Abstract
To evaluate the degradation of gelatin and polyethylene glycol (PEG) added to the electrolyte for Cu electrorefining, the time-dependence of the cathode potential was measured during long-term electrolysis. Gelatin and PEG acted as a polarizer for Cu deposition to shift the cathode potential to less noble direction. The polarization caused by the additives gradually disappeared with an increase in the electrolysis duration. The effective duration of additives increased with an increase in the molecular weight and was longer in PEG-containing solution than in gelatin-containing solution. The longer effectiveness of PEG may be attributed to its stability in the solution. The degree of polarization by the additives was decreased with time even when the additive-containing solutions were left un-electrolyzed. The effective duration of additives was slightly shorter in the solutions electrolyzed continuously than in the solution left un-electrolyzed. On the other hand, the morphology and the crystal orientation of Cu obtained by long-term electrolysis were in good agreement with the cathode potential change with time regardless of the kinds of additives. With an increase in the polarization of cathode potential , the deposits showed the smooth surface composed of fine grains and decreased the preferred orientation. The deposits showed the same morphology as that in the additive-free solution when the polarization was decreased by the degradation of additives.
