Interpretation of D.T.A. diagrams: the low temperature endothermic peak

Extract

Differential thermal analysis has been used by Hendricks, Nelson and Alexander (1940) to study the sorption of water by montmorillonite. They measured the water uptake at a number of different relative humidities and then traced the low temperature endothermic peak of the resultant material on a differential thermal apparatus. They found that the resultant curves of Mg, Ca, Sr, Ba and Li-montmorillonite showed a division into two components at low relative humidities. Assuming that the area under the D.T.A. curve was proportional to the weight of water lost, a division of the total sorbed water was made between the two peaks. The authors found that for Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ the high temperature component represented approximately 5—6 water molecules per exchange ion, whilst for Li⁺ it corresponded to 3·3 water molecules per exchange ion.