Une méthode de synthèse directe de complexes entre un silicate phylliteux et des pigments azoïques a été mise au point. L'étude des complexes obtenus montre que le mécanisme d'interaction entre le feuillet phylliteux et le colorant azoïque fait intervenir des réactions de transfert de charges. On a pu mettre en évidence des phénomènes d'oxydo-réduction et des réactions acide-base. Le mécanisme d'interaction dépend du mode de préparation du complexe. Suivant les conditions de pH du milieu, la fixation du colorant s'effectue soit par une simple ‘précipitation’ dans la structure, soit par échange d'ions. La molécule de colorant subit généralement une protonation au cours de son incorporation avec formation de cations à structure quinonique. La protonation peut se faire soit à partir de protons, cations échangeables du minéral, soit à partir de protons provenant d'une ionisation de groupements structuraux AlMgOH. Le phénomène de protonation apparait prédominant vis-à-vis des réactions d'oxydo-réduction. La présente étude montre également qu'il est difficile de savoir si les phénomènes d'oxydo-réduction ont lieu par l'intermédiaire des atomes d'aluminium ou de fer de la structure ou par des cations Al3+ et de l'alumine eventuellement formés au cours de l'attaque du réseau.

The spectrum of Ni-substituted lizardite, (Mg,Ni)3Si2O5(OH)4, has been discussed by many authors, who have successively given contradictory interpretations concerning the symmetry of the Ni-sites. Lakshman & Reddy (1973) affirmed that in garnierites Ni is in a tetrahedral site. Faye (1974) rejected this conclusion and showed that Ni2+ occupies an octahedral site. However, the Ni … O distance of 2·01 Å which he deduced from the intensity of the crystal field is unacceptable. Recently, using a completely different approach to the interpretation of the spectrum, Cervelle & Maquet (1982) claimed that Ni2+ occupies a six-coordinated site of C3v symmetry, and concluded that the mean Ni … O distance is 2·06 Å.

The aim of this note is to show that it is possible to interpret the spectrum of Ni-lizardite as arising from a predominantly octahedral field with a weak C2v component which provokes a small increase in width of the absorption bands.

X-ray analyses indicate that chlorite, illite and mixed-layer chloritesmectite are present in the < 2μ fraction of the Precambrian Gowganda Formation near Bruce Mines, Ontario. The mixed-layer material is restricted to the porous graywacke sandstones and is epigenetic in origin. The chlorite and illite are ubiquitous and may reflect high-grade diagenesis, low-grade metamorphism or a source rich in these minerals.

The Weissenberg method has been used to study crystalline fragments of hydrobiotites from Stupná near Křemže, Czechoslovakia. The intensity distribution for basal reflections recorded in zero-level photographs indicates that most ‘single crystals’ are nearly regular interstratifications of vermiculite and biotite. Proportions of vermiculite in these interstratifications lie between 12 and 60%.

Non-isothermal dehydration kinetics of a heulandite-type zeolite-rich tuff from Turkey was investigated using thermogravimetric data recorded at three different heating rates (5, 10 and 20°C/min) under nitrogen flow. Isoconversional model-free methods gave a constant activation energy over the temperature range 30–200°C suggesting that the dehydration is a single-step process within this temperature range. The apparent activation energy was determined as: 34.54±1.18, 30.99±1.14 and 27.79±1.42 kJ/mol by the Flynn–Wall–Ozawa, the Kissinger–Akahira–Sunose and the Friedman methods, respectively. The activation energy values determined were less than the activation energy for vaporization of bulk water, indicating control of the dehydration rate by diffusion of water within this temperature range.

