In situ phase analysis of the thermal decomposition products of zirconium salts

X-ray powder diffraction at high temperature was used to determine the phas e composition of the thermal decomposition products of two zirconium salts, Zr(SO4)(2). 4H(2)O and ZrO(NO3)(2). 2 H2O, and of a mixture of zirconium n itrates having Zr(OH)(2)(NO3)(2). 4.7 H2O and ZrO(NO3)(2). 2H(2)O as domina nt components. Heating of the samples up to 1200 degrees C was performed in side a high-temperature chamber, attached to a diffractometer, at an air pr essure of approximate to 2 x 10(-3) Pa. Regardless of the structural differ ences in the starting salts, thermal decomposition products crystallized to t-ZrO2 which remained stable up to 1200 degrees C. This result indicated t hat the structural nature of the starting materials was not the most import ant factor of metastable t-ZrO2 formation. The thermodynamically stable m-Z rO2 appeared after the cooling of the samples to room temperature. If the c ooling was performed at low air pressure, the m-ZrO2 content was small. Int roduction of air, even at RT, caused a considerable increase of m-ZrO2, whi ch became the dominant phase in all cases. The important role of oxygen in the t-ZrO2 --> m-ZrO2 transition indicates that the lack of oxygen in the z irconia lattice favours the formation of metastable t-ZrO2.