JPS60204607A - Synthesis of cubic boron nitride crystal - Google Patents

Abstract

PURPOSE:To synthesize a cubic boron nitride crystal, in an extremely high conversion, by reacting a mixture of boron nitride and a catalyst composed of a metal or metallic compound under specific condition, and removing the catayst from the reaction product. CONSTITUTION:50-95mol% boron nitride obtained by the thermal decomposition of borazine and/or a borazine derivtive is mixed with 5-50mol% catalyst composed of a metal and/or a metallic compound, e.g. aluminum nitride. The mixture is made to react under >=3GPa pressure at >=70 deg.C, and the catalyst is removed from the reaction product to obtain the objective cubic boron nitride crystal.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to a method for synthesizing cubic boron.

[Background technology]

Boron nitride in a high-pressure stable phase is known as cubic densified boron nitride and urucite-type boron nitride, both of which do not exist in nature. It is synthesized with

Among these, methods for synthesizing cubic boron nitride include a direct method under hydrostatic pressure without using a catalyst and a catalytic method using a specific catalyst substance. The high-pressure stable boron nitride obtained by the direct method is a mixture of cubic boron nitride and wurtzite boron nitride, and pure cubic boron nitride cannot be synthesized by the direct method. The drawback is that boron and wurtzite boron nitride cannot be separated.

Furthermore, the synthesis conditions for the direct method require high pressure of 100 Pa or more and high temperature of 2000℃ at the front edge. Therefore, special pressurizing methods are used, heating device jigs including heaters, cylinders, pistons, etc. There is a problem in that the pressurizing parts of the press are subject to rapid wear and tear.

On the other hand, the catalytic method uses one or more metals selected from the group consisting of alkali metals, alkaline earth metals, lead, antimony, tin, alloys thereof, and nitrides thereof, as described in the Central Patent Publication Publication No. 38-14. and (11) Aluminum nitride described in Japanese Patent Publication No. 52-17838, in which at least one member selected from the group consisting of lb, IIJ■a*Vaw■"p■a, ■ group elements, and silicon is added. The main known method is to use a system containing the following as a catalyst. Boron nitride in a high-pressure stable phase obtained by catalytic methods such as these (1) and (11) does not contain boron nitride of the same type as boron nitride, which is different from boron nitride in a high-pressure stable phase obtained by a direct method. In the case of synthesis disputes, it has become possible to synthesize cubic boron nitride under lower pressure and temperature conditions than the synthesis conditions of the direct method. However, the synthesis methods associated with these catalytic methods use macrogonal boron nitride as a starting material, and impurities, mainly oxygen, that are mixed into the hexagonal boron nitride during the manufacturing process of hexagonal boron nitride are There is a problem that the conversion rate to boron nitride is low due to the presence of a mixture of boron nitrides, leaving largely cubic boron nitride, or that higher pressure and high temperature conditions are required to increase the conversion rate.

[Purpose of the invention]

The present invention solves the drawbacks and problems of the conventional cubic boron nitride synthesis method as described above. Specifically, boron nitride (hereinafter referred to as Boron nitride (abbreviated as boron nitride) with borazine is treated with a catalyst made of metal and/or metal compound (hereinafter referred to as
The purpose of the present invention is to provide a method for synthesizing cubic boron nitride, which is converted into cubic boron nitride by the action of a catalyst (abbreviated as "catalyst"), has an extremely high conversion rate to cubic boron nitride, and has little impurities such as oxygen.

[Disclosure of the invention]

The inventors of the present invention have found that the factors that have the greatest influence on the conversion rate from raw material boron nitride to cubic boron nitride are the crystal plane of raw material boron nitride and the oxygen content of raw material boron nitride. .

Therefore, in 1983, a method for producing cubic boron nitride was developed that suppressed the oxygen content in the raw material boron to the required limit.
-37200. That is, hexagonal boron nitride as raw material boron nitride and aluminum nitride which acts as a catalyst for the conversion reaction of hexagonal boron nitride to cubic boron nitride are mixed, this mixture is filled into a container, and then toluene and xylene are added. , by injecting an organic solvent such as ethyl alcohol into the container and adding more than enough to cover the mixture, or by replacing the atmosphere in the container with an inert gas such as nitrogen or argon, the acid system in the container can be removed.
The volume is adjusted to be equal to or less than φ, and then the container is treated under high pressure and high temperature to obtain cubic 7J boron nitride.

