Mutual Diffusion Coefficients of the Systems (Rb,Ag)Cl and (AIk,Ag)NO_3 with Alk=Li, Na, K, Rb, and Cs, Measured with Interferometric Methods

摘要

Mutual diffusion coefficients of the systems (Rb,Ag)Cl and (Alk,Ag)NO_3 with Alk = 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 = a_2x-2~2 + a_1x_2 + a_0. where x_2 denotes the mole fraction of the silver nitrate. For all systems, except (Li,Ag)NO_3, parameters a_2, a_1 and a_0 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 x_(AgCl) = 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) m~2s~(-1) exp(-(20.7 +- 0.4) kJ mol~(-1)/(RT)).