JPS6024044B2 - diamond manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for synthesizing diamond by subjecting carbon to high temperature and high pressure conditions in the presence of a solvent metal that dissolves the carbon, in particular by using a metal carbide as an accelerator for diamond crystal formation. This invention relates to a method for synthesizing diamond with good crystallinity under lower temperature and pressure conditions than conventional methods.

One method for producing diamond crystals is to produce diamond crystals from a solvent metal in which non-diamond carbon such as graphite is dissolved, as known from Japanese Patent Publications No. 37-4407 and 37-83. There is a method of precipitation under pressure and temperature conditions.

(In this case, it is said that the nucleus for diamond crystal formation is nickel carbide, for example when nickel is used as the solvent metal. Furthermore, it is known that crystal nuclei are generally likely to spontaneously grow during synthesis. ) The range of temperature and pressure conditions in which diamond can be synthesized without using such seeds is, for example, when cobalt is used as the solvent metal, on the higher pressure and higher temperature side than curve A-B in the carbon phase diagram shown in Figure 1. It is defined as a part of This is the region where diamond is thermodynamically stable and approximately 5°C above the eutectic temperature of carbon and solvent metal, so the lowest pressure temperature value in this curve is determined by the type of solvent metal used. be done. Diamonds can also be obtained by growing diamond granules added as seeds.

This method is described in, for example, Japanese Patent Publication No. 38-511 and U.S. Patent No. 3,423,177, but the pressure and temperature condition range for these growth reactions is also on the high pressure and high temperature side of the curve A-B. include. The area surrounded by the eutectic temperature curve A-B and the Benman-Simon curve is a region surrounded by the conventional diamond manufacturing method because the above-mentioned known method has an extremely low crystal growth rate and only poor crystals can be obtained. It was not considered to be a practical area. The present invention induces the formation of diamond crystals by metal carbide grains scattered at the carbon-solvent metal interface. In the subordinate method,
As mentioned above, it has made it possible to synthesize diamond with good crystallinity in an area that has not been considered practical for diamond synthesis, and in an even lower temperature area, and its gist is as follows: When synthesizing diamond by subjecting carbon placed in contact with each other and a solvent metal consisting of iron, cobalt, nickel, or an alloy containing these under pressure and temperature conditions within the diamond stability region, first the carbon and the solvent metal are are arranged in alternating layers, grains of carbide of at least one metal selected from vanadium, chromium, manganese, niobium, tantalum, and tungsten are dotted on the interface between adjacent layers, and then such carbon and a solvent are interspersed. The present invention relates to a method for producing diamond, characterized in that reactants consisting of a metal and a metal carbide are subjected to pressure and temperature conditions within a diamond stability region.

In the present invention, metal carbides such as chromium carbide, tantalum carbide, tungsten carbide, and vanadium carbide, or metals that form stable carbides in a carbon atmosphere such as chromium, manganese, and tantalum are used as crystal formation promoting agents. .

All of these are selected so that during diamond formation, a liquid phase is produced at a temperature lower than the melting temperature of the solvent metal due to the formation of a eutectic consisting of the solvent metal and the carbide. The amount of inducer used varies depending on the size and dispersion conditions when charging the reactor, but 0.1% or less of the solvent metal by weight is sufficient, and if used in a relatively large amount, especially 1% or more, ,
Since the crystals are formed adjacent to each other, diamond with good crystallinity cannot be obtained. In the method of the present invention, for example,
When chromium carbide powder is added as an accelerator in a diamond synthesis reaction using cobalt as the solvent metal, the Co-Cr-C ternary eutectic generates a higher concentration than the case of Co-C at locations where chromium carbide, cobalt, and graphite coexist. A liquid phase is formed at an even lower temperature, and diamond formation occurs due to the action of this liquid phase.

At this time, by scattering chromium carbide in advance, the locations where the liquid phase is generated can be limited, and from this the number of diamonds to be generated can be determined. As the shape of the diamond progresses, the liquid phase containing most of the carbides is pushed out around the diamond, and the presence of this liquid phase further promotes diamond crystal growth.

In addition, diamond crystal growth on the seed crystal proceeds under conditions of temperature and pressure lower than those in which the diamond nucleus grows naturally, so the use of an inducing agent is necessary, and it is incorporated into the diamond as inclusions during crystal formation. Even in such cases, it is possible to continue diamond growth on already formed crystals. In this way, diamond formation occurs only in areas where chromium carbide is dotted in contact with cobalt, so the formed crystals do not interfere with each other, and because the reaction temperature is relatively low, the formation rate is slow, so each crystal is A diamond with uniformly developed surfaces, ie, a perfect crystal, is obtained.

Furthermore, although the diamond obtained by this method undergoes crystal growth at relatively low temperature and low pressure, the reaction proceeds consistently from nucleation to completion of the crystal, so the crystal is homogeneous and cannot be grown on a seed crystal. In this case, there are no discontinuous surfaces between the seed crystal and the growth layer, which are presently observed, and therefore a crystal with high strength can be obtained. The same effect can be obtained by using metal grains such as chromium, manganese, tantalum, etc. instead of metal carbide. This is due to the formation of carbides due to carbon diffusion during the temperature rise prior to the diamond synthesis reaction. These metals have a high ability to form carbides, the carbides are stable under pressure, and carbon diffusion proceeds quickly, so there is almost no difference in effectiveness compared to when metal carbide particles are used. . If the particle size of the suspending agent used is too large, the amount of liquid phase during diamond formation will be too large, resulting in the formation of multiple crystal nuclei at the same time, and the growth rate will be high, making it difficult to form complex shapes. It becomes a diamond and does not meet the purpose of use.

