A comparative study of the effects of surface condition and amalgamation on the corrosion and polarisation characteristics of pure zinc and two battery zinc alloys in leclanche related electrolyte

The effect of surface preparation and amalgamation on the corrosion and polarisation characteristics of pure zinc and two battery zinc alloys (ZnPdCd) and (ZnPbCdFe) has been compared and contrasted in concentrated NH 4Cl solution. Polished metal surfaces have been used to simulate the surface condition of the anode materials during initial battery storage periods and etched surfaces have been used to simulate conditions after high rate discharge. The investigation highlights the extreme sensitivity of the corrosion behaviour to small changes in regard to the high (Pb, Cd) or low (Fe) hydrogen overvoltage components. In order to explain the corrosion characteristics of the etched alloys consideration must be given to the effect of surface accumulation of minor alloying constituents in addition to surface roughness changes. Amalgamation of the polished specimens produces a significant reduction in their corrosion rate. Amalgamation of the etched metals removes the effect of the accumulated minor alloying components Pb and Cd, probably by surface amalgam formation. In the case of the Fe containing alloy, however, the deleterious effects of the surface accumulation of Fe cannot be removed.