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Cell Dimensions and Composition of Nanocrystalline Calcium Silicate Hydrate Solid Solutions. Part 1: Synchrotron‐Based X‐Ray Diffraction
Author(s) -
Garbev Krassimir,
Beuchle Günter,
Bornefeld Marc,
Black Leon,
Stemmermann Peter
Publication year - 2008
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.1551-2916.2008.02484.x
Subject(s) - tobermorite , calcium silicate hydrate , materials science , orthorhombic crystal system , crystallography , calcium silicate , hydrate , x ray crystallography , phase (matter) , portlandite , analytical chemistry (journal) , crystal structure , diffraction , chemistry , cement , portland cement , physics , organic chemistry , optics , metallurgy , composite material , chromatography
Synchrotron‐based X‐ray diffraction has been used to analyze a series of mechanochemically prepared calcium silicate hydrate (C–S–H) phases with aimed Ca/Si ratios from 1/5 to 3/2. Fumed silica and CaO were used as starting materials. All samples contain 3‐dimensionally ordered C–S–H phases. Pure C–S–H phases are present in samples with Ca/Si ratios from 2/3 to 6/5. The samples with C/S ratios 1/5 and 1/2 contain unreacted silica, while those with C/S ratios 4/3 and 3/2 contain portlandite as minor component. A new approach has been used to follow structural changes with C/S ratio, involving assignment of an orthorhombic space group ( I2mm ) to the C–S–H phase followed by refinement of the unit cell parameters by the whole powder pattern decomposition (WPPD) method. The results reveal a discontinuity in the c parameter at C/S=5/6–1/1, indicating that at least two different structural types separated by a miscibility gap are needed to describe C–S–H, there being two ordered end members with C/S ratios of 2/3 and 5/4, respectively. Nevertheless the structure of C–S–H phases within this interval may be well described by the defect‐tobermorite model. At C/S=2/3 it consists of tobermorite slabs linked via H‐bonds without interlayer Ca. At this C/S ratio, the layer thickness is 13.2 Å. Increasing the C/S ratio leads to little change in the layer thickness, but increased disorder due to competitive omission of bridging tetrahedra and incorporation of Ca in the interlayer in samples with 2/3