The partial ionic and electronic conductivity of Y-containing and Y-free chromia scales

This work reports on the ionic and electronic partial conductivity, determined in situ by the Wagner asymmetry-polarization technique, of chromia scales thermally grown in 1 atm flowing oxygen at 900°C. Results show an activation energy of 0.3 eV for ionic conductivity and of 0.6 eV for electronic conductivity in the temperature range 300-700°C. After treatment with yttria, both the ionic and electronic conductivity were reduced; however, the activation energy was the same as the Y-free scales. This is consistent with previous results obtained from chromia scales grown in H2/H2O vapor. Comparison of the data between scales grown at low and high PO2 suggests that hydrogen doping in the scale can reduce both ionic and electronic conductivity by approximately one order of magnitude.