Determination of the Corrosion Behavior of Painted Iron and the Inhibitive Action of Paints

Abstract

The corrosion behavior of bare iron can be determined by measurements of its potential and change in potential with time. With the aid of a vacuum tube electrometer this method of study has been extended to the determination of the corrosion behavior of painted iron and the mechanism of the inhibitive action of paints. Red oxide (Fe 2 O 3 ) and red lead (Pb 3 O 4 ) have been studied both as pigments and primers. The validity of the method has been demonstrated by the fact that it confirms conclusions which have been obtained only after many years of practical experience, i.e. , that the corrosion inhibitive action of red oxide primer is purely physical, while that of red lead is essentially chemical. Both types of protective paint may maintain iron in the passive condition; the former by keeping the iron dry, the latter by chemically passivating it in the presence of moisture.