Sol-gel processing of alumina-zirconia minispheres

Alumina-zirconia minispheres were prepared by the sol-gel method. The starting material used for the preparation of alumina sol was aluminium-tri-isopropoxide. Zirconia sol was prepared from zirconium oxychloride. Required quantity of zirconia sol was added to alumina sol, so that the final composite contains 5, 10, 15, and 20 wt.% zirconia. A suitable binder was added to the mixed sol and aged at room temperature for some gelation to occur. At the appropriate viscosity, spheres were formed in ammonia solution. The spheres were dried at room temperature and then sintered at 1300 °C for 2 h. X-ray diffraction (XRD) analysis shows the presence of α-Al2O3 in alumina spheres and α-Al2O3 and t-ZrO2 in spheres containing 5 wt.% zirconia. Monoclinic ZrO2 is also present in spheres containing higher amount of ZrO2. Thermogravimetric analysis indicated the removal of most of the volatile up to 600 °C. Differential thermal analysis shows, that the α-Al2O3 phase transformation temperature is higher for sample containing zirconia. Fourier transform infrared spectroscopy (FTIR) indicated the phase transition to α-Al2O3 in corroboration with X-ray studies. The density of the sintered spheres was found to be highest for spheres containing 10 wt.% zirconia.