TETRAGONAL NANOPHASE STABILIZATION IN NONDOPED SOL-GEL ZIRCONIA PREPARED WITH DIFFERENT HYDROLYSIS CATALYSTS

Sol-gel zirconia was prepared with zirconium n-butoxide and HCl, H2SO4 , C2H4O2, and NH4OH as hydrolysis catalysts, Samples were characterize d with DTA and TG analysis, X-ray powder diffraction, and FTIR spectro scopy, The structure of the crystalline phases was refined by the Riet veld method, When samples were annealed below 300 degrees C, they lost weight and had an amorphous structure that, by annealing at higher te mperatures, crystallized into nanostructures. For H2SO4 as hydrolysis catalyst, the amorphous structure was stable even at higher temperatur es, which was probably caused by the presence of SOx ions in the struc ture, The local order in the amorphous phase was similar to the local order in the tetragonal zirconia, Crystallization of the amorphous pha se produced tetragonal and monoclinic nanophases, with the tetragonal as the main phase. Both phases had a similar average crystallite size, By annealing, the tetragonal nanophase, which was more stable when C2 H4O2 was the hydrolysis catalyst,,vas transformed into the monolinic n anophase, Since not only OH- ions in the structure were detected with FTIR spectroscopy but also Zr vacancies were measured with X-ray powde r diffraction in the zirconia crystalline structure, we propose that t hese defects stabilized the tetragonal phase, Both defects disappeared when samples were annealed at high temperatures, which brought about the irreversible transformation of the tetragonal into the monoclinic structure, (C) 1998 Academic Press.