The use of ellipsometry for studying adsorption of organic corrosion inhibitors from aqueous solutions on metals. Review. Part 1. Methods for obtaining adsorption isotherms1

The review is devoted to the application of the ellipsometry method to study the adsorption of organic corrosion inhibitors (CIs) from solutions on the surfaces of metals and alloys. Part 1 of the review focuses on the basics of the method and discusses the necessary simplifications that should be taken into account in the study of real reflective systems. A rationale for using the ellipsometric method to determine small thicknesses of surface layers around 1 nm is given, since the basic equation of ellipsometry is derived for bulk phases. Various methods for obtaining adsorption isotherms from solutions are discussed and a brief analysis of theoretical adsorption isotherms is given. Particular attention is paid to the logarithmic Temkin isotherm. This isotherm is valid in the region of medium coverages (0.2< Theta <0.8) and at sufficiently large heterogeneous factors f (>4). The modified Temkin isotherm proposed by S.F. Timashev is valid in the entire range 0< Theta <1 and for f >0. Articles are cited in which ellipsometry is used to determine the thicknesses of CI surface layers. Other methods of obtaining isotherms of CI adsorption from aqueous solutions are considered: analysis of anodic polarization curves, the concentration dependence of the degree of metal protection from the results of corrosion tests, electrochemical impedance spectroscopy, and quartz crystal microbalance. Part 1 presents a methodology for obtaining adsorption isotherms by the ellipsometric method and discusses as an example the adsorption of sodium N-phenylanthranilate on the surface of iron from a neutral solution. The adsorption isotherm thus obtained is also confirmed by another independent method, electrochemical impedance spectroscopy.