DIFFUSION OF TRANSITION-METALS (CO,NI) AND ITS EFFECTS ON SOL-GEL DERIVED ZRO2 POLYMORPHIC STABILITIES

Transition-metal-incorporated ZrO2 gel matrices have been prepared by an impregnation method. The polymorphic forms of the studied gels at r oom temperature were determined by Fourier-transform IR (FTIR) spectro scopy and X-ray diffraction (XRD) techniques, and the phase transforma tion behaviour of the gels was investigated with using differential th ermal analysis (DTA) methods. For both undoped and doped ZrO2 gels, DT A reveals metastable tetragonal-monoclinic-tetragonal-cubic phase tran sformations in the heating process up to 1400 degrees C. A high-temper ature tetragonal-monoclinic transition is also observed in the cooling process. For the metal-loaded ZrO2 gels, it is found that the diffusi ng metal cations stabilize the low-temperature tetragonal phase. Howev er, for high-temperature (900 degrees C) calcined gels, both as-prepar ed and metal-stabilized tetragonal phases are reduced substantially, C orrelations between metal diffusion and gel polymorphic stabilities ar e also demonstrated.