The present invention aims to provide a new invention regarding the crystal plane of raw material boron nitride, which is another issue for increasing the conversion rate to cubic boron nitride. That is, according to the inventors of the present invention, the conversion rate to cubic boron nitride is higher as the crystal plane of the raw material boron nitride is lower. It is known that the desired state is ideal, especially in the point where the crystal plane is low. This point will be described in more detail below.

First, borazine was obtained by reduction of β-trichloroborazine, which was then sealed in a gold capsule and thermally decomposed using a hydrothermal synthesizer under pressure and heating up to 100 MPa and 70'O<0>C. High purity boron nitride was prepared. The crystallinity and bonding of the obtained high-purity boron nitride was investigated by powder X-ray diffraction, infrared absorption spectroscopy, and transmission electron microscopy. As a result, boron nitride produced by heating up to 100 MPa and 700°C was found to be amorphous as shown in Figure 1, while the morphology of the high purity boron nitride was examined using a scanning electron microscope and found to be spherical or fibrous. It was boron nitride with These results indicate that in the pressurized thermal decomposition of borazine, the cleavage reaction and condensation reaction of the borazine ring occur in parallel in the coexistence of gas and liquid phases.

Also, 6. of a mixture of amorphous boron nitride and 20 mol aluminum nitride synthesized by pressurized pyrolysis of borazine.
Figure 2 shows the conversion rate under 5 GPa. Furthermore, amorphous boron nitride converts to cubic boron nitride more easily than crystalline boron nitride, and the activation energy for conversion is 20 K compared to 60 Kcal/mot for crystalline boron nitride.
This is a low value of cIIt/m ot. The above research results form the basis of the present invention.

That is, in the method for synthesizing cubic boron nitride of the present invention, a mixture of boron nitride using borazine and a catalyst that promotes the conversion of the boron nitride to cubic boron nitride is heated at a pressure of 3
In this method, cubic boron nitride is obtained by reacting at a temperature of 700° C. or higher at a temperature of 700° C. or higher, and then removing the catalyst from the resulting product.

To explain in more detail the method for synthesizing cubic boron nitride according to the present invention, a predetermined amount of boron nitride prepared by borazine and an appropriate amount of catalyst added thereto is weighed, mixed in a mixer such as a V-type mixer, and the resulting mixture is mixed. Metals such as Zr gr rt,
Alternatively, it is filled into a container made of an inorganic compound such as hexagonal boron nitride or aluminum oxide, and the atmosphere inside the container is replaced with an inert gas such as nitrogen or argon. Installed in a high temperature device, pressurized to 30 Pa or more, preferably 5.0 to 8.0 GPa, and set the temperature to 700°C or more, preferably 1200°C.
℃ ~ 2000 ℃, increase the temperature, preferably 1 minute or more, 1 time 5 ~
After holding for 30 minutes, the temperature and pressure are lowered, the product is taken out from the container, and then the catalyst is removed from the product, thereby obtaining cubic boron nitride.

Borazine used in the present invention has a chemical formula of BN3H6, and borazine derivatives have a chemical formula of BxNyH.
It is a boron compound consisting of boron, nitrogen, and hydrogen represented by z (x*'/+1 each represents an integer).

The boron compound as a borazine derivative may be in a gaseous, liquid or solid form, but it is preferably in a liquid or solid form from the viewpoint of handling.
B, N, H8), borazobiphenyl (B6N6H,.

), 2,4-diaminoborazine (88NI5H, ), and the like. The borazine and/or borazine derivative is preferably a boron compound consisting of an inorganic cyclic compound, such as a six-membered cyclic compound such as borazine, or a hole-membered cyclic compound such as po-2-sina-7-talene.

The catalyst added to boron nitride by borazine is a catalyst conventionally used for conversion to cubic boron nitride, such as Li, Na, K, Li, Os, Fr.
alkali metals, Oa, Sr, Ra, Ra
, Be, Mg alkaline earth Kinzo, At, old,
Tl, Zr*Hf, VrNb, Ta
, Or, Mo, W, Sb, an,
Ph'l any metals, their alloys as well as Li3N
, Li5FIN2. Na8N, Na, BN,.

