Polyurethane Topcoat Research Articles

Low-frequency EIS interpretation with the potential to predict the durability of protective coatings

Obtaining impedance response with predictive value for coating durability is central to meeting today's protective coatings end-user requirements. Here we present a novel approach to interpreting the low-frequency impedance of industrial coatings that takes into account the relevance of the coating properties that determine their barrier and adhesion durability. Modern, high adhesion, low VOC polymer coatings utilize cross-linking chemistry with polar or hydrogen bonding materials, leading to the apparent paradox that coatings exhibit corrosion creep values that are very low and inversely related to the barrier effect derived from the EIS response. In practice, once the corrosion creep rate is negligible, the ability of a coating to act as a long-term effective barrier, especially at edges and welds, becomes a major concern, and the improvement in durability relies on the improvement of the barrier. In the present study, we investigated the barrier effect of conventional partial and full offshore coating systems with epoxy and epoxy mastic layers applied without and with zinc-rich or zinc phosphate primers and polyurethane topcoats. The panels were aged for two years in an atmospheric offshore-like conditions and subsequently exhibited defects due to inadequate coating thickness, number of layers, surface preparation and inadequate application practice. EIS measurements were performed on the panels in the laboratory in dry and wet state. EIS provided a quantitative rating of the barrier effect that can serve as a basis for informed upgrading of coating solutions, application practices or workmanship quality, particularly in structures with limited access where high durability is an imperative.

Fabrication of superhydrophobic surface by spraying hydrophobically modified silica nanoparticles on partially cured polyurethane paint

ABSTRACT There is an increasing demand for superhydrophobic surfaces due to their unique properties like self-cleaning, anti-icing, corrosion resistance, etc. The development of polyurethane (PU)-based superhydrophobic coating has garnered significant attention for aircraft applications. Polyurethane (PU) topcoat is widely used in aircraft and is hydrophilic in nature with a water contact angle (WCA) of 75 ± 3°. In the present work, a hydrophilic PU clear coat on aircraft-grade aluminum substrate is transformed to a superhydrophobic (SHP) surface by spraying environmentally friendly hydrophobically modified silica nanoparticles (HSiNps) oonto a PU layer that was partially cured in a hot air oven at 60°C for 1.5 h. The SHP surface exhibited a WCA of 162 ± 3° and a sliding angle (SA) of 8 ± 3°. With the incorporation of HSiNps, micro – nano dual-scale surface roughness is created and the surface roughness of the PU coating is increased from 0.35 to 2.42 µm. The coating exhibits good adhesion (5B) with excellent water repelling property and remains thermally stable and superhydrophobic even after subjecting it to 100°C for one week. Durability of the coatings is studied by immersing the coatings in various liquids. The retention of superhydrophobic property after anti-fogging, water sprinkler, and sand paper abrasion tests further demonstrate the robustness of the coating.

Impact of polymer structure in polyurethane topcoats on anti-icing properties

Icing on the topcoat layer of structures or mobility systems can be a factor leading to functional failures or accidents. Material engineering approach to prevent icing involves creating hydrophobic surfaces. In this study, it was confirmed that the method of controlling the structure of polymers using solvents to adjust surface hydrophobicity and ice prevention effects is effective. Polyurethane (PU) topcoats are primarily used on the exterior of mobility devices; therefore, structure of PU was manipulated using xylene. Through the adjustment of the ratio between PU and xylene, changes in the curing enthalpy and crystal structure were observed, which led to alterations in tensile strength. Additionally, changes in surface energy and contact angle occurred depends on xylene content, and de-icing property of PU topcoat was enhanced by 66 % on the surface of the 20 vol% xylene PU topcoat, compared to the pure PU topcoat. It was confirmed that the basic method of manipulating the polymer structure through solvent amount in topcoats could be utilized as a technique in hydrophobic surface research, such as ice prevention.

Tensile Properties of Aircraft Coating Systems and Applied Strain Modeling

In this work, we develop a structural model for the fracturing of an aircraft coating system applied to a complex airframe structure that includes aluminum panels and stainless-steel fasteners. The mechanical properties of the coating system, which consisted of an MIL-PRF-85582E, Type II, Class C1, two-part epoxy primer and an MIL-PRF-85285 Rev E, Type IV, Class H, two-part polyurethane topcoat, were measured before and after 8 months of atmospheric exposure. The loads applied to the coating occurred from local deformations of the fastener-panel system in response to flight stresses. Two types of flight stresses, compression dominated and tension dominated, were modeled. The degradation of the mechanical properties of the coating after atmospheric exposure increases the severity of cracking of the coating at a critical fastener–skin interface.

