Corrosion Protection Capacity Research Articles

Assessment of Oil Paints for Corrosion Protection of Reinforcing Steel Bars in Concrete

Corrosion becomes a threat to reinforced concrete structural integrity during the service life of the structural member. This situation has become a global concern because of the economic and safety implications. Hence, many corrosion inhibition techniques including coating with materials (organic and inorganic) were used to prevent its devastating effects. The present study used three oil paint brands (mat, red-oxide and gloss Leyland oil paints in Ghana) to variedly coat reinforcing steel bars to ascertain their corrosion protection capacity in concrete. There were zero, one, two and three paint coats of average film thickness, 72 µm, 129 µm and 220 µm respectively explored. An Electrochemical process involved simulated concrete pore solution made of 10% sodium chloride (NaCl) in distilled water with three electrode systems to represent a corrosion medium was used to determine corrosion protection capacity of the paints. The results indicate over 90% corrosion resistance of the paints used. Comparing the corrosion rates of the coated and uncoated reinforcing steel bars, while it would take a one coat steel bar 342.5 years and 237 years respectively for spraying and manual brushing modes to reduce in diameter by 0.616mm, it would take only one year for an uncoated steel bar to reduce by this same 0.616mm. The protection capacity proved better with increasing coats on all corrosion variables for the selected paints used. The implication is that the selected oil paint brands are capable of protecting reinforcing steel bars in concrete against corrosion and therefore recommended for application to reduce maintenance cost. Statistically, no significant difference existed between coating mode, number of coatings, paint type and steel type on the corrosion variables for the coated steel bars. However, a further study about the durability of the coating in the concrete during its service time is recommended.

The effect of polylactic acid ordering on the long-term corrosion protection capacity of biodegradable magnesium alloys

The polylactic acid (PLA) coatings of different crystallinity were prepared on biodegradable Mg-2.2Zn-0.3Ca alloy wires to improve the long-term anti-corrosion properties. The composition characteristics and microstructure of the samples were investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscope (FTIR), wide angle X-ray diffraction (WAXD) and scanning electron microscope (SEM). The corrosion resistance of all samples was investigated by immersion tests and electrochemical techniques in vitro simulated body fluid (SBF). The results indicated heat treatment improved the crystallinity of PLA coating and heated-coating performed protective behaviors in the short and long-term immersion. The corrosion rate of heated samples was lower than that of unheated samples and exhibited superior long term protective effect for Mg alloy wires. The lifetime of heated sample (H2) increased significantly from 33 to 55 days. The initial electrochemical performance of unheated coating was better than heated coating, but it declined more rapidly during the long-term immersion. These results indicated that PLA coating could not ignore the effect of its crystallinity to anti-corrosion ability, and only the suit heat treatment makes PLA coating more ordering and achieves higher corrosion resistance in vitro immersion. Therefore, it has promising potential by controlling effectively the PLA ordering for surgical implant applications.

Synthesis of a waterborne epoxy curing agent based on polyether triols and its application in 2K waterborne epoxy coatings

AbstractPolyether polyols can improve the performance of waterborne epoxy curing agent. In this paper, intermediates were synthesized from polyether triols with epoxy resin E‐51 and introduced into the epoxy curing agent by reacting with TETA. This paper focuses on the process of synthesizing the intermediates. The 2K waterborne epoxy coating film prepared with polyether triols‐modified waterborne epoxy curing agent exhibits desirable corrosion protection capacity and neutral salt spray resistance up to 600 h. In addition, the 2K waterborne epoxy coating film prepared using the modified waterborne epoxy curing agent with polyether triols displayed improved surface appearance, mechanical properties, and water resistance.

Water-soluble N-methylpolypyrrole nanoparticles as a highly efficient eco-friendly corrosion inhibitor for carbon steel in 3.5 wt% NaCl solution

Metal corrosion is a significant problem in industrial units that can disrupt operations and increase costs. A corrosion inhibitor (CI) is an effective solution to this issue. Organic compounds are suitable and efficient CIs for carbon steel (CS) against corrosion. Among them, intrinsically conducting polymers (ICPs) are gaining traction in numerous industries due to their eco-friendliness, low cost, high stability, and simple production process. One of the major obstacles associated with employing ICPs as CI is their limited solubility in aqueous media. The present study aimed to synthesize water-soluble N-methylpolypyrrole (NmPPy) nanoparticles through a facile, rapid, and cost-effective approach. The successful synthesis of the NmPPy nanoparticles has been confirmed through characterization using scanning electron microscopic (SEM), Fourier transform infrared (FTIR) spectroscopy, and UV–vis spectra. The effectiveness of NmPPy nanoparticles in protecting CS against corrosion in a 3.5 wt% NaCl solution with varying concentrations at ambient temperature was evaluated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) measurements. The findings from the study indicate that the NmPPy nanoparticles exhibit a noteworthy corrosion protection capacity for CS. At a concentration of 300 mg L−1, the NmPPy acted as a mixed-type inhibitor and yielded around 95% inhibition efficiency. Moreover, the adsorption behavior of the particles followed the Langmuir isotherm model with chemical adsorption. Surface morphology analysis techniques, including scanning Kelvin probe (SKP), field-emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDX), have confirmed the development of a protective film on the CS. The analysis indicates that the CS has a smooth surface, and the NmPPy nanoparticles exhibit high inhibition efficiency. Therefore, the water-soluble NmPPy nanoparticles effectively inhibit CS corrosion in NaCl solution. They hold immense promise for the future development of advanced protective materials.

Corrosion Inhibition Evaluation of Chitosan–CuO Nanocomposite for Carbon Steel in 5% HCl Solution and Effect of KI Addition

Chitosan–copper oxide (CHT–CuO) nanocomposite was made by an in-situ method utilizing olive leaf extract (OLE) as reductant. The OLE mediated CHT–CuO nanocomposite containing varying amount of chitosan (0.5, 1.0 and 2.0 g) was evaluated as corrosion inhibitor for X60 carbon steel in 5 wt% hydrochloric acid solution. The corrosion inhibitive performance was assessed utilizing weight loss and electrochemical impedance spectroscopy, linear polarization resistance and potentiodynamic polarization techniques complemented with surface assessment of the corroded X60 carbon steel without and with the additives using scanning electron microscopy/energy dispersive X-ray spectroscopy and 3D optical profilometer. The effect of KI addition on the corrosion protection capacity of the nanocomposites was also examined. Corrosion inhibitive effect was observed to increase with increase in the nanocomposites dosage with the highest inhibition efficiency (IE) achieved at the optimum dosage of 0.5%. The order of corrosion inhibition performance followed the trend CHT1.0–CuO (90.35%) > CHT0.5–CuO (90.16%) > CHT2.0–CuO (89.52%) nanocomposite from impedance measurements. Also, IE was found to increase as the temperature was raised from 25 to 40 °C and afterwards a decline in IE was observed with further increase in temperature to 50 and 60 °C. The potentiodynamic polarization results suggest that the nanocomposites alone and in combination with KI inhibited the corrosion of X60 carbon steel by an active site blocking mechanism. Addition of KI upgrades the IE of the nanocomposites but is not attributable to synergistic influence. The lack of synergistic influence was confirmed from the computed synergism parameter (S1) which was found to be less than unity with values of 0.89, 0.74 and 0.75 for CHT0.5–CuO, CHT1.0–CuO and CHT2.0–CuO nanocomposites, respectively, at 60 °C. Furthermore, KI addition improved the IE with rise in temperature from 25 to 60 °C. Surface analysis results confirm the formation of a protective film which could be attributed to the adsorption of the nanocomposites on the carbon steel surface.

Experimental and In-Silico Computational Modeling of Cerium Oxide Nanoparticles Functionalized by Gelatin as an Eco-Friendly Anti-Corrosion Barrier on X60 Steel Alloys in Acidic Environments.

An eco-friendly and a facile route successfully prepared novel cerium oxide nanoparticles functionalized by gelatin. The introduced CeO2@gelatin was investigated in terms of FE-SEM, EDX, TEM, chemical mapping, FT-IR, and (TGA) thermal analyses. These characterization tools indicate the successful synthesis of a material having CeO2 and gelatin as a composite material. The prepared composite CeO2@gelatin was used as an environment-friendly coated film or X60 steel alloys in acidizing oil well medium. Moreover, the effect of CeO2 percent on film composition was investigated. LPR corrosion rate, Eocp-time, EIS, and PDP tools determined the corrosion protection capacity. The CeO2@gelatin composite exhibited high protection capacity compared to pure gelatin; in particular, 5.0% CeO2@gelatin coating film shows the highest protection capacity (98.2%), with long-term anti-corrosive features. The % CeO2@gelatin-coated films formed the protective adsorbed layer on the steel interface by developing a strong bond among nitrogen atoms in the CeO2@gelatin film and the electrode interface. Surface morphology using FESEM measurements confirmed the high efficiency of the fabricated CeO2@gelatin composite on the protection X60 steel alloys. DFT calculations and MC simulations were explored to study the relations between the protection action and the molecular construction of the coated systems, which were in good alignment with the empirical findings.

Corrosion resistance of a superelastic NiTi alloy coated with graphene–based coatings

The mechanical responses under superelastic loading cycles and the corrosion protection capacity of two graphene–based coatings applied to a NiTi alloy were evaluated. Graphene oxide (GO) and a composite of reduced graphene oxide (rGO) incorporated in a block copolymer of styrene–ethylene–butylene–styrene (SEBS) were deposited on the substrate via dip–coating. The morphology of the coatings was characterized by scanning electron microscopy (SEM) before and after uniaxial loading cycles up to 6%. Atomic force microscopy (AFM) was also used to evaluate the roughness of the coatings, which was expressed in terms of average roughness (Ra). The corrosion behavior was studied by potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), and Mott–Schottky analysis (MSA). SEM images suggested that both GO and rGO + SEBS create uniform coatings on the substrate. The measured Ra was 25 ± 3 nm for the bare NiTi, 24 ± 3 nm for the GO coated NiTi, and 8 ± 2 nm for the rGO + SEBS coated NiTi. Both coatings presented the capacity of following several superelastic cycles, maintaining their morphological integrity. PP and EIS showed that only the rGO + SEBS coating results in a significant improvement in terms of corrosion resistance. Furthermore, rGO + SEBS decreased the oxygen vacancies in the passive film when compared with the bare NiTi and GO coating.

Steel protection in acidified 3.5% NaCl by novel hybrid composite of CoCrO3/polyaniline: Chemical fabrication, physicochemical properties, and corrosion inhibition performance

Perovskite-type oxide (CoCrO3) was used as a core content of the material to synthesize oxide/PANI nanocomposite. The introduced composite was synthesized by two steps; oxide formation followed by in situ polymerization to cover the oxide surface by the conductive polyaniline polymer (PANI). The as-prepared oxide/PANI material was studied in terms of FE-SEM, TEM, XRD, FT-IR, BET, and XPS analyses. These characterization tools indicate the successful synthesis of a material having oxide and PANI as a composite material. The corrosion protection performance of an oxide/PANI material in a comparison with individual PANI was tested for carbon steel 1018 (CS-1018) in acidified 3.5% NaCl solution. The corrosion protection capacity was determined by LPR corrosion rate, Eocp-time, EIS, and PDP tools. The CoCrO3/PANI composite exhibited high protection capacity around 98.8% at the concentration of 150 mg/L and acted as a mixed type inhibitor i.e., inhibited both anodic and cathodic reactions. The adsorption behavior obeyed the Langmuir isotherm model with competitive physical and chemical adsorption. Surface morphology using FESEM/EDX measurements confirmed the high efficiency of the fabricated CoCrO3/PANI composite on the protection CS-1018 in acidified brine. It was observed that transition metal oxide (CoCrO3) nanoparticles reinforce the barrier and anticorrosive characteristics of PANI. The attained findings indicate that the prepared stabilized system (CoCrO3/PANI composite) is an outstanding inhibitor for CS-1018 corrosion in acidic solutions containing chloride.

In-situ grafted graphene oxide-based waterborne epoxy curing agent for reinforcement corrosion protection of waterborne epoxy coating

Abstract Well-dispersed graphene oxide (GO) in resin matrix has been found for improving corrosion protection performance of the coatings. In this paper, a new strategy relying on waterborne epoxy curing agent contained GO (GO-WCA) was developed, which was prepared via endcapping, modifying and in-situ grafting process. Wherein, endcapping includes blocking the high-activity hydrogen which is used to modulate curing activity. And the modifying process introduces homologous epoxy segment so as to improve compatibility between curing agent, resin matrix and GO. Attributing to this evolvement of WCA and superior barrier effects of GO, the epoxy coatings cured by GO-WCA exhibit desirable corrosion protection capacity. Besides, the failure mode is discovered as bubbling. This environmentally-friendly waterborne curing agent, only with 4.2 g/L VOC content, is anticipated to become available in diverse waterborne epoxy coatings system with excellent barrier property.

Gemini Surfactants with Different Function Groups as High Efficiency Corrosion Inhibitors for Low Carbon Steel

AbstractThis study pioneered in applying two Gemini surfactants with different spacers to corrosion protection. Bis‐N, N, N,‐hexadecyldimethyl‐p‐biphenylenediammonium dichloride (BHBP) and 1,3‐bis (hexadecyldimethylammonio)‐2‐hydroxypropane dichloride (BHHP) were successfully prepared. In order to study the impact of various spacer functional groups on the performance of corrosion inhibitors, a number of different tests were conducted, including electrochemical experiments, weight loss test, surface analysis and so on. According to the experimental results, BHHP with hydroxyl group has better corrosion protection capacity on P110 steel in HCl than BHBP with biphenyl group, with the maximum efficiency reaching 95.67 % for BHBP, and 76.32 % for BHHP. Meanwhile, the results from quantum chemistry demonstrated that theoretically the hydroxyl spacer is superior to biphenyl spacer, which inspires the development of Gemini inhibitors.

Electrodeposited Zn-Al layered double hydroxide films for corrosion protection of aluminum alloys

This work provides a simple strategy to enhance the corrosion resistance of layered double hydroxide (Zn-Al LDH) films on AA2024 aluminum alloys by an electrodeposition method. Inhibitor anion vanadates are further intercalated into the interlayer galleries of LDHs through an ion-exchange process to improve their corrosion performance. Vanadates enhance the barrier property of the LDH films and are enriched in the corrosion sites to actively protect aluminum alloys. A literature survey shows that the electrodeposited LDH films exhibit comparable corrosion protection capacity to those prepared by the traditional hydrothermal method, although the former have the smallest thickness.

The corrosion protection afforded by a commercial rust converter doped with graphene oxide

The present work is devoted to study the effect of the Graphene Oxide (GO) addition in the corrosion protection capacity of a commercial Rust Converter (RC). These substances are designed to be applied over corroded surfaces. It is supposed that they react with rust generating a stable layer, which protects to the metallic substrate. The RC used here is a commercial product that contains gallic acid as reactive compound, which reduces the GO added to reduced-GO (r-GO).Electrochemical Impedance Spectroscopy (EIS) was used to characterize the barrier properties of RC and RC + r-GO treatments, both as in free-standing films and in supported coatings on rusted steel. The results suggest that the RC + r-GO treatment generates more stable and protective films. For the interpretation of the impedance diagrams, the semiconducting character of the film obtained from the RC + r-GO treatment was considered. The initial lower impedance values observed in these samples are related to the presence of electronic paths in parallel with the ionic paths. The impedance values remain stable during long-term immersion. On the contrary, samples coated with the RC treatment undergo a continuous impedance decrease indicating a loss of the barrier properties of the coating.

Cationic gemini-surfactants based on waste cooking oil as new ‘green’ inhibitors for N80-steel corrosion in sulphuric acid: A combined empirical and theoretical approaches

The objective of this report is to investigate the inhibition of cationic gemini-surfactants based on waste cooking, as a green source of inhibitors against acidic corrosion of N80-steel. Two Gemini cationic surfactants have been prepared based on waste frying oil with full characterization by different spectral tools (FTIR, 1H NMR and 13C NMR), and investigated as sustainable inhibitors for N80-steel corrosion in 1.0 M sulphuric acid. The activities of the prepared Gemini cationic compounds were evaluated from the surface-tension studies. The corrosion protection capacity was evaluated by utilizing electrochemical tools namely; LPR corrosion rate, electrochemical impedance-spectroscopy (EIS) and potentiodynamic-polarization (PDP) methods. The PDP findings demonstrated that these surfactants behaved as mixed-typed inhibitors. The surfactants prohibited N80-steel corrosion at a lower [inhibitor] and supplied an inhibition capacity of 96.48–97.86% in 1 × 10−3 mol/l. The protection power increased with increasing both [surfactant] and alkyl group length. The surfactants adsorb on N80-steel in the studied corrosive medium through chemisorption interactions and their adsorption followed the adsorption model of Langmuir. Surface morphology observations (FE-SEM and FTIR) suggest that the surfactant species formed a defensive layer on the N80-steel interface. The electronic properties of the prepared surfactants were examined by using DFT calculations (density functional theory). Theoretical findings are consistent with the empirical outcomes.

