Abstract
Single phases calcium silicate hydrates (1.1 nm tobermorite; Ca 5Si 6O 16(OH) 2·4H 2O), with Fe 3+ and Mg 2+ substitutions, were synthesized under hydrothermal conditions at 175 °C. The structure of different tobermorite samples was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The results indicated that Fe and Mg ions played a key role in crystallization, morphology and structure of tobermorite. Mg 2+ increases crystallinity of tobermorite and changes its morphology from platy-shape at 4 h curing time to lamellar-shape at longer curing time. Fe 3+ increases imperfection of tobermerite at short curing time, however it increases crystallinity at longer curing time and the morphology of tobermorite changes magnificently from reticulated-shape to fiber-shape. FTIR proved that Fe + and Mg + increase silicate chains polymerization and increase the chain cross-linkage, which is consistent with tobermorite lamellar and fibers morphology that grow parallel to the b-axis (along the silicate chains). The cations exchange capacity (CEC) of Fe- and Mg-substituted tobermorites is lower than that of the unsubstituted tobermorite. Cross-linkage in the silicate chains was found to cause a reduction in cation exchange capacity.
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