RU2560380C1 - Method of obtaining artificial diamonds from graphite - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: artificial diamonds are obtained from graphite on a substrate in the presence of electrodes by placing of graphite on the substrate representing a negatively-charged electrode placed in a quartz tube, and with heating to 1000°C under atmospheric pressure in a radiation furnace. Another electrode, positively charged, is placed on the external side of the tube; direct current is supplied with the voltage of 2.0-10 kV to the electrodes without the creation of a closed electric circuit.

EFFECT: technology simplification, reduction of energy consumption and reduction of the prime cost of diamond synthesis due to the simplicity of the technological solution, availability of applied materials and equipment.

Description

The invention relates to methods for producing diamonds, and more specifically to methods for the direct conversion of graphite to diamond in the field of thermodynamic stability of the latter.

A known method of producing superhard materials (diamonds), in which the converted material (graphite) is placed in durable metal storage ampoules of a flat or cylindrical type, in the body of which generate shock waves by detonation of the charge BB in contact with the body of the ampoule, or by hitting the walls of the ampoule of the liner accelerated by air to high speeds [RU 94029279, IPC B01J 3/08, 07/10/1996]. Under the influence of high dynamic pressures and temperatures, a graphite-diamond phase transition occurs in the region of thermodynamic stability of the latter.

The disadvantage of this method is the low (≅20%) material yield. The combined effect of residual temperatures and a rarefaction wave (removal of high pressure to almost zero in a few microseconds) leads to a partial reverse transition of diamond into graphite.

A known method of producing diamond-like phases of carbon, including exposure to carbon-containing material pulses of electric current with a pulse energy of 3.5-18.0 kJ per 1 g of carbon in carbon-containing material [RU 2038294 from 06/27/1995].

The disadvantage of this method is the difficulty of obtaining diamond-like phases due to the pulsed current, which requires an additional device.

There is a method of producing artificial diamonds from graphite by heating it in the presence of electrodes, to which a direct current is supplied, creating a closed electric circuit, while graphite is heated to 1000 ° C at atmospheric pressure [US 5516500 from 05/14/1996].

However, in this method for producing diamonds create a closed electrical circuit, which leads to the re-sublimation of graphite from one electrode to another while passing current.

This method is selected for the prototype.

The objective of the invention is to obtain artificial diamonds from graphite in the absence of sublimation of graphite.

The solution to this technical problem will simplify and cheapen the synthesis of artificial diamonds, as well as obtain artificial diamonds without changing the shape of the original graphite.

This is achieved by the fact that in the method for producing artificial diamonds from graphite on a substrate in the presence of electrodes to which voltage is applied, according to the invention, graphite is placed on a substrate, which is a negative-charge electrode, located in a quartz tube, another electrode, positively charged, is placed on the outside of the tube, the tube is placed in a radiation furnace and heated to 1000 ° C at atmospheric pressure, and a direct current of 2.0-10 kV is applied to the electrodes without creating a closed electric circuit bastard.

These conditions of exposure to graphite are the most optimal for the phase transition of graphite to diamond. At temperatures below 1000 ° C and a voltage of less than 2 kV, the process will be slow and not economically feasible, and an increase in temperature above 1000 ° C and a voltage of more than 10 kV leads to thermal destruction of the graphite layers and excessive energy consumption.

The method is as follows.

The initial sample is preliminarily prepared. For this purpose, crystalline graphite elements (extended fibers with a diameter of up to several microns, a length of several mm, individual particles several tens of microns in size) are placed on a metal substrate. The substrate metal is selected based on their necessary requirements:

- low temperature heating, providing a phase transition of graphite-diamond in the field of thermodynamic stability of the latter.

- high density of the metal in a compressed state in the field of thermodynamic stability of diamond compared to the last

- extremely low solubility of carbon in it (<0.5%) under the influence of temperatures.

To carry out the method, 3 experiments were performed: a graphite sample was placed on a steel plate, which is a negatively charged electrode, placed in a quartz tube, and heated to 1000 ° C in a radiation furnace. The effect on graphite is carried out by supplying an electric current of a constant voltage of 2.0 kV to the electrodes, a positively charged electrode is located on the outer surface of the quartz tube, without creating a closed electrical circuit, i.e. current did not pass through graphite.

When current is applied to the plate, the internal energy of graphite increases above the internal energy of diamond, due to which spontaneous conversion of high-energy graphite to a less energy diamond occurs with the crystal lattice being rearranged during phase transformation. The rate of conversion of graphite to diamond was observed for 1 hour.

When graphite was exposed to an electric current of a constant voltage of 5.0 kV on the electrodes, the rate of conversion of graphite to diamond was observed for 30 minutes.

When graphite was exposed to an electric current of a direct voltage of 10.0 kV on the electrodes, the rate of conversion of graphite to diamond was observed for 20 minutes.

An increase in voltage of more than 10 kV leads to thermal destruction of graphite layers. Therefore, the optimal effect on graphite is 2.0-10 kV.

In this way, diamond production can be easily controlled by the DC voltage.

The method provides the following advantages compared with previously known:

improving the quality of the synthesized product;

simplification of technology, reduction of energy costs and reduction in the cost of diamond synthesis due to the simplicity of the technical solution, the availability of materials and equipment used.

Claims (1)

A method of producing artificial diamonds from graphite on a substrate in the presence of electrodes to which voltage is applied, characterized in that the graphite is placed on a substrate that is a negative-charge electrode located in a quartz tube, another positively charged electrode is placed on the outside of the tube, tube placed in a radiation furnace and heated to 1000 ° C at atmospheric pressure, and direct current voltage of 2.0-10 kV was applied to the electrodes without creating a closed electrical circuit.