Cation mixing in natural MgAl₂O₄spinel; a high-temperature²⁷Al NMR study

Abstract

Other| December 01, 1997 Cation mixing in natural MgAl 2 O 4 spinel; a high-temperature 27 Al NMR study Hideki Maekawa; Hideki Maekawa Hokkaido University, Division of Chemistry, Sapporo, Japan Search for other works by this author on: GSW Google Scholar Satoshi Kato; Satoshi Kato Search for other works by this author on: GSW Google Scholar Katsuyuki Kawamura; Katsuyuki Kawamura Search for other works by this author on: GSW Google Scholar Toshio Yokokawa Toshio Yokokawa Search for other works by this author on: GSW Google Scholar Author and Article Information Hideki Maekawa Hokkaido University, Division of Chemistry, Sapporo, Japan Satoshi Kato Katsuyuki Kawamura Toshio Yokokawa Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online ISSN: 1945-3027 Print ISSN: 0003-004X Copyright © 1997 by the Mineralogical Society of America American Mineralogist (1997) 82 (11-12): 1125–1132. https://doi.org/10.2138/am-1997-11-1210 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Hideki Maekawa, Satoshi Kato, Katsuyuki Kawamura, Toshio Yokokawa; Cation mixing in natural MgAl 2 O 4 spinel; a high-temperature 27 Al NMR study. American Mineralogist 1997;; 82 (11-12): 1125–1132. doi: https://doi.org/10.2138/am-1997-11-1210 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 The positional disorder of Mg2+ and Al3+ cations between the tetrahedral and octahedral sites in natural MgAl2O4 spinel has been investigated by 27Al MAS NMR at room temperature and in-situ high-temperature 27Al NMR spectroscopy up to 1600 °C. The inversion parameter describing the disorder, x, where x stands for the positional disorder between Mg and Al cations in Mg1–xAlx(MgxAl2–x)O4, increased with temperature. Below 1100 °C the inversion parameter, x, can be determined from MAS NMR measurements of quenched samples at room temperature. Above 1100 °C, x was estimated from the peak position in the high-temperature 27Al NMR spectra up to 1600 °C. The observed dependence of x with temperature was fitted using the model of O'Neill and Navrotsky (1983). The coefficients of the model obtained are α = 35 ±5 kJ and β = –32 ±5 kJ, which are approximately equal in magnitude and opposite in sign. The x values observed in the present investigation are in agreement with the model. However the introduction of an additional entropy term, ΔSD, improved the fitting. ΔSD reduces the entropy of disorder relative to a random mixing model. This would reflect either a nonconfigurational entropy contribution or short-range Mg-Al order because of local charge balance. On the other hand, above 1400 °C a narrow peak appeared at about 60 ppm. This peak became narrower with increasing temperature up to 1600 °C. This behavior might suggest that a rapid exchange process among the fourfold-coordinated Al sites occurs in this temperature range. 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.