ELLIPSOMETRIC STUDY OF THE OXIDATION OF MILD STEEL IN AQUEOUS SOLUTIONS.
ARMY WEAPONS COMMAND ROCK ISLAND ILL RESEARCH AND ENGINEERING DIRECTORATE
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Combined ellipsometric and potentiostatic measurements were made on the oxidation of mild steel in pH 7.4 borate-boric acid buffer solutions. The ellipsometric results are described in this report. The potentiostatic data are presented in a report on another work unit. Anodic film thicknesses on the steel surface ranged from 19 to 88A in the anodic overpotential range of 0.7 to 1.7 volts. Film thicknesses increased rapidly near the potential for pitting. Chloride ions in the solution narrowed the potential range for stability of the anodic film, but did not change its thickness appreciably. Films formed by aging the steel in the buffer solution with no potential applied, developed to average thicknesses of 58-60A in three hours. Adsorbed films of barium dinonylnaphthalene sulfonate desorbed rapidly from the steel surface under anodic polarization, but were stable in an overpotential range of 0.1 to 0.2 volt cathodic. Desorption of the sulfonate film, as observed ellipsometrically, occurred at an electrode potential of approximately -400 millivolts vs. the standard calomel electrode. The behavior of the octadecylamine adsorbed films was similar to that of the sulfonate. Stearic acid under some conditions reacts with the steel or its oxide-coated surface. Author
- Properties of Metals and Alloys