Hydrothermal synthesis and sintering of fine powders in CeO2-ZrO2 system

Abstract

Fine powders in CeO2-ZrO2 system have been prepared from the precipitate mixtures of cerium (III) nitrate solution, zirconium oxychloride solution and an excess amount of ammonia under hydrothermal conditions at 180°C, and their changes in crystal phase and surface area by calcination, sinterability, the crystal phase and the microstructure of the sintered bodies have been investigated. Twelve mol% CeO2-doped fine zirconia powders hydrothermally synthesized showed metastable cubic zirconia phase without monoclinic phase and they gradually transformed into tetragonal phase by calcining at above 600°C. The samples except for 12 mol% CeO2-ZrO2 consisted of two phase mixtures of zirconia and ceria. The crystallite size of 12 mol% CeO2-doped zirconia particles and CeO2 particles in the 70 mol% CeO2-ZrO2 powder was about 6 nm and 20 nm, respectively. Dense CeO2-ZrO2 ceramics were obtained by sintering these powders at above 1400°C for 1h. The sinterability of the powders increased with increasing CeO2 concentration. The calcined 80 mol% CeO2-ZrO2 powders pressed at 98 MPa reached a maximum density with single cubic CeO2 solid solution at 1300°C for 1h. The average grain size of 12 mol% CeO2-doped tetragonal zirconia ceramics sintered at 1500°C was 1.5 μm. Although the grain size of the sintered body in the two-phase region (tetragonal zirconia and cubic CeO2 solid solution) was below 1.0 μm, it increased with increasing CeO2 concentration within the single phase region of cubic CeO2 solid solution.