www.ceramics.org | American Ceramic Society Bulletin, Vol. 92, No. 518

Graphene nanocomposite coatings for protecting low-alloy steels from corrosion

By Robert V. Dennis, Lasantha T. Viyannalage, Anil V. Gaikwad, Tapan K. Rout, and

Sarbajit Banerjee

A scalable roller-coating approach adapts new materials to

solving persistent corrosion problems using existing manu-

facturing methods.

Graphene nanocomposite

coatings for protecting low-

alloy steels from corrosion

A ceramic engineer or scientist unfortunately must admit that

there is an unwelcome member of the fam-ily among us—iron oxide, or rust. This unpleasant family member is disruptive at best. More often it is destructive, nearly impossible to control, and a consumer of resources that are devoted to it in an attempt to mitigate its impact or at least slow it down. Metal bars, wires, and sheets require protective coatings to prolong their use on exposure to service environ-ments wherein they inevitably encounter corrodant species and conditions condu-cive to the initiation of rust formation. Society invests enormous amounts of time and financial resources to rust preven-tion, repair, and replacement. Indeed, the Department of Defense has a long his-tory of fighting rust (Figure 1), and the Government Accountability Office esti-mates that today the United States military spends more than $20 billion per year in corrosion-related expenses.

As the advanced manufacturing industry in the United States rejuvenates, sustainable processes and materials will be increasingly important.1,2 New materials will offer opportuni-ties for new solutions to old problems. Graphene and carbon nanotubes represent a class of new materials with unique

Figure 1. Army truck cab assemblies enter-ing massive rust-proofing ovens. The sheet metal is treated with chemicals before applying finishing coats to prevent rust., circa 1945.

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19American Ceramic Society Bulletin, Vol. 92, No. 5 | www.ceramics.org

properties that are just beginning to find applications in emerging and existing industries. This article presents promis-ing results of an active–passive approach to protecting low-alloy steels from corrosion using a nanocomposite coat-ing comprising exfoliated graphene or multiwalled carbon nanotubes dispersed within a polyetherimide matrix.

Keeping rust at bay The earliest reports of efforts to

prevent fouling of surfaces date back to 412 BC when explorers coated the wooden hulls of ships with tallow and pitch poisoned with arsenic and sulfur to keep barnacles at bay.

Today, zinc-based alloys are the “gold standard” sacrificial electroactive cor-rosion coatings for low-alloy steels. The extent of protection is proportional to the thickness of the coating, with inevi-table cost penalties for sensitive compo-nents requiring prolonged corrosion pro-tection.3 Zinc coatings are less ductile than the steel substrates they protect. Deformation of the steel can induce flaking or cracking of the galvanic coat-ing and compromise the coating’s corro-sion-resistance properties.4 Furthermore, zinc coatings are susceptible to fluctua-tions in precursor prices, an issue that has increased in importance in recent years. Zinc and tin prices spiked dramat-ically in 2005–2006, but have stabilized since the discovery of new mines and mitigation of supply chain restrictions. Nevertheless, many steel companies anticipate a severe shortage of zinc in 20 to 25 years resulting in substantial research efforts dedicated to mitigating reliance on this material.

Manufacturers used chromium and various chromate coatings to plate carbon steel, zinc, and aluminum substrates for most of the last century because of the ease of plating, excel-lent corrosion resistance, remarkable wear resistance, Vickers hardness values ranging up to 1000 kg/mm2, and lustrous surface finish.5 However, because of the potent carcinogenicity of hexavalent chromium and environ-mental concerns regarding disposal of electroplating dips, and the harmful effects of the mist created during the

plating process,6 the European Union’s stringent regulations— the Restriction of Hazardous Substances (RoHS) direc-tives—limit chromate use to 0.1 wt% in conversion coatings.7

The growth of chrome electroplating and metal-finishing shops paralleled the boom in the US steel industry between the late 19th century to the middle of the 20th century as railroads linked an integrated supply chain across the Great Lakes region that would become the bedrock of the manufacturing base. Historically, small- and medium-sized customized metal-finishing enterprises dominated this sector, and, not surpris-ingly, these businesses were buffeted by the upheavals in the steel industry starting from the 1970s.

