X-ray and thermogravimetric studies of hydrated Li2WO4

Anhydrous Li2WO4 is moisture sensitive. On hydration, the X-ray diffraction (XRD) pattern of Li2WO4 exhibits dominant peaks attributable to 7Li2WO4·4H2O (cubic) and Li2WO4 (hexagonal), and thus reveals the extent of hydration of the material. The composition varies on heating at several temperatures as shown by the presence of new peaks in the diffractograms. On heating at 450 °C, diffraction peaks attributable to Li2W2O7 and LiOH.H2O are observed in the diffractogram. However, further heating at 550, 611, 645, 670 and 695 °C leads to the same dominant peaks due to Li2WO4, Li2W2O7 and Li2O. From the X-ray data, a reaction scheme or sequence of decomposition of hydrated Li2WO4 due to thermal effects is proposed, and from thermogravimetric (TG) analysis it is possible to correlate the decomposition curve with the X-ray data.