Nucleation is much more important for clay minerals than for other authigenic cements as clay crystals are very small, so that a very large number of clay crystals must be nucleated. The role of this difficult kinetic step in the diagenesis of sandstones has not been considered adequately as a ratedetermining process. The relationship between pore-fluid supersaturation and the rate of nucleation of a mineral is very different from the relationship between supersaturation and the rate of crystal enlargement; thus the two processes will act at very different rates. A diagenetic model that predicts claymineral formation but omits the nucleation stage may make unreliable predictions. This may account partially for the discrepancy between numerical simulations of CO2 injection that predict high degrees of reaction between the CO2 and the host rock, and the results of studies of natural analogues that have much lower degrees of reaction.

Following a round-table discussion at the Mid-European Clay Conference in Dresden 2014, new recommendations for illite ‘crystallinity’ Kübler index standardization have been agreed upon. The use of Crystallinity Index standards in the form of rock-fragment samples will be continued, along with the same numerical scale of measurement presented by Warr & Rice (1994). However, in order to be compatible with the original working definition of Kübler's (1967) anchizone, the upper and lower boundary limits of the Crystallinity Index Standard (CIS) scale are adjusted appropriately from 0.25°2θ and 0.42°2θ to 0.32°2θ and 0.52°2θ. This adjustment is based on an inter-laboratory correlation between the laboratories of Basel, Neuchâtel and the CIS scale. The details of this correction are presented in this first note, as discussed at the round-table meeting and will be further substantiated by a correlation program between CIS and former Kübler–Frey–Kisch standards.

X-ray diffraction is one of the most effective tools for the characterization of the stacking defects which occur frequently in clay minerals. Modelling of the diffraction patterns of oriented mounts is often used for obtaining structural information about the nature of stacking order. Manual matching of calculated and observed patterns is time consuming and the results are user dependent and especially troublesome if a consistent model of the same mineral measured under different conditions needs to be obtained. It was shown recently that the Rietveld method could be applied successfully for the evaluation of the X-ray patterns of oriented mounts. Nevertheless, this automatic refinement procedure can also lead to inconsistent results if independent refinements are performed that describe the same sample measured under different conditions. One way to solve this problem is the application of parametric Rietveld refinement. For this approach a set of different measurements of the same sample was collected and fitted in one combined refinement by the connection of the structural models via external parameters. These conditions may involve different pre-treatments (e.g. different intercalations), different temperatures or relative humidities and/or different experimental setup (powder or oriented samples). All patterns were fitted in one overall refinement process by the BGMN software.

This approach was demonstrated on a mixture of two disordered reference materials and on a set of geological samples. Two different states for each sample were refined independently and parametrically and it was shown that this approach leads to consistent results, saves computation time and may even resolve small structural differences.

The rectorite, a regular mixed layer mineral consisting of dioctahedral swelling and non-swelling 2:1 layers, from North Little Rock, Arkansas, was studied to define the crystal chemistry and structural parameters (e.g. layer charge of the different layers, presence of cis/trans-vacancies). X-ray diffraction, simultaneous thermal analysis coupled with mass spectrometry, X-ray fluorescence and cation exchange capacity are used to characterize this rectorite. The rectorite has a coefficient of variation (CV) of 0.19 and a cation exchange capacity of 60 cmol(+)/kg, as determined by the ammonium acetate method. The mineral is best described as a regular interstratification of brammallite-like and highcharged beidellite-like layers. Dehydration occurs at ≈118°C with a mass loss of 6.77% and dehydroxylation occurs in two steps at 470°C and 588°C with an overall mass loss of 4.67%. Peak decomposition of the mass spectrometer curve of evolved water shows ≈20% peak area with a maximum higher than 600°C, indicating ≈20% cis-vacant layers.

