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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16 MAY 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 5 MATERIAL MATTERS Graphene Nanoplatelets Provide Extra Barrier Protection to Epoxy Coatings G raphene, due to its exceptional electrical and mechanical proper- ties, has attracted attention as a potential material for imparting anticorrosive performance. Graphene is a carbon allotrope with a two-dimensional molec- ular structure comprised of a single layer of carbon atoms bonded together in a hexagonal lattice structure. Bohm 1 proposed that graphene's two-dimen- sional platelet structure enables excellent performance in barrier coatings based on its high surface area, electrical conduc- tivity, and impermeable nature. This enhanced performance may be explained by the combination of three characteristics: graphene makes the path of water permeation more diff icult; the impermeability of graphene's molecular structure reduces the penetration of oxy- gen, water, and other corrosive materials; and graphene provides an alternative path for electrons and breaks the electro- chemical cell that is necessary for corro- sion. Subsequently, graphene has been investigated to explore its corrosion- resistant capabilities. Literature notes that work has included doping graphene with corrosion inhibitors 1 and depositing it on substrates using chemical vapor deposition (CV D). Potentiometric analysis and traditional corrosion testing has suggested that gra- phene can provide signif icant perfor- mance improvement. 2-3 A large part of this work has been done with discrete lay- ers of graphene grown via CV D or applied directly to surfaces. Applied Graphene Materials (AGM) (Cleveland, United K ingdom) has devel- oped and patented a unique graphene synthesis process to produce dispersion- ready graphene nanoplatelets using sus- tainable raw material sources rather than exfoliating graphene from graphite. Development work is underway that explores the ability of graphene nano- platelets distributed throughout a coat- ing f ilm to function in a comparable man- ner to a monolayer of graphene applied by CV D, and evaluates their ability to pre- vent corrosion. Such an approach could open up the opportu- nity for coating man- ufacturers to utilize graphene when for- mulating coatings with improved performance. Independent industry experts Paint Research Association (PR A) (Leicestershire, United K ingdom) and The Welding Institute (TW I) (Cambridge, United K ingdom) worked with AGM to complete an evalua- tion of graphene nanoplatelets in an epoxy coating, with the aim of demon- strating how a graphene-enhanced coating may be useful in preventing corrosion. Two grades of gra- phene platelets were evaluated—A-GNP 10, a medium density graphene with a rigid platelet structure and built-in oxygen func- tionality that pro- vides good dispers- ibility (Sample 1); and A-GNP 35(T), an ultra-low-density, high-surface-area graphene that has a f lexible, crumpled sheet morpholog y (Sample 2). These ma- terials were selected because they each Figure 1: Epoxy-coated steel panels before (A, B, C) and after (D, E, F) 1,000 h of salt fog testing: (A) 0% graphene control at 0 h; (B) 0.5% Sample 2 at 0 h; (C) 5.0% Sample 1 at 0 h; (D) 0% graphene control at 1,000 h; (E) 0.5% Sample 2 at 1,000 h; and (F) 5.0% Sample 1 at 1,000 h. Photos courtesy of AGM. Figure 2: Epoxy-coated steel panels before (A, B, C) and after (D, E, F) 30 days of immersion testing in synthetic seawater: (A) 0% graphene control at 0 days; (B) 1.0% Sample 2 at 0 days; (C) 1.0% Sample 1 at 0 days; (D) 0% graphene control at 30 days; (E) 1.0% Sample 2 at 30 days; and (F) 1.0% Sample 1 at 30 days. Photo courtesy of AGM.