On the other hand, if the particle size of the enhancer placed in contact with the solvent metal is too small, it may diffuse into the solvent metal and disappear during temperature rise. Therefore, the raising agent used in the method of the present invention preferably has a grain size of about 10 to 100 meters. The reaction product recovered from the high-pressure apparatus after operating according to the method of the invention shows the presence of well-grown diamond crystals in contact with the unmolten solvent metal.

These crystals mainly have well-developed hexagonal octahedral crystal faces and are transparent yellow in color, indicating the formation of subordinate structures that were said to produce only poor hexahedral crystals in this region. This shows that the diamond synthesis method is different from the method used in this study. In the method of the present invention, diamond formation occurs only at the locations where the inducing agent solvent metal graphite comes into contact with the inducing agent, and the amount of diamond growth at the location where the inducing agent is placed is determined by the type of solvent metal, reaction temperature, and heating time. The size of the crystals produced is determined by the distribution density of the enhancing agent.

The present invention will be explained below with reference to Examples.

Example 1 Cobalt plates with a diameter of 3 ribs and 2 skins in thickness and graphite plates with a thickness of 6 skins were placed alternately as reactants in an indirect heating container with an inner diameter of 3 walls, height of 4 holes, and contact between the two. 30 pieces of chromium carbide crushed to a particle size of approximately 5 tsubom were placed in the chamber.

Both ends of this container were covered with waxite disks, and the container was placed in a conventional uniaxial pressure type high temperature and high pressure device to pressurize it to about 50 kb, and a heater placed around the reaction chamber was energized to give about 13 kb.
00qo and maintained for 15 minutes. As a result, approximately 16 tar of yellow to yellow-green diamonds with well-developed crystal planes and an average grain size of 0.1 to 0.2 were obtained. Example 2 Using a reaction vessel with the same dimensions as in the above example, 2-thickness nickel plates and 6-thickness graphite plates were arranged alternately, and carbonized particles with a particle size of about 100 m were placed in the contact area between the two. A layer of 10 chrome grains was placed.

The reactants were maintained at pressure and temperature conditions of about 52 kb and about 1350 pm for 4 minutes.
-As a result, about 15 tare of diamonds with a grain size on the 0.3-0.4 side were obtained.

Example 3 Using the same configuration as Example 2, 30/9 of 300/400 mesh tantalum carbide grains were placed in the contact area between the nickel plate and the graphite plate.

The reactant was maintained at a pressure and temperature condition of about 54 kb and about 140,000 for 30 minutes, yielding about 18 tar of diamonds having a particle size of 0.2 to 0.3 skin. Example 4 Using the same reaction vessel configuration as in Example 1, 3 out of 15 metal chromium grains each having a diameter of about 1 m were placed in the contact area between the cobalt plate and the graphite plate.

This reaction material was maintained for about 50 kb and about 1,300,0030 minutes to obtain about 12 tar of diamonds with an average grain size of 0.3. Example 5 Using the same reaction vessel configuration as in Example 1, metallic manganese grains with a particle size of about 10 m were arranged at the contact area between the iron plate with a thickness of 2 and the graphite plate with a thickness of 6. Supervised.

This was maintained under pressure and temperature conditions of about 5 water b and about 1350° C. for 40 minutes to obtain about 18 ta r of hexa-octahedral crystals with a grain size of 0.4 to 0.5. As described above, in the method of the present invention, diamond can be synthesized in a temperature range close to the melting temperature of the solvent metal or even lower than the melting temperature of the solvent metal by adding a certain amount of a crystal formation inducer. became possible.

In this way, the crystal growth rate for low-temperature synthesis can be controlled to a relatively low level, and the growth rate of each crystal plane can be made almost uniform, making it possible to produce diamonds with high symmetry and well-developed crystal planes. is obtained. ■ Since crystal growth occurs only at the location where the inducing agent is placed, the number and size of diamonds to be produced can be determined by the amount of inducing agent. '3} Because the inducer is a metal carbide or a metal that forms a stable carbide, the phenomenon of seeds disappearing prior to the synthesis reaction does not occur in the case of a reaction method that uses diamond seeds to lower the synthesis, temperature, and pressure conditions. , the reproducibility of the reaction is good. ■ By using an inducing agent, it is now possible to synthesize high-quality diamonds using lower pressure and temperature conditions than in conventional diamond synthesis methods.

Therefore, the number of lifetimes of the reactor used can be increased. Has characteristics.

[Brief explanation of drawings]

Figure 1 shows the phase diagram of carbon, where the vertical axis is pressure;
In the diagram where the axis represents temperature, the curve A-B shows the limit at which diamond crystal nuclei can spontaneously grow when cobalt is used as a solvent metal.

Claims (1)

[Claims] 1. Diamond is synthesized by subjecting carbon and a solvent metal consisting of iron, cobalt, nickel, or an alloy containing these, which are arranged in contact with each other, to pressure and temperature conditions within the diamond stability region. In this process, carbon and solvent metal are first layered alternately, and the interface between adjacent layers is dotted with grains of carbide of at least one metal among vanadium, chromium, manganese, niobium, tantalum, and tungsten. , and then pressurizing and heating the reactant consisting of carbon, solvent metal, and metal carbide under pressure and temperature conditions within the diamond stability region. 2. The diamond manufacturing method according to claim 1, wherein the metal carbide grains are placed on the boundary surface in advance before pressurizing and heating. 3. The diamond manufacturing method according to claim 1, wherein the metal that forms the metal carbide is placed on the boundary surface as metal grains prior to pressurization and heating, and the metal carbide is formed only during heating.