JPH0380533B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention relates to a diamond synthesis method using a temperature difference method, and relates to a method for improving the method and increasing the yield of diamond.

(b) Conventional technology and its problems Synthesizing diamond using the temperature difference method has a slower growth rate than the method of directly converting ordinary graphite into diamond, and therefore it is possible to synthesize large crystals of good quality. However, on the other hand, the drawbacks are that there is only a small amount of space suitable for crystal growth within the reaction vessel, and that the synthesis time is long, resulting in high production costs.

The conventional method is to place a sample with the configuration shown in Figure 1 in a belt-type ultra-high pressure device, pressurize it, apply electricity to a cylindrical heating element, and maintain the sample at 50-60Kb and 1400-1600℃. Utilizes the temperature difference in the axial direction that occurs within the container. In other words, the carbon supply source placed near the axial center of the sample container has a higher temperature than the solvent metal part placed below it, and the seed crystal placed at the lowest or lowest temperature part within the solvent metal. There will be a temperature difference of 20-50℃ between the two. This temperature difference results in a difference in the solubility of carbon to the solvent metal,
Using this as a driving force, carbon flows from the carbon supply source toward the seed crystal, and diamond grows on the seed crystal.

Similarly, attempts have been made to utilize the temperature difference that occurs in the upper half of the sample container as shown in Figure 2, but in this method, the upper half of the sample container is free from diamond crystals that grow from seed crystals. However, an extremely large number of diamonds are generated due to spontaneous nucleation, and the resulting crystals are aggregates or crystals come into contact with each other, stress concentration occurs, and cracks and fractures occur due to cleavage. It is virtually impossible to synthesize large single-crystal diamonds of good quality. The following two points are possible causes of this phenomenon.

(1) Minute diamond crystals generated in the carbon source placed below the solvent metal float to the surface and grow around the seed crystal placed above the solvent metal.

(2) Because the density of the high-temperature solvent with a high carbon content in the lower part of the solvent metal is lower than that in the upper part, solvent convection occurs and the amount of carbon supplied becomes excessive.

(c) Disclosure of the Invention The present invention is the result of research conducted to solve the above-mentioned problems, and is a method that makes it possible to effectively utilize the limited space inside a reaction vessel. The present inventors have discovered that the problem with the conventional method lies in the positional relationship between the solvent metal and the carbon supply source. That is, in the conventional method, the above-mentioned problem arises because the carbon supply source is arranged in the direction of gravity with respect to the solvent metal.In contrast, in the present invention, the carbon supply source is arranged in the direction of gravity with respect to the solvent metal. By placing it between the solvent metal and the cylindrical heating element, it is possible to prevent the diamond crystals generated in the carbon source from floating, and the difference in height between the carbon source and the seed crystal is smaller than in conventional methods. Convection is less likely to occur, and spontaneous nucleation from sources other than the seed crystal can be significantly reduced. Therefore, according to the present invention, whereas conventionally only the lower half of the space within the reaction vessel could be used, the upper half can now also be used, and the yield can be doubled at once.

Further, the temperature difference necessary for crystal growth can be sufficiently ensured by such a method. In other words, the temperature distribution inside the cylindrical heating element has a gradient in which the temperature decreases from the center in the axial direction toward the top and bottom, and at the same time, the temperature decreases from the inside of the heater in the radial direction toward the central axis. There is a gradient that appears to be increasing. This is because the conventional method utilizes only the temperature difference in the axial direction, whereas the method of the present invention utilizes the temperature difference in the radial direction.

The structure inside the reaction chamber of an ultra-high pressure device that meets these requirements is such that an insulator, a cylindrical carbon source, and a cylindrical solvent metal are arranged concentrically inside a cylindrical heating element, in order from the outer periphery. A suitable method is to grow a diamond crystal on a seed crystal that is placed on the contact surface between the solvent metal and the pressure medium that holds it. In addition, the contact surface between the solvent metal and the pressure medium that holds it is specifically as shown in Figures 3 and 4, but when using a cylindrical solvent metal, one or both sides of the upper end surface and the lower end surface are used. The invention can be practiced at one or more locations.

Furthermore, the present invention aims to increase the yield of diamond, and includes a method of growing diamond crystals by using two or more sets of the above-mentioned segments in a reaction chamber, or by combining a segment using a cylindrical carbon source with a segment described above. is desirable.

The shape of the solvent metal is preferably cylindrical, and the seed crystal position is preferably at a low temperature in the solvent metal, that is, on the top surface of the solvent. It is also possible to grow crystals on the bottom surface if the temperature difference is properly adjusted.

