Montpellier, France


Montpellier, France
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Woignier T.,Aix - Marseille University | Woignier T.,IRD Montpellier | Duffours L.,PRIME Verre | Colombel P.,PRIME Verre | Dieudonne P.,CNRS Charles Coulomb Laboratory
European Physical Journal: Special Topics | Year: 2015

A thorough understanding of the mechanisms and factors involved in the dynamics of organic carbon in soils is required to identify and enhance natural sinks for greenhouse gases. Some tropical soils, such as Andosols, have 3–6 fold higher concentrations of organic carbon than other kinds of soils containing classical clays. In the tropics, toxic pesticides permanently pollute soils and contaminate crops, water resources, and ecosystems. However, not all soils are equal in terms of pesticide contamination or in their ability to transfer pollution to the ecosystem. Andosols are generally more polluted than the other kinds of soils but, surprisingly, they retain and trap more pesticides, thereby reducing the transfer of pesticides to ecosystems, water resources, and crops. Andosols thus have interesting environmental properties in terms of soil carbon sequestration and pesticide retention. Andosols contain a nano porous clay (allophane) with unique structures and physical properties compared to more common clays; these are large pore volume, specific surface area, and a tortuous and fractal porous arrangement. The purpose of this mini review is to discuss the importance of the allophane fractal microstructure for carbon sequestration and pesticide trapping in the soil. We suggest that the tortuous microstructure (which resembles a labyrinths) of allophane aggregates and the associated low accessibility partly explain the poor availability of soil organic matter and of any pesticides trapped in andosols. © 2015, EDP Sciences and Springer.

Etter S.,CNRS Charles Coulomb Laboratory | Faivre A.,CNRS Charles Coulomb Laboratory | Solignac P.,CNRS Charles Coulomb Laboratory | Clement S.,CNRS Charles Coulomb Laboratory | And 3 more authors.
Journal of Materials Science | Year: 2015

Subcritical crack growth and crack closure are analysed using the double cleavage drilled compression method, in two calcium phosphate-based glasses. The measurements of the crack velocity as a function of temperature, from ambient to 250 °C, are reported for two different relative humidity levels. Studied glasses present unusual trends characterized by a non-gradual shift of V–KI curves versus temperature. Moreover, when the load is released and crack closes, expulsion of a “liquid-like” phase is observed forming droplets along the crack path. These droplets are only formed at certain temperatures, but both under high and low water humidity. They evolve towards residues when temperature is decreased. © 2015, Springer Science+Business Media New York.

Woignier T.,IRD Montpellier | Morell M.,IRD Caraibes | Morell O.,Meteo Mak | Duffours L.,Prime Verre | Soler A.,Cirad PRAM le Lamentin
Ecohydrology and Hydrobiology | Year: 2011

Chlordecone, a toxic organochlorine insecticide, is a major long term source of pollution of soils and water resources in West Indies. Allophanic soils have been strongly polluted and we show that the clay microstructure should be an important physicochemical characteristic limiting the transfer of the pesticide in water. We demonstrate the fractal structure of the allophane clay, at the nanoscale and show that it exist a correlation between the allophane fractal structure and the poor pesticides transfer from allophanic clay to water. We propose that the fractal features and associated poor low transport properties could explain why allophane clay is able to retain pesticides. Comparatively, these allophanic clays could be highly polluted but less contaminant for water resources and diffusion in environment.

Woignier T.,IRD Montpellier | Woignier T.,CNRS Mediterranean Institute for Biodiversity and Ecology Marine and Continental | Duffours L.,PRIME Verre | Colombel P.,PRIME Verre | Durin C.,French National Center for Space Studies
Advances in Materials Science and Engineering | Year: 2013

Material degradation due to the specific space environment becomes a key parameter for space missions. The use of large surface of brittle materials on satellites can produce, if impacted by hypervelocity particles, ejected volumes of mater 100 times higher than the impacting one. The presented work is devoted to the use of silica aerogels as passive detectors. Aerogels have been exposed to the low earth orbit of the ISS for 18 months. The study describes the aerogels process and the choice of synthesis parameters in such a way to get expected features in terms of porosity, mechanical properties, internal stresses, and transparency. Low-density aerogels (0.09 g·cm-3) have been prepared. The control of transparency necessary to see and identify particles and fragments collected is obtained using a base catalysis during gel synthesis. After return to earth, the aerogels samples have been observed using optical microscopy to detect and quantify craters on the exposed surface. First results obtained on a small part of the aerogels indicate a large number of debris collected in the materials. © 2013 Thierry Woignier et al.

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