Vaporization Behavior of Europium Dicarbide

The temperature dependence of the vapor pressure of europium in equilibrium with solid europium dicarbide (EuC1.87±0.07) and graphite has been measured over the temperature range 1130° to 1600°K by both time-of-flight mass spectrometric and target collection techniques. From the vapor-pressure equation, the enthalpy of disproportionation of europium dicarbide is calculated to be 51.06±1.25 kcal/gfw by a second-law treatment of the data, and 51.24±2.0 kcal/gfw by the third-law method. The entropy of dissociation is calculated to be 18.43±1.70 eu/gfw. Combination of these data with the reported enthalpy and entropy of vaporization of elemental europium gives −9.17±1.15 kcal/gfw as the standard heat of formation and −7.47±1.87 kcal/gfw as the standard free energy of formation of europium dicarbide.