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.

Lors de l'étude du gonflement des smectites par analyse de la diffusion des rayons X aux petits angles, Pons et al. (1981) et Ben Rhaiem (1983) ont obtenu des diagrammes de diffusion caractérisés dans le domaine étudié par des modulations plus ou moins prononcées de la courbe d'intensité.

L'analyse quantitative des courbes de diffusion, et en particulier de ces modulations, permet alors de remonter à une description de la structure du gel ou de la pâte et aux relations existant entre texture et structure (Pons et al., 1981; Pons et al., 1982). La méthode générale d'interprétation proposée par Pons et al. (1981) repose sur une comparaison entre intensité expérimentale et intensité théorique calculée à partir de modèles.

This study focuses on the main factors determining the apparent porosity of porous bioceramics prepared using small organic foam spheres as the pore-making reagent, in order to determine the best technical parameters for preparing porous bioceramics. In every experiment, only one of these factors (the time of heating, the sintering temperature, the mass ratio between small organic foam spheres and beta-tricalcium phosphate (β-TCP) powder, and the rate of the temperature rise) was changed, while the others were kept constant. In each case the apparent porosity was tested and the relation between the specific variable and apparent porosity was observed. Finally, the optimum technical parameters were deduced. The apparent porosity shows an inverse linear relation to the time of heating and the sintering temperature, and is approximately proportional to the mass ratio between the small organic foam spheres and the β-TCP powder and the rate of temperature rise. These factors have important influences on the apparent porosity. The optimum conditions were: heating time (soak time) 120 min, sintering temperature 850ºC, mass ratio 0.25, and a rate of temperature increase of 120ºC h–1.

Complexes formed between 0·034 m dimethyltin dichloride solutions and Na-montmorillonite at pH 2·4 and 4·0 have been characterized using 119Sn Mössbauer spectroscopy, X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and water sorption isotherms. The dominant exchange cation at pH 2·4 is Me2Sn2+ characterized by an isomer shift, δ, and quadrupole splitting, Δ values of 1·25 and 3·80 mm s−1, respectively. The major exchange cation at pH 4·0 is the dimer, [Me2SnOH]22+, (δ = 1·38, Δ = 3·34 mm s−1) although the monomer, Me2Sn(OH)+, (δ = 0·95, Δ = 3·29 mm s−1) is also present. These complexes have basal spacings of 15·0 and 16·0 Å, respectively, which are stable up to 200°C. Mössbauer spectroscopy has shown that these ions are converted to SnO2 via Me2SnO upon thermal degradation. The temperature at which these oxides appear coincides with the collapse of the basal spacing. Both complexes display BET Type IV isotherms for the adsorption of water, following thermal pretreatment at 150°C, but the complex prepared at pH 4·0 has a lower sorption capacity. Both complexes, contrary to the normal behaviour of layer-silicates, have a definite pore volume and no further uptake occurs when this is filled.

Magnetite-rich waste from a niobium mine near Araxá, State of Minas Gerais, Brazil, was heated to 500°C and 1000°C under an O2 atmosphere. The original waste and its oxidized products were characterized by energy-dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), room-temperature 57Fe Mössbauer spectroscopy, thermogravimetric analysis (TG) and temperature-programmed reduction (TPR).

Semiquantitative analyses by EDS and quantitative chemical analyses showed the waste to be constituted primarily of Fe with minor amounts of Ti, Ba, Al, Si, Nb, Mn, S and P. Mössbauer and XRD showed the waste to consist predominantly of magnetite and hematite. The magnetite content decreases when the temperature increases due to its direct conversion to hematite. However, at 500°C only 10 wt.% of original magnetite was converted to hematite, confirming the high stability of this magnetite, which could still be detected at 1000°C. The TG profile shows no significant weight gain on heating, indicating a high stability of the magnetite. The TPR profiles show that the hematite in the waste is sintered after treatment at 1000°C and the reduction peaks are consequently shifted to higher temperatures. This high thermal stability is attributed to a moderate isomorphous replacement of Fe by other cations present in the Nb mining waste.

The use of clay materials as selective sorbents for different contaminants requires very efficient methods. A natural kaolinite was calcined to metakaolinite and than rehydrated at different temperatures to produce a highly porous sorbent. The kinetics of this process were measured, with subsequent IR characterization of the phases formed. The surface and pore distribution of new phases were also assigned. In addition, the kaolinite obtained was pre-treated with Fe3+ ions to improve its sorption affinity for anionic particles. The rehydrated kaolinite and its Fe-modification were used for the adsorption of toxic cations (Zn, Cd, Pb) and anions (As, Se). Adsorption capacities depending on the physical chemical properties of the initial solution (pH, concentration of toxic ions) and the surface properties of the sorbent (specific surface area, modification method) were investigated. The adsorption properties of the sorbents were defined by the Langmuir model.

