Fe ordering in kaolinite; insights from29Si and27Al MAS NMR spectroscopy

Abstract

Other| February 01, 1996 Fe ordering in kaolinite; insights from 29Si and 27Al MAS NMR spectroscopy Paul A. Schroeder; Paul A. Schroeder University of Georgia, Department of Geology, Athens, GA, United States Search for other works by this author on: GSW Google Scholar Robert J. Pruett Robert J. Pruett ECC International, United States Search for other works by this author on: GSW Google Scholar American Mineralogist (1996) 81 (1-2): 26–38. https://doi.org/10.2138/am-1996-1-204 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Paul A. Schroeder, Robert J. Pruett; Fe ordering in kaolinite; insights from 29Si and 27Al MAS NMR spectroscopy. American Mineralogist 1996;; 81 (1-2): 26–38. doi: https://doi.org/10.2138/am-1996-1-204 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 Kaolinite-rich samples were selected for 27Al and 29Si MAS NMR study to explore the effect of Fe on their spectra and provide insight into the nature of Fe ordering in kaolinite. Initial characterization by chemical analysis, TEM, X-ray diffraction, and magnetic mass susceptibility (χg) measurement was conducted to obtain five samples of high purity and with a range of Fe content. Secondary iron oxide and hydroxide phases were extracted using an HCl treatment. TEM study of the samples before and after treatment revealed the effective removal of secondary Fe phases and pristine kaolinite crystal habits.MAS NMR experiments included measurement of 29Si spin-lattice relaxation times (T1) at 6.36 T and quantitative 27Al measurements at 8.46 T. The 29Si T1 studies show a general increase in T1, with decreasing Fe content. It is probable that the relaxation mechanism occurs dominantly through the dipole-dipole interaction with unpaired electron spins in Fe centers of the dioctahedral sheet. Data fitting indicates that spin relaxations are not best described by a single T1. Improved fitting using double exponential or power-law behavior to describe 29Si spin-relaxation phenomena indicates a heterogeneous distribution of Fe centers. The relatively longer T1 values for two samples suggest their dioctahedral Fe domains may have a more clustered distribution within the kaolinite structure. Results from 27Al studies indicate very good correlation between Fe content, χg, and spinning sideband (SSB) intensity. There is very little correlation between total integrated27Al intensity and Fe content. When 27Al NMR intensity variations are compared with estimates of 27Al NMR signal loss predicted by a paramagnetic line-broadening wipeout-sphere model that uses an idealized kaolinite structure with regularly ordered dioctahedral Fe sites, the two samples appear to have a more clustered distribution of Fe. The relative increase in SSB intensity is consistent with an increase in the number of antiferromagnetic or ferrimagnetic domains. 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.