17 NACE INTERNATIONAL: VOL. 56, NO. 5 MATERIALS PERFORMANCE MAY 2017
Information on corrosion control and prevention
Continued on page 18
have properties that can be useful in pre-
venting corrosion. A two-pack epoxy sys-
tem, cured with a proprietary unmodif ied
aliphatic amine hardener system, was se-
lected to represent epoxy primer systems
used to protect steel and aluminum
structures.
The graphene was dispersed directly
into the resin at loading levels that
ranged from 0.1 to 5.0 w t%. Sample 2 was
limited to a maximum loading level of 1.0
w t% due to its very high surface area. The
graphene coatings were applied to mild
steel panels that were hand-abraded
according to ISO 1514
4
and cleaned with
xylene. The panels were then cured for
seven days at 18 to 25 °C to create a dry
f ilm thickness of 40 µm for testing using a
draw-down method.
Cyclic corrosion resistance was tested
according to BS EN ISO 11997-2
5
modif ied
to remove ultraviolet light exposure.
Using a repeating cycle for a total of
1,000 h, duplicate specimens were
exposed for 60 min to dilute electroly te
fog (0.35% ammonium sulfate [(NH
4
)
2
SO
4
]
and 0.05% sodium chloride [NaCl]) at
~24 °C followed by 60 min drying time
with temperatures rising to 35 °C. Panels
were checked regularly to monitor the
progression of corrosion and were rated
at three and six weeks for defects such as
blistering and rusting following the
guidelines of ISO 4628-2.
6
Figure 1 shows representative images
of a selection of panels before and after
Figure 3: SEM micrographs of cross-sectioned steel panels coated with graphene-loaded epoxy after immersion testing: (A) 0% graphene control shows
growth of corrosion products under the epoxy coating—the inset red box marks the area examined using energy dispersive x-ray analysis; and (B) 0.5%
Sample 2 showing no corrosion of the steel substrate under the coating. Images courtesy of AGM.
1,000 h of salt fog testing. The graphene-
loaded epoxy-coated samples remained
corrosion free for up to 12 days, and then
only showed very small, localized spot-
ting. This localized corrosion appeared to
be limited to regions where there had
been defects or pitting in the coating.
There was also an increase in the time
it took for the onset of corrosion—