Thermal stability of transition phases in zirconia-doped alumina

Alumina was prepared from an aqueous salt solution by homogeneous precipitation followed by calcination in air. Dependence of the thermal stability of transition phases on the presence of a zirconia dopant and on autoclave treatment prior to calcination was investigated using X-ray diffraction (XRD), differential thermal analysis coupled with thermogravimetric analysis (DTA-TGA) and transmission electron microscope (TEM) analysis. Homogeneous precipitation produced an amorphous trihydrate precipitate; the autoclave treatment converted this to crystalline boehmite (monohydrate). The zirconia was soluble in the transition alumina but was insoluble in alpha-Al2O3 so that phase transformation to alpha-Al2O3 was accompanied by a phase separation to form an alumina-zirconia nanocomposite. The thermal stability of the transition phases was increased both by the dopant and by the autoclave treatment. A combination of both parameters yielded the most stable transition alumina, which withstood 1 h at 1200 degrees C without transformation to alpha-Al2O3.