The polarization conductivity, σ'(ω) of a Ca-montmorillonite has been determined by complex impedance spectroscopy. The technique of thermally-stimulated currents (TSC) leads to the determination of the different relaxation parameters, such as the distribution function of the different relaxation processes. The results demonstrated the coherence of the two approaches, and confirmed that the conducting phenomenon is due to the hopping of charge carriers between localized sites. The energy corresponding to the hopping process is evaluated using two different methods of analysis of the TSC signal. The values obtained are compared to those observed on a Na-montmorillonite.

Montmorillonite-water-cation systems were characterized using high-frequency impedance spectroscopy by studying the influence of the solid concentration and the nature of the exchangeable cation (Na+, K+, Ca2+) on the dielectric characteristics of the dispersions. A new method is proposed to calculate the relaxation frequency (fr) and the dispersion factor (α) from a limited number of impedance measurements. By comparison with rheology, microscopy, X-ray diffraction and immersion calorimetry results, it is shown that impedance spectroscopy is a very powerful technique which yields structural information on a complex system. For Na-montmorillonite, two transitions are observed at 2.5% and 3.6% in solids. The cation mobility and the number of connections between particles are described by fr and α, respectively. The two transitions can then be attributed to the formation of the gel and to the reduction of the macroporosity within the gel, respectively. For Ca-montmorillonite, thick layer-stacks form at the lowest concentrations, and connections between these stacks are observed at 9% in solids, in good aggrement with rheological measurements. The K-montmorillonite displays progressive thickening of the tactoids, and no formation of a unique connected network, as revealed by the smooth evolution of fr and α.

Ammoniation of montmorillonites pillared with polyhydroxo-complexes of Al was performed in flow conditions at 773–1073 K and monitored by IR spectroscopy. Interaction of the clay with ammonia revealed exchange of terminal and bridging -OH groups by NH2-, NH- and N- species depending on the reaction temperature. Amination begins at 773 K while formation of NH groups starts at 873 K. Transformation of NH- into N-species occurs at 973 K. A mechanism for the ammoniation reaction is proposed and the series of the relative reactivity of OH groups was established: Si–OH > Mg–OH–Mg > Al–OH–Mg > Al–OH–Al. This series was rationalized in terms of accessibility of the OH groups.

The thermal energy necessary for the removal of molecular water from Li+-, Na+-, Cs+-, Mg2+-, Ca2+-, Ba2+-, Alx(OH)yz+- and La3+-homoionic montmorillonite powders was determined by thermogravimetric analysis under atmospheric pressure. The weight loss curves and their derivatives exhibit one or several features related to the various populations of water molecules. The activation energy for water removal, which is the sum of the adsorption energy and the activation energy for diffusion, was calculated in each case using a simple first-order differentiation method. The results allow the physisorbed water and the water coordinated to the cations to be clearly separated. For the later population and with the exception of the Na-clay, a good correlation was found between the temperatures and activation energies for water removal and the polarizing power of the cations. Comparison with the results of mechanical tests performed on similar samples suggests that the creep of smectite clays is not controlled by mobility of the individual water molecules but by the mobility of the interlayer cations surrounded by their hydration shell.

Smectites of sedimentary series from a playa lake system from Calatayud Basin have been studied by XRD and TEM chemical microanalyses. Clay particle microanalyses show complete continuity between dioctahedral aluminous and trioctahedral magnesian smectites. Aluminous smectites have been classified as montmorillonites and ferribeidellites, both with compositional variability. They represent detrital phases resulting from weathering in the source area. Compositionally-intermediate smectites (beidellite-saponite and montmorillonite-stevensite) seem to correspond to weighted mean compositions of di- and trioctahedral phases stacked together in the same particle. They represent intermediate transitional stages from detrital to authigenic smectites in more distal basin facies. Trioctahedral smectites, although called saponites and stevensites, are actually random mixed-layer kerolite-Mg-smectite with a high percentage of expandable layers. They represent authigenic clays formed from solutions with high pH and Mg content as a result of evaporative concentration. The variability in composition of smectites, both within the same sample and amongst different samples, is a possible consequence of the heterogeneity in the local chemical environment, and so, equilibrium may be only reached locally in a large variety of microsystems.

Three clay minerals from southern and central Tunisia were characterized. Both XRD quantitative analysis and a chemical method were used to determine the mineralogical and physico-chemical characteristics of the <2 μm clay fractions. The XRD, CEC and specific surface measurement analyses showed that the dominant phase in all samples is illite-smectite with kaolinite and traces of quartz also present. From quantitative XRD, the abundances of the minerals identified are consistent with the measured CEC, specific surface area and TG/DTA properties. Analysis by XRD also showed that the illite-smectite phases are composed of thin stacks (two to a maximum of ten layers per stack) of random illite-smectite and ordered (R1) illite-smectite. There is also some discrete illite.

