OBSERVED PHASE-TRANSFORMATIONS OF OXALATE-DERIVED LEAD MONOXIDE POWDER

The purpose of this study is to elucidate the nature of the phase transformations of lead monoxide powder. Lead monoxide is prepared by calcination of a lead oxalate precursor salt, and its phase transformations are studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TG). Analysis reveals that the phase transformations observed for oxalate-derived lead monoxide powder are highly dependent on the firing atmosphere. In nitrogen, as the temperature is increased 1 deg/min from room temperature, lead monoxide undergoes a reconstructive litharge-to-massicot phase transformation in a temperature range of 525-575-degrees-C. In air, litharge, metastable at room temperature, slowly oxidizes to the Pb3O4 phase at a temperature of 350-degrees-C and rapidly reduces to litharge at 560-degrees-C. At temperatures greater than 560-degrees-C, litharge converts to massicot. With heating rates of 10 deg/min or higher, formation of Pb3O4 is not observed.