Accession Number : AD0608836

Title :   THERMODYNAMICS OF INTERSTITIAL SOLID SOLUTIONS AND REFRACTORY COMPOUNDS.

Descriptive Note : Rept. for Sep 63-Sep 64,

Corporate Author : MANLABS INC CAMBRIDGE MASS

Personal Author(s) : Bernstein,Harold ; Kaufman,Larry

Report Date : OCT 1964

Pagination or Media Count : 74

Abstract : The vaporization kinetics of a non-stoichiometric solid phase such as NbC has been analyzed on the basis of a Schottky-Wagner vacancy model of the solid, Langmuir vaporization rates of the elements, and non-diffusion limited mass transport. The time dependence of the instantaneous composition, weight, and vaporization rate for a specimen of constant area has been calculated for the conditions of a Langmuir vaporization experiment. Congruent and non-congruent vaporization are controlled by the magnitude of the congruent composition, which can be calculated from equilibrium thermodynamic data. The parameters required to specify the vaporization behavior are starting composition, stoichiometric composition, vapor pressures and molecular weights of the pure elements, temperature dependence of the phase boundaries, free energy of formation of the stoichiometric compound, and specimen geometry. The phases NbC and TaC are treated as examples of congruently and noncongruently vaporizing systems. The predicted vaporization behavior of these materials agrees well with the data from Langmuir vaporization experiments available in the literature. (Author)

Descriptors :   (*REFRACTORY MATERIALS, THERMODYNAMICS), (*THERMODYNAMICS, REFRACTORY MATERIALS), SOLID SOLUTIONS, REFRACTORY METALS, CARBIDES, NITRIDES, OXIDES, VAPORIZATION, KINETIC THEORY, TRANSPORT PROPERTIES, PHASE STUDIES, TANTALUM COMPOUNDS, NIOBIUM COMPOUNDS, IMPURITIES, MATHEMATICAL MODELS, EQUATIONS OF STATE

Distribution Statement : APPROVED FOR PUBLIC RELEASE