Bernard Kübler measured illite ‘crystallinity’, the half-height width or full width at half maximum (FWHM) of the X-ray diffraction line of illite/mica at 10 Å, directly on the diffraction traces; this procedure has since been followed by the vast majority of workers. However, some workers have recently measured the FWHM of the fitted Pearson VII function rather than on the diffraction traces. The FWHM of this function for low-angle phyllosilicate diffraction peaks (FWHM*PVII) is almost consistently ‘broader’ than those measured directly on the diffraction trace profiles (FWHMtrace) by up to 0.08°Δ2θ for the broader peaks. The Pearson VII function shows gentle curvature (‘smoothing’) at its tops and fast fading of the tails relative to virtually all 10 Å diffraction traces. The broad FWHM*PVII results from the consequent lowering/’under-fitting’ of the peak tops and the upper tails and compensatory broadening/’over-fitting’ of the intermediate peak flanks. FWHM*PVII ‘contraction’ with respect to FWHMtrace and enhancement of the peak maximum is found on traces of muscovite strips. The fitting reliabilities of the Cauchy function are almost invariably better than those of the Pearson VII function. Their FWHM*Cauchy values are narrower for both the illite/mica 10 Å and the chlorite 7 Å reflections; although they still differ somewhat from the FWHMtrace, they are much closer, usually within 0.02°Δ2θ. This markedly lesser broadening of FWHM* of the Cauchy of the Pearson VII function is the result of its stronger top curvature and notably faster tail fading (less ‘smoothening’). For higher-angle mica peaks, the FWHM* values of the Pearson VII and Cauchy functions converge, usually differing only by 0.01–0.03°Δ2θ for the 5 Å peak, and even less for the 3.3 Å peak. It is therefore strongly recommended that FWHM values of the illite/mica 10 Å reflections be measured on the diffraction traces rather than on fitted functions. Where peak fitting is unavoidable (e.g. in order to separate the contributions of adjoining, partly resolved or unresolved reflections on broadened 10 Å reflections), Cauchy rather than Pearson VII functions should be used.

The interface performance between clay–sand mixtures and concrete structures is governed by the mixture's composition and its physical properties. Moisture content and particle-size distribution play important roles in deciding the mixture's arrangement of soil particles, porosity, hydraulic conductivity and behaviour under various mechanical loadings. Application of a polymer interfacial coating can improve the bond performance between soils and concrete mainly via interfacial friction/mechanical interlocking. The present work analyses the development of interfacial strength between clay–sand mixtures and a polymer coating with changes in particle gradation. The multi-scale mechanisms at the interface are investigated, giving primary attention to soil porosity. A 50:50 clay–sand mixture exhibited a greater interfacial adhesive performance compared to other soil mixtures. In addition, the moisture-controlled pores and gradation-controlled pores demonstrated differences in macroscale interfacial strength. Both mercury intrusion porosimetry (MIP) and 129Xe nuclear magnetic resonance (NMR) were utilized to detect the pore structure of the mixtures. 129Xe-NMR revealed the pore distribution of the mixtures as ranging from macropores to nanopores, and MIP complemented the pore information by determining the critical pore entry diameter in the macropore regime. Mesopores dominated with increasing fine sand content until a threshold value was reached; thereafter, merging of pores occurred and macropores dominated.

High-whiteness kaolinite mining reserves are scarce. In some locations, it is necessary to remove material to access them (adding to the cost). Therefore, processes have been developed to eliminate contaminants, such as iron, and provide alternatives to the used contaminated materials that, after being treated, meet quality criteria. In our previous research, we developed an electrochemical process for kaolin whitening at the laboratory level and bench scale, demonstrating the reaction mechanisms that occur during the removal of iron from kaolin. However, the geometry used at the laboratory level does not present the most suitable position for the electrodes. Therefore, in the present study, we focused on the geometry and the function of the electrodes. This is necessary during the escalation process to reach the pilot-scale level. The study was carried out using computer-aided engineering in the COMSOL Multiphysics computer program and by analysing the distribution of the electric potential and the electric current of the geometries considered while performing the scaling. The results indicated that the change in the anode position from perpendicular to parallel to the discs improved the distribution of electric current density on the cathode surface and so increased the elimination of iron through electrochemical deposition. Similarly, to reduce the amount of material used in the construction of the reactor, the anode-size effect was analysed, revealing that relatively small anodes improved the distribution of electric current density over the entire surface of the electrode and not only at the edges.