Fast Corrosion Research Articles

Precision Electrochemical Micro-Machining of Molybdenum in Neutral Salt Solution Based on Electrochemical Analysis

Molybdenum is an important material in modern industry, widely used in extreme environments such as rocket engine nozzles and microelectrodes due to its high melting point, excellent mechanical properties, and thermal conductivity. However, as a difficult-to-machine metal, traditional machining methods struggle to achieve the desired microstructures in molybdenum. Electrochemical machining (ECM) offers unique advantages in manufacturing fine structures from hard-to-machine metals. Studies have shown that molybdenum exhibits a fast corrosion rate in alkaline or acidic solutions, posing significant environmental pressure. Therefore, this study investigates the electrochemical machining of molybdenum in neutral salt solutions to achieve high-precision microstructure fabrication. First, the polarization curves and electrochemical impedance spectroscopy (EIS) of molybdenum in NaNO3 solutions of varying concentrations were measured to determine its electrochemical reaction characteristics. The results demonstrate that molybdenum exhibits good electrochemical reactivity in NaNO3 solutions, leading to favorable surface erosion morphology. Subsequently, a mask electrochemical machining technique was employed to fabricate arrayed microstructures on the molybdenum surface. To minimize interference between factors, an orthogonal experiment was used to optimize the parameter combination, determining the optimal machining process parameters. Under these optimal conditions, an array of micro-groove structures was successfully fabricated with an average groove width of 110 μm, a depth-to-width ratio of 0.21, an aspect ratio of 9000, and a groove width error of less than 5 μm.

Zinc-doped phosphate coatings for enhanced corrosion resistance, antibacterial properties, and biocompatibility of AZ91D Mg alloy

Magnesium and its alloys have been foreseen as promising bone-implant owing to good biocompatibility, high strength, mechanical properties, and biodegradability to replace the conventional bio-metals (Titanium, stainless-steel, Co-Cr alloys) in orthopedic applications. However, high corrosion rate and high degradation rates adversely effects like abrupt evolution of H2 gas and localized alkalization in a physiological environment limit its medical applications. To overcome these issues, phosphate-based surface coating is developed on Mg-alloy to resist the high biodegradation and corrosion rate utilizing magnesium substrate as source of magnesium ion through a single-step hydrothermal process. Controlling the fast corrosion rate and localized alkalization would reduce the antibacterial character of magnesium-based implants therefore, the simple phosphate-based coatings has been induced by doping it with zinc ions due to its physiological tolerance and excellent antibacterial efficacy. The doping of zinc ions may provide a sustained drug-free antibacterial characteristic for potential application in orthopedics. The synthesized phosphate-based coating was characterized using advanced techniques like Scanning Electron Microscopy, X-ray Diffraction, and wettability test, followed by comprehensive electrochemical testing to assess its corrosion behavior. The in vitro immersion test in simulated body fluid (SBF) indicates that deposition of phosphate and zinc doped phosphate coatings reduces the degradation rate consequently minimized the fast dissolution of Mg2+ ions and OH- in physiological environment. Additionally, cytotoxicity and biocompatibility were evaluated using Alamar Blue and live/dead assays on the MC3T3-E1 mouse osteoblast cell line. These assays demonstrated good cell viability, indicating the coatings possess favorable cytocompatibility and support cellular metabolic activity.

Investigating the corrosion behavior of as‐cast Mg‐Zn‐Ca alloys with the same Zn/Ca atomic ratio by in situ observation

AbstractThe alloying contents with the same Zn/Ca atomic ratio of 0.13 on the corrosion behavior of Mg‐Zn‐Ca (ZX) alloys were investigated. The second phases in ZX10, ZX20, ZX30, and ZX51 alloys were identical with a majority of Mg2Ca and very few Ca2Mg6Zn3 and their distribution changed from isolated to continuous state in ZX30 and ZX51. ZX10 had the lowest corrosion rate of 0.55 mm/year after 168 h immersion in simulated body fluid solution due to the smallest number of sites of galvanic corrosion. The corrosion rate of ZX30 alloy was the highest (0.72 mm/year), while though ZX51 alloy had the most Mg2Ca, its corrosion rate was reduced to 0.69 mm/year, resulting from the small size and thin Mg2Ca. In situ microstructure observation demonstrated the high fraction Mg2Ca phase and continuous Mg2Ca with bulky size were the main reason for the fast corrosion rate.