Despite the nation’s increasing reli-ance on imported steel, metal-finishing shops continue to be important to the manufacturing economy in traditional steel towns across the “Rust Belt.” In the Buffalo–Niagara region that is home to the primary authors of this article, for example, the closing of the Bethlehem Steel plant in Lackawanna, N.Y., devastated the local economy. Even so, the Brookings Institute esti-mates the region provides more than 14,500 jobs directly related to metal finishing, fabrication, and tool manu-facturing and has enjoyed strong job growth during the last two years.

Beyond the economics of the steel industry, increasing alarm regarding the environmental impact of heavy met-als from the metal finishing industry is reframing the national conversation regarding the environmental conse-quences of a manufacturing economy. The Environmental Protection Agency (EPA), the Occupational Safety and Health Administration (OSHA), and the National Institute for Occupational Safety and Health (NIOSH) have issued successively more restrictive reg-ulations regarding disposal of chromi-um-based effluents. The Clean Air Act, the Clean Water Act, the Resources Conservation and Recovery Act (RCRA), and the Toxic Substances Control Act8 directly address chromium concentrations in air, water, and soil.

As the Buffalo–Niagara region, along

with other manufacturing towns, seeks to once again “seize the manufactur-ing moment,” there is opportunity for a renewed focus on sustainability and sustainable materials, process efficiency, and additive approaches to manufac-turing that could potentially bring innovation to metal-finishing, joining, and forming industries that will enable them to once again be important driv-ers of economic growth.

Hybrid nanocomposites: Putting graphene to work in coatings

The vast array of materials that have been tested as alternatives to zinc and chromate coatings includes engineered polymers, conductive poly-mers, polysiloxanes, metal oxides, ther-mally sprayed cermets, self-assembled monolayers, active corrosion inhibitor technologies, encapsulated monomers, and bioactive or biomimetic materi-als.5,9–11 Polymeric coatings have shown potential as corrosion inhibitors, but adhere poorly to metal substrates.12,13 Nanostructured coatings show promise, but suffer from inherent porosity, which creates channels for water and ions to permeate the coating and corrode the metal surface.14

There is growing interest in design-ing hybrid nanocomposites compris-ing multiple components, where the individual components act in concert to deliver corrosion resistance, form-ability, and adhesion to steel sub-strates.15,16 Herein, we present a hybrid nanocomposite coating system that combines the electroactivity of carbon nanomaterials, such as multiwall carbon nanotubes (MWCNT) and exfoliated graphene, with the water impermeabil-ity and excellent adhesion properties of a specialty polymer, polyetherimide (PEI). The nanocomposite protects low-alloy steel substrates through an “active–passive” approach, serving as a physical barrier to water permeation, preventing formation of ion channels at the metal surface, and passivating the metal/metal oxide surface through elec-tron depletion at the interface, likely through establishment of a Schottky barrier.3,9,17,18 Two coating systems were studied: a graphene/PEI composite with

www.ceramics.org | American Ceramic Society Bulletin, Vol. 92, No. 520

Graphene nanocomposite coatings for protecting low-alloy steels from corrosion

high loading of the nanomaterial filler; and a combined graphene/MWCNT/PEI system with a much lower loading of each filler to study synergistic effects between the two types of carbon nano-materials. (A MWCNT/PEI system also was tested, but it showed no enhanced corrosion-resistance properties.)

