Diffusion et transport ionique dans les halogénures alcalins fondus

Molten Salts and Isotope Separation

“…A more marked crossing was observed, whatever the temperature; the mobility of the lithium ions decreased much more rapidly than that of the potassium ions. However, surprisingly, as already obtained for the nitrate melts, the diffusion measurements did not show any crossing, the lighter ions moved always faster than the heavier ones in the whole concentration range [30].…”

A New Analysis of Internal Cation Mobilities in the Molten Binary System (Li, K)Cl

“…It has been found , that the binary system (Li, K)Br containing a trace amount of radioactive Na + , investigated by Chemla’s group, − can be regarded as an “ideal system” in the sense that C ILi , C IK , and even C INa for Na + are constant over the whole investigated concentration range, both in the lower temperature range (below 923 K) and at a higher temperature (1023 K), except for one case: the C IK in pure LiBr (radioisotope 42 K was used) at 1023 K is significantly higher than that at the other concentrations. , This has been attributed to the agitation effect by the abundant Li + ions; we assume that this effect overcomes the tranquilization effect. This is in contrast with the present case, probably because the mass of Br − A as the attracting anion is too large compared with that of the tranquilizer Li + (see Figure b), and the second step of Br − (see Figure b) will not be retarded as much by the cohesive tranquilizer.…”

“…Chemla discovered the Chemla effect more than 50 years ago; he submitted a French patent in 1958, in which he claimed that in countercurrent electromigration (the Klemm method) of the binary mixture of molten (Li, K)Br, the molar ratio of Li/K attains to a limited value at the anode, whereas the isotope ratio ( 7 Li/ 6 Li) (and also ( 41 K/ 39 K)) continues to increase with time. It was found later that this strange behavior is caused by the crossing of the isotherms of the mobilities of Li + and K + as a function of the mole fraction in the (Li, K)Br mixture. − At a higher concentration of LiBr, Li + is more mobile, and at a lower concentration of LiBr, K + is more mobile. That is, the more enriched cation than at the crossing-point concentration migrates faster in the anode compartment, where the ratio of the two cations, therefore, attains to that at the crossing point.…”

“…By an analysis of the original data presented by Chemla’s group, − this binary system (Li, K)Br has been found to be an “ideal system” , in the following sense: The C IM ’s, defined by C IM = u M ( V m − V 0M ), are constant practically over the whole investigated concentration range at a given temperature; M + is Li + , K + , and even Na + (which is contained as a trace amount of the radioisotope 22 Na), u M the internal mobility of the cation M + (i.e., the cation mobility with reference to the common anion, Br − ), V m the molar volume, and V 0M a correction factor characteristic of M + .…”

“…It was found later that this strange behavior is caused by the crossing of the isotherms of the mobilities of Li + and K + as a function of the mole fraction in the (Li, K)Br mixture. [3][4][5][6][7] At a higher concentration of LiBr, Li + is more mobile, and at a lower concentration of LiBr, K + is more mobile. That is, the more enriched cation than at the crossing-point concentration migrates faster in the anode compartment, where the ratio of the two cations, therefore, attains to that at the crossing point.…”