Adsorption of the inhibiting anions on passive iron from an aqueous solution

Adsorption of sodium phenylanthranilate (SPA) and dioctyl phosphate (DOP) o n the iron surface from a neutral borate buffer in a E range from 0.0 to 0. 8 V was studied by ellipsometry and diffuse reflection IR spectroscopy. The adsorption of SPA is enhanced with potential only for the low concentratio ns of the adsorbate. The oxidation of aromatic amino acid at high anodic po tentials reduces its adsorption. In the same potential range, the adsorptio n of sodium DOP is enhanced with an increase in E. The data obtained were u sed to plot an adsorption isotherm and determine adsorption constants. The IR studies of the oxidized iron exposed to borate solutions containing orga nic anions confirmed that DOP adsorbs on the iron surface more strongly tha n SPA is. The IR spectrum of DOP changes during its adsorption, suggesting the formation of a saltlike surface complex.