Impact of sodium aluminate on the hydration process of alkali-activated ground granulated blast furnace slag

In the present investigation, the effect of the presence of highly soluble alumina source (sodium aluminate, NaAlO2) on Ground Granulated Blast furnace Slag (GGBS) hydration was considered. The GGBS was alkali-activated with sodium hydroxide (NaOH) or sodium carbonate (Na2CO3). The impact on the evolution on the setting time, hydration kinetics and strength development was first considered. In the case of NaOH-activated mixes, the presence of the alumina source led to the delay in setting and an extension of the induction period. The alumina additive led then to an extension of the workable time of the binder. For instance the initial setting time was extended from 30 min to more than 6 hours when adding 1% by weight of NaAlO2. The strength development was also significantly improved with addition of NaAlO2, both at early age and long term. In contrast, addition of NaAlO2 to the Na2CO3-activated mixes led to almost complete cessation of hydration (no measurable strength) within the whole dosage rate interval considered (0.1% to 2% of NaAlO2). Different techniques were used to investigate the impact of NaAlO2 on the hydration products development, including XRD, SEM image analysis and 27Al/29Si/23Na high-resolution NMR spectroscopy. It was found that the presence of the highly soluble alumina source led to rapid precipitation of Afm phases. It is suspected that, due to the low pH level in the case of the Na2CO3-activated mixes, the calcium ions are mainly distributed near the slag grain surfaces. The Afm phases may then mainly precipitate on the slag grains leading hydration blockage. Actually only Afm phases and Gaylussite were detected in the case of NaAlO2 blended Na2CO3-blended mixes

Structure and dynamics of Oxide Melts and Glasses : a view from multinuclear and high temperature NMR

Solid State Nuclear Magnetic Resonance (NMR) experiments allow characterizing the local structure and dynamics of oxide glasses and melts. Thanks to the development of new experiments, it now becomes possible to evidence not only the details of the coordination state of the network formers of glasses but also to characterize the nature of polyatomic molecular motifs extending over several chemical bonds. We present results involving 31P homonuclear experiments that allow description of groups of up to three phosphate units and 27Al/17O heteronuclear that allows evidencing μ3 oxygen bridges in aluminate glasses and rediscussion of the structure of high temperature melts.Comment: Journal of Non-Crystalline Solids (2007) in press; Also available online at: http://crmht.cnrs-orleans.fr/Intranet/Publications/?id=207

The response of pre-osteoblasts and osteoclasts to gallium containing mesoporous bioactive glasses.

Mesoporous bioactive glasses (MBGs) in the system SiO2-CaO-P2O5-Ga2O3 have been synthesized by the evaporation induced self-assembly method and subsequent impregnation with Ga cations. Two different compositions have been prepared and the local environment of Ga(III) has been characterized using 29Si, 71Ga and 31P NMR analysis, demonstrating that Ga(III) is efficiently incorporated as both, network former (GaO4 units) and network modifier (GaO6 units). In vitro bioactivity tests evidenced that Ga-containing MBGs retain their capability for nucleation and growth of an apatite-like layer in contact with a simulated body fluid with ion concentrations nearly equal to those of human blood plasma. Finally, in vitro cell culture tests evidenced that Ga incorporation results in a selective effect on osteoblasts and osteoclasts. Indeed, the presence of this element enhances the early differentiation towards osteoblast phenotype while disturbing osteoclastogenesis. Considering these results, Ga-doped MBGs might be proposed as bone substitutes, especially in osteoporosis scenarios

An infrared and solid-state nmr study of the H(2)S adsorption on basic zeolite

International audienc

An infrared and solid-state nmr study of the H(2)S adsorption on basic zeolite

International audienc

Local Al site distribution in aluminosilicate glasses by 27Al MQMAS NMR

Coordination and local environment around Al in glasses and liquids is a long-standing question, which has been a controversial issue in geochemistry and glass science. Nuclear magnetic resonance at high-field (750 MHz) was employed to investigate the geochemically and industrially important CaO–Al2O3–SiO2 system. We show that Al remains mainly in tetrahedral position in glasses, however, the presence of five-fold coordinated aluminum is the general rule throughout the ternary CaO–SiO2–Al2O3 system, except for the low silica percalcic region. The proportion of five-fold (AlV) and six-fold (AlVI) coordinated Al was quantified to determine the effects of composition overall the peralkaline part. Moreover our results indicate that Al may occupy more polymerized positions than Si. These two findings do put new questions to the modeling/understanding of these glasses and their parent liquids

An infrared and solid-state NMR study of the H2S adsorption on basic zeolite

International audienceThe modification of surface properties resulting from H2S adsorption on a fully sodium-exchanged Y zeolite was studied in situ using a combination of Infrared and Solid-State NMR spectroscopy. In order to perform in situ measurement in the same conditions with both techniques, a homebuilt device for preparing the NMR samples under vacuum or controlled atmosphere was used. Double-resonance NMR methods were achieved for a complete assignment of the different lines in proton NMR spectra. A small fraction of H2S is shown to adsorb dissociatively on NaY whereas the main part of H2S interacts non-dissociatively, either by coordination with the Na+ cations or by H-bonding

Raman and 27Al NMR structure investigations of aluminate glasses : (1-x)Al2O3- x MO, with M=Ca, Sr, Ba and 0.5

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Effect of composition on peraluminous glass properties: An application to HLW containment

International audiencePart of the Research and Development program concerning high level nuclear waste (HLW) glasses aims to assess new glass formulations able to incorporate a high waste content with enhanced properties in terms of thermal stability, chemical durability, and process ability. This study focuses on peraluminous glasses of the SiO2 – Al2O3 – B2O3 – Na2O – Li2O – CaO – La2O3 system, defined by an excess of aluminum ions Al3+ in comparison with modifier elements such as Na+, Li+ or Ca2+. To understand the effect of composition on physical properties of glasses (viscosity, density, Tg), a Design Of Experiments (DOE) approach was applied to investigate the peraluminous glass domain. The influence of each oxide was quantified to build predictive models for each property. Lanthanum and lithium oxides appear to be the most influential factors on peraluminous glass properties

Characterization of acid sites in dehydrated H-Beta zeolite by solid state NMR

International audienceA large panel of solid-state NMR techniques is used to characterize acid sites in steamed H-Beta. The structural environment of aluminum in hydrated H-Beta zeolite can be classically probed by 27Al MAS NMR. In the case of dehydrated samples, structural information extracted from 1H MAS and double resonance NMR experiments is used to propose a deconvolution of the 27Al Hahn-Echo and QPASS spectra. This provides an estimation of the number and the geometry of aluminum sites