JPS5918105A - Boron nitride type compound and preparation thereof and preparation of cubic boron nitride using the same - Google Patents

Abstract

PURPOSE:A quaternary novel boron niride compound, expressed by the formula LiBaBN2, and capable of synthesizing a cubic boron nitride having exceptionally improved strength and shape in using as a catalyst. CONSTITUTION:A quaternary novel boron nitride compound prepared by the following method: Li3N or metallic Li is mixed with Ba3N2 or metallic Ba and BN, and the mixed powder is then containined in a suitable vessel and heated in an atmosphere of an inert gas, e.g. N2 or Ar. In this case, the powder is kept at 800 deg.C or above, preferably about 900 deg.C, to make the melt reaction proceed. The reaction product is then cooled and coagulated in the atmosphere of the inert gas to give the above-mentioned boron nitride compound (compound A). For preparing the titled cubic boron nitride, the compound (A) is used as a catalyst, and the cubic boron nitride is kept in a thermodynamically stable high- temperature and high-pressure region in the presence of the compound (A) and hexagonal boron nitride together. Thus, the aimed cubic boron nitride can be synthesized.

Description

Detailed Description of the Invention The present invention provides a novel boron nitride compound useful as a catalyst in producing cubic boron nitride, a method for producing the same, and a method for producing cubic boron nitride using the boron nitride compound as a catalyst. The present invention relates to a method for producing boron.

As is well known, cubic boron nitride has a hardness close to that of diamond, and is superior to diamond in terms of chemical stability, so its demand as a grinding material (abrasive grain) is increasing.

An industrial method for manufacturing cubic boron nitride as described above involves mixing hexagonal boron nitride powder and catalyst powder,
This is heated to a high pressure of about 40 to 60 kbar, 1400 to
A common method is to convert hexagonal boron nitride into cubic crystal by processing at a high temperature of about 160° 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 Ba3B2 N4 and Li3BN2. Are known. This method involves dissolving hexagonal boron nitride into the catalyst melt and taking advantage of the fact that cubic boron nitride has a lower solubility in the eutectic melt than hexagonal boron nitride under the synthesis conditions. This method precipitates cubic boron nitride.

By the way, grinding materials (abrasive grains) need to have high mechanical strength, especially crushing strength, and in relation to the strength, the particles must have good shape, that is, they have a flat shape and an acute angle. 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 nitride (binary compound) or boron nitride-based ternary compound as a catalyst, it is not always possible to obtain optical mechanical strength,
The reality is that it is not always possible to obtain cubic boron nitride with good shape properties. 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 to establish a method for improving the strength and shape of cubic boron nitride using a catalyst material different from the conventionally used catalyst. In addition to successfully synthesizing a new substance that had not been previously used, the new substance was found to be useful as a catalyst in the synthesis of cubic boron nitride, and by using this substance as a catalyst, it was possible to achieve significantly superior strength and strength compared to conventional methods.
They discovered that it is possible to synthesize cubic boron nitride with morphological characteristics, leading to the present invention.

That is, the present invention provides a novel compound useful as a catalyst for the synthesis of cubic boron nitride, a method for synthesizing the new compound, and a method for producing cubic boron nitride with high strength and excellent shape using the new compound. The purpose is to provide the following.

The present inventor previously filed a patent application regarding a novel quaternary compound represented by LicaBN2 and a method for producing cubic boron nitride using the same as a catalyst. As a result of subsequent research, a new compound was discovered, and when this compound was used as a catalyst for the synthesis of cubic boron nitride, it was found that it had the same excellent effects as the previous invention. .

Specifically, the novel compound of this invention has the molecular formula LiBa
It is a boron nitride-based quaternary compound represented by BN2, that is, lithium barium boron nitride.

