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Enthalpic Analysis of Potassium Heptafluorotantalate

I. Nerád, E. Mikšíková, and V. Daněk

Institute of Inorganic Chemistry, Slovak Academy of Sciences, SK-845 36 Bratislava


Received: 13 June 2002

Abstract: The relative enthalpies of two crystalline samples K2TaF7 A, K2TaF7 B and of K2TaF7 melt have been measured by the use of the drop calorimetry in the temperature intervals 600—752°C, 615—750°C, and 758—880◦C, respectively. The heat capacities have been determined differentiating the temperature dependences of the relative enthalpies: Cp(K2TaF7 cr, A) = (314 ± 6) J mol−1 K−1, Cp(K2TaF7 cr, B) = (356 ± 7) J mol−1 K−1, and Cp(K2TaF7 melt) = (315 ± 9) J mol−1 K−1. Considerable prefreezing was observed in the temperature dependence of the relative enthalpy of the melt. The onset of the prefreezing effect at cooling of the melt was estimated to be at about 820°C. The depression of the freezing temperature reached down to the temperature of crystallization of 755°C. The calorimetric experiments have shown the temperature of fusion to be 752°C < tfus < 758°C. The enthalpies of fusion at the temperature of 755°C, ΔfusH(K2TaF7 A, 755°C) = (37.2 ± 0.7) kJ mol−1 and ΔfusH(K2TaF7 B, 755°C) = (34.6 ± 1.0) kJ mol−1, inclusive enthalpy of prefreezing, have been determined from experimental data.

Full paper in Portable Document Format: 572a73.pdf


Chemical Papers 57 (2) 73–77 (2003)

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