科研之友
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摘要
The identification of iron sulfates on Mars by the Mars Exploration Rovers (MERs) and the Mars Reconnaissance Orbiter emphasized the importance of studying iron sulfates in laboratory simulation experiments. The copiapite group of minerals was suggested as one of the potential iron sulfates occurring on the surface and subsurface on Mars, so it is meaningful to study their spectroscopic features, especially the spectral changes caused by cation substitutions. Four copiapite samples with cation substitutions (Fe3+, Al3+, Fe2+, Mg2+) were synthesized in our laboratory. Their identities were confirmed by powder X-ray diffraction (XRD). Spectroscopic characterizations by Raman, mid-IR, vis-NIR and laser-induced-breakdown spectroscopy (LIBS) were conducted on those synthetic copiapite samples, as these technologies are being (and will be) used in current (and future) missions to Mars. We have found a systematic nu(1)peak shift in the Raman spectra of the copiapite samples with cation substitutions, a consistent atomic ratio detection by LIBS, a set of systematic XRD line shifts representing structural change caused by the cation substitutions and a weakening of selection rules in mid-IR spectra caused by the low site symmetry of (SO4)(2-) in the copiapite structures. The near-infrared (NIR) spectra of the trivalent copiapite species show two strong diagnostic water features near 1.4 and 1.9 mu m, with two additional bands near 2.0 mu m. In the vis-NIR spectra, the position of an electronic band shifts from 0.85 mu m for ferricopiapite to 0.866 mu m for copiapite, and this shift suggests the appearance of a Fe2+ electronic transition band near 0.9 mu m.
- 出版日期2011-5
- 单位山东大学
