Abstract
In accordance with the phase diagram of carbon the graphite {r_arrow} diamond polymorphic trans-formation is possible at a pressure of {similar_to}130 kbar and temperature of {similar_to}1200{degrees}C. However, in the presence of iron the processes of formation of diamond from graphite and a number of non-graphite forms of carbon (soot, coke, carbon glasses, etc.) occur even at a pressure of 40-60 kbar, that is, in the area of thermodynamic stability of graphite. The physicochemical nature of the processes leading to formation of diamond crystals under these conditions i still not clear. Nevertheless it is assumed that in the given case polymorphic transformation of graphite into diamond, on which iron has some catalytic action causing a decrease in the necessary pressure within the limits of thermodynamic stability of diamond, occurs. A number of hypotheses have been proposed. 9 refs., 3 figs.
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