Thermodynamic Study of SiC Utilizing a Mass Spectrometer

The sublimation of hexagonal SiC has been studied under equilibrium conditions. The predominant gaseous species above SiC are Si, SiC2, and Si2C. By combining the heat of formation of gaseous Si from solid SiC and the known standard heat of formation of SiC, a value of 113 kcal/g atom is obtained for the heat of sublimation of Si at 298°K. From the measured partial pressures, using estimated free energy functions, dissociation energies for Si2, Si3, SiC, SiC2, Si2C, Si2C2, Si2C3, and Si3C are calculated and compared with previously known dissociation energies for group IV B molecules.