Molecular cluster models, developed for an exfoliated kaolinite, provide a structural description comparable to that of periodic slab models for a fraction of the computational cost. These models include both the octahedral and the tetrahedral sheets of kaolinite. The first-generation model (G1) contains the inner and outer coordination sphere of the Al- and Si-honeycombs as the preferred sites for adsorption of small organic molecules. Since no experimental information is available to date at the atomic level for exfoliated kaolinite, we carried out a systematic density functional theory evaluation for establishing the most reasonable coordinates of the ions and groups. The results of molecular cluster and periodic calculations were utilized for evaluating semi-empirical Hamiltonians on larger models. Using a PM7 Hamiltonian, the structure of cluster models containing 1 + 6 (second generation) and 1 + 6 + 12 (third generation) Al- and Si-honeycombs which are out of reach for ab initio calculations, were determined. These molecular slab models offer a structural platform for adsorption, intercalation and delamination studies.

Clay-based nanostructures were prepared from kaolinites of varying structural order by two different methods. In the first method the kaolinite-urea precursor, obtained by dry grinding, was intercalated further with triethanolamine and the tetraalkylammonium salt was synthesized in the interlamellar space. Exfoliation was achieved by the use of sodium polyacrylate (PAS). In the second method, the kaolinite-potassium acetate (kaolinite-KAc) precursor, obtained via two different methods, was intercalated further with ethylene glycol (EG) and then n-hexylamine (HA). Intercalation with EG was also achieved by heating either directly or with microwaves. The morphology that results depends on the method of precursor preparation, the method of heat treatment and the degree of structural order of the original clay. Higher structural order facilitates the formation of a tubular morphology, while mechanical treatment and microwave agitation may result in broken tubes. Molecular mechanical (MM) calculations showed that organo-complexes may be exfoliated to a d value of 10–11 Å.

The present work describes the effect of montmorillonite (MMT) particles on the alignment of conducting polyaniline (PANI) chains in a PANI/MMT composite. The composite was prepared both as a powder, pressed into pellets, and as thin films deposited on glass surfaces. For comparison, pure PANI was also prepared in these two forms. A combination of X-ray powder diffraction analysis and molecular modelling confirmed the successful intercalation of the PANI into theMMT, while Raman spectroscopy confirmed the presence of the conducting form of PANI (i.e. the emeraldine salt) in all samples. Scanning electron microscopy, transmission electron microscopy and atomic force microscopy were used to study the morphologies of all samples. Conductivity measurements showed that the presence of the MMT particles in the PANI/MMT composites contributes to a significant increase in the electrical conductivity in comparison with the pure PANI samples. Moreover, in the pressed pellets the presence of theMMT particles led to an extremely high electrical anisotropy. TheUV-VIS spectroscopy results showed that the PANI/MMT thin film exhibited a selective transmittance in the range 450–650 nm; therefore, the PANI/MMT thin film is not only conductive, but also suitable for use in various optical applications.

Organoclays are sorbent materials prepared from clays by exchanging inorganic with organic cations. Their properties depend on the loading and conformational structure of the organic cations, but little information is available about the surface structures of organoclays. In this work, X-ray photoelectron spectroscopy (XPS) and classical molecular dynamics (MD) simulations are combined to characterize the external interface of an organoclay prepared from hexadecylpyridinium (HDPy+) and bentonite. The XPS survey spectra show well the varying elemental composition of the surface with increasing amount of surfactant, showing a decreasing contribution of clay-derived elements with increasing organic coverage. The high-resolution C 1s XPS spectra depict sensitively the surface arrangement of the surfactant. In combination with MD simulations, the results implied a monolayer coating for low surfactant coverage and a disordered bilayer arrangement at high surfactant uptakes. Molecular dynamics simulations showed that for very high cation uptake a quasi-paraffin-like configuration is also possible. The combination of experimental and modelling methods yielded congruent information on the molecular-scale arrangement of organic cations at the organoclay surfaces and the controlling mechanisms.