, 0a8N, , Mr13N2. The catalyst can be selected from metallized Fr such as ktN, and it is particularly preferable to use aluminum nitride as a catalyst because it has a high effect of promoting the conversion to cubic densified boron. If the mixing ratio of aluminum nitride as a catalyst is less than 5 mol, the catalytic effect will be low, and if it exceeds 50 mol, the catalytic action will reach saturation. Mole ratio ~ 50 mole ratio Sushikake 10-4
It is 0 morti. This starting material and 1. After the synthesis of cubic boron nitride is completed, for example, in the case of aluminum dielectric, the catalyst used is
Caustic alkaline solution such as H, KOH, or boiled Nr
Aluminum nitride can be removed by immersing it in a strong caustic alkaline aqueous solution such as +ON for alkali treatment.

In the method for synthesizing cubic boron nitride of the present invention, which is produced in this way, the starting materials are of high purity and consist of fine boron nitride with low crystallinity and a catalyst, so cubic boron nitride can be produced under low pressure and temperature conditions. 100q6 converted to boron nitride is obtained.

The cubic boron nitride obtained by the synthesis method of the present invention has high purity and fine particles, so it has excellent sinterability.
For example, when a cubic boron nitride sintered body is produced under high pressure and high temperature conditions using a mixture with other additives, a dense and highly hard sintered body can be obtained under low pressure and temperature conditions.

[Representative embodiment of the invention]

Example 1 Borazine was heated at 70°C in an argon atmosphere of 100 MPa.
80 mol of boron nitride obtained by decomposition and 2 mol of aluminum nitride were weighed, mixed in an agate mortar in a glove box filled with argon, and filled into a zirconium container. Next, this container was transferred into a desiccator, and after degassing with a vacuum bonder, the inside of the desiccator was filled with argon. Place the lid on the container in a desiccator, puncture the mouth, and then place the container in a desiccator.
It was taken out and placed in a girdle-type high-pressure and high-temperature device, and the pressure of this high-pressure and high-temperature device was set at 6.50 Pa and the temperature at 1400°C.
Sample 1 was prepared by the synthesis method of the present invention by holding the sample for 10 minutes at [7].

As a result of X-ray diffraction of Sample 1 thus obtained, the presence of hexagonal boron nitride was not detected, and the diffraction line was 10014 cubic boron nitride. Further, since this sample 1 was a dense sintered body, the hardness was measured using a micro Vickers, and the hardness was 6000 Kf/12 HV.

For comparison purposes, commercially available hexagonal boron nitride (170 ml) and aluminum nitride (20,000 ml) were prepared under similar high-pressure, high-temperature conditions. As a result of Xd diffraction, both cubic boron nitride and 60,000-crystal perforated boron were observed. and its hardness is 3000 Ky
/urn MY.

Example 2゜Example 1. 60 mol of boron nitride and 40 mol of aluminum nitride obtained by thermal decomposition of borazine in the same manner as in Example 1 were weighed to give a total fi of 550 mlF, and placed in a girdle-type high-pressure and high-temperature apparatus in the same manner as in Example 1. Then, under these high pressure and high temperature conditions, a pressure of 6.50 Pa and a temperature of 1300° C. were maintained for 15 minutes to prepare Sample 2 according to the synthesis method of the present invention. As a result of xA9 diffraction, the presence of hexagonal boron nitride is detected in sample A) 2 obtained in this way. ft, and as a result of measuring the hardness of sample 2, it was 5500 Kf/rmF I
It was IV.

For comparison purposes, 60 moles of commercially available boron nitride and 40 moles of aluminum nitride were prepared under similar high pressure and high temperature conditions, and as a result of XIP1 diffraction, both cubic boron nitride and hexagonal boron nitride were detected. and its hardness is 2500
Ky/mm' HV.

