Recent development of the intersalation method by which kaolinite (as well as dickite and halloysite) is expanded makes possible the application of X-ray diffraction to qualitative and semiquantitative determinations of these mineral species. It also permits their distinction from the X-ray-thermally similar intergradient 2:1–2:2 layer silicates which are not affected by the treatment. Intergradient 2:1–2:2 layer silicates are developed by interlayer precipitation of hydroxides of aluminum, iron, and magnesium during pedogeochemical weathering and probably also during burial in sediments. The quantitative determination of kaolinite-halloysite by NaOH differential dissolution is completely corroborated by the qualitative, semiquantitative X-ray diffraction intersalation technique with respect to their clear differentiation from chlorite and intergradient clays.

Alumina-pillared montmorillonite clays (Al-PILC), prepared under ultrasonic (US) agitation and normal stirring (S) methods, have been used as a host material to encapsulate Co phthalocyanine (CoPc) complex. The amount of Co varies from 0.27 to 1.48 wt.% in the samples, depending on the input concentration of Co. Powder X-ray diffraction and other characterization techniques reveal that the structure of Al-PILC remains intact after the incorporation of the complex into the pores through a pyridine solution of the complex by ultrasonic agitation. A substantial decrease in the BET surface area and total pore volume of Al-PILC points to the occupation of the CoPc moieties within the porous structure of the pillared clay. This is further supported by the observation of a band at 1489 cm−1 in the Fourier transform infrared (FTIR) spectra of the encapsulated samples. The FTIR and diffuse reflectance ultraviolet-visible (DRUV-Vis) spectral results indicate that the encapsulated CoPc complex in the clay matrix undergoes distortion in order to accommodate itself within the pores of the Al-PILC. The encapsulated samples prepared by ultrasonification show better dispersion of the complex than the samples prepared under normal stirring conditions. Compared to the ‘neat’ complex, the encapsulated samples (CoPc in Al-PILC) exhibit greater turnover in the test reaction of the oxidation of benzyl alcohol to benzaldehyde with tertbutyl hydroperoxide as the oxidant at 373 K. The method of preparation and consequent site isolation of CoPc in Al-PILC influence the catalytic activity.

This contribution reviews the work done at Ghent University, together with some unpublished recent work. Next to the survey of clay minerals from soil samples for the soil mapping organization, the group has been concerned with the polytypism of micas, the alteration and transformation of clay minerals, and the role of migration of iron in mica-type structures under influence of temperature or chemical treatment. A study of growth spirals of biotite crystals threw some light on the origin and possibility of the existence of ordered sequences with great repeat distances, and also on the complexity of crystals of this type. The presence of dislocations in mica is also shown by examination of “bending figures” produced by indentation. A study of clay minerais in soil fractions from a limited area, reclaimed from the sea between the eleventh and nineteenth centuries, indicated great variation in mineral composition. If one accepts the logical working hypothesis that the mineral composition was homogeneously distributed at the start, one must accept a rapid transformation at particular spots. This evolution seems to proceed from muscovite (illite) toward montmorillo-nite. Neoformation of a small quantity of kaolinite accompanies the transformation to mont-morillonite.

Experiments carried out to achieve this process in the laboratory showed that micas submitted to a stream of CO2 dissolve rather rapidly in presence of water. All attempts to obtain clay minerals from the obtained solutions failed, except one, when small quantities of mont-morillonite and kaolinite were formed. The thermal evolution of glauconite and the location of iron ions were also studied. Some remarks on formulas of clay minerals are presented.

A recently described phenomenon, the shear induced decrease of moisture suction in saturated clay—water systems and its subsequent recovery, has been investigated with the aid of a parallel plate shearing device. The apparatus allowed a more quantitative description of the phenomenon than was previously possible. In 4–6% Na-montmorillonite pastes it demonstrated a well defined suction response to shear oven for shear angles as small as one degree. The observed decrease in suction was rapid at first. It terminated within a few minutes and was followed by an approximately exponential, occasionally incomplete recovery. All the tests carried out exhibited the same general features of suction change.

It is postulated that shear induces a displacement or change in configuration of particles and that subsequently they return to their original states due to thermal motion. The shapes of the recovery curves can be interpreted in terms of the relaxation spectrum functions encountered in linear viscoelasticity theory. By utilizing a characteristic relaxation time for these spectra, rate process theory has been employed to interpret the bonding mechanism in terms of the experimental activation free energy. The results suggest that the bonds which are re-established during the recovery are primarily of the Coulombic type.

Shear induced suction changes should be considered when dealing with deformation theories and structural models of wet soils and clays. Indeed they provide a means of testing certain aspects of soil structure.

For the last 20 years, the Ceramic Division at the Massachusetts Institute of Technology has been carrying on basic work with the kaolinite-water system. The results have been published from time to time in the Journal of the American Ceramic Society under the title of “Fundamental Study of Clay.”

At the start, it was realized that natutal clays were so complex that it would be impossible to consider them as a basis for quantitative calculations. Therefore, most of our research has been carried out on specially prepared samples taken from the natural clay. These kaolinite samples had a known particle size, were free from organic matter, and had controlled adsorbed ions. In this way, the effect of anyone variable on the rheological properties could be studied in a logical way.