Anisotropy and compositional and structural heterogeneity in clays are causes of considerable deviations from homogeneous diffusion, in particular in terms of direction-dependent transport rates and preferred transport zones. Conventional diffusion experiments, in which the sample is treated as a homogeneous black box in a concentration gradient, are interminable and insensitive to spatial effects. In contrast, tomographic imaging methods are capable of both reducing the amount of observation time required and revealing space-dependent features of the diffusion process.

In the present study, positron-emission-tomography (PET) was applied as the most sensitive quantitative spatiotemporal tomographic modality for direct observation of positron-emitting radiotracers in opaque media at reasonable resolution (1 mm) on a laboratory scale (100 mm).

Geoscientific applications of PET, or GeoPET, have revealed anisotropic and heterogeneous effects in diffusion experiments that have been conducted on Opalinus clay samples of different sizes, as well as on other rock types. Applying the Comsol Optimization Module to 2D-image sections of the PET tomograms, effective parameter values were derived, thereby quantifying the anisotropic diffusion.

Calcigel bentonite-polyacrylamide (PAA) composites were investigated for their formation characteristics and their macroscopic hydro-mechanical and microscopic structural properties. The composites prepared were different in terms of the polymer charge, i.e. cationic (PAA+), anionic (PAA−), non-ionic (PAA°) and in terms of the polymer-to-clay ratio. The latter varied according to the individual maximum sorption capacity established from adsorption isotherms. Oedometer and waterretention testswere conducted on composites prepared under initial slurry conditions. The microstructure of the composites was investigated using environmental scanning electron microscopy (ESEM). At low stress, distinctly increased void ratios were found for all types of the composites, whereas under highstress conditions only the PAA+-composite prepared at 100% of the maximum sorption capacity showed an increase in void ratio. Analyses by ESEM on this composite indicated structural changes related to the preferential face-to-face aggregation, which help to explain the macroscopic behaviour and also account for the increased hydraulic permeabilities observed.

The two high-pressure water-retaining dams at the Ibbenbüren coalmine in Münsterland (Germany) have to perform reliably under the induced tension caused by further exploitation of the current mining area. The load-bearing and the sealing functions of the new barriers were separated and new sealing materials were developed. An innovative multilayer sealing system of bentonite and sandwiched equipotential layers (SANDWICH) supporting homogeneous swelling and sealing, independent of formation water (Nüesch et al., 2002), was applied in this project. A testing program of strain-controlled swelling pressure tests on compacted bentonite specimens and on a bentonite/sand mixture was conducted to ensure an adequate potential for swelling-pressure development.

The measurements under constant volume for dry densities between 1.45 g/cm3 and 1.67 g/cm3 showed an evolving swelling pressure between 1.04 and 1.8 MPa for 100% bentonite samples. Straincontrolled oedometer tests for zero strain and step-wise applied strain up to 2% revealed that a sufficient magnitude of swelling pressure existed at maximum applied strain.

The present study determined the mineralogy and thermal properties of kaolin from Acoculco (Puebla), at the eastern Trans-Mexican Volcanic Belt and compared it with the nearby deposits of Agua Blanca (Hidalgo) and Huayacocotla (Veracruz). The mineralogy of the kaolins was determined by X-ray diffraction, infrared spectroscopy and scanning electron microscopy. Thermal behaviour was studied by differential thermal analysis, dilatometry and hot-stage microscopy. The Acoculco deposit is composed mainly of kaolinite and SiO2 minerals. In the case of Agua Blanca and Huayacocotla, alunite is abundant in places and minor anatase is also present locally. The Acoculco kaolins are Fe-poor and relatively rich in some potentially toxic elements (Zr, Sb, Pb). They undergo a relatively small amount of shrinkage (∼3–4 vol.%), during firing at 20–1300°C and cooling down to 20°C, except when >10 wt.% alunite is present. These kaolins are a suitable raw material for the ceramics industry. Other applications (pharmaceuticals, cosmetics) would require an enrichment process to eliminate impurities such as Fe oxides.