Rearrangement of the structure during nucleation of a cordierite glass doped with TiO2

Ordering of disordered materials occurs during the activated process of nucleation that requires the formation of critical clusters that have to surmount a thermodynamic barrier. The characterization of these clusters is experimentally challenging but mandatory to improve nucleation theory. In this paper, the nucleation of a magnesium aluminosilicate glass containing the nucleating oxide TiO2 is investigated using neutron scattering with Ti isotopic substitution and 27Al NMR. We identified the structural changes induced by the formation of crystals around Ti atoms and evidenced important structural reorganization of the glassy matrix

Mechanism of Calcium Incorporation Inside Sol–Gel Silicate Bioactive Glass and the Advantage of Using Ca(OH)2 over Other Calcium Sources

Calcium is an essential component of osteogenesis and is often required for imparting significant bioactivity to synthetic bone substitutes and, in particular, silicate-based materials. However, the mechanism of calcium incorporation inside sol–gel silicates is poorly understood. In this work, we shed light on the determinant parameters for incorporation of calcium into acid–base-catalyzed sol–gel silicates at ambient temperature: increasing the pH above the isoelectric point of silicic acid and the nature of the calcium counterion in the calcium precursor are found to be the key. Based on our proposed reaction sequence, we were able to compare calcium precursors and select an ideal candidate compound for the synthesis of bioactive glasses (BG) and organic–inorganic hybrids at ambient temperature. Reproducible syntheses and gel times of SiO2–CaO BG were obtained using calcium hydroxide (CH), and we demonstrate its usability in the synthesis of promising BG–polycaprolactone hybrid scaffolds. BG and hybrids prepared with CH were able to form nanocrystalline nonstoichiometric apatite in simulated body fluid. The increased reliability of low-temperature syntheses associated with the use of a stable and inexpensive alkaline-earth precursor are major steps toward the translation of calcium silicate hybrids or other alkaline-earth silicates from bench to clinic

Vitrification, cristallisation et structure des verres d'aluminosilicate de zinc

International audienceThe glass formation, crystallization behavior and structure were investigated in the ZnO-Al2O3-SiO2 system. The boundaries of the glass forming region are defined, indicating the absence of glasses along the ZnO-SiO2 binary and the role of Al to improve glass formation. The crystallization behavior has been clarified for representative glass compositions showing first crystallization of willemite near the ZnO-SiO2 binary and a metastable zinc aluminosilicate solid solution for higher Al2O3/SiO2 content. Gahnite appears as a second phase and is mainly present near the center of the tectosilicate join. Glass structure was studied using 27 Al NMR spectroscopy, neutron and X-ray diffraction and molecular dynamics simulation. Both Al and Zn are shown to be distributed between four-fold and five-fold sites. The proportion of [4] Al is more important near the ZnAl2O4-SiO2 join. A remarkable similar behavior is revealed for the glass forming ability and structural properties between MgO and ZnO aluminosilicate systems.La formation du verre, le comportement en cristallisation et la structure ont été étudiés dans le système ZnO-Al2O3-SiO2. Les limites de la région de formation du verre sont définies, indiquant l’absence de verres le long du binaire ZnO-SiO2 et le rôle d’Al pour améliorer la formation du verre. Le comportement en cristallisation a été clarifié pour des compositions de verre représentatives montrant la première cristallisation de willemite près du binaire ZnO-SiO2 et une solution solide d’aluminosilicate de zinc métastable pour une teneur plus élevée en Al2O3/SiO2. La gahnite apparaît comme une deuxième phase et est principalement présente près du centre du joint tectosilicate. La structure du verre a été étudiée en utilisant la spectroscopie 27Al RMN, la diffraction des neutrons et des rayons X et la simulation par dynamique moléculaire. Il est démontré que Al et Zn sont répartis entre des sites de coordinence quatre et cinq La proportion de [4]Al est plus importante près du joint ZnAl2O4-SiO2. Un comportement similaire est révélé pour la capacité de formation du verre et les propriétés structurelles entre les systèmes d'aluminosilicate de MgO et de ZnO

Bioactive glass hybrids: a simple route towards the gelatin–SiO 2 –CaO system

International audienceBioactive glass hybrids are among the most promising materials for bone regeneration, but the incorporation of calcium, a key element for mineralization properties of the implant, into the inorganic part of the hybrid network is challenging. We present here a new synthesis route to both class I and II gelatin-bioactive glass hybrids allowing the efficient incorporation of calcium ions at low temperature

Characterization of boron incorporation and speciation in calcite and aragonite from co-precipitation experiments under controlled pH, temperature and precipitation rate

International audienceAbout 20 years ago, the boron isotopic composition of marine carbonates was proposed as a proxy of ancient seawater pH. Since that time, a large body of studies has used boron isotopes in carbonates to reconstruct seawater paleo-pH and atmospheric paleo-CO2 concentration. To date, however, no systematic investigation of the physicochemical parameters that control boron incorporation in calcite and aragonite (pH, temperature, precipitation rate, etc.) has been performed. To fill this gap, we have experimentally investigated the inorganic co-precipitation of boron with calcite and aragonite at 5 and 25 °C in the presence and absence of seed crystals and over the pHNBS range 7.4 B, between CaCO3 and the fluid is defined as

Bioactive glass–gelatin hybrids: building scaffolds with enhanced calcium incorporation and controlled porosity for bone regeneration

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Double-resonance decoupling for resolution enhancement of P-31 solid-state MAS and Al-27 -> P-31 MQHETCOR NMR

International audience27Al decoupling has been used to remove residual J-coupling interactions between31 P and 27Al in microporous aluminophosphates AlPO4-14 and AlPO4-40. In combination with 1H high-power decoupling, 27Al adapted decoupling yields 31P spectra with optimal sensitivity and resolution. The importance of double-resonance decoupling is further demonstrated by incorporating this technique in the MQHETCOR sequence. Unambiguous assignment of all the AlPO4-14 nuclear magnetic resonances is achieved by combining multiple-quantum evolution in the 27Al dimension and double-resonance decoupling in the 31P acquisition domain