Graphene, a single-atom-thick layer of sp2-hybridized carbon atoms, has remarkable electronic, mechanical, and thermal properties. Since their discov-ery in 1991, carbon nanotubes have been researched extensively. However, their exceedingly high costs and environmental concerns have slowed large-scale commercial implementation. Many methods for producing graphene have been developed, but the facile non-oxidative solution-phase exfolia-tion of graphite is particularly interest-ing, because it is scalable and avoids the oxidative functionalization that tends to disrupt the π-conjugated structure (pristine aromatic ring system), which is critically important to many of gra-

phene’s remarkable proper-ties.19 We denote exfoli-ated graphene derived from ultrasonication of graphite in N-methylpyrrolidone (NMP) as unfunctionalized graphene (UFG).

Several approaches exist for dispersing graphene and MWCNTs in polymer matrices, although com-posites with PEI have not been reported to the best of our knowledge.20,21 PEI is an optimal candidate for the polymer host matrix because of its flexibility, high glass transition tem-perature (155°C), excel-lent thermal stability, and radiation resistance, while also serving as a perfect host for carbon nanofillers through π–π stacking.3,17,20,22,23 The lat-ter noncovalent stacking mode describes the attrac-tive interactions between aromatic ring systems derived primarily from the

alignment of positive and negative electrostatic potentials on adjacent aro-matic rings. Using in-situ polymeriza-tion, the carbon nanomaterials disperse in the PEI precursor (poly(amic acid), PAA) prior to polymerization, results in improved dispersion of the nano-structured carbon fillers in the eventual polymer matrix. The uniform disper-sion of nanomaterial in the matrix, along with the remarkable adhesion of the tailored PEI to the steel substrate, facilitates improved corrosion resistance under accelerated corrosion testing conditions (Figure 2).3,17

A manufacturing perspectiveApplying coatings in a continuous

process to low-alloy steel must be fully scalable, allow for high-throughput integration with rolling or casting pro-cesses, enable precise control of coating thickness, and not require expensive capital equipment. We have devel-oped coating formulations that can be applied through standard wire-bar and

spray-coating processes. The former translates readily to roller-coating (gra-vure, reverse roll, and knife-over-roll) methods, which tend to be preferred by many metal-finishing shops and steel mills, thereby requiring little retooling. In past work, we also demonstrated electroplating of graphene onto metal substrates from an aqueous solution using a process similar to chrome electroplating.24 Although the results reported here correspond to NMP dis-persions, research proceeds on aqueous analogs of these formulations.

Graphene is a potential sustainable replacement for metals, such as zinc and chromium, especially if graphite byproducts from the steel industry can be transformed to high-quality gra-phene. The cost of sustainable coatings can represent a major impediment to their widespread adoption. As with any new material and the absence of economies of scale, reliable financial projections are yet to be conclusively established for the graphene production. Nevertheless, some industry leaders sug-gest that a price goal of $20 per pound for graphene is attainable in the short term and that costs of production could soon be as low as $5 per pound. Given the low graphene loadings in our formu-lations and the high efficacy of much thinner coatings (an order of magnitude thinner than sacrificial metallic coat-ings), the price proposition of the mate-rials presented here is quite attractive.

Related to sustainable manufac-turing, previous work demonstrated the use of blast furnace gases to grow directly well-adhered layers of carbon nanotubes, multilayered graphene, and carbon nanofibers onto low-alloy steel substrates.25 After deposition of PEI, the carbon-nanomaterial/PEI composite coatings provide excellent corrosion resistance.17 This method represents an attractive route for designing a closed-loop process that reduces the carbon footprint of steel plants while adding value to steel substrates.

Corrosion rate drops two orders of magnitude

We synthesized UFG from natu-ral flake graphite through ultrasonic

Figure 2. Synthesis and coating of nanomaterial–PEI composite coatings. SEM image of graphene platelets, chemical structure of polyamic acid, photograph of the graphene/PAA dispersions, photographs of two coating methods (wire-bar coating and spray coating) and an oven used for curing, and, lastly, photographs of the coatings on steel.

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exfoliation of graphite powder in NMP. The MWCNTs used in this study are more than 99 percent pure by weight and have outer diameters 13–18 nm with lengths 3–30 µm.

