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Raman, Conventional Infrared and Synchrotron Infrared Spectroscopy in Mineralogy and Geochemistry: Basics and Applications 79 intense n 1 CO 3 doublet at 1076 and 1091 cm -1 ; split in-plane n 4 CO 3 bending at 740 and 750 cm -1 ) and aragonite at Ca/Si 0.5 (e.g. intense n 1 CO 3 ~ 1080 cm -1 ; n 4 CO 3 ~700 cm -1 ). Calcite was not observed as a primary carbonation product within the time frame investigated. Thus, the most probable mechanism of C-S-H carbonation appeared to be of dissolution-precipitation character. Carbonation leads to decalcification of the C-S-H resulting in silicate polymerization (the SB mode at 672 cm -1 in the fresh samples sharpened and shifted to 668 cm -1 due to polymerization of the Q 1 units). Structural studies: polarized spectra As IR activity is dependent on a changing dipole moment, the orientation of the dipole moment change of a given vibration and hence the orientation of a particular bond involved in this vibration relative to the crystallographic crystal axes can be determined, which can give information on the crystal structure and the nature of the vibrational modes. This type of analysis has been particularly useful in the analysis of O-H stretching vibrations in minerals (e.g. Hawthorne, 1988). Synchrotron IR FIGURE 11. OH stretching of OH involved in strong H-bonding in -C 2 SH. (Garbev et al., in prep.). microspectroscopy has been used by Garbev et al. (2008) to study the mechanisms of the phase transformations in the 2CaO-SiO 2 -H 2 O system, which understanding has crucial importance for the development of low-energy belite cement materials. The new materials should substitute the common cement clinker produced at 1450°C, with the goal of lowering both the production costs of cement as well as the CO 2 emissions. Part of these studies focus on the dehydration process of - Ca 2 [SiO 3 (OH)](OH) (-C 2 SH) because it transforms into hydraulic Ca 2 SiO 4 polymorphs at temperatures much lower than 1450°C. Although often studied the structure of - C 2 SH and the mechanism of its dehydration have been not fully resolved. IR studies of -C 2 SH single crystals were carried out under the IR microscope at the ANKA-IR beamline. The brilliance of SR-IR allowed the selection of untwined and homogeneous areas. Study of polarized IR spectra of -C 2 SH contributes to the refinement of its crystal
80 Biliana Gasharova structure. For example, when the orientation of the electric field vector (E) is set to be parallel to the crystallographic b axis (E || b, Fig. 11) three bands are observed between 1600 and 3000 cm -1 typical for OH stretching of hydroxyl involved in strong hydrogen bonding. They are denoted C (1715 cm -1 ), B (2380 cm -1 , very broad), and A (2780 cm -1 , very broad). Rotating the crystal by 90º (E || a) leads to disappearance of these bands. This observation not only proves the existence of hydroxylated SiO 3 (OH) tetrahedra in the -C 2 SH structure, but also suggests that they are interconnected in a chain-like pattern by H-bonds with orientation along the b axis (Fig. 11, right). Studies between 18 and 470 K in a liquid-He cryostat under the IR microscope suggest that the hydrogen bonds are triggering the phase transformation reactions of -C 2 SH upon thermal treatment (Garbev et al., in prep.). RAIR studies of thin films Vibrational spectroscopy has great advantages over other techniques such as x-ray diffraction (XRD) and even synchrotron XRD in detecting crystalline particles with a size of just a few unit cells. In addition, the vibrational spectra can unambiguously distinguish between amorphous and crystalline features, which are sometimes a problem for other surface-sensitive spectroscopic methods. In a recent experiment at the IR beamline at ANKA it has been shown that RAIR experiments in grazing incidence geometry are very suitable to examine the efficiency of synthesis methods for ultrathin zeolite film growth (Tosheva et al., submitted). The ultrathin films were transferred to Au coated slides and the spectra were collected using p-polarized light. The enhancement of the IR absorption due to the presence of a strongly reflecting noble metal surface allows the detection of even monomolecular layers when grazing-incident RAIR spectroscopy is used. The utilization of the synchrotron IR source ensured the acquisition of highest quality RAIR spectra due to the natural collimation of the beam. Overcoming the diffraction limit: near-field Raman and IR nanospectroscopy The possibility to measure samples at a nano-scale spatial resolution with Raman and even with infrared radiation will soon become a further attraction for mineralogists. Near-field Raman and IR spectroscopy (also called tip-enhanced spectroscopy) will be briefly introduced during the oral presentation.
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INDEX Electron back-scattered diffr
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