Titanium versus plasma electrolytic oxidation surface-modified magnesium miniplates in a forehead secondary fracture healing model in sheep

Magnesium as a biodegradable material offers promising results in recent studies of different maxillo-facial fracture models. To overcome adverse effects caused by the fast corrosion of pure magnesium in fluid surroundings, various alloys, and surface modifications are tested in animal models. In specified cases, magnesium screws already appeared for clinical use in maxillofacial surgery. The present study aims to compare the bone healing outcome in a non-load-bearing fracture scenario of the forehead in sheep when fixed with standard-sized WE43 magnesium fixation plates and screws with plasma electrolytic oxidation (PEO) surface modification in contrast to titanium osteosynthesis. Surgery was performed on 24 merino mix sheep. The plates and screws were explanted en-bloc with the surrounding tissue after four and twelve weeks. The outcome of bone healing was investigated with micro-computed tomography, histological, immunohistological, and fluorescence analysis. There was no significant difference between groups concerning the bone volume, bone volume/ total volume, and newly formed bone in volumetric and histological analysis at both times of investigation. The fluorescence analysis revealed a significantly lower signal in the magnesium group after one week, although there was no difference in the number of osteoclasts per mm2. The magnesium group had significantly fewer vessels per mm2 in the healing tissue. In conclusion, the non-inferiority of WE43-based magnesium implants with PEO surface modification was verified concerning fracture healing under non-load-bearing conditions in a defect model. Statement of significanceTitanium implants, the current gold standard of fracture fixation, can lead to adverse effects linked to the implant material and often require surgical removal. Therefore, degradable metals like the magnesium alloy WE43 with plasma electrolytic oxidation (PEO) surface modification gained interest. Yet, miniplates of this alloy with PEO surface modification have not been examined in a fracture defect model of the facial skeleton in a large animal model. This study shows, for the first time, the non-inferiority of magnesium miniplates compared to titanium miniplates. In radiological and histological analysis, bone healing was undisturbed. Magnesium miniplates can reduce the number of interventions for implant removal, thus reducing the risk for the patient and minimizing the costs.

Corrosion Rate and Mechanism of Degradation of Chitosan/TiO2 Coatings Deposited on MgZnCa Alloy in Hank's Solution.

Overly fast corrosion degradation of biodegradable magnesium alloys has been a major problem over the last several years. The development of protective coatings by using biocompatible, biodegradable, and non-toxic material such as chitosan ensures a reduction in the rate of corrosion of Mg alloys in simulated body fluids. In this study, chitosan/TiO2 nanocomposite coating was used for the first time to hinder the corrosion rate of Mg19Zn1Ca alloy in Hank's solution. The main goal of this research is to investigate and explain the corrosion degradation mechanism of Mg19Zn1Ca alloy coated by nanocomposite chitosan-based coating. The chemical composition, structural analyses, and corrosion tests were used to evaluate the protective properties of the chitosan/TiO2 coating deposited on the Mg19Zn1Ca substrate. The chitosan/TiO2 coating slows down the corrosion rate of the magnesium alloy by more than threefold (3.6 times). The interaction of TiO2 (NPs) with the hydroxy and amine groups present in the chitosan molecule cause their uniform distribution in the chitosan matrix. The chitosan/TiO2 coating limits the contact of the substrate with Hank's solution.

Stabilization of active ultrathin amorphous ruthenium oxide via constructing electronically interacted heterostructure for acidic water oxidation

Amorphous RuOx (a-RuOx) with disordered atomic arrangement and abundant coordinatively unsaturated Ru sites possesses high intrinsic electrocatalytic activity for oxygen evolution reaction (OER). However, the a-RuOx is prone to fast corrosion during OER in strong acid. Here, we realized the stabilization of an ultrathin a-RuOx layer via constructing heterointerface with crystalline α-MnO2 nanorods array (MnO2@a-RuOx). Benefiting from the strong electronic interfacial interaction, the as-formed MnO2@a-RuOx electrocatalyst display an ultralow overpotential of 128 mV to reach 10 mA cm−2 and stable operation for over 100 h in 0.1 M HClO4. The assembled proton exchange membrane (PEM) water electrolyzer reach 1 A cm−2 at applied cell voltage of 1.71 V. Extensive characterizations indicate the MnO2 substrate work as an electron donor pool to prevent the overoxidation of Ru sites and the OER proceeds in adsorbent evolution mechanism process without involving lattice oxygen. Our work provides a promising route to construct robust amorphous phase electrocatalysts.

