Effect of Phase Composition in Solid Electrolytes of ZrO₂-8.1 mol%MgO on Oxygen Activity Measurement in Molten Steel

Abstract

Thermal-shock resistance and response performance of solid electrolytes for an oxygen probe applied in steelmaking processes were studied. One-end closed tubes of ZrO₂-8.1 mol% MgO with various volume fraction of cubic phase (V_c) were used for measuring oxygen activity in a production line, and changes of phase composition in ZrO₂ during immersion into molten steel were investigated. Good thermal-shock resistance was realized by decrease in the cubic phase whereas good response performance was obtained by increase in the cubic phase. For the ZrO₂-8.1 mol% MgO, an optimum fraction of cubic phase was 27%. The relationship between reliability of measured oxygen activity and the phase composition was also discussed.