Abstract
The bound water dehydration of sepiolite was studied by high temperature X-ray diffractometry, thermogravimetry under controlled water vapour pressure and kinetic analysis of TG curves. The results show that the uniform folding of sepiolite crystals occurs when about 50% of the bound water is lost, entrapping the rest in the crystals. Before the folding, the dehydration rate is controlled by the water separation process from the magnesium atoms at the edges of channels, while, after the folding the rate is determined by the water diffusion process in the folded channels. Kinetic evaluation of TG curves yields an activation energy of 94 kJ mol −1 for the Kuzuu sepiolite and 106 kJ mol −1 for the Eskisehir sepiolite before the folding. The energy increases to 176 kJ mol −1 for the Kuzuu and 170 kJ mol −1 for the Eskisehir after the folding. It has been confirmed that the two-step dehydration of bound water is caused by the following two factors: (1) the difference in the activation energy of dehydration between the water in the unfolded open channel and that in the folded one, and (2) the change in the rate determining process from the water separation process to the water diffusion one.
Published Version
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