Electrochemical Corrosion Rate Research Articles

Molecular insights into the effect of adsorption and reaction of H2O-O2-