It was recalled that O transport through a dense O-conducting ceramic membrane was driven by an O-activity gradient which was imposed by gas streams on opposite sides of the membrane. The O activity on each side of the membrane was altered as O was transported across the membrane. Thus, the O activity gradient was not the same in each region of the membrane, and generated a different O flux. This interaction between the O gradient and the O flux could produce a lower average O flux across the membrane, mask differences between materials and explain the dependence of O-flux upon O-activity. An O flux model was developed which took account of the rate of O transport across the membrane, the reducing-gas flow rate and the reducing-gas composition when determining the O activity gradient which was imposed on the membrane. The model was checked by collecting O-flux data for a dense perovskite ceramic membrane at 1000C, under a wide range of concentrations and flow rates of CO and CO2, on one side, and air on the other side of the membrane. The results showed that an order of magnitude variation in the O flux could be produced merely by changing the reducing-gas flow-rate. The results helped to explain observed differences in O-flux data which had been reported for a range of conditions, and clarified the rate-limiting step in O transport through dense O-conducting ceramic membranes.

Influence of Gas Flow Rate upon Oxygen Flux Measurements for Dense Oxygen Conducting Ceramic Membranes. W.T.Stephens, T.J.Mazanec, H.U.Anderson: Solid State Ionics, 2000, 129[1-4], 271-84