De Siqueira, Ascenso Vieira da Cruz; (2001) High pressure and temperature studies of 2:1 swelling clays. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The aim of the project was to study the effect of pressure and temperature on smectite clays. Monte Carlo modelling and Neutron Diffraction experiments were the main techniques used throughout this work. In this thesis, computer simulations of swelling clays under sedimentary basin conditions have been carried out for the first time. This has led to the first predictions of the interlayer water structure at elevated temperatures and pressures. In the course of this work, both Na- and Ca-saturated smectites and vermiculites have been simulated. As a result, this work has encompassed the first simulations of Ca++ ions in a confined environment. An altemative stmcture for the hydration shell of Ca++ in vermiculite is proposed that suggests partial hydration by the basal oxygen atoms. This reduces the number of water molecules in the hydration shell from 8 to 6. Experimentally, this has been the first in situ measurement of clay dehydration with higher p/T at the correct 'depth' for I/S transition. The work has demonstrated that this reaction is reversible up to a point, beyond which dehydroxylation and structural changes at the clay sheet level take place, rendering rehydration impossible. The experimental work has resulted in the first direct confirmation that interlayer water density is higher than in the bulk, under the same p/T conditions.

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