Electron spin resonance (ESR) spectroscopy has contributed significantly to the identification and characterization of paramagnetic impurities associated with clays. Following a brief discussion of the general principles of the technique, a review is given of the application of ESR to the study of those paramagnetic species (chiefly iron and radiation-induced lattice defects) located either within the aluminosilicate structure or present as an external impurity phase.

A review is given of the application of ESR spectroscopy to the study of hydrated transition metal ions and nitroxide spin probes in the interlamellar region of smectites and vermiculites. These investigations have not only provided information regarding the structure and mobility of the intracrystalline water-cation layers but have also demonstrated the reactivity and catalytic properties of certain transition metal exchange forms of smectites. Several novel coordination complexes and redox reactions between the exchange ions and a variety of simple organic molecules have been characterized.

Après avoir défini la notion de charge minérale, on étudie la nature et le nombre des défauts cristallins d'argiles kaoliniques. On montre l'influence des défauts d'empilement (interstratification de feuillets potassiques) et des défauts dans le plan (conséquence des substitutions de l'aluminium) sur les propriétés mécaniques des caoutchoucs chargés. Puis on étudie l'influence de la pureté minéralogique et de certains paramètres superficiels sur les performances des produits chargés. Enfin, on propose des méthodes de traitement qui permettent d'accroître les propriétés renforçatrices de la charge. On présente l'évolution comparée de 64 paramètres descriptifs de la charge et du produit fini en définissant des guides de prospection et de traitement qui permettent l'utilisation optimale des réserves charentaises dans le domaine des caoutchoucs naturels.

Small amounts of Fe(III) induce precipitation of Fe(II) from carbonate solutions around neutral pH values. The reaction involves the formation of Fe(II)Fe(III) hydroxycarbonate, a green, layer-structured compound of the pyroaurite group of minerals. Variations in the concentration of Fe(II) in the solution phase, and in the form and amounts of the total Fe(III) in the system, may cause other phases such as magnetite and siderite to form also. Freeze-dried Fe(II)Fe(III) hydroxy-carbonate undergoes topotactic alteration to a magnetic phase, presumably maghemite, when stored under vacuum. The compound is readily oxidized in air in either the moist or dry state, rapidly becoming yellow or yellow-brown in colour. Oxidation leads to the formation of either goethite, lepidocrocite, ferrihydrite or mixtures of these phases, depending on the mode of oxidation and the impurities present. The similarity between the rapid colour changes and the oxidation products of the blue-green precipitates in gleyed soil horizons and this Fe(II)Fe(III) hydroxy-carbonate leads to the speculation that this and related compounds may be the meta-stable precipitates in such soils, rather than a previously postulated hydro-magnetite phase. Eh and pH conditions for the formation of Fe(II)Fe(III) hydroxy-carbonate are given, and are in the range encountered in the soil environment.

En milieu organique, la formation de l'acide hippurique par contact d'un complexe montmorillonite-glycine avec de l'acide benzoīque est relativement facile. Dans ces conditions le peptide formé n'est pas hydrolysé. En milieu aqueux, par contre, l'activité catalytique de l'argile est insuffisante pour préparer l'acide hippurique à température ambiante. Une température minimale de 60°C est alors indispensable. Le rendement de la réaction qui est toujours faible dépend principalement de la nature du cation échangeable de l'argile. Les meilleurs résultats sont obtenus avec les montmorillonites contenant des éléments de transition tels que le cuivre, le nickel ou le zinc. Un phénomène d'activation faisant intervenir un complexe de coordination entre la glycine et le cation échangeable de l'argile constitue vraisemblablement l'étape intermédiaire dans la formation du peptide.

A general expression for diffracted intensities from partially ordered layer structures with a ‘mistake’ has been calculated. The ‘mistake’ consists of a shift of a layer parallel to adjacent layers by any arbitrary fraction b/q along the b axis, q being any integer. The expression is free from any simplifying approximations.

L'étude porte sur la décomposition du massif de bandes de vibration de valence O-D centré vers 2500 cm−1 que présentent les spectres infrarouge des hydrates à deux couches des vermiculites -Ca et -Mg partiellement deutérées. La détermination des bandes composantes a été effectuée à partir, d'une part de l'étude du dichroïsme des bandes de vibration infrarouge, d'autre part des données structurales disponibles sur les couches interfoliaires de ces minéraux. Ces deux méthodes conduisent—avec un accord satisfaisant—à une décomposition en 4 bandes composantes correspondant à 4 types de liaisons O-D...O. Parmi ces liaisons entre molécules d'eau, certaines sont relativement courtes, ce qui conduit à penser qu'il existe dans la couche interfoliaire de ces hydrates une charpente de molécules d'eau un peu analogue à une charpente anionique.

A method for the preparation of Ln-montmorillonite (Ln = La, Ce, Sm, Gd, Er and Y) that ensures saturation of the CEC is described and the most favourable equilibrium conditions are discussed. The H+- Ln3+ exchange rate in acid montmorillonite and the effect of concentration and pH on the retention of Ln3+ ions by the clay are also investigated. The presence of montmorillonite modifies the pH value at which precipitation of hydroxides begins, a process that actually occurs at pH ∼ 5.

Hydration/dehydration behaviour and the effect of various thermal treatments on montmorillonites saturated with lanthanide ions have been investigated by X-ray diffraction, thermal analysis (DTA, TG, DTG), IR spectroscopy and sorption-desorption of water vapour techniques. Heating at 150°C under 10−5 torr did not eliminate all the interlayer water of the montmorillonite, neither did it affect the CEC. Heating above 160°C caused a reduction in CEC. At 25°C La-montmorillonite takes up a maximum of three water layers in the interlayer space, the water molecules adopting a nonacoordinated distribution around the La3+ cation.

The thermal behaviour of a ferrous doped kaolin has been studied by Mössbauer spectroscopy and electron paramagnetic resonance spectroscopy. From the observations it is concluded that the iron substitutes trioctahedrally as Fe2+ in the ‘gibbsite-like’ sheet in place of dioctahedral aluminium. The g = 2 EPR signal is shown to be associated with these ferrous ‘cells’ which appear to occur in clusters. It is suggested that these ferrous cells are trapped within the normal dioctahedral aluminium structure. Dehydroxylation of the ferrous iron cells takes place between 623 and 673 K leading to the formation of an iron-rich pyroxene and, by 723 K, a ferric oxide. At temperatures > 723 K the pyroxene itself oxidizes to a second ferric oxide. The EPR signal changes at 623 K and disappears at 723 K. The signal is attributed to a trapped hole induced by X-irradiation, located near a silicon atom on the boundary between normal dioctahedral cells and trioctahedral Fe2+ cells. It is possible to extend the model to explain some puzzling features concerning the g = 2 EPR signals reported by other authors and to propose other effects which might result from the presence of these cells.

The main clay mineral in weathered basaltic rubble has been shown by X-ray diffraction, chemical, infrared and differential thermal methods to be an interstratification of montmorillonite, vermiculite and illite in the approximate ratio 2:1:1, the montmorillonite having some degree of segregation and the vermiculite and illite being randomly interstratified. All three components are dioctahedral, the swelling ones having a high tetrahedral charge, a large aluminium content, and very little iron. Despite the 50% montmorillonite content of the mineral, its infrared absorption pattern is generally illitic in character.