PHASE-CHANGE OF YTTRIUM-CONTAINING HYDROU S-ZIRCONIA FINE PARTICLES

Yttrium-containing monoclinic hydrous-zirconia fine particles were hea ted from 300 to 700 degrees C to investigate the phase change to 2.8 m ol% Y2O3-doped tetragonal ZrO2. Both ZrOCl2 . 8H(2)O and YCl3 . 6H(2)O were dissolved into aqueous solutions and then boiled to make the hyd rous-zirconia particles, The hydrous-zirconia particles containing Y(O H)(3) were prepared by dropping aqueous ammonia into the boiled soluti ons, while hydrous-zirconia particles containing YClx(OH)(y) . nH(2)O were obtained by spray-drying of the boiled solutions. The monoclinic- to-tetragonal phase change of hydrous-zirconias containing Y(OH)(3) wa s observed at 400 degrees C by X-ray diffraction. The hydrous-zirconia s containing YClx(OH)(y) . nH(2)O transformed to tetragonal phase at 5 00 degrees C. The results of chemical analysis indicated that the atom ic ratio of Cl/Y decreased with increasing heat-treatment temperature, At 500 degrees C, this atomic ratio became less than 1, These experim ental results suggested that the hydrous-zirconias containing YClx (OH )(y) . nH(2)O transformed to tetragonal phase through the decompositio n reaction of YClx(OH)(y) . nH(2)O. Therefore, it is concluded that as the decomposition of YClx (OH)(y) . nH(2)O affects phase change, the temperature of phase change of hydrous-zirconias containing YClx (OH)( y) . nH(2)O becomes higher than those containing Y(OH)(3). X-ray diffr action and BET specific surface area measurements revealed that for hy drous-zirconia containing Y(OH)(3), the primary particle of small size with monoclinic phase was transformable to tetragonal phase at lower temperature comparing with that of large size, The hydrous-zirconias c ontaining YClx(OH)(y) . nH(2)O with smaller particle size also showed the similar tendency, This tendency can be explained by the increase o f the points contacted with yttrium and the shortening of diffusion le ngth in the hydrous-zirconia particle with small size.