Abstract
The author investigated the thermal dehydration of purified Japanese bentonites from three different origins. One of them is of a typical yellow species and the other two are of a white one. The chemical compositions are the following:
The thermal dehydration curves of each of these three samples belong to quite the same type, and a clear distinction may be made from that of other clay-like minerals, such as kaolinite, acid clays, silica or alumina gels. The curve can be cut into three distinct parts, that is, S-shaped (50-30°C), straight (100-600°C) and hook-like shaped (600-1100°C) part (Fig.)
Having discussed many known facts related to bentonites, the author can not help coming the following conclusions:
(a) In the dehydration curve, the S-shaped section corresponds to the loss of gel waters, the straight part to the dehydration of loosely fixed water of hydrated colloidal silica, and the hooklike shaped part to the so-called constitutional water of crystalline alsilicate.
(b) The empirical formulae of the ultimate particle of bentonite can be denoted as follows:
2Al2O3⋅(10-x)SiO2⋅H2O⋅xSiO2⋅Aq.
(c) The micelles in water may presumably have a construction like this that the very thin molecularordered crystalline layers of al-silicate plate hold colloidal silica between them with ample water in common. And the highly water-imbibing property can be attributed to the hydration and diffusion powers of swarmed ions which distribute between the plates.
Temp. in °C S5: yellow type: T1, Or: white type
