Thermochemistry of gaseous compounds of metals. Final report 5 Dec 77-4 Dec 80

The results obtained during a three-year program of thermochemical studies of gaseous inorganic metal compounds are summarized in this report. The metal compounds studied were primarily the fluorides, oxides, and oxyfluorides of the transition and lanthanide metals, potential hot corrosion products and/or reaction products of chemical pumping steps in potential lasing processes. Specific chemical systems studied were the gaseous fluorides of Mo, Ta, Zr, B, Sc, Y, La, Ni, Sm, Eu, and Tm; the oxides of Lu and Tm; and the oxyfluorides of Ta and W. Derived thermochemical data include the standard enthalpies of formation, bond dissociation energies, ionization energies, and in most cases absolute entropy data that can be used to check the assignment of spectroscopic and molecular constants; the latter proved to be particularly important for the scandium group lanthanide group metal compounds, which have large but uncertain electronic contributions to the entropy and Gibbs energy function. The entropy and enthalpy data can be used together to evaluate the equilibrium behavior of these systems over wide temperature ranges. Bond dissociation energy data for the scandium-group and lanthanide fluorides, which have sufficient ionic bonding for valid comparisons, correlate well with the predictions of the polarizable ion model, providing further more » corroboration for the usefulness of this model in generating thermomechanical data for species not studied experimentally. The thermochemical data for the tantalum fluorides provide a clear explanation for the observed resistance of tantalum to attack by fluorine at high temperatures and low pressures. « less