Processing of kaolin micro-composite functional fillers for enhancing the near-IR reflective performance of polyurethane resin coatings

Polyurethane (PU) resin products meant for protective coatings are chemically composed of two-phase microstructures; soft ‘polyols’ and hard ‘diisocyanates and chain extenders’. For durable high-performance specialty PU coatings, their surface heat reflectance property is to be enhanced; otherwise, the absorption of solar heat energy eventually generates heat build-up that finally induces microstructural changes and chemical degradation. Hence, in this work, an attempt is made to improve the poor IR reflectance property of PU resin by incorporating kaolin micro-composite functional fillers. In this study, kaolin delamination was first carried out using alumina and zirconia milling media. Delaminated kaolin was treated with colloidal oxides, SiO2, Al2O3, and TiO2, to produce kaolin micro-composite fillers. The filler effect, chemical interaction, heat build-up, scratch resistance, and hydrophobic properties were examined, and results were presented. The study confirmed that when Al2O3-modified kaolin micro-composites improved the scratch resistance, the incorporation of 10 mass% mixed oxide kaolin micro-composite fillers enhanced the NIR reflecting property of PU coats from 4% to 53%. A facile strategy to enhance the solar heat shielding property of PU top coats for obtaining long-life durable protective coatings is presented in this work.

Acid resistance and failure mechanism of zinc-rich primer/micaceous iron oxide/polyurethane composite coating immersed in 5 wt% sulfuric acid

In order to study the reliable resistance to sulfuric acid corrosion of epoxy zinc rich primer/micairon oxide intermediate paint/acrylic polyurethane topcoat composite coatings for power transmission and transformation equipment. In this paper, under the condition of immersion in 5 wt% sulfuric acid, the sulfuric acid resistance behaviour of zinc-rich epoxy/micaceous iron oxide/polyurethane composite coating was evaluated by performing soaking tests for 50 h, 100 h and 150 h, and the failure mechanism of the film was studied. The changes in the surface properties of the coating during sulfuric acid soaking were evaluated by testing the hardness, glossiness and adhesion, and the changes in the capacitance and resistance characteristics of the coating during acid soaking were studied by Electrochemical Impedance Spectroscopy (EIS). The micromorphology and chemical element distribution of the cross-section of the composite coatings were studied by Scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDS). The functional group changes were studied by Fourier transform infrared spectroscopy (FT-IR). The results show that the corrosive effect of sulfuric acid solution immersion on acrylic polyurethane is weak, while the hydrolysis of water molecules will lead to aging and failure of acrylic polyurethane. Sulfuric acid leads to the formation of zinc deficient areas in zinc-rich primers, which reduces the cathodic protection effect of zinc-rich primers. The service life of the zinc-rich primer/ Micaceous Iron Oxide/acrylic polyurethane composite coating is less than 150 h.

Experimental and Numerical Investigation into the Effect of Water Uptake on the Capacitance of an Organic Coating.

Water uptake by organic coating systems used for corrosion prevention on airframes is one of the principal contributors to the loss of barrier properties of the coating. We used equivalent circuit analyses of electrochemical impedance spectroscopy (EIS) data to track changes in coating layer capacitance for a two-layer coating system consisting of an epoxy primer and polyurethane topcoat immersed in NaCl solutions with different concentrations and temperatures. The capacitance curve exhibited two different response regions, consistent with the "two-stage kinetics" mechanisms for water uptake by the polymers. We tested several numerical diffusion models of water sorption and found the most successful to be one that varied the diffusion coefficient as a function of polymer type and immersion time and accounted for physical aging processes in the polymer. We employed the Brasher mixing law along with the water sorption model to estimate the coating capacitance as a function of water uptake. The predicted capacitance of the coating was found to be consistent with the capacitance obtained from the EIS data, which is consistent with theories that water uptake occurs via initial rapid transport followed by a much slower aging process. Thus, both these water uptake processes need to be considered when making EIS measurements to assess the state of a coating system.

