Electrochemical Polarization Tests Research Articles

Microstructure refinement, mechanical performances and degradability of biomedical Zn-2Cu alloy by ultrasonic melting and homogenization treatment

Zn alloys are deemed to be desired body implant materials because of their moderate degradation rate. In this paper, the microstructural evolution, mechanical performances, and degradability of Zn-2Cu alloy prepared by ultrasonic melt treatment (UMT) with different ultrasonic powers (0 W, 300 W, 600 W, and 900 W) were systematically studied. Under the condition of UMT, the coarse α-Zn grains of Zn-2Cu alloy were refined into fine equiaxed grains and the mean size was significantly decreased from 133.4 μm to 65.3 μm when the ultrasound power was enhanced. The precipitating CuZn5 phase was significantly refined from the coarse block into the spherical shape. Moreover, the fraction of the CuZn5 precipitates of the Zn-2Cu alloy was greatly reduced with the increase of ultrasonic power. Tensile tests showed that the ultimate tensile strength (UTS), yield strength (YS), and elongation (El) of Zn-2Cu alloy were remarkably enhanced to 203 MPa, 167 MPa, and 8.14 %, respectively, when the Zn-2Cu alloy melting was treated by 600 W power. It was found by electrochemical polarization test that the degradation rate of Zn-2Cu alloy treated by UMT with 0 W, 300 W, 600 W, and 900 W power in Hank’s solution was gradually decreased to 1.6312 mm/a, 1.3206 mm/a, 1.0992 mm/a, and 1.2832 mm/a, respectively. In addition, after the Zn-2Cu alloys were immersed in Hank’s solution for 30 days, the degradation rate of samples was summarized as 0 W alloy (0.472 mm/a) > 300 W alloy (0.436 mm/a) > 900 W alloy (0.412 mm/a) > 600 W alloy (0.398 mm/a). The studies verified that the UMT was a very valuable technology for preparing Zn-2Cu alloy, which can meet the requirement of mechanical properties and degradable rate as a promising implant material.

Enhancement of PEO-coated ZK60 Mg alloy: Curcumin-enriched mesoporous silica and PLA/bioglass for antibacterial properties, bioactivity and biocorrosion resistance

The corrosion resistance and antibacterial properties of ZK60 magnesium alloy implants have been enhanced via Plasma Electrolytic Oxidation (PEO) and electrospinning techniques. A robust, porous oxide coating was created on the ZK60 alloy using the PEO process, with characterization performed via SEM and XRD. Improved corrosion resistance of the PEO-coated samples was demonstrated through electrochemical analyses, including EIS and polarization tests. In addition to the PEO treatment, composite electrospun nanofibrous coatings were developed, incorporating curcumin-loaded mesoporous silica nanoparticles and bioactive glass. The electrospun nanofibers, which exhibited a diameter of 350 nm without beads, were characterized by Dynamic Light Scattering, Zeta Potential, Infrared Spectroscopy, BET, and XRD, confirming a curcumin loading of 10 wt%. Significant antibacterial activity against Escherichia coli and Staphylococcus aureus was shown by these fibers, and high bioactivity was observed after 14 days of immersion in simulated body fluid (SBF). The combination of PEO coatings and electrospun nanofibers highlights an enhancement in both corrosion resistance and antibacterial properties for implant applications.

Formation and properties of nitrided layer on 2205 duplex stainless steel by anodic plasma-nitriding assisted with hollow cathode discharge

2205 duplex stainless steel (2205DSS) was nitrided at 420 °C by plasma nitriding in an ammonia atmosphere under anodic potential. The nitrided layer was characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The impact of the nitrided layer on the corrosion and wear resistance of 2205DSS was evaluated through electrochemical polarization tests and pin-on-disc wear experiments. The results revealed that nitrogen-expanded austenite was formed on the substrate, and the nitrided layer developed on the samples nitrided for 4 and 10 h enhanced both the corrosion and wear resistance of 2205DSS.

