Internal Cation Mobilities in the Molten Systems (Li-Rb)N0 3 and (Li-Cs)NO s

Abstract

The relative differences in internal cation mobilities are measured for the molten systems (Li-Rb)N03 and (Li-Cs)N03 over a wide range of temperatures and concentrations with a countercurrent electromigration method, and the internal mobilities are calculated from these results and the available data on the electrical conductivity.The following phenomena are observed: (a) under some conditions the electrical mobility of Li+ is lower than that of the larger cation, (b) at a given temperature the mobility of Li+ decreases with increasing molar volume of the mixture, and (c) at low temperatures the isotherms of the mobility of the large cation show a maximum at some low concentration of that ion. These phenomena are interpreted in terms of the free space and the pair potential between cation and anion.

High-Dilution Diffusion of K + , Rb + , Cs + , and Tl + in the Molten System (Li-K)NOs Studied by Wave-Front-Shearing Interferometry

“…Thus, the diffusion coefficients of the alkali ions and Tl + in the system (Li-K)N03 measured in the present study could qualitatively be explained on the assumption that the size of the diffusing ions as compared with that of the free space and the pair potential between cation and anion would be the main factors which govern a diffusion process as well as an electromigration process [18,19]. Tracer diffusion coefficients of Rb + and Cs + have been measured in the systems (Li-Na)NOa, (Li-K)N03, (LiRb) N03, and (Li-Cs) N03 with a paper strip method [20]; the results can also be explained qualitatively on the same assumption.…”

“…Meanwhile, for the motion of somewhat larger ions such as K + , Rb + , and Tl + , the influence of the free space would become effective in the region rich in LiN03 . Also in the data on the internal electrical mobilities of Rb + and Tl + in the respective systems (Li-Rb) N03 [18] and (Li-T1)N03 [19], the effect of the free space is evident at high concentration of LiN03 . Thus, it is expected that Dk , ÖRb, and Dy 1 would increase first on adding LiN03 to KN03 and then decrease in the region rich in LiN03 .…”

High Enrichment of 6Li in Molten Nitrates by the Klemm Method

“…In (Li, Rb)NO 3 and (Li, Cs)NO 3 at considerably high concentrations of LiNO 3 , the mobilities of Rb + and Cs + decrease, respectively, with increasing concentration of LiNO 3 [4]. This is because the free space becomes too small for the large Rb + and Cs + ions to move away from its reference NO − 3 anion.…”

“…Some 70 years ago, Klemm devised a countercurrent electomigration method in molten salts for enriching isotopes, particularly of alkali and alkaline earth elements [1,2], which has been later named 'la méthode de Klemm' [3], Klemm's method [4] or the Klemm method [5]. This Klemm method may be regarded as a kind of the Hittorf method, as seen from a comparison of the principles of the Klemm (or column) method with the Hittorf (or disk) method [6] in Figure 1.…”

“…It took almost 20 years for the very amazing phenomenon discovered by Chemla in 1958 [24] to be named the Chemla effect later [4]. As for the definition: A crossing point appears when plotting as a function of two isotherms, for identical temperature T , for the (internal or external) mobilities of two species in a mixture defines, sensu stricto, the existence of a Chemla effect.…”