The electrolyte composition and temperature play a critical role in passivation. Numerous researchers have shown that passivation is aggravated by increasing the copper concentration, the acid concentration, or decreasing the temperature. Noguchi et al. showed that time to passivation decreased with increasing Sb3+, As3+, Bi3+ and dissolved O2 in the electrolyte. Abe et al. demonstrated that passivation time decreased with increasing nickel added as nickel sulfate. Several recent studies have focused on the effect of additives on passivation in laboratory experiments. Hiskey and Cheng illustrated that time to passivation is a function of thiourea . For small addition, 1-5 ppm, thiourea improves the passivation behavior, but for large addition, greater than 15 ppm, passivation times decreased. Jin et al. showed that the addition of amino acid chelating agents can inhibit passivation. In particular ethylenediaminetetraacetic acid (EDTA), diethylenediamine-pentaacetic acid (DTPA), and triethylenediaminehexaacetic acid (TTHA) show some benefit. All three exhibit an optimal concentration for extending passivation times . Jin and Ghali studied the effects of several aromatic nitro compounds. The most beneficial to inhibiting passivation were 3, 5 - dinitrosalicylic acid and 3, 5 - dinitrobenzoic acid . All of the additive compounds listed above have the ability to stabilize cuprous ions. Therefore, it would appear that increasing the cuprous concentration increases the time to passivation. This coincides with the combined observations of Noguchi et al. and Bombach et al. Recall that Noguchi showed that passivation time decreased with increasing dissolved O2. Bombach et al. demonstrated that Cu+ ion decreased with increasing dissolved O2. Combining these two observations would seem to indicate that increasing the cuprous content might be beneficial to passivation. Therefore, cuprous stabilizing compounds might be interesting to study. Parker et al. studied several copper(I) complexing ligands in aqueous solutions and ranked them by strength accordingly: CN- >> S2O32- > Me2NCHS > KI > NH3 > C3H5N > KBr > KCl > C3H5OH
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Passivation of Impure Copper Anodes
Secondary Phases Within the Anode
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