ISSN print edition: 0366-6352
ISSN electronic edition: 1336-9075
Registr. No.: MK SR 9/7
Silver as anode in cryolite—alumina-based melts
M. Kucharík, P. Chamelot, L. Cassayre, and P. Taxil
Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 36 Bratislava, Slovakia
Received: 9 August 2006 Revised: 7 November 2006 Accepted: 8 November 2006
Abstract: 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.
Keywords: silver electrode - cryolite - alumina - low-temperature electrolyte
Full paper is available at www.springerlink.com.
Chemical Papers 61 (2) 142–145 (2007)