JPH0360766B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a diamond synthesis method using diamond seeds, and its purpose is to synthesize high-purity diamond with good euhedral property and few crystal defects. In diamond synthesis, the method of using diamond seed crystals to enlarge crystal particles has been known for a long time. In this case, a method is also known in which a solvent (catalyst) metal for diamond synthesis is plated around the seed, and this and carbon are used to synthesize diamond to grow seed crystals (Japanese Patent Publication No. 49-4630). . When diamond is used as an abrasive grain, it is important that the outer shape of the diamond is not uniform, that is, it is excellent in so-called euhedral property, and that there are few crystal defects such as pores inside the grain. Impurities have a large influence on this euhedorality and crystal defects. As a result of various studies on these points, the inventor of the present invention found that although the method of plating seeds with a solvent metal as described above is an effective method, mere electrolytic or electroless plating, as proposed in the past, does not result in high-quality diamonds. . It was found that most of the causes were due to impurities that were introduced during plating. Oxygen and nitrogen are particularly influential impurities. Therefore, when diamond seeds are coated with a solvent metal and used, the present invention reduces the oxygen content in the metal.
The nitrogen content is 100 PPM or less, preferably 50 PPM or less, and the nitrogen content is 100 PPM or less, preferably 50 PPM or less. Coated diamond seeds only need to contain these impurities within the above range when used.
In the coating method itself, a method that prevents impurities from entering may be adopted, or impurities may be removed after coating. In addition to chemical plating, this coating
Also includes physical vapor deposition and coating. Below, diamond seeds are coated with solvent metal,
Various methods for bringing the oxygen and nitrogen contents of the metal into the above range will be explained. The first method is to plate a solvent metal using a chemical method such as solid-phase decomposition or reduction of a compound, and then heat treat it in a reducing atmosphere to remove impurities. A method of coating a diamond seed with a target metal by thermal decomposition of a compound is, for example, coating a diamond seed with an organic acid salt such as acetate of a solvent metal, heating it to decompose the compound, and removing the remaining metal. coat the diamond with As is well known, reduction plating methods include electroless plating and electrolytic plating. The present invention may be applied to any of these. Generally, the metal plated in this manner often has an oxygen or nitrogen content exceeding the above range. For example, in the thermal decomposition method, diamond grains are mixed with an aqueous solution of chloroplatinic acid, nickel acetate, etc., the water is evaporated to dryness, and the nickel-coated diamond grains, which do not contain oxygen or nitrogen, are treated at 500 to 600°C in a hydrogen stream. can be obtained. In the electrolytic method, a small amount of nickel or the like is first coated electrolessly, and then a metal is coated on top of this by electrolysis of an aqueous solution of a metal salt. In the electroless method, diamond grains are immersed in an aqueous solution of nickel sulfate, etc., and then reduced with sodium hypophosphite, hydrazine, etc., and coated with nickel. In order to reduce this oxygen and nitrogen, heat treatment is performed in a reducing atmosphere such as a hydrogen atmosphere. Heating temperature is 400
A range of ~900°C is suitable. After this heating, it is desirable to further heat under reduced pressure to remove hydrogen and the like. The second coating method is to adopt a method that prevents impurities from entering the coating method itself. This includes chemical vapor deposition (CVD) from the gas phase, vacuum evaporation,
A physical vapor deposition method such as an ion plating method can be used. For example, the CVD method uses NiCl ₂ ,
Compounds such as FeCl ₂ are heated in a hydrogen atmosphere to reduce them and at the same time attach Ni, etc. to diamond particles. At this time, in order to coat the periphery of the diamond particles, the diamond particles are stirred. In the vacuum evaporation method, diamond particles are coated with metal using a vacuum evaporation device while stirring. Other well-known ion plating methods, sputtering methods, thermal spraying methods, etc. can be used. According to these methods, a highly pure metal coating can be obtained, so subsequent reduction treatment etc. are not necessary in many cases, but if there are many impurities, post-treatment may be performed. A third method of solvent metal coating is mechanical compression of metal powder onto the diamond seeds. This method involves making the metal powder finer than the diamond seed, mixing the two, milling them together, and applying the metal powder to the diamond so as to press it into place. In this method, oxygen and nitrogen easily enter the apparatus. Therefore, post-processing is performed in the same manner as in the first method. By using metal-coated diamond seeds with reduced oxygen and nitrogen contents, high-quality diamonds can be obtained. As the solvent metal, Group 8 metals such as Fe, Co, and Ni, metals such as Cr, Mo, and Ta, and alloys thereof are used. Generally speaking, the size of diamond seeds is
A material of 30 μm or more is used, and there is no upper limit. The thickness of the coating metal is preferably about 1 μm to 100 μm. Examples Example 1 (1) After thoroughly cleaning the surface of 100 g of #120/140 diamond grains with an organic solvent, acid, or alkali, sensitize it with an aqueous solution of stannous chloride, hydrochloric acid, and palladium chloride. Activated in aqueous solution. Ordinary electroless nickel coat bath (nickel sulfate)
0.1M, sodium hypophosphite 0.2M, sodium acetate 0.3M, sodium succinate 0.02M, sodium citrate 0.02M) 100CT of the above diamond particles were placed in 800ml at a temperature of 80°C, and stirred to the extent that they did not settle. Meanwhile, the diamond surface was coated with nickel to a thickness of approximately 1 μm. Next, a thick coating of nickel (approximately 30 μm) was applied using an electrolytic cell rotation type electrolyzer. Next, in order to remove impurities such as hydroxides that were simultaneously electrodeposited during electrolysis, the electrodes were heated in an electric furnace for 700°C in a hydrogen stream.
Reduction treatment was carried out at ℃. The oxygen and nitrogen contents in the coated nickel were 70 ppm and 50 ppm, respectively. Moreover, the crystals were pale yellow. 2 parts by weight of the nickel-coated diamond thus obtained, 100 parts by weight of graphite plate, 30Ni
100 parts by weight of -70Fe alloy plates were stacked and placed in an ultra-high pressure device, and diamond seed crystals were grown at 58,000 atm and 1,450°C. The obtained diamond is approximately 400 μm in diameter and has a shape of 6 to 6.
It had an octahedral shape and was a good crystal with few crystal defects. Comparative Example 1 No cleaning treatment for comparison, i.e. Example 1
If reduction treatment is not performed in a hydrogen stream, oxygen,
The nitrogen content was 300 ppm and 80 ppm, respectively.
Diamond synthesis was carried out in the same manner as in Example 1 without performing the reduction treatment. The diamond obtained here was approximately 400 μm in size and had a hexagonal to octahedral shape, but it had many crystal defects, with many air bubbles and carbides trapped inside the crystal, and it was a dark yellow crystal with many defects. . Example 2 50 g of #100/120 diamond grains were vapor-phase plated with nickel to a thickness of 50 μm. The method is Ni
(Co) ₄ was plated at 200℃ in an Ar flow, and then treated for 1 hour at 700℃ in a hydrogen flow, and finally
Degas treatment was performed at 600° C. for 1 hour in a vacuum of 10 ⁻⁷ Torr.
The oxygen and nitrogen contents in the coated nickel were 20 ppm and 30 ppm, respectively. Using this coated diamond, a diamond crystal was obtained in the same manner as in Example 1. Comparative Example 2 In Example 1, the hydrogen flow rate was halved. As a result, the oxygen and nitrogen contents were 140 and 100 ppm, respectively. Comparative Example 3 100 g of #120/140 diamond grains were coated with cobalt to a thickness of 20 μm in a vapor phase. The method is CoCl ₃
The experiments were carried out at 400° C. in a H ₂ stream. The oxygen and nitrogen contents in the coated cobalt are respectively
They were 60ppm and 180ppm. The color of the diamond crystal is
It was dark yellow to pale green. After baking for 1 hour at 1100℃ in H ₂ + N ₂ atmosphere,
A summary of the single grain crushing strength ratio with that before treatment is shown.

