JPS6225602B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for synthesizing cubic boron titanide (hereinafter referred to as CBN) using hexagonal boron titanide (hereinafter referred to as HBN) as a starting material under high temperature and high pressure.

As is well known, CBN is a substance with hardness comparable to diamond and is used in abrasives, abrasives, cutting materials, etc. Especially for grinding special steel, etc.
CBN is considered important because it is stable even at high temperatures during grinding.

It has been known for a long time that CBN is synthesized from HBN under high temperature and pressure, and the phase equilibrium relationship between the two has also been elucidated. Many catalysts have been proposed for synthesis.

For example, catalysts include alkali metals, alkaline earth metals, their titanides, and Sn, Sb, and Pb. However, CBN synthesized using these catalysts is often fine, and the grains are bulky and bulky, making them undesirable for use as abrasives, etc.

It is said that grains used in abrasives and the like are preferably polygonal, self-shaped (hereinafter referred to as Brodsky-shaped in the present invention) grains.

In addition to the above catalysts, catalysts using Al or a mixture of AlN and Si have also been proposed. According to this method, relatively blocky CBN can be produced, but the drawbacks are that the amount produced is small despite the high synthesis pressure, and the particles are small.

Furthermore, according to a research presentation at the High Pressure Symposium (1978, October 24, jointly sponsored by the Chemical Society of Japan and others), calcium boron oxide (Ca ₃ B ₂ N ₄ ) was mentioned as a catalyst for CBN synthesis. According to research conducted by the present inventor using this catalyst, it has been found that this catalyst is effective in obtaining Brodsky grains. However, this requires strictly controlled pressure-temperature conditions. In other words, it must be synthesized within a narrow range of CBN stability near the phase equilibrium line of HBN-CBN, and if it deviates from this range, the amount produced will not decrease, but there will be many fine particles, and moreover, those with a Brodsky shape. is not obtained. In high-temperature, high-pressure equipment, it is difficult to control the temperature and pressure conditions within a very narrow range, and it is not always possible to operate stably, that is, with good reproducibility. Needless to say, in operations using high-temperature, high-pressure equipment such as CBN synthesis, it is desirable for the control conditions to be gentle in terms of operation.

Based on the above background, the present invention aims to obtain tough CBN using Brodsky and have a large particle strength, and further to control the CBN under relatively gentle control conditions, that is, over a relatively wide range of temperature and pressure. The aim is to develop a catalyst that can be synthesized.

The present invention is characterized in that a mixture of calcium boron nitride and at least one of barium nitride, barium boron nitride, strontium nitride, and strontium boron nitride is used as a CBN synthesis catalyst.

Calcium boron nitride is as described above, and its chemical formula is mainly expressed as Ca ₃ B ₂ N ₄ , but it is not necessarily fixed exactly to this formula, and may be based on crystal defects etc. Some have slightly different compositions. In the present invention, these are included as calcium boron oxide, and hereinafter they are typically expressed as Ca ₃ B ₂ N ₄ .

In general, alkaline earth metal nitrides are known as CBN synthesis catalysts, and barium nitride (Ba ₃ N ₂ ) and strontium nitride (Sr ₃ N ₂ ) also fall into this category; Compared to chemical compounds, there are many unknowns about its mechanism of action.

In CBN synthesis, it is thought that first a CBN nucleus is generated, and then the nucleus grows. Generation of an appropriate number of nuclei and their growth
It is an important factor in increasing the yield of CBN and increasing the size of its particles. In addition, when the particles have grown sufficiently, the shape of the particles becomes Brodsky. Catalysts are thought to have a major effect on the generation and growth of these nuclei.

According to the research conducted by the present inventors, Ca ₃ B ₂ N ₄ has a strong growth effect within a narrow range of temperature and pressure, but outside of this range, more nuclei are generated, growth is insufficient, and no gain is obtained. The resulting CBN particles are fine and non-Brodsky.

Ba ₃ N ₂ and Sr ₃ N ₂ alone or in combination have a strong nucleation effect, so the resulting CBN particles are often fine and non-Brodsky.

