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Cell Dimensions and Composition of Nanocrystalline Calcium Silicate Hydrate Solid Solutions. Part 2: X‐Ray and Thermogravimetry Study
Author(s) -
Garbev Krassimir,
Bornefeld Marc,
Beuchle Günter,
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.1551-2916.2008.02601.x
Subject(s) - tobermorite , calcium silicate , calcium silicate hydrate , thermogravimetry , crystallography , nanocrystalline material , hydrate , silicate , materials science , mineralogy , chemistry , analytical chemistry (journal) , inorganic chemistry , metallurgy , organic chemistry , chromatography , cement , composite material
X‐ray diffraction and thermogravimetry have been used to analyze the limits of incorporation of Ca in a series of mechanochemically synthesized, nanocrystalline calcium silicate hydrate (C–S–H) phases. Results based on bulk weight loss and Rietveld refinements show higher C/S ratios than those corrected additionally for X‐ray‐silent CaCO 3 and Ca(OH) 2 . A pure C–S–H phase exists over the C/S range 2/3–5/4, with two ordered end members. The structure of C–S–H phases within the interval 2/3–5/4 may well be described by the so‐called defect‐tobermorite model. At C/S=2/3, the C–S–H consists of 14 Å tobermorite slabs linked via H‐bonds without interlayer Ca, resulting in the formula Ca 4 [H 2 Si 3 O 9 ] 2 · x H 2 O, where x =4. After heating up to 1000°C, X‐ray diffraction has shown that even samples with a low Ca content (Ca/Si <2/3) contain solely the calcium silicate wollastonite. This supports the idea of a slightly defective, unbranched single chain silicate anion. Increasing the C/S ratio leads to increased disorder due to the competitive omission of bridging tetrahedra and the incorporation of Ca into the interlayer in samples with 2/3 < C/S <5/4. The Ca‐rich end member with C/S=5/4 exhibits structural features of a tobermorite‐based dimer: {Ca 4 [HSi 2 O 7 ] 2 } . Ca . x H 2 O, where x =4. The observed change in the d ‐value of the basal reflection upon X‐ray irradiation further supports the proposed model, relating the observed shrinkage with the loss of H 2 O molecules from the interlayer, where they coordinate calcium.