Effect of Coating Process on Properties of Two-Component Waterborne Polyurethane Coatings for Wood

Acrylic acid has good environmental weather resistance, water resistance, alcohol resistance, dirt resistance, and other properties. An acrylic acid dispersion with a core–shell structure was prepared and reacted with a polyisocyanate-type curing agent to prepare a waterborne polyurethane topcoat suitable for wood. The prepared two-component polyurethane topcoat was used in combination with a waterborne primer and a waterborne sealing primer and applied to Pine (Pinus strobus) boards to carry out gloss, wear resistance, and adhesion experiments. The effects of different coating amounts and spraying times on the comprehensive properties of the wood coatings were studied. The experimental results showed that when the self-made two-component polyurethane topcoat for wood was matched with the primer and the sealing primer, the coating amount of the sealing primer had little effect on improving the adhesion and wear resistance but had a significant effect on the gloss. The spraying times of the primer and the topcoat greatly impacted the adhesion, but they had no decisive impact on the improvement of the gloss. When the coating amount was 60 g/m2 for the waterborne sealing primer, 100 g/m2 for waterborne primer, and 120 g/m2 for the self-made topcoat and the coating was sprayed twice, the comprehensive performance of the obtained film on the wood was the best. This research on the preparation and coating process optimization of the two-component waterborne polyurethane coatings for wood can provide a technical basis for the application of two-component waterborne polyurethane topcoats for wood.

Anticorrosion performance of an eco-friendly coating system including an epoxy tie primer with aluminum tripolyphosphates and a polyurethane topcoat for marine aluminum alloy

The anticorrosion performance of an eco-friendly coating system, including an epoxy tie primer with aluminum tripolyphosphates (ATP) and a polyurethane topcoat for marine aluminum alloy was studied by pull-off adhesion test, electrochemical measurements, and salt spray test. Pull-off adhesion test showed a strong adhesion force between the epoxy tie primer and aluminum alloy substrate. Electrochemical measurements showed that the epoxy tie primer had an excellent corrosion resistance, as also confirmed by the salt spray test. The corrosion protection effect was better when the primer was used in conjunction with polyurethane topcoat. In addition, the compositions of the epoxy tie primer before and after immersion in 3.5 % NaCl solution and corrosion products were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The excellent anticorrosion performance was mainly attributed to the hydrolysis of the ATP into complex ions, which reacted with metal ions on the surface of the aluminum alloy to form a dense phosphating film. Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) analysis proved the diffusion of ATP at aluminum alloy/coating interface and chelating reaction between ATP and aluminum alloy substrate.

Ice-phobic polyurethane composite coating characterized by surface micro silicone loops with crumpling edges

This study developed a tactic to attain an ice-phobic polyurethane (PU) composite coating, which was fabricated by incorporating minor dosages of hybrid silica particles and silicone oil (SO) into the formulation of a commercial aerospace PU topcoat. The hybrid silica particles were synthesized by anchoring polydimethylsiloxane (PDMS) oligomers to silica microspheres. Both hybrid particles and SO amalgamate in the surface matrix of PU to induce a spread of wrinkling micro-loops over the coating. This coating surface morphology is structurally different from the well-known slippery liquid-infused porous surface since no liquid bulk is embedded in the surface matrix of PU coating. The icephobic property was characterized on a thermoelectric Peltier cooling plate, over which the frosting extents with cooling in ambient humidity conditions (~75 % RH) were compared. We have identified three coating fabrication factors responding to the delay of frosting inside the condensed water droplets overlying the PU coating. At the same time, they are cooled: the fuzzy PDMS layer on silica microspheres, i.e., hybrid particles, the fusion of SO with the hybrid particles, and the dosages of the hybrid particles and SO applied. Typically, when the PU composite topcoat comprises 0.4 wt% (based on PU matrix) hybrid particles and 0.4 wt% SO of the hybrid particle, it adjourns the onset of frosting to ~ −10 of from - 5.6 °C on the aerospace PU topcoat. This outcome is attributed to the micro round loops with folding edges and peripheric wrinkles that possess low-temperature softness and play a pivotal role in deferring icing inside the overlying water droplets.