Application of novel sol–gel composites on magnesium alloy

Abstract Application of defect-free, adherent, and corrosion protective sol–gel film on the magnesium alloys is generally difficult. In this study, two novel sol–gel/conversion coating composites were successfully deposited on AM60B magnesium alloy in order to provide sufficient protection against the corrosion. The first composite (Ti–Zr/hybrid) was obtained via combination of a hybrid sol–gel film (synthesized by mixing tetraethoxysilane (TEOS), and 3-glycidyloxypropyl-trimethoxysilane (GPTMS)) as outer layer and Ti–Zr conversion coating as primer. Also, the second composite (Ti–Zr/PTMS) was applied in a similar manner by combination of phenyl-trimethoxysilane (PTMS) sol–gel film with the Ti–Zr conversion coating. The morphology and elemental composition of the Ti–Zr conversion film were assessed by the Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS), respectively. A cracky conversion film was applied on the alloy surface after immersion in the Ti–Zr conversion coating bath which was mainly composed of MgO, TiO2, ZrO2, and MgF2 compounds. Uniform, but not-adherent PTMS and hybrid sol–gel films (pure sol–gel films) with obvious defects were directly deposited onto the magnesium alloy without the Ti–Zr pretreatment which were morphologically characterized by the SEM. However, formation of relatively uniform and completely defect-free Ti–Zr/hybrid and Ti–Zr/PTMS composites after using the Ti–Zr conversion coating as pretreatment was revealed by the SEM observations. In addition, the defects of the Ti–Zr conversion coating were completely filled by the sol–gel layers. The Ti–Zr/PTMS and Ti–Zr/hybrid composite coatings were provided much better corrosion protection capacity than the pure PTMS and hybrid sol–gel films, respectively which was confirmed by the Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PDP) examinations in 0.05 M NaCl solution.

The Effectiveness of Some Organic Polymers As Corrosion Inhibitors for Carbon Steel and Brass in Acidic Media

Three organic polymers were studied as corrosion inhibitors for carbon steel type OLC 45 and brass in 1M H2SO4 and 1M HCl solution using potentiostatic and potentiodynamic polarization methods, electrochemical impedance spectroscopy (EIS), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and metallurgical microscopy techniques. The polymers involved in the study are three sodium polyacrylates hydrophobically modified with linear and cyclo-dodecyl and respectively, dihexyl chain. We suppose that, these polymers inhibit corrosion of metal electrodes by a protective mechanism can be owed to either the adsorption of inhibitor molecules forming a protective film or obtaining a insoluble compound and repairing the porous oxide layers. Experimental data showed that these polymers achieved a significant inhibiting action on brass and carbon steel corrosion and act that a mixed corrosion inhibitors and it could be proved by the effects of polymers on the electrochemical properties of metal electrodes. The adsorption of the polymers on the electrodes surface obeys to the Langmuir isotherm model. The temperature influence on the corrosion behaviour of the metal electrodes in 1M H2SO4 and 1M HCl with and without the inhibitor at 500 ppm was analyzed in the temperature domain from 293 to 313 K. The negative value of thermodynamic parameter like Gibbs free energy of adsorption shows the spontaneity of adsorption process. The experimental results indicated that the corrosion rate have been meaningfully reduced in inhibited solutions when in comparison with the corrosive medium and to increase of the protection effect. Moreover, characterization utilizing FT-IR confirms the adsorption of inhibitors and the constitution of corrosion products on the working electrode surface. EIS and potentiodynamic polarization results demonstrate its corrosion protection capacity. The examined polymers exhibited very good inhibition properties for OLC 45 and brass electrode in 1M H2SO4 and 1M HCl medium while the corrosion current density decreased and the inhibitor efficiency increased with increasing inhibitors concentrations.

