Internal Cation Mobilities in the Molten Binary Systems KNO3-Sr(NO3)2 and KNO3-Ba(NO3)2

The relative differences in internal cation mobilities for the molten binary systems (K, Sr0.5)NO3 and (K, Ba0.5)NO3 have been measured with the Klemm method in the concentration range up to 34 mol% of the alkaline earth cations. From these and available data on the densities and conductivities, the internal mobilities of these cations, bK, bSr and bBa, have been calculated. In these systems bK and bSr or bBa decrease with decreasing concentration of the K+ ion. bK is well expressed by bK = fK ·bK *=fK·[A/(V-V0)] exp (-E/RT), where bK * is the internal mobility of the K+ ion in such melts as (K,Cs)NO3 in which the Coulombic attraction is the dominant factor for the internal mobility of the K+ ion, the constants A, V0, and E being independent of the coion, V is the molar volume of the present mixture and fK the volume fraction of KNO3 in the mixture. At a given mole fraction of K+ ions, the internal mobilities are in the order: Ca<Sr<Ba. This order could be interpreted as the decreasing order of the Coulombic attraction of these cations with the anion.