Figure 3 depicts the overall process for depos-iting of PEI nanocom-posite coatings. Briefly, PAA is synthesized by copolymerization of an anhydride and diamines in the pres-ence of UFG and UFG/MWCNTs. The desired concentration of UFG or MWCNTs is added to the NMP and ultrasoni-cated to create a visually nonscattering solution prior to polymerization. The nanomaterial filler disperses well in the viscous UFG/PAA (or UFG/MWCNT/PAA) (Figure 2) allowing it to be roller coated onto freshly cleaned and degreased low-alloy steel substrates (Figure 3). PEI is synthesized in-situ on the steel surface through an imidization reaction. Although the mecha-nism details have not yet been fully investigated, results show that the in-situ imidization proto-col yields coatings with substantially improved adhesion of the polymer to steel, fashioning a robust composite with a dry coating thickness of 15–20 µm.3,17,26 The m-phenylendiamine component prevents crystallization of the polymer and improves flexibility and formabil-ity as the coating adopts the contours of the low-alloy steel surface.3

The nanocomposite coatings were deposited by wire-bar coating (chemical coating) onto a clean cold-rolled steel surface using either an automatic film applicator or a spray coating method (Figure 2). The PAA was cured at 150°C for 5 min, followed by a 250°C curing step for 5 min to complete the imidization of the PEI (Figure 3) and to remove residual NMP.

We characterized the UFG synthe-sized for use in the PEI nanocompos-ites by scanning electron microscopy and transmission electron microscopy as shown in Figure 4. UFG tends to agglomerate into large fragments on dry-ing as shown in Figures 4(a) and 4(b). However, Figures 4(c) and 4(d) show that the UFG morphology is sheet like, adding to the flexibility of the coating and the formability of coated pieces.

Notably, the agglomeration and phase segregation of UFG in nano-composites is substantially mitigated by the in-situ polymerization approach. MWCNTs and graphene interact strongly with polyimides via strong π–π stacking interactions. Because of the structural similarity of these materials, good wettability and chemical compat-ibility between the matrix and the filler are expected.20,27 The PAA envelopes the UFG platelets, and PAA chains interacting with UFG likely impart steric stabilization to the UFG colloids in NMP. Figure 2 shows the highly concentrated, stable UFG/PAA disper-sions without phase segregation or floc-culation of the UFG filler after several months. Figures 4(e) and 4(f) show high purity of the MWCNTs with outer diameters of 13–18 nm and lengths of 3–30 µm. Analogous to UFG, bundling of MWCNTs is mitigated by ultrasonic treatment in NMP.

Photographs of the coatings are depicted in Figure 2. A top-view inspection of coatings in the SEM reveals a fairly smooth surface finish with no cracks or visible pinholes. Furthermore, we observed no phase seg-regation of UFG or MWCNT fillers at the surface.

MWCNT and UFG sheets are dispersed in the PEI matrix, as the SEM images of cross-sections of cryo-

Figure 3. Schematic depictions of (a) UFG/PEI and (b) UFG/MWCNT/PEI nanocomposite coatings on steel. The wavy lines represent PEI polymer, the web-like sheets represent graphene, and the tubes are MWCNTs.

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Figure 4. (a) and (b) SEM images of UFG, (c) and (d) TEM images of UFG, (e) SEM image of MWCNTs, and (f) TEM image of MWCNTs.

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Graphene nanocomposite coatings for protecting low-alloy steels from corrosion

fractured surfaces of the free-standing composite samples show (Figure 5). Figures 5(a) and 5(b) show the PEI is relatively featureless. In contrast, clear-ly visible UFG and MWCNTs protru-sions appear in the fractured composite surfaces (Figures 5(c)–5(f)). Figures 5(c) and 5(e) show that the MWCNTs and UFG sheets are well dispersed, and, again, there is no visible phase segregation of the fillers from the PEI

matrix. The images further suggest the presence of an amorphous polymer coat-ing around the UFG sheets and individual MWCNTs. The excellent dispersion of the carbon nanomateri-als in the PEI matrix is likely a result of the π–π interactions between the π-conjugated graphene basal planes and the aro-matic moieties on the polymer backbone.17,20,23,27,28 Such excellent dispersion of the conductive fillers helps prevent delamination of the composite coating from the metal and appears to aid formation of a pas-sivation layer at the metal surface.