Investigation of date seed powder as green corrosion inhibitor for mild steel: A study of solution and coating phases

Herein, firstly, sodium montmorillonite (Na+-MMT) was modified with date seed (DS) powder, and then the anti-corrosion properties of new nanoparticles (DS-MMT) were evaluated on mild steel (MS) in the saline solution phase. Next, DS-MMT was added to epoxy (EP), and their nanocomposite was prepared. Electrochemical impedance spectroscopy (EIS), polarization, and salt spray tests showed that DS-MMT improved corrosion resistance. According to the results of EIS, the coating resistance (Rc) of EP/3 % DS-MMT after 24 days of immersion was 2473 MΩ cm2, while this value was 7.9 MΩ cm2 for EP. Also, the visual observation test showed that after 24 h, the entire surface of the blank sample was filled with rust and corrosion products, but no evidence of corrosion products was observed in the DS-MMT sample. Moreover, the antimicrobial results showed that EP/3 % DS-MMT is inhibitory and killing against Bacillus subtilis and Staphylococcus aureus.

Simultaneously Regulating Electrochemical Corrosion Behavior and Wettability of Magnesium-Neodymium Alloy by Self-Layered Chemical Conversion Coating.

Rapid corrosion in aqueous solutions of magnesium alloys is one of the major obstacles to their wide application, and coating plays a crucial role in their corrosion protection. Recently, protection- and function-integrated coatings have attracted much attention in the research field of magnesium alloys. In this work, a simple chemical conversion process is proposed to fabricate a composite coating on a magnesium-neodymium alloy through immersion in an aqueous solution made of Ca(OH)2 and NaHCO3. After the immersion process, a coating consisting of two spontaneously formed layers is acquired. The top flower-like layer is composed of Mg5(OH)2(CO3)4∙4H2O, Mg(OH)2 and CaCO3, and the inner dense layer is speculated to be Mg(OH)2. Electrochemical impedance spectroscopy, polarization tests, and hydrogen evolution are combined to evaluate the corrosion resistance in simulated body fluid, simulated seawater solution, and simulated concrete pore solution, which reveals that the coated sample has better corrosion resistance than the uncoated one. After the coated sample is modified with fluorinated silane, a water-repellent surface can be achieved with an average water contact angle of 151.74° and a sliding angle of about 4°. Therefore, our results indicate that effective corrosion protection and potential self-cleaning ability have been integrated on the surface of the magnesium alloy in this study. In addition, the formation mechanism of the self-layered coating is discussed from the viewpoint of the interaction between the substrate and its external solution.

Impact of Cu and Ce on the electrochemical, antibacterial, and wear properties of 316 L stainless steel: Insights for biomedical applications

This study provides a comprehensive investigation of the tribological, electrochemical, and antibacterial characteristics of austenitic stainless steel, type 316 L, doped with Ce and Cu. The samples were doped with varying concentrations of Ce (0.5, 1.5, and 3 wt%) and Cu (1.5, 2.5, and 3.5 wt%). The initial measurements focused on determining the final density values of each sample. Subsequently, friction wear tests were conducted under both dry and wet conditions, shedding light on the wear resistance of the materials. In addition, electrochemical polarization tests were employed to assess the influence of Ce and Cu on the corrosion resistance of AISI 316 L. Furthermore, antibacterial assessments were conducted against bacterial cultures of Staphylococcus aureus (ATCC 29213) and Escherichia coli (ATCC 25922). The findings of this study illuminate several noteworthy outcomes. Namely, the results showed that all Ce and Cu-doped samples exhibited an increase in final density values when compared with the as-received AISI 316 L. The wear test results revealed that samples doped with 0.5 wt% Ce and 2.5 wt% Cu exhibited the highest wear resistance, in both dry and wet environments. Polarization curve analysis indicated that Ce was more effective in enhancing the corrosion resistance of AISI 316 L than Cu. Notably, Ce and Cu modifications endowed the material with antibacterial properties, effectively inhibiting bacterial growth in both S. aureus and E. coli cultures. In summary, this study demonstrates that the addition of even trace amounts of Ce and Cu to AISI 316 L leads to noticeable improvements in the material's tribological, electrochemical, and antibacterial performance, underscoring its potential for diverse biomedical applications. The enhanced mechanical strength, corrosion resistance, and antibacterial activity make the doped material promising for use in various medical devices, implants, and other biomedical applications.