Further, the method for synthesizing a boron nitride compound of the present invention includes mixing lithium nitride or metallic lithium, barium nitride or metallic barium, and BN, and heating the mixture in an inert gas atmosphere such as argon gas or nitrogen gas. 80
It is held at a high temperature of about 0° C. or lower, and after melting, it is cooled and solidified.

Furthermore, the method for producing cubic boron nitride of the present invention uses the boron nitride-based quaternary compound as a catalyst.
1. Cubic boron nitride is synthesized by maintaining the quaternary boron nitride compound as a catalyst and hexagonal boron nitride in a high temperature and high pressure region where cubic boron nitride is thermodynamically stable. It is something.

This invention will be explained in more detail below.

First, a method for producing the novel compound of the present invention, that is, a boron nitride-based quaternary compound, will be explained.

In producing the new compound, as raw materials,
Prepare a powder of lithium nitride or metallic lithium such as Li3N, barium nitride or metallic lithium powder such as Ba3N2, Li38N2 powder, Ba3B2N4 powder, and BN (hexagonal boron nitride is, of course, sufficient) powder. Then, mix these in the proportions described below, store the mixed powder in a suitable container, and store it in N2.
Alternatively, it is heated in an inert gas atmosphere such as M. During this heating and temperature rise, heat was generated from about 700°C, and it is presumed that the reaction had started. and 800℃~90
Since it is melted at about 0°C, it is heated and maintained at 800°C or higher, preferably about 900°C, to advance the melting reaction. The holding time is preferably about 20 minutes or more, and it is usually desirable to heat and hold for about 40 minutes.

After heating and holding in this manner, the novel compound of the first invention can be obtained by cooling and solidifying in an inert gas atmosphere. In addition, when producing cubic boron nitride using this compound, the solidified compound is ground to 150 metric tons or less in an inert gas atmosphere.

Here, to explain the blending ratio of each of the raw materials, when lithium nitride, e.g., Li3N, barium nitride, e.g., Ba3N2, and BN are used as raw materials, the blending ratio is determined by the atomic ratio of Li, Ba, B, and H in the mixture. It is desirable to set it so that it becomes (1-1.4):(1-1.4):l:2. Therefore, when Li, N is used as lithium nitride and l3a3N2 is used as barium nitride, Li3N, Ba3N, , BN
.

The molar ratio is preferably (1-1.4):(1-1.4):3. In addition, when metallic lithium is used as a lithium source, when metallic barium is used as a barium source, or when metallic barium is used as a lithium source or barium source, Li
When something other than 3N or (7) other than Ba3N2 is used, the molecular ratio of Li, Ba, and H in the mixture is (1-1.4): (1-1.4):I(! l
: Even if the molecular ratio of N in the mixture is set to be 2 or less, in this case, the inert gas atmosphere during heating of the mixture should be made into a nitrogen gas atmosphere to compensate for the nitrogen deficiency. It is desirable to supplement.

Next, an example of the method for synthesizing the above-mentioned new compound will be described.

Example 1 5 g of Li3N powder, 20 g of Ba, N2 powder, and 10 g of hexagonal BN powder were each ground to 150 meshes or less. !
Mix il, store it in a platinum container and add N2 gas to 81/-
fd) Heat and raise the temperature in an electric furnace while flowing at a flow rate of 90
It was kept at 0°C for 40 minutes. The reaction product was cooled in an electric furnace in a N2 gas stream, and then heated for 15 minutes in a N2 gas atmosphere.
It was crushed to less than 0 mesh.

