Liquid-Phase Formation in Reaction Process of 3PbO⋅Fe₂O₃⋅WO₃

Abstract

The liquid-phase formation around 690°C in the system of 3PbO⋅Fe₂O₃⋅WO₃ as a raw material of low-temperature-firing PbFe_2/3W_1/3O₃ was investigated. In DTA a sharp endothermic peak was observed at 690°C on heating, and an exothermic peak was found at 670°C on cooling immediately after that endothermic peak. The endothermic peak is interpreted as to be due to the formation of the liquid-phase from a certain intermediate unknown phase, and the exothermic peak on cooling is due to solidification of the liquid-phase. A rapid shrinkage in specimens was observed by TMA, and drastic changes in microstructure were also investigated by SFM and high temperature optical microscopy. A pyrochlore phase formed from the liquid-phase was determined to be Pb:Fe:W≈2:1:1.