ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Viscosity of the System KF—KCl—KBF₄

V. Daněk and D. K. Nguyen

Institute of Inorganic Chemistry, Slovak Academy of Sciences, SK-842 36 Bratislava

Abstract: The viscosity of the melts of the system KF-KCI-KBF₄ has been measured by means of the computerized torsional pendulum method.Additivity of the logarithms of viscosity was adopted as the ideal behaviour of the mixture. Negative deviations from such additive behaviour were found in all the boundary binary and ternary systems.In the pure KBF₄ melt BF₄^- tetrahedra tend to link, forming relatively weak B-F-B bonds. Introducing F^- ions into the KBF₄ melt by addition of KF, the B-F-B bridges break off, which leads to the lowering of the viscosity and the negative deviation from the ideal behaviour in the KF-KBF₄ systerm. Introducing Cl- ions into the KBF₄ melt, the exchange of fluoride atoms in the BF₄^-tetrahedron for the chloride ones according to the general schemeBF₄^- + nCl^- = [BF₄-nCl_n]^- + n F^-  takes place. Consequently, the less stability of the B-Cl-B bridges and the lower concentration of the B-F-B ones lead to the negative deviation of the viscosity course in the KCl-KBF₄ system. These processes take place obviously in the ternary system as well.

Full paper in Portable Document Format: 492a64.pdf

Chemical Papers 49 (2) 64–67 (1995)