Mg alloys with antitumor and anticorrosion properties for orthopedic oncology: A review from mechanisms to application strategies.

As a primary malignant bone cancer, osteosarcoma (OS) poses a great threat to human health and is still a huge challenge for clinicians. At present, surgical resection is the main treatment strategy for OS. However, surgical intervention will result in a large bone defect, and some tumor cells remaining around the excised bone tissue often lead to the recurrence and metastasis of OS. Biomedical Mg-based materials have been widely employed as orthopedic implants in bone defect reconstruction, and, especially, they can eradicate the residual OS cells due to the antitumor activities of their degradation products. Nevertheless, the fast corrosion rate of Mg alloys has greatly limited their application scope in the biomedical field, and the improvement of the corrosion resistance will impair the antitumor effects, which mainly arise from their rapid corrosion. Hence, it is vital to balance the corrosion resistance and the antitumor activities of Mg alloys. The presented review systematically discussed the potential antitumor mechanisms of three corrosion products of Mg alloys. Moreover, several strategies to simultaneously enhance the anticorrosion properties and antitumor effects of Mg alloys were also proposed.

An amorphous Si-O-N coating on magnesium to retard corrosion & improve biocompatibility

Fast corrosion and the resulting adverse biological responses impede the applications of magnesium-based implants. Here, an amorphous Si-O-N coating is prepared on Mg via radio frequency plasma-enhanced chemical vapor deposition (PECVD) to address those issues. This coating is compact and uniform, which can firmly adhere to the substrate. It provides efficient shielding, thus reduces corrosion rate from 36.16 μm/y to 16.14 μm/y. The coating itself is biocompatible, and coated Mg exhibits excellent biocompatibility to rat/mouse mesenchymal stem cells. PECVD-obtained amorphous coatings based on biocompatible elements could be a solution for Mg-based implants.

Enhanced Mechanical Properties, Corrosion Resistance, Cytocompatibility, Osteogenesis, and Antibacterial Performance of Biodegradable Mg-2Zn-0.5Ca-0.5Sr/Zr Alloys for Bone-Implant Application.

Magnesium (Mg) alloys are widely used in bone fixation and bone repair as biodegradable bone-implant materials. However, their clinical application is limited due to their fast corrosion rate and poor mechanical stability. Here, the development of Mg-2Zn-0.5Ca-0.5Sr (MZCS) and Mg-2Zn-0.5Ca-0.5Zr (MZCZ) alloys with improved mechanical properties, corrosion resistance, cytocompatibility, osteogenesis performance, and antibacterial capability is reported. The hot-extruded (HE) MZCZ sample exhibits the highest ultimate tensile strength of 255.8 ± 2.4MPa and the highest yield strength of 208.4 ± 2.8MPa and an elongation of 15.7 ± 0.5%. The HE MZCS sample shows the highest corrosion resistance, with the lowest corrosion current density of 0.2 ± 0.1µA cm-2 and the lowest corrosion rate of 4 ± 2µm per year obtained from electrochemical testing, and a degradation rate of 368µm per year and hydrogen evolution rate of 0.83 ± 0.03mL cm-2 per day obtained from immersion testing. The MZCZ sample shows the highest cell viability in relation to MC3T3-E1 cells among all alloy extracts, indicating good cytocompatibility except at 25% concentration. Furthermore, the MZCZ alloy shows good antibacterial capability against Staphylococcus aureus.