Solutions obtained from soils in the Galicia Region of NW Spain had considerably lower activities of Al3+ when obtained by a speciation procedure (fractionation with an ionic column and application of specific software) than when obtained from concentrations of reactive Al (colorimetry with pyrocatechol violet) by a calculation that only considers simple hydroxylated species. Using the speciation method, many of the solutions obtained from surface horizons are unsaturated for most minerals, especially in granitic areas.

On étudie l'influence des cations compensateurs sur le spectre P.I.R. d'une vermiculite hydratée à deux couches. La définition d'un paramètre IR permet de quantifier cet effet. On conclue que l'énergie d'hydratation du cation est en relation avec la rigidité de la couche interfoliaire.

The purpose of this study was to develop a simple and efficient method for manufacturing porous bioceramics, in which small organic foam spheres were taken as the poremaking reagent and green bodies were made by hot die-casting in moulds. The raw materials (small organic foam spheres, paraffin, oleic acid and β-TCP powder) were mixed into a slurry at 30–120ºC and moulded into green bodies using a hot die-casting machine at 30–90ºC; the green bodies were then sintered and the porous bioceramics obtained. The main characteristics (structure and size of pores, water permeability, apparent porosity and shrinkage) were tested. The results indicated that the apparent porosity was high and directly proportional to the mass ratio between the small organic foam spheres and the β-TCP powder. The pores connected with each other in three dimensions; the size, distribution of the shapes and structures of the pores were clearly related to the dimensions of the small organic foam spheres. The water permeability was proportional to the hot die-casting pressures and the shapes of the samples could easily be controlled by selecting different moulds. This study indicated that the method can be used to manufacture porous bioceramics with controlled pore structures and different shapes effectively and easily by adding different amounts and sizes of small organic foam spheres, mixing the raw materials evenly, and by selection of the hot die-casting pressure and by the use of different moulds.

Talc [ideal formula: Mg3Si4O10(OH)2] is one of the classical 2:1 trioctahedral phyllosilicates that has been analysed intensively with respect to its formation, thermal stability, chemical properties and structure (e.g. Wilkins & Ito, 1967; Rayner &Brown, 1973; Ward, 1975; Martin et al., 1996). Single crystal structure refinement by X-ray diffraction (XRD) showed clearly that talc is triclinic and crystallizes in the space group CI (e.g. Rayner & Brown, 1973; Perdikatsis & Burzlaff, 1981). Based on this structural model, two coordination arrangements of OH groups to Mg in the octahedral sheets can be deduced. Since XRD data give only an insight into the average structure, local information on the ligand field of the cations is limited. Currently, no analytical tool is known to determine directly the ligand field of Mg in the octahedral sites.

Basalts and other mafic rocks are frequently used for road construction. The aggregates have to provide intrinsic mechanical strength and skid resistance. However, smectite contents stemming from alteration processes may deteriorate these mechanical properties considerably because of the resulting contrast in hardness. Quantitative relationships between smectite content, kind of distribution, and aggregate stability are rare except for a recent study by Kaufhold et al. (2012). In this work thirteen basalt and andesite samples from German quarries were analysed by X-ray diffraction (XRD) for their mineral contents (including clay minerals), their cation exchange capacities (CEC) and their resistance against disaggregation in dimethyl sulfoxide. Smectite contents from XRD exceeded those calculated from the CEC regardless of the kind of occurrence of smectite observed in thin sections. The hypothesis that rocks with smectites occurring mostly in patches should differ in terms of CEC and mechanical properties from those rocks where smectites are more disseminated could not be confirmed. However, the amounts of smectite accessible to cation exchange correlated with the DMSO losses. Therefore, the fast CEC determination with Cu-Trien exchange can be substituted for the time-consuming DMSO test.

Size graded fractions of ground quartz and other silica minerals are prepared by gravity settling for particles greater than 2 microns Stokes' diameter and by centrifugal methods for smaller sizes. The size distributions of the prepared fractions are determined by counting and sizing with an optical microscope or with an electron microscope. The volume-surface diameter ΣND3/ΣND2 is used both for calculating the specific surface of the fractions and for comparing the projected area diameters used in counting, with the Stokes' diameters.

Se realiza un estudio detallado de las distintas fases minerales (caolínicas y silíceas) que aparecen en rocas silicificadas tanto graniticas como sedimentarias de la provincia de Avila.

Las técnicas utilizadas (A.T.D., difracción de rayos X, microscopía electrónica de trasmisión y de barrido) permiten establecer una clasificación de estos minerales segun sus propiedades térmicas, parámetros cristaloquímicos, y morfologías identificadas al scaning.

Sa dá una interpretación genética a cada uno de los tipos de caolinitas encontrados (macrocaolinitas en acordeón, microcaolinitas en gusanillo y criptocaolinitas). Los dos primeros tipos pueden ser explicados por procesos conjuntos de alteración hidrotermal y ‘weathering’ de feldespatos y micas. El tercer tipo (criptocaolinitas) es de más difícil interpretación al aso-ciarse con ópalo C-T en diques que cortan a rocas granitoideas y otras veces al presentarse como matriz de areniscas sedimentarias.