Solid-state vibrational spectroscopy. Part IV. A vibrational and differential scanning calorimetry study of the polymorphism of sodium and potassium sulphates

Abstract

The polymorphism of sodium and potassium sulphates has been studied using differential scanning calorimetry (d.s.c.) and vibrational spectroscopy. For Na₂[SO₄] the d.s.c. study has yielded enthalpy changes for the various phase transitions. The polymorphs have distinct Raman spectra whereas the i.r. spectra do not show such distinct differences. The phase-transition temperature of K₂[SO₄] is outside the range of the d.s.c. instrument, but the vibrational spectra indicate that K₂[SO₄], unlike Na₂[SO₄], does not exist in a metastable phase on cooling below the transition temperature.