DOUBLE-DOPED CALCIUM PHOSPHATE COATINGS WITH ANTIMICROBIAL EFFICACY FOR BIODEGRADABLE METAL BIOMEDICAL IMPLANTS

Over the last decades, biodegradable metals emerged as promising materials for various biomedical implant applications, aiming to reduce the use of permanent metallic implants and, therefore, to avoid additional surgeries for implant removal. However, among the important issue to be solved is their fast corrosion - too high to match the healing rate of the bone tissue. The most effective way to improve this characteristic is to coat biodegradable metals with substituted calcium phosphates. Tricalcium phosphate (β-TCP) is a resorbable bioceramic widely used as synthetic bone graft. In order to modulate and enhance its biological performance, the substitution of Ca2+ by various metal ions, such as strontium (Sr2+), magnesium (Mg2+), iron (Fe2+) etc., can be carried out. Among them, copper (Cu2+), manganese (Mn2+), zinc (Zn2+) etc. could add antimicrobial properties against implant-related infections. Double substitutions of TCP containing couples of Cu2+/Sr2+ or Mn2+/Sr2+ ions are considered to be the most perspective based on the results of our study. We established that single phase Ca3−2x(MˊMˊˊ)x(PO4)2 solid solutions are formed only at x ≤ 0.286, where Mˊ and Mˊˊ—divalent metal ions, such as Zn2+, Mg2+, Cu2+, Mn2+, and that in case of double substitutions, the incorporation of Sr2+ ions allows one to extend the limit of solid solution due to the enlargement of the unit cell structure. We also reported that antimicrobial properties depend on the substitution ion occupation of Ca2+ crystal sites in the β-TCP structure. The combination of two different ions in the Ca5 position, on one side, and in the Ca1, Ca2, Ca3, and Ca4 positions, on another side, significantly boosts antimicrobial properties. In the present work, zinc-lithium (Zn-Li) biodegradable alloys were coated with double substituted Mn2+/Sr2+ β-TCP and double substituted Cu2+/ Sr2+ β-TCP, with the scope to promote osteoinductive effect (due to the Sr2+ presence) and to impart antimicrobial properties (thanks to Cu2+ or Mn2+ ions). The Pulsed Laser Deposition (PLD) method was applied as the coating's preparation technique. It was shown that films deposited using PLD present good adhesion strength and hardness and are characterized by a nanostructured background with random microparticles on the surface. For coatings characterization, Fourier Transform Infrared Spectroscopy, X-ray Diffraction, and Scanning Electron Microscopy coupled with Energy Dispersive X-ray and X-ray Photoelectron Spectroscopy were applied. The microbiology tests on the prepared coated Zn-Li alloys were performed with the Gram-positive (Staphylococcus aureus, Enterococcus faecalis) and Gram-negative (Salmonella typhimurium, Escherichia coli) bacteria strains and Candida albicans fungus. The antimicrobial activity tests showed that Mn2+/Sr2+ β-TCP -coated and Cu2+/Sr2+ β-TCP coated Zn-Li alloys were able to inhibit the growth of all five microorganisms. The prepared coatings are promising in improving the degradation behavior and biological properties of Zn-Li alloys, and further studies are necessary before a possible clinical translation.

Graphene–calcium carbonate coating to improve the degradation resistance and mechanical integrity of a biodegradable implant

Biodegradable implants are critical for regenerative orthopaedic procedures, but they may suffer from too fast corrosion in human-body environment. This necessitates the synthesis of a suitable coating that may improve the corrosion resistance of these implants without compromising their mechanical integrity. In this study, an AZ91 magnesium alloy, as a representative for a biodegradable Mg implant material, was modified with a thin reduced graphene oxide (RGO)-calcium carbonate (CaCO3) composite coating. Detailed analytical and in-vitro electrochemical characterization reveals that this coating significantly improves the corrosion resistance and mechanical integrity, and thus has the potential to greatly extend the related application field.

