Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Patent
1981-04-30
1983-09-27
Meros, Edward J.
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
C01B 3106
Patent
active
044068719
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE ART
The present invention relates to processes for crystal growing and, more specifically, to a process for growing diamonds from carbonaceous compounds at high temperatures and pressures within the range of thermodynamic stability of the diamond.
BACKGROUND ART
A process is well known in the art for growing diamonds under pressures and at temperatures corresponding to its thermodynamic stability in the carbon-metal system. In the state diagram of graphite-diamond the range of working pressures is above the equilibrium line for graphite-diamond (range of thermodynamic stability of diamond), wherefore the range of growing temperatures is limited, on the one hand, by the metal melting curve and, on the other hand, by the equilibrium line. In the chamber of a solid-phase high-pressure unit, pressure is created and a container made of an elasto-plastic material (such as lithographic stone) with a reaction space volume of from 1.0 to 3.0 cm.sup.3 is placed thereinto. In the reaction space there is present graphite or any other carbonaceous substance and metal-catalyst-solvent. Heating is effected by passing electric current directly through the reaction space on a special heater provided therein. In one of the embodiments the known process stipulates the creation of high temperatures and pressures necessary for the synthesis of diamond within the range of its thermodynamic stability (cf. U.S. Pat. No. 3,124,422, published in 1964).
In this embodiment of the prior art process for growing diamonds the residence of the growth system in the stage of thermodynamic stability of graphite at a temperature exceeding the melting point of the metal-solvent-catalyst is accompanied by the formation of a graphite phase capable of initiating the process of recrystallization of metastable graphite within the range of thermodynamic stability of diamond so as to compete with the diamond-formation process, thus hindering the formation of substantially large (above 0.4 mm) fractions of diamond crystals and limiting the yield of these fractions to 13-15%.
Also known in the art is a process for growing diamonds, wherein, unlike in the above-described process, into the growth system there are added active compounds-nitrides of such metals as titanium, zirconium, hafnium, vanadium, boron, and silicon (see Japanese Pat. No. 4605, published in 1972).
The addition of said active substances contributes to a certain increase in the yields of large size fractions of diamond crystals. However, this increase is limited to several percent of the total weight of the synthesized crystals. The stable yield of large-size (above 0.4 mm) fractions of diamond crystals is, in the discussed embodiment of the process, not more than 20% which is insufficient for their industrial manufacture.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to improve the process for growing diamonds in such a way as to ensure in the course of growing, both suppression of the nucleation process of the metastable graphite phase and limiting the number of diamond phase nuclei, which would lead to an increase in the stable yield of large size (with particle of more than 0.4 mm) fractions of commercially suitable crystals.
This object is accomplished by a process for growing diamonds from carbonaceous substances at high (within the range of thermodynamic stability of diamond) temperatures and pressures in the presence of metals-catalysts-solvents and active compounds. In accordance with the present invention, use is made of cyanamide and/or its metal derivatives of the first, second or eighth Groups.
It is preferable that the process for growing diamonds be effected using, as the carbonaceous substance, graphite and, as metals-catalysts-solvents-manganese and nickel taken in the ratio of 6:4. Active compounds should be preferably added in an amount of from 0.05 to 1.5% by weight and the growing should be carried out under a pressure of from 43 to 45 kbar and at a temperature of from 1,250.degree. to 1,350.degree. C.
To shorten the time
REFERENCES:
patent: 2947609 (1960-08-01), Strong
patent: 2947610 (1960-08-01), Hall et al.
patent: 2992900 (1961-07-01), Bovenkerk
patent: 3597158 (1971-08-01), Horton
Radyansky et al. "Sverkhtuerdye Materialy" No. 2, Apr. 1979, pp. 8-11.
Nikitin Albert V.
Putilin Jury M.
Radyansky Vladimir M.
Samoilovich Mikhail I.
Shaposhnikov Anatoly A.
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