RELIABILITY OF KINETIC MEASUREMENTS FOR THE THERMAL DEHYDRATION OF LITHIUM-SULFATE MONOHYDRATE .2. THERMOGRAVIMETRY AND DIFFERENTIAL SCANNING CALORIMETRY

There is a great need for objective assessments of the quality, reliability and significance of kinetic data obtained for thermal decompositions of solids. In the first part of this study, kinetic parameters for the thermal dehydration of single crystal and powdered samples of lithium sulphate monohydrate (Li2SO4 . H2O) derived from isothermal measurements of the pressure of water vapour evolved in an initially evacuated, constant-volume apparatus, were examined critically. In this complementary study, kinetic parameters derived from thermogravimetry (TG) and differential scanning calorimetry (DSC), in both isothermal and programmed-temperature modes, are compared with the earlier results. The reproducibilities of the several techniques have been examined and the problems of calibration of TG instruments in the low-temperature region are discussed. Arrhenius parameters are compared with previously published values, and parameters from isothermal measurements are compared with those obtained using programmed-temperature measurements. Differences in behaviour arising from different sample preparations and from the different experimental techniques are discussed.