The Effect of Sc2O3 on the Physicochemical Properties of Low-Melting Cryolite Melts КF–AlF3 and КF–NaF–AlF3

Abstract

Quasibinary phase diagrams of the system “low-melting cryolite–Sc2O3” the potential media for synthesizing alloyed alloys Al–Sc are plotted by the method of thermal analysis. The phase diagrams of (KF–NaF–AlF3)–Sc2O3 with different content of NaF and the cryolite ratio (CR) 1.3 and 1.5 are the diagrams with simple eutectics. The liquidus temperature of the (KF–AlF3)–Sc2O3 system increases with the increase in the Sc2O3 concentration due to the formation of a high-melting compound: potassium hexafluoroscandiate К3ScF6. The solubility of Sc2O3 in low-melting cryolite melts KF–NaF–AlF3 increases with the increase in temperature and CR. In contrast Al2O3, the solubility of Sc2O3 in melts containing KF–AlF3 with CR = 1.3–1.5 is much lower than in cryolite melts containing NaF. The conductivity of low-melting cryolite melts measured by the method of impedance spectroscopy decreases in proportion to the Sc2O3 concentration in the similar way as in salt melts containing Al2O3. Based on the experimental data obtained, the compositions of low-melting cryolite melts are proposed for the synthesis of doped Al–Sc alloys.