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Advances in Molten Salts

ISSN:
1-56700-142-4 (Print)

Mutual diffusion coefficients of the systems (Rb,Ag)Cl and (Alk,Ag)NO3 with Alk = Li, Na, K, Rb, and Cs, measured with interferometric methods

Axel Leuchter
Institut fur Physikalische Chemie der RWTH Aachen

Joachim Richter
Institut fur Physikalische Chemie der RWTH Aachen

Abstract

Mutual diffusion coefficients of the systems (Rb,Ag)Cl and (Alk,Ag)NO3 with Aik = Li, Na, K, Rb, and Cs are reported. Experiments in the nitrate systems were performed with either holographic real-time interferometry or Savart interferometry under free-diffusion boundary conditions. Initial diffusion boundaries were created using a flowing junction cell or bottom layer cells. Mutual diffusion coefficients in the system (Rb,Ag)Cl were measured with digital image holography, a newly developed interferometric technique. Some experiments were performed with Savart interferometry as an internal consistency check. In the nitrate systems diffusion data were collected in a temperature range from the melting points of the mixtures up to 603 K over the whole accessible concentration range. The D values are considered to be accurate to ±1-3 %. The results have been correlated using Arrhenius-type equations. Furthermore the concentration dependence of the mutual diffusion coefficient at 573 K is discussed. The data are fitted to parabolas of the form D = a2x22 + a1x2 + a0, where x2 denotes the mole fraction of the silver nitrate. For all systems, except (Li,Ag)NO3, parameters a2, a1 and a0 show a clear linear proportionality to the radii of the alkali ions. Trace diffusion coefficients are extrapolated and discussed. Mutual diffusion coefficients in the system (Rb,Ag)Cl with xAgCl = 0.61 were measured in a temperature range between 573 K and 748 K. The results show an Arrhenius behaviour with D = (1.37 ± 0.10) m2s-1 exp(-(20.7 ± 0.4) kJ mol-1(RT)).