Solubility and activity of oxygen in liquid nickel in equilibrium with α-Al₂O₃ and NiO·(1+x)Al₂O₃

Abstract

The limiting solubility of oxygen in liquid nickel in equilibrium withα-alumina and nickel aluminate has been measured by inert gas fusion analysis of suction samples in the temperature range 1730 to 1975 K. The corresponding oxygen potential has been monitored by a solid electrolyte cell consisting of calcia stabilized zirconia as the electrolyte and Mo + MoO₂ as the reference electrode. The results can be summarized by the following equations: log(at.pct O)=−10,005/T+4.944(±0.012) Δμ_O2/4.606RT=logPO₂1/2=−13,550/T+4.411(±0.009) From simultaneous measurements of the potential and concentration of oxygen in melts, not in thermodynamic equilibrium with alumina and aluminate phases, information on the composition dependence of the activity coefficient and the standard free energy of solution of oxygen is obtained. For the reaction, 1/2O₂→O−N1 ΔG° = -72,930 - 7.11T (±840) J gr.at.^–1 logf_O={−500/T+0.216}at.pct O where the standard state for dissolved oxygen is that which makes the value of activity equal to the concentration (in at. pct) in the limit as concentration approaches zero. The oxygen solubility in liquid nickel in equilibrium with solid NiO, evaluated from thermodynamic data, is compared with information reported in the literature. Implications of the results to the deoxidation equilibria of aluminum in nickel are discussed.