[Table] This result shows that it is effective to reduce the oxygen and nitrogen contents in the coated metal of the present invention to 100 ppm or less, respectively.

Claims (1)

[Claims] 1. In a diamond synthesis method using a solvent metal, carbon, and a diamond seed, the diamond seed is coated with a solvent metal, and the coated metal has an oxygen content of 100 PPM or less and a nitrogen content of 100 PPM or less. A diamond synthesis method characterized by: 2 Diamond seeds are plated with solvent metal by solid-phase decomposition, electroless or electrolytic, and heat treated in a reducing atmosphere to reduce the oxygen content of the plated metal to 100 PPM or less.
The diamond synthesis method according to claim 1, characterized in that the nitrogen content is 100 PPM or less. 3. The diamond according to claim 1, wherein diamond seeds are plated with a solvent metal by chemical vapor deposition or physical vapor deposition, and the plated metal has an oxygen content of 50 PPM or less and a nitrogen content of 50 PPM or less. Synthesis method. 4 Milling a mixed powder of diamond seeds and solvent metal powder, mechanically applying the solvent metal powder to the surface of the diamond particles, and heat-treating in a reducing atmosphere to reduce the oxygen content of the coated metal to 100 PPM or less and the nitrogen content to 100 PPM. A diamond synthesis method according to claim 1, characterized in that: