JPS5957905A - Production of cubic boron nitride - Google Patents

Abstract

PURPOSE:To obtain cubic BN having excellent mechanical strength and shape in a method for mixing a catalyst with hexagonal BN and subjecting the mixture to a high temp. and high pressure treatment, by using a preliminarily calcined compd. of the nitride which is specified in kind and compsn. ratio for the catalyst. CONSTITUTION:This novel catalyst is obtd. by compounding Li3N:X: BN at (1- 1,4):(1-1.4):3 molar ratio and heating the mixture at 800-1,300 deg.C in an inert atmosphere of N2, Ar or the like (X is Mg3N2 or Sr3N2 or Be3N2). The structure, etc. of the material is unknown but the material is considered not to be a simple mixture. Since the mixture is obtd. as a melt, the melt is cooled to solidify in an inert gaseous atmosphere and the solidified mixture is ground. The resulted powder is compounded as the catalyst with hexagonal BN powder and both are uniformly mixed and the mixture is molded by compaction. The green compact is subjected to a high temp. and high pressure treatment, whereby the cubic BN is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing cubic boron nitride (hereinafter referred to as CBN) from hexagonal boron nitride (hereinafter referred to as HBN) using a novel catalyst.

As is well known, CB N1-t has a hardness close to that of diamond, and is even more chemically stable than diamond!
As a result, the demand for grinding materials (abrasive grains) is increasing.

As an industrial manufacturing method of CBN as described above, HB
Mix N powder and catalyst powder to form a powder of 40 to 60 kb.
A common method is to convert HBN into CBN by processing at a high pressure of about ar and a high temperature range of about 1400 to 1600°C. Catalysts used in such methods include nitrides of alkali metals or alkaline earth metals, or boron nitride-based ternary compounds consisting of alkali metals or alkaline earth metals, nitrogen, and boron, such as C83B2N,
CBN is precipitated by taking advantage of the fact that CBN has a lower solubility in the eutectic melt than HBN at low temperatures.

By the way, grinding materials (abrasive grains) need to have high mechanical strength, especially crushing strength, and in relation to strength, the particles must have good shape, such as flat or acute-angled shapes. It is required that the shape be as close to a sphere as possible, or that the surface have few irregularities.

However, as mentioned above, in the conventional cubic boron nitride production method using a nitride (binary compound) or boron nitride-based ternary compound as a catalyst, it is not always possible to obtain CBN with sufficient mechanical strength and good shape. The reality is that this is not always possible.

In other words, in the conventional method using a catalyst, the actual situation is that strength and shape cannot be improved unless manufacturing conditions are controlled very precisely and complicated.

Therefore, the present inventors conducted extensive experiments and research in order to establish a method for improving the strength and shape of CBN, and developed a new catalyst.By using this, CBH with excellent strength, shape, etc. It was successfully manufactured.

This new catalyst contains Li3N:X:BN in a molar ratio of (1-1.4): (1-1.4):3 and is prepared under an inert atmosphere such as N2 or \'iAr. , 80
It is obtained by heating at 0 to 1300°C. ``In the above, X is Mg5N, 5r3N2, Be, or N2.

The structure of the substance produced by this heat treatment is not clear. However, it is thought that it is not just a mixture. This is because the effects are different when CBN is produced using a mixture of these as a catalyst and when this product is used as a catalyst.

In the above treatment, the effect of heating does not appear below 800°C. Moreover, when the temperature exceeds 1300°C, it is thought that decomposition of the product occurs. A heating time of about 20 to 60 minutes is sufficient. The mixture melts exothermically in the above temperature range. From these points, it is presumed that some kind of compound was produced from the mixture. The reason for specifying the molar ratio above is that when mixed and heated to this ratio, the effect as a catalyst becomes greater.

The melt was cooled and solidified in an inert gas atmosphere at 150
Grind it to a size smaller than mesh and use it as a catalyst.

It was then obtained as described above. A method for producing cubic boron nitride using a catalyst will be explained.

First, 5 to 50 parts by weight, preferably 10 to 30 parts by weight of powder of the above product, preferably 150 mesh or less, is blended as a catalyst to 100 parts by weight of hexagonal boron nitride powder, preferably 150 mesh or less; Mix uniformly and compact. Alternatively, the hexagonal boron nitride powder and the above-mentioned catalyst powder are individually compacted into thin plate shapes, and these are alternately stacked in the above-mentioned mixing ratio. The thermodynamic stability range of CBN for the mixed powder compact or laminate thus obtained, preferably I/i, 1300
A high pressure of 40-60 kbar is applied at a high temperature of ~1600°C and held for 5-40 minutes. In this way, crystal grains of cubic boron nitride are obtained. Naoko 1% hot water temperature, pressure,
The retention time is the same as before.

As mentioned above, various means for applying high temperature and high pressure can be considered, but for example, the mixed powder compact or laminate is placed in a reaction vessel as shown in Fig. 1, and electricity is applied and pressure is applied using a press. Good. In Fig. 1, the outer wall 1 of the container is made of pyrophyllite as a pressure transmitting body in a cylindrical shape, and inside the outer wall 1 there is a heater 2 made of a graphite cylinder.
And pyrophyllite 8 is provided as a partition wall material. In addition, steel rings 3 for energizing are attached to the upper and lower ends of the container.
A sintered aluminum plate 5 and a pyrophyllite 6 as a pressure transmitting body are disposed inside thereof, and the pyrophyllite 6 and pyrophyllite 8 as a partition wall material are disposed. The space surrounded by is a storage chamber 7 that accommodates reaction raw materials.

