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Structure and Dynamics in Calcium Aluminate Liquids: High‐Temperature 27 Al NMR and Raman Spectroscopy
Author(s) -
Poe Brent T.,
McMillan Paul F.,
Coté Bertrand,
Massiot Dominique,
Coutures JeanPierre
Publication year - 1994
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1994.tb07058.x
Subject(s) - raman spectroscopy , aluminate , nmr spectra database , analytical chemistry (journal) , chemistry , relaxation (psychology) , spectral line , anisotropy , materials science , psychology , social psychology , physics , chromatography , quantum mechanics , astronomy , cement , optics , metallurgy
27 Al NMR spectra of CaO–Al 2 O 3 liquids at 2500 K have been obtained using a recently developed technique that involves CO 2 laser heating and sample levitation inside the NMR magnet. The spectra consist of single, narrow lines (100 to 200 Hz FWHM), indicating that rapid chemical exchange among molecular species occurs in the liquids. Isotropic chemical shifts vary linearly with composition, becoming more shielded with increasing Al 2 O 3 content. This is most likely due to an increase in the average nearest‐neighbor coordination of Al, as the proportion of higher coordinate Al species (AlO 5 and AlO 6 ) has been observed to increase with alumina content in glasses along this join. This is also in agreement with ion dynamics simulations of liquids along the CaO–Al 2 O 3 join, which show the average Al coordination to range from 4 at low alumina content to 5 for Al 2 O 3 liquid. Correlation times for 27 Al spin–lattice relaxation estimated from the NMR line widths are in agreement with shear relaxation times determined from experimental viscosity measurements. This may indicate that oxygen exchange between neighboring aluminate polyhedra is a key component in the mechanism for viscous flow. Viscosities determined from oxygen ion diffusion coefficients via ion dynamics simulation agree well with extrapolation of experimental data, in further support of this. We have also obtained high‐temperature Raman spectra of CaAl 2 O 4 and Ca 12 Al 14 O 33 glasses and liquids up to 1928 K. The liquid spectra contain structure similar to those of glasses, indicating that the aluminate liquids consist of AlO n polyhedral units on the vibrational time scale, rather than simple ionic species.