ABSTRACT
For corrosion protective coatings to be successful, they rely, to a great extent, on having a satisfactory barrier property, signifying the coating’s inherent ability to withstand the permeation of seawater and oxygen. Aluminum flakes have for several decades been used to enhance this barrier property in coating formulation work, albeit with a lack of evidence. In the present work, we have thus explored the truth about aluminum flakes in protective coatings by investigating a series of coatings, in which the aluminum concentration has varied from 0 to 9 wt%. This has been tackled by a combination of traditional testing, including salt spray and cyclic ageing, as well as more advanced methods such as EIS. The results from all testing demonstrate no correlation between the aluminum flake concentration used and the coatings’ protective performance. Moreover, by extracting the coating capacitance from EIS measurements, we find minimal to no differences in the barrier property as a result of changes in the aluminum concentration. This is also demonstrated in the calculated water diffusivity coefficients, which increase in the order; 6 → 9 → 0 → 3 % with values varying from 3.0 to 3.7 cm2 s-1 for the entire range. Interestingly, a linear correlation between aluminum concentration and the coatings’ dielectric constants is demonstrated, with values ranging from 4.5 to 18.4 for fully saturated coatings upon going from 0 to 9 wt% aluminum.