IBA-modified gypsum-containing epoxy resin coating for rebar: corrosion performance and bonding characteristics

In this study, epoxy resin-based coating was developed for concrete reinforcement mild steel bar (rebar), and the corrosion behaviors of the uncoated rebar, single-cured epoxy resin-coated rebar, and indole butyric acid (IBA)-modified gypsum-containing epoxy resin-coated rebar were investigated in NaCl, CaCl2, and NaOH solution. Triethylene tetramine was used as curing agent for the epoxy resin, and IBA along with gypsum or silica was used in the composition of epoxy coating as inhibitor. Gypsum or silica was used separately as carrier of the IBA. Assessment was carried out on the basis of the corrosion resistance performance and bonding characteristics of the coated rebar. Corrosion resistance performance of the coating was evaluated using polarization resistance test, cathodic disbonding test, and corrosion-induced cracking study. Electrochemical tests showed that incorporation of IBA significantly improved the corrosion protection capacity of the epoxy coating against rebar corrosion. This was related to its healing effect on surface passivation against attack by a corrosive environment. In addition to corrosion protection capacity, bond strength between concrete and rebar is determined through pullout test. It was found that the coating has no adverse effect on the bond strength between embedded rebar and concrete, and additionally, it contributes to the bond strength due to adhesion properties of the resin.

Synergetic Properties of Some Polymers with Antiscaling and Anticorrosive Action for Industrial Cooling Water Systems Protection

In this study, to examine synergistic effect of various combinations of the following polymers: PSO-1 (an oligomer phosphinosuccinic in neutralized state) and PMA-M1 (mixture by weight ratio 1/1 from 2-phosphonobutane-1-2, 4 tricarboxilic acid with polymaleic acid) were investigated as corrosion inhibitors for carbon steel of type OL 37, OLC 45 and for copper and brass. Using the microwaves energy, new polymers with antiscaling and anticorrosive properties were synthesized in microwaves field. These new polymers were obtained by radical polymerization of acrylic and/or acrylsulfonate water-soluble monomers in presence of microwaves field chain transfer agents, under the action of peroxidic initiators. The inhibitive properties of these organic compounds were analyzed by electrochemical measurements, FT-IR spectroscopy and by scanning electron microscopy (SEM) of the electrode surface. Also, a variety of short-time corrosion tests on laboratory scale were used to determine the performance and application parameters under different environmental conditions. The metallographic micrographies and scanning electron microscopy made before and after the potentiodynamic polarizations pointed out the evolution of the corrosion process. The inhibition activity analysis of the organic compounds was made by assuming that, the mechanism of inhibition by organic molecules is chemisorption and that the energetic of the corrosion process per se is unaffected by the addition of substituients on the parent compound. We presume that, these organic compounds inhibit corrosion of these materials by a protective mechanism, forming insoluble complexes and repairing the porous oxide layer. The addition of these new organic polymers offers protection by forming an adsorption organic barrier film at the electrode surface. The corrosion parameters obtained from polarization curves and from EIS spectra are in good concordance and point out the inhibitory action of these new organic polymers. The addition of the organic inhibitors led in all the cases to inhibition of the corrosion rate. The organic compounds used are adsorbed on the electrode surface according to a Langmuir isotherm. The inhibition process was attributed to the formation of the adsorbed film on the metal surface that protects the metal against corrosive agents. The EIS measurements have confirmed this protection and pointed out the formation of adsorption layers on the electrode surface The negative value of thermodynamic parameter like Gibbs free energy of adsorption indicates the spontaneity of adsorption process. Moreover, characterization utilizing FT-IR confirms the adsorption of inhibitors and the constitution of corrosion products on the materials surface. EIS and potentiodynamic polarization results demonstrate its corrosion protection capacity

Electrochemical noise analysis to examine the corrosion behavior of Ni-P deposit on AM60B alloy plated by Zr pretreatment

Electroless Ni-P coating was applied on AM60B magnesium alloy using eco-friendly zirconium pretreatment. Firstly, the alloy surface was entirely covered by a network-like cracked Zr conversion film after appropriate pretreatment time which was determined by Continuous Noise Resistance Calculation (CNRC). Energy Dispersive X-ray Spectroscopy (EDS) was used to elemental analysis of the conversion coating. Next, the pretreated surface was plated by dense, pore-free, and uniform electroless Ni-P coating with fine cauliflower-like nodules. Elemental analysis revealed that Ni-P coating has moderate amount of phosphorus corresponding to a mixed crystalline-amorphous structure which was confirmed by X-ray Diffraction (XRD). CNRC technique was also used to analyze corrosion protection capacity of the electroless layer in acidified 3.5 wt% NaCl solution. Variation of noise resistance versus time for the bare and Ni-P coating revealed that the corrosion resistance remarkably improved by the electroless plating. The noise resistance was initially decreased because of slow diffusion of the corrosive species into intergranular spaces and then increased due to the filling of the solution pathways by corrosion products. Finally, the noise resistance continuously decreased as a result of corrosion products dissolution. There was no numerical agreement between the results of EIS and CNRC techniques due to localization of the corrosion which was confirmed by SEM. Also, Continuous Localization Index (CLI) was utilized to show the localization of the corrosion in Ni-P/Mg system. Microhardness and adhesion of the obtained coating were also evaluated.