However, when a catalyst containing Ca ₃ B ₂ N ₄ mixed with Ba ₃ N ₂ or Sr ₃ N ₂ is used, the temperature-pressure range in which Brodsky CBN particles can be obtained expands, and HBN-CBN From the vicinity of the equilibrium line
Brodsky even if it deviates considerably within the CBN stability region.
CBN is obtained. And the yield of CBN is also low. Therefore, Brodsky CBN can be easily obtained with good reproducibility. Furthermore, while Ca ₃ B ₂ N ₄ alone tends to cause crystal defects inside the CBN particles, the mixed catalyst described above does not have such defects.

Furthermore, if this mixed catalyst is used, the temperature and pressure during synthesis can be lowered compared to when Ca ₃ B ₂ N ₄ is used alone. This is thought to be because in the mixed catalyst, they form a solid solution, lowering the melting point. For example, in the case of 55Kb, the minimum for Ca ₃ B ₂ N ₄ alone is
While the temperature must be around 1450°C, the mixed catalyst of the present invention has a low temperature limit of 1350°C, which is considerably lower.

As a result of further research on barium boron nitride (Ba ₃ B ₂ N ₄ ) and strontium boron nitride (Sr ₃ B ₂ N ₄ ), the present inventor found that these
When mixed with Ca ₃ B ₂ N ₄ , Ba ₃ N ₂ is added to Ca ₃ B ₂ N ₄ ,
It was found that the result was almost the same as when Sr ₃ N ₂ was mixed. Ba ₃ N ₂ and Sr ₃ N ₂ react with the raw material HBN in the CBN synthesis process, resulting in Ba ₃ B ₂ N ₄ and
It is thought that Sr ₃ B ₂ N ₄ is generated. The results show that there is no difference in the mixed system with Ca ₃ B ₂ N ₄ even if Ba ₃ B 2 N ₄ and Sr ₃ B ₂ N ₄ are used as starting materials, or they are generated during the _synthesis . be.

Ca ₃ B ₂ N ₄ is prepared in advance by the method described below and mixed with the raw material HBN.

In the mixed catalyst of the present invention, the mixing ratio is
For 100 parts by weight of Ca ₃ B ₂ N ₄ , 10 to 300 parts by weight of Ba ₃ N ₂ etc. is suitable, preferably 30 to 200 parts by weight.
Two or more types of Ba ₃ N ₂ and the like to be mixed with Ca ₃ B ₂ N ₄ may be used in combination. When used together, the total amount is within the above range.

To synthesize CBN using these mixed catalysts, HBN powder and catalyst powder are mixed, or they are alternately stacked and subjected to high temperature and pressure. Alternatively, as shown in FIG. 2, the catalyst can be filled in an HBN container. When mixed, use 10 to 10 parts of mixed catalyst per 100 parts by weight of HBN.
50 parts by weight is suitable. The appropriate range of temperature and pressure is 1350
The stable range of CBN is above ℃ and 40 Kb, but in practical terms it is 1350 ℃ to 1800 ℃ and 40 to 70 Kb.

Next, one example of the method for producing the catalyst used in the present invention will be described.

Ca ₃ B ₂ N ₄ can be obtained by mixing metallic calcium and HBN at a molar ratio of 3:2 and heating the mixture to 950 to 1050° C. in a nitrogen or ammonia stream. It can also be obtained from Ca ₃ N ₂ and HBN.

For Ba ₃ N ₂ , metal barium is placed in a molybdenum container, reacted at 450 to 800°C for 2 hours in a nitrogen atmosphere, and after cooling, taken out in a nitrogen atmosphere and pulverized.

Ba ₃ B ₂ N ₄ can be obtained by mixing and molding the Ba ₃ N ₂ powder obtained above and HBN powder at a molar ratio of 1:2 and holding it at 1000°C for about 5 hours in a nitrogen or ammonia atmosphere to form a black powder. obtained as. The handling is carried out in a chitso atmosphere.

Sr ₃ N ₂ and Sr ₃ B ₂ N ₄ can also be produced in the same manner as above.

Example 1 Ca ₃ B ₂ N ₄ and Ba ₃ N ₂ powders were mixed at a weight ratio of 2:1, and then HBN powder in an amount of about 5 times the total weight was mixed, molded into a cylinder, and Assembled as shown in Figure 1. In the figure, 1 is a graphite cylindrical heating element in which the cylindrical molded body 2 is housed. Heating is performed by supplying electricity to the heating element 3 through a current-carrying ring 3 and a current-carrying plate (molybdenum) 4. In the figure, 5 and 6 are heat insulating materials such as pyrofilite, and 7 is a pressure medium made of the same material. This assembly was loaded into an ultra-high pressure device that compresses it from above and below, and the temperature and pressure were controlled to a target of 60Kb and 1500℃, and the same conditions were maintained for 15 minutes. After a period of time, heating was stopped, and after cooling to near room temperature, the pressure was lowered. The sample was taken out, and CBN was extracted by a conventional method. As a result, 2.1 g of transparent Brodsky CBN with a size of 100 to 200 microns was obtained. (The yield based on HBN is 40%.) The crushing strength of this product is
It was larger than that of Ca ₃ B ₂ N ₄ alone.

