Surface Graphitization of Diamond in K_2CO_3 Melt at High Pressure

摘要

Surface graphitization of diamond is a chemical catalytic process, in contrast to bulk graphitization, a physical process of diamond/graphite polymorphic transition. Both processes occur at P- T parameters of graphite thermodynamic stability. The boundary temperature between these two processes in a vacuum, i.e., at low values of oxygen partial pressure, is 1600-1700℃ [1, 2]. Because of this, surface graphitization is often called low-temperature. According to [3], surface graphitization of diamond results from precipitation of nondiamond carbon on a diamond surface due to surface chemical reactions in the presence of gaseous reagents (catalysts), such as O_2, H_2O, and CO_2. However, any component of the medium chemically interacting with diamond may be a catalyst of the process. It is established that surface graphitization first proceeds along edges, and on faces it is mainly developed on growth steps, etching pits, and fractures. Graphite nucleation inside diamonds during spontaneous (high-temperature) graphitization is initiated on admixture and structural defects.