JPS6253218B2 - - 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. CBN is used as a grinding and abrasive material as it has a hardness equivalent to that of diamond, and is said to surpass diamond in grinding special steel. CBN has been synthesized for quite some time, and many catalysts have been proposed since then.
The important things in CBN synthesis are high yield and as large grains as possible, and what cannot be overlooked is the shape of the grains. As CBN grinding abrasive grains, it is undesirable to use grains that look like skeletons with no flesh, but grains with a well-formed polygonal shape (referred to here as Brodsky grains) with high particle strength (tough) have good performance. In addition to the synthesis pressure and temperature conditions, the type of catalyst has a large influence on the yield, shape, etc. Catalysts that have been proposed so far include alkali metals, alkaline earth metals, their silicides, aluminum, and silicon. but. The CBN particles obtained using these catalysts are mainly black in color, not Brodsky, have low particle strength, and are often small. According to a research presentation at the High Pressure Symposium (October 24, 1978, jointly sponsored by the Chemical Society of Japan and others), calcium boron titanide (Ca ₃ B ₂ N ₄ ) was mentioned as a catalyst for CBN synthesis. According to the research of the present inventor, this catalyst
If the temperature-pressure conditions for CBN synthesis are maintained in the CBN stability region near the HBN-CBN phase equilibrium line, Brodsky
The effect of CBN generation is recognized. However, in industrial production, it is often difficult to constantly maintain high temperature and high pressure conditions near the equilibrium line, which poses a problem in terms of reproducibility. By adding various additives to the Ca ₃ B ₂ N ₄ catalyst, the present inventor has developed Brodsky and high-strength catalysts.
The present invention was achieved by discovering that CBN is produced under relatively mild synthesis conditions. That is, the present invention synthesizes CBN under high temperature and high pressure using HBN as a raw material, and uses Ca ₃ B ₂ N ₄ as a catalyst, phosphorus (P), boron phosphide (BP), phosphorus titanide (P ₃ N ₅ ), Silicon (Si), silicon titanide (Si ₃ N ₄ ),
Aluminum (Al), aluminum titanium (AlN), aluminum boride (AlB ₁₂ ), sulfur (S), calcium sulfide (CaS), boron sulfide (B ₂ S ₃ ), barium titanium sulfide (BaTiS ₃ ), zircon sulfide A substance selected from strontium (SrZrS ₃ ) and ammonium borate ((NH ₄ ) ₃ BO ₃ ) by weight.
It is characterized by the use of 0.1 to 5% additive. These additives may be a mixture of two or more. In that case, the total amount is 0.1 to 5%. Calcium boron oxide is typically Ca ₃ B ₂ N ₄
However, according to the research of the present inventor, there are some compositions with slight deviations due to crystal defects, etc., but there is no difference in the action of these catalysts, so the following is a representative one. Expressed as Ca ₃ B ₂ N ₄ . Phosphorus, etc. added to Ca ₃ B ₂ N ₄ was selected as a result of experiments with many substances with the aim of expanding the CBN synthesis conditions without impairing the Brodsky CBN production effect of Ca ₃ B ₂ N ₄ . It is what was done. In addition to being effective for the above purpose, this additive also has the effect of eliminating internal defects in CBN particles and increasing the strength of the particles themselves. Furthermore, by adding additives, the synthesis temperature shifts to a slightly lower temperature compared to Ca ₃ B ₂ N ₄ alone. When a catalyst containing these additives is added to Ca ₃ B ₂ N _4, the CBN obtained is reddish-orange, transparent, and strong, but when Ca ₃ B ₂ N ₄ is used alone, the CBN is white-yellow to yellow in color. Many have internal defects. The reason why the temperature and pressure range of Brodsky CBN is expanded by adding the above-mentioned additives compared to the Ca ₃ B ₂ N ₄ catalyst is considered to be as follows. In the production of CBN, it is desirable that the generation and growth of CBN nuclei proceed in a balanced manner, whereby particles with Brodsky growth can be obtained. If too many nuclei are generated, the particles will look like a collection of fine particles, and the growth of individual particles will be small. According to the research conducted by the present inventors, a Ca ₃ B ₂ N ₄ single catalyst attains the above-mentioned balanced state in a narrow temperature and pressure range, but when it deviates from this, it becomes an aggregate of fine particles.
