The Electrical Conductivity of Molten Oxide-Fluoride Cryolite Mixtures

A new way to reduce the energy consumption during the operation of powerful aluminum reduction cells is suggested via reducing the resistance of the electrolyte, i.e., increasing its electrical conductivity. The electrical conductivity of molten cryolite mixtures NaF-AlF3-CaF2-Al2O3 with cryolite ratio (CR) of 2.1–3.0 and content of CaF2 and Al2O3, up to 8 wt%, was measured at the temperatures from liquidus to 1300 K. Based on the experimental results, a multifunctional equation for the electrical conductivity of oxide-fluoride cryolite melts was evaluated. The experimental and calculated values of the electrical conductivity agree within 1.5%. The activation energy of the electrical conductivity of the NaF-AlF3-CaF2-Al2O3 melts was estimated. The activation energy of electrical conductivity for molten NaF-AlF3 mixtures with CR 3.0 and 2.1, determined by the most mobile cations Na+, increased from 15.8 kJ/mol up to 18.5 kJ/mol. It was found that CR had a greater impact on the activation energy than the changes in the Al2O3 or CaF2 concentrations. Based on the ratio of the activation energies of the electrical conductivity and the viscous flow, the correlation between the electrical conductivity and viscosity of molten cryolite mixtures NaF-AlF3-CaF2-Al2O3 was illustrated.

An investigation into dissolution behavior of pre-oxidized Ni-6Al-10Cu-11Fe-15Cr nickel base alloy in molten cryolite

Purpose – The purpose of this paper was the investigation of corrosion behaviour of Ni-6Al-10Cu-11Fe-15Cr alloy, as a candidate material for inert anodes in aluminium electrolysis industries. Design/methodology/approach – The samples were prepared by casting, and then were oxidized at 1,000°C for 30, 70 and 100 hours, respectively. To determine corrosion resistant of the samples, they were exposed to molten cryolite at 930°C for 70 hours. Then the surface layers were studied. Findings – Results showed that by extension of corrosion time, thickness of oxide layers increases. In addition, it was found that Al2O3 and Cr2O3 are the major oxide compounds that appear on the surface of the sample. Originality/value – In this paper, the Ni-6Al-10Cu-11Fe-15Cr nickel base alloy has been selected to study its corrosion behaviour in molten cryolite as a candidate for inert anodes. It was found out that by addition Al and Cr into the alloy composition, due to formation of Al2O3 and Cr2O3 following oxidation, the substrate was protected from corrosion attacks.