SU329761A1 - Method of manufacturing polycristalline diamono aggregates of preset shape - Google Patents

Description

The invention relates to the field of industrial diamond production. It can be used in mechanical engineering, instrument making, mining, watch industry, etc.

A known method for the synthesis of polycrystalline diamond, according to which the graphite preform, which is initial for the synthesis, is heated in two stages with a synthesis time of 30–60 min, which favors the growth of diamond grains. The result is a large-crystalline diamond formation. In addition, in the aforementioned method, the catalyst is applied in the form of metal plates, which leads to a high content of metal inclusions in diamonds, deteriorating their strength properties.

According to the proposed method, durable diamond aggregates of a given shape are obtained, consisting of fine crystallites that are joined together during the synthesis process. The method makes it possible to obtain large diamond products with high purity of the surface, which have the shape of the working parts of the tools: cutters, cutters, glass cutters, dies, drill bits, etc. and the heating is carried out by a pulse

electric current. The crystallization process is carried out in the region of the thermodynamic stability of diamond at a pressure above 80 kbar and temperatures exceeding 1500 ° C. It is known that the formation of a fine-grained structure is favored by rapid crystallization under conditions of strong supersaturation of the uterine medium.

The high rate of conversion of graphite and diamond is achieved due to the highly developed

contact surface of fine powdered catalyst with reactive graphite. The powder form of the catalyst is also used to select the amount of its catalytic activity by replacing part of the catalyst with an inert filler. In addition to),

the fine powder of the catalyst acts as a medium for the almost hydrostatic transfer of pressure to graphite, which makes it possible to retain its shape to a high degree under compression.

Heating by a pulse of electric current simultaneously initiates its transformation into diamond over the entire surface of graphite. Such a transformation is ensured by the creation in the entire contact zone of the catalyst with graphite equal to the temperature sufficient for the selected

heating leads to an increase in pressure in the chamber; o, apparently, facilitates the kinetics of the conversion of graphite to diamond, increasing the instability of the graphite lattice. Heating is completed at the time of the rapid increase in the electrical resistance of the reaction cell several times. The location of the catalyst in the form of a powder on the periphery of a graphite billet leads to the growth of a polycrystalline diamond in the direction from the surface to the center of graphite, which thus turns into a strong diamond aggregate that does not contain large inclusions of catalyst. The catalyst fragments are present in the aggregate in the inner layers of micron thickness between some diamond grains.

Example. A high-temperature reaction cell is placed in a high-pressure chamber that provides a higher pressure. The cell consists of an electric heater, resistance (graphite), reactive graphite having the form of a finished allotment, and a catalyst in the powder (for example, metals of the Vlil group and nx alloys, mixtures

for solid alloys of the type TK and BK), which surround reactive graphite as a shell. The reaction cell is subjected to simultaneous exposure to high pressures (100 kbar n above) n high temperatures (2000 ° C and above). These parameters are maintained for a period of time (from 0.1 to W s, depending on the pressure and size of the reaction graphite) required for the complete transition of graphite to diamond. After that, the temperature (by turning off the electric current immediately), and then n, the pressure is reduced. The diamond aggregate of a given shape is separated by simple mechanical removal of the remaining parts of the reaction cell, which does not require special chemical treatment.

Example 2. For obtaining diamond aggregates of a given shape with a surface of high purity (not lower than 7th grade), reaction graphite with a bulk density of 2.00-2.2 g / cm with a surface not lower than the 5th grade of purity is used. The catalyst activity is preliminarily selected in separate experiments. The rest is carried out according to example I. Foreign particles that are not completely removed mechanically from the surface of al

The ointment aggregate is finally removed by chemical treatment with acids or alkalis. Diamond aggregates of various predetermined shapes and various sizes, for example, 5x5x5 mm, were synthesized. Their mechanical strength and abrasion resistance are tested in laboratory and factory conditions. These characteristics are comparable with G. The same characteristics of natural diamonds, and in some cases higher.

Claims (2)

Invention Formula I. The method of obtaining polycrystalline diamond aggregates of a given shape in the presence of a catalyst from a reactive carbon-containing material, such as graphite, is made in the shape of the finished unit under pressure above 80 kbar and temperatures above 1500 ° C, characterized in that with an improved mechanical properties of diamond units, heating is carried out by a pulse of electric current with a duration of 0.1 -. 10 seconds, and the reaction graphite is surrounded by a sheath of powdery catalyst. 2. A method according to claim I, characterized in that the powdered catalyst may contain an inert refractory filler.