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Author

Haydn Davies

Date of Award

5-1973

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Metallurgy and Materials Science

Supervisor

W. W. Smeltzer

Abstract

This thesis concerned with the experimental determinations of the thermodynamic parameters describing the Fe-Ni-O and Ni-Cr-O ternaries between 900°C and 1100°C.

Equilibrium oxygen pressures for Fe-Ni and Ni-Cr allows equilibrated with their oxides have been measured by an electrochemical cell with a calcia stabilised zirconia electrolyte. These pressures were related to compositional determinations of the solid phases, using an electron probe microanalyser, and correlated with the ternary isotherms. Both the Fe-Ni-O and Ni-Cr-O systems have been described by equilibrium oxygen pressure diagrams which relate oxyren activity to the compositions of the equilibrated phases.

The variation of metal activities with alloy composition for Fe-Ni and Ni-Cr alloys has been determined between 900°C and 1100°C. Spinel-alloy equilibria in the Fe-Ni-O system have been described by a Gibba-Duhem calculation and by a structural model for the spinel based on a lattice point defect model.

Experimental observations of the scales formed on Fe-Ni-Cr alloys are qualitatively discussed with respect to thermodynamic considerations.

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