Monotropic type transformations of diamond below the Berman-Simon line

We construct the phase diagram of a monotropic type for carbon under the Berman-Simon line. It describes metastable phase transformations occurring in diamond when the graphitization is delayed. However, thus far, monotropic phase transition of metastable diamond could not be experimentally observed. To produced delay conditions, we introduced at diamond surface a droplet of graphite melt with a temperature of about 4800K. We demonstrate that thermal shock provided mechanical stress and competition between phase transformations occurring at two high temperature and high pressure branches. At the so called “fast graphitization line” (reported by F.P. Bundy et al., Carbon 34 (1996) 141) the transformations take place tending to the spontaneous diamond graphitization, whereas at the line of monotropic phase diagram, they tend toward the melting of diamond. The transition can start as the graphitization, whereas change-over to the second branch can occur as a result of rapid unloading of mechanical stresses. The melting wins this is competition due to its faster kinetics. We have also found out the characteristic features underlying the initiation of processes near the “fast graphitization line” as are dealing with the spontaneous formation in diamond of a network of compressed graphite, and with the melting of such graphite in the course of its expansion taking place owing to the loss of mechanical stability of diamond caused by the network. This mechanism, apparently reveals a liquid-like nature of the transformations at the “fast graphitization line”.