Silver as Anode in Cryolite—Alumina-Based Melts

Marian Kucharik (1) , Pierre Chamelot (1) , Laurent Cassayre (1) , Pierre Taxil (1)

1 LGC - Laboratoire de Génie Chimique

The anodic behaviour of silver was investigated in cryolite—alumina-based melt. Silver has a lower melting point (ca. 960◦C) than the other metals considered as possible inert materials for aluminium electrolysis. The working temperature used in aluminium industry is approximately 960◦C, depending on the melt composition. Therefore, the stability of silver during the anodic process was tested at 870◦C in an acidic electrolyte consisting of 65.5 mass % Na3AlF6 + 22.9 mass % AlF3 + 5.7 mass % CaF2 + 3.9 mass % LiF + 2 mass % Al2O3 with the melting point ca. 850◦C. The electrolyte without alumina was prepared as well, with the melting point ca. 860◦C. The resulting cryolite ratio (CR = n(NaF)/n(AlF3)) for both electrolytes was equal to 1.6. The behaviour of the silver anode was studied by voltammetry measurements. The electrochemical study showed that an oxidation reaction occurred at a potential below the oxygen evolution potential. Silver was not found to be stable under oxygen evolution. The degradation of the silver anode was apparent after electrolysis.

Mots clés: Silver electrode; Cryolite- Alumina; Low-temperature electrolyte

Domaines: Génie chimique

Marian Kucharik, Pierre Chamelot, Laurent Cassayre, Pierre Taxil. Silver as Anode in Cryolite—Alumina-Based Melts. Chemical Papers, 2007, 61 (2), pp.142-145. ⟨10.2478/s11696-007-0011-x⟩. ⟨hal-03594299⟩