DISSOLUTION AND PASSIVATION PROCESSES IN THE CORROSION OF COPPER AND NICKEL IN KF.2HF AT 85 DEGREES-C

The process of electrolytic production of fluorine is conducted in a m elt of KF.2HF at about 85 degrees C. The metallic cell materials, copp er and copper-nickel alloys (Monel), and the steel electrodes that are used as the cathode, are subject to substantial corrosion in the liqu id electrolyte. Comparative studies are reported on the relative exten t of corrosion of copper and nickel in the above melt, and the respect ive passivation behaviours of these two metals. The formation of fluor ide films on the two metals is examined by means of cyclic voltammetry and complementarily through recording of open-circuit potential-decay transients, following passivation. Flade behaviour is observed and th e role of diffusion-controlled processes in depassivation is quantitat ively evaluated. Weight-change measurements also support the electroch emically derived results. The passive film at Ni is much less easily r educible than at Cu.