MAN-MADE DIAMONDS — SUITS 441 



of pistons and cylinders at extremes of pressure, tlie project to which 

 we have referred has developed equipment capable of withstanding 

 pressures of up to 3,000,000 pounds per square inch. This is 200,000 

 times atmosplieric pressure, or, as the scientists put it, 200 kilobars. It 

 is the pressure that would be found some 330 miles beneath the earth's 

 surface. Or, expressed another way, it represents the pressure of 

 a column of mercury 100 miles high, a rather substantial barometer 

 reading. These astounding pressures, however, are not a record. 

 Bridgmnn attained much higher pressures by far simpler means. The 

 new progress, in apparatus, came from a chamber design that per- 

 mitted the simultaneous attainment of high pressure and high 

 temperature. 



In terms of temperature, we have consistently referred to ''5000 

 degrees.'' In the early days of diamond-making we meant Fahrenheit, 

 and 5000° F. is still the temperature wliich can be held for "a long- 

 time" — hours if need be. More recently, temperatures of 5000° K.— 

 about 9000° F. — have been achieved for periods of a few hundredths 

 of a second in our superpressure chambers. This is nearly the tem- 

 perature of the sun's surface. 



The development of these pressure chambers has been described in 

 detail on another occasion.* The present form of the high pressure 

 "belt" is show^n in diagrammatic view in figure 1. 



Chemistry was at least as important to the initial achievement of 

 diamond-making as the temperature-pressure combination. It has 

 been found that certain metals, wliich are molten in the process en- 

 vironment, act as catalysts and greatly enhance the rate of the required 

 change in the lattice arrangement. The net result of catalysis is a 

 higher yield at a higher rate, at significantly reduced temperatures 

 and pressures. Thanks to pressure, temperature, and chemistry, the 

 graphite "stayed squz" and emerged as diamond. 



As we have seen, it is possible in superpressure chambers to hold the 

 chamber conditions for long periods of time and thus to achieve a 

 steady state for reactions under study. A temperature limit of about 

 3000° K. is set for such steady state use primarily by the available ma- 

 terial properties, particularly the melting points of ceramic bodies. 

 Under steady state conditions, say, 1.5 million pounds per square inch 

 and 1500° K., the diamond stable region of the carbon phase diagram 

 is attained, but the diamond transition was not originally observed 

 except in the presence of the catalyst. Francis Bundy showed, in static 

 apparatus, by extending the temperature to 5000° K. for transient 

 excursions, that the direct conversion of graphite to diamond — that is, 

 without catalyst action — takes place. This is illustrated strikingly 



* C. G. Suits, "The Synthesis of Diamond — A Case History in Modern Science," read 

 November 3, 1960, before the American Chemical Society, General Electric Research 

 Laboratory Report No. 60-GP-1S9. 



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