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Crystal Chemistry of Hydrous Calcium Silicates: III, Morphology and Other Properties of Tobermorite and Related Phases
Author(s) -
KALOUSEK G. L.,
PREBUS ALBERT F.
Publication year - 1958
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1958.tb13525.x
Subject(s) - tobermorite , differential thermal analysis , hydrate , materials science , crystallography , mineralogy , chemistry , crystal (programming language) , triclinic crystal system , chemical engineering , crystal structure , cement , diffraction , composite material , organic chemistry , physics , computer science , optics , programming language , engineering
Three very similar hydrous calcium silicates that serve as binders for, or are closely related to the binding material of, autoclaved and moist‐air‐cured concrete and related products have been differentiated by electron microscopy, X‐ray diffraction, differential thermal analysis, infrared absorption, degree of stability to the acetoacetic ester, and oxide composition. Tobermorite, 4–5CaO.5SiO 2 .5H 2 O, is the binder of properly autoclaved concrete and related products. It integrates uniformly into a dimension‐ally stable solid of high strength. This phase is identified by X‐ray diffraction lines at 11, 3.07, and 2.97 a.u. of strong intensity, by a basal spacing at 11 a.u., and by a flat platy crystal habit. The analogous hydrate of similar CaO/SiO 2 molar ratio (C/S) and designated the 0.8 to 1.33 C/S hydrate, generally shows a basal spacing at 14 a.u., occurs in crinkly foils, and exhibits a strong exothermic effect in differential thermal analysis at 835° C. This phase differs markedly from tobermorite, does not undergo any crystal‐to‐crystal binding, and shows some of the physical characteristics of clay. It is the low‐lime intermediate in the formation of tobermorite. The binder of low‐pressure‐steam‐cured concrete occurs in part in gel‐like globules, sometimes in the shape of spheres. This phase, having a probable composition anywhere between 1.5 and 2.0 C/S, depending on the time of curing, is characterized by the gel‐like morphological characteristic, a basal spacing of about 10 a.u., and variable but still characteristic differential thermal analysis effects. Apparently the same product is obtained by reacting lime and silicic acid, but it Occurs in the form of distinctly fibrous crystals.