Abstract
Corrosion inhibitive pigments, based on the cations Ce4+ and Cr3+ exchanged into smart release resins, are dispersed in a polyvinyl butyral (PVB) model coating and applied to a hot dip galvanised steel (HDG) substrate. An investigation is made into the influence of different pigment volume fractions (øpig) of Ce(IV) and Cr(III) based inhibitors, used both in isolation and combination, on the kinetics and mechanism of corrosion driven cathodic coating delamination. The rate of coating delamination is obtained using scanning Kelvin probe (SKP) potentiometry and time lapse photography, and the efficiency with which each inhibitor combination is able to resist cathodic coating delamination is calculated. Isobolograms, commonly utilized within the field of drug interaction, are presented as an effective method for characterising corrosion inhibitor interactions. In some cases, the sum of the efficiencies calculated for Ce(IV) and Cr(III) based pigments is shown to be greater than the sum of their individual efficiencies. It is proposed that Ce4+, released upon electrolyte exposure, is able to oxidize the Cr3+ species resulting in the formation of transient CrO4−2.
Highlights
Cathodic delamination typically became initiated in all cases and the extent of cathodic coating delamination on the coated hot dip galvanised steel (HDG) samples was clearly visible in the time lapse photography images
A systematic time lapse photography study into the inhibition of cathodic polyvinyl butyral (PVB) coating disbondment from a HDG substrate has been completed to show that;
Both Amb-Cr and Amb-Ce based pigments are able to reduce the rate of PVB coating disbondment when used in isolation
Summary
The size of the container meant that a range of inhibitor øpig values could be investigated simultaneously and a delamination rate could subsequently be obtained for each coating pigment combination.
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