Microcellular Electrode Material for Microbial Bioelectrochemical Systems Synthesized by Hydrothermal Carbonization of Biomass Derived Precursors

V.F. acknowledges a UQ Postdoctoral Fellowship. This work was supported by the Australian Research Council Grant DP110100539. The authors acknowledge the facilities and the scientific and technical assistance of the Australian Microscopy & Microanalysis Research Facility at the Centre for Microscopy and Microanalysis (The University of Queensland). The Ghent University Special Research Fund (BOF) is acknowledged for the postdoctoral grant of M.N.B

Mechanical behaviour of nano composite aerogels

In order to improve the mechanical properties of silica aerogels, we propose the synthesis of nano composite aerogels. Silica particles (20-100 nm) are added in the monomer solution, just before gelling and supercritical drying. The silica particles addition increases the mechanical properties, but also affects the aggregation process, the aerogel structure and the pore sizes. We discuss the different parameters which infer in the mechanical behaviour of silica aerogel such as: brittle behaviour, load bearing fraction of solid (pore volume), internal stresses (shrinkage), size and distribution of flaws, subcritical flaws propagation (chemical susceptibility). With silica particles addition, the mechanical properties rapidly increase, stiffening and strengthening the structure by a factor 4-8. Moreover, the mechanical strength distribution and the Weibull modulus characterizing the statistical nature of flaws size in brittle materials show a more homogeneous strength distribution. The composite structure is made of two imbricate networks, the polymeric silica and the particles silica networks. Ultra Small Angle X-ray Scattering experiments show that besides the fractal network usually built up by the organosiloxane, the silica particles is forming another fractal structure at a higher scale. The fractal structure could be related to the low Weibull parameter characteristic of a large flaws size distribution, pores being the critical flaws

Spectroscopic characterisation of sol-gel organo-siloxane materials synthesised from aliphatic and aromatic alkoxysilanes

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Radiation-induced defects in clay minerals : a review

Extensive information has been collected on radiation effects on clay minerals over the last 35 years, providing a wealth of information on environmental and geological processes. The fields of applications include the reconstruction of past radioelement migrations, the dating of clay minerals or the evolution of the physico-chemical properties under irradiation. The investigation of several clay minerals, namely kaolinite, dickite, montmorillonite, illite and sudoite, by Electron Paramagnetic Resonance Spectroscopy has shown the presence of defects produced by natural or artificial radiations. These defects consist mostly of electron holes located on oxygen atoms of the structure. The various radiation-induced defects are differentiated through their nature and their thermal stability. Most of them are associated with a pi orbital on a Si-O bond. The most abundant defect in clay minerals is oriented perpendicular to the silicate layer. Thermal annealing indicates this defect in kaolinite (A-center) to be stable over geological periods at ambient temperature. Besides, electron or heavy ion irradiation easily leads to an amorphization in smectites, depending on the type of interlayer cation. The amorphization dose exhibits a bell-shaped variation as a function of temperature, with a decreasing part that indicates the influence of thermal dehydroxylation. Two main applications of the knowledge of radiation-induced defects in clay minerals are derived: (i) The use of defects as tracers of past radioactivity. In geological systems where the age of the clay can be constrained, ancient migrations of radioelements can be reconstructed in natural analogues of high level nuclear waste repositories. When the dose rate may be assumed constant over time, the paleodose is used to date clay populations, an approach applied to fault gouges or laterites of the Amazon basin. (ii) The influence of irradiation over physico-chemical properties of clay minerals. An environmental application concerns the performance assessment of the engineered barrier of nuclear waste disposals. In case of a leakage of transuranic elements from the radioactive waste form, alpha recoil nuclei can amorphize smectite after periods of the order of 1000 years according to a worst case scenario, whereas amorphization from ionizing radiation is unlikely. As amorphization greatly enhances the dissolution kinetics of smectite, the sensitivity of the smectites must be taken into account in the prediction of the long term behavior of engineered barriers

Sol-Gel Derived Organic and Inorganic Hybrid Materials for photonic applications: Contribution to the correlation between the material structure and the transmission in the near Infrared Region

International audienceA promising way of fabricating integrated optics components is based on the sol-gel synthesis and photocuring of organic-inorganic hybrid materials. However, the main factor limiting the development of passive devices is the propagation losses. Moreover, the possibility to compensate these attenuations by optical amplification is competed with the multiphonon relaxation associated to the presence of OH groups. To our knowledge, OH groups were always shown as the main responsible for attenuation at the telecommunication wavelengths, namely at 1310 and 1550 nm, although the matrix is composed of organic species which can contribute to absorptions in this spectral range. This paper deals with spectroscopic and optical characterizations of a well established organic and inorganic hybrid material in order to determine the contribution of each molecular groups to the attenuation at the aforementioned wavelengths