Calcia stabilised tetragonal zirconia powders prepared by urea formaldehyde polymeric route

Tetragonal zirconia powder stabilised by 15 mol-% calcia was prepared via a urea formaldehyde polymeric route. Two different concentrations equivalent to I and 4 mole zirconium oxide in the form of zirconium chloride were added to the resin during formation. The content of volatiles affected the grain size of the zirconia phases developed. A change in the dopant content of the tetragonal zirconia phase was detected by EDAX in the original grains, in white spots that appeared near the periphery of the original grains, and in small intragranular particles. The growth of the intra-granular particles beyond the critical grain size induced stresses that led to partial transformation to the monoclinic phase in powders fired at 1500? C for 2 h and those annealed at 1300?C for 5 h. BCT/384 The authors are in the Department of Ceramics, National Research Centre, Dokki, Giza, Egypt. Manuscript received 13 May 1999; in final form 12 April 2000.