JPH052369B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for synthesizing cubic boron nitride (hereinafter referred to as CBN) used for grinding, cutting tools, etc. Prior Art Cubic boron nitride has a hardness second only to diamond, and is particularly stable against iron than diamond, so it is considered important for grinding steel. Generally, CBN is synthesized using hexagonal boron nitride (hereinafter referred to as HBN) as a raw material and using a catalyst to keep it below the stable region of CBN. At this time, CBN seeds are also mixed into the raw material and grown. CBN used for grinding, etc. is preferably Brodsky, with uniform particle size and a certain size or more. In response to these demands, improvements to conventional catalysts, such as
The use of composite catalysts such as Li ₃ BN ₂ , Ca ₃ B ₂ N ₄ has been proposed. In addition, the synthesis method has also been devised, such as the temperature difference method and the film growth method. The former is a method in which a temperature difference is created between the HBN dissolution region and the CBN precipitation region in the synthesis reaction chamber, while the latter is a method in which a thin film of catalyst is provided around the CBN seeds, and HBN dissolution and CBN precipitation occur through the film. This is the way to do it. By improving the catalyst, a fairly Brodsky product can be obtained, but it is still insufficient and it is difficult to obtain large particles. The disadvantages of the temperature difference method are that it takes a long time to synthesize and cannot be produced in large quantities. In the film growth method, the film becomes thinner as the grains grow and eventually breaks, so there is a limit to the grain size. Purpose of the present invention The purpose of the present invention is to synthesize a large amount of CBN particles with uniform particle size using Brodsky. Means for Achieving the Objective The present invention uses CBN seeds and heats an HBN molded body as a raw material in a catalyst substance to diffuse the catalyst substance into the molded body, and synthesizes CBN using this as a starting material. , is a method of growing seeds. In this case, the seeds are preferably distributed regularly in the molded body. HBN molded body is 0.5 to 10 mm to diffuse the catalyst.
It is desirable to make it into a thin plate shape. Seeds are placed in this molded body and a catalyst substance is diffused therein.
This order may be such that the seeds are placed and then the catalyst is diffused, or vice versa. Seeds can be arranged by making a large number of small holes on the surface of the HBN molded body and charging the seeds into these, or by dispersing and adhering the seeds to the surface of the HBN molded body. A method of including seeds may also be used. It is desirable that the seeds are arranged regularly, preferably at equal intervals. This is because each seed grows equally and grains of uniform size can be obtained. To arrange seeds regularly, it is sufficient to make small holes at regular intervals on the surface of the HBN molded body, place a large number of seeds on this surface, and shake them. Seeds can be charged one at a time. In the synthesis of CBN, there is a limit to the amount of growth, but the higher the growth rate of the seeds, the better, so it is undesirable for the seeds to be too large, and if they are too small, large CBN particles cannot be obtained, so the size is 20 to 500 μm.
The degree is appropriate. In order to make these seeds appear larger and easier to handle, they can be coated with metal, ceramic, etc. before use. Furthermore, as a method for placing CBN seeds in HBN molded bodies, fine CBN powder is mixed with an adhesive such as printing ink used for forming electric circuits, etc.
A method of plotting at equal intervals on the surface of the HBN molded body can also be used. In this case, the particle size of the fine powder may be smaller than those mentioned above, and there may be one or more seeds in one plot. In this seed growth, some seeds grow preferentially and exclude others, or particles are obtained in the form of aggregates of all seeds. It is necessary to ensure that the growth of the seeds is not affected by other seeds around them, and for this purpose they are placed at a certain distance. On the other hand, if the interval is too large, productivity will decrease. For these reasons, the spacing between seeds (the spacing between surfaces) is preferably in the range of 0.1 mm to 3 mm, although it depends on the size of the seeds. When a large number of molded bodies having seeds arranged thereon are used in a stacked manner, this interval is the interval in the plane of each molded body and the distance between the seeds between each molded body. Therefore, in the present invention, the regularly distributed arrangement of seeds means a planar or three-dimensional arrangement. When placing seeds on the surface of the HBN compact,
Seeds can be placed on a thin plate of metal such as Co or Cu that does not interfere with the catalytic action, and this can be stacked on the HBN molded body, and if a large number of them are used, these can be stacked alternately. To diffuse the CBN synthesis catalyst into the HBN molded body, there are two ways to diffuse the CBN synthesis catalyst into the HBN molded body.
Method of immersing HBN molded body in catalyst vapor
There are methods such as placing an HBN molded body, and in either case, it is sufficient to incorporate the required amount of catalyst into the molded body. Catalysts used include alkali metals, alkaline earth metals, nitrides thereof, and nitrides and HBN.
All catalysts effective for CBN synthesis can be used, such as composites with Al, alloys of Al, and nitrides.
Naturally, the present invention also includes the diffusion of the catalyst substance in this case, where it reacts with HBN to form a new catalyst. The amount of catalyst diffused is
A suitable amount is 0.01 to 0.5 mol per 1 mol of HBN. One feature of the present invention is that it uses a catalyst substance diffused into an HBN molded body. The reason why the present invention is more effective in achieving the above object than the known methods of mixing and molding these two methods is considered to be as follows. (1) Purity of reaction surface In mixed powders, the surfaces of HBN and catalyst particles are often exposed to the external atmosphere. Therefore, the activity on the surface of these particles is likely to be lost. (2) In the case of diffusion, the mixing is uniform.While mixed powders are mixed on the particle order, diffusion is mixed on the atomic order, resulting in extremely uniform mixing. Therefore, the catalyst is always evenly supplied to the seeds, and the isotropic raw material supply necessary for producing good crystals of CBN is achieved. Another advantage of the present invention is that the HBN molded body can be used in the form of a thin plate. Since HBN is difficult to sinter, it must be fired at a high temperature if it is to be made into a molded body. A thin plate is usually produced by cutting this molded body. However, since catalysts cannot be fired at such high temperatures, HBN mixed with catalysts must be fired at low temperatures, and the strength of the compact is insufficient, making it difficult to cut into thin plates. There is,
It is also difficult to form it into a thin plate from the beginning. On the other hand, the catalyst diffusion method does not have such limitations, so thin plates of HBN can be easily obtained. This is extremely advantageous when the CBN seeds are arranged at equal intervals in the compact. In the evenly spaced arrangement, the CBN seeds are effectively confined to the surface arrangement of the compact. In this case, a large number of thin plates can be stacked and used, greatly improving productivity. Synthesis of CBN is carried out using an ultra-high pressure device such as a belt type or girdle type under the stable range of CBN, and particularly preferred is a range of 40 to 60 Kb and 1300 to 1800°C. The synthesis time is finally obtained
For grains smaller than 300μ, wait 10 to 60 minutes or longer.
Some require about 10 hours. The synthesized product is processed by known methods such as pickling and alkali melting to remove catalyst and unreacted products.
By removing HBN, CBN is separated and extracted. Example 1 An HBN molded body was processed into a thin disc shape (diameter 25
mm, thickness 1.0mm). This disk was synthesized in advance
Buried in _LiCaBN2 catalyst powder, 850 °C in _N2 atmosphere
heated for 24 hours. It contained about 5 mol% of LiCaBN ₂ diffused. (Measured from the increase in weight excluding the adhesion) Using a tsurugisan, the distance between the front, back, left and right (center distance)
A small hole with a diameter of 1 mm, a hole diameter of 130 μm, and a depth of 80 μm was made, and one CBN seed of about 100 μm was charged into each small hole, and 35 of these disks were stacked and loaded into a belt-type high-pressure device. The synthesis conditions were: first, the pressure was raised to 50Kb, then the temperature was raised to 1500℃, held for 2 minutes, and then 57Kb was generated in 30 minutes.
The pressure was increased to After the temperature was lowered, the pressure was returned to atmospheric pressure. The product is taken out from the high-pressure equipment, first treated with hydrochloric acid to remove the catalyst, and then treated with an alkali melting method.
HBN was removed and CBN particles were extracted. In addition, when observing the cross section of the product under a microscope, it was found that the seeds had grown.
Only CBN occurred, and no new outbreaks were observed.
The resulting particles were yellow-orange, blocky particles with an average diameter of 300 μm. For comparison, the amount of the catalyst corresponding to the amount of diffusion was
Mix it with HBN, mold it and use the seeds in the same way.
Synthesized CBN. However, since it is difficult to form a thin plate with a thickness of 1 mm using powder molding, the thickness was reduced to 5 mm.
CBN seeds were placed therein in the same manner as in Example 1. In this comparison, since there are fewer CBN seeds than in Example 1, the yield of CBN produced is naturally lower. This is an experiment to compare the variation in particle size, shape, etc. of particles with those of the present invention. These results are shown below.

[Table] Brodsky, especially large grains.
stomach.
Example 2 Li ₃ BN ₂ was diffused into an HBN disk in the same manner as in Example 1. However, the diffusion conditions were 700°C and N ₂ for 48 hours. About 20 mol% of Li ₃ BN ₂ was diffusely contained.
The method of filling the device is the same as in Example 1. 52Kb
After increasing the pressure to 1550℃, the temperature was increased for 1 hour.
Boosted to 58Kb. The CBN taken out had a grain shape concentrated around 400μ, and was a transparent yellow Brodsky grain with a smooth growth surface. Example 3 HBN disk (same size as Example 1)
Mixed with Ca ₃ B ₂ N ₄ powder and treated at 900 °C in N ₂ for 24 h. About 7 mol% of Ca ₃ B ₂ N ₄ was diffusely contained.
On the other hand, holes with an interval of 600 μm, a diameter of 100 μm, and a hole depth of 60 μm were regularly made in a Co plate (diameter 25 mm, thickness 0.25 mm) using the photo etching method. This contains particles with a particle size of 70 to 90μ.
One CBN particle was placed in each hole, and 27 sets of the above HBN plates were stacked alternately and loaded into a belt-type high-pressure device. Synthesis conditions are first 50Kb, held at 1550℃ for 2 minutes, then 60Kb.
Boosted to 57Kb in minutes. After the temperature was lowered, the pressure was returned to atmospheric pressure. CBN particles were extracted using a conventional method. Yellow transparent Brodsky grains with an average grain size of 400μ were obtained. Example 4 HBN molded body (diameter 25 mm, thickness 1.5 mm)
Mixed with LiCaBN ₂ powder in N ₂ at 750 °C for 60 h
LiCaBN ₂ was diffused and contained. The amount of LiCaBN ₂ diffused was about 30 mol%. Holes with a distance of 2 mm from front to back and left to right and a depth of 0.5 to 0.7 mm were drilled in this disk using a 0.5φ drill. On the other hand, 400μCBN particles were coated with Cu to improve their handling properties. Particle size after coating is 410 ~
It was 420μ. One grain of this material was put into each hole of the HBN disc, and 23 discs were stacked and loaded into the device. The synthesis conditions were to first increase the pressure to 46Kb, then
The temperature was 1450°C. After holding for 2 minutes, in 1 hour
Increase the pressure to 57Kb, hold it for 5 hours, and then use the usual method.
I took out CBN. A yellow-orange CBN with a smooth plane and well-organized phase crystals and a thickness of 1 to 1.5 mm was obtained. Example 5 An alumina porcelain tube was placed in a furnace, and a temperature gradient was created in the length direction. Inside this tube is an HBN disc (diameter 25
mm, thickness 1 mm) and Mg ₃ N ₂ powder are placed apart,
The former was set at 1150°C, and the latter at 1300°C. that time
The HBN disk was placed on a small support stand with most of its bottom surface directly exposed to the atmosphere, and the Mg ₃ N ₂ powder was placed in a molybdenum container (open). N ₂ gas was flowed from the Mg ₃ N ₂ side of the alumina porcelain tube and maintained for 24 hours. As a result, in the HBN molded body
Mg ₃ N ₂ was contained 0.5% by weight diffused. 70~ for this
CBN seeds of 90 μm were placed as in Example 1.
35 sheets of this are stacked and loaded into a belt-type high-pressure device.
First, it was 50Kb and held at 1550°C for 2 minutes, and then increased to 56Kb in 30 minutes. After lowering the temperature, the pressure was returned to atmospheric pressure, and CBN particles were extracted in the same manner as in Example 1. Transparent crystals with an average particle size of 320μ with little variation were obtained. Effects of the Invention According to the present invention, as specifically shown in Examples, the growth of particles is large, resulting in an increase in production volume, and the variation in particle size is also small. Furthermore, it produces Brodsky and tough abrasive grains with well-organized crystal planes. Furthermore, since raw materials can be supplied uniformly, coarse grains with a better shape than before can be obtained. In addition, HBN molded bodies can be processed thinly,
In addition, the catalyst is diffused and the seeds are arranged regularly (equally spaced), and a large number of these can be stacked and used, thereby improving productivity.

Claims (1)

[Claims] 1. A hexagonal boron nitride molded body is heated in a cubic boron nitride synthesis catalyst, the catalyst material is diffused into the molded body, and cubic boron nitride seeds are dispersed therein. Alternatively, hexagonal boron nitride compacts having cubic boron nitride seeds dispersed therein are heated in a cubic boron nitride synthesis catalyst to diffuse the catalyst material into the compacts; A method for synthesizing cubic boron nitride, characterized in that the seeds are grown by treating them under the stability range of cubic boron nitride, and the cubic boron nitride is separated from the obtained product. 2. The method for synthesizing cubic boron nitride according to claim 1, wherein seeds of cubic boron nitride are regularly dispersed.