Aluminium silicate

About: Aluminium silicate is a research topic. Over the lifetime, 765 publications have been published within this topic receiving 7434 citations. The topic is also known as: aluminum silicate.

Imogolite, a Hydrated Aluminium Silicate of Tubular Structure

Abstract: IMOGOLITE, a gel-like hydrous aluminium silicate identified in several volcanic ash soils and other weathered pyroclastic deposits, has been shown by electron microscopy1 to consist of bundles of fine tubes, each about 20 A in diameter. Electron diffraction patterns2,3 indicate a repeat distance along the tube axis of 8.4 A and a repeat distance perpendicular to this axis of 22 to 23 A, corresponding to centre-to-centre tube separations. X-ray diffraction patterns are more diffuse and differ principally in that the highest spacing observed for desiccated material is 18.4 A. Two empirical formulae have been proposed: 1.5SiO2·Al2O3·2.5H20 (ref. 2) and 1.1SiO2·Al2O3·2.3−2.8H2O (ref. 3); these two papers also advance tentative structures which assign the 8.4 A repeat distance to a gibbsite-like chain or ribbon, although they differ in the nature of the postulated silicate anion. Neither accounts for the cylindrical structure later established.

Fabrication of Mullite and Mullite-Matrix Composites by Transient Viscous Sintering of Composite Powders

Abstract: Mullite was fabricated by a process referred to as transient viscous sintering (TVS). Composite particles which consisted of inner cores of α-alumina and outer coatings of amorphous silica were used. Powder compacts prepared with these particles were viscously sintered to almost full density at relatively low temperatures (∼1300°C). Compacts were subsequently converted to dense, fine-grained mullite at higher temperatures (∼1500°C) by reaction between the alumina and silica. The TVS process was also used to fabricate mullite/zirconia/alumina, mullite/silicon carbide particle, and mullite/silicon carbide whisker composites. Densification was enhanced compared with other recent studies of sintering of mullite-based composites. This was attributed to three factors: viscous flow of the amorphous silica coating on the particles, avoidance of mullite formation until higher temperatures, and increased threshold concentration for the development of percolation networks.

Imogolite and proto‐imogolite allophane in spodic horizons: evidence for a mobile aluminium silicate complex in podzol formation

Abstract: Summary Examination by infrared spectroscopy and electron microscopy of the fine clays (<0.5 μm) dispersed at pH 3.5 from H2O2-treated soil indicates that imogolite and proto-imogolite allophanes are concentrated in podzolic B2 and B3 horizons, and make up at least 6 percent of one B2 horizon soil, which contains virtually no layer silicate clays. It is argued here that imogolite-type components are the principal source of extractable aluminium and silicon in such horizons, that they may act as cementing agents in indurated horizons, and that proto-imogolite, a soluble aluminium-silicate complex, is the predominant mobile form in which aluminium is transported to B2 and lower horizons of podzols. Comparison of the amounts of aluminium extracted by acetic acid with those extracted by EDTA indicates that extractable aluminium in Bhg, Bh, and organic-rich A2 horizons is present principally in organic complexes. It is proposed that the aluminium fulvates concentrated in these horizons are formed in situ.

Synthesis of imogolite: a tubular aluminium silicate polymer

Abstract: Heating weakly acidic dilute solutions containing hydroxyaluminium orthosilicate complexes gives a fibrous polymer, each fibre consisting of tubes about 2·2 nm external diameter and 1·0 nm internal diameter, essentially identical with those of the natural mineral, imogolite.