The structure of the reaction product powder obtained in this example was analyzed by X-ray diffraction, and the structure was found to be as shown in the rightmost column of Table 1. On the other hand, ASTM card data of known substances such as raw materials used in this reaction are also shown in Table 1. From Table 1, it is clear that the substances obtained in the examples are not mere mixtures of known starting materials, but are new substances with completely new structures. And the chemical analysis results (Ll was analyzed using the flame method, Ba was analyzed using the EDTA method, I3 was analyzed using the mannitol method, and N was calculated by subtracting from the total)
As a result of the investigation, it was revealed that it is a new boron nitride compound with the molecular formula LiBaBN2, and that its structure is a body-centered cubic structure and that each unit cell contains 12 molecules. This was confirmed from the integer ratio in the table and the h k lO value. Furthermore, as a result of thermal analysis of this new compound,
The melting point and freezing point were found to be approximately 800°C. On the other hand, the actual measured value of specific gravity is about 2.50, and 1 cell has a specific gravity of about 2.50.
From the theoretical calculation of a body-centered cubic structure containing two molecules (average of 7872 holes in ao), the specific gravity was calculated to be 2.494, and it became clear that the measured value and the theoretical value were in good agreement.

In the above-mentioned Example 1, as shown in sample number 1 in Table 2 below, the amounts of Li3N, Ba3N2, and BN were adjusted to a molar ratio (1:1) at which LiBaBN2 was stoichiometrically synthesized from them. :3), but in the following Example 2, a case where the blended amounts of i3N and Ba3N2 are slightly different from that of BN will be described.

Example 2 Li3N at molar ratios as shown in sample numbers 2 to 5 in Table 2.
The powder, Ba3N2 powder, and BN powder were mixed and treated in the same manner as in Example 1.

Table 2 X-ray analysis of the material obtained in Example 2 confirmed that the quaternary compound phase obtained in Example 1 and an excess component of Li3N or Ba3N2 were combined.

In addition to the above-mentioned combinations, the following combinations (1) to (3) can be used as starting materials for producing the novel compound Li Ba BN2 of the present invention.

(1) Lithium nitride or metallic lithium and Ba
3B2N4 and BN (21Li, BN2 and nitride) (lium or metal) (1noum and BN (3) L ts B N2 and Bas 132 N
4 In any of these cases (1) to (3), mix in the same manner as above, heat and hold at 800°C or higher in an inert gas atmosphere such as Ar, N2, etc. to react and melt, and then cool and solidify. Just let it happen. In addition, the blending ratio of raw materials in these cases is basically Li, Ba, and B in the mixture.
, the molecular ratio of N is (1-14):(1-1.4):1:2
It is desirable to set it so that +1>,
In the case of +2+, metallic lithium is also used [7] If the molecular ratio of N becomes 2 or less due to the use of metallic barium, use N2 gas as an inert gas during heating to make up for the lack of N. is desirable.

Next, as mentioned above, the quaternary compound obtained with 1- (1・1T
3a A method for producing cubic boron nitride using I3N, , ) as a catalyst will be described.

First, hexagonal boron nitride preferably has a thickness of 150 mm or more.
1 to 100 parts by weight of the powder, the quaternary compound (Lil3a BN2) (7) as a catalyst, preferably 1
5 to 50 parts by weight of powder with a weight of 1 or less, preferably 1
0 to 30 ij parts are blended, mixed uniformly, and compacted. Alternatively, hexagonal boron nitride powder and the above-mentioned catalyst powder are each individually compacted into a thin plate shape,
These are alternately laminated in the above-mentioned mixing ratio. 130% for the mixed powder compact or laminate thus obtained.
A high pressure of 40 to 5 Q kbar is applied at a high temperature of 0 to 1600°C and held for 5 to 40 minutes. If IJi <, then the intercrystals of cubic boron nitride are the same as in the conventional case.

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 a partition wall material (7 and pyrophyllite) 8 are provided. 'Furthermore, a current-carrying steel ring 3 and a current-carrying steel plate 4 are arranged at the upper and lower ends of the container, respectively, and inside of these rings, a sintered alumina plate 5, a pressure transmitting body, and silica fluorite 6 are arranged. , 17 and the space surrounded by the pyrophyllite 6 and the pyrophyllite 8 serving as a partition wall material serves as a storage chamber 7 for accommodating the reaction raw materials.

