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Miroslav Boca, Zuzana Ivanová, Marian Kucharik, Jarmila Cibulková, Roman Vasiljev, Marta Chrenková

Density and Surface Tension of the System KF–K₂TaF₇–Ta₂O₅

Keywords: Tantalum, Density, Molar Volume, Partial Molar Volume, Surface Tension

The density of the system KF–K₂TaF₇–Ta₂O₅ was measured by the Archimedean method and the surface tension by the maximum bubble pressure method in the composition range up to 20 mol% Ta₂O₅.
The density in the system KF–K₂TaF₇–Ta₂O₅ increases from KF through K₂TaF₇ to Ta₂O₅ and the surface tension increases from K₂TaF₇ through KF to Ta₂O₅. Based on the measured density values, the molar volumes of the binary and ternary melts at 860 °C, 900 °C and 950 °C were calculated as well as the partial molar volumes of particular components in different binaries. The small negative deviation from ideal behaviour in the binary system KF–K₂TaF₇ was identified by the calculation of the molar excess volume. The formation of complex anions [TaF₈]³⁻ is expected in this binary system.
The surface tension decreases monotonically from KF to K₂TaF₇ in the binary system KF–K₂TaF₇. In the next two binaries KF–Ta₂O₅ and K₂TaF₇–Ta₂O₅ decrease of the surface tension was observed with the initial addition of Ta₂O₅ followed by the increase of the surface tension by further addition of Ta₂O₅. Based on measured data it was concluded that in binaries KF–Ta₂O₅ and K₂TaF₇–Ta₂O₅ the surface active component is Ta₂O₅ and in the binary KF–K₂TaF₇ the surface active component is K₂TaF₇.
Mathematical description of the concentration dependence of the molar volume and surface tension of the measured ternary system was done by the polynomial function at 860 °C, 900 °C, and at 950 °C.

Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag

Print ISSN: 0942-9352
Volume: 220, 09/2006
Pages: 1159 - 1180

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