Abstract
The passivation and passivity of zinc in 1 M NA2CO3 (a), 0·1 M NAHCO3 (b) and 0·01 M NaHCO3 (c) have been investigated by measuring galvanostatic charging and discharging curves in the range between 1 ms and 30 min. In (a) passivation is fast and brought about by small amounts of oxide, at 20°C by an approximately mono-molecular oxide layer. In (a) the first traces of reducible oxide are formed immediately after charging of the double layer. In (b) and (c) passivation is very slow, involving the formation of thick oxide layers. In this case a marked dependence of the amount of oxide necessary for passivation on the temperature indicates a similar dependence of the number initially formed oxide nuclei. In (a) current efficiency with respect to oxide formation prior to passivation is high; it is very small in (c) due to parallel dissolution of Zn to Zn2+. Quasi-stationary current/voltage curves are presented for both (a) and (c).
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