Potentiodynamic electrochemi-cal tests (following the ASTM-G59 standard) measured corrosion behavior of coated samples, bare steel, and gal-vanized steel in saline environments. Figure 6 plots current density versus potential for samples tested in 3.5% NaCl solution. The current density for nanocomposite-coated samples was sev-eral orders of magnitude less (down to about 10–9 A/cm2) than bare low-alloy

steel and galvanized steel (which have current densities on the order of about 10–5 A/cm2). This correlates directly to diminished corrosion of the steel surface and demonstrates the efficacy of the coatings as barrier materials. The poten-tiodynamic measurements provide fur-ther evidence of the formation of a pas-sivation band from –0.243 V to 0.576 V for the 20 wt% UFG/PEI nanocomposite coating and from 0.010 V to 0.576 V for the 2 wt% UFG/MWCNT/PEI coating. The formation of a passivation band for the nanocomposite coatings—but not for PEI alone—suggests that the conduc-tive carbon nanomaterials are important in forming the passivation layer at the metal surface.9,17,26

Furthermore, incorporating UFG and MWCNTs in the coatings shifts the potentiodynamic plots to more posi-tive potentials, suggesting more “noble” behavior for these systems. Although the precise nature of the passivation layer remains unclear, a Schottky bar-rier often is seen at metal/nanotube and metal/graphene junctions and requires more bias to facilitate electron transfer.29,30 This type of potential bar-rier at the interface likely impedes the corrosion reaction by restricting the flow of electrons to the steel surface, which is required for oxidation. Also,

By Joshua Caris

MesoCoat Inc. (Euclid, Ohio) has developed a high-density infrared (HDIR) process for applying a uniform, metallurgically bonded metal layer—or clad—to carbon-steel surfaces for corrosion- and wear-resistance applications. Clad materials include the nickel-based superalloy, Alloy 625, and stainless steels as well as composites containing tungsten and chrome carbides. This new technology has the potential to be a “game changer,” especially in the emerging oil sands and shale gas industries.

The advantages of this technology are

• Fast application rate (coverage of 75–280 ft2/h with a single system);

• Low potential heat input to the substrate (small heat-affected zone);

• True metallurgical bond (bond strength greater than 75,000 psi);

• Lower initial cost, lowest life cycle cost (50 percent reduction); and

• Better cladding (smooth, pinhole free, low dilu-tion, and no decarburization).

HDIR processing is a heating and coating appli-cation technology that developed concurrently with lamp design improvements using broad frequency thermal emitters, such as plasma arc lamps and tungsten filament bulbs. Coupling these irradiation sources with reflectors of vari-ous geometries achieves the required irradiance (W/cm2) for surface processing.

Tungsten filament lamps typically operate at temperatures between 2000 K and 4000 K. The Planck blackbody distribution peaks in the IR range. However, there is a broad distribution through the visible range, and the light appears white.

Plasma arc lamps electrically induce a noble gas plasma within a water-cooled, fused quartz tube. These ceramic components are critical, because they are transparent within the IR, permitting containment of the plasma and transmission of the light required to melt and fuse the cladding.

(A slurry loaded with cladding powders is depos-ited on the surface to be clad.)

Oak Ridge National Laboratory developed the plasma arc lamp technology for cladding sur-faces in the early 2000s. Recently, MesoCoat purchased exclusive rights to the technology and has since commercialized it.