Influence of Al addition on microstructure and electrochemical behaviour of CrMnFeCoNi high-entropy alloy

To develop new corrosion-resistant materials for structural applications, CrMnFeCoNiAlx high-entropy alloys (HEAs) are produced via semi-industrial induction casting. The study aimed to investigate the influence of Al content (x = 0–0.3) on both microstructure evolution and corrosion properties of the alloys. X-ray diffraction and scanning electron microscopy (SEM) analysis revealed that all the alloys exhibited a single-phase face-centered cubic structure, with dendritic (Fe, Co, Cr-rich) and interdendritic (Mn, Ni, Al-rich) regions distinguished by elemental segregations. Furthermore, the incorporation of Al atoms into the solid solution led to an increase in the lattice parameter, indicating alloy strengthening. The corrosion resistance of the CrMnFeCoNiAlx alloy improved with higher Al addition. Electrochemical polarisation tests demonstrated a slight increase in the corrosion potential (Ecorr) and a significant decrease in the corrosion current density (icorr) upon Al addition. Additionally, slower kinetics for pit nucleation (higher E'corr) were observed, particularly notable for x = 0.3. Analysis of the corroded surfaces revealed a mixed degradation mechanism, involving pitting corrosion and selective dissolution of the interdendritic zone, which decreased as the Al content of the HEA increased. These findings underscore the effectiveness of Al addition in not only enhancing the mechanical properties of the Cantor alloy through solid solution strengthening, but also improving its corrosion resistance.

Enhancing mechanical strength, tribological properties, cytocompatibility, osteogenic differentiation, and antibacterial capacity of biodegradable Zn-5RE (RE = Nd, Y, and Ho) alloys for potential bone-implant application

Degradable zinc (Zn) based metals exhibit great promise as potential load-bearing bone-implant materials due to their suitable biodegradability, good fabricate-friendliness, biocompatibility, and favorable osteogenesis-promoting capacity. Nevertheless, most as-cast Zn-based metals display poor mechanical properties due to their coarse grain size and few slip systems, which is challenging to meet bone-implant application requirements. Herein, the alloying using rare earth (RE) elements of neodymium (Nd), yttrium (Y), and holmium (Ho) combined with hot-rolling was used to prepare the hot-rolled (HR) Zn-5RE binary alloys for load-bearing bone fixation or bone repair applications. HR Zn–5Y sample demonstrated the best mechanical properties matching with an ultimate tensile strength of ∼260 MPa, yield strength of ∼200 MPa, elongation of ∼43.5%, strength-elongation product of ∼11.3 GPa%, and macro-hardness of ∼104.7 HB among the HR samples, close to the requirements of mechanical properties for degradable bone-implant materials. HR Zn–5Y sample exhibited the lowest corrosion rate of ∼178 μm/y measured by electrochemical polarization testing, the degradation rate of ∼29 μm/y measured by static immersion testing, and high tribological properties in Hanks’ solution. The diluted Zn–5Y extract showed an appropriate cytocompatibility to 3T3 and MG-63 cells and moderate osteogenic differentiation ability to 3T3 cells among HR Zn-5RE and pure Zn extracts. Meanwhile, the HR Zn–5Y sample showed a suitable and effective antibacterial capacity against S. aureus and E. coli. Overall, the HR Zn–5Y sample is a promising moderate load-bearing bone-implant material for bone pins, plates, and guiding bone regeneration membrane application.

Surface Modification of Ti-6Al-4V Alloy by Polycaprolactone-Graphene Oxide Composite Coating

In this research, Polycaprolactone-graphene oxide Nanocomposite coating was synthesized and characterized by Electrospinning on Ti6AL4V alloy. In order to create a uniform coating with optimal thickness, the effective parameters of Electrospinning coating, including solvent, polymer concentration, and bioceramic percentage, were investigated. Also, the cytotoxicity and corrosion tests were evaluated by the electrochemical polarization test method of the created coating in comparisons and different percentages. In order to characterize the coating, a test such as a scanning electron microscope was used. The results showed that as much as the amount of Graphene oxide is increased, the diameter of Nanofibers decreases. The diameter of Polycaprolactone Nanofibers was 1.3 micrometers, which increases to 56.0 micrometers by adding Graphene oxide. The results of the corrosion test showed that the use of Nano composite coating increased the corrosion resistance to the size of the coating. The nanocomposite coating consists of polycaprolactone nanofibers and graphene oxide, which mimics the behavior of the extracellular matrix and improves the biological and antibacterial behavior of the titanium surface. So far, there has been no report on the creation of this fibrous nanocomposite coating on titanium. The results of the cytotoxicity test showed that the use of Nanocomposite coating has effectively reduced the cytotoxicity on the scaffolds. By creating a polycaprolactone-graphene oxide nanofiber composite coating, the biological and antibacterial properties of titanium alloy will be improved and its corrosion resistance will probably change. In this project, the main question is extracting effective parameters in creating a composite coating on titanium surface by electrospinning method and characterizing and biological evaluation of the created coating.