The studies undertaken by the Instituto de Edafologia y Fisiologfa Vegetal on clay minerals and related silicates can be classified into three main groups: (A) Mineralogical identification and crystalline structure: (B) physico-chemical behavior; and (C) technical applications. They are summarized briefly.

Study of the behavior of landfill lining materials (clays) in organic solvents is important because, in waste management, lining prevents groundwater contamination by the adsorption of various pollutants such as chemicals and organic solvents. Although scaling behavior and the self-association property of clays in water-alcohol binary solvents have been studied by many researchers, the anomalous behavior of Laponite XLG in binary solvents requires investigation as suggested by previous studies. In the present study, Laponite® RD, which is structurally similar to Laponite XLG, was used to gain further insight into the reasons for the anomalous viscosity, aggregation, and non-ergodic behavior of clay in a water–methanol binary solvent. Dynamic light scattering (DLS) revealed the emergence of the non-ergodic phase of 3% w/v Laponite® RD in the water–methanol binary solvent, which increased in the presence of a large methanol content as well as with aging time in the binary solvent. Viscosity measurements further indicated that aggregation was responsible for the non-ergodic behavior, and small-angle X-ray scattering (SAXS) revealed that a large methanol content enhanced the aggregation. Moreover, SAXS data also revealed that the surface charge was responsible for anomalous viscosity fluctuations in the binary solvent due to interparticle repulsion within aggregates. Rheological studies showed that the large methanol content in the binary solvent led to frequency-independent behavior of the storage modulus of Laponite® RD.

To date, ~1% of all bacteria that occur in environmental ecosystems such as soil, sedimentary rocks, and groundwater have been described. Comprehensive explanation of ecological interactions on a microscale level is thus almost impossible. The Dynamic Cultivation System (DCS) was developed in order to detect more microbial taxa than with common cultivation approaches, as well as previously undescribed bacterial species. The DCS is a quick and easy in situ method for the cultivation of numerous bacterial taxa in support of the description of microbial colonized ecosystems. To investigate the bacterial populations within a clay-maturation process after mining the raw material, the DCS was used to increase the microbial biomass for further molecular analysis. Two different methods were applied to extract the bacteria from the DCS and these were compared in terms of efficiency at detection of large numbers of different taxa and in terms of applicability to the detection of previously undescribed species in raw clays. A collection of different undescribed species was detected with sequencing. While direct picking of bacterial colonies leads to the detection of different genera, species mainly of the genus Arthobacter were proved in the phosphate-buffered saline-suspended biomass. Thus, a combination of the approaches mentioned above is recommended to increase the number of detectable species. The DCS will help to describe better the microbial content of ecosystems, especially soils that contain charged particles.

The bonding in a cronstedtite layer was studied using a ninefold ordered supercell band structure calculation. The tight-binding scheme based upon the extended Hückel method was used to predict the electronic structure. The size of the problem was 162 atoms with 798 valence orbitals. The calculation showed different orbital interactions of oxygen p-orbitals with neighboring atoms with respect to the position in the layer. Substitution of Fe for Si in the terahedra reduced the role of the valence p-orbitals of the central Fe atoms. The d-orbitals of Fe were split in accordance with the rule of t2g-eg splitting. Although the density of states at the Fermi level was high, the partially filled 3d-bands were too narrow to permit normal metallic conduction.

A wick structure is the core part of a heat pipe that produces capillaries to move liquid from a condenser to an evaporator. The purpose of the current study was to develop a wick structure from zeolite and kaolin using various sintering methods. Due to significant porosity and water-adsorption properties, zeolite and kaolin can produce a large capillary force inside the heat pipe. A porous wick specimen is developed from pure zeolite together with a mixture of zeolite and kaolin by using pressureless (loosely packed) and conventional pressurized sintering for thermosiphon heat-pipe applications. Major properties such as porosity, water adsorption, and permeability were noted to be better under pressureless sintering compared to pressurized sintering. Significant and uneven shrinkage in both radial and linear directions is a major problem in loosely packed sintering of pure zeolite. However, the addition of kaolin helps to overcome the problem of porosity and shrinkage in pure zeolite; but the permeability and strength of the wick structure are reduced with the addition of kaolin. A general trend is that increasing porosity causes increasing permeability. Due to grain size and compaction, however, permeability is reduced with the addition of kaolin. Based on the experimental results for porosity and permeability, the wick structure formed from zeolite with 5–10% of kaolin has better thermal properties for heat-pipe applications.

Cored specimens of several commercial bentonite beds were preserved at field moisture levels for laboratory examination. Green strength, water content, and x-ray diffraction character of undisturbed material were found to conform substantially to the relation that strength is proportional to the solid fraction.

The viscosity of clay-water suspensions is an important factor in determining commercial uses of Georgia Kaolins. Impurities, such as montmorillonite type minerals, in these basically kaolinite clays play a part in causing variations in viscosity. However, seemingly pure kaolinite clays also show variations which seem to be related to morphology and degree of crystallinity. Studies are underway to determine the various factors involved.