High-temperature Raman spectroscopic study of CO2-containing melanophlogite

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Abstract

CO2-containing melanophlogite from Fortunillo, Italy was studied using a micro-Raman spectrometer with the ability to measure the low-frequency region. A very intense and broad feature was found below 100 cm-1. To clarify the origin of this feature in relation with CO2, heat treatment experiments and in-situ high-temperature Raman measurements were conducted up to 1100 °C. As a result of the heat treatment experiments, nearly CO2- free melanophlogite was obtained at 950 °C for 6 h. For shorter time duration or lower treatment temperature, CO2 vibrational Raman peaks (Fermi diad) were still observed, and those peaks were split. The low-frequency feature also reduced its intensity in these degassed samples. For the in-situ study, the intensity of CO2 Raman peaks started to drop at around 450 °C, and simultaneously the low-frequency feature intensity decreased. The splitting of the CO2 Raman peaks started from 450 °C, and it was interpreted as redistribution of CO2 molecules in two distinct cages in the structure. The low-frequency feature completely disappeared at 1100 °C. It was concluded that the low-frequency feature is originated from CO2 molecules. Librational and translational modes of CO2 molecules in the cages of melanophlogite would be responsible for the low-frequency feature. The high- temperature Raman spectroscopic study thus provides us insight into CO2 diffusion in melanophlogite structure.

Original languageEnglish
Pages (from-to)122-129
Number of pages8
JournalJournal of Mineralogical and Petrological Sciences
Volume114
Issue number3
DOIs
Publication statusPublished - Jan 1 2019

Keywords

  • Clathrasil
  • CO
  • Guest molecule
  • Low-frequency Raman spectroscopy
  • Melanophlogite

ASJC Scopus subject areas

  • Geophysics
  • Geology

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