The smectitic minerals in a bentonite deposit from melo (Uruguay)

International audienceA nearly monomineralic 1.5 m thick bentonite bed sampled in Melo (Uruguay) appears to be a pure high-charge montmorillonite: [Si3.94 Al0.06] (Al1.40 Fe 3+ 0.11 Ti0.02 Mg0.49 Mn0.01) O10 (OH)2 Na0.01 K0.08 Ca0.18. However, contrasting swelling behaviors have been evidenced by fitting the experimental X-ray diffraction patterns recorded on oriented preparations of the same sample in different saturation states. According to the expandability of the layers in the Ca-, K- and K-Ca-saturated (that is saturated first with K + and subsequently with Ca2+) states, three "layer types" were defined. Low-, intermediate-, and high-charge layers are fully, partly, and not expandable, respectively, after K-saturation. Collapse of high-charge layers is not reversible after subsequent Ca-saturation, most likely because of tetrahedral substitutions. These three different layer types are segregated in two distinct randomly interstratified mixedlayer phases. TSA and CEC are shown to depend on the interlayer cation composition

THE FATE OF SMECTITE IN KOH SOLUTIONS

International audienceThe aim of the present study was to investigate the detailed evolution of the SAz-1 smectite in 1 M KOH at 80°C at a solid/liquid ratio of 1/80. AFM observations indicated no change in crystal size or shape. XRD measurements at 40% relative humidity revealed changes in expandability of the smectite. The 001 reflection profile of smectite was modelled using the trial-and-error approach of Sakharov et al., 1999b. The results indicate that with increasing run time the number of non expandable layers with zero or one water layer increases and that the coherent scattering domain size of the smectite decreases. Infrared spectroscopy of the reacted smectite suggests that there is no change from the initial clay products. The dehydroxylation temperature showed a slight decrease from 619° to 605°C. STA measurements demonstrated that the cis-vacant character of the octahedral sheet remained nearly unchanged throughout the experiment. Determination of the average layer charge showed a continuous increase from 0.32 to 0.42 eq/Si (Si/Al)4O10 whereas the layer charge distribution indicated the appearance of high charged smectite layers with a charge of ~ 0.6 eq/Si (Si/Al)4O10 and the disappearance of the low charged layers. XPS and SEM measurements indicate an increase of the aluminium in the smectite samples. Isotope data support the theory of a internal diffusion mechanism by gradual changes in δ 18O values. From these data it appears that KOH solutions provoke a mineralogical change in the 2:1 layer of the smectite minerals which increases the layer charge by increasing the Al content. This mineralogical change does not involve dissolution/crystallization processes and then must show solid state transformation of the clays at 80°C

Effect of Temperature and Pressure on Surface Tension of Polystyrene in Supercritical Carbon Dioxide

This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry B., 111, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/jp065851tThe surface tension of polymers in a supercritical fluid is one of the most important physicochemical parameters in many engineering processes, such as microcellular foaming where the surface tension between a polymer melt and a fluid is a principal factor in determining cell nucleation and growth. This paper presents experimental results of the surface tension of polystyrene in supercritical carbon dioxide, together with theoretical calculations for a corresponding system. The surface tension is determined by Axisymmetric Drop Shape Analysis-Profile (ADSA-P), where a high pressure and temperature cell is designed and constructed to facilitate the formation of a pendant drop of polystyrene melt. Self-consistent field theory (SCFT) calculations are applied to simulate the surface tension of a corresponding system, and good qualitative agreement with experiment is obtained. The physical mechanisms for three main experimental trends are explained using SCFT, and none of the explanations quantitatively depend on the configurational entropy of the polymer constituents. These calculations therefore rationalize the use of simple liquid models for the quantitative prediction of surface tensions of polymers. As pressure and temperature increase, the surface tension of polystyrene decreases. A linear relationship is found between surface tension and temperature, and between surface tension and pressure; the slope of surface tension change with temperature is dependent on pressure.Natural Sciences and Engineering Research Council of Canada (NSERC) Canadian Foundation for Innovation (CFI) Canada Research Chairs (CRC) Progra

Formation of Zn–Ca phyllomanganate nanoparticles in grass roots

International audienceIt is now well established that a number of terrestrial and aquatic microorganisms have the capacity to oxidize and precipitate Mn as phyllomanganate. However, this biomineralization has never been shown to occur in plant tissues, nor has the structure of a natural Mn(IV) biooxide been characterized in detail. We show that the graminaceous plant Festuca rubra (red fescue) produces a Zn-rich phyllomanganate with constant Zn:Mn and Ca:Mn atomic ratios (0.46 and 0.38, respectively) when grown on a contaminated sediment. This new phase is so far the Zn-richest manganate known to form in nature (chalcophanite has a Zn:Mn ratio of 0.33) and has no synthetic equivalent. Visual examination of root fragments under a microscope shows black precipitates about ten to several tens of microns in size, and their imaging with backscattered and secondary electrons demonstrates that they are located in the root epidermis. In situ measurements by Mn and Zn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray diffraction (XRD) with a micro-focused beam can be quantitatively described by a single-phase model consisting of Mn(IV) octahedral layers with 22% vacant sites capped with tetrahedral and octahedral Zn in proportions of 3:1. The layer charge deficit is also partly balanced by interlayer Mn and Ca. Diffracting crystallites have a domain radius of 33 Å in the ab plane and contain only 1.2 layers (not, vert, similar8.6 Å) on average. Since this biogenic Mn oxide consists mostly of isolated layers, basal 00l reflections are essentially absent despite its lamellar structure. Individual Mn layers are probably held together in the Mn–Zn precipitates by stabilizing organic molecules. Zinc biomineralization by plants likely is a defense mechanism against toxicity induced by excess concentrations of this metal in the rhizosphere

The Journal of the Friends' Historical Society vol. 5 No. 2

1. Notices. 2. Notes and Queries. 3. Obituary. 4. Quaker Ministers and French Police. 5. Documents from the Paris National Archives relating to Stephen Grellet I. 6. Presentations of Quakers in Episcopal Visitations, 1662-1679. 7. Bernard Barton's Dream. 8. A Glimpse of Ancient Friends in Dorset II. 9. Death of John Ellis, of Poole, 1707. 10. Hannah Lightfoot. 11. Editors' Notes. 12. Records respecting John and Margaret Lynam in England and Maryland. 13. Islington Road School. 14. Richard Cubham of Bickerstaffe, Yeoman. 15. Certificate respecting James Graham and William Armstrong, from Long Island, 1717. 16. Friends in Current Literature

The Journal of the Friends' Historical Society vol. 5 No. 3

1. Notices. 2. Notes and Queries. 3. Documents from the Paris National Archives relating to Stephen Grellet II. 4. Presentations of Quakers in Episcopal Visitations, 1662-1679. 5. Extracts from the Minute Book of the Women's Quarterly Meeting of Nottingham and Mansfield II. 6. Pennsylvenian Motions. 7. The Quaker Allusions in "The Diary of Samuel Pepys" III. 8. Obituary. 9. An Eighteenth Century Friends - Thomas Pole, M.D. 10. A Glimpse of Ancient Friends in Dorset III. 11. Friends in Current Literature. 12. Some Addenda to First Publishers of Truth in Staffordshire. 13. Officers for the Year 1908-9. 14. Balance Sheet for 1907

Transformation of Co-containing birnessite to todorokite: Effects of Co on the transformation and implications for Co mobility

The mobility and fate of bioessential transition metals, such as Ni and Co, are strongly controlled by their association with phyllomanganate minerals such as birnessite. These minerals however, can transform to tectomanganates such as todorokite during soil and sediment diagenesis, yet the mobility and fate of most metals during the transformation process remain largely unknown. Here this research investigates the effect of Co on, and the mobility and fate of Co during the transformation of birnessite into tunnel structure minerals. A range of Co-containing birnessite precursors with up to 20% Co/(Co+Mn) molar ratios were synthesised, and subsequently transformed via a mild reflux procedure designed to mimic the diagenesis of these layered precursors into tunnel structures. The layered precursors and reflux products were characterized using a combination of mineralogical and geochemical techniques, including powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), high resolution transmission electron microscopy (HRTEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The results show that Co(III) is structurally incorporated into the layered precursors and reflux products, through the isomorphic substitution of Mn(III). The structural incorporation of Co(III) into the layered precursors leads to an overall reduction of Jahn-Teller distorted Mn(III) octahedra in these minerals, a key factor for their transformation to tunnel structures. As a consequence, the presence of such structural Co(III) disrupts the transformation of birnessite into todorokite, leading to the coexistence of 9.6 Å asbolane-like phyllomanganate and non-ideal 3×n, or a-disordered, todorokite-like tectomanganates in the transformation products. Newly formed todorokite exhibits a wide range of 3×n tunnel dimensions (n up to 13) and a plate-like morphology. Overall the structural incorporation of non Jahn-Teller distorted cations like Co(III) into birnessite might help explain the often observed predominance of phyllomanganates over tectomanganates in soils and sediments, and the persistence of phyllomanganates in ferromanganese deposits that can be many millions of years old. The results also indicate that Co(III) initially associated with birnessite is retained in the solid phase during transformation, and thus the mobility of Co(III) is limited. EXAFS data suggest that Co is mainly located in the octahedral layers of asbolane-like phyllomanganate and at non-edge sites in non-ideal todorokite. Overall the transformation of Co-containing birnessite into non-ideal todorokite and asbolane-like layered structures maintains the strong sequestration of Co by Mn oxides