One‐step immersion method for fabricating superhydrophobic aluminum alloy with excellent corrosion resistance

This work develops a facile one‐step immersion method for preparing the superhydrophobic aluminum alloy, i.e. the aluminum alloy is treated with stearic acid (STA)–ethanol–H₂O solution at 60 °C for 35 h. Results show that the aluminum alloy achieves flower‐like structure with both a great deal of pillars and pores, while the long hydrophobic alkyl chains are chemically grafted onto the hierarchical surface. Meanwhile, the water contact angle at the aluminum alloy surface gradually enhances with the decrease of the ethanol–H₂O volume ratio, and the water contact angle and rolling angle of 156.2° and 5°, respectively, are obtained when the ethanol–H₂O volume ratio is 1:3. Moreover, results show that the higher water contact angle at the aluminum alloy, the better corrosion resistance of the aluminum alloy. Consequently, the aluminum alloy with the superhydrophobic property has the best corrosion resistance, durability, and stability in corrosive environments. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of TiO2–Ti and TiO2–TiN composite coatings on corrosion behavior of NiTi alloy

Two kinds of biocompatible coatings were produced in order to improve the corrosion resistance of nickel titanium (NiTi) alloy. A titanium oxide–titanium (TiO₂–Ti) composite was coated on NiTi alloy using electrophoretic method. After the coating process, the samples were heat‐treated at 1000 °C in two tube furnaces, the first one in argon atmosphere and the second one in nitrogen atmosphere at 1000 °C. The morphology and phase analysis of coatings were investigated using scanning electron microscopy and X‐ray diffraction analysis, respectively. The electrochemical behavior of the NiTi and coated samples was examined using polarization and electrochemical impedance spectroscopy tests. Electrochemical tests in simulated body fluid demonstrated a considerable increase in corrosion resistance of composite‐coated NiTi specimens compared to the non‐coated one. The heat‐treated composite coating sample in nitrogen atmosphere had a higher level of corrosion resistance compared to the heat‐treated sample in argon atmosphere, which is mainly due to having nitride phases. Copyright © 2014 John Wiley & Sons, Ltd.     

Pitting Corrosion Mechanisms and Characteristics of Aluminum in Solar Heating Systems

The complex characteristics and mechanisms of aluminum pitting corrosion in a solar heating system were studied by the chemical immersion method and electrochemical techniques as well as fractal theory. The results showed that pitting corrosion of Al occurred in a tap water environment due to the local enrichment of Cl^? ions. The higher the Cl^? ions concentration, the more negative the critical pitting potential (E_b) of Al. A linear relationship between E_b and the logarithm of Cl^? ions concentration was observed. The pitting corrosion mechanism of Al in neutral water was explained in terms of complexation corrosion theory. The corrosion surface images of aluminum immersed in tap water were captured and analyzed by image processing technique and box‐dimension method. The fractal characteristics of pit distribution, described by fractal dimension, have been identified. The fractal dimension of the pit distribution increased with the increase of immersion time and had the same trend as that of the weight loss. Fractal dimension can, thus, be used as an important parameter for quantitative evaluation of pitting corrosion of aluminum.     

Micro‐arc oxidation and electrophoretic deposition of nano‐grain merwinite (Ca3MgSi2O8) surface coating on magnesium alloy as biodegradable metallic implant

Magnesium alloys are promising biomaterials as biodegradable implant for orthopedic applications. However, their low corrosion resistance and poor bioactivity have prohibited their implant applications. In order to enhance these two properties, a nano‐grain merwinite coating was prepared on magnesium alloy. Its corrosion and the bioactivity behavior were characterized with electrochemical and immersion tests. The results showed that the nano‐grain merwinite coating can improve both the corrosion resistance and the bioactivity of the magnesium alloy making it an appropriate material for biodegradable bone implants. Copyright © 2014 John Wiley & Sons, Ltd.     

Effectiveness of 2‐mercaptobenzothiazole, 8‐hydroxyquinoline and benzotriazole as corrosion inhibitors on AA 2024‐T3 assessed by electrochemical methods

In this study, the effectiveness of 2‐mercaptobenzothiazole (2‐MBT), 8‐hydroxyquinoline and benzotriazole as corrosion inhibitors for AA 2024‐T3 aluminium alloy was evaluated. The corrosion behaviour in the presence of each compound was investigated by image‐assisted electrochemical noise analysis, electrochemical impedance spectroscopy, potentiodynamic polarization and the split cell technique. It was found that 2‐MBT has superior inhibition properties compared with the other inhibitors. In particular, the specimens immersed in 3.5% NaCl in the presence of 2‐MBT displayed high values of noise resistance that were maintained for over 400 h of testing, and high values of low‐frequency impedance, measured after immersion for 24 h. The split cell technique and potentiodynamic polarization tests indicated that only 2‐MBT decreases significantly both the anodic and the cathodic reaction rates. Scanning electron microscopy observations and energy dispersive X‐ray measurements complement the findings from electrochemical measurements indicating that only 2‐MBT protects the second phase particles, preventing dealloying, trenching and initiation of corrosion. © 2015 The Authors. Surface and Interface Analysis published by John Wiley & Sons Ltd.     

