Electrode processes in the KF-AlF-AlO melt

• Published in: New journal of chemistry 2020-03, Vol.44 (13), p.5152-5164
• Main Authors: Padamata, Sai Krishna, Yasinskiy, Andrey, Polyakov, Peter
• Format: Article
• Language: English
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/d0nj00016g

The kinetics of anodic and cathodic processes in KF-AlF 3 and KF-AlF 3 -Al 2 O 3 melts obtained by means of stationary polarization and cyclic voltammetry have been studied. Studies were conducted at different cryolite ratios [CRs, (moles of KF)/(moles of AlF 3 )] and different alumina contents at 700-800 °C for the Cu-Al anode and at 800 °C for the tungsten cathode. The limiting current density of oxygen evolution on the Cu-Al anode was 0.31 A cm −2 at 700 °C and CR = 1.4. It drastically increases with CR and temperature. The limiting current density of aluminium reduction on the W cathode was in the range 0.45-0.50 A cm −2 . The cathodic process is diffusion-controlled while the anodic one shows mixed kinetics. The diffusion and mass transfer coefficients for the cathodic process (W electrode) and the mass transfer coefficient for the anodic process (Cu-Al electrode) were determined. Based on the obtained results, the electrolysis of 1.4KF-AlF 3 -Al 2 O 3 (sat) with the Cu-Al anode and W cathode was performed. The aluminium purity was determined using an optical emission spectrometer. The XRD and SEM-EDX methods were used to study the phases formed on the anode surface. SEM-EDX image of the oxide layer on the surface of the 90Cu-Al anode after the electrolysis process.