The MudMaster computer program, based on the modified Bertaut-Warren- Averbach (BWA) XRD method, was used in the study of diagenetic evolution of illitic material in shales. The illitic material was characterized by XRD as a mixture of illite-smectite (I-S) and discrete illite. The experimental conditions for complete dehydration of swelling clays, necessary in this method, were established for a climate of high relative humidity (RH >40%). It was found that the distribution of crystallite thickness of dehydrated illitic material of shales is described by the lognormal law, as was established earlier by the BWA method for pure I-S from pyroclastic rocks. The parameters characterizing this distribution evolve with depth: the mean crystallite thickness (Te), the distribution broadening (DW) and the parameter of a lognormal distribution (β2) increase, whereas the percentage of the most frequent crystallite thickness decreases. The observed scatter of values is not random but indicates fluctuations in the characteristics of the illitic material of shales. The results imply that the modified Scherrer technique of measuring mean crystal thickness from the broadening of XRD reflections can be extended at least to some shales.

Lower Cretaceous clay minerals suites of the Alava Block, analysed by XRD, are dominated either by illite or kaolinite. These assemblages are mainly inherited in origin, although textural evidence (SEM) indicates some diagenetic clay. Precipitation of blocky kaolinite took place in sandstones from the southern domain of the Block, characterized by low sedimentation and subsidence rates and by low vitrinite reflectance values (%Rr <0.8). In the northern domain, where sedimentation and subsidence rates were high (%Rr >3.3), illitization of kaolinite and smectitic clays and precipitation of authigenic chlorite occurred. Some chemical aspects of these reactions are discussed.

Allophane-like materials occur in the weathered zones of the phosphate-rich veins hosted in Silurian metasediments of the Catalonian Coastal Ranges. These metasediments also host sulphide and phosphate sedimentary mineralizations. Mineralogical and geochemical investigations of the allophanic samples indicate that they comprise Si-rich allophane, with a molar SiO2/Al2O3 ratio ranging between 1.19 and 2.23, with amorphous Al-(Ca) phosphate and hydroxylapatite as major minerals, and minor goethite and quartz. It is assumed that allophane, amorphous Al-(Ca) phosphate and hydroxylapatite come from the reaction of acid solutions, released during the weathering of sulphide interbedded in black shales, with phosphate-rich veins and volcano- sedimentary host rocks. Silica-alumina gels were deposited in fissures and cavities left by a previous dissolution of the phosphate-rich veins. Later the phosphate minerals filled the conchoidal microfractures and shrinkage microcracks of the allophane.

The Bertaut-Warren-Averbach (BWA) technique and high-resolution transmission electron microscopy (HRTEM) were used to characterize the products of dry-ground pyrophyllite. Mean crystallite thickness and crystallite thickness distributions were measured for each sample using the BWA technique. Mean crystallite thickness decreases during the treatment with respect to grinding time and energy applied per unit mass. The BWA data were checked by HRTEM measurements and good fits were obtained for samples having small mean particle thicknesses. Samples with thicker particles could not be measured properly by HRTEM because the number of particles counted from images is statistically insufficient. The shape of the crystallite and the particle-size distribution were used to determine the mechanism of pyrophyllite particle degradation. Particles initially having a lognormal size distribution are first delaminated randomly, then some are delaminated preferentially, thereby producing polymodal thickness distributions. Finally all particles undergo delamination yielding a lognormal thickness distribution.

Five palygorskite samples with different chemical compositions and specific surface areas (SSA) were used for this study. Batch experiments in dilute salt solutions under neutral conditions were conducted to study the kinetics of clay hydrolysis. The rates of release of Mg and Si differ significantly among the palygorskite samples. It was found that differences in release rate of Mg among the palygorskite samples are due to differences in both surface area and chemical composition. The rate of release of Mg was greater in palygorskites with high SSA and high Mg and Fe contents than that in palygorskites with low SSA and high Al content. The rate of release of Si depends on the SSA of the mineral and is not related to chemical composition. The initial amount of Si released increases with SSA, while the Si rate of release decreases with increasing SSA. These data suggest that the decomposition of palygorskite in soils and sediments also takes place under neutral conditions.

Kaolinite hydroxyls in dimethylsulphoxide-intercalated (DMSO-intercalated) kaolinites have been determined using Raman spectroscopy at 298 and 77 K. The inner surface hydroxyl frequencies at 3650, 3670, 3684 and 3693 cm-1 move to higher wavenumbers upon cooling to 77 K and are observed at 3659, 3676, 3692 and 3702 cm-1. The inner hydroxyl frequency is at 3620 cm-1 at 298 K and is at 3615 cm-1 at 77 K. Upon intercalation with DMSO, additional bands are found at 3660, 3536 and 3501 cm-1 for the low-defect kaolinite and at 3664, 3543 and 3509 cm-1 for the high-defect kaolinite at 298 K. The 3660 cm-1 band at 298 K is resolved into two bands at 3658 and 3663 cm-1 at 77 K for the low-defect kaolinite and these bands are assigned to the inner surface hydroxyl groups, hydrogen-bonded to the DMSO molecule. It is proposed that the DMSO molecule exists with two different orientations in the intercalate and these two molecular forms are differentiated by the OH-stretching bands of the inner surface hydroxyl groups. This band for the high-defect kaolinite is found at 3664 cm-1 at 298 K and resolves into two bands at 3664 and 3673 cm-1 at 77 K.