It is also possible to stack two or more such structures in multiple stages to further improve the yield, and is particularly suitable for synthesizing relatively small crystals of about 1/5 to 1/30 carat. Note that the cylindrical or cylindrical shape may be a disc or an annular shape.

Comparative Example For comparison with the present invention, experimental results using a conventional method will be shown. The configuration of the reaction chamber is shown in Figure 2. A graphite cylinder with an outer diameter of 24 mm and an inner diameter of 22 mm is placed as a heating element inside a cylindrical pyrofluorite 6 that is a pressure medium, and an Fe with an outer diameter of 18 mm is placed inside the graphite cylinder with an outer diameter of 24 mm and an inner diameter of 22 mm. -50Ni cylinders were used as the solvent metals 2 and 2', and two embossed bodies 3 and 3' of a mixture of graphite powder and diamond abrasive grains were arranged vertically symmetrically as shown in Figure 2. , using the surroundings as a pressure medium
Surrounded by NaCl4, seven 35/40 mesh synthetic diamonds were each embedded as seed crystals 5 in the bottom and top surfaces of the solvent metal 2 and 2', respectively.

This structure was pressurized using a girdle type ultra-high pressure device to apply a pressure of 55 Kb, and then the heater was energized to heat the carbon supply sources 3 and 3' to a temperature of 1500°C. After maintaining this condition for 50 hours, heating was stopped and the sample was taken out after reducing the pressure. Seven diamond single crystals with an average weight of 113 mg were obtained from the solvent metal 2 placed below, each from a seed crystal. It was growing. On the other hand, from the solvent placed above, over a hundred crystals with an average size of 8 mg were obtained, with the largest size being 21 mg, most of which were in contact with each other and formed aggregates. .

Example 1 As shown in Fig. 3, a cylindrical carbon source embossing body 8 with an inner diameter of 12 mm and an outer diameter of 18 mm was arranged around the outer periphery of a Fe-50Ni solvent metal 7 with an outer diameter of 12 mm, and a cylindrical carbon source embossing body 8 with an inner diameter of 12 mm and an outer diameter of 18 mm was placed on the upper surface of the solvent metal. When an experiment was conducted under the same conditions as the comparative example using a structure in which seven seed crystals were embedded in the contacting NaCl4 and the composition of the lower half was the same as that of the comparative example, an average of 102 mg was obtained from the lower solvent 2. 7 diamond single crystals were obtained, and from the upper solvent, the average
Seven crystals of 140 mg were obtained. All of the crystals were of good quality grown from seed crystals, and no spontaneous nucleation occurred in either the upper or lower solvent, which was a significant improvement over the comparative example.

Example 2 As shown in Fig. 4, Fe-50Ni solvent metals 9, 9', 9'' with an outer diameter of 12 mm are stacked so that NaCl4 is placed between them.
mm, a carbon source stamping body 8 with an outer diameter of 18 mm is arranged,
A structure in which a total of 28 seed crystals were placed on the bottom surface of solvent metal 9, the top and bottom surfaces of 9′, and the top surface of 9″ was used, the holding time was 20 hours, and other conditions were the same as in the comparative example. In the same experiment, crystals grew from all 28 seed crystals, with an average of 29
mg, and a total of 810 mg of good quality crystals were obtained.

[Brief explanation of drawings]

Figures 1 to 4 are axial cross-sectional views of the reaction chamber, Figures 1 and 2 are explanatory diagrams of the conventional diamond synthesis method, and Figures 3 to 4 are illustrations of the diamond synthesis method of the present invention. be. 1: Cylindrical heating element, 2,2': Solvent metal, 3:
Carbon source, 4: NaCl (pressure medium), 5: Seed crystal,
6: Pyrofilite (pressure medium), 7,7': Solvent metal, 8: Cylindrical carbon source, 9,9',9'':
Solvent metal, 10,10': Solvent metal.

Claims (1)

[Claims] 1. An insulator (pressure medium), an insulator (pressure medium),
A cylindrical carbon supply source and a cylindrical solvent metal are arranged concentrically, and the upper end surface of the cylindrical solvent metal,
A method for synthesizing diamond characterized by arranging a seed crystal on one or both sides of the lower end face and growing a diamond single crystal on the seed crystal. 2. The diamond according to claim 1, characterized in that two or more sets of segments each consisting of a cylindrical carbon source, a cylindrical solvent metal, and a seed crystal are arranged in a reaction chamber of an ultra-high pressure device. Synthesis method.