Mixed ionic and electronic conduction in zirconia and its applications in metallurgy

Abstract

Mixed ionic and electronic conduction in Zr0₂-based solid electrolytes was studied.The effect of impurities and second-phase particles on the mixed conduction parameter, P,, was measured for different types of ZrO₂ electrolytes. The performance of solid-state sensors incorporating ZrO₂ electrolytes is sometimes limited by electronic conduction in ZrO₂, especially at temperatures > I800 K. Methods for eliminating or minimizing errors in measured emf due to electronically driven transport of oxygen anions are discussed. Examples include probes for monitoring oxygen content in liquid steel as well as the newly developed sulfur sensor based on a ZrO₂(Ca0) + CaS electrolyte. The use of mixed conducting ZrO₂ as a semipermeable membrane or chemically selective sieve for oxygen at high temperatures is discussed. Oxygen transport from liquid iron to CO + C & gas mixtures through a ZrO₂ membrane driven by a chemical potential gradient, in the absence of electrical leads or imposed potentials, was experimentally observed.