Abstract
The oxidation behavior of an alloy system with unique electronic properties and the challenge to prepare a planar model for the very active oxidation catalyst, Hopcalite, were attacked. Surface segregation phenomena of binary alloys, oxidation stages of Cu-Mn alloys and preparation of the planar model for Hopcalite, a thin film of copper manganite on the Cu-Mn alloys, were studied. Segregation calculations have been made using several models including the unified Miedema model. Agreement in the qualitative comparison of theory and experiment appears extremely good. Quantitative predictions serve to design experiments and develop further models. In order to demonstrate the general applicability of the present calculations of surface enrichment predictions for catalytically important alloys, calculations have been made with arbitrary transition metal partners. These predictions are of interest in the field of catalysis. Systematic measurements of photoemission lines as a function of temperature, pressure, exposure and time have been made to obtain kinetic and thermodynamic information about surface segregation, oxygen adsorption and desorption, oxygen bulk penetration, oxide formation and decomposition, and oxide displacement reactions. Based on the above thermodynamic and kinetic information, a planar model for Hopcalite has been prepared for the first time. It was prepared by oxidation of Cu-Mn alloys (30-50 % Mn) at high temperatures (400-500°C) in 1 atm oxygen atmosphere. It was established by XPS that for the Cu-Mn (33%) surface oxidized at 400°C, the surface region is dominated by Cu(I) in tetrahedral environment and Mn(IV) perhaps in octahedral environment with lesser amounts of Cu(II) and Mn(III). The limited experimental conditions where the mixed oxides were prepared can be explained by thermodynamic and kinetic reasoning. Now the charge transfer resonance which appears to be invaluable in oxidation catalysis with Hopcalite using this new planar model is open for further investigation.
Yoon, Cheonho (1986). A surface segregation and oxidation study of alloys with unique electronic properties-implications in catalysis and corrosion. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -609799.