Professor Jimmie G. Edwards's Faculty Page

HIGH TEMPERATURE CHEMISTRY:
Structure, thermodynamics, and phases of binary and ternary metal chalcogenides; high temperature vaporization processes; effusion kinetics, heterogeneous photocatalysis.

Knowledge of high temperature properties of materials is necessary in manufacture of electronic devices, ceramics, nuclear fission and fusion technology, metallurgy, geology, environmental chemistry, etc. Development of techniques to study these properties has been one of the great accomplishments of science.

We have developed a new way to apply effusion techniques to the study of high temperature vapors. We solve the equation of motion of a torsion-effusion pendulum to obtain the pressure of the effusing vapor. Simultaneously mass-effusion of the vapor is studied. The entire apparatus has been automated and interfaced to a laboratory computer. Results are obtained and displayed in real time.

The high temperature properties of many binary systems, e.g., sulfides, oxides, and carbides, as well as ternary systems, all with practical applications, still require study. We currently are working on chalcogonides CuBS, ZnGa2Se4, SrGa2Se4, CdGa2Se4, CaGa2Se4, Ga2S3, Ga2Se3, and Ga-Te as well as on MxC60 phases. At high temperatures the properties of such materials vary owing to stoichiometry changes, valence disproportionations, ion packing changes, and a variety of other effects.

Recently we discovered that all condensed-phase transitions near triple points are hysteretic on the temperature axis and that transition temperatures depend on direction of temperature changes; such effects are different within effusion cells than in other enclosures. New interpretations of data underlying our understanding of some high temperature chemical properties are called for.

The degradation of ammonia and oxidized-nitrogen species under sunlight is important in agriculture and in environmental studies. In collaboration with Professor J.A. Davies, we are investigating the chemistry of inorganic nitrogen-containing ions in water under ultraviolet radiation in the presence of doped ceramic catalysts. Techniques include isotope exchange, Moessbauer spectroscopy, flow and stationary solution reactors, and fluidized-bed reactors. Catalyst-development systems based on photooxidation and photodegradation reactions from these studies are proposed.