On the cathodic overvoltage on aluminium in cryolite-alumina melts—I

✍ Scribed by Jomar Thonstad; Sverre Rolseth

• Publisher: Elsevier Science
• Year: 1978
• Tongue: English
• Weight: 798 KB
• Volume: 23
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(78)85050-6

✦ Synopsis

When a constant cathodic current is applied to an aluminium electrode in a Na3A1F6-AlaO, melt at lOlO"C, the potential decreases gradually and linearly with the square root of time to more negative values. Pronounced potential oscillations occurred at cds above 2A/cm2 and the evolution of sodium gas was observed at very high cds. Steady state measurements yielded straight y vs log i plots with a slope of -0.23 V/decade, the overvoltage being -0.19 V at 1 A/cm'. The overvoltage decreased markedly when th? melt was stirred. Potential decay measurements yielded linear log time plots with slopes of 0.0145 V/decade. The charge-transfer resistance ias determined by double pulse measurements to be 0.0031 ohm cm'. AC impedance measurements gave a similar result. The charge transfer overvoltage accounts for only about two percent of the total overvoltage, the rest is apparently diffusion controlled. The cathodic overvoltage in industrial aluminium cells is of similar magnitude as found in the laboratory investigations. INTRODUCTlON Early