When the above additives are added to Ca ₃ B ₂ N ₄ , the solid-liquid coexistence region expands due to the formation of eutectic compounds, etc.
It is thought that the generation and growth area of CBN nuclei will expand. Furthermore, the reason why there are fewer defects inside the CBN particles is thought to be due to the fact that when the growth rate is appropriately controlled, there are very few inclusions or unfilled inclusions that cause crystal defects within the particles. When the additive is ammonium borate, in addition to the above effects, since this compound is easily melted, it also has the effect of equalizing the pressure within the sample under pressure. To synthesize CBN using a catalyst containing Ca ₃ B ₂ N ₄ and these additives, either Ca ₃ B ₂ N ₄ and the additives are powdered and mixed well, and the raw material HBN powder is mixed with this. Alternatively, the catalyst and HBN may be stacked alternately and loaded into an ultra-high pressure device. In these cases, 10 to 50 parts by weight of catalyst is suitable for 100 parts by weight of HBN. Further, as shown in FIG. 2, it is also possible to constitute a catalyst with HBN. The lower limit of the synthesis pressure and temperature may be slightly lower than that of Ca ₃ B ₂ N ₄ alone, approximately 45 to 70 Kb and 1400 to 1800 °C.
It is. Ca ₃ B ₂ N ₄ used in the present invention is, for example, commercially available
Ca ₃ B ₂ N ₄ and HBN were mixed in a molar ratio of 1:2, placed in a molybdenum crucible, and heated at 1000°C in a nitrogen atmosphere.
The mixture may be reacted for 5 hours, cooled, and then crushed in the same atmosphere. Examples 1 to 16 Ca ₃ B ₂ N ₄ powder was mixed with 3% P (red phosphorus) powder by weight, and 5 times the weight of this mixture was added.
HBN powder was mixed, molded into a cylinder, and assembled as shown in Figure 1. This was loaded into a normal up-and-down ultra-high pressure device and held for 15 minutes at a target temperature of 60 Kb and 1500°C. After holding, the sample was cooled to near room temperature, the pressure was lowered, and the sample was taken out. When CBN particles were extracted from the sample according to a conventional method, 2.5g of 100-200μ red-orange transparent Brodsky CBN particles with high strength were obtained.
Obtained. (Yield 30% based on HBN) Examples using other additives are also summarized in Table 1 below. In Fig. 1, 1 is a graphite cylindrical heating element, and 2 is a graphite cylindrical heating element.
A mixed molded body of HBN and catalyst, 3 is a current-carrying ring, 4 is a current-carrying plate, 5 and 6 are insulating materials such as pyrofluorite, 7
is a pressure medium such as pyrofluorite.

[Table] In the table, the amount of additive is the weight % of the additive in the total amount of Ca ₃ B ₂ N ₄ and the additive, and the catalyst content is the weight % of the catalyst in the total amount of HBN and the catalyst. Yield is the amount of CBN expressed as a percentage of the raw material HBN.
Although there are some fluctuations in temperature and pressure, the central values are shown. Note that No. 17 is an example of a catalyst containing Ca ₃ B ₂ N ₄ alone. Example 17 A catalyst 9 consisting of Ca ₃ B ₂ N ₄ mixed with 2% P was filled into an HBN container 8 as shown in FIG. 1
The sample was assembled by inserting the sample into the sample and placing the insulating material 5 on the top and bottom. Put this assembled sample into an ultra-high pressure device,
65Kb, held at 1700°C for 30 minutes. When the sample was taken out after cooling and pressure reduction, transparent blocky CBN was formed at the interface between the catalyst and HBN, and the particle size was as large as 500 μm, and the total amount was 0.6 g.
Note that the amount of catalyst used was 0.5 g.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views showing the assembled state of a sample to be loaded into an ultra-high pressure device. 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. In a method for synthesizing cubic boron titanide using hexagonal boron titanide as a raw material under high temperature and high pressure,
Calcium boron titanide as a catalyst, phosphorus, boron phosphide, phosphorus titanide, silicon, silicon titanide,
It is characterized by using a substance to which 0.1 to 5% by weight of a substance selected from aluminum, aluminum titride, aluminum boride, sulfur, calcium sulfide, boron sulfide, barium titanium sulfide, strontium zirconium sulfide, and ammonium borate is added. how to.