These lamps operate at a much higher tem-perature, approximately 10,000 K. At this temperature, the constrained plasma acts as a blackbody emitter with a peak primarily in the ultraviolet range. However, there are distinct IR peaks characteristic of the noble gas, argon in this case, superimposed on the blackbody back-ground radiation. This high-intensity spectrum is collected and carefully reflected and directed to melt the slurry of corrosion- or wear-resistant alloy or composite to the surface of a component in what MesoCoat calls the CermaClad process.

The focused plasma arc lamp emission has measured heat irradiances of 500–2000 W/cm2, which encompass the irradiance regime

New uses for carbon steel pipe thanks to corrosion- and wear-resistant claddings

Figure 5. Cryo-fractured SEM images of (a) and (b) PEI (without filler), (c) and (d) 2 wt% UFG/MWCNT/PEI, and (e) and (f) 20 wt% UFG/PEI.

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the hybridization of graphene with metal surfaces can open a bandgap in the semimetallic graphene, resulting in semiconducting behavior for the metal/UFG interfaces.31,32 Charge depletion from the passivating semiconducting layer also could suppress corrosion.

The photographs in Figure 7 provide a qualitative measure of the relative corrosion rates of the various test sub-strates of samples immersed in 3.5% NaCl solution for various durations: 0 h; 234.5 h; 1,752 h; and 3,144 h (the end of the immersion test). After 234.5 h exposure, extensive red rust formed on the low-alloy steel surface. Similarly, white powdery deposits on the galvanized sample suggest sacrificial corrosion of the zinc layer. The nano-composite coatings and the filler-free PEI coating show no visible signs of corrosion. After 1,752 h of exposure to 3.5% NaCl solution, red rust formation on the galvanized steel sample indicates complete oxidation of the galvanic coating. The coating of the PEI-coated steel has partially delaminated, allow-ing for corrosion to begin. In contrast, the UFG/PEI and UFG/MWCNT/PEI nanocomposite systems appear to have avoided such a fate. Finally, after com-pletion of this test at 3,144 h, extensive corrosion across the test substrates is

apparent for all samples, except for the two coated with 20 wt% UFG/PEI and 2 wt% UFG/MWCNT/PEI. Some specks of corrosion are apparent for the latter two samples, especially under microscopic exam-ination, but they are clearly superior to PEI alone or galvanized steel for protecting the low-alloy steel substrates from corrosion. (Despite the differences in appearance in the photographs, the two samples corroded approximately the same amount.)

Weight-loss measurements pro-vide a more quantitative perspective of the inhibitory properties of the nanocomposite coatings. The weight-loss measurements of the samples shown in Figure 7 were conducted per ASTM-G1. According to this protocol, the corrosion rate (CR) in millimeters per year is

CR = 87.6(W/DAt) (1),

where 87.6 is a constant, W the weight loss in milligrams, D the density of the metal in g/cm3, A the surface area exposed to the NaCl solution in cm2, and t the duration of exposure to the NaCl solution in hours. The calculated CR values for the samples are listed in Table 1. The 20 wt% UFG/PEI nanocomposite coating corrodes almost three orders of magnitude slower than

of continuous-wave lasers, but with several unique differences. Laser-processing light has a relatively small beam diameter from a mono-chromatic light source. HDIR processing takes advantage of a broad spectrum of irradiation with a focus area that corresponds to the diam-eter and length of the quartz tube containing the plasma. Because the irradiances are similar, a qualitative comparison is that laser processing is like a brush used to paint a portrait, while HDIR focused plasma processing is like a roller for painting a wall.

Figure 1(a) shows the interior pipe surface arc lamp just after ignition. To clad the pipe interior, the 10-inch-diameter pipe translates over a lance onto which the lamp is mounted. Once the pipe is extended fully over the lance, the lamp is brought to operating power, and the rotating pipe translates over the lamp (Figure 1(b)).