Developing a Highly Stable Quaternary Sn-Sb-Mo-W Scaffold to Protect Active Metals for Corrosion during the Oxygen Evolution in Acidic Media

Proton exchange membrane (PEM) water electrolysis powered by renewable energies is seen as one of the most powerful techniques for the high production of ultra-pure hydrogen. However, PEM requires of noble metals as catalysts while operating under harsh acidic conditions, creating a detrimental environment which conducts to fast corrosion of the catalyst. Reducing and extending the lifetime of noble metals under acidic conditions will benefit the hydrogen economy. Currently, one of the major limitations relies on the high corrosion that anode electrocatalysts suffer, where the oxygen evolution reaction (OER) takes place. The best performing electrocatalysts are based on ruthenium (Ru) and iridium (Ir) either in the pure oxide form or as engineered composites, being Ru the most active but less stable even at moderate cell potentials. Here, we investigate the quaternary Sn-Sb-Mo-W mixed oxide (MO) as an effective scaffold to protect RuO2 for corrosion. The acid-stable MO was produced via plasma spraying forming an interconnected network of nanostructured WO3, Sb2O3, SnO2, and MoO3. Low quantities of Ru (2.64% w/w Ru) were stabilized into the matrix (Ru-MO) and finally supported on FTO. The Ru deactivation was described by a second-order reaction with a deactivation rate constant of k = 0.067 cm2 (mA·min)-1. Titanium fiber felt was later used as support (Ru-MO@Ti) where a mass activity of 4440 A g-1 Ru@1.8V(RHE) was obtained, and solely a reduction of 20% was seen in the OER activity after 2000 CVs (1.2 – 1.8 V vs RHE), in contrast to unprotected RuO2 (RuO2@Ti) which showed an activity loss of nearly 90%. In addition, chronopotentiometry studies on Ru-MO@Ti (2.5 A cm-2 @ 1.7V) confirmed the high satiability of the Ru experienced only a minor increase in potential of 10 mV, while RuO2@Ti exhibited a significant degradation of 500 mV after 10 h. The superior stability of Ru-MO@Ti was possible due to impeded formation of higher valence ruthenium (Ru+8), a typical dissolution path for Ru-based electrocatalysts. Our work shows that multi-metal oxides have the potential to host and extend the lifetime of active metals and Ti substrates when used for water electrolysis in acidic media. Figure 1

Interfacial Water Tuning by Intermolecular Spacing for Stable CO2 Electroreduction to C2+ Products.

Electroreduction of CO2 to multi-carbon (C2+ ) products is a promising approach for utilization of renewable energy, in which the interfacial water quantity is critical for both the C2+ product selectivity and the stability of Cu-based electrocatalytic sites. Functionalization of long-chain alkyl molecules on a catalyst surface can help to increase its stability, while it also tends to block the transport of water, thus inhibiting the C2+ product formation. Herein, we demonstrate the fine tuning of interfacial water by surface assembly of toluene on Cu nanosheets, allowing for sustained and enriched CO2 supply but retarded water transfer to catalytic surface. Compared to bare Cu with fast cathodic corrosion and long-chain alkyl-modified Cu with main CO product, the toluene assembly on Cu nanosheet surface enabled a high Faradaic efficiency of 78 % for C2+ and a partial current density of 1.81 A cm-2 . The toluene-modified Cu catalyst further exhibited highly stable CO2 -to-C2 H4 conversion of 400 h in a membrane-electrode-assembly electrolyzer, suggesting the attractive feature for both efficient C2+ selectivity and excellent stability.

Interfacial Water Tuning by Intermolecular Spacing for Stable CO2 Electroreduction to C2+ Products

AbstractElectroreduction of CO2 to multi‐carbon (C2+) products is a promising approach for utilization of renewable energy, in which the interfacial water quantity is critical for both the C2+ product selectivity and the stability of Cu‐based electrocatalytic sites. Functionalization of long‐chain alkyl molecules on a catalyst surface can help to increase its stability, while it also tends to block the transport of water, thus inhibiting the C2+ product formation. Herein, we demonstrate the fine tuning of interfacial water by surface assembly of toluene on Cu nanosheets, allowing for sustained and enriched CO2 supply but retarded water transfer to catalytic surface. Compared to bare Cu with fast cathodic corrosion and long‐chain alkyl‐modified Cu with main CO product, the toluene assembly on Cu nanosheet surface enabled a high Faradaic efficiency of 78 % for C2+ and a partial current density of 1.81 A cm−2. The toluene‐modified Cu catalyst further exhibited highly stable CO2‐to‐C2H4 conversion of 400 h in a membrane‐electrode‐assembly electrolyzer, suggesting the attractive feature for both efficient C2+ selectivity and excellent stability.