Gallic acid-infused LDH nano-containers: A durable protection against mild steel corrosion in simulated seawater

A novel low-dimensional composite nanoparticle is created by using magnesium/aluminum layered double hydroxide (Mg|Al LDH) as a carrier for Gallic acid (GA). The GA is then integrated into the LDH, forming LDH/GA, at varying ratios. These composite systems are then evaluated for their ability to prevent corrosion on steel substrates in a neutral 3.5 wt.% NaCl environment at different concentrations.To understand the structural changes, the chemical composition of GA, LDH, and the crystal structures of LDH/GA are examined using Fourier-transform infrared spectroscopy (FT-IR) and X-Ray diffraction (XRD) and Ultraviolet–visible (UV–Vis) tests. Also, the corrosion inhibition performance of these composite particles is assessed using Electrochemical impedance spectroscopy (EIS) and polarization tests, helping to elucidate the protective mechanism. The morphology of both corroded and protected substrates is visualized using Field Emission Scanning Electron Microscope (FE-SEM).EIS and polarization results indicate that the incorporation of 800 ppm GA into LDH significantly improves the corrosion inhibition performance, achieving up to 73 % and 78 % inhibition, respectively. Contact angle measurements reveal that the corroded samples exhibit hydrophilic characteristics, while the formation of a GA layer enhances their hydrophilicity. Increasing the concentrations of GA and LDH/GA also results in a higher degree of hydrophilicity.

Comparison of surface modification and corrosion resistance of Ti6Al4V alloy using matcha tea extract-based silver and copper oxide nanoparticles

In this study, our aim was to investigate the application of green-synthesized silver nanoparticles (Ag NPs) and copper oxide nanoparticles (CuO NPs) for surface modification, specifically focusing on their influence on the corrosion properties of Ti6Al4V alloy. The green NPs were thoroughly characterized, and their role in enhancing the anticorrosive performance of Ti6Al4V was carefully evaluated. Various coating methods and drying temperatures were utilized to coat Ti6Al4V samples with the NPs, aiming to assess their impact on corrosion resistance. The electrochemical corrosion behavior was examined through electrochemical polarization tests in Ringer's bio-liquid. The study underscored the significant impact of coating type, coating method, and drying temperature (25 °C and 60 °C) in achieving favorable anticorrosive performance. Notably, samples oven-dried at both temperatures and coated with Ag NPs and CuO NPs using spray coating demonstrated the most effective substrate protection, achieving protection efficiencies of 97.37 % and 90.56 %, respectively. This outcome can be attributed to the unique spherical and homogeneously dispersed particulate structure of the NPs, effectively reducing microporosity. In summary, the combination of increased surface area and reduced microporosity resulting from the surface properties of the NPs underscores the potential of well-designed surface modification approaches in advancing the development of titanium-based implants for biomedical applications.

Aluminum Co-Deposition via DC Magnetron Sputtering for Enhanced Pitting Resistance of Copper–Nickel Alloys

To investigate the improvements in the resistance of Cu–Ni alloys to surface pitting corrosion, Cu–Ni thin films containing Al were fabricated via DC magnetron sputtering. The morphologies of the fabricated samples were obtained using a scanning electron microscopy, which yielded information on the crystal size and sample surface before and after corrosion tests. X-ray diffraction was employed for the structural characterization of the as-deposited films, and vibrational spectroscopy was used to verify the corrosion products. The corrosion behaviors of the Cu–Ni and Cu–Ni–Al samples were examined using electrochemical polarization and cyclic corrosion tests. The Al co-deposited samples showed a refined crystal size as compared to the Cu–Ni sample, suggesting that they are more susceptible to the formation of a passivation film. The corrosion current density of the Cu–Ni–Al was reduced, and the corrosion potential was lower than that without Al content. The negative shift in the corrosion potential of the Al-containing samples indicates that the Al2O3 film suppressed the cathodic reaction, resulting in a decrease in the corrosion rate. These results are consistent with the cyclic corrosion test results, in which no pitting corrosion is observed in the Cu–Ni–Al sample.

