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Dielectric relaxation of concentrated alkaline aluminate solutions

Buchner, R., Sipos, P., Hefter, G. and May, P.M. (2002) Dielectric relaxation of concentrated alkaline aluminate solutions. Journal of Physical Chemistry A, 106 (28). pp. 6527-6532.

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The complex dielectric permittivity of concentrated aqueous alkaline aluminate solutions at total concentrations 1 ≲ [Al]T/mol dm-3 ≲ 6 with either [Na]T = 8.33 mol dm-3 or [Al]T/[Na]T = 0.750 has been determined at 25 °C in the frequency range 0.5 ≲ ν/GHz ≤ 20. All solution spectra could be represented as a superposition of a Cole-Cole relaxation-time distribution for the solvent relaxation with an additional low-frequency Debye dispersion assigned to the solute. The variation of the effective hydration number, deduced from the water dispersion amplitude, shows that the aluminate ion, Al(OH)4-, is less strongly solvated than the hydroxide ion, OH-. Additionally, a "melting" of the hydration shells is observed at high concentration, probably due to co-sphere overlap and/or packing effects. The features of the solute relaxation are consistent with solvent-shared ion pairs of Na+ with a previously proposed dimeric anion, [(HO)3Al-O-Al(OH)3]2-. However, the data are not sufficient for an unequivocal assignment.

Item Type: Journal Article
Murdoch Affiliation(s): School of Chemical and Mathematical Science
Publisher: American Chemical Society
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