Thermal stability of flame-made zirconia-based mixed oxides

The thermal stability of pure and doped zirconia fabricated by flame spray pyrolysis (FSP) is studied by calcination at various temperatures and residence times. Powders are analyzed by X-ray diffraction (XRD), nitrogen adsorption (Brunauer-Emmett-Teller), energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). The metastable tetragonal structure of flame-made ZrO2 transformed to the monoclinic phase after sintering. Doping zirconia with yttria, ceria, lanthanum oxide, alumina, or silica increased its thermal stability and also hindered that phase transformation. For all doped powders, no monoclinic phase is formed during calcination. The combination of 25 wt % ceria, 10 wt % lanthanum oxide, and 65 wt % zirconia had the highest thermal stability.