ELECTROCHEMICAL-BEHAVIOR AND CORROSION OF LEAD IN SOME CARBOXYLIC-ACID SOLUTIONS

The electrochemical behaviour and corrosion of lead in various concent rations of acetic, lactic (0.01 M-1.0 M), oxalic and tartaric (0 01 M- 0.15 M) acid solutions were studied at 25 degrees C by a potentiodynam ic method. The lead anode is readily soluble both in acetic and lactic acid solutions up to 2000 mV. In these two acid solutions, the anodic dissolution of lead increases with increases in the acid concentratio n and the dissolution process is under charge transfer control. Lactic acid is more corrosive than acetic acid. However, in oxalic and tarta ric acid solutions, the E/i profiles depend on the acid concentration. Above a certain specific concentration, the profiles exhibit an anodi c current peak associated with a dissolution of the metal and the form ation of a passivating lead salt film and a cathodic peak which is rel ated to the reduction of the film. The active dissolution of the lead increases with the acid concentration, the scan rate and stirring of t he solution. The passivation of lead in these two acid solutions occur s by a dissolution-precipitation mechanism and the process is controll ed by diffusion. X-ray diffraction analysis confirmed the presence of a passivating salt film (either lead oxalate or lead tartrate) on the electrode surface. (C) 1998 SCI.