Millimetre-sized flakes of a homogeneous, high layer charge vermiculite from S. Olalla (Spain) saturated with l'ornithine cations were made to swell in l'ornithine hydrochloride solutions of various concentrations, and the gel-like structures formed were subjected to uniaxial loads up to 150 g/cm2. Small-angle X-ray diffraction measurements from the swollen flakes show well-modulated intensity patterns from which the equilibrium interlayer distances were obtained for the various swelling conditions. The interlayer spacings can be adequately expressed as normal-logarithmic distribution functions of probability density. The gel texture is described in terms of the average number of elementary layers, all in parallel orientation, constituting independent coherent domains within the swollen flake. Changes in structure and in texture taking place as the gel volume increases, or as water is expelled from the interlayer volume under mechanical compression, are followed by the variation of the corresponding parameters of order.

Par diffraction des Rayons X sur la vermiculite-Li de Santa-Olalla, il a été montré en fonction de la température qu'il existait différentes phases homogènes (d001 = 12·17 Å, T = 25°C; d001 = 12·02 Å, T = 60°C; d001 = 11·89 Å, T = 70°C; d001 = 10·04 Å, T = 100°C). Par ailleurs, pendant le processus de déshydratation entre les phases homogènes à 11·89 Å et 10·04 Å, il a été mis en évidence l'apparition d'états inhomogènes (interstratifiés). L'utilisation parallèle des méthodes directes d'étude des diagrammes de rayons X par transformée de Fourier monodimentionnelle pour les phases homogènes et d'une méthode indirecte de modélisation pour les états interstratifiés a permis de montrer que le passage de la phase 11·89 Å à la phase 10·04 Å se fait conjointement par une ségrégation de ces phases et un interstratifié aléatoire (11·89–10·04). Ce travail a en outre montré que la caractérisation des états intermédiaires entre phases homogènes ne peut être faite sans une étude structurale préalable des phases homogènes.

Porous, high surface area solids have been prepared by intercalation of a trinuclear acetato hydroxy-iron(III) complex cation between the layers of montmorillonite and the resulting materials have been characterized in order to identify the nature of the iron intercalates formed during and after the cation exchange step. Spectroscopic studies demonstrated that at 623 K, the iron complex was partially decomposed and α-Fe2O3 was only detected in samples heated at high temperatures, > 923 K. Under these conditions, the dehydroxylation of the montmorillonite layers led to the collapse of the structure.

Differential heat of water vapour adsorption for Cs+-saturated montmorillonite, kaolinite and allophane was measured over a low relative humidity range from 10−4 to 10−1. Two interactions (clay surface atom-water and counterion-water) are mainly involved in the water vapour adsorption process. To assess the affinity of water to the clay surface, the amounts of adsorbed water and the differential heat due to Cs+ were estimated from equilibrium constants in the gas phase reactions. It is tentatively concluded that (i) a dominant role of water adsorption due to the Cs+-water interaction in the adsorption process is evident only for montmorillonite; (ii) the affinity of water to the clay surface is strongest for allophane and weakest for montmorillonite.

Dehydroxylation of synthetic and natural goethites with a range of Al-substitution from 0–28 mole% was investigated with a view to predicting the behaviour of soil goethites heated by bush fires. Hematites formed at temperatures ≤ 500°C retain the initial Al-content of the precursor goethite up to a maximum of 28 mole% Al. Loss of Al from the hematite structure occurred at 700°C for synthetic hematites with levels of substitution ≥18 mole% Al, but no crystalline alumina phase was present. Crystallization of corundum occurred for synthetic Al-goethites with levels of substitution ≥18 mole% when heated at 900°C. Formation of corundum reduces the maximum level of Al-substitution in hematites to ∼ 12 mole%. The exsolved corundum occurs as aggregated, platy crystals, 40–45 nm in diameter, containing a maximum of 7 mole% Fe. Al-substituted maghemite (7 mole% Al) formed from high Al-goethites heated at 900°C. Although some corundum in soils may be produced by heating of aluminous goethite by fires, the absence of corundum in natural Al-goethites calcined at 900°C, and the very high temperature (900°C) at which corundum formed from synthetic goethite suggest that other sources of Al may be required as precursors for the corundum formed by heating of soils.

Bayerite forms a cascading, travertine-like deposit over volcanic tuffs on Raoul Island in the South Pacific where it is produced from episodic discharge of spent, caustic aluminate solutions from a hydrogen generator. Textural evidence indicates microbial activity has possibly been involved in formation of the hydroxide, as well as sodium carbonate aluminate, present in minor amounts. X-ray powder diffraction and infrared spectral studies failed to give confident identification of the bayerite, the identity being confirmed by laser Raman spectroscopy. A high quality spectrum was obtained extending from 3280 to 3680 cm−1 and from 100 to 1000 cm−1.

Kaolins have been separated from sandstones from the Pugu Hills deposit, Tanzania, using a 15 mm glass hydrocyclone and a laboratory-scale multiple unit consisting of six 10 mm cyclones. Two types of sandstone were treated—containing a disordered kaolin (Pugu D) and a well-ordered variety (Pugu K)—to see whether products could be obtained that met particle-size specifications for paper manufacture. Pugu D gave a product that would meet specifications for both paper-filling and -coating applications with minimal processing, although the extremely fine-grained nature of this kaolin could lead to high viscosities in suspension. Processing of Pugu K gave products containing up to 97% kaolin and particle-size distributions that would meet specifications for filler and, possibly, coating clay. However, it was impossible to eliminate 3% or so of fine-grained quartz from these products and this could militate against use in paper manufacture.