Example 3 in which cubic boron nitrogen was produced using the quaternary compound (Li Ba BN2) as a catalyst, and a comparative example in which cubic boron nitride was produced using a known substance as a catalyst will be described below.

Example 3 1) 15 of the 11 quaternary compounds obtained by Example 1
Powder below 07 tsunyu 2. J19 and 80 g of hexagonal boron nitride of 150 mesh were mixed uniformly in a nitrogen atmosphere, and formed into a round bar shape with an outer diameter of 20 mm and a length of 20 mm using a surface pressure cuff 00 Kid, as shown in Fig. 2. Indication-1-Accommodate in a reaction vessel and press at 50 kbar, 1450
15 molecules fl were maintained at .degree. C. to produce cubic boron nitride.

Comparative Example 1 I, 13N powder of 150 mesh or less as a catalyst 2.
5g and 150 pieces of hexagonal boron nitride 8 (]
cubic boron nitride was produced in the same manner as in Example 3.

Comparative Example 2 Cubic boron nitride was produced in the same manner as Comparative Example 1 except that -CBa3B2N4 was used as a catalyst.

Comparative Example 3 Catalyst 1. i. Cubic boron nitride was produced in the same manner as Comparative Example 1 except that BN2 was used.

Comparative Example 4 Powder of 150 mesh or less of 'f3a3B2N4 and T,
i, a powder of 150 meters or less of BN2 in a molar ratio of 1
2.5 g of the mixed catalyst and 8.5 g of hexagonal boron nitride were mixed in a ratio of 1:1. OI was uniformly mixed in a nitrogen atmosphere, and cubic boron nitride was produced in the same manner as in Example 3.

The cubic boron nitride crystal grains obtained in Example 3 and Comparative Examples 1 to 4 described above were subjected to a crush test.

When the fracture strength of the crystal grains was calculated, the results shown in Table 3 were obtained. This crushing test 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 1-lower cylinder made of WC-Co and had a diameter of 10 mm, and the -L cylinder was lowered by driving a DC motor. Then, the position where the first cylinder contacts the sample grains on the lower cylinder is electrically detected,
The corresponding distance between the surfaces of the upper and lower cylinders was determined and this was determined as 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 equation (1) σ
l = W/ (0,32A)...
...The fracture strength σt of 9 grains was determined according to (1). However, in reality, the above-mentioned test was conducted on 50 samples each, the average value of D and the average value of W were determined, and the average breaking strength was calculated from equation (1). The formula (1) is clarified by Hiroyuki Yoshikawa, for example, in "RIKEN Report Vol. 39, Nα6" (published in 1960), page 310. Table 3 also shows the reaction yields in Example 3 and each comparative example.

From Table 3 Table 3, the new quaternary compound LiBa synthesized in advance
It is clear that in Example 3 using BNx as a catalyst, the fracture strength was considerably improved and the reaction yield was also improved compared to each comparative example using a known catalyst material. be. In particular, in Comparative Example 4, Ba3B2N was
, and a catalyst containing Li3BN2, but in this case, the strength was not improved as in Example 3, in which pre-synthesized LiBaBN2 was used, and for this reason, in order to improve the strength, It was confirmed that it is necessary to use the quaternary compound LiBaBN2 synthesized in advance.

Further, Fig. 2 shows an enlarged microscopic photograph of the cubic boron nitride crystal grains obtained in Example 3, and Fig. 3 shows an enlarged microscopic photograph of the cubic boron nitride crystal grains obtained in Comparative Example 2. show. The cubic boron nitride crystal grains obtained in other comparative examples were also almost the same as the photograph shown in FIG.

Comparing these photographs, it can be seen that the cubic boron nitride crystal grains obtained in Example 3 of the present invention have a nearly spherical shape as a whole, and have fewer fine irregularities on the surface, and therefore have a shape suitable for abrasive grains. It is clear that it has

Example 4 The reaction product obtained according to Example 2 above, ie L13N in a molar ratio of sample numbers 2 to 50 in Table 2.

