GIBBS FREE-ENERGIES OF FORMATION OF AMORPHOUS SI2O3, SIO AND SI2O

A thermodynamic methodology was put forward to assess the standard hea ts of formation and absolute entropies of silicon oxides, based on var ious thermal behaviors such as decomposition temperatures. The standar d heats of formation at 298 K thus calculated are 1345.53, 426.08 and 342.84 kJ/mol for Si2O3(am), SiO(am) and Si2O(am), respectively. The s tandard entropies obtained by this method are 105.67, 61.60 and 133.08 (J/K)/mol for Si2O3(am), SiO(am) and Si2O(am) at 298 K, respectively. Using these data, the equilibrium phase relations in the Si-O system have been computed and shown graphically as a function of oxygen poten tial for the temperature range of 298-2500 K.