Example 2 Ca ₃ B ₂ N ₄ and Ba ₃ B ₂ N ₄ powders were mixed at a weight ratio of 1:1, and then 5 times the weight of HBN powder was mixed, and the mixture was molded into a cylinder. CBN was synthesized in the same manner as in Example 1. 1.9g of transparent Brodsky CBN of 150-250μ was obtained.

Example 3 Ca ₃ B ₂ N ₄ powder and Sr ₃ N ₂ powder in a weight ratio of 2:1
CBN was synthesized in the same manner as in Example 1 by mixing the total amount with 5 times the weight of HBN powder and molding it into a cylinder. The obtained CBN was transparent Brodsky, the size was 130-170μ, and the amount was 2.0g.

Example 4 A container as shown at 8 in FIG. 2 was manufactured by molding HBN powder. In this container there is Ca ₃ B ₂ N ₄ powder and
A mixed molded body 9 containing Sr ₃ B ₂ N ₄ powder in a weight ratio of 1:1 was packed, and an HBN molded body 10 was further placed on top of it. This assembly was inserted into a graphite cylinder 1, and insulating materials 5 were arranged above and below. Load this into an ultra-high pressure device,
50Kb, held at 1400°C for 30 minutes. When the sample was taken out, transparent Brodsky CBN was observed near the interface between HBN and the catalyst, and the amount recovered was 0.45g.
It was hot. The amount of HBN used was 5g, and the catalyst was 0.6g.
It is g.

In addition, by using Ba ₃ N ₂ , Sr ₃ N ₂ , etc.
The same results as above were obtained when a mixture of Ca ₃ B ₂ N ₄ was used.

Comparative Example 1 CBN was synthesized in the same manner as in Example 1, except that Ca ₃ B ₂ N ₄ powder was used as a catalyst, 5 times the weight of HBN powder was mixed therein, and the temperature was 1600°C. As a result, the yield of CBN was 2.0 g, which was the same as in Example 1, but the particles were as fine as 40 to 80 microns, and the shape was not Brodsky.

Comparative Examples 2 to 5 Ba ₃ N ₂ , Ba ₃ B ₂ N ₄ , Sr ₃ N ₂ , and Sr ₃ B ₂ N ₄ were each used alone as a catalyst, and 5 times the weight of HBN powder was mixed with each of them, and the mixture was heated under temperature and pressure. CBN was synthesized in the same manner as in Example 1 except that 1600°C and 60 Kb were used. The results showed that the CBN particles obtained were much finer in the range of 20 to 100μ than those of the examples, and the shape was not Brodsky.

According to the method of the present invention, the synthesis control conditions are relaxed, and the resulting CBN is transparent Brodsky and tough. Therefore, this CBN particle is extremely excellent as a grinding, polishing, and cutting material.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views showing an example of an assembled state of a sample to be loaded into an ultra-high pressure apparatus. 1...Graphite cylindrical heating element, 2...Mixture of raw material and catalyst, 3...Electrification ring, 4...Electrification plate, 5, 6, 7
...Pyrophyllite, 8,10...Hexagonal boron titanide, 9...Catalyst.

Claims (1)

[Claims] 1. A method for synthesizing cubic boron titanide using hexagonal boron titanide as a raw material under high temperature and high pressure,
A method characterized by using as a catalyst a mixture of calcium boron nitride and at least one selected from barium nitride, barium boron nitride, strontium nitride, and strontium boron nitride. 2. Claim 1 in which the high temperature and high pressure are in the stability range of cubic boron titanide of 1350°C or higher and 40 Kb or higher
The method described in section. 3 For 100 parts by weight of calcium boron oxide,
3. The method according to claim 1 or 2, wherein at least one of barium titide, barium boron titide, strontium nitride, and strontium boron titide is contained in an amount of 30 to 200 parts by weight.