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Show moreThis invention relates as indicated to an improved process for the growth of diamonds from seed crystals. It is to be distinguished from the production of industrial diamonds from carbon under conditions of extremely high temperature and pressure. This invention provides conditions for increasing the growth rate of diamonds from seed crystals to acceptable levels and for decreasing the rate of the undesired side reaction to graphite, and for growing such diamonds of such crystal structure that they have application as abrasive materials and semiconductors. The conditions which have been found to yield improvement in overall growth rate and in crystal structure are relatively low temperatures in the range of from 800.degree. C. to 1350.degree. C., and at pressures which are very much lower than have heretofore been used. A primary difficulty with prior so-called low-pressure processes for the growth of diamonds with polycarbon atom materials is that the growth rate of unwanted graphite is too high. This invention provides means for suppressing the growth rate of graphite and at the same time, means for producing diamond of improved crystalline quality. The term "low pressure" insofar as it is applied to the production of diamond contemplates anything below 40,000 p.s.i. One "low pressure" process (Hibshman, U.S. Pat. No. 3,371,996 ) contemplates pressures of from 1 to 2,000 atmospheres, and temperatures which are limited to 1,100.degree. C. or less. This process is characterized by utilization of a platinum catalyst to promote the production of carbon from carbon monoxide. The present improvements contemplate very much lower pressures, preferably a hydrocarbon source for the carbon and an absence of metallic catalysts. Another process (Eversole, U.S. Pat. No. 3,030,187 and -188 ) contemplates temperatures in the range of from 600.degree. C. to 1,600.degree. C. and pressures of from 0.03 mm. to 10 atmospheres. A special type of low-pressure carbon transport process is taught by Brinkman U.S. Pat. No. 3,142,539 which contemplates temperatures in the range of from 1,000.degree. C. to 1,800.degree. C., and a molten metallic medium for transporting carbon to the seed crystals. Brinkman in U.S. Pat. No. 3,175,885 discloses another carbon transport process utilizing a vapor transport for carbon evaporated from pure graphite at very high temperatures, distinguished by maintaining the seeds and carbon source at different temperatures.As an example of an extremely high-pressure process, reference may be had to U.S. Pat. No. 3,334,968 to Ishizuka who contemplates pressures of 75,000 atmospheres. Also reference may be had to the U.S. Pat. to Wentorf, No. 3,297,407, which utilizes seed crystals but extremely high pressures on the order of 75,000 atmospheres. There are quite a few other patents which contemplate high-pressure equilibrium processes and these are exemplified by the U.S. Pats. to Darrow No. 3,310,501; Strong, No. 3,303,053.
http://www.google.com/patents?vid=USPAT3615208
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