Thermo-Raman spectroscopic studies on polymorphism in Na2SO4

The phase transformations involved in Na2SO4 (Na2SO4.10H(2)O as starting ma terial) and predried Na2SO4 in a dynamic thermal process of heating from 30 to 500 degrees C and then cooling down to 30 degrees C, with a heating/coo ling rate of 2 degrees C min(-1) in two consecutive thermal cycles, were mo nitored at 1 degrees C intervals by thermo-Raman spectroscopy (TRS). The tr ansformations were characterized on the basis of the disappearance of the b ands, appearance of new bands, splitting in the internal modes, change in t he spectral profile, intensity (area) changes in the internal modes, full w idth at half maximum (FWHM) of the totally symmetric stretching mode and ev en the variations observed in the background during the thermal process. Th is thermo-Raman investigation provided some evidence for the existence of a n intermediate phase between phase V and phase I and also for the changes o bserved in the phase I structure at higher temperatures, in addition to the dynamic transformations between the well known phase V, phase I, phase II and phase III. The intensity study on the nu(3) mode of SO42- clearly demon strated the thermal hysteresis involved among the phases during the heating and cooling process. The differences observed in the polymorphisms of Na2S O4 (Na2SO4.10H(2)O as starting material) and predried Na2SO4 were also disc ussed.