Assessment of durability and zinc activity of zinc-rich primer coatings by electrochemical noise technique

The three-coat system consisting of a zinc-rich primer, epoxy midcoat, and polyurethane topcoat has been widely adopted for corrosion protection of structural steel bridges. Corrosion mitigation is afforded by the barrier characteristics of the various layers as well as beneficial galvanic coupling of the zinc pigments in the primer to the steel substrate when subjected to corrosive environments such as with moisture ingress and coating defects. The dispersed zinc pigments in the binder require adequate electronic coupling in order to provide the beneficial electrochemical coupling of the zinc to the steel. The application of the electrochemical noise (EN) technique to identify coating corrosion performance was reviewed in controlled laboratory tests. Zinc pigment activation and transition to passive-like conditions in defect and defect-free coating specimens could be identified by EN. The characteristic charge of noise events resolved by shot noise analysis was demonstrated to be related to anodic polarization of extended active zinc pigments adjacent to coating defect sites galvanically coupled to the exposed steel and passivated zinc pigments. Electrochemical noise resistance was shown to convey zinc/steel interfacial behavior in cases with sufficient activity but largely reflects coating barrier quality for intact coatings.

Evaluation of paint systems on A36 steel through electro-chemical techniques: Corrosion resistance of container tanks

In this research work, the corrosion resistance of plate steel used in the construction of cylindrical container tanks of seawater was evaluated. These container tanks are usually used for fighting fires on the coast of the Arequipa-Peru region, where the shortage of drinking water is significant. The study was based on immersion tests of 2 × 2 cm square test plates in 3.5 wt.% NaCl solution. Five paint systems were studied, varying only in the primers: P1-860 (inorganic zinc silicate); P1-ZC (epoxy-zinchromate); P1-850 (organic rich in zinc); P1-600 (reinforced inorganic zinc) and P1-SP1000 (high solids epoxy-amine). All systems consisted of a primer coat, an epoxy middle coat and a polyurethane topcoat. To characterize the behaviour of each system, the electrochemical impedance spectroscopy (EIS) was mostly used. In addition, the scanning Kelvin probe (SKP) and scanning electro­che­mical microscopy (SECM) were used as local techniques. The first three paint systems (P1-860, P1-ZC and P1-850) showed an invariable value of impedance modulus up to 3360 h of immersion in NaCl. The last two paint systems (P1-600 and P1-SP1000) showed a decrease in impedance modulus by more than one order of magnitude. This research provides a clear contribution of results obtained by global electrochemical techniques such as EIS, estab­lishing excellent tools for monitoring the performance of organic anticorrosive coatings.

Performance Assessment of Differently Dried Coating Systems for Potential Application in the Power Transformer Industry

Many companies in the power transformer industry are striving to speed up the drying process of coatings, which is why alternative drying methods are constantly being explored while maintaining the same coating protection properties. The infrared (IR) drying of protective coatings is a potential solution for their higher productivity, but has not yet been extensively investigated. In this paper, two solvent-borne coating systems, with and without zinc in the primer, from two different manufacturers, dried by infrared radiation and under atmospheric conditions, were studied. The coating systems consisted of epoxy primer, epoxy intermediate coat, and polyurethane topcoat. Anti-corrosion performance of the coatings was characterized using a salt spray chamber, pull-off adhesion testing, electrochemical impedance spectroscopy (EIS) investigation, and open circuit potential (OCP) measurement. All samples were analyzed using stereo microscope. A scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDX) for detailed study and chemical composition determination was used. The results showed that infrared technology notably reduced coating drying times while maintaining or improving anticorrosion performance properties compared to the coatings dried under atmospheric conditions.

Synergetic Design of Transparent Topcoats on ITO-Coated Plastic Substrate to Boost Surface Erosion Performance

Transparent conductive films (TCFs) have received much research attention in the area of aeronautical canopies. However, bad wear, corrosion resistance and weak erosion performance of TCFs dramatically limit their scalable application in the next-generation aeronautical and optoelectronic devices. To address these drawbacks, three types of optically transparent coatings, including acrylic, silicone and polyurethane (PU) coatings were developed and comparatively investigated ex situ in terms of Taber abrasion, nanoindentation and sand erosion tests to improve the wear-resistance and sand erosion abilities of ITO-coated PMMA substrates. To elucidate the sand erosion failure of the coatings, the nanoindentation technique was employed for quantitative assessment of the shape recovery abilities under probe indentation. Results show that the PU topcoats can greatly enhance the sand erosion properties, which were superior to those of acrylic and silicone topcoats. This result can be attributed to the good toughness and self-healing properties of PU topcoats. Additionally, high hardness and good Taber abrasion properties of the ITO films and silicone topcoats did not have an obvious or affirmatory effect on the sand erosion abilities, based on their brittleness and irreparable properties under sand erosion.