Electrochemical properties and corrosion inhibition of AA6061 in tropical seawater

The corrosion inhibition of aluminum and its alloys is the subject of tremendous technological importance due to the increased industrial applications of these materials. This study reports the results of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) on the corrosion inhibition of AA6061 aluminum alloys in seawater using sodium benzoate as an inhibitor. The electrochemical measurements for aluminum alloys in seawater after varied immersion period showed that the presence of sodium benzoate significantly decreases the corrosion currents densities (i_corr), corrosion rates and double layer capacitance (C_dl), as simultaneously increase the values of polarization resistance (R_p). Charge transfer process and development of thin film on the specimen have been proven by morphology study using SEM.     

The electrochemical corrosion of bulk nanocrystalline ingot iron in acidic sulfate solution

The corrosion properties of bulk nanocrystalline ingot iron (BNII) fabricated from conventional polycrystalline ingot iron (CPII) by severe rolling were investigated by means of immersion test, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) tests, and scanning electron microscopy (SEM) observation. These experimental results indicate that BNII possesses excellent corrosion resistance in comparison with CPII in acidic sulfate solution at room temperature. It may mainly result from different surface microstructures between CPII and BNII. However, the corrosion resistance of nanocrystalline materials is usually degraded because of their metastable microstructure nature, and the residual stress in nanocrystalline materials also can result in degradation of corrosion resistance according to the traditional point of view.     

Use of rare earth metal salt solutions for corrosion protection of aluminum alloys and mild steel

The rare earth metal salt (REMS) compounds which are non-toxic and inexpensive have been used successfully for the corrosion protection of commercial aluminum alloys as well as of mild steel. The resistance to localized corrosion of aluminum alloys such as Al 2024, Al 6061 and Al 7075 has been greatly improved by immersion in hot cerium salt solutions. Cerium oxides/hydroxides were formed at sites where intermetallic compounds containing copper were located and eliminated the formation of local cathodes. REMS solutions were also used for sealing of anodized layer on Al alloys replacing toxic chromates. In addition to increased corrosion resistance excellent paint adhesion was observed. Cerium nitrate and yttrium sulfate solutions produced the most satisfactory results. Cerium salts were also applied successfully as inhibitors and as pretreatment for the corrosion protection of carbon steel in hot NH₃/water solutions used in absorption heat pumps. Factorial design experiments have been used to determine the optimum concentrations of CeCl₃ and H₂O₂ as well as the treatment time used in the cerating process for mild steel. The corrosion protection provided by the cerated layer was further improved by cathodic polarization in cerium chloride. A dual corrosion protection strategy employing cerating and addition of a REMS to the working solution is expected to provide long-lasting corrosion protection of mild steel. Dedicated to the ninetieth anniversary of Ya.M. Kolotyrkin’s birth. This article was submitted by the author in English.     

铈、锂盐对铝阳极氧化膜的协同封闭作用

研究了铈、锂盐在铝阳极氧化膜封闭处理中的协同作用.场发射扫描电镜和X射线衍射谱对铈、锂盐协同封闭前后铝阳极氧化膜形貌和结构的研究结果表明，封闭后膜表面的孔洞消失，封闭产物分布均匀，封闭后膜仍然以非晶态形式存在.根据X射线光电子能谱的结果，封闭后的膜主要由含结晶水的Al2O3及铈、锂的混合氢氧化物组成，同时膜中还含有及封闭溶液组分中的一些阴离子.电化学阻抗谱的研究结果表明铈、锂盐协同封闭能够显著提高膜的耐蚀性能.在实验结果基础上，初步认为铈、锂盐封闭是通过生成结构紧密的封闭产物填充、覆盖膜孔，从而显著提高铝阳极氧化膜的耐蚀性能.     

Effect of processing parameters on the corrosion behaviour of friction stir processed AA 2219 aluminum alloy

The effect of processing parameters (rotation speed and traverse speed) on the corrosion behaviour of friction stir processed high strength precipitation hardenable AA 2219-T87 alloy was investigated. The results indicate that the rotation speed has a major influence in determining the rate of corrosion, which is attributed to the breaking down and dissolution of the intermetallic particles. Corrosion resistance of friction stir processed alloy was studied by potentiodynamic polarization, electrochemical impedance spectroscopy, salt spray and immersion tests.     

