Hydrothermal synthesis and characterization of dioctahedral smectites: A montmorillonites series

International audienceThe aim of this study is to synthesize and finely characterize montmorillonite samples, dioctahedral smectites without tetrahedral charges (structural formulae Nax(Al(2 − x)Mgx)Si4O10(OH)2), to allow their use as reference samples in clay science. The montmorillonites synthesis under hydrothermal conditions at different pressures and with various layer charge deficit has been attempted. The temperature was fixed at 320 °C, the pressure parameter values were 20 MPa, 80 MPa, 120 MPa and 200 MPa. The Mg content varied from 0.25 to 0.60 per half unit cell. The reaction products have been characterized with multi-technique analyses (ICP-AES, EMP, CEC, XRD, FTIR, NMR and TGA). Montmorillonite phase was only produced at 120 and 200 MPa. At 20 and 80 MPa, the results suggest that a 0.33 and 0.16-tetrahedral charge deficit exist in the formed samples. Moreover, the octahedral occupancies are higher than two (2.15 and 2.07 at 20 and 80 MPa respectively). In these experimental conditions, the synthetic smectites are mixtures between montmorillonite, beidellite and saponite. At 120 MPa and for a Mg content of 0.25 or higher than 0.33, the synthetic products were also mixtures of smectites. Tetrahedral charge deficits of 0.11, 0.11 and 0.15 were found for Mg contents of 0.25, 0.50 and 0.60 respectively. The octahedral occupancy was also higher than 2.00. A montmorillonite phase with only octahedral charges and an octahedral occupancy near 2.00 was synthesized for a Mg content of 0.33 and at pressures equal to or higher than 120 MPa. This low charge reference smectite shows a very low amount of accessory minerals and an octahedral charge deficit only created by the presence of magnesium in the structure. This montmorillonite can be compared structurally to the most studied natural one: the montmorillonite SWy-2 from Wyoming

Investisseurs institutionnels non-résidents, corporate governance et stratégies d’entreprise

À partir d’un panel de sociétés françaises et allemandes, cotées au CAC-40 et au DAX-30 au 31/12/2007, l’article se propose de mesurer la montée des investisseurs institutionnels (II) dans la structure de la propriété du capital des firmes du panel, et d’évaluer leur impact sur le comportement et la stratégie de ces entreprises. Après avoir analysé les évolutions dans la structure de propriété des sociétés (section 1), nous examinons (section 2) les effets de la montée des investisseurs institutionnels dans la structure du capital à partir d’une série d’indicateurs: évolution des profits, de la rentabilité des capitaux propres, du montant des dividendes distribués et celui des rachats d’actions. Enfin (section 3) nous examinons les évolutions de stratégies industrielles qui accompagnent la montée des investisseurs institutionnels et mettons en évidence une tendance claire au recentrage d’activités et à la consolidation. L’analyse couvre la période 1999-2007. Les données sont extraites des documents de référence annuels des firmes et des bases de données Thomson One Banker, Fininfo et Worldscope.Based on a panel of French and German companies, listed on the CAC-40 and DAX-30 to 31 December 2007, the paper is intended to measure the impact of the foreign Institutional Investors (II) in the capital structure, and to evaluate their impact on the behaviors and strategies of these firms. After analyzing the changes in the ownership capital structure of these companies (Section 1), we examine (Section 2) the effects of the II. A series of indicators are used, such as: firms’ profits, returns on equity, dividends distributed to shareholders and share buybacks. Finally (Section 3), we examine the evolution of industrial strategies that accompany the II arrival and highlight a clear trend towards refocusing of activities and consolidation. The data are extracted from annual reports and databases Thomson One Banker, Worldscope and Fininfo, and cover the period 1999-2007

Thermodynamic assessment of the variation of the surface areas of two synthetic swelling clays during adsorption of water

International audienceTwo synthetic smectites (montmorillonite and beidellite) are studied by a water adsorption technique in order to assess their specific surface areas under atmospheric conditions. A route recently proposed for extracting the thermodynamic data from experimental adsorption isotherms is used. The variation of the specific surface area during water adsorption is obtained, which can be linked to the enlargement of the interlayer space determined using X-ray diffraction. This variation is compared to an idealized specific surface area obtained from TEM and X-ray measurements in agreement with crystallographic models. All these results are also compared with those obtained previously for a natural montmorillonite. A simple view of swelling is proposed

Experimental study of smectite interaction with metal iron at low temperature: 1. Smectite destabilization.