A Wind Tunnel Experimental Study of Icing on NACA0012 Aircraft Airfoil with Silicon Compounds Modified Polyurethane Coatings.

Ice formation on the aerodynamic surfaces of an aircraft is regarded as a major problem in the aerospace industry. Ice accumulation may damage parts, sensors and controllers and alter the aerodynamics of the airplane, leading to a range of undesired consequences, including flight delays, emergency landings, damaged parts and increased energy consumption. There are various approaches to reducing ice accretion, one of them being the application of icephobic coatings. In this work, commercially available polyurethane-based coatings were modified and deposited on NACA 0012 aircraft airfoils. A hybrid modification of polyurethane (PUR) topcoats was adopted by the addition of nanosilica and three-functional spherosilicates (a variety of silsesqioxane compound), which owe their unique properties to the presence of three different groups. The ice accretion on the manufactured nanocomposites was determined in an icing wind tunnel. The tests were performed under three different icing conditions: glaze ice, rime ice and mixed ice. Furthermore, the surface topography and wetting behavior (static contact angle and contact angle hysteresis) were investigated. It was found that the anti-icing properties of polyurethane nanocomposite coatings strongly depend on the icing conditions under which they are tested. Moreover, the addition of nanosilica and spherosilicates enabled the reduction of accreted ice by 65% in comparison to the neat topcoat.

Monitoring Coating System Changes Using Equivalent Circuit Fit Parameters

Organic coating systems are used to manage the corrosion of metal surfaces subjected to atmospheric degradation. These coating systems are frequently complex and multilayered and capable of providing several functions, including: substrate adhesion, corrosion inhibition and electrolytic barriers. In addition, the service environment can be equally complex with exposure to UV radiation, wet/dry cycling, and application of thermal and physical stresses on the substrate and coating system alike.Refining our ability to predict service life and explain how these coatings evolve over the course of their lifetimes provides an opportunity to decrease maintenance costs and aid in future coating development. These objectives can be achieved by the development of predictive models that incorporate the fundamental effects of relevant service environment parameters. This would provide reliable damage predictions based upon the measured environmental data thereby decreasing our dependence on proxy corrosion sensors.To that end, the first phase of this project has focused on testing and monitoring an aircraft coating system that is comprised of a surface pretreatment, an epoxy primer with inhibitors, and a polyurethane topcoat exposed to a variety of degradation conditions that simulate the extreme ranges of environmental stresses expected to be seen in-service. Coating condition was monitored using electrochemical impedance spectroscopy (EIS) and characterized with equivalent-circuit models so that changes to the coating system properties could be quantified and tracked over time.Regression models for the changes in the coating system properties are being developed and will be validated by follow-on outdoor exposure testing in the next phase of the program. Acknowledgments The Department of Defense Strategic Environmental Research and Development Program (SERDP) sponsored this work under program WP19-1017. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the Office of Naval Research, the U.S. Navy, or the U.S. government.

Effects of adhesive type on the mechanical properties of adhesive joints between polyurethane top coats and polyurethane-based adhesives after accelerated atmospheric ageing

The performance of a sealed stainless steel bracket system, adhesively bonded with two polyurethane-based adhesives (flexible adhesive, stiff adhesive) onto a marine polyurethane top coat, is investigated. The investigated joint connections on the coatings exhibited a high mechanical stability even after accelerated ageing (salt spray exposure, cyclic temperature variations, high relative humidity). The aged joints retained up to 81% of their tensile strength and up to 92% of their lap-shear strength. The torsional rigidity of the adhesive joint exceeded the required clamping torque of the designed bolt. A cyclical lifetime of >9·106 load cycles was estimated. Effects of cyclic ageing on the creep performance of the adhesive joint were found to be insignificant. Under tensile loads, the joints with stiff adhesive material exhibited a linear-elastic performance without the capability to deform prior to failure. The joints with the flexible adhesive material, in contrast, exhibited a behavior typically for ductile materials featuring a pronounced yield plateau prior to failure. Failure loads were higher, and displacement was notably lower, for the joints with stiff adhesive material. All joint connections met the requirements for a safety factor for the design for marine applications (11.6 for the flexible adhesive; 14.3 for the stiff adhesive). When the flexible adhesive is applied, the cohesive strength of the adhesive material is the limiting design factor. When the stiff adhesive is utilized, the load carrying capacity is higher, and the interface between priming coat and steel substrate is the limiting design area of the joints. The strength utilization of the adhesive materials depended on the particular structure of the entire joint configuration, particularly on the interface between steel substrate and the coating material. A number of assessment factors, namely stress limit factor, coating adhesion factor and safety factor, are introduced and discussed for tensile and shear loads.

