Materials Performance

MAY 2017

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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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—

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