Effect of Temperature on Anodic Passivation of Lead

Abstract

The effect of temperature on the anodic passivation of lead is studied by measuring the changes of anodic potential with the lapse of time under the condition of constant anodic current in dilute sodium sulfate solution. The experimental results show that lead dioxide forming the passive film on lead anode is reduced rapidly by local action before the surface is covered completely with the passive film and then the anode potential falls down to the low value which corresponds to active state of lead. As the lead sulfate film which is formed before the formation of passive lead dioxide film is considered to have a considerable effect on the formation of lead dioxide, the state of this film is studied by caluculating the ionic conductivity σ from the potential-time curve, X-ray diffraction and electron microscope. The logσ−1⁄T plot is divided into two linear parts corresponding to different activation energy. Comparing this results with electron microphotograph, we can conclude that the lead sulfate film becomes very porous due to recrystallization at higher temperature range. Due to this porosity of the lead sulfate film, the electrode potential of lead anode cannot reach high potential value at which passivation is accomplished.