Examples in which cubic boron nitride was produced using the catalyst of the present invention and comparative examples in which cubic boron nitride was produced using a known substance as a catalyst are shown below.

Examples 1 to 6 Compounds pulverized to 150 mesh or less were mixed in the proportions shown in Table 1, placed in a platinum container, and heated with N2
The sample was heated and heated in an electric furnace while flowing gas at a flow rate of st7 minutes, and maintained under the conditions shown in the table.

The reaction product was cooled in an electric furnace in a N2 gas stream, and then ground to 150 meshes or less in a N2 gas atmosphere.

Table 1 The powder of 150 mesh or less obtained in each of the above Examples and the HBN powder of 150 mesh or less were uniformly mixed in a nitrogen atmosphere, and a surface pressure cuff of 00 Kq/cJr, an outer diameter of 20 tans and a length of 20 mm was prepared. It is molded into a cylindrical shape, placed in a container shown in Fig. 1, and pressed under high pressure to form Li3N powder and M
g s N2 powder, C powder mixed at a molar ratio of 1.1:1.22 (Comparative Example 2), Li3N powder, S
C
BH was produced.

Table 2 shows the conditions and results of these Examples and Comparative Examples.

The crush test in Table 2 was conducted as follows. That is, one sample grain with a diameter of 100 to 150 μm was placed on the lower cylinder of the upper and lower cylinders each having a diameter of 10 sections made of WC-Co, and the upper cylinder was lowered by driving a DC motor. Then, the position where the upper cylinder contacts the sample grain on the lower cylinder is electrically detected, and the corresponding distance between the surfaces of the upper and lower cylinders is determined.
is the grain diameter. As the load is further increased, from the total load W at which the grains break, as is well known, the following formula (1) % formula % (
1) The fracture strength σt of the Yoshi grains was determined. However, in reality, we conducted the above-mentioned test on the F150 sample.
The average value of D and the average value of W were determined, and the average breaking strength was calculated from equation (1). In addition, formula (1) is, for example, "RIKEN Report Vo139.Nα6" (published in 1960),
This is clarified by Hiroyuki Yoshikawa on page 310.

Furthermore, in the table, the yield is the ratio of CBN produced to blended HBN (excluding catalyst).

A representative diagram of the nine CBH grains obtained in the above Examples and Comparative Examples is that of Comparative Example 3. The same was true for other Examples and Comparative Examples. As you can see from this photo, CB according to the present invention
It can be seen that N has a nearly spherical shape as a whole and has a smooth shape with few minute irregularities on the surface.

Further, according to the present invention, in addition to being able to increase the yield of CBN, there are the following effects.

Since the catalyst composition is calcined in advance, the time required for high-temperature, high-pressure treatment to produce CBN can be shortened, and the time that the public mold is exposed to high pressure and high pressure is shortened, thereby extending the life of the mold. Since Li3N%Mg5N, etc. have been mixed with BN and treated in advance, it is thought that a reaction is occurring during this time.
'L, this reaction does not occur during CBN production, allowing smooth dissolution and precipitation of HBH in the catalyst, and high-grade CBN is produced. It is thought that a pre-calcined catalyst can form a stable structure, and since it is sufficiently stable in the atmosphere, it has become extremely easy to store and handle catalysts that could previously only be handled in an atmosphere box. , the reproducibility in CBN production is improved.

Reference Example Grinding tests for representative examples of abrasive grains obtained in the above Examples and Comparative Examples are shown below.

Particle size flJIs #120/140 -1
An electrodeposited grindstone was manufactured according to a conventional method. The grindstone specifications and grinding conditions are as follows.

O [Rigid type wet surface grinding (traverse cut) (i
ffi stone finishing IAl 180J)X10TX3
XX76.2H Grain size # 120/140 Concentration 100 Grinding wheel peripheral speed 150077i/min Table feed 15ηl/min Cross feed 2 panes/bath cutting 20μ/pass Grinding fluid Soluble type work material 5KH-57 (HRC=62) Results is as follows.

Example 4 Comparative example 3 Grinding ratio 580 410

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing an example of a reaction vessel used in producing CBN, FIG. The figure is an enlarged micrograph (100 times magnification) of CBN grains obtained in Comparative Example 3. ■... Container outer wall, 2... Heater, 3...
...Steel plate ring for current-carrying, 4...Steel plate for current-carrying, 5...
Alumina plate, 7. Raw material storage chamber. Patent applicant Showa Denko K.K. agent Sei Kikuchi - Figure 1

Claims (1)

[Claims] Li3N: : BN in molar ratio (1 to 1.
4): (1-1.4):3
A method for producing cubic boron nitride (X in the above is Mg3N2, Sr3N2 or Be3N2), characterized in that it is fired in an inert atmosphere at a temperature of 1300°C to 1300°C.