Interaction between metal Fe and a variety of natural and synthetic smectite samples with contrasting crystal chemistry was studied by scanning electron microscopy and X-ray diffraction from experiments conducted at 80°C. These experiments demonstrate an important reactivity contrast as a function of smectite crystal chemistry. An XRD method involving the use of an internal standard allowed quantification of the relative proportion of smectite destabilized as a function of initial pH conditions as well as of smectite structural parameters. In mildly acidic to neutral pH conditions, a significant proportion of metal Fe is corroded to form magnetite without smectite destabilization. Under basic pH conditions, smectite and metal Fe are partly destabilized to form magnetite and newly-formed 1:1 phyllosilicate phases (odinite and crondstedtite). More specifically, systematic destabilization of both metal Fe and smectite is observed for dioctahedral smectites while trioctahedral smectites are essentially unaffected under similar experimental conditions. In addition, smectite reactivity is enhanced with increasing Fe3+ content and with the presence of Na+ cations in smectite interlayers. A conceptual model for smectite destabilization is proposed. This model involves first the release of protons from smectite structure, MeFe3+OH groups being deprotonated preferentially and metal Fe acting as proton acceptor. Corrosion of metal Fe results from its interaction with these protons. The Fe2+ cations resulting from this corrosion process sorb on the edges of smectite particles to induce the reduction of structural Fe3+ and migrate into smectite interlayers to compensate for the increased layer-charge deficit. Interlayer Fe2+ cations subsequently migrate to the octahedral sheet of smectite because of the extremely large layer-charge deficit. At low temperature, this migration is favored by the reaction time and by the absence of protons within the ditrigonal cavity. Smectite destabilization results from the inability of the tetrahedral sheets to accommodate the larger dimensions of the newly formed trioctahedral domains resulting from the migration of Fe2+ cations

Investisseurs institutionnels non-résidents, corporate governance et stratégies d’entreprise

À partir d’un panel de sociétés françaises et allemandes, cotées au CAC-40 et au DAX-30 au 31/12/2007, l’article se propose de mesurer la montée des investisseurs institutionnels (II) dans la structure de la propriété du capital des firmes du panel, et d’évaluer leur impact sur le comportement et la stratégie de ces entreprises. Après avoir analysé les évolutions dans la structure de propriété des sociétés (section 1), nous examinons (section 2) les effets de la montée des investisseurs institutionnels dans la structure du capital à partir d’une série d’indicateurs: évolution des profits, de la rentabilité des capitaux propres, du montant des dividendes distribués et celui des rachats d’actions. Enfin (section 3) nous examinons les évolutions de stratégies industrielles qui accompagnent la montée des investisseurs institutionnels et mettons en évidence une tendance claire au recentrage d’activités et à la consolidation. L’analyse couvre la période 1999-2007. Les données sont extraites des documents de référence annuels des firmes et des bases de données Thomson One Banker, Fininfo et Worldscope.Based on a panel of French and German companies, listed on the CAC-40 and DAX-30 to 31 December 2007, the paper is intended to measure the impact of the foreign Institutional Investors (II) in the capital structure, and to evaluate their impact on the behaviors and strategies of these firms. After analyzing the changes in the ownership capital structure of these companies (Section 1), we examine (Section 2) the effects of the II. A series of indicators are used, such as: firms’ profits, returns on equity, dividends distributed to shareholders and share buybacks. Finally (Section 3), we examine the evolution of industrial strategies that accompany the II arrival and highlight a clear trend towards refocusing of activities and consolidation. The data are extracted from annual reports and databases Thomson One Banker, Worldscope and Fininfo, and cover the period 1999-2007

A new strategy against hostile takeovers: a model of defense in participations

This article examines the efficacy of a “defense in participations” policy consisting of competitors acquiring cross equity participations within the same industry to prevent hostile takeovers. This defense in participations strategy provides disincentive for raiders as partial ownerships increase market power of competitors and then reinforce the “outsider effect”. Also, we find conditions for a general result which states that takeovers are less profitable in an industry with participations rather than in an industry without any capital links. We provide information to regulators about the positive social impact of cross participations in the context of mergers, and expose an economic dilemma between a “laisser-faire” and an interventionist approach

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

Takeover deterrents and cross partial ownership: The case of golden shares

We analyse takeovers in an industry with bilateral capital‐linked firms in cross partial ownership (CPO). Before merger, CPO reduces the profitability of involved firms, confirming the “outsider effect.” However, the impact of CPO upon merger profitability is two‐sided in a Cournot setting. CPO, by cointegrating profits, increases output collusion leading to anticompetitive effects with facilitated mergers in most cases. Nonetheless, a protective threshold exists for which CPO arrangements can reduce the incentives for hostile takeovers. This has potentially significant regulatory implications. An illustrative example showcases the potential relevance of CPO as a defence against hostile takeovers across different industries