Example 3゜Example 1. 90 moles of boron nitride obtained by convex decomposition of borazine in the same manner as above and 1 ° mole of complexed aluminum were weighed so that the total amount was 550 mf, and placed in the same machine as in Example 1 in a girdle-type high-pressure and high-temperature device. The pressure of this high-pressure, high-temperature apparatus was maintained at 8.0 GPa s at a temperature of 1800° C. for 5 minutes to prepare Sample 3 according to the synthesis method of the present invention.

As a result of X-ray diffraction of Sample 3# thus obtained, the presence of hexagonal densified boron was not recognized, and the diffraction line was that of 100-inch cubic boron nitride.

The hardness of this sample 3 is 63oKf/r+/)IV
Met.

For comparison purposes, commercially available hexagonal boron nitride (90,000 ruci) and aluminum nitride (90,000 ruci) were prepared under temperature conditions, and as a result of X-ray diffraction, both cubic boron nitride and hexagonal boron nitride were observed. The power was 3200 Ky/lam HV.

Actual 16 cases 4.

Example 1. A total of 54 ml of boron nitride 80 ml and aluminum nitride 20,000 ml obtained by heating in the same manner as in Example 1 using Po2Sina7talene in place of borazine υ.
A mixed powder containing 0mG' and 10tnf of aluminum was prepared in the same manner as in Example 1 at a pressure of 4.50P♂ and a temperature of 17%.
Sample 4 produced by the synthesis method of the present invention by holding at 00°C for 15 minutes
As a result of X-static diffraction, the thus obtained sample 4 showed no presence of hexagonal boron nitride, and the diffraction line was 100% cubic boron nitride. The hardness of sample 4 is 5
It was 800Ff/throat 2■V.

For comparison purposes, 170 mol% of commercially available hexagonal boron nitride, 20 mol% of aluminum Q oxide, and 10 mol% of aluminum fy/A were prepared in the same manner, and as a result of Xh horizontal diffraction, both cubic boron nitride and hexagonal boron nitride were found. was observed, and its hardness was 28001FF/+♂HV.

In addition, the cubic boron nitride obtained by the synthesis method of Examples 1 to 4 was obtained by X-ray diffraction and hardness measurement, and then boiled for 30 minutes in a 2N caustic soda aqueous solution to obtain 100 cm of cubic boron nitride) ( I made it.

[Industrial use nJ ability]

As a result of the above, the method for synthesizing cubic boron nitride of the present invention enables the synthesis of cubic boron nitride at lower pressure and temperature than the conventional method using macrogonal boron nitride as a starting material. The conversion rate to crystalline boron nitride is 100, and the cubic static boron nitride is highly purified and has a purity of only 10. In addition, the sintered body using cubic boron nitride obtained by the synthesis method of Wood's invention has excellent sinterability.
Since the resulting sintered body is highly hard and dense, it is suitable for use in cutting tools, including turning tools and rotary tools used as drilling tools such as millers, end mills, and drills, or wear-resistant tools, including machine parts jigs and cutting tools. It can be applied to tools such as cutting tools and even grinding tools, and due to the high thermal conductivity and high electrical resistance that cubic boron nitride has, it can also be applied to heat sinks in electronic circuits, making it industrially useful. It's extremely expensive.

[Brief explanation of drawings]

Figure 1 is a diffraction diagram based on an infrared absorption spectrum showing the crystallinity of densified boron obtained by thermal decomposition with borazine. FIG. 2 is an explanatory diagram of the conversion rate of boron nitride obtained by thermally decomposing borazine to cubic boron nitride at a pressure of 6.50 Pa. Patent applicant: Toshiba Tungaloy Co., Ltd. Nippon Insulators Co., Ltd.

Claims (2)

[Claims] (1) A mixture of boron nitride obtained by thermally decomposing borazine and/or borazine derivatives and a catalyst consisting of a metal and/or a metal compound is heated at a temperature of 700° C. at a pressure of 3 GPa or more.
A method for synthesizing cubic boron nitride, characterized in that the catalyst is removed from the product obtained after the above reaction. (2) The above-mentioned mixture comprises 50 to 95 mol% of boron nitride obtained by thermally decomposing borazine and/or a borazine derivative, and 5 to 50 mol% of aluminum nitride. A method for synthesizing cubic boron nitride according to item 1.