The stoichiometry of synthetic alunite as a function of hydrothermal aging investigated by solid-state NMR spectroscopy, powder X-ray diffraction and infrared spectroscopy

被引:0
作者
Elisabeth Grube
Ulla Gro Nielsen
机构
[1] University of Southern Denmark,Department of Physics, Chemistry, and Pharmacy
[2] Aarhus University,Interdisciplinary Nanoscience Center and Department of Chemistry
来源
Physics and Chemistry of Minerals | 2015年 / 42卷
关键词
Alunite; Solid-state nuclear magnetic resonance; Stoichiometry; Defects; Reaction time;
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摘要
The stoichiometry of a series of synthetic alunite [nominally KAl3(SO4)2(OH)6] samples prepared by hydrothermal methods as a function of reaction time (1–31 days) has been investigated by powder X-ray diffraction, Fourier transform infrared spectroscopy as well as solid-state 1H and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The 1H MAS NMR spectra recorded at high magnetic field (21.1 T, 900 MHz) allowed for a clear separation of the different proton environments and for quantitative determination of the aluminum vacancy concentration as a function of time. The concentration of structural defects determined from, i.e., aluminum vacancies was reduced from 4 to 1 %, as the reaction time was extended from one to 31 days based on 1H MAS NMR. This was further supported by an increase of the unit cell parameter c, which is indicative of the relative concentration of potassium defects present, from 17.261(1) to 17.324(5) Å. Solid-state 27Al MAS NMR revealed a decrease in the defect concentration as a function of time and showed the presence of 7–10 % impurities in the samples.
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页码:337 / 345
页数:8
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