Figure 2(a) shows a wear-resistant cermet clad-ding on a white-cast-iron substrate (20 mm × 35 mm × 150 mm). The cladding is composed of angular tungsten carbide particles in a

Ni-Cr-B-Si alloy matrix and was applied in two stages with an overlap region (designated by the yellow box in Figure 2(a)). Optical micrographs reveal uniform distribution of WC particles at the surface (Figure 2(a)) and at the interface (Figure 2(b)). Figure 2(b) also shows an absence of microcracking in the white cast iron despite multiple thermal cycles. Current plans for wear-resistant claddings such as these are to combine

a flat-plate cladding technology with the pro-cessing understanding of interior pipe clad with Alloy 625 and apply wear-resistant claddings on large-area pipe interior surfaces for use in oil sand fields in Alberta, Canada.

Joshua Caris is a metallurgist at MesoCoat Inc. Contact: Joshua Caris at jcaris@mesocoat.com. n

Figure 1. Plasma arc lamp during (a) ignition sequence and (b) processing of a 10-inch-diameter carbon steel pipe.

Figure 2. A white-cast-iron sample (a) clad with WC composite and microstruc-tures of the (b) surface and (c) interface between cladding and substrate.

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Figure 6. Potentiodynamic plots showing the relatively enhanced corrosion resistance provided by the composite coatings as compared with the behavior of the PEI coating (without fillers), uncoated steel, and galvanized steel. A scan rate of 1.67 mV/s was used with a platinum strip and standard calomel electrode as the counter and reference electrodes, respectively.

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Graphene nanocomposite coatings for protecting low-alloy steels from corrosion

bare low-alloy steel. The inclusion of UFG or MWCNTs also reduces corro-sion by an order of magnitude over the pure polymeric coating.

ConclusionsIn summary, tests show that two novel

nonmetallic nanocomposite systems protect low alloy steels from corrosion. The in-situ copolymerization of an anhydride and a diamine is used to prepare PAA in the pres-ence of UFG and MWCNTs. PAA disperses and stabilizes the carbon nanomaterials in NMP through π–π interactions. Roller coat-ing and subsequent imidization of the nano-composite blends yields well-adhered UFG/

PEI and UFG/MWCNT/PEI coat-ings on steel. The nanocomposite coatings combine the water imper-meability and excellent formability of the polymer with the electroac-tivity of the carbon nanomaterial fillers. Potentiodynamic testing and saltwater immersion tests indicate more than three orders of enhance-ment in efficacy of corrosion pro-tection as compared with bare steel. The developed nanocomposites represent a scalable solution for replacement of hexavalent chro-mium in anticorrosive coatings.

AcknowledgmentsThis work was supported by

Tata Steel and the New York State Pollution Prevention Institute.

About the authorsRobert V. Dennis is a gradu-

ate student and Lasantha T. Viyannalage is a postdocotal researcher at the University at Buffalo, The State University of New York, Buffalo, N.Y. Sarbajit Banerjee is an associate professor in the Department of Chemistry, also at University at Buffalo. Anil V. Gaikwad and Tapan K. Rout are research associates with the Research & Development Department, Tata Steel Ltd., Jamshedpur, India. Contact:

Sarbajit Banerjee at sb244@buffalo.edu.

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Table 1. Corrosion rate of samples

Sample Corrosion rate (mm/year) Galvanized steel 3.87 × 10–2

Uncoated low-alloy steel 1.22 × 10–1

PEI coating 9.24 × 10–3

2 wt% UFG/MWCNT/PEI coating 5.52 × 10–4

20 wt% UFG/PEI coating 8.46 × 10–4

Figure 7. Saltwater (3.5% NaCl) immersion mea-surements on (a) galvanized steel, (b) uncoated low-alloy steel, (c) low-alloy steel with PEI coating, (d) low-alloy steel with 2 wt% UFG/MWCNT/PEI coating, and (e) low-alloy steel with 20 wt% UFG/PEI coating. Sample exposure diameter 3.5 cm.

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