JPH0380535B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a diamond synthesis method, and more particularly to a diamond synthesis method that uses diamond seeds and measures their growth.

It has been known for a long time that diamond can be synthesized from non-diamond carbon (hereinafter referred to as carbon) and solvent metals under ultra-high pressure and high temperature. Are known.

Diamond seeds can be mixed as they are, or diamonds can be coated with a solvent metal in advance (Japanese Patent Publication No. 49-4630).

Synthetic diamonds are mostly used as abrasive grains, but in order to improve their performance as abrasive grains, the outer shape of the diamond is not flat, so-called euhedral properties, and the grains must have crystal defects such as air bubbles. It is required that the diamond be of high quality, with a small number of diamonds, and be of high purity.

The present invention aims to provide a diamond that meets these requirements.

In the synthetic growth method using diamond seeds, it is said that in order to obtain high quality diamonds, it is desirable to avoid direct contact between the diamond seeds and carbon. Diamond grows when carbon, which has been dissolved in a solvent metal, precipitates, but if the diamond seed and carbon are in direct contact, carbon impurities may invade the diamond, resulting in poor growth. Crystal growth is not carried out.

In this sense, the method described above of coating diamond seeds with a solvent metal is effective. However, the use of solvent metals dissolves the diamond seeds at high temperatures. Diamond synthesis operations usually involve first increasing the pressure and then increasing the temperature, as shown by the dotted line in Figure 1. In order to obtain high quality diamonds, the synthesis conditions should be as close to 1 as possible to the phase equilibrium line 3.
is said to be desirable. This means growing under mild conditions. Points that are far from the equilibrium line, such as point 2 in the diagram, are not desirable.

When a diamond seed is coated with a solvent metal and synthesized as shown in Figure 1, the surface of the diamond first dissolves, and then the coated metal reaches a predetermined carbon concentration due to the dissolution of carbon other than the diamond. When depositing on diamond, the precipitation rate is fast and it is difficult to obtain crystals of sufficiently high quality. However, when the euhedral property of the seed crystal is poor, the solvent metal preferentially dissolves the corners of the seed grain, improving the euhedral property of the seed. The present invention does not require such dissolution, ie it is particularly suitable where relatively well-shaped diamond granules are used in the seeds.

In the present invention, the non-solvent metals include Cu, Ag,
Au, Sn, Zn, Pb, etc. are used. In addition to known electrolytic and non-electrolytic coating methods, known material coating methods include vapor deposition, thermal decomposition, mechanical coating, and the like.

Diamond seeds with a diameter of 30 μm or more are generally suitable.

This diamond seed is coated with the above-mentioned metal, and the thickness thereof is suitably 1 to 100 μm.

The action of the non-solvent metal in the present invention is to prevent the dissolution of diamond in the early stage of diamond synthesis, especially near point 2 in Figure 1, to lower the carbon concentration in the metal around the seed, and to prevent the non-solvent metal from dissolving the diamond during diamond precipitation. is alloyed with the solvent metal, and carbon is dissolved in it, but at this time, since the inside of the synthesis system is near point 1 in FIG. 1, the precipitation of this dissolved carbon is gradual. It is believed that this mechanism of action produces diamonds of high quality.

Solvent metals include Fe, Co, and Co, which are well known in diamond synthesis.
Elements of group 8 of the periodic table such as Ni, Cr, Ta, etc., and alloys thereof are used.

The mixing ratio of each substance is based on 100 parts by weight of solvent metal.
Suitable amounts are 30 to 500 parts by weight of carbon and 5 parts by weight or less of diamond seeds (including the coated part).

Synthesis methods include simply mixing powders of these substances, and processing carbon and solvent metal into thin plates and laminating them alternately. Diamond seeds are interposed between these plates. Seeds should be distributed as evenly as possible, preferably in regular order. For example, there is a method in which small holes are provided at equal intervals in a carbon plate or a solvent metal plate, and seeds are sealed in the holes. Of course, they may be fixed regularly on the board.

Example Diamond seeds with particles of 105 to 125 μm were plated with Cu using an electroless method. The thickness of the plating layer is about 10 μm.

A 0.25 mm thick disk of 30Ni-70Fe was used as the solvent metal, and a 0.2 mm diameter disk was used at 0.6 mm intervals (center to center).
A small hole was provided. The above seeds were placed in this small hole.

A graphite disk (thickness 1.6 mm) was used as the carbon.
A large number of these metal plates and carbon plates were alternately stacked and loaded into an ultra-high pressure device to perform diamond synthesis. As shown in Figure 1, the pressure and temperature were increased, and the final conditions were estimated to be a temperature of 1,450°C and a pressure of 53,000 atmospheres.
Holding time is approximately 30 minutes.

Most of the diamonds obtained were grown seeds, and the size was 400 to 500 μm.
It had a regular hexahedral to octahedral structure, had no internal crystal defects, and was highly pure.

[Brief explanation of drawings]

FIG. 1 is a graph showing the phase equilibrium line of diamond and carbon and the diamond synthesis operation. 3...Equilibrium line.

Claims (1)

[Claims] 1. A method for synthesizing diamond from non-diamond carbon, solvent metal and diamond seeds under high temperature and pressure, characterized by using a diamond seed coated with a non-solvent metal.