Improved Corrosion Protection Research Articles

On surface Modification of Ti Alloy by Electro Discharge Coating Using Hydroxyapatite Powder Mixed Dielectric with Graphite Tool

Ti alloys from the family of metallic biomaterials are extensively used on account of their biological properties, functionality, and longevity within the human body. Due to the reactive elements such as vanadium, Ti alloys react with enzymes and body fluids causing the release of harmful ions in the body. The release of such ions promotes corrosion, bone-implant wear, and infection within the individual. However, in the recent scenario, coating of bioactive material on the substrate is one of best solution to conquer such issues. This article addresses the surface modification of medical grade Ti–6Al–4V alloy substrate with hydroxyapatite (HA) powder via Electro Discharge Coating (EDC). The experiments were performed as per Taguchi’s L8 orthogonal array considering current, pulse-on-time, pulse-off-time as input parameters. The output responses are assessed in terms of material deposition rate, surface roughness, and microhardness of coated samples. Surface morphology and phase analysis confirmed the porous texture and formation of bioactive compounds on the HA–EDC treated surface. Furthermore, in vitro wear and electrochemical corrosion behavior of the substrate and HA–EDC sample was scrutinize to analyze the improved resistance of modified surface. The results confirmed the significance of coating on substrate with improved corrosion protection efficiency (91.26%) and wear resistivity (87%) compared to untreated surface. Based on the observations, the EDC treated surface validates the surface modification offering improved bioactivity to the substrate material.

Developing a mechanochemical surface pretreatment to increase the adhesion strength of hydroxyapatite electrophoretic coating on the NiTi alloy as a bone implant

In this work, the pretreatments of sandblasting for 5, 15, 20, and 30 s followed by acid-etching were conducted to improve the adhesion strength amid the NiTi substrate and an electrophoretic coating of hydroxyapatite as a bone implant. The composition, microstructure, and surface topography of materials govern their properties. Therefore, characterizations of prepared specimens were performed using X-ray diffraction as well as quantitative phase analysis, differential scanning calorimetry, optical microscopy, scanning electron microscopy, atomic force microscopy and a roughness measuring device. The micro-scale mechanical properties were evaluated using a nanoindentation test. The electrochemical measurements were done using a multipurpose electrochemical test rig. The results display that the sandblasting for 20 s followed by acid-etching results in the suitable average roughness of Ra = 1.543 ± 0.053 μm and the adhesion strength is improved by 50% compared to sandblasted state. Also, the mentioned mechanochemical pretreatment make it more effective during electrochemical reactions and improve corrosion protection efficiency by 57.61%. Therefore, this surface pretreatment can be considered as a proper approach before the electrophoretic coating of hydroxyapatite on the NiTi substrate to increase the adhesion strength and diminish the stress shielding effect after implantation as a bone implant.

Microstructure, synergistic mechanism and corrosion behavior of tin oxide conversion film modified by chitosan on aluminum alloy surface

In this paper, a chitosan‑tin oxide composite film (CTOF) composed of clusters of micro-flowers was prepared on aluminum alloy to improve corrosion protection in the 0.1 M H2SO4 and 0.001 M NaF acidic solution by the hydrothermal method. The surface morphology of the film was analyzed by scanning electron microscopy (SEM). The structure and ingredient of the film were research by using X-Ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FT-IR). The method we used is very simple, convenient and pollution-free. The film shows good protective efficiency as high as 99.998% in solution of 0.1 M H2SO4 and 0.001 M NaF which indicates that the films can improve corrosion resistance of aluminum alloy under acidic solution.

Functionalization of Silica with Triazine Hydrazide to Improve Corrosion Protection and Interfacial Adhesion Properties of Epoxy Coating and Steel Substrate

The chemical bonding of modified filler surfaces with coating networks is an advanced approach for improving the interfacial adhesion force of fillers with coating and substrate surfaces. In this respect, silica gel surfaces were activated and modified by grafting 1,3–dihydrazide-2,4,6-triazine onto hydroxyl groups of activated silica surfaces. The chemical structure, thermal stability and surface morphologies of the modified silica were investigated. The modified silica fillers were blended during the curing of the epoxy resin with the polyamine hardener. The data regarding the chemical structure and thermal stability of the cured epoxy networks in the presence of modified silica elucidated the chemical bonding of amine groups on the silica surfaces cured with the oxirane epoxy resin. Moreover, the incorporation of modified silica in surfaces with epoxy networks improved their adhesion with steel surfaces and enhanced the mechanical, thermal and anticorrosion characteristics of the epoxy to protect steel surfaces against seawater.

A crosslinkable graphene oxide in waterborne polyurethane anticorrosive coatings: Experiments and simulation

A crosslinkable graphene oxide (GO) was synthesized and employed as reinforcement in waterborne polyurethane (WPU) composite coatings for improving corrosion protection properties. Polycarbodiimide (PCD), a crosslinking agent of WPU, was chosen to modify GO. Three different conformations of functionalized graphene will be generated: grape cluster conformation, network conformation and tail conformation, varying mainly with the PCD/GO ratio. Experiments and molecular dynamics simulation were carried out to study the correlations between the PCD/GO ratio, the conformations of functionalized graphene, as well as the dispersion state of graphene layers. The functionalized graphene with tail conformation was crosslinkable with WPU molecules along the interfaces. Electrochemical impedance spectroscopy showed that the WPU coatings with 0.2 wt% crosslinkable graphene remained at a maximum impedance modulus of 109 Ω cm2 after 120 days immersion without any decrease. The superior anticorrosive properties benefited from the barrier properties of well-dispersed graphene layers, the crosslinking structure along the functionalized graphene/WPU interfaces, as well as the improved water resistance of the coatings.

Polypyrrole/graphene oxide composite coating on Ti implants: a promising material for biomedical applications

Advanced materials can be developed by the combination of synthetic polymer and nanomaterial for biomedical application. Polypyrrole/graphene oxide (PPy/GO) composite coating on Ti metal was developed through electropolymerization of pyrrole by varying the amount of GO in aqueous oxalic acid solution. The influence of GO in the PPy matrix was confirmed by scanning electron microscopy studies. Structural interactions between PPy and GO in the composite coating were studied using ATR-FTIR, solid 13C NMR and Raman spectroscopy. The higher surface roughness and the lower wettability of the composite-coated Ti favor biocompatibility. The increase in adhesion strength of the composite coating was analyzed by the cross-hatch adhesion test. Potentiodynamic polarization studies showed a higher polarization resistance (Rp) and lower corrosion rates for composite coatings. Dynamic electrochemical impedance spectroscopy studies confirmed the PPy/GO composite coating exhibited a higher impedance from − 0.55 to 1.25 V in SBF solution. Bode impedance and Bode phase angle results revealed a higher resistance for PPy/GO composite-coated Ti. Immersion studies of PPy/GO composite coating in SBF solution revealed the growth of dense hydroxyapatite (Hap.) over Ti metal. Further, in vitro cell culture studies were carried out by MG-63 cells to assess the biocompatibility of PPy/GO composite coating on the substrate. Improved corrosion protection and biocompatibility behavior of PPy/GO composite-coated Ti suggests the potential candidate for biomedical applications.

The sandwich-like structures of polydopamine and 8-hydroxyquinoline coated graphene oxide for excellent corrosion resistance of epoxy coatings

A novel sandwich-like structure material was exploited for the fabrication of an effective corrosion resistance system. An environmentally friendly composite material was synthesized by installing 8-hydroxyquinoline (8-HQ) on the surface of graphene oxide (GO). In order to prevent leakage of corrosion inhibitor 8-HQ, GO/8-HQ was modified by polydopamine (PDA), denoted as GO/8-HQ/PDA. A sandwich-like structure (GO/8-HQ/PDA) enables long-term stable storage of corrosion inhibitor in the protective matrix. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were utilized to verify the sandwich-like structure of GO/8-HQ/PDA. The electrochemical tests in a 3.5 wt% NaCl solution showed that the addition of well-dispersed GO/8-HQ/PDA into epoxy system (GO/8-HQ/PDA-EP) remarkably improved corrosion protection of AZ31b magnesium alloy compared with pure epoxy (EP) coating. The sandwich structure protects the activity and structural integrity of the corrosion inhibitor (8-HQ). The corrosion inhibitor (8-HQ) of the GO/8-HQ/PDA sandwich structure cuts off the ion exchange between the metal alloy and the electrolyte solution, which hinders the electrochemical corrosion of the metal. A possible corrosion resistance mechanism of GO/8-HQ/PDA is fully discussed. This study provides feasibilities for the immobilization of corrosion inhibitors on the metal surface.

Synergistic effect of polypyrrole functionalized graphene oxide and zinc phosphate for enhanced anticorrosion performance of epoxy coatings

A promising novel composite coating based on compound pigment of zinc phosphate and polypyrrole (PPy) functionalized graphene (ZGP) was reported for carbon steel in 3.5 wt% NaCl solution. Two ratios of PPy functionalized graphene oxide (GO-PPy) nanocomposites were prepared by in-situ polymerization of pyrrol (Py) on the surface of graphene oxide (GO). PPy film deposited on the surface of graphene oxide guaranteed excellent dispersion in the coating owing to hydrophilic groups. Embedding a small amount of ZGP-2 composite pigment (mPy/mGO = 2:1) into the waterborne epoxy coating significantly improved corrosion protection of the prepared composite coating. The corrosion protection mechanism of the desirable coating was attributed to the synergistic protection of impermeable GO-PPy nanosheets and passivation function of zinc phosphate, which was proved by the identification of corrosion products. Therefore, this work may provide a new direction for further study on compound pigments composed of functional graphene nanomaterials and inorganic salt inhibitors.

Microbiologically influenced corrosion mechanism of 304L stainless steel in treated urban wastewater and protective effect of silane-TiO2 coating

Microbiologically influenced corrosion (MIC) of bare and silane-TiO2 sol-gel coated stainless steel (SS) was studied in treated urban wastewater (TUWW). Combining the electrochemical impedance spectroscopy (EIS) and the scanning vibrating electrode technique (SVET) showed that SS surface colonization occurs, at earlier stages, by iron-oxidizing bacteria (IOB), and later by sulphate-reducing bacteria (SRB). The SVET results showed that chemical corrosion process and bacterial respiration led to the depletion of dissolved oxygen, creating a differential aeration cell and thus a localized corrosion phenomenon. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that the growth of a bacterial biofilm on 304L SS was a dynamic process, stimulating the localized oxidation of SS. To improve corrosion protection, a silane-TiO2 sol-gel coating for SS is proposed. SEM showed that the coating reduced bacterial adhesion and EIS study demonstrated that the coating improved the barrier properties and corrosion resistance of 304L SS in TUWW over a short period of immersion.

Polyacrylonitrile/Polysulfone Blends for Corrosion Protection of Copper

Polyacrylonitrile/polysulphone blends (PBs) was synthesized through in situ polymerization in N-methyl pyrrolidone under microwave irradiation. PBs were characterized through Uv-vis spectra and atomic force microscopy. Performance of corrosion protection of PBs of copper was investigated through electrochemical impedence spectra and DC polarization in NaCl (0.25 M). Electrochemical data reveals improved corrosion protection of copper by PBs over PSF. PBs display marginal delamination over copper at the rate of 0.53 mm/yr till 29 h. Present work demonstrates the potential of PBs towards corrosion protection of copper and the same may onwards be executed for protection of other metals by PBs in saline media.

Improved corrosion protection of CrN hard coating on steel sealed with TiOxNy-TiN composite layers

Based on the excellent conformality and uniformity of atomic layer deposition (ALD), ALD thin films can seal the defects in magnetron sputtered CrN coating. In this work, atomic layer deposited TiN layer is adopted to seal CrN to improve its anti-corrosion properties. The oxidization of TiN forms TiOxNy-TiN composite layer including TiN bottom layer and TiOxNy upper layer, which can limit the charge transport, inhibit the diffusion of corrosive media, such as chlorine ions. Therefore, the addition of TiOxNy-TiN sealing layer significantly improves the corrosion resistance of CrN coated steel, and decreases its corrosion current density, due to the synergistic effect of TiOxNy and TiN in the composite sealing layer.

High performance corrosion and wear resistant Ti-6Al-4V alloy by the hybrid treatment method

A hybrid treatment approach involving large pulse electron beam (LPEB) irradiation and plasma electrolytic oxidation (PEO) is explored for the first time to improve the corrosion and wear resistance of Ti-6Al-4V alloy. The LPEB irradiation decreased the surface roughness, reduced the grain size, and transformed the α + β mixed phase of the Ti-6Al-4V alloy to a single α′-martensite phase. The LPEB treated surface increased the growth rate, promoted uniform discharge characteristics during PEO that has led to a higher breakdown potential and final potential. The PEO coating formed on LPEB irradiated alloy is compact with a lower pore size and pore population density. The hybrid LPEB-PEO treated Ti-6Al-4V alloy offered a ~92% improvement in corrosion protection in 0.9% NaCl and ~71% improvement in wear resistance, when compared to the untreated one. In this study, these inferences suggest that a hybrid LPEB-PEO treatment is a viable approach to improve the corrosion and wear resistance of Ti-6Al-4V alloy.

Functional properties of the novel hybrid coatings combined of the oxide and DLC layer as a protective coating for AZ91E magnesium alloy

Magnesium alloys are essential materials for aircraft applications however their corrosion protection is still a challenge and restriction from the spread of the applications. Owing to there is still need to search a new way to protect magnesium alloys from corrosion in replacement of currently used chromate coatings which manufacturing process is dangerous and harmful for living organism and will be soon forbidden by law restrictions. In this work, the novel surface modification of magnesium alloy AZ91E was realized. A novel hybrid coating made by combining of the oxide and Diamond-Like Carbon (DLC) layer were elaborated and explored to find out is there any improvements in functional properties when compared to chromate coatings. The corrosion testing in 3.5% NaCl solution and salt fog condition revealed the clear improvements in corrosion protection of AZ91E alloy. Additionally, It was found that oxide coating has lower microhardness and young modulus when compared to DLC and thus it decreases internals stress within the hybrid coating. The wear test revealed that DLC coating significantly improves abrasion resistance when compared to raw, unmodified AZ91 or AZ91E covered with chromate coating.

Microcontainers with 3-amino-1,2,4-triazole-5-thiol for Enhancing Anticorrosion Waterborne Coatings for AA2024-T3

Using organic coatings with high barrier property in combination with active corrosion protection can improve corrosion protection of aluminum alloys. In this work, 3-Amino-1,2,4-triazole-5-thiol (ATAT) was used as organic inhibitor in developing anticorrosion coatings for AA2024-T3. The delivery of ATAT was achieved by using smart microcontainers with ATAT that respond to pH change caused by corrosion reaction at the coating-substrate interface. The developed coatings with low concentration of smart microcontainers showed a slight reduction of barrier properties, but gained active corrosion protection capability. The resistance of the coatings reduced the rate of penetration of corrosive species and the active corrosion protection stopped the damaging reactions at the coating-substrate interface. The active corrosion protection is also evident in the case of coatings with mechanical damages, when the barrier property of coatings is compromised. Waterborne coatings with smart microcontainers for delivery of ATAT exhibited enhanced performance for corrosion protection of AA2024-T3.

Few-Layers Graphene Film and Copper Surface Morphology for Improved Corrosion Protection of Copper

Graphene has shown excellent corrosion protection of copper (Cu). The corrosion protection of Cu is governed by the characteristics of the deposited graphene and Cu surface morphology underneath. In this work, graphene films (1-2, 4-5 layers) were deposited on Cu using a chemical vapor deposition by changing hydrogen (H2) concentration during the annealing stage. The chemical structure and surface microstructural features of graphene/Cu were inspected by Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The electrochemical corrosion performance of graphene/Cu was studied in 0.5 M sodium chloride solution using potentiodynamic polarization and electrochemical impedance spectroscopic measurements. The 1-2 layers of graphene and rough Cu surface were obtained for low H2 concentrations (0 and 2.5%), whereas high H2 concentrations, 20 and 50%, resulted in a smooth Cu surface and 4-5 layers of graphene. Our results showed that Cu with a smooth surface and multilayer graphene film exhibited the best corrosion resistance against electrochemical degradation. Tafel analysis revealed that Cu with 4-5 layers of graphene coating corroded nearly three orders of magnitude slower than the annealed Cu, without graphene coating. The results of this study can be useful for several applications where Cu is in close contact with salt species.

Preparation of transparent nanocomposites from UV‐ and thermo‐curable epoxyacrylate and graphene oxide for the application of corrosion protection coatings

AbstractIn this study, we report UV‐ and thermo‐curable epoxyacrylate/graphene oxide (EA/GO) nanocomposites that present good transparency, excellent pencil hardness and promising improvement in corrosion protection. A dual‐curable EA oligomer with one terminal epoxide and one double bond at the other end was synthesized by reaction of diglycidyl ether of bisphenol‐A and acrylic acid. After mixing EA and GO with the curing agents and reactive diluent followed by UV cure and thermo‐cure, the resulting EA/GO films on a glass slide with GO loading up to 3 phr exhibited over 86% light transmittance. Furthermore, the pencil hardness was enhanced from 3H for EA to 6H for the EA/GO composite at 2 phr GO loading. The corrosion protection of the EA/GO coatings was evaluated by a potentiodynamic polarization technique and electrochemical impedance spectra. The corrosion potential (Ecorr) of the EA/GO‐coated steel increased with increasing GO loading. Meanwhile, Nyquist and Bode plots indicated that the higher the GO content in the EA/GO coating was, the higher was the coating resistance and also the charge transfer resistance after immersion in salt solution. All these results proved that the GO had positive effects on enhancement of the corrosion resistance. The improved corrosion protection by the EA/GO coatings was mainly due to the enhanced hydrophobicity, the deviation of electron transfer and the increased tortuosity of the diffusion path. The improved corrosion protection and hardness together with the useful dual‐curability make the EA/GO nanocomposite a competitive candidate for corrosion protection coatings. © 2019 Society of Chemical Industry

Capped and uncapped nickel tungstate (NiWO4) nanomaterials: A comparison study for anti-corrosion of copper metal in NaCl solution

We report for the first time, the role of capping agent and size effect of nickel tungstate (NiWO4) nanomaterials (NTN) in mitigation of copper corrosion in chloride medium. NTN were synthesized firstly, via a simple wet-chemical precipitation route without any capping agents (conventional process) and secondly with citric acid as capping agent, both in the presence of sodium tungstate (Na2WO4). Electrochemical analyses for corrosion protection have been tested and results indicated an improved corrosion protection of copper by the capped particles compared to the uncapped (conventional method) particles. A comparison was also made against Na2WO4 (a commercially available corrosion inhibitor).

Trivalent chromium conversion coating on AA2024‐T3 used in aeronautical and aerospace industry

Significant research has been conducted to replace the chromium(VI)‐based surface treatments, and some commercial substitute systems are now available and needs to be tested to evaluate their performance and to know how they comply with the required specifications. The anticorrosion properties provided by a commercially available trivalent chromium‐based product—PreCoat A32—when applied to AA2024‐T3 aluminium alloy substrates were evaluated in this work and compared with those obtained with a chromium(VI)‐based pretreatment well‐recognized reference (Alodine 1200S). The morphology and elemental composition of the conversion coatings were investigated by high‐resolution microscopy and energy‐dispersive X‐ray analysis, respectively, being the wettability of the modified surface measured by contact angle goniometry. The data obtained reveal that PreCoat A32–treated surfaces are more apt to receive aqueous paint schemes than those healed with Alodine 1200S. The corrosion resistance of the treated samples was monitored by potentiodynamic polarisation assays and electrochemical impedance spectroscopy analysis, revealing that PreCoat A32 coatings provide improved corrosion protection for AA2024‐T3. The corrosion resistance effectiveness of PreCoat A32 was also confirmed in trials realised in salt‐spray chamber, humidity tests, and thermal cycling assays, where more severe exposure conditions were simulated. The gathered data clearly indicate that the PreCoat A32 brings together the mandatory qualities to successfully substitute the conventional and undesirable chromium(VI)‐based treatments, in aeronautical and aerospace industry.

Nano ZnO-assisted formation of zinc phosphate conversion coating for improving corrosion protection of AZ91D magnesium alloy

In this work, micron and nano ZnO powders were used to assist in the formation of zinc phosphate coatings to improve the corrosion resistance of AZ91D magnesium alloy, respectively. The results showed that the ZnO particles acted as the nucleation sites to promote the formation of flower-like Zn3(PO4)2 · 4H2O phase, which was the main component of the zinc phosphate conversion coatings. In addition, the micron ZnO-assisted zinc phosphate conversion coatings (MACC) reduced the corrosion rate of AZ91D alloy from 3.36 to 3.20 mm · a−1. Besides, the corrosion resistance nano ZnO-assisted zinc phosphate conversion coating (NACC) was four times as high as that of MACC, due to that the NACC had the finer grains and more compact structure. The more compact structure resulted from that the nano ZnO particles not only increased the number of nucleation sites but also decreased the concentration of Zn2+ in the phosphatization solution to inhibit the growth of Zn3(PO4)2 · 4H2O phase.

The Effects of Citric Acid on the Mechanical and Corrosion Resistant Properties of Ni-Y2O3 Coatings for Enhanced Corrosion Protection

The need to reduce the corrosion rate of metal structures in the oil and gas industry leads to increasing cost. Among different methods of protecting metals in corrosive environments; addition of coatings as a protective layer on the surface of metal components has been a useful technique in minimizing the impact of corrosion. Nanocomposite materials are composite materials that are made of two or more materials in which at least one dimension is in the nanometer scale. By decreasing the size of a particle embedded in a matrix, it helps to enhance the interactions between the metal matrix and reinforcements at phase interfaces. Therefore, incorporating nanoparticles into a metal or alloy matrix has shown an improvement to the mechanical and physical properties of the resulting coating. Yttrium oxide (Y2O3) is included in the rare earth (RE) sesquioxides group, it has a number of interesting properties such as high mechanical strength, high thermal conductivity, high melting point (2410 oC), wide bandgap (Eg is approximately 5.5 eV), and photoluminescence. It is also known to improve corrosion protection in corrosive environments when incorporate into metal and alloy coatings such as nickel, titanium, zinc, and Fe-Cr alloys. However, yttrium oxide was found to have high potential of absorbing hydrogen ions in aqueous solution to become a hydroxide, which leads to agglomeration of the nanoparticles in the electrolyte solution, making it difficult to form the coating when increasing the concentration of added Y2O3 nanoparticles. This agglomeration makes it difficult to insert high enough concentrations of nanoparticles to affect the corrosion resistance properties. A nickel-yttrium(III) oxide nanocomposite has been electrodeposited onto metal substrates using varying concentrations of yttrium(III) oxide nanoparticles in the nickel plating bath. In this environment, nickel and hydrogen ions tends to naturally absorb onto the surface of the yttrium(III) oxide nanoparticles during the electrodeposition process of Ni-Y2O3 coatings, thus, making the formation of Ni-Y2O3 coatings more challenging . Therefore, citric acid has been added to the electrolytic bath, not only as a buffer to aid in controlling the pH of the system, but also as a stabilizing agent for the nanoparticles prior to deposition. The effect of citric acid on the formation, morphology, and composition of the nickel-yttrium(III) oxide coatings was investigated by solution studies, powder x-ray diffraction, scanning electron microscopy, and microhardness measurement. The corrosion resistant properties of the coatings were investigated by exposure to chloride solutions, potentiodynamic polarization, and electrochemical impedance spectroscopy. The addition of Y2O3 nanoparticles was found to enhance the mechanical properties of the coatings which leads to an inherent improvement in their corrosion resistance. Figure 1