DEHYDRATION AND REHYDRATION OF VERMICUL ITES: II. PHLOGOPIT IC CA-VERMICULITE

ABSTRACT: Dehydration and rehydration of a phlogopitic Ca-vermiculite were studied by thermoanalysis (TG, DSC) and by in situ X-ray powder diffractometry. A detailed analysis of the relationship between temperature and state of hydration of the vermiculite close to equilibrium at atmospheric pressure was rendered possible by use of low heating rates in combination with a fast recording position-sensitive detector. The results reveal the existence ofa number of distinct states of hydration characterized by basal spacings of 1.515, 1.493, 1.473, 1.188, 1.176 and 0.95 nm. In confirmation of results obtained earlier with Mg-vermiculite, regular interstratification occurred at dehydration during the transition between two- to one- and between one- to zero-layer hydrates showing integral series of 001 reflections with basal spacings of 2.67 and 2.11 nm, respectively. In a previous paper describing hydration and dehydrat ion of Mg-vermicul i te (Graf v. Reichenbach & Beyer, 1994) a later publication of analogous data from vermiculites aturated with other species of divalent cations was promised. Accordingly, in the present paper, results obtaine