High-temperature Raman spectroscopic and X-ray diffraction study of beta -Mg2SiO4; insights into its high-temperature thermodynamic properties and the beta - to alpha -phase-transition mechanism and kinetics

Abstract

Other| June 01, 1996 High-temperature Raman spectroscopic and X-ray diffraction study of beta -Mg 2 SiO 4 ; insights into its high-temperature thermodynamic properties and the beta - to alpha -phase-transition mechanism and kinetics Bruno Reynard; Bruno Reynard Universite de Rennes, Institut de Geologie, Rennes, France Search for other works by this author on: GSW Google Scholar Fouzia Takir; Fouzia Takir Search for other works by this author on: GSW Google Scholar Francois Guyot; Francois Guyot Search for other works by this author on: GSW Google Scholar Gabriel D. Gwanmesia; Gabriel D. Gwanmesia Search for other works by this author on: GSW Google Scholar Robert C. Liebermann; Robert C. Liebermann Search for other works by this author on: GSW Google Scholar Philippe Gillet Philippe Gillet Search for other works by this author on: GSW Google Scholar Author and Article Information Bruno Reynard Universite de Rennes, Institut de Geologie, Rennes, France Fouzia Takir Francois Guyot Gabriel D. Gwanmesia Robert C. Liebermann Philippe Gillet Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online Issn: 1945-3027 Print Issn: 0003-004X Copyright © 1996 by the Mineralogical Society of America American Mineralogist (1996) 81 (5-6): 585–594. https://doi.org/10.2138/am-1996-5-605 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Bruno Reynard, Fouzia Takir, Francois Guyot, Gabriel D. Gwanmesia, Robert C. Liebermann, Philippe Gillet; High-temperature Raman spectroscopic and X-ray diffraction study of beta -Mg 2 SiO 4 ; insights into its high-temperature thermodynamic properties and the beta - to alpha -phase-transition mechanism and kinetics. American Mineralogist 1996;; 81 (5-6): 585–594. doi: https://doi.org/10.2138/am-1996-5-605 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract We performed in-situ Raman spectroscopy and X-ray diffraction experiments at high temperature and ambient pressure to investigate the intrinsic anharmonic properties of β-Mg2SiO4 and the mechanism and kinetics of its back-transformation to forsterite. High-temperature Raman spectra of β-Mg2SiO4 and its back-transformed products were recorded up to 1200 K. β-Mg2SiO4 persists metastably up to 800-900 K, and the Raman frequency shifts with temperature were determined. Between 800 and 1000 K, new peaks are observed at about 670 and 1020 cm-1. Above 1000 K,a direct transformation to forsterite occurs. The peaks that appear between 800 and 1000 K are attributed to a defective spinelloid that forms as an intermediate phase during the back-transformation of β-Mg2SiO4 to forsterite. Similar features are observed in the Raman spectrum of partially transformed γ-Ni2SiO4 heated at 1073 K and ambient pressure for 10 min. These results indicate that a two-step mechanism, possibly martensitic, is operative in the backtransformation of the β- and γ-phases to olivine at low to moderate temperatures and for a large overstepping of the equilibrium conditions.The kinetics of the β- to α-Mg2Si04 back-transformation were monitored between 1023 and 1120 K at ambient pressure using X-ray powder diffraction. For the kinetic data obtained in air, two regimes are evident from an Avrami analysis. The first regime is characterized by an exponent n ≈ 2 for a low transformed fraction (X < 0.5); the second has n ≈ 1 for higher transformed fractions. For this second regime, an activation energy of 432 ± 64 kJ/mol is derived for the growth process from the kinetic data. A smaller data set collected in vacuum indicates much slower transformation rates and suggests a significant effect of the O2 or H2O partial pressures on the kinetics.Intrinsic mode anharmonic parameters can be calculated from the Raman frequency shifts with temperature and used to correct vibrational heat capacity models for intrinsic anharmonic effects. These corrections are slightly higher for the β-phase than for forsterite but the difference is within the experimental error. This indicates that, within the resolution of our experiments, no significant effect of intrinsic anharmonicity on the location and slope of the α-β phase transition can be predicted. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.