Observed phase transformations of oxalate-derived lead monoxide powder

Abstract

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-massieot phase transformation in a temperature range of 525-575~ In air, litharge, metastable at room temperature, slowly oxidizes to the Pb304 phase at a temperature of 350~ and rapidly reduces to litharge at 560~ At temperatures greater than 560~ litharge converts to massieot. With heating rates of 10 deg/min or higher, formation of Pb304 is not observed.

Crystal Structures and Topological Aspects of the High‐Temperature Phases and Decomposition Products of the Alkali‐Metal Oxalates M2[C2O4] (M=K, Rb, Cs)

“…In particular, in solid-state synthesis they are widely employed as versatile precursors for the preparation of multinary oxides along all-solid-state routes. [1][2][3][4][5] Two approaches are commonly used: either individual oxalates or mixtures of oxalates and oxides are decomposed thermally under mild conditions, thus providing particularly reactive binary oxides that can serve as reactants for solid-state synthesis, or various alternative precursors are treated directly with oxalates to yield the desired multinary oxide. In either case it would be highly desirable to know the conditions under which the decompositions occur and the structural evolutions during the course of the transformations to the corresponding intermediate carbonates, or oxides, respectively.…”

Selected-control hydrothermal growths of α- and β-PbO crystals and orientated pressure-induced phase transition

“…It is well known that the phase transition from the lowtemperature a-phase to high-temperature b-phase occurs at about 488 uC, [19][20][21][22][23] so that we performed the heat treatment of a-PbO crystal sheets at 600 uC for 10 hours and the results were as expected. The red a-PbO crystal has transformed into yellow b-PbO modification without shape breakage, as shown in Fig.…”

“…[12][13][14][15][16][17][18] The former two are also represented as minerals in nature: litharge, the red tetragonal a-PbO stable at room temperature; massicot, the yellow orthorhombic b-PbO stable above 488 uC. [19][20][21][22][23] Both of them adopt similar open-packed rocksalt-like structures which arise from the stereochemically active lone pair of Pb 2+ , but with different orientations and distortions of PbO 4 pyramid units (Fig. 1).…”

Comparative physicochemical evaluation of a marketed herbomineral formulation: Naga bhasma

“…As per scientific knowledge if pure PbO is heated in nitrogen atmosphere up to 600°, it contains substantially more massicot than those heated in air which is more acceptable form for preparing this formulation[15]. However, it was not clear how Naga bhasma is prepared by different manufacturers that have shown significant weight changes among themselves i.e., from -27.5 to +3.5% w/w.…”

“…A reconstructive litharge (PbO L ) to massicot (PbO M ) phase transformation occurs at temperature range of 525-575°. PbO L has tetragonal crystalline dark red color particles and PbO M has orthorhombic crystalline bright yellow color particles[1516]. This shows that all formulations contain PbO in litharge form in very high ratio which can be potentially dangerous for human health.…”