IN-SITU ELLIPSOMETRIC STUDY OF LEAD SULFATE FILM ELECTROFORMATION ON LEAD IN A SULFURIC-ACID-SOLUTION

The process of lead sulfate film formation on a Pb electrode in 0.5 M H2SO4 has been investigated using the insitu ellipsometric technique c omplemented with scanning electron microscopic imaging, The quality of a polished lead electrode surface was first evaluated by spectroscopi c ellipsometric measurements. The results of the present work confirm that the passive film has a two-layer lead sulfate structure. The mech anism of growth of the inner layer is explained by nucleation and a th ree dimensional growth model. The inner layer appears to be porous and Pb2+ ions diffuse through this semi-impermeable barrier. As a consequ ence;an outer layer of larger crystals is observed on SEM micrographs. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.