Magnetic energy drives mass transfer processes to accelerate the degradation of Fe-based implant

The main obstacle of Fe towards the orthopedic application is the slow degradation rate. In this work, a FeGa alloy is developed by mechanical alloying and selective laser melting, and exposed to magnetic field to investigate the influence of magnetic energy on the degradation behavior of the alloy. The magnetic field magnetizes the FeGa alloy and establishes an induced magnetic field, which forms gradient magnetic energy around the corrosion pits during the degradation period. The gradient magnetic energy transfers the paramagnetism corrosion product particles like FexOy and GaOx to the edge of the corrosion pits and avoids the deposition of passive corrosion product layer, thereby maintaining the erosion of immersion solution to achieve a continuous corrosion process. Moreover, the magnetic field subjects Lorentz forces to oxygen and the corrosive ions in the medium, which provides driving forces for transferring them to the alloy surface, thereby accelerating the oxygen absorption degradation reaction. Results indicate that FeGa alloy coupled with magnetic field has a smaller charge transfer resistance of 3297.8 Ω than FeGa alloy (4877.2 Ω) and Fe (5951.1 Ω) in the absence of magnetic field, indicating a lower corrosion resistance of the corrosion product layer. Furthermore, the FeGa alloy in magnetic field exhibits high corrosion current density of 28.12 ± 0.35 μA/cm2 and fast corrosion rate of 0.25 ± 0.02 mm/year, which are significantly higher than FeGa alloy and Fe without magnetic field. The findings of this work suggest that combining component design with external field interactions can effectively regulate the degradation of Fe-based implants.

The roles of different Fe-based materials in alleviating the stress of Cr(VI) on anammox activity: Performance and mechanism

Hexavalent chromium Cr(VI) is widely present in industrial wastewater, which can inhibit anammox performance significantly. Iron is a critical element of anammox metabolism and also has the capacity to remove Cr(VI). In this study, batch experiments were conducted to investigate the effects of commercial zero-valent iron (Fe0) and ferroferric oxide (Fe3O4) in the nano-(n) and micron-(m) scales (mFe0, nFe0, mFe3O4, and nFe3O4, respectively) on recovering anammox activity with inhibition of Cr(VI). Their recovery efficiencies on the anammox process were in the order of mFe0, mFe3O4, nFe0, and nFe3O4 at their minimum effective dosages, with specific anammox activities being promoted by 95.2%, 57.0%, 45.0%, and 15.8%, respectively, in comparison to the control. More hydroxyl groups in extracellular polymeric substances (EPS) were observed with mFe0, and the electron transport performances of soluble and loosely-bound EPS were particularly enhanced. By contrast, Fe3O4 stimulated more production of EPS than mFe0, which helped remove Cr(VI) outside the cell membrane. Moreover, the contents of heme c and cytochrome c were improved most with mFe3O4 by 10.9% and 41.3%, respectively, and hydrazine dehydrogenase activity was enhanced by 47.7% with mFe0, at their optimal dosages. In addition, cytochrome c showed a significant positive correlation with recovery performance for all four materials (R2 > 0.82, P < 0.05), indicating its pivotal role in alleviation effectiveness. More FeOOH was found on the two micron-scale materials detected by X-ray diffractometry and Fourier transform infrared spectroscopy, which would help electron transfer between materials and anammox bacteria. In contrast, the fast corrosion and adsorption processes and biological toxicity of nanoscale materials may lead to their poor performance.

An Experimental Study on Secondary Transfer Performances of Prestress after Anchoring Failure of Steel Wire Strands

To understand the secondary transfer performances of residual prestress after the anchoring failure of end-anchored steel wire strands due to corrosion fracture, six steel wire strand components of post-tensioning prestress were designed and fabricated. One-side fast corrosion was applied to the steel wire strand components using the electrochemical method until anchoring failure was reached. The sphere of influence, stress changes, and the retraction and swelling effect of broken beams after failure were investigated. The influences of factors such as concrete strength, stirrup area, and the length of the component on the secondary transfer length of residual prestress were discussed. Based on the deformation relationship between prestressed steel wire strands and concrete in the stress transfer zone, a stress equation was established and solved through a bond constitutive model. A prediction model of the effective stress transfer length of prestressed steel wire strand after failure was proposed. The results demonstrated that residual prestress can have a secondary transfer after the corrosion fracture of end-anchored steel wire strands, but some effective prestress may be lost. Moreover, the loss of prestress is inversely proportional to concrete compressive strength. When the specimens are relatively short, the prestress loss increases significantly. Concrete strength has significant influences on the length of secondary transfer. The proposed simplified calculation method of the secondary transfer length of residual prestress has a relatively high accuracy, with an average error of 2.9% and a maximum error of 5.2%.