5083铝合金在海水中的腐蚀电化学行为及活性氯影响研究

采用动电位极化、循环极化和全浸腐蚀试验方法,研究了5083铝合金在静止海水中的腐蚀电化学性能以及活性氯的影响.结果表明,在本文设置的防污活性氯浓度范围(0.2～0.5mg/L)内,活性氯对铝合金的阴极和阳极电化学极化以及腐蚀行为没有明显影响,并可提高铝合金的耐点蚀能力,海水的pH值对铝合金的腐蚀具有显著的影响.该研究为海水中5083铝合金的防腐防污提供了依据.     

hytic Acid Conversion Coatings of Magnesium

A chrome‐free conversion coating treatment for magnesium by phytic acid solution was developed. The immersion experiments were used for evaluating the effects of the processing parameters (such as conversion temperature and time, concentration and pH value of phytic acid solution) on the corrosion resistance of the phytic acid conversion coating. The morphologies and compositions of the coatings were determined by SEM and EDS respectively. The experimental results indicated that the corrosion resistance of the conversion coating formed in the solution containing 0.5% phytic acid at 25°C and pH=4 for 30 min was higher than that of natural oxide, and the conversion coating formed on the surface of magnesium was of multilayer mainly consisting of Mg, C, O and P. The thicknesses of the conversion coatings were approximately 1.0–15 µm and the conversion coatings presented obvious network‐like cracks. The electrochemical potentiodynamic polarization experiment indicated that the free corrosion potential of the magnesium with phytic acid conversion coating was increased, and its corrosion current and corrosion rate declined in 3.5% NaCl solution. Phytic acid conversion coating could improve the electrochemical property of magnesium and provide effective protection, which can improve the corrosion resistance of magnesium.     

Superhydrophobic ceria on aluminum and its corrosion resistance

Superhydrophobic ceria on the aluminum substrate was fabricated, and its corrosion resistance was investigated by different techniques. For example, the so‐obtained superhydrophobic sample was immersed into the NaCl aqueous solution, and the variations in the surface wettability as well as the surface morphology were monitored; potentiodynamic polarization in the NaCl aqueous solution was adopted to evaluate its electrochemical corrosion resistance; a droplet of the aqueous solution HCl was dripped onto the superhydrophobic surface, and the corrosion process as well as the surface morphology after corrosion was monitored. The experimental results showed that the superhydrophobic ceria possessed a good corrosion resistance because of the entrapped air in the solid/liquid interface. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation and electrochemical corrosion behavior of bulk nanocrystalline ingot iron in HCl acid solution

Bulk nanocrystalline ingot iron (BNII) was produced by the severe rolling technique. The corrosion behaviors of BNII and as-received conventional polycrystalline ingot iron (CPII) in 1 M HCl solution were investigated by potentiodynamic polarization tests, electrochemical impedance spectroscopy measurement, and immersion tests at room temperature. For BNII, the anodic dissolution process is inhibited, but the cathodic process is enhanced. The corrosion current and average corrosion rate of BNII are 0.479 and 0.391 those of CPII, respectively. The resistance of the charge transfer of BNII is about 1.59 times higher than that of CPII. These results indicate that the corrosion resistance of BNII is improved in comparison with CPII.     

Dissolved carbon dioxide effect on the behavior of carbon steel in a simulated solution at different temperatures and immersion times

Dissolved carbon dioxide effect on the behavior of carbon steel (0.4%carbon), in a simulated solution at different temperatures and immersion times, has been investigated using different techniques as potentiodynamic polarization, linear polarization resistance, and electrochemical impedance spectroscopy. The observation of the steel surface was done by scanning electron microscopy. All measurements reveal that the corrosion resistance is strongly dependent on both the temperature and immersion times. The corrosion resistance of carbon steel decreases in the solution considered as the temperature increases from 20?°C to 50?°C. Potentiodynamic polarization curves showed that cathodic and anodic current densities increase with the increased temperature. Besides, the study concluded that the addition of CO₂ gas to the simulated solution affects negatively the corrosion resistance in one hand and that, on the other hand, the higher the time of immersion the higher is the resistance to corrosion.     

Durability of aluminum cooling system in electric power plants

The final step in gas turbine electric power production plants is the cooling of water after the turbine expansion. In some thermal plants, the temperature reduction of the recycling fluid is partially obtained by heat exchanging with the atmosphere by passing the fluid through huge aluminum heat exchangers. From the corrosion point of view, most critical is the starting step of the power plant, when the aluminum cooling system comes in contact with water for the first time and reaches a surface condition in dynamic equilibrium with the liquid. This paper describes a systematic study of aluminum surface evolution in the cooling system of an electric power plant during the first weeks of operation. Some aluminum samples were placed inside the cooling system in significant locations and removed after scheduled times. The surface conditions of the samples were characterized using surface analyses, electrochemical techniques and microscopic observations. At the same time, the chemical conditions of the recycling fluids were monitored. The obtained results describe the corrosion resistance of the aluminum surface as a function of the conditioning time, proving the growth of a partially protective layer able to produce corrosion decrease during the service time of the energy production plant. Copyright © 2009 John Wiley & Sons, Ltd.     

