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Limoges, France

Bollinger J.-C.,GRESE
Actualite Chimique | Year: 2015

About Jules Verne, diamond geo-genesis and the review Nature Browsing through recent issues of the respected scientific journal Nature, the author has found a number of explicit references to Jules Verne's famous novel Journey to the Center of the Earth. For example, in a pape about the analysis of a solid inclusion within a diamond, diamond formation from a solution is mentioned. But this is in fact a main topic within another and lesser known novel, The Southern Star. Then a discussion concerning diamond formation is presented, followed by some considerations on Verne's representation in the mind of his readers, either scientists or not.

Prud'Homme E.,CNRS Heterogeneous Materials Study Group | Michaud P.,CNRS Heterogeneous Materials Study Group | Joussein E.,GRESE | Rossignol S.,CNRS Heterogeneous Materials Study Group
Journal of Non-Crystalline Solids | Year: 2012

The development of porous materials based on geopolymers allows the benefits of eco-consumption, good insulating properties and good mechanical properties to be combined. For geopolymers to be useful, the development of an understanding of their properties under various conditions is important. Attention was given to the structural evolution of porous materials with heating. The structural evolutions were investigated using thermal analysis and infrared spectroscopy. The formation of a crystalline phase was observed and identified as a zeolite. To elucidate the roles played by the raw materials, silicon concentration and potassium concentration on the formation of the crystalline phase, three parameters in the foam synthesis process were modified. The influence of silica fume and metakaolin on the appearance of the crystalline phase was examined through the reactivity of the raw materials in contact with a potassium solution. Different behaviors directly linked to the network composition were observed. Silica-fume-based samples showed phase crystallization and dehydroxylation due to the large concentration of silicon, which likely led to the formation of hydrated silica species. The formation of the zeolite-phase network upon the application of heat depended only on the silica dissolution and was linked to the composition of silica in terms of the silicon species and grain size. Studying the crystalline phase formation by variation of the amount of potassium allowed the determination of a maximum silicon concentration and a minimum potassium concentration. The formation of the zeolite phase occurred at a potassium concentration greater than 3.5 mol·L - 1 and a silicon concentration lower than 16.5 mol·L - 1, which confirmed the presence of F-zeolites. © 2012 Elsevier B.V. All rights reserved.

Autef A.,Limoges National Superior School of Industrial Ceramics | Joussein E.,GRESE | Gasgnier G.,Imerys | Rossignol S.,Limoges National Superior School of Industrial Ceramics
Ceramic Engineering and Science Proceedings | Year: 2013

Geopolymers have been the object of numerous studies because of their low environmental impact. The synthesis of these geomaterials is achieved by the alkaline activation of aluminosilicates. Alkaline activation is typically accomplished by the activation of potassium silicate or sodium silicate. These alkaline silicate solutions are relatively expensive. We thus attempted to create these solutions by the dissolution of potassium hydroxide and silica in water. This study focuses on the various parameters that can influence the dissolution of silica in basic media (pH>13). The samples used were amorphous silica, quartz sand and quartz ground to five different size distributions. The study of the dissolution of siliceous species was performed mainly by infrared spectroscopy by varying several factors. Stirring and solution volume played no significant role. However, the size distribution and crystallinity of silica were observed to significantly affect the kinetics of dissolution and the quantities of siliceous species in solution, which varied greatly according to the quantity of KOH introduced.

Prud'homme E.,CNRS Heterogeneous Materials Study Group | Michaud P.,CNRS Heterogeneous Materials Study Group | Joussein E.,GRESE | Peyratout C.,CNRS Heterogeneous Materials Study Group | And 4 more authors.
Journal of the European Ceramic Society | Year: 2010

The synthesis of geopolymers based on alkaline polysialate was achieved at low temperature (∼25-80 °C) by the alkaline activation of raw minerals and silica fume. The materials were prepared from a solution containing dehydroxylated kaolinite and alkaline hydroxide pellets dissolved in potassium silicate. Then the mixture was transferred to a polyethylene mold sealed with a top and placed in an oven at 70 °C for 24 h. For all geopolymer materials, following dissolution of the raw materials, a polycondensation reaction was used to form the amorphous solid, which was studied by FTIR-ATR spectroscopy. The in situ inorganic foam based on silica fume was synthesized from the in situ gaseous production of dihydrogen due to oxidation of free silicon (content in the silica fume) by water in alkaline medium, which was confirmed via TGA-MS experiments. This foam has potential as an insulating material for applications in building materials since the thermal measurement has a value of 0.22 W m-1 K-1. © 2010 Elsevier Ltd. All rights reserved.

Prud'Homme E.,CNRS Heterogeneous Materials Study Group | Michaud P.,CNRS Heterogeneous Materials Study Group | Joussein E.,GRESE | Smith A.,CNRS Heterogeneous Materials Study Group | And 4 more authors.
Journal of Sol-Gel Science and Technology | Year: 2012

The geomaterial foams studied is based on geopolymerization reactions, which is a type of geosynthesis that involves silico-aluminates. Its study during formation has however revealed a different behavior than geopolymer, suggesting the formation of various networks. This work investigates the interaction between initial compounds (metakaolin, silica fume, potassium-based solution) by a kind of mixture decomposition to ultimately understand the formation mechanism of foam. The structural evolution was determined using thermal analysis, FTIR spectroscopy and 27Al and 29Si MAS-NMR measurements. The use of different raw materials in combination with various solutions demonstrates the formation of various species in solution. The reactivity of the solution will then evolve in different ways. The Si/K ratio controlled the type of species created and, particularly, the reactivity in the mixture. From the various reactions of dissolution and polycondensation that were deduced, we could identify the composition of the four networks (K 0.5SiAl 0.75O 6.8H 8.6; K 2Si 2O 5; KAlSi 2O 4,1. 5H 2O; and amorphous silica) constituting the foam. © 2011 Springer Science+Business Media, LLC.

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