Thesis (Ph. D.)--University of New South Wales, 2005. / Also available online.

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Coastal clay deposits are an increasingly important focus of environmental and geotechnical studies, and to date, geophysical techniques for mapping them have almost exclusively relied on bulk conductivity measurements. However, direct correlation of bulk conductivity data is difficult, as it is a non-unique parameter. A potential alternative geophysical mapping tool is the complex conductivity technique, where both in-phase and out-of-phase conductivity are measured concurrently. Using similar principles, the induced polarisation field technique measures the charge polarisation parameter chargeability. Studies that utilise these techniques have almost exclusively concentrated on the charge polarisation properties of sediments with low clay contents, and these sediments have intuitively credible positive chargeability values. However, the few studies that include high-clay-content sediments ??? like those encountered in coastal clay deposits ??? have often reported negative chargeabilities. No mechanism has been presented that accounts for this effect. Similar negative chargeability effects have been noted in other sciences, but often remain unexplained. Negative chargeability is shown here to be a non-linear property of clay gels ??? unique to sediments with bulk membrane properties and a potential new clay mapping parameter. A new clay polarisation model is presented which accounts for negative chargeability. Clay sediments are considered as a clay gel membrane, as opposed to traditional models ??? of clay zones within a solid substrate. In the revised model, non-linear ionic gradients occur within the sample, due to the bulk membrane properties of clay gels. Charge dispersion is described in terms of anomalous diffusion Warburg impedances, which create currents in the opposite sense to the applied potential. Negative chargeability is then a unique feature of sediments with bulk membrane properties. Laboratory electrical impedance spectroscopy (EIS) data are presented. The experimental data covers a variety of clay types at a variety of water contents. For pure clay samples, negative chargeability is shown to occur when the clay???s water content is such that it is in a gel state. The threshold water content is shown to be a function of the clay???s liquid limit. This trend is more complicated for natural clays. Field measurements of negative chargeability are presented. The Conductivity Cone Penetrometer (CCPT) is utilised as a chargeability-logging tool at a field site at Hexham, New South Wales. In the first study of its kind, negative chargeability CCPT logging is shown to be effective in mapping a coastal clay deposit.

Coastal clay deposits are an increasingly important focus of environmental and geotechnical studies, and to date, geophysical techniques for mapping them have almost exclusively relied on bulk conductivity measurements. However, direct correlation of bulk conductivity data is difficult, as it is a non-unique parameter. A potential alternative geophysical mapping tool is the complex conductivity technique, where both in-phase and out-of-phase conductivity are measured concurrently. Using similar principles, the induced polarisation field technique measures the charge polarisation parameter chargeability. Studies that utilise these techniques have almost exclusively concentrated on the charge polarisation properties of sediments with low clay contents, and these sediments have intuitively credible positive chargeability values. However, the few studies that include high-clay-content sediments ??? like those encountered in coastal clay deposits ??? have often reported negative chargeabilities. No mechanism has been presented that accounts for this effect. Similar negative chargeability effects have been noted in other sciences, but often remain unexplained. Negative chargeability is shown here to be a non-linear property of clay gels ??? unique to sediments with bulk membrane properties and a potential new clay mapping parameter. A new clay polarisation model is presented which accounts for negative chargeability. Clay sediments are considered as a clay gel membrane, as opposed to traditional models ??? of clay zones within a solid substrate. In the revised model, non-linear ionic gradients occur within the sample, due to the bulk membrane properties of clay gels. Charge dispersion is described in terms of anomalous diffusion Warburg impedances, which create currents in the opposite sense to the applied potential. Negative chargeability is then a unique feature of sediments with bulk membrane properties. Laboratory electrical impedance spectroscopy (EIS) data are presented. The experimental data covers a variety of clay types at a variety of water contents. For pure clay samples, negative chargeability is shown to occur when the clay???s water content is such that it is in a gel state. The threshold water content is shown to be a function of the clay???s liquid limit. This trend is more complicated for natural clays. Field measurements of negative chargeability are presented. The Conductivity Cone Penetrometer (CCPT) is utilised as a chargeability-logging tool at a field site at Hexham, New South Wales. In the first study of its kind, negative chargeability CCPT logging is shown to be effective in mapping a coastal clay deposit.

This thesis is submitted in a format of published papers by the candidate. Advanced methods of electron microscopy and X-ray spectroscopy have been used to study the relationship between the pillars and the silicate structure ranging from Al13 and Ga13 complexes to the final products Al- and Ga-pillared clays. The Al13 and Ga13 pillared montmorillonites have been prepared by conventional and ultrasonic methods. The ultrasonic method has been proven to be effective and showed very good catalytically activity. Transmission electron microscopy combined with elemental mapping by EDS showed the distribution of the Ga and Al pillars in the clay structure. The use of gallium allowed the independent observation of the Ga pillar distribution from the Al distribution in the clay structure. XPS spectra of the Ga13 pillared montmorillonites showed that the pillars has been changed from the original Keggin structure with a 7+ charge to something more stable with a lower charge upon intercalation. No direct evidence of the inverted silicon tetrahedron structure bonding to the pillar structure, as suggested by Plee in his original thesis, was observed. For comparative reasons the major aluminium hydroxide minerals in bauxite (gibbsite, bayerite and (pseudo-) boehmite) were studied. Detailed information about the Al13 structure was obtained by studying the basic sulphate and nitrate salts with XPS. The XPS results of a set of starting clays in comparison to the pillared clays indicated that small changes in the binding energy could explain the changes in the pillar structure and the formation of chemical bonds to the clay tetrahedral sheets during the calcination leading to the final products.

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