Links of Science & Technology
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rectly involved but knew or met most of the players while their memories were still reliable. There is no need to rehash that story. Here we have chosen to isolate a narrow theme based on the contribution of Russian scientists to the HPHT and CVD routes to diamond. Both paths share very-much-ahead-of-their-time experimental discoveries or theories and a remarkable lack of follow-up technology until it was too late to be the first to capitalize on the findings. The reasons for this are complex but include lack of communication, World War II, language barriers, bias, and perhaps, market orientation. Part I: O.I. Leipunskii and the HPHT process It had long been appreciated that diamond was a high-pressure mineral and that it would be useful to know the P-T equilibrium describing the stability of diamond with respect to graphite.20"22 However, before 1938 sufficiently accurate thermodynamic data did not really exist to do this properly in a theoretical manner, and experimentally the world was not really ready until after 1955 (although hindsight suggests somewhat earlier). In 1938 Rossini and Jessup of the then U.S. National Bureau of Standards did careful measurements of the heats of formation of CO2 from well-characterized samples of diamond and graphite23 (further refined later by Prosen, Rossini, and Jessup in 1944),24 and calculated the difference in free energies of diamond and graphite as a function of pressure and temperature. The Rossini and Jessup work was a major contribution, and they provided a basis for a diamond/graphite equilibrium curve that was subsequently recalculated and extrapolated by others. The first of these revisions appears to be by Leipunskii, who made the calculations and published them in a Russian journal in 1939.25 He bravely made a lin-
Links of Science & Technology describes the origin, science, technology, and unique accomplishments of advances in materials science that have had significant practical value.
ear extrapolation of the Rossini-Jessup curve from 1400 K and 42,200 atm to 4400 K and 125,000 atm, a part of which is shown in Figure 5. In addition he was willing to state a pressure and temperature for the direct conversion of graphite to diamond and the same parameters for the conversion in a solvent (iron) to handle the kinetic problem in this transformation. He noted, on the basis of Bridgman's work,26 that the pressure capability to achieve the solution regime (50,000 atm) existed already, that internal heating would present lesser difficulties, and that the 60,000-70,000-atm regime would be achieved in the not too distant future. His comment on internal heating apparently is based in part on his own experience since he refers to himself25 and also to Basset27 in this regard. Starting from Basset's data for the melting of graphite (—4000 K at one atmosphere),27 Leipunskii also presented a graphitemelting line that had a slow increase in temperature with pressure and a widening error bar to accommodate parameters inadequately defined at that time. In this same paper he was
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