Defects Mediated Corrosion in Graphene Coating Layer

Self-healing and corrosion-sensing multifunctional coatings containing pH-sensitive TiO2-based composites

Polyelectrolyte-encapsulated nanocontainers can effectively respond to changes of pH and thus control the on-demand release of corrosion inhibitors. A pH-responsive release system (Phen-Tpp@MTNs-PDDA) was developed based on the cationic polyelectrolyte poly dimethyl diallyl ammonium chloride (PDDA) encapsulated mesoporous TiO2 nanocontainers (MTNs) loaded with 1,10-phenanthroline (Phen) and tripolyphosphate ions (Tpp) corrosion inhibitors. The epoxy coating (EP) embedded with Phen-Tpp@MTNs-PDDA (Phen-Tpp@MTNs-PDDA/EP) demonstrates superior self-healing properties and confers long-term protection on the metal substrate through the cooperative effect of Phen and Tpp. Simultaneously, this hybrid coating is endowed with corrosion sensing capability based on the color development originating from the interaction of Phen and carbon steel. This self-healing and corrosion-sensing multifunctional coating provides an effective strategy for the corrosion protection of metals.

SEM Electron-Beam-Induced Ultrathin Carbon Deposition Layer on Cu Substrate: Improved Dry Oxidation Protection Performance than CVD Single Layer Graphene

An amorphous carbon deposition layer (CDL) with nanoscale thickness induced by scanning electron microscope (SEM) electron beam is studied as a carbon-based protective layer on copper (Cu). CDL is prepared by inducing the deposition of pollutants or hydrocarbons in the cavity of SEM through electron beam irradiation (EBI). Wrinkles and cracks will not form and the interfacial spacing of CDL/Cu is smaller than Graphene/Cu (Gr/Cu). The thickness and coverage of the interfacial oxide layer of CDL/Cu are all smaller than that of the Gr/Cu after the same oxidation conditions. Characterization of Raman mapping also demonstrates that CDL shows better oxidation inhibition effects than graphene. The structure of CDL is determined to be C = C and C = O, CH3- and C-O can be loaded vertically on CDL. Density functional theory (DFT) is employed for demonstrating the smaller interfacial gap of CDL/Cu, less wrinkles and cracks and larger adsorbing energy of water/oxygen compared with Gr/Cu. Molecular dynamic (MD) simulation also indicates that the diffusion of water or oxygen into CDL/Cu is more difficult and the oxidation of Cu covered by CDL is well suppressed. This work provides a new approach for the study of carbon-based antioxidant materials on Cu.

An overview of contemporary developments and the application of graphene-based materials in anticorrosive coatings

Although graphene and graphene-based materials (GBMs) offer a wide range of possible applications, interest in their use as barrier layers or as reinforcements in coatings for the mitigation of corrosion has grown during the past decade. Because of its unique two-dimensional nanostructure and exceptional physicochemical characteristics, graphene has gotten a lot of attention as an anti-corrosion material. This enthusiasm is largely driven by the requirement to integrate more features, improve anti-corrosion effectiveness, and eventually prolong the service duration of metallic components. As barriers against metal corrosion, graphene nanosheets can be applied singly or in combination to create thin films, layered frameworks, or composites. Concurrently, over the past few years, significant advancements have been made in the establishment of scalable production methods for graphene and materials based on graphene. Since there is currently a wide variety of graphene material with various morphologies and characteristics, it is even more important that the production approach and the intended application be properly matched. This review gathers the most recent data and aims to give the reader a comprehensive overview of the most recent developments in the use of graphene and GBMs in various anti-corrosion strategies. The structure-property correlation and anticorrosion techniques in these systems are given special consideration. The current article offers a critical examination of this topic as well, stressing the areas that require more research.

The Wet-Oxidation of a Cu(111) Foil Coated by Single Crystal Graphene

The wet-oxidation of a single crystal Cu(111) foil is studied by growing single crystal graphene islands on it followed by soaking it in water. ¹⁸ O-labeled water is also used; the oxygen atoms in the formed copper oxides in both the bare and graphene-coated Cu regions come from water. The oxidation of the graphene-coated Cu regions is enabled by water diffusing from the edges of graphene along the bunched Cu steps, and along some graphene ripples where such are present. This interfacial diffusion of water can occur because of the separation between the graphene and the "step corner" of bunched Cu steps. Density functional theory simulations suggest that adsorption of water in this gap is thermodynamically stable; the "step-induced-diffusion model" also applies to graphene-coated Cu surfaces of various other crystal orientations. Since bunched Cu steps and graphene ripples are diffusion pathways for water, ripple-free graphene is prepared on ultrasmooth Cu(111) surfaces and it is found that the graphene completely shields the underlying Cu from wet-oxidation. This study greatly deepens the understanding of how a graphene-coated copper surface is oxidized, and shows that graphene completely prevents the oxidation when that surface is ultrasmooth and when the graphene has no ripples or wrinkles.