Ba3N2. Composite nitride (1-
r B a B N2 and excess raw material) was used as a catalyst, and this was mixed with hexagonal boron nitride under the same conditions as in Example 3.
Cubic boron nitride was synthesized by heating under pressure, and the fracture strength of crystal grains was determined in the same manner as described above. The results are shown in Table 4 together with the breaking strength in Example 3.

Table 4 From Table 4, it can be seen that the raw material (L
i3N, Ba3N2. BN) blending amount is LiBaB
The chemical equivalent is slightly different from that required for N2 synthesis (1 to 1
．． 4:1 to 1.4:1), in other words, as a catalyst L + Ba
It is clear that almost the same strength improvement effect as in Example 3 can be obtained even when a composite nitride containing an excess component in addition to BN2 is used.

As described above, the novel boron nitride-based quaternary compound (I) i Ba B N2 ) of the present invention is useful as a catalyst for the synthesis of cubic boron nitride, and this boron nitride-based quaternary compound can also be used as a catalyst. By synthesizing cubic boron nitride, we have created cubic boron nitride, which is suitable for grinding abrasive grains and has much higher crystal grain strength and better shape than when using known catalyst materials under the same conditions. Obtainable.

[Brief explanation of the drawing]

Fig. 1 is a thin sectional view showing an example of a reaction vessel used in producing cubic boron nitride using the novel compound of this invention as a catalyst, and Fig. 2 is a practical example 3v of the invention of (-). (
Microscope of boron nitride crystal grains obtained by ゛yo≦),
Magnified human photograph j'i-(i 0 (1x), 2f93 figure t', comparison j+113 f. PersonV Hai;(10(1
3) Applicant: Showa Electric Co., Ltd. Attorney 1 Sei Kikuchi - Figure 1

Claims (1)

[Claims] (11) A novel quaternary boron nitride compound whose molecular formula is L+BaBN2. (2) Mix powders of L13N, Ba3N2, and BN, and heat the mixture in an inert gas atmosphere for 800 min. A method for producing LiBaBN2, which is characterized by reacting and melting it while maintaining it at a high temperature of ℃ or higher, and then cooling and solidifying it. (3) Li3N, 13a3N2, and BN (
7) Mixing ratio in molar ratio (1-1.4): (1-1.4)
LiBaBN2 according to claim 2 set forth in claim 23
manufacturing method. (4) A method for producing LiBaBN2, which comprises mixing Li5N or Li, Ba3B2N4, and BN, holding the mixture at a high temperature of 800° C. or higher in an inert atmosphere, reacting and melting it, and then cooling and solidifying it. (5) Mix Li3BN2, Ba3N2 or Ba, and BN, and heat this in an inert gas atmosphere for 80°C.
A method for producing LiBaBN2, which is characterized in that it is maintained at a high temperature of 0° C. or higher to react and melt, and then cooled and solidified. (6) Mix Li3BN2 and Ba3B2N4,
A method for producing LiBa B N2, which comprises reacting and melting by holding at a high temperature of 800° C. or higher in an inert atmosphere, followed by cooling and solidifying. (For each element Li, which accounts for the proportion of raw materials in the mixture,
Ba% B, N atomic ratio (1 to 1.4): (
1:1.4):1:2 The method for manufacturing LiBaBN2 according to claims 2 to 6. (8) When synthesizing cubic boron nitride by maintaining hexagonal boron nitride and a catalyst in a high temperature and high pressure region where cubic boron nitride is thermodynamically stable, the catalyst A method for producing cubic boron nitride, characterized in that LiBaBN2 is used as the material. (9) The cubic boron nitride according to claim 8, wherein 5 to 50 parts by weight of L+ Ba B N2 as a catalyst is blended with 100 parts by weight of hexagonal boron nitride and maintained in the high temperature and high pressure region. Production method.