DEMIXING OF MATERIALS UNDER TEMPERATURE GRADIENT (DIFFUSION)
Abstract
The purpose of this research is to investigate how the practically important problem of demixing of materials can be treated theoretically. Specifically, we calculated the problem of steady-state demixing in oxide materials under the coexistence of oxygen partial pressure gradient and temperature gradient. The problem is treated based on the pair approximation of the Path Probability method (PPM) of irreversible statistical mechanics. Along with our previous treatment of demixing under isothermal conditions, this work represents the first attempt to treat demixing problem systematically based on microscopic model of atomic diffusion. Demixing problem is reduced to a a steady-state problem and equations are derived based on such steady state. Calculations are done under two different boundary conditions: open case and closed case. The difference between these two cases with respect to demixing behavior is emphasized. To understand the qualitative features of the phenomenon, the general equations are simplified based on the assumption of ideal solution. Demixing equations are solved both analytically and numerically. Quantities determining the mixing characteristics are clearly identified. Solutions are reduced to several individual cases (e.g. temperature gradient only, partial pressure gradient only etc.) Contributions of the driving forces to the demixing curve are shown. Effect of the temperature gradient is emphasized. Results of the calculation are compared with available experimental data. Some controversies in the past work are pointed out in the light of this calculation.
Degree
Ph.D.
Subject Area
Materials science
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