Unified Model for the Degradation of Organic Coatings on Steel in a Neutral Electrolyte.
Unified Model for the Degradation of Organic Coatings on
Steel in a Neutral Electrolyte.
Nguyen, T.; Hubbard, J. B.; Pommersheim, J. M.
Annual Meeting, 73rd. Federation of Societies for
Coatings Technology (FSCT). Proceedings. October 10,
1995, St. Louis, MO, 1995.
Journal of Coatings Technology, Vol. 68, No. 855,
45-56, April 1996.
coatings; corrosion; degradation; electrolyte;
A unified model is presented for the degradation of an
organic protective coating on a steel substrate exposed
to a neutral electrolytic environment. This model is
based on theoretical and experimental studies from our
laboratory and on current understanding of the
degradation process. The assumptions of the model are
based on the concept that degradation of a coating/steel
system occurs following the transport of ions through
conductive pathways, which are presumably formed by an
attack by water in the "hydrophylic",
low-molecular-weight/low-cross-linked regions, followed
by the connections of these regions. Models for the
blistering and delamination resulting from corrosion
processes are based on the diffusion of cations along
the coating/steel interface from the detects to cathodic
sites under the coatings. The resulting equations are
solved to predict ion fluxes and concentration profiels
along the interface and within blisters. Model
variables include blister size, distance between blister
and defect, ion diffusivity, and potential gradients.
Experimental results agree well with theoretical