Phase stability and microstructural characteristics of 12 mol% (Mg, Ca)-PSZ prepared via polymeric route

Urea-formaldehyde resin was used as a precursor for the processing of ultrafine 12 mol% (Mg, Ca)-PSZ powders with uniform morphology. 12 mol% CaO stabilized zirconia was subjected to extensive cracking on reheating between 1400 and 1500 °C. The cracking phenomenon was found to be due to the tetragonal to monoclinic phase transformation. MgO equal to CaO was added at 3, 6 and 9 mol% to improve the stability of tetragonal zirconia. The crystallization of tetragonal zirconia from the amorphous powders occurs between 400 and 500 °C. The stability of tetragonal zirconia was found to increase with addition of MgO. The addition of MgO, combined with fast heating during hot pressing, activates the densification process by acting as a sintering aid and reducing the relative degree of structural coarsening. Optimized stability of tetragonal zirconia and good microstructure were achieved at equal proportions of MgO and CaO.