Effect of the cationic composition of cryolite-alumina melts on the anodic overvoltage

Abstract

Steady-state polarization of anodes prepared from platinum or glassy carbon is studied in a laboratory cell in a cryolite-alumina melt containing small amounts of potassium and lithium fluorides and various alumina amounts. The surface area of the anodes reaches a few centimeters squared. An insignificant depolarization of the anodic process is discovered following the replacement of a fraction of sodium ions in the electrolyte by potassium ions in an amount of ∼3.9 mol % KF (∼4.1 wt %) and a noticeable depolarization, following the substitution of K+ in an amount of ∼7.1 mol % KF (∼7.6 wt %). Substituting lithium ions in an amount of ∼3.7 mol % LiF (∼1.8 wt %) for a fraction of sodium ions leads to an insignificant polarization. A significant effect of a general cryolite ratio on polarization is discovered. A noticeable increase in the anodic polarization is fixed at an alumina concentration equal to 5–5.5 wt %.