Ettringite: Mineral information, data and localities. скачать в хорошем качестве

Ettringite: Mineral information, data and localities.

Ettringite is a hydrous calcium aluminium sulfate mineral with formula: Ca6Al2(SO4)3(OH)12·26H2O. It is a colorless to yellow mineral crystallizing in the trigonal system. The prismatic crystals are typically colorless, turning white on partial dehydration.[2][3] It is part of the ettringite-group which includes other sulfates such as thaumasite and bentorite.[4] Contents 1 Discovery and occurrence 2 Occurrence in cement 2.1 AFt and AFm phases 3 Structure 4 Further research 5 See also 6 References Discovery and occurrence Ettringite, 6.5×3.2 cm. N'Chwaning Mines, Kalahari manganese fields, Northern Cape Province, South Africa Ettringite was first described in 1874 by J.Lehmann,[5] for an occurrence near the Ettringer Bellerberg Volcano, Ettringen, Rheinland-Pfalz, Germany.[2][3] It occurs within metamorphically altered limestone adjacent to igneous intrusive rocks or within xenoliths. It also occurs as weathering crusts on larnite in the Hatrurim Formation of Israel.[2] It occurs associated with portlandite, afwillite and hydrocalumite at Scawt Hill, Ireland and with afwillite, hydrocalumite, mayenite and gypsum in the Hatrurim Formation.[2] It has also been reported from the Zeilberg quarry, Maroldsweisach, Bavaria; at Boisséjour, near Clermont-Ferrand, Puy-de-Dôme, Auvergne, France; the N’Chwaning mine, Kuruman district, Cape Province, South Africa; in the US, occurrences were found in spurrite-merwinite-gehlenite skarn at the 910 level of the Commercial quarry, Crestmore, Riverside County, California[6] and in the Lucky Cuss mine, Tombstone, Arizona.[2][3] Occurrence in cement SEM image of fractured hardened cement paste, showing plates of calcium hydroxide and needles of ettringite (micron scale) In concrete chemistry ettringite is a hexacalcium aluminate trisulfate hydrate, of general formula: (CaO)6(Al2O3)(SO3)3·32H2O or (CaO)3(Al2O3)(CaSO4)3·32H2O. Ettringite is formed in hydrated Portland cement system as a result of the reaction of calcium aluminate with calcium sulfate, both present in Portland cement.[7] Ettringite, the more prominent representative of AFt phases or (Al2O3-Fe2O3-tri), can also be synthesized in the laboratory by reacting stoichiometric amounts of calcium, aluminium and sulfate in water. C3A + 3 CaSO4 → ettringite In the cement system, the presence of ettringite depends on the ratio of calcium sulfate to tri-calcium aluminate (C3A); when this ratio is low, ettringite forms during early hydration and then converts to the calcium aluminate monosulfate (AFm phase or (Al2O3-Fe2O3-mono)). When the ratio is intermediate, only a portion of the ettringite converts to AFm and both can coexist, while ettringite is unlikely to convert to AFm at high ratios. The following characters designate standard notations:[8]