The atmospheric corrosion of zinc: The effects of salt concentration, droplet size and droplet shape

The influence of droplet characteristics on the atmospheric corrosion of zinc was investigated using a multi-microelectrode approach. Arrays of close-packed zinc wires, 500 mu m in diameter, were coupled such that the net anodic and cathodic current flowing through each electrode interface was measured as a function of time. Droplets in the range of 1-10 mu L placed onto the array showed that electrochemical fields are immediately established and can remain unaltered for significant periods of time. The total charge passed was found to be almost identical for 0.6 M NaCl droplets of varying size when compensating for the electrolyte-zinc contact area, however significant differences in current exchange were observed when varying electrolyte concentration. In contrast to studies on other metals, the highest rates of zinc corrosion, as measured by the microelectrode array, did not occur during drying cycles. It was observed that the initial wetting and subsequent holding at high relative humidity led to the highest measured currents. Corrosion damage during drying cycles, however, appears to be enhanced for large droplets with high contact angle and increased electrolyte concentration. The importance of these observations to the modeling of atmospheric corrosion has been discussed and future developments of the technique are outlined.