Calculation of thermodynamic parameters of melts from experimentally determined liquidus‐curves

Thermodynamic parameters of melts (ΔH S , A 0 , A 1 ) in the system Anorthite‐Diopside and Bi 2 O 3 ‐Bi 4 B 2 O 9 have been calculated by a rigorous application of solution thermodynamics. The data are internally consistent and yield values of ΔH S for Anorthite = 133 kJ/mole, Diopside = 81 kJ/mole, Bi 2 O 3 = 19 kJ/mole and Bi 4 B 2 O 9 = 39 kJ/mole. The activity of Anorthite and Diopside in an anorhtitic melt deviates negative from ideality, whereas a diopsidic melt behaves almost ideal. In a “Bi 2 O 3 ” melt the activity of the Bi 2 O 3 component is strongly positive, that of Bi 4 B 2 O 9 is strongly negative. The opposite is observed for the “Bi 4 B 2 O 9 ” melt. All calculated liquidi except the Bi 4 B 2 O 9 liquidus closely match the experimental ones. In contrast to the experimental liquidus the calculated Bi 4 B 2 O 9 liquidus has an inflection point. The crest of the metastable spinode (solvus) for a “Bi 2 O 3 ” melt is close to the liquidus indicating melt separation at undercooling. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)