Thermodynamics of Rare-Earth–Carbon Systems. I. The Cerium–Carbon System

The gaseous phase in thermodynamic equilibrium with the condensed cerium–carbon system has been investigated by means of the combined Knudsen‐cell–mass‐spectrometric technique in the temperature range 1990°–2300°K. In addition to cerium atoms, the gaseous carbide molecules CeC₂ and CeC₄ were identified and their partial pressures measured. Using this information, the following dissociation and atomization energies were derived: $$D_0\text{°\hspace{0.17em}=\hspace{0.17em}162\hspace{0.17em}±\hspace{0.17em}2}\mathrm{kcal}/\mathrm{mole}$$ for the Ce–C₂ bond energy in CeC₂; $${\mathrm{\Delta H}}_0\text{°\hspace{0.17em}=\hspace{0.17em}304.5\hspace{0.17em}±\hspace{0.17em}1.5}\mathrm{kcal}/\mathrm{mole}$$ for the atomization energy of CeC₂; $${\mathrm{\Delta H}}_0\text{°\hspace{0.17em}=\hspace{0.17em}609\hspace{0.17em}±\hspace{0.17em}5}\mathrm{kcal}/\mathrm{mole}$$ for the atomization energy of CeC₄. A heat of formation for the solid cerium dicarbide was also obtained.