Synthesis of hybrid organosilicon materials of various chemistries as efficient protective coatings for mild steels in NaCl media

This study focuses on optimizing the thermal, morphological, scratch resistance, and anti-barrier characteristics of newly developed hybrid sol-gel coatings. The coatings were formulated by varying the synthetic precursors and incorporating a clay additive. The hybrid coatings were prepared using a mixture of organosilane and zirconium propoxide precursors, and further modified with polydimethylsiloxane (PDMS) and Cloisite 20 A (C20A) clay additives. The coatings were applied onto mild steel substrates and their corrosion protection in 3.5 wt% NaCl solutions were evaluated through electrochemical and visual observation testing. Contact angle measurements revealed a hydrophobic nature of the developed coatings on the steel surfaces, primarily attributed to the presence of an organosilane precursor with a long C18-alkyl chain functionality in all formulations. Electrochemical testing data demonstrated that the coating formulation containing the polydimethylsiloxane precursor exhibited good corrosion protection. After 14 days of immersion in a saline medium, this sample exhibited impedance values higher than 106 Ω.cm2 and a low corrosion rate of 3.5 × 10−3 mpy, as determined by electrochemical impedance spectroscopy (EIS) and polarization testing, respectively. Morphological analyzes confirmed the homogeneous and integrated coating layer of this sample, which contributed to its enhanced corrosion protection. Furthermore, the inclusion of the Zr-propoxide precursor in a formulation containing only silane precursors demonstrated favorable effects on the desired coating properties. The hybrid sol-gel coatings exhibited excellent anti-barrier characteristics, which can be attributed to the formation of highly cross-linked Si-O-Si networks. Overall, the reported hybrid coating formulations offer promising alternatives to commercially available toxic conversion coatings, as they exhibit excellent anti-barrier properties and can be considered environmentally friendly.

Corrosion resistance and other utility properties of selected austenitic nodular cast irons

This study deals with the evaluation of corrosion resistance and other utility properties of selected austenitic nodular cast irons and their comparison with other (non-austenitic) nodular cast irons. For the investigations, two types of austenitic nodular cast iron were selected: nickel-manganese nodular cast iron EN-GJSA-XNiMn13-7 and nickel-chromium nodular cast iron EN-GJSA-XNiCr20-2. Basic mechanical properties, such as yield strength, tensile strength, elongation, absorbed energy and hardness, were evaluated using mechanical tests. The fatigue limit was determined using low-frequency fatigue tests. Corrosion properties, such as average corrosion rate, corrosion potential and corrosion current density, were determined by the exposure immersion test and the electrochemical potentiodynamic polarisation test. Both corrosion tests were performed in a 3.5% NaCl solution (to simulate seawater) at room temperature. The results of mechanical, fatigue and corrosion tests show that austenitic nodular cast irons have lower strength and fatigue properties but significantly higher plastic properties and corrosion resistance compared to non-austenitic nodular cast irons.

Corrosion Behavior of Al Alloy A6061 Jointed with High-Tensile Strength Steel By Friction Stir Welding in NaCl Solution

In recent years, weight reduction of automobile bodies has been effective in reducing carbon dioxide emissions. For this reason, the replacement of steel, which has a large specific gravity, with aluminum alloys and carbon fiber reinforced plastics is being promoted for the right materials in the right places. In this case, an appropriate dissimilar material joining method is needed in terms of ease of assembly, joining performance, and cost. Friction stir welding (FSW) has emerged as a promising joining method for a variety of engineering applications. FSW is a solid-phase joining technique that has been shown to have significant advantages over conventional welding in terms of the strength and quality of the joints produced. However, during joining of metallic materials by FSW, microstructural changes may occur that affect their corrosion degradation. In this study, the corrosion behavior of A6061 jointed with high-strength steel (SPCC980) by FSW in aqueous NaCl solution and the effect of Al alloy microstructural changes on it were investigated.In this study, FSW was performed on A6061 and SPCC980 steel plates, and galvanic corrosion behavior was investigated by immersion tests and surface observations, as well as electrochemical measurements of Al alloys. Immersion tests were performed in 1 M NaCl solution. Micro electrochemical polarization tests of A6061 were also performed to investigate the corrosion behavior.In the immersion test of the galvanic couple of A6061 and SPCC980 steel plates in NaCl solution, galvanic corrosion occurred with the Al alloy as the anode and the steel plate as the cathode, and hydrogen evolution was observed mainly from the BM site on A6061 in the initial stage of immersion. This is due to the hydrogen evolution reaction occurring inside the pitting corrosion of the A6061. The pits was formed near Fe-rich inclusions in the BM site. In the HAZ site, corrosion propagated from Fe-rich inclusions along grain boundaries, but no pitting corrosion was formed. In the NZ site, minor localized corrosion was developed. These results indicate that the susceptibility to localized corrosion and its morphology differ in each site on the A6061. The difference in localized corrosion susceptibility on the A6061 was considered to be caused by the difference in the distribution of Fe-rich inclusions. However, the fact that the size and number of Fe-rich inclusions in each site did not differ suggests that the difference in anodic dissolution activity near Fe-rich inclusions affects pitting corrosion susceptibility in each site. A6061 alloy is a precipitation-strengthened Al alloy reinforced by β'' phase, which is a metastable phase of Mg2Si, and dense precipitation of β'' phase was observed in the BM site. Therefore, the reason for the higher localized corrosion susceptibility of BM is related to the precipitation of the β'' phase.This paper is based on results obtained from a project, JPNP14014, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Cold metal transfer welding of 316L/430 dissimilar stainless-steel welds

Purpose This paper aims to examine dissimilar joints for various applications in chemical, petrochemical, oil, gas, shipbuilding, defense, rail and nuclear industry. Design/methodology/approach This study examined the effects of cold metal transfer welding on stainless steel welds for 316L austenitic and 430 ferritic dissimilar welds with ER316L, ER309L and without (autogenous) fillers. The microstructural observation was done with an optical microscope. The mechanical test was done to reveal the strength, hardness and toughness of the joint. The electrochemical polarization tests were done to reveal intergranular and pitting corrosion in the dissimilar joints. Findings This microstructural study shows the presence of austenitic and ferritic phases with vermicular ferrite for ER309L filler weld, and for ER316L filler weld specimen shows predominately martensitic phase in the weld region, whereas the autogenous weld shows lathy ferrite mixed with martensitic phase. Mechanical test results indicated that filler welded specimen (ER316L and ER309L) has relatively higher strength and hardness than the autogenous weld, whereas ER316L filler weld exhibited the highest impact toughness than ER309L filler weld and lowest in autogenous weld. The electrochemical corrosion results displayed the highest degree of sensitization (DOS) in without filler welded specimen (45.62%) and lower in case of filler welded specimen ER309L (4.95%) and least in case of ER316L filler welded specimen (3.51%). The high DOS in non-filler welded specimen is correlated with the chromium carbide formation. The non-filler welded specimen shows the highest pitting corrosion attack as compared to the ER316L filler weld specimen and relatively better in ER309L filler welded specimen. The highest pitting corrosion resistance is related with the high chromium content in ER309L composition. Originality/value This experimental study is original and conducted with 316L and 430 stainless steel with ER316L, ER309 and without fillers, which will help the oil, shipbuilding and chemical industries.

Anticorrosion studies of 5-acetyl-4-(3-methoxyphenyl)-6-methyl-1-phenyl-3,4-dihydropyrimidin-2(1H)-one: approach from experimental, DFT studies, and MD simulation

Abstract The effectiveness of 5-acetyl-4-(3-methoxyphenyl)-6-methyl-1-phenyl-3,4-dihydropyrimidin-2(1H)-one as a corrosion inhibitor for mild steel in acidic conditions was investigated herein through the experimental and theoretical approach. Experimental results demonstrated that this compound acts as a reliable corrosion inhibitor (η %) for mild steel in acidic environments, with its inhibition efficiency increasing as the inhibitor concentration rises. Adsorption behavior on the mild steel surface followed Langmuir and Temkin adsorption isotherms. Electrochemical polarization tests indicated that the compound exhibited a mixed corrosion type, and impedance spectroscopy revealed an increase in charge transfer resistance with higher inhibitor concentrations. Examination of the mild steel surface using SEM and Atomic Force Microscopy (AFM) confirmed the formation of a protective film. Wettability characteristics were assessed using the contact angle method. Frontier molecular orbital analysis revealed the HOMO and LUMO values for both the neutral and protonated forms of the compound. At 289 °C, the interaction energy for adsorption was found to be approximately −146.3006 kJ/mol for the neutral system and −135.8122 kJ/mol for the protonated system, while at 318 °C, the corresponding values were −140.6106 kJ/mol and −147.6022 kJ/mol. These findings collectively suggest the potential industrial utility of the investigated inhibitor as an effective corrosion inhibitor.

