Surface Tension of KPO₃-WO₃ Melts

Abstract

The temperatures T liq of molten xWO 3 -(1 − x)KPO 3 mixtures with a molar content between x = 0 and x = 0.60 have been determined by differential thermal analysis. The surface tension of the xWO 3 -(1 − x)KPO 3 melts in the interval from x = 0 to x = 0.5 has been measured by ring tensiometry for temperatures 10 K -20 K above the melting points, up to 1373 K. The data obtained for KPO 3 were fitted by a linear dependence on the temperature and compared with data available in the literature. The surface tension of the xWO 3 -(1 − x)KPO 3 melts was found to decrease non-monotonously with x. Three bends at x ∼ 0.15, 0.30, and 0.45 were observed in the surface tension vs. molar fraction curve. The first and the third bends correspond to eutectic compositions; the second one is related to the formation of congruently melting K 2 WO 2 P 2 O 7 . Equations describing the temperature and concentration dependences of the surface tension are proposed.