Effect of mineral pigments on the water uptake in organic films

Abstract

The paper presents the results of the electrochemical study (electrochemical impedance spectroscopy and anodic polarization) regarding the water uptake in alkyd films with various mineral pigments (white titanium dioxide, yellow iron oxide, and iron blue). The films were realized on carbon steel substrate; dry film thickness in the range 20- 25 urn for the film without pigments and 30 -35 urn for the films with pigments were obtained. The measurements were carried out in 5% NaCI solution at 25°C temperature during a 1500 immersion hours period. The interpretation of the impedance spectra established the presence of two time constants: one for the paint film and another for the reactions at the organic film/carbon steel interface. The evaluation of the time trends of the electrical film capacitance was permitted to determine the water permeability of the studied films. The volume fraction of uptaken water in the films was calculated and the absorption diagram was established. This experimental data were correlated with electrochemical parameters determined from anodic polarization curves. It resulted that white titanium dioxide and iron blue pigments present a beneficial effect and decrease very much the water permeability of the alkyd paint film