Thermodynamic properties of liquids in the system KF-KBF4

Relative enthalpies of melts in the system KF-KBF4 at mole fractions of KBF 4 equal to 0.35, 0.42, 0.60 and 0.80 have been determined from drop-calorim etry measurements at temperatures up to 1082 K. The temperature dependences of relative enthalpies of melts have been found to be linear. The heat cap acities of melted mixtures indicate a positive deviation from additivity. T he enthalpy of mixing shows a negative deviation from ideality in the entir e composition range of the system. The exothermic effect at mixing reaches its minimum of about -3 kJ mol(-1) at the composition around x(KBF4) = 0.7. Negative enthalpy of mixing is explained by forming of individual BF4- ion s, following the breaking of B-F-B bridges in KBF4 melt during the mixing p rocess. (C) 1999 Elsevier Science B.V. All rights reserved.