Role of vapour oversaturation in the thermal decomposition of solids

Elementary thermochemical calculations show that in all cases of formation of solid product in the process of the congruent dissociative vaporization of reactants, the equilibrium partial pressure of the main product greatly exceeds its saturation vapour pressure, and therefore causes the appearance of vapour oversaturation. The oversaturation is responsible for the formation and growth of nuclei, their shape and position, the transfer of condensation energy to the reactant, the existence of induction and acceleration decomposition periods, the reaction localization, the epitaxial/topotaxy effects and the nanocrystal structure of the solid product. Variations in the energy transfer explain an increase of the molar enthalpy with temperature and the decelerating influence of melting on the rate of decomposition.