Use of Stabilized ZrO2 to Measure O2 Permeation

The rate of permeation of CaO-stabilized ZrO₂ (CSZ) by O₂ gas was measured from 640° to 1200°C with the CSZ tubing used simultaneously as the sample and the O₂ pressure detector. The apparent permeation rate depended significantly on the O₂ pressure at the low-pressure side. The rate measured by this method was orders of magnitude smaller than that measured under steady-state conditions, except when the O₂ partial pressure was high (>10^?4 atm), in which case the agreement was good. The difference between steady-state permeability and non-steady-state permeability is related to the deviation in stoichiometry in a sample or detector. The transient response (measured under variable pressure difference) may be very different from steady-state permeation (measured under constant differential pressures across the membranes). To apply CSZ to typical O₂ gas permeability measurements, the O₂ pressure must be kept above ～ 10^?3.5 atm. In this range, the permeability of CSZ may be regarded as a temperature-dependent material property which is governed by the electron-hole mobility. At lower O₂ pressures the permeation rate is a more complex function of the pressure difference and level.