INVESTIGATION OF THE SURFACE-PROPERTIES O F METALS BY RADIOTRACER TECHNIQUE .8.

The present work is focused on the investigation of the time, potentia l and pH dependence of SO42- and HSO3- accumulations on surface oxide layers of low carbon steel. From the experimental results it can be co ncluded that 1. Surface excess values of SO42- and HSO3- ions on steel surface undergoing structural transformation are very high and the Ga mma values corresponding to the quasi-stationary state cannot be attai ned even after 4 hours. The high surface coverages measured (between 4 and 10 monolayers) give a strong indication that significant incorpor ation of both aggressive anions into the surface oxide layer occurs. T he presence of sulfite ions in the solution phase accelerates the corr osion of low carbon steel. 2. Changes in the solution pH have no signi ficant effect on the time and potential dependence of sorption process es in the pH region studied (between 3.5 and 6.5). 3. During anodic po larization of low carbon steel at more positive potentials than 0.40 V the surface excess concentration of anions increases. On the other ha nd, in the course of potential shirts in the negative direction at: pH = 3.5 below E = 0.40 V (or at pH = 6.5 below E = 0.20 V) a significan t decrease in the Gamma values can be observed. The latter effect, in accordance with literature data (1-2), reveals that dissolution of low carbon steel taking place in the above mentioned potential regions le ads to a decomposition of the surface layer and, therefore, to a decre ase in the surface excess concentration of incorporated anions. 4. The surface intensity versus time curves measured in studies of the mobil ity of labeled sorbed species can be considered to be superpositions o f - at least - two processes (exchange and increased accumulation of l abeled aggressive anions). The strong embedding of anions detected is probably the result of some selective chemical interactions (chemisorp tion) between SO42-/HSO3- ions and the active sites of tile steel surf ace undergoing structural transformation.