Thermodynamics of Rare-Earth–Carbon Systems. III. The Erbium–Carbon System

Abstract

A sample of erbium dicarbide has been prepared by direct reaction of the elements in a graphite lined molybdenum crucible. The vaporization of the dicarbide has been studied by means of the Knudsen-effusion–mass-spectrometric technique over the temperature range 1750–2500°K. The vapor species above ErC2(s) were found to be Er(g) and, as minor constituent, ErC2(g). From the vapor-pressure equation the enthalpy of vaporization of ErC2(s) to Er(g) was found to be ΔH°298 = 101.1 ± 0.4 kcal/mole. From this value the standard heat of formation of C-rich ErC2(s) was calculated to be − 18.5 ± 0.4 kcal/mole. The stability of ErC2(g) molecule has also been determined.