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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-nCln]- + 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)

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