One‐step electrochemical deposition to achieve superhydrophobic cobalt incorporated amorphous carbon‐based film with self‐cleaning and anti‐corrosion

Exploiting a superhydrophobic surface is very significant due to its excellent water repellency which has many practical applications in various fields. In this work, the cobalt incorporated amorphous carbon‐based (Co/a‐C:H) film was prepared successfully on Si substrate via a simple 1‐step electrochemical deposition where electrochemical deposition technology was using cobalt (II) acetylacetonate methanol solution as electrolyte under high voltage, atmospheric pressure, and low temperature. Surprisingly, the as‐prepared film showed a superior superhydrophobic surface with a water contact angle of 153 ± 1° and a sliding angle of 7.6° without any further modification of low surface energy materials. Especially, the tape adhesive, corrosion resistance, and self‐cleaning tests demonstrated that the as‐prepared carbon‐based film could possess fairly well adhesion, superior anti‐corrosion resistance, and self‐cleaning ability, respectively. It indicated that the superhydrophobic Co/a‐C:H film might have potential promising applications in the field of anti‐fouling, anti‐corrosion, and drag resistance, such as the above‐deck structures on icebreaker vessels, ship hulls, and offshore wind turbine blades.     

Relationships between microstructure and pitting corrosion of ADI in sodium chloride solution

Austempered ductile iron (ADI) has complex microstructure containing a multiphase matrix (called ‘ausferrite’), graphite spheres and oxide inclusions. The corrosion resistance of ADI is related to its microstructure which is determined by heat treatment parameters (like austempering temperature, austempering time, austenitising temperature and austenitising time). In the present paper, the electrochemical behaviour and corrosion resistance of ADI have been investigated by means of the electrochemical microcell technique and classical electrochemical measurements in sodium chloride solution. Particular attention has been paid to the influence of austempering temperature on the microstructure and pitting corrosion. It has been shown that ADI austempered at 430 °C has upper ausferritic microstructure and reveals a better corrosion resistance in sodium chloride solution than ADI austempered at 280 °C. Moreover, the corrosion resistance increases as the volume fracture of ferrite increases and the carbon content of austenite decreases. The good corrosion behaviour of ADI austempered at 430 °C was also related to the good coarsening of the austenite grains and broad ferrite needles (less ferrite/austenite interfaces). It has been demonstrated that silicon is the alloying element hindering the anodic dissolution of the alloy.     

Electrochemical testing practices of environmentally friendly aerospace coatings for corrosion performance assessment

Hexavalent chromium has been successfully employed for corrosion protection purposes in aerospace coatings for decades. However, legislation will restrict the use of Cr⁶⁺ in the future and therefore the aerospace sector needs to identify alternative environmentally friendly coatings for corrosion protection. Before implementation of newly developed systems into actual components is possible, rigorous and time-consuming testing practices are required to ensure the new systems can achieve the strict aerospace standards requirements. The emerging number of coating systems being developed, and the vast research conducted on the subject worldwide, make the selection of suitable replacements for industrial application challenging. In this work, differently pretreated aluminium AA2024 alloy surfaces are coated with conventional Cr⁶⁺ containing coating and compared with a number of industrial alternative coatings. Corrosion performance is assessed by real-time imaging while immersed, by electrochemical impedance spectroscopy (EIS), and by standardised salt-spray testing (SST). Results reveal that the performance ranking acquired by SST can be readily replaced by short-term immersion tests, and the time to failure in SST can be estimated from key corrosion indicators arising from EIS measurements at specific immersion times.     

Corrosion inhibition of carbon steel immersed in a 1 M HCl solution using benzothiazole derivatives

Corrosion inhibition effect of 2-mercaptobenzothiazole (MBT) and 2-aminobenzothiazole (ABT) compounds on ST-37 carbon steel in 1 M hydrochloric acid solution was investigated by electrochemical impedance spectroscopy (EIS), and it was observed that both of these compounds have corrosion inhibition effect on carbon steel. Evaluation of electrochemical behavior in test solutions showed that by increasing the immersion time from 15 to 300 min, corrosion resistance of samples is increased and at the same immersion time MBT has a better corrosion inhibition in comparison to ABT. AFM technique was performed for MBT and ABT. The results of calculations showed superior inhibition efficiency of MBT in comparison to ABT. This can cause easier protonation and consequently adsorption on the metal surface occurs.