Sol-emulsion-gel synthesis of alumina-zirconia composite microspheres

Oxide microspheres in the system Al2O3-ZrO2 (AZ), with the Al2O3:ZrO2 molar ratios as 87:13, 78:22, 74: 26 and 64: 36 were obtained from emulsified bi-component sols by the sol-emulsion-gel method. The surfactant concentration and viscosity of the sols were found to affect the characteristics of the derived microspheres. The gel and calcined microspheres were investigated by using thermogravimetry analysis (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD), optical and scanning electron microscopy (SEM) and particle size analysis. TGA indicated the removal of most of the volatiles, i.e. 40 +/- 2 wt% up to about 500degreesC. Crystallization of gel microspheres at about 900degreesC was confirmed by DTA and XRD. XRD results also indicated the retainment of tetragonal (t-) ZrO2, in the absence of stabilizers, at 1600degreesC. The optical and scanning electron microscopy confirmed the spherical morphology of the gel and calcined particles. The particle size distribution of the AZ microspheres calcined at 1200degreesC for 1 h exhibited a size range of 5-60 mum with the average particle size (d(50)) varied from 23 to 26 mum.