Micro-droplets phenomenon and atmospheric corrosion III. Spreading behaviors of micro-droplets under cyclic wet-dry conditions

Under the cyclic wet-dry conditions of 50% RH and 90% RH at 25 °C, the spreading behaviors of micro-droplets were investigated in situ with the stereomicroscope with and without the electrochemical polarization. The results indicated that there was an unobvious influence of the wet-dry cycles on the formation and spreading of micro-droplets in a condition without the electrochemical polarization. Under the external polarization, with the advance of the wet-dry cycles, the areas covered with micro-droplets alternately expanded and dwindled, and the polarization current I_p and polarization resistance R_p changed impulsively. The maximum of I_p in each cycle increased gradually with the increase of the wet-dry cycles and the corresponding maximum of R_p followed a reverse changing rule. Under cyclic wet-dry conditions, it showed a closed relation between the spreading of micro-droplets and corrosion current. They were influenced and promoted with each other.