47 NACE INTERNATIONAL: VOL. 56, NO. 11 MATERIALS PERFORMANCE NOVEMBER 2017
COATINGS & LININGS ESSENTIALS
Continued on page 49
Nanoparticles Enrich Zinc-Rich
Primer for Highway Bridges
Nanoparticles are being considered in the
development of durable coating systems for
structural steel highway bridge structures
due to their beneficial electrical and me-
chanical properties. Since the 1980s, three-
coat zinc-rich primer coatings have become
widely used to protect steel bridges against
corrosion. Still, around $500 million is
spent annually for maintenance painting of
steel bridges, triggering a trend to enhance
coating system durability and reduce main-
tenance requirements.
In CORROSION 2017 paper no. 9539,
"Corrosion Performance of Nano-Particle
Enriched Epoxy Primer for Marine Highway
Bridge Application," by S.F. Fancy, M.A.
Sabbir, K. Lau, and D. DeFord, the authors
report on a study that investigated the cor-
rosion performance of a nanoparticle-
enriched zinc-rich primer (NPE-ZRP) for
structural steel under aggressive marine
exposures. Corrosion protection by a zinc-
rich primer is provided by galvanic coupling
of the zinc pigments with the steel sub-
strate; therefore, an important parameter
for the primer is electrical conductivity
between zinc pigments and the steel. e
authors note that the quantity of zinc pig-
ments alone, even with content as high as
80 to 90% by weight, cannot ensure effective
electrical continuity to provide long-term
galvanic corrosion protection. Other factors
can affect electrical continuity, including
the shape of the zinc pigment and forma-
tion of zinc oxidation products. Studies
have found, for example, that efficient elec-
trical contact can't be provided by spherical
pigments.
Improving electrical conductivity by
adding materials such as di-iron phosphide,
carbon black, extender pigments, and alu-
minum pigments to the epoxy resin with
zinc particles has been studied. Reports
indicate that adding carbon nanoparticles
improves the mechanical and electrical per-
formance of a zinc-rich epoxy primer, and
with a lower zinc concentration than typi-
cal zinc-rich primer formulations.