FTIR study and cation exchange capacity of Fe3+- and Mg2+-substituted calcium silicate hydrates

Single phases calcium silicate hydrates (1.1 nm tobermorite; Ca5Si6O16(OH)(2)center dot 4H(2)O), with Fe3+ and Mg2+ substitutions, were synthesized under hydrothermal conditions at 175 degrees 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. Mg2+ increases crystallinity of tobermorite and changes its morphology from platy-shape at 4 h curing time to lamellar-shape at longer curing time. Fe3+ 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. (c) 2008 Elsevier B.V. All rights reserved.