Galvanic Corrosion of Low-Hydrogen-Embrittlement Cd-Ti 300M Steel Coupled with Composite-Coated TC4 Titanium Alloy in an Industrial-Marine Atmospheric Environment

The atmospheric exposure test of low-hydrogen-embrittlement Cd-Ti plated (LHE Cd-Ti) 300M steel coupled with TC4 titanium alloy of different surfaces was conducted in Qingdao industrial-marine atmospheric environment. The corrosion behavior and mechanism of LHE Cd-Ti 300M steel in the galvanic couples were investigated by means of morphology observation, corrosion product analysis, electrochemical measurement and mechanical property tests. The results show that the composite coating of epoxy polyamide primer and acrylic polyurethane topcoat on the surface of TC4 titanium alloy can significantly reduce the galvanic corrosion behavior of LHE Cd-Ti 300M steel and TC4 titanium alloy, and delay the corrosion process of anode LHE Cd-Ti 300M steel, thus reducing the loss of its mechanical properties. The corrosion of LHE 300M steel in the industrial marine atmosphere of Qingdao is induced by pitting corrosion. After Cd-Ti coating layer gradually dissolves, the corrosive medium reaches the substrate-plating layer interface, and the generated corrosion products accumulate and overflow the surface. The Cl- in Qingdao atmospheric environment severely destructs the surface oxide film, which induces pitting corrosion. In addition, the corrosive media containing sulfate ions can directly participate in the reaction and further aggravate the corrosion.

Evaluation of Adhesion, Hydrophobicity and Color Gamut of Nanoparticle embedded Polyurethane Topcoat for Aircraft with 3 Different Nanoparticles

Evaluation of Adhesion, Hydrophobicity and Color Gamut of Nanoparticle embedded Polyurethane Topcoat for Aircraft with 3 Different Nanoparticles

Preparation of Graphene-Modified Anticorrosion Coating and Study on Its Corrosion Resistance Mechanism

When aluminum alloy is present in a Cl−-rich environment, the surface oxide film is easily damaged, resulting in faster dissolution of the substrate. The application of graphene-modified anticorrosion coating can effectively prevent the occurrence of corrosion. In this study, to explore the corrosion resistance of graphene-modified anticorrosion coating on the surface of aluminum alloy, we prepared graphene-modified anticorrosion coating on the surface of aluminum alloy and investigated the corrosion resistance mechanism. Epoxy resin primer and polyurethane top coat were modified by predispersed reduced graphene oxide (rGO). Scanning electron microscope (SEM) and Raman spectrum were used to investigate the microstructure of graphene-modified anticorrosion coating, and it was found that the addition of rGO could effectively improve the porosity defect of epoxy resin primer. Electrochemical workstation was used to quickly characterize the corrosion resistance of graphene-modified anticorrosion coating, and the change of the electrochemical curve during soaking in 3.5% NaCl was investigated every 5 hours. It was found that the application of rGO to modify the anticorrosion coating could improve the corrosion resistance of the anticorrosion coating, and as the soaking time increased, the corrosion resistance of graphene-modified anticorrosion coating changed regularly. The study results indicated that when the content of rGO was 0.4%, the porosity of epoxy coating decreased from 1.54% to 0.33%, the porosity dropped by an order of magnitude, and the self-corrosion voltage was relatively positive (-0.72434 V). The self-corrosion current density was the lowest ( 1.948 × 10 − 6 A / c m 2 ), and at the low frequency, the impedance modulus was the highest (103). After the equivalent circuit fitting, the dispersion index was relatively high, the dispersion effect was relatively weak, and the corrosion resistance of the coating was improved. For graphene-modified anticorrosion coating, in the early stage of corrosion protection, the existence of pores and other defects in the coating might increase the dispersion effect, resulting in greatly decreased corrosion resistance of the coating. In the middle stage of corrosion protection, the pores in the coating would be completely filled by corrosive ions, resulting in a weakened dispersion effect. Therefore, the decrease in the corrosion resistance of the coating was slowed down and became stable.