科研之友
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摘要
Near infrared (NIR) and Fourier transform infrared (FT-IR) spectroscopy have been used to determine the mineralogical character of isomorphic substitutions for Mg(2+) by divalent transition metals Fe, Mn, Co and Ni in natural halotrichite series The minerals are characterised by d-->d transitions in the NIR region 12,000-7500cm(-1). The NIR spectrum of halotrichite reveals broad features from 12,000cm(-1) to 7500cm(-1) with a splitting of two bands resulting from ferrous ion transition 5T(2g)-->(5)E(g) The presence of overtones of OH(-) fundamentals near 7000cm(-1) confirms molecular water in the mineral structure of the halotrichite series. The appearance of the most intense peak at around 5132cm(-1) is a common feature in the three minerals and is derived from a combination of OH(-) vibrations of water molecules and nu(2) water-bending modes. The influence of cations such as Mg(2+), Fe(2+), Mn(2+). Co(2+) and Ni(2+) shows on the spectra of halotrichites, especially for wupatkiite-OH stretching vibrations in which bands are distorted conspicuously to low wavenumbers at 3270cm(-1), 2904cm(-1) and 2456 cm(-1). The observation of a high-frequency nu(2) mode in the infrared spectrum at 1640cm(-1) indicates that the coordination of water molecules is strongly hydrogen bonded in natural halotrichites The splitting of bands in nu(3) and nu(4) (SO(4))(2-) stretching regions may be attributed to the reduction of symmetry from T(d) to C(2v) for sulphate ion. This work has shown the usefulness of NIR spectroscopy for the rapid identification and classification of the halotrichite minerals.
- 出版日期2010