PTMS/OH-MWCNT sol-gel nanocomposite for corrosion protection of magnesium alloy

In this work, hydroxylated Multi-Walled Carbon Nanotubes (OH-MWCNTs) were embedded in phenyl-trimethoxysilane (PTMS) sol-gel coating at different concentrations to improve the corrosion protection capacity. The obtained nanocomposites (PTMS/OH-MWCNT) were applied on AM60B magnesium alloy for effective corrosion protection. Chemical interaction between OH-MWCNTs and PTMS silane matrix was confirmed by FTIR. The SEM images were revealed that a uniform but cracked sol-gel coating was obtained without incorporation of OH-MWCNTs. Also, uniform sol-gel nanocomposites without any micro-cracks were achieved when various concentrations of OH-MWCNT (200, 500, and 1000ppm) were embedded in the silica film. Both the pure and nanocomposite coatings showed suitable adhesion to the substrate and thickness of the pure coating (1.4–1.5μm) was not changed significantly by incorporation of OH-MWCNTs. The average roughness of the pure PTMS film was about 0.2nm and was increased to 0.5nm by incorporation of OH-MWCNTs at 200ppm concentration. However, the surface roughness was decreased by further increasing the carbon nanotube content in the sol-gel coating probably due to formation of more compact silica film. Corrosion resistance of the magnesium alloy in Harrison's corrosive electrolyte was significantly increased after application of PTMS coating which was ascribed to barrier properties of the film along with hydrophobic nature of the phenyl group. Also, the corrosion resistance of PTMS sol-gel film was considerably promoted after incorporation of OH-MWCNTs at 500ppm concentration which was attributed to the chemical interaction between incorporated OH-MWCNTs and silane matrix, filling of the defects of coating by the carbon nanotubes, and also formation of longer tortuous pathways for the corrosive species. The water contact angle on the pure sol-gel coating was increased from about 86.95 to 94.65° by incorporating 500ppm of OH-MWCNTs indicating considerable improvement in the hydrophobic property.

Duplex Ni-Zn-Cu-P/Ni-P electroless coating on magnesium alloy via maleic acid pretreatment

In this work, the duplex Ni-Zn-Cu-P/Ni-P electroless coating was applied on the AM60B magnesium alloy via new maleic acid pretreatment for potential applications in automobile industry. Also, the binary Ni-P coating was applied using the same pretreatment in order to compare the results. Scanning Electron Microscopy (SEM) images revealed that a cracked conversion film was created on the AM60B alloy after pretreatment in maleic acid solution. The binary Ni-P and duplex Ni-Zn-Cu-P/Ni-P electroless coatings with cauliflower-like micromorphology were successfully applied on the alloy surface after the maleic acid pretreatment. The duplex coating showed more regular and compact surface morphology as compared to the binary coating. The thickness of the electroless coatings were estimated by the cross-sectional SEM images which revealed that the inhibitory action of Zn2+ ions on the plating rate was fully compensated by the addition of Cu2+ ions. The microstructure and elemental composition of the electroless coatings were assessed by the X-ray Diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDS), respectively. The binary coating demonstrated semi-amorphous microstructure while the duplex coating showed almost fully amorphous structure due to its high phosphorus (10.25wt%) and considerable zinc (7.55wt%) contents. Large ennoblement of the corrosion potential after application of the electroless coatings was revealed by Potentiodynamic Polarization (PDP) experiments in 3.5wt% NaCl solution. Also, the corrosion current density of the bare alloy was significantly diminished after the electroless plating. The duplex coating showed relatively better corrosion protection capacity than the binary coating. The results of the PDP tests were confirmed by Electrochemical Impedance Spectroscopy (EIS) experiments in the same corrosive media. The micro-hardness of the bare alloy was remarkably increased after application of both the binary and duplex electroless coatings. The duplex coating showed relatively higher micro-hardness as compared to the binary coating due to the gain refinement. The applied electroless coatings were adherent which was revealed by the thermal shock and pull-off tests.