Thermodynamic analysis for vapor-grown diamond

A non-equilibrium thermodynamic coupling model is applied to diamond growth in CH4/H-2 gas mixtures and oxyacetylene flames, and the phase diagrams of diamond synthesis in these two systems are calculated. These phase diagrams are different from those predicted by classical equilibrium thermodynamics, because a diamond growth region, where diamond is a stable phase, exists in each calculated phase diagram. The appearance of the diamond growth region is attributed to the super-equilibrium atomic hydrogen and/or oxygen during the growth processes. According to the calculated phase diagrams stable growth of diamond in CH4/H-2 and C2H2/O-2 mixtures can be well understood.