Cation Diffusion at the Polymer Coating/Metal Interface.
Cation Diffusion at the Polymer Coating/Metal Interface.
(959 K)
Pommersheim, J. M.; Nguyen, T.; Zhang, Z.; Lin, C.
Journal of Adhesion Science Technology, Vol. 9, No. 7,
935-951, 1995.
Keywords:
building technology; cation ions; coatings; defect;
diffusion; model; polymer/metal interface
Abstract:
Theoretical and experimental studies were carried out on
the transport of cations in the channel between a
polymer coating and a metal substrate from a defect in
the absence of an applied electrical potential. The
model consists of two stages: an initial period during
which ions diffuse in the coating/metal interfacial
'channel' and adsorb on the coating surface, and a
propagation period during which ions also diffuse into
the coating. The mathematical models were solved to
predict the cation concentration and flux under the
coating and the relative rate of diffusion between the
initial and propagation periods. Model parameter values
were derived from the results of an experiment conducted
in a specially designed diffusion cell. The experiment
measured the depletion of Na+ ions in a cylindrical,
central reservoir, which was placed within the perimeter
of a defect through the coating of an epoxy-coated steel
panel. Model predictions of concentration versus time
agreed well with the experimental results, which showed
that most of Na+ ions were removed by lateral diffusion
from the reservoir during the initial period. Further,
the transport during the initial period was much faster
than that during the propagation period. The results
also indicated that during the propagation period, the
rate-limiting step was the lateral diffusion along the
coating/metal interface rather than diffusion through
the coating.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899