Metal and oxygen activities in the Fe-Ni-O and Ni-Cr-O systems between 900°C and 1100°C

Abstract

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