Determination of the equilibrium temperatures and enthalpies of the solid–solid transitions of rubidium nitrate by differential scanning calorimetry

The equilibrium temperatures of the three solid–solid phase transitions of high purity rubidium nitrate have been measured accurately by stepwise heating and by the extrapolation to zero heating rate method. Mean values of 164.9 ± 0.1 °C (transition 1), 222.2 ± 0.5 °C (transition 2) and 284.0 ± 0.1 °C (transition 3) were obtained using two different types of heat flux DSC instruments. The enthalpies of transitions 1 and 2 were determined using both heat flux and power compensated DSC instruments. The mean values were 3.83 ± 0.02 kJ mol−1 (transition 1) and 3.14 ± 0.03 kJ mol−1 (transition 2). For transition 3 the shape of the DSC curve prevented an unequivocal determination of the enthalpy. Values obtained using two alternative interpretations of the DSC peak shape are discussed in the text.