Phase transformations of n-layer graphenes into diamond at high pressures and temperatures

The effect of high pressure (7.7 GPa) and temperature (1700°C) on the phase transformations of both graphene plates with a high degree of crystallinity having less than four layers and thickness not exceeding 5 nm and powders of multilayer graphenes (of 10–20 monolayers) and 8–12 nm in thickness was experimentally studied in the presence of carbon solvents (Ni–Mn alloy, iron). Factors both contributing and inhibiting the diamond synthesis from graphene in the presence of the solvents for carbon are defined. It is shown that the transformation of multilayer graphenes into diamond at high pressure and temperature by a two-stage scheme of the diamond synthesis (i.e., after three-dimensional structural ordering of graphene at the first stage) is preferable.