Integration of iron in natural and synthetic Al-pyrophyllites: an infrared spectroscopic study

Numerous studies focus on the relationships between chemical composition and OHband positions in the infrared (IR) spectra of micaceous minerals. These studies are based on the coexistence, in dioctahedral micas or smectites, of several cationic pairs around the hydroxyl group which each produce a characteristic band in the IR spectrum. The aim of this work is to obtain the wavenumber values of the IR OH vibration bands of the (Al-Fe3+)-OH and (Fe3+-Fe3+)-OH local cationic environments of 'pyrophyllite type' in order to prove, disprove or modify a model of dioctahedral phyllosilicate OH-stretching band decomposition. Natural samples are characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopies and electron microprobe; the hydrothermal synthesis products are also analysed by powder XRD and FTIR after inductively coupled plasma measurements to obtain the chemical compositions of nascent gel phases. Natural samples contain some impurities which were eliminated after acid treatment; nevertheless, a small Fe content is found in the pyrophyllite structure. The amount of Fe which is incorporated within the pyrophyllite structure is much more important for the synthetic samples than for the natural ones. The IR OH bands were clearly observed in both natural and synthetic pyrophyllites and assigned to hydroxides bonded to (Al-Al), (Al-Fe) and (Fe-Fe) cationic pairs. During this study, three samples were analysed by DTG to check the cis- or trans-vacant character of the layers and to determine the influence of this structural character on the OH-stretching band position in IR spectroscopy

Separation versus affiliation with partial vertical ownership in network industries

The separation of integrated monopolies and new market entrants have changed vertical interactions between suppliers and dealers. Firms have substituted full integration with vertical restraints leading to collusive behaviour harmful to competition. We examine how a partial vertical ownership (an affiliation) of one of the competing downstream retailers by the upstream monopoly could help internalise the production decision after a complete divestiture. Our results in a Cournot framework confirm the positive role of partial integration on firms' profits and consumer surplus in increasing social welfare. These results are consistent with empirical studies of economies after vertical separation in network industries

Experimental investigation of smectite interaction with metal iron at 80 °C: Structural characterization of newly formed Fe-rich phyllosilicates

International audienceInteractions between metallic iron and clay minerals have been extensively studied under low-temperature anoxic conditions owing to their potential impact on the long-term safety of high-level nuclear waste disposal in deep geological repositories. To complement the studies investigating the destabilization mechanisms and rates of various initial clay minerals, the prediction of the storage long-term performance requires a comprehensive characterization of the reaction products. The Fe-rich 1:1 phyllosilicates resulting from interactions at 80 °C and in the absence of O2 between metallic iron and smectites with contrasting compositions are thus characterized chemically and structurally using various experimental techniques (X-ray and electron diffractions, infrared, energy-dispersive, and electron energy loss spectroscopies, and high-resolution electron microscopy). Cronstedtite and odinite are the two Fe-rich 1:1 phyllosilicates formed under the experimental conditions investigated, both species differing from their relative contents and the average valence state of structural Fe. No parental link has been evidenced between the two minerals despite their contrasting crystal morphologies and thermodynamical predictions. The formation of the 1:1 phyllosilicates apparently results from the destabilization of the initial smectite through the formation of an intermediate gel

Effect of Nanoscale Pore Space Confinement on Cadmium Adsorption from Aqueous Solution onto Ordered Mesoporous Silica: A Combined Adsorption and Flow Calorimetry Study

International audienc