On the mechanism of passivation of the cadmium electrode in alkaline solutions

✍ Scribed by A.A. Abdul Azim; K.M. El-Sobki

• Publisher: Elsevier Science
• Year: 1972
• Tongue: English
• Weight: 493 KB
• Volume: 17
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(72)80061-6

✦ Synopsis

The electrochemical behaviour of the Cd electrode in O-1-6 N NaOH has been investigated. Both the potentiostatic and galvanostatic techniques were employed. It has been shown that the electrode surface is primarily covered with a porous layer of Cd(OH), which is precipitated from the solution. Above the Flade potential Cd0 starts to form at the exposed metal parts. The results are discussed in the light of the dissolution-precipitation and the solid-phase transport mechanisms, R&m&Etude du comportement &ctrochimique de lWectrode au Cd dans NaOH O,l-6N. On emploie conjointement les techniques potentiostatique et galvanostatique. On montre que la surface de l'electrode est recouverte primairement d'une couche poreuse de Cd(OH)B, prdcipit& il partir de la solution. Au-dessus du potentiel de Flade Cd0 commence a se former sur les parties metalliques exposees. Les resultats sont discutb a la lumi&re des m&anismes de dissolution-precipitation et de transport en phase solide. Zusammenfassung-Das elektrochernische Verhalten der Cd-Elektrode in O,l-6 N NaOH wurde mit potentiostatischen und galvanostatischen Methoden untersucht. Es konnte gezeigt werden, dass die EIektrodenoberlGhe primZir mit einer porSsen Schicht von Cd(OH), bedeckt ist, welche aus der Liisung ausfallt. Oberhalb des Flade-Potentials setzt an freien Stellen des Metalls die Bildung von Cd0 ein. Die Ergebuisse werden auf der Basis des Mechanismus der Aufliisung/Flillung und des Transports in der festen Phase diskutiert. EXPERIMENTAL TECHNIQUE The Cd electrodes were rods 1 cm in length and 0.75 cm dia., supplied by Johnson, Matthey Ltd. The solutions were O-1, 1, 2, 3 and 6 N NaOH. These were prepared from a concentrated (1: 1) solution and double-distilled water. Prior to each experiment, dissolved oxygen was driven out by passing purified N, through the solution, and stirring was effected by maintaining the gas stream throughout the experiment. The electronic potentiostat was of the Amel type 556 (MiIano).l" A Speedomax recording potentiometer model S60000, provided by Leeds and Northrup, U.S.A., was applied in recording the changes in potential with time.