ABSTRACT
Using impedance spectra series the swelling of four coatings was investigated with respect to water uptake and changes of diffusion in the coatings. For the interpretation of the measured data a fitting algorithm with some physical models was applied to represent the measured data. The results were compared to obtain a suitable and understandable physical model. Models with more than four parameters were found to be not useful because of the limited frequency range and sometimes physically meaningless values. Therefore, a model with only four adjustable parameters was used to describe the swelling of the coatings. The comparison of the parameters from the different coatings showed significant effects such as increased water uptake of a coating pigmented with micaceous iron oxide. This finding is in contradiction to the widely used term ‘barrier type pigment’. Thus, in this case, the correlation that is often postulated between water uptake and corrosion protection performance is not valid, although this coating material is reliable in industrial practice.