X80 U-bend stress corrosion cracking (SCC) crack tip dissolution by fast corroding Desulfovibrio ferrophilus IS5 biofilm

Stress corrosion cracking (SCC) is a serious problem threatening structural integrity and safety. Metal corrosion pits can develop into more harmful cracks under mechanical stress. It is known in abiotic corrosion that fast corrosion does not necessarily cause more severe SCC. This is because fast corrosion can prevent or dissolve crack tips and convert them into less harmful pits if the uniform corrosion rate is fast enough. This work experimentally proved the hypothesis that the same phenomenon occurs in biotic corrosion. It was found that a highly corrosive SRB (sulfate reducing bacterium) strain, namely Desulfovibrio ferrophilus (strain IS5), caused fast uniform corrosion and dull pits, but no SCC cracks against X80 carbon steel U-bend coupons (stressed). In comparison, Desulfovibrio vulgaris, a far less corrosive SRB strain caused less corrosion, but generated sharp pits and SCC cracks in a 3-month lab test. This work also revealed that the X80 U-bend had a 44% higher sessile cell count and 34% higher weight loss after a 14-d D. ferrophilus incubation in deoxygenated enriched artificial seawater culture medium at 28 °C when compared with the (flat) square coupons (no stress). This weight loss trend was corroborated by transient electrochemical measurements.

Enhanced corrosion resistance of Mg and Mg alloys with fs-laser printed hydrophobic and periodically microrippled surface for armor application

Magnesium (Mg) and its alloys have properties such as high strength-to-weight ratio and good castability, which make them quite promising in industrial applications. Future widespread application of them needs to overcome the limitations such as the fast corrosion rate of Mg and Mg alloys. In this study, an anticorrosion armor with was printed using femtosecond (fs) laser direct writing method. This protective armor is covered with controllable micro-nano structures. Thus, it has a controllable water contact angle ranged from 68° to 158°. In addition, due to the fs laser energy deposition, a grain refined layer less than 15 μm consisting of nanocrystals forms on the surface. Under the synergistic effects of the superhydrophobic surface and nanocrystal layer, Mg and Mg alloys (AZ91D) exhibit significantly enhanced corrosion voltage and exponentially decreased corrosion current density. In particular, pitting on the surface is largely improved, and the corrosion pits on the surface after laser-treatment are approximately 200 times smaller in depth (<2.5 μm) than those of the pristine surface (531 μm). Therefore, the armor on Mg and Mg alloys with enhanced corrosion resistance can be successfully fabricated by the fs-laser direct printing method, extensively used in Mg and Mg alloys applications.

Performance of Anticorrosive Measures of Steel in Concrete Infrastructure by Plant‐Based Extracts

AbstractCompetence to combat corrosion of steel‐reinforced concrete (SRC) infrastructures for long periods has become a fascinating topic for corrosion scientists. The longevity of such infrastructures is limited mainly by the corrosion process. Hence, urgent demands for developing effective and practical methods are necessary to minimize the corrosion of such concrete structures. The anti‐corrosive components can be designed from the green plants' parts to mitigate the SRC corrosion in recent years. The ongoing research aims to substantiate the success of the leaf extract of Psidium guajava (LEPG) and its 50% blend (BnD) with the leaf extract of Mangifera indica (LEMI) for assessing the steel corrosion condition in a concrete slab. For this purpose, a fast corrosion potential monitoring (CPM) method is applied per the ASTM procedure. Outcomes of the work summarized that the additions of 500–4000 ppm LEPG and its 50% BnD blend have significant corrosion‐inhibiting action. The corrosion potential (ϕcorr) shifts toward a less corrosion‐risk area of the steel bar for 6 months at ambient conditions.