Influence of aluminosilicate source and silicate solution on geopolymerization reactions

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Influence of hydration on 23Na, 27Al, and 29Si MAS-NMR spectra of sodium saponites and sodium micas

International audienceSynthetic sodium saponites, NaxMg3(Si4–xAlx)O10(OH)2·nH2O, with 0.33 ≤ x ≤ 1, and trioctahedral sodium micas series, Na(Mg3–yAly)(Si3–yAl1+y)O10(OH)2·nH2O, with 0 ≤ y ≤ 1, have been investigated by MAS-NMR spectroscopy. The presence of anhydrous, one-layer and two-layer hydrates, deduced by X‑ray diffraction, has been associated with specific lines detected in 23Na MAS-NMR spectra. In these phyllosilicates, the location of tetra- and octahedral charge has been analyzed by 27Al MAS-NMR spectroscopy. The salient result is the major effect of the interlayer charge on 29Si chemical shift of the four NMR components ascribed to Si3, Si2Al, SiAl2, and Al3 environments. This effect is much more important than the most commonly accepted contribution of the ditrigonal distortion of tetrahedral sheets. In saponites, 29Si MAS-NMR spectra change considerably with the sodium hydration. In dehydrated samples, where Na cations are engaged in two pseudo-hexagonal cavities, 29Si MAS-NMR components split as a consequence of the partial sodium occupancy of three neighboring hexagonal rings that surrounds a particular tetrahedron. In hydrated samples, where Na+ cations interact with water, chemical shifts of resolved components are averaged as a consequence of interlayer water and cation mobilities

Effect of Aluminum and Alkali Cation Earth Reactivity on Alkali-activated Materials Formation and Structure

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Alkali-activated materials from different aluminosilicate sources: Effect of aluminum and calcium availability

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Anatase nanoparticles boundaries resulting from titanium tetrachloride hydrolysis

An important factor that governs solar energy transformation into electrical or chemical energy, when using nanoparticles-based devices, is the spatial location of traps limiting electron transport. Evidences have been presented indicating that the electron diffusion is strongly influenced by nanoparticle boundaries, whose characteristics depend on the particles preparation. In the present work we have studied the role of hydrated excess proton structures in the formation of anatase nanoparticles boundaries in samples prepared by TiCl4 hydrolysis at low temperature and strong acidic conditions. The samples, constituted by anatase nanocrystals but, mainly, by amorphous titania, are studied by H-1-MAS NMR, FT-IR and HRTEM. The results indicate that hydrated excess proton species, generated by solvation of bridging hydroxyls protons of highly defective anatase and/or amorphous titania chains, favor the chains bonding to anatase nanoparticles and/or their condensation at the nanoparticles surface. The chains' bonding facilitates the anatase particles aggregation producing oriented self-assemblings. The preparation conditions determine a strong condensation of amorphous titania chains and it should favor anatase transformation into rutile. (C) 2016 Elsevier B.V. All rights reserved

The structure of "orthorhombic" KAlSiO4-O1: evidence for Al-Si order from MAS-NMR data combined with Rietveld refinement and electron microscopy.

Dry synthesis of KAlSiO4 at temperatures from 900 to 1500°C yielded products with slightly different powder X-ray-diffraction patterns. “Orthorhombic” KxAlxSi2–xO4-O1 with x ≈ 1 was obtained as a substantially single phase after heating at 1000°C for one day; we refined its crystal structure from powder X-ray-diffraction data in space group P1211 [MM = 158.17 g/mol, a 15.669(2), b 9.057(1), c 8.621(1) Å, b 90.16(1)°, V 1223.5 Å3, Z = 12, Dx = 2.57 g cm–3, RB = 0.080]. It is composed of a relatively open [AlSiO4] framework that is a topological variant of tridymite (t) having the supercell (s) metric as ≈ 3at, bs ≈ at + 2bt, cs ≈ ct. The space group P1211 allows for Al–Si ordering, and refinement of distance-least-squares restrained models, although problematic owing to the pronounced pseudosymmetry, indicates preference for an ordered pattern where Al and Si are distributed on alternating tetrahedra [dSi–O/dAl–O = 1.628(1)/1.719(1) Å], so that every SiO4 tetrahedron is coordinated to four AlO4 tetrahedra and vice versa. The alternating distribution was independently inferred from 29Si and 27Al MAS NMR spectroscopic data, and the framework model obtained from Rietveld refinement with Si on tetrahedron T1 could be used to successfully simulate the observed Si(Al4) doublet peak in the 29Si spectrum. Electron diffraction showed that triple twinning with a rotation of 120° around c of the metrically almost hexagonal P1211 cell is ubiquitous and enhances, in the diffraction experiment, the pseudosymmetry inherited from the tridymite subcell. Furthermore, the diffraction aspect of single individuals (P*21*) confirms that the screw axes 21-- and --21 of the orthorhombic supergroup P212121 are only approximated

Control of polycondensation reaction generated from different metakaolins and alkaline solutions

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