CALPHAD: Phase diagram of the system KFK 2MoO 4SiO 2

Abstract

The phase diagrams of the binary systems KFK 2MoO 4, KFSiO 2, and K 2MoO 4SiO 2, as well as that of the ternary system KFK 2MoO 4SiO 2 in the range up to 50 mole % SiO 2, were measured using the thermal analysis method. The thermodynamically consistent phase diagrams were calculated using the coupled analysis of the thermodynamic and phase diagram data. In the system KFK 2MoO 4 the intermediate compound K 3FMoO 4, melting congruently at 751 °C, is formed. This compound divides this system into two simple eutectic ones. The coordinates of the individual eutectic points are: E 1: 30.5 mole % K 2MoO 4, 720.4 °C, and E 2: 58.8 mole % K 2MoO 4, 744.9 °C. In the binary system KFSiO 2 the liquidus curve of KF shows an inflex point, characteristic for reciprocal systems with chemical reaction taking place between components. Similar course of the liquidus curve of K 2MoO 4 was found in the binary system K 2MoO 4SiO 2, indicating the presence of the chemical reaction between components as well. The strong positive deviation from ideal behavior of the ternary system KFK 2MoO 4SiO 2 was ascribed to the possible formation of heteropolyanions [SiMo 12O 40] 4− in the melt. In the investigated concentration range of the ternary system no eutectic point has been found. It lies most probably beyond the investigated part of the system. The standard deviation of approximation of the calculated ternary phase diagram is ± 5.9 °C, which is approximately on the same level of magnitude as the estimated experimental error of ± 4 °C.