Thermo-raman studies on dehydration of Na4P2O7•10H2O and phase transformations of Na4P2O7

In this work, dehydration of sodium diphosphate decahydrate Na4P2O7. 10H(2)O and phase transformations of Na4P2O7 in open air have been studied in detail by thermo-Raman spectroscopy. The spectra were measured continuously in a temperature range from room temperature up to 600 degreesC for the bands of P2O74- and H2O. The spectral variation showed one step of dehydration and four-phase transformations. The thermo-Raman intensity (TRI) and differential thermo-Raman intensity (DTRI) curves calculated from the characteristic bands of H2O also showed one step of dehydration with the loss of all hydrated water in the temperature interval from 45 to 69 degreesC. Thermogravimetric measurements supported this result. The thermo-Raman investigation indicated the transformation of Na4P2O7 from low temperature phase to high temperature phase proceed through pre-transitional region from 75 to 410 degreesC before the major orientational disorder at 418 degreesC and minor structural modifications at 511, 540 and 560 degreesC. The results from differential scanning calorimetry and differential thermal analysis on Na4P2O7 showed endotherms at 407, 517, 523, 548, 557 degreesC and 426, 528, 534, 555, 565 degreesC, respectively.