The dehydration of two sepiolites (the Kuzuu and the Sangju) was studied by means of DSC in the temperature range of 20°C-650°C. DSC curves show three endothermic peaks corresponding to the losses of zeolitic water (step I) and of bound water (step II and III).
Estimated ΔH-values in the Kuzuu are 10.6 kcal/H₂O mol for step I; 12.7, step II; 14.9, step III; and in the Sangju, 12.2 kcal/H2O mol for step I; 7.7, step II; 9.0, step III. Steps II and III follow a kinetic equation-1n (1-α)=kt except step II of the Kuzuu which follows 1-(1-α) ^1/3=kt. The kinetic compensation effect taking the form log A=α*+b characterizes the kinetic parameters obtained here as for step II log A=0.30*-0.93 and for step III log A=0.28*-1.57. No remarkable difference, however, is observed in the kinetic parameters for each step of two sepiolites.
Such thermal behaviors observed for these two sepiolites suggest that there is no difference in the structural properties of water molecules of two sepiolites, and that only the situation of the structural channels of sepiolite, which reflects such static conditions as crystalline-size, mode of the aggregation of crystallites and degree of regularity of structure, influences the ΔH-values and the reaction processes of dehydration.