Microstructural, mechanical and corrosion characterization of (C-HA)SiCnws coating on AZ31 magnesium alloy surface

A composite coating was developed to address the issues of low binding force and poor wear resistance of the hydroxyapatite coating on the surface of magnesium alloy. The composite coating, known as (C-HA)SiCnws coating, was prepared on the surface of AZ31 magnesium alloy using the carbonation-oxidation method of phenolic resin and electrophoretic deposition. The (C-HA)SiCnws coating is composed of a carbon coating as the middle layer, a hydroxyapatite coating as the surface layer, and SiC nanowires that connect the carbon layer and the HA coating. The morphology and infrared spectrum of the coating were characterized, and tests were conducted to evaluate the adhesion, wear performance, electrochemical properties, and corrosion resistance of the coating. The results demonstrate that the (C-HA)SiCnws coating is uniform and flat. The adhesion of the coating, as determined by tensile, is 3.51 ± 0.54 MPa, which is 88 % higher than that of the pure HA coating. Furthermore, the wear performance of the (C-HA)SiCnws coating is excellent, with a wear rate of only 0.96 × 10−3 mm3/(N·m), representing a reduction of 68.2 %. Additionally, the (C-HA)SiCnws coating demonstrates a favorable corrosion protection effect in both electrochemical polarization and corrosion tests. Overall, the prepared (C-HA)SiCnws coating exhibits significant enhancements in terms of adhesion, wear resistance, and corrosion resistance.

Comparative Study on the Corrosion Behavior of Materials in Heat Recovery Steam Generators for Combined Cycle Power Plant, Based on Sulfuric Acid Concentrations: Carbon Steels vs. Duplex Stainless Steel (UNS S32205)

This study examined the effects of sulfuric acid concentrations on the corrosion behaviors of three types of commercial steels, conventional carbon steel (SA192), sulfuric acid dew resistant steel (S-TEN), and duplex stainless steel (S32205), considered to be potential materials for the heat recovery steam generator (HRSG) in combined cycle power plants. Based on the results of electrochemical polarization, immersion and wet-dry cycle tests, when exposed to a high sulfuric acid concentration (50%), SA192 and S-TEN exhibited higher corrosion resistance than S32205, which was due to the formation of a stable FeSO4 scale on the carbon steel materials. With prolonged exposure, S-TEN with slightly higher concentrations of Cu and Sb showed lower weight loss than SA192. Conversely, when subjected to low sulfuric acid concentrations (5 and 10%), S32205 exhibited passivation behavior, and showed significantly superior corrosion resistance (i.e., much smaller weight loss) than the other two steel samples. The examination of localized corrosion damages through cross-section observation using a scanning electron microscope revealed also that S32205 suffered less damages from the wet-dry cycling. The long-term superior corrosion resistance of duplex stainless steel in low sulfuric acid concentrations, compared to carbon steel and sulfuric acid due resistant steel, make it a promising candidate material for the HRSG in combined cycle power plants.

Effect of microstructure and texture of AZ31 magnesium alloy substrate on nucleation and growth of biomimetic calcium phosphate coating

Magnesium has a special place in biomedical applications due to its biocompatibility and biodegradability properties. The high corrosion rate of magnesium in the body environment requires the use of a biocompatible coating such as calcium phosphate. In this paper, the effect of microstructure and crystalline texture of AZ31 magnesium alloy substrate on the morphology of calcium phosphate coating and the corrosion behavior of the material was investigated. The results imply that apatite crystals can form and grow on the surfaces of the biomimetic coating after soaking in simulated body fluid (SBF). The corrosion behavior of the material was investigated using an electrochemical polarization test in SBF solution for 3 days. The results showed that changes in the microstructure and crystalline texture of the substrate changed the coating morphology so that the growth of calcium phosphate changed from a rod-shaped with a diameter of 100–150 nm to a blade-shaped with a thickness of 20–50 nm. An increase in the corrosion resistance of the coated specimens with the corrosion rate of 0.65 mm/year was obtained compared to the uncoated specimen with the corrosion rate of 2.62 mm/year.