Ultra High Temperature Gas-Solid Reactions Involving Group 4 and 5 Transition Metal Carbides

Featuring Darryl P. Butt, Ph.D.
Professor and Chair
Department of Materials Science and Engineering
Boise State University

Location: McDonnell Douglas Engineering Auditorium

Abstract:
Transition metal carbides exhibit a wide range of stoichiometry.  For example, the substoichiometric compound ZrCx exists as a single phase between approximately ZrC0.6 and near ZrC1.0.  During high temperature (2000-3100 K) vaporization of transition metal carbides the near-surface composition changes with time due to incongruent loss of metal and carbon atoms.  Eventually a congruently vaporizing composition (CVC) can be reached under constant temperature and atmosphere.  At the CVC, metal and carbon atoms are removed in a ratio equal to that present on the solid surface.  In hydrogen it was found that the rate of mass loss is controlled by gaseous transport of the transition metal atom.  Thus, the rate of loss is controlled by the instantaneous activities of the metal and carbon which can vary by many orders of magnitude across the compositional range of the transition metal carbide.  By considering together solid state and gaseous diffusion relationships the rate of vaporization can be calculated at any point in time for many geometries.  It is shown that the mass loss calculated from theory agrees with most experimental data in vacuum and hydrogen.

Biography:
Darryl P. Butt, Ph.D., is professor and chair of materials science and engineering at Boise State University. He received his Ph.D. in ceramic science in 1991 and his B.S. in ceramic science and engineering with a minor in technical writing in 1984 from the Pennsylvania State University.