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Anomalous fluorescence in near-infrared Raman spectroscopy of cementitious materials |
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| Authors: | Steven P Newman Simon J Clifford Peter V Coveney Vijay Gupta Frank Serafin Sidney Diamond |
| Affiliation: | a Centre for Computational Science, Queen Mary, University of London, London E1 4NS, UK b W.R. Grace and Co.-Conn., 62 Whittemore Avenue, Cambridge, MA 02140, USA c Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA d School of Civil Engineering, Purdue University, West Lafayette, IN 47907, USA |
| Abstract: | The results of near-infrared Fourier transform Raman spectral examination of cement minerals, several commercial Portland cements, and hydrating Portland cements are critically examined. It is shown that structured fluorescent effects dominate the observed spectra for C3S, C2S, and cement, and none of the bands generated by this mode of examination is a true Raman band. The apparent bands for the Portland cements are in different positions to those for the individual cement minerals. The fluorescence-derived spectra for different cements are similar to each other but vary enormously in intensity for different cements. Hydration progressively reduces the intensity of the bands, but does not generate bands at new locations. It is tentatively suggested that the fluorescence effect may be somehow associated with the status of the cement components as orthosilicates (i.e., composed of isolated silica tetrahedra. Samples of high-purity C2S exhibit the fluorescence effect, but samples of CS (wollastonite) of similar purity do not. The latter are metasilicates (i.e., composed of linked chains of silica tetrahedra). They exhibit normal Raman Stokes and anti-Stokes bands. |
| Keywords: | Spectroscopy Raman spectroscopy Fluorescence Ca3SiO5 Ca2SiO4 |
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