Spin Echo Self-Diffusion Measurements in Molten Salts

Abstract

An NMR probe head for diffusion measurements in molten salts at temperatures up to 673 K is described. The spin echo technique using pulsed magnetic field gradients was employed. Resulting self-diffusion coefficients of Na+ in molten NaNO3 in the temperature range 596-670 K are compa­red with literature data obtained by other methods.

Molecular Dynamics Simulation of Molten Alkali Nitrates

“…Our original ambition to explain the measured dis crepancy in the cations' self diffusion coefficients in mixtures of 6L iN 03 and 7L iN 03 [ 9] could not be achieved because the mass of the cation showed no influence on the cation's self diffusion coefficient. Though the way of the cation's motion is dominated by the mass of the cation (which can be seen in the velocity autocorrelation functions) the mean square displacement even of an artificial Li-isotope with ten fold mass shows no observable difference; therefore the mean square displacement is governed by the size of the cation.…”

Self-diffusion measurements of polycyclic aromatic hydrocarbon alkali metal salts

“…No significant deviation from linearity with gradient strength was detectable as is to be expected from other reports. 32 The maximum gradient strength on the spectrometer was 0.537 T m Ϫ1 in non-polar solvents regardless of temperature. The calibration was repeated many times and the estimated error is 0.8% leading to an absolute error in the self-diffusion constant of 1.6%.…”

Self-Diffusion in Molten Lithium Nitrate

“…In lack of an established reference sample for molten salts we chose NaN0 3 for which D values were obtained by us previously through NMR spin-echo measurements [21]. These values are in good agreement with those from the tracer capillary technique [7].…”

“…Details of the apparatus and the experimental procedure were basically the same as in our previously published work on self-diffusion in molten NaN0 3 [21]. Some points are briefly described below.…”

“…The radio frequency 90°-pulse, which was produced by a coil with two windings of silver wire, was 18 ps long. The field gradient was produced by a quadrupolar coil described previously [21]. The time intervals between the 90° and 180° radio frequency pulses, T, and between the gradient pulses, A, were set to 20 ms.…”