Polymer Nanocomposite-based Coatings for Corrosion Protection

Corrosion of metals induces enormous loss of material performance and increase of cost, which has been a common and intractable issue that needs to be addressed urgently. Coating technology has been acknowledged to be the most economic and efficient approach to retard the metal corrosion. For several decades, polymers have been recognized as an effective anticorrosion coating material in both industries and scientific communities, as they demonstrate good barrier properties, ease of altering properties and massive production. Nanomaterials show distinctively different physical and chemical properties compared with their bulk counterparts, which have been considered as highly promising functional materials in various applications, impacting virtually all the fields of science and technologies. Recently, the introduction of nanomaterials with various properties into polymer matrix to form a polymer nanocomposite has been devoted to improve anticorrosive ability of polymer coatings. In this review article, we highlight the recent advances and synopsis of these high-performance polymer nanocomposites as anticorrosive coating materials. We expect that this work could be helpful for the researchers who are interested in the development of functional nanomaterials and advanced corrosion protection technology.

Investigation of the Oxidation Behavior of Graphene/Ge(001) Versus Graphene/Ge(110) Systems

The oxidation behavior of Ge(001) and Ge(110) surfaces underneath the chemical vapor deposition (CVD)-grown graphene films has been investigated experimentally and interpreted on the basis of ab initio calculations. Freshly grown samples were exposed to air for more than 7 months and periodically monitored by X-ray photoelectron spectroscopy, scanning electron microscopy, and Raman spectroscopy. The oxidation of Ge(110) started with incubation time of several days, during which the oxidation rate was supposedly exponential. After an ultrathin oxide grew, the oxidation continued with a slow but constant rate. No incubation was detected for Ge(001). The oxide thickness was initially proportional to the square root of time. After 2 weeks, the rate saturated at a value fivefold higher than that for Ge(110). We argue that after the initial phase, the oxidation is limited by the diffusion of oxidizing species through atomic-size openings at graphene domain boundaries and is influenced by the areal density and by the structural quality of the boundaries, whereby the latter determines the initial behavior. Prolonged exposure affected the surface topography and reduced the strain in graphene. In the last step, both the air-exposed samples were annealed in vacuum at 850 °C. This removed oxygen from the substrate and restored the samples to their initial state. These findings might constitute an important step toward further optimization of graphene grown on Ge.

Corrosion Protection of Monel Alloy Coated with Graphene Quantum Dots Starts with a Surge

There has been an active interest in protecting metals and alloys using graphene coating. The mechanism by which corrosion protection occurs has not been well understood as the couple involved are both good electron conductors. In this work, we demonstrate that Monel alloy coated with graphene quantum dots (GQD) changes the corrosion rate with a surge (increase) caused by the galvanic coupling of the two materials. This surge results in the protective layer formation on Monel to inhibit the corrosion. X-ray fluorescence spectrum of Monel (400) alloy showed the composition of it as Ni (67.05%) and Cu (29.42%). The Tafel experiments carried out in NaCl and Na2SO4 electrolytes showed an initial enhancement of the corrosion rate followed by a decrease upon successive polarizations. Monel coated with graphene oxide (an insulator) shows no initial enhancement of corrosion rate; the coated samples showed a lower corrosion rate in comparison to the uncoated samples. X-ray fluorescence, Fourier Transform spectroscopy (FTIR) and Raman imaging studies have been carried out for understanding this transformation. Distinct peaks due to Ni-O stretching and Ni-O-H bending vibration were observed in the FTIR spectrum.

Avoiding oxidation with coating: graphene protected magnesium surfaces

Magnesium is a promising material for automotive technology. Avoiding its spontaneous oxidation is, however, mandatory for a feasible industrial application of this metal. We perform computer simulations to demonstrate that a protective graphene layer can successfully avoid the oxidation of a magnesium material. This feature remains true even when the graphene layer has several simple defects, such as vacancies and Stone-Wales transformations. In fact, the defects actually increase the strength of the graphene/metal interaction, further enhancing the protective properties. These results are rationalized in terms of the low Mg cohesive energy, which allows the system to quickly reconstruct and adapt.

