Phase transition behavior of MnO2 and CeO2 co-doped calcia stabilized zirconia under CaF2-based basic flux at high temperature

Abstract

MnO2 and CeO2 co-doped 5 mol% calcia stabilized zirconia (CSZ) was investigated for its phase stability, and chemical stability under CaF2-based basic flux at high temperature. The MnO2 content was fixed at 1 mol%, while CeO2 varied from 0.5 to 2.0 mol%. Monoclinic phase fraction was reduced from 33.7 % to 10.3 %, with higher CeO2 content. After the reaction at 1550 degrees C, the monoclinic phase fractions in all samples were increased, but they were remained lower with higher CeO2. Mn and Ce ions existed mainly as Mn2+ and Ce4+, while the Mn4+ and Ce3+ ratios were increased with CeO2 addition by electrochemical equilibrium. Flux composition analysis revealed MnO2 content in the flux increased with doping, while CeO2 content remained below 0.007 %. The phase stability was improved through size effects due to changes in the oxidation state of dopant ions, and the chemical stability was enhanced due to the low solubility of CeO2 under basic flux at high temperatures.