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Clays and Clay Minerals
Published in Benny K.G. Theng, Clay Mineral Catalysis of Organic Reactions, 2018
Allophane has a variable chemical composition. Two extreme forms of allophane have been recognized having the composition of SiO2Al2O3.2.5H2O (Al/Si = 2) and 2SiO2Al2O3.3H2O (Al/Si = 1), respectively. On this basis, it seems likely that natural specimens with an Al/Si ratio between 1 and 2 represent physical mixtures of the two end-members, rather than distinct species within a series (Parfitt et al. 1980). By contrast, naturally occurring imogolites have compositions close to the ideal of SiO2Al2O3.2H2O. Because of the similarity to imogolite, not only as to composition but also in terms of infrared spectral features, notably the presence of a well-defined band near 346 cm−1 (Farmer et al. 1977), allophane with an Al/Si ratio of ≈2 has been referred to as imogolite-like allophane (Parfitt and Henmi 1980).
Natural Nanomaterials
Published in M. H. Fulekar, Bhawana Pathak, Environmental Nanotechnology, 2017
Montmorillonite and allophane are the most important nano clays. Montmorillonite is a crystalline hydrous phyllosilicate (layer silicate). Organically modified montmorillonites or ‘organoclays’, formed by intercalation of quaternary ammonium cations, are reported to be used as rheological modifiers and additives in paints, inks, greases and cosmetics and as carriers and delivery systems for the controlled release of drugs. In recent years, the largest single usage of organoclays has been in the manufacture of polymer clay nanocomposites. These organic–inorganic hybrid materials show superior mechanical, thermal and gas-barrier properties. Organoclays are also useful in pollution control and water treatment. Allophane is a non-crystalline aluminosilicate derived from the weathering of volcanic ash. There is increased interest in nanoclay-based polymer nanocomposites due to the layered structure, large surface area and high aspect ratio of nanoclay. These materials have been successfully used to improve mechanical, thermal and barrier properties. They are considered for applications in a wide variety of areas, such as aerospace, marine, electronics, sports and automotive engineering. Use of organoclays as precursors to nanocomposite formation has been extended to various polymer systems including epoxy, vinylester, polyurethanes, polyimides and polyesters. Vinylester-based nanocomposites are important due to their wide range of applications owing to their superior mechanical properties (Raghavendra, et al. 2013).
Sensitive pyroclastic-derived halloysitic soils in northern New Zealand: Interplay of microstructure, minerals, and geomechanics
Published in Tatiana Rotonda, Manuela Cecconi, Francesco Silvestri, Paolo Tommasi, Volcanic Rocks and Soils, 2016
Vicki G. Moon, David J. Lowe, Michael J. Cunningham, Justin B. Wyatt, Willem P. de Lange, G.J. (Jock) Churchman, Tobias Mörz, Stefan Kreiter, Max O. Kluger, M. Ehsan Jorat
Although previously described (erroneously) as amorphous because of the broad, low-intensity humps it generates on X-ray diffraction (XRD) traces (Lowe, 1995; Churchman and Lowe, 2012), allophane is now recognised as being “nanocrystalline”, meaning that it has a structure (or short-range order) at the nanometer scale, i.e., in the 1–100 nm range (Theng and Yuan, 2008; Churchman and Lowe, 2012). Unit particles of allophane comprise tiny hollow spherules or “nanoballs” ~3.5 to 5.0 nm in diameter with a chemical composition (1–2)SiO2·Al2O3·(2–3)H2O (Abidin et al., 2007). The most-common, Al-rich, form is also referred to as proto-imogolite allophane (Al: Si ~2: 1) (Parfitt, 1990, 2009).
Effect of reinforcements at different scales on mechanical properties of epoxy adhesives and adhesive joints: a review
Published in The Journal of Adhesion, 2018
Ali Nemati Giv, Majid R. Ayatollahi, S. Hengameh Ghaffari, Lucas F.M. da Silva
Nano clays are natural platelet structured nano materials. They have two main species including montmorillonite and allophane. The structure of montmorillonite is a crystalline hydrous phyllosilicate (layer silicate). The basic structural unit of phyllosilicates (clay minerals) contains two layers of tetrahedral silica and octahedral alumina. Allophane is a non-crystalline aluminosilicate and is generated by the weathering of volcanic ash. It is appropriate for enzyme immobilization.[26] Nano clays are inexpensive materials[51] which can improve fire, liquid infusion and mechanical properties of polymers.[28] In addition, they can enhance the mechanical and thermal properties of cement matrices.[59] Organoclays (hybrid) are organically-modified montmorillonites that have been utilized as rheological modifiers and additives in paints, inks, greases, cosmetic and as carriers and delivery systems for the controlled release of drugs.[26] Moreover, they have shown excellent mechanical, thermal and gas-barrier properties. Furthermore, they have great role in pollution control and water treatment.[60]