Waterborne reduced graphene oxide dispersed bio-polyesteramide nanocomposites: an approach towards eco-friendly anticorrosive coatings

RGO dispersed waterborne soy polyester amide nanocomposites were formulated utilizing a solventless VOC free green approach for use as low cost anticorrosive coatings.

Revisiting graphene-polymer nanocomposite for enhancing anticorrosion performance: a new insight into interface chemistry and diffusion model

Graphene is impermeable to all molecules and has high chemical stability, which makes it an excellent anticorrosion coating for metals. However, current studies have indicated that galvanic coupling between graphene and a metal actually accelerates corrosion at the interface. Due to the insulating nature of polymers, graphene-polymer composite coatings with a strong interaction between the filler and the polymer matrix are an alternative means of addressing this issue. Nevertheless, such coatings require well-dispersed graphene flakes to lengthen the diffusion paths of gases or liquids, while preventing the formation of a conducting network from graphene to the metal. The difficulty in preparing such coatings was mainly due to problems with the control of the assembled phase during interfacial reactions. Herein, the interactions between the filler and the polymer were found to be a key factor governing anticorrosion performance, which has scarcely been previously reported. The advantage of graphene as a filler in anticorrosion coatings lies in its dispersibility and miscibility with both the casting solvent and the polymer. Electrochemically exfoliated graphene (EC-graphene) with appropriate surface functionalities that allow high miscibility with waterborne polyurethane (PU) and hydrophobic epoxy has been found to be an ideal filler that outperforms other graphene materials such as graphene oxide (GO) and reduced graphene oxide (rGO). Furthermore, a bilayer coating with EC-graphene additives for PU over epoxy has been found to reduce the corrosion rate (CR) to 1.81 × 10-5 mm per year. With a graphene loading of less than 1%, this represents the lowest CR ever achieved for copper and steel substrates and a diffusion coefficient that is lower by a factor of nearly 2.2 than that of the pristine polymer. Furthermore, we have shown that by controlling the amount of graphene loaded in the polymer galvanic corrosion favored by the formation of an interconnected graphene percolation network can successfully be limited. The present study, together with a facile and eco-friendly method of nanocomposite synthesis, may pave the way toward practical applications in the development of graphene-based anticorrosion coatings.

Extraordinary Corrosion Protection from Polymer-Clay Nanobrick Wall Thin Films

Metals across all industries demand anticorrosion surface treatments and drive a continual need for high-performing and low-cost coatings. Here we demonstrate polymer-clay nanocomposite thin films as a new class of transparent conformal barrier coatings for protection in corrosive atmospheres. Films assembled via layer-by-layer deposition, as thin as 90 nm, are shown to reduce copper corrosion rates by >1000× in an aggressive H₂S atmosphere. These multilayer nanobrick wall coatings hold promise as high-performing anticorrosion treatment alternatives to costlier, more toxic, and less scalable thin films, such as graphene, hexavalent chromium, or atomic-layer-deposited metal oxides.

Different graphene layers to enhance or prevent corrosion of polycrystalline copper

Graphene was used as an anticorrosive coating for metals as it can effectively isolate the corrosion factors such as oxygen. However, we found that the anticorrosive and corrosive effects on metal surface were related to graphene layers and metal crystal faces. In this paper, we found that different layers of graphene had significantly different effects on the corrosion of polycrystalline copper during long-term storage under atmospheric conditions. Optical images and Raman spectra showed that single layer graphene (SLG)-coated copper had a higher degree of corrosion than bare copper. However, when covered with CVD in situ-grown bilayer graphene (BLG), the copper foil was effectively prevented from being etched as it exhibited a bright yellow color despite the differences in crystal faces. The surface potential differences measured by an electric force microscope (EFM) showed that a contact potential difference (V_CPD) between 30 and 40 mV existed between Cu/SLG and bare copper. The SLG-coated areas had a higher surface potential (SP), which meant that the (SLG)-coated copper was more prone to lose electrons to exhibit galvanic corrosion. The BLG coating made SP of underlying copper lower making it harder to lose electrons; thus, BLG successfully protected the copper from being corroded. These findings have a foreseeable significance for graphene as a metal anti-corrosion coating.

The degree of corrosion depends on the crystal faces and number of graphene layers, whereas BLG can be used as an anticorrosion coating.

Bio-inspired electrochemical corrosion coatings derived from graphene/natural lacquer composites

To develop green efficient anti-corrosion coatings, graphene/lacquer composite coatings were demonstrated.