Thermo-Raman studies on NaH2PO4•2H2O for dehydration, condensation, and phase transformation

Thermo-Raman spectroscopy was applied to study the thermal properties of NaH2PO4. 2H(2)O from room temperature up to 600 degreesC. Raman spectra recorded at every degree of the temperature interval by monitoring the internal modes gave the microscopic picture of dehydration of NaH2PO4. 2H(2)O, the condensation of NaH2PO4, and the phase transformation of NaPO3. The spectral variation observed could distinguish two steps of dehydration, resulting in the formation of NaH2PO4.H2O and NaH2PO4 as compositional species from NaH2PO4. 2H(2)O. The thermo-Raman intensity (TRI) and differential thermo-Raman intensity (DTRI) thermograms also showed two steps of dehydration in the temperature range from 42 to 52 degreesC and from 60 to 72 degreesC with a maximum rate at 48 and 68 degreesC, respectively. Furthermore, condensation resulted in sodium dihydrogen diphosphate (Na2H2P2O7) and sodium metaphosphate (NaPO3) in two steps at 212-224 and 60-360 degreesC, respectively. Clear evidence in the, spectral variation representing two phase transformations of NaPO3 at the temperature of 345 and 515 degreesC with three different polymorphs (phase III, phase H, and phase I of NaPO3 in increasing order of temperature) was also observed. The thermal methods thermogravimetry, differential thermogravimetry, differential thermal analysis, and differential scanning calorimetry also supported the results but could not give a clear idea due to the lack of direct structural information.