxidizing pretreatment process that is required when using ordinary hexagonal boron nitride as a starting material. be.

In the present invention, there is no need to perform deoxygenation pretreatment of the starting material, and the material has high fracture toughness and wear resistance under mild high temperature and high pressure conditions that are within the thermodynamic stability range of cubic boron nitride and are advantageous for industrial production. It is possible to obtain polycrystalline cubic boron nitride with excellent properties and no residual catalyst in a high yield, and the resulting polycrystalline cubic boron nitride is suitable as an abrasive grain for grinding difficult-to-grind materials. It has characteristics.

(Example) The present invention will be described below with reference to Examples and Comparative Examples.

Example 1 A commercially available pyrolytic boron nitride having a thickness of 1 mm was pulverized using a vibration mill to obtain a pyrolytic boron nitride powder bundle having an average particle size of about 1 μm. The purity of this pyrolytic boron nitride powder bundle was 99.9% by weight or higher, which was extremely high purity.

This powder was mixed with urea powder and formed into pellets at a temperature of 1,450°C in a belt-type high-temperature, high-pressure device.
, and maintained under a pressure of 45 Kbar for 90 minutes to obtain cubic boron nitride. Regarding the obtained cubic nitride borium, the produced phase was identified by X-ray diffraction, the residual catalyst component was quantified by chemical analysis, the particle size was measured by an electron microscope, and the microstructure was observed. These results are shown in Table 1.

Furthermore, the cubic boron nitride particles were plated with approximately 50% nickel by weight, and then sieved to an 80/100 mesh to produce a resin bonded grindstone, subjected to wet surface grinding, and the grinding ratio was determined. .

The results are shown in Table 1. In addition, Table 2 shows the manufacturing conditions and grinding conditions for the grindstone.

Example 2 The same pyrolytic boron nitride powder bundle as in Example 1 was mixed with ammonium borate powder and formed into pellets, which was then treated at high temperature and pressure under the same conditions as in Example 1 to form cubic boron nitride. I got the basics. Regarding the obtained cubic boron nitride, the produced phase was identified, the particle size was measured, and the microstructure was observed in the same manner as in Example 1. Furthermore, a resin pound grindstone was manufactured in the same manner as in Example 1, and a grinding test was conducted under the same conditions as in Example 1. These results are shown in Table 1.

Example 3 Water was dropped and mixed into the same pyrolytic boron nitride powder bundle as in Example 1, formed into pellets, and treated at high temperature and high pressure under the same conditions as in Examples 1 and 2 to form cubic boron nitride. I got it. Table 1 shows the results of evaluation using the same items as in Examples 1 and 2.

Comparative example Commercially available high-purity hexagonal boron nitride powder bundle with average particle size of approximately 1 μm
A hexagonal boron nitride powder bundle with an oxygen content of 2% by weight or less was obtained by exposing it to a temperature of 1950°C in a nitrogen gas atmosphere of 1 atm for 5 hours. This powder was mixed with urea powder, molded into pellets, and kept under the same temperature and pressure conditions in the same apparatus as in the example to obtain cubic boron nitride. Regarding the obtained cubic boron nitride, identification of the generated phase, quantitative determination of residual catalyst components, measurement of particle size, and observation of microstructure were performed in the same manner as in Examples. Furthermore, a grinding test was conducted under the same conditions as in the example. These results are shown in Table 1.

In addition, in Table 1, the absence of crystal habit in the microstructure means high fracture toughness, and the high grinding ratio means excellent wear resistance, which makes it suitable for application to tool materials such as abrasive grains for grinding wheels. means it is suitable for

(Effects of the Invention) According to the present invention, polycrystalline cubic boron nitride with high fracture toughness and excellent wear resistance can be obtained, and therefore the cubic boron nitride produced can be used as abrasive grains for grinding wheels, etc. Suitable for application to tool materials. In particular, in the present invention, unlike conventional manufacturing methods,
Since pyrolytic boron nitride is used as the starting material, there is no need for a pretreatment step for deoxidizing the starting material, and by adding a cubic boron nitride conversion catalyst, it is possible to produce polycrystalline cubic boron nitride using conventional methods. Polycrystalline cubic boron nitride can be produced under conditions of high temperature and high pressure, which are much milder than the previous conditions, so damage to high temperature and high pressure equipment is less likely to occur, making it possible to extend the life of the equipment and significantly improve industrial productivity. It has the advantage of

Claims (1)

[Scope of Claims] 1. One or more compounds selected from the group consisting of water, urea, and ammonium salts are added to pyrolytic boron nitride as a catalyst, and this is used to thermally decompose cubic boron nitride. 1. A method for producing cubic boron nitride, which comprises converting pyrolytic boron nitride into polycrystalline cubic boron nitride by holding the boron nitride under high temperature and high pressure conditions within a stable range. 2. The method according to claim 1, wherein the pyrolytic boron nitride has a purity of 99.9% by weight or more.