JPH0595B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to a method for producing cubic boron nitride (hereinafter referred to as CBN) used for abrasive materials, cutting materials, etc. (Prior Art) Generally, CBN is produced from hexagonal boron nitride (hereinafter referred to as HBN) at high temperatures and high pressures, which are the thermodynamic stability range of CBN. CBN has a hardness second only to diamond, and its chemical stability, especially with respect to ferrous work materials, is superior to that of diamond, so demand for it as an abrasive is increasing. An industrial method for producing CBN is to mix HBN powder and catalyst powder (alkali metals, alkaline earth metals and their nitrides, alloys, or boronitrides) and heat the mixture at 1300-1600℃ and 40-60kbar. high temperature,
A method of applying high pressure is being used. By the way, it is desirable that the CBN particles used as the abrasive be of high quality, dense and transparent, have sharp cutting edges, and have high crushing strength. However, the reality is that conventional methods do not necessarily yield products of sufficient quality. Patent Application No. 73359/1989 states that CBN abrasive grains that satisfy the above objectives can be obtained by adding 0.01 to 1.0% by weight of Si to HBN, but it is not possible to obtain CBN abrasive grains that satisfy the above objectives by mechanically mixing. As a result, they are not mixed completely uniformly, and in order to obtain the effect of Si, it is necessary to add an excess amount of Si, resulting in a decrease in yield. (Objective of the Invention) In view of the above circumstances, an object of the present invention is to provide a strong CBN in which the corners of the particles form sharp cutting edges and the (111) crystal planes are developed. Still another object is to provide CBN with excellent esomorphism using a relatively easy-to-handle catalyst. (Structure of the Invention) The gist of the present invention is to provide a method for synthesizing CBN from HBN, in which LiMBN ₂ (M is an alkaline earth metal) and
The purpose is to use Ca ₅ Si ₂ N ₆ as a catalyst. Since Si is contained in the catalyst material, Si acts uniformly during CBN synthesis, allowing CBN particles to have sharp cutting edges and strong CBN.
A similar effect can be obtained by using Li ₈ SiN ₄ instead of Ca ₅ Si ₂ N ₆ , but Ca ₅ Si ₂ N ₆ has the effect of producing CBN with even better euhedral properties. Also
Ca ₅ Si ₂ N ₆ has greater stability against moisture than Li ₈ SiN ₄ and is easier to handle. Although Ca ₅ Si ₂ N ₆ has a low solubility in BN, it has a catalytic effect, so even if it is added in excess, the growth of CBN is hardly inhibited. The present invention will be explained in detail below. The present invention uses LiMBN ₂ and Ca ₅ Si ₂ N ₆ as catalysts, which are powdered and mixed with a predetermined amount of HBN powder. In the above, M is an alkaline earth metal, preferably Ca, Ba, or Sr. One example of the manufacturing method for LiMBN ₂ is Li ₃ N, M ₃ N ₂ ,
Using BN as a starting material, these are mixed in the above order at a molar ratio of 1 to 1.4:1 to 1.4:3, and the mixture is heated and dissolved to react. A temperature of about 200°C above the melting temperature is suitable. The melting temperature is approximately 800℃ for the above composition.
~1000℃. LiMBN ₂ can be obtained by holding at the above temperature for about 1 hour and then cooling. The manufacturing method for Ca ₅ SiN ₆ is to mix Ca ₃ N ₂ :Si ₃ N ₄ in a ratio of 2.5 to 3:1.
They may be mixed at a ratio of 1,000° C. and kept at about 1000° C. for about 1 hour in an inert gas to react. The two types of catalysts mentioned above are used after being ground to 150 mesh or less under an inert gas atmosphere. The amount of catalyst used is based on 100 parts by weight of HBN.
LiMBN ₂ 5 to 50 parts by weight, preferably 10 to 30 parts by weight. If it is less than 5 parts by weight, the yield of CBN decreases,
If it exceeds 50 parts by weight, a good CBN product cannot be obtained. In addition, Ca ₅ Si ₂ N ₆ is 0.01 to 100 parts by weight of HBN.
The amount is 5.0 parts by weight, preferably 0.05 to 20 parts by weight.
If it is less than 0.01 parts by weight, the effect of forming a sharp cutting edge in CBN is small and the shape becomes rounded, and if it exceeds 5.0 parts by weight, the yield of CBN decreases. When synthesizing CBN, the raw material HBN and the above-mentioned catalyst can be constructed by uniformly mixing a predetermined amount of these three materials and compacting, or by mixing Li ₈ SiN ₄ with HBN or the above catalyst.
The method used is to mix it with LiMBN ₂ , compact it into a thin plate, and then stack it in a predetermined ratio. In the present invention, the catalyst is previously LiMBN ₂ ,
It is important to synthesize Ca ₅ Si ₂ N ₆ in advance. If CBN were synthesized using these components, it is possible that the same catalyst compound as above would be produced during the heating process, but that method would result in crystals catalyzed by the components. Crystals produced only from Li ₃ N and M ₃ N ₂ cannot provide transparent crystals with excellent euhorphism. The above-mentioned molded body or laminate is loaded into a well-known high-temperature, high-pressure device and maintained under predetermined conditions to synthesize CBN. The synthesis is carried out under conditions of 1300°C to 1600°C and 40 to 60 Kbar, which are the thermodynamic stability range of CBN. (Effects) According to the method of the present invention, a small amount of Si is incorporated into the growing CBN particles, and it appears on a specific plane, so the (111) plane of the crystal develops and the corners of the particle become sharp. CBN becomes a solid solution, the lattice constant increases, and the CBN particles become tougher. moreover
CBN grains have almost no oblate grains and have excellent self-shape properties. Therefore, use of the abrasive grains of the present invention improves the grinding ratio and reduces power consumption. Furthermore, in the present invention, since Si is included in the catalyst material, Si acts uniformly during CBN synthesis.
Compared to mixing Si or a non-catalytic Si compound,
Only a small amount of Si is required, and the yield of CBN does not decrease. Examples and comparative examples will be shown below to clarify the effects of the present invention. Example: HBN of 325 meshes or less, LiCaBN ₂ ,
Ca ₅ Si ₂ N ₆ was mixed at a weight ratio of 100:10:1 and molded into a cylindrical shape of 26 mmφ×32 mmh at a molding pressure of 1.5 t/cm ² . Its density was 1.72 g/cm ³ . This was loaded into a high temperature, high pressure reactor and maintained at a pressure of 50 kbar and a temperature of 1450°C for 10 minutes to synthesize CBN.
As a result, the conversion rate of CBN to HBN was 32%. When the particles were observed under a microscope, they were found to have sharp edges. Comparative Example CBN was synthesized in the same manner as in Example except that Ca ₅ Si ₂ N ₆ was not used. Although the conversion rate was the same as in the example, the sharpness of the particle corners was slightly inferior. CBN particles of the above examples and comparative examples, respectively.
Classified according to JIS, B4130 method, #120/140 CBN
Particles were obtained. Next, grinding wheels were made using each particle, and the grinding ratio and power used were compared. The method for making a grindstone is to first plate CBN #120/140 particles so that Ni/(Ni+CBN) is 60%, and then use the Ni-plated CBN particles.
35 parts of phenolic resin, 25 parts of phenolic resin, and 40 parts of finely divided silicon carbide were mixed, molded, and heat-cured to form a grindstone. Grinding tests were conducted using these grindstones. The steel type used in the grinding test was special steel SKH-57.
(HRc64), grinding ratio (= grinding amount / grinding wheel wear amount) and the The power consumption W was compared. The results are shown in the table below.

[Table] CBN synthesized by the method of the present invention
It can be seen that the grindstone made with particles has excellent grinding performance.

Claims (1)

[Claims] 1. In a method for producing cubic boron nitride from hexagonal boron nitride at high temperature and under high pressure, as a catalyst
LiMBN ₂ (where M is an alkaline earth metal) and
A method characterized by using Ca ₅ Si ₂ N ₆ . 2 For 100 parts by weight of hexagonal boron nitride,
The method according to claim 1, wherein 5 to 50 parts by weight of LiMBN ₂ and 0.01 to 5.0 parts by weight of Ca ₅ Si ₂ N ₆ are used.