Showing papers by "Jean-Marie Nedelec published in 2007"

A Raman Study of the Sulfated Cement Hydrates: Ettringite and Monosulfoaluminate

Abstract: Ettringite (the AFt Ca6Al2(OH)12·(SO4)3·26H2O compound) and monosulfoaluminate (the AFm Ca4Al2(OH)12·SO4·6H2O compound) phases were synthesised by the coprecipitation method and studied by micro-Raman spectroscopy. Hydrogen bond network, involving sulfate anions, ensures the cohesion of the structure of these two compounds; the columnar struture of ettringite as well as the lamellar structure of monosulfoaluminate. Raman spectroscopy has been used as a probe to investigate mainly the inter-columnar and the inter-lamellar regions of the structures. Raman spectra allowed the characterization of the local environment of sulfate anions and the hydrogen bond networks. A significant asset brought by Raman spectroscopy is the ability to work on hydrated cement products without specific sample preparation; i.e. without a risk to dammage these hydrated compounds. Several examples of the possibilities brought by Raman spectroscopy in cement chemistry are given in this paper. A space group redetermination of the ettringite structure was performed on the basis of the point symmetry of sulfate tetrahedra. The inter-columnar region of ettringite was compared to the inter-lamellar region of monosulfoaluminate as these two structural parts contain the same species. The thermal behaviors at the beginning of the dehydration (up to 390 K) and the iron substitution in ettringite were also investigated.

Sol-gel processing of nanostructured inorganic scintillating materials

Abstract: The development of scintillating materials is believed to reach a new step by controlling their preparation on a nanometric level. Sol-Gel chemistry offers very unique tools for nanoscale mastering of the materials preparation. In particular, shaping of the materials as thin films or nanoparticles offers new application in medical imaging. The control of doping ions dispersion thanks to soft chemistry is also a great advantage of such synthetic routes. In this paper, we will review recent work devoted to the sol-gel preparation of inorganic scintillating materials. We will focus on the new possibilities and advantages offered by sol-gel chemistry for the preparation of new scintillators and improvement of existing ones.

Biological activity of a SiO2–CaO–P2O5 sol–gel glass highlighted by PIXE–RBS methods

Abstract: It is proposed in this study to observe the influence of P2O5 on the formation of the apatite-like layer in a bioactive glass via a complete PIXE characterization A glass in the SiO2-CaO-P2O5 ternary system was elaborated by sol-gel processing Glass samples were soaked in biological fluids for periods up to 10 days The surface changes were characterized using Particle Induced X-ray Emission (PIXE) associated to Rutherford Backscattering Spectroscopy (RBS), which are efficient methods for multielemental analysis Elemental maps of major and trace elements were obtained at a micrometer scale and revealed the bone bonding ability of the material The formation of a calcium phosphate-rich layer containing magnesium occurs after a few days of interaction We demonstrate that the presence of phosphorus in the material has an impact on the development and the formation rate of the bone-like apatite layer Indeed, the Ca/P atomic ratio at the glass/biological fluids interface is closer to the nominal value of pure apatite compared to P2O5 free glasses It would permit, in vivo, an improved chemical bond between the biomaterials and bone

Isothermal crystallization kinetics of in situ photo and thermo aged poly(ethylene oxide) using photoDSC.

Abstract: Isothermal crystallization of a high molecular weight PEO (Mw = 4 000 000) has been investigated using photoDSC. Combining light irradiation, heating and DSC analysis, photoDSC demonstrates good capability to follow the in situ photo- and thermo-ageing of semi-crystalline polymers. Isothermal crystallization of PEO was performed at 55 °C. After ageing at different temperatures ranging from 0 to 90 °C and for various periods of time, the kinetics of this crystallization was found following the Avrami theory. Avrami exponent, n, was found between 0.9 and 1.4 evidencing a one-dimension growth process. It was also found that the isothermal crystallization rate (i.e. reciprocal crystallization half-time) was exposure time, ageing temperature and light intensity dependent which makes this kinetic parameter a good indicator of following and comparing the degradation of the semi-crystalline polymers.

Crystallization of carbon tetrachloride in confined geometries

Abstract: The thermal behaviour of carbon tetrachloride confined in silica gels of different porosities was studied by differential scanning calorimetry. Both the melting point and the low temperature phase transition were measured and found to be inextricably dependant on the degree of confinement. The amount of solvent was varied through two sets of experiments, sequential addition and original progressive evaporation allowing the measurement of DSC signals for the various transitions as a function of the amount of CCl4. These experiments allowed the determination of the transition enthalpies in the confined state, which in turn allowed the determination of the exact quantities of solvent undergoing these transitions. A clear correlation was found between the amounts of solvent (both free and confined) undergoing the two transitions, demonstrating that the formation of the adsorbed layer t does not interfere with the second transition. The thickness of this layer and the porous volumes of the two silica samples were measured and found to be in very close agreement with the values determined by gas sorption.