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Abstract. The effect of alumina additions on the ionic conductivity and mechanical properties of 3 and 8 mol% Y203-ZrO 2 compositions has been investigated. Such materials are of interest for use in fuel cells and other similar applications. Sintered specimens were characterised by XRD, SEM, impedance spectroscopy, four -probe DC conductivity and mechanical strength measurements. Alumina additions had no affect on the conductivity degradation behaviour at 1000 ~ and the activation energy but resulted in an increase in the strength of 8 mol% Y203 -ZrO2 composition by about 25%. However, a significant drop in the ionic conductivity well above what could be accounted for by the decrease in the volume fraction of the conducting phase, was observed.

The grain-boundary resistivity of tetragonal zirconia polycrystals, which had undergone creep with different applied compressive loads and at different temperatures, has been measured with impedance spectroscopy. A stress exponent of unity was determined from strain rate versus stress data. The grain-boundary resistivity decreased significantly with increasing stress at a constant creep temperature indicating squeezing out of the glassy phase from interfaces between grains. This, however, had no effect on the activation energy for the grain-boundary resistivity. [

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Abstract. Oxygen-ion conducting ceramic membrane materials (pure ionic or mixed ionic / electronic conductors) allow selective transport of oxygen in the form of ionic flux at high temperatures and can be used for the production of high purity oxygen. Such materials are also more appropriate for gas purification (residual oxygen removal) and control of oxygen levels in a gas stream to produce gases with known oxygen partial pressure. In this paper, operation and limitations of laboratory scale prototypes constructed from tubular zirconia -yttria membranes have been described for the removal of oxygen from air and low oxygen containing gases to produce oxygen-free gas streams and generation of calibration gases with pre-defined levels of oxygen.

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