▎ 摘　　要

An approximate equation of state of nanocarbon is used to estimate changes in the enthalpy of formation of single- and multilayer graphene and the graphene-nanodiamond phase equilibrium pressure as a function of geometrical shape, number of layers, and size of a graphene nanoparticle. It is found that upon an increase in the number of layers in graphene with particle sizes of 100-300 nm, the phase equilibrium pressure falls and tends to that of graphite-diamond equilibrium. An agreement between the estimations, the data from MD simulations of the graphene-nanodiamond phase equilibrium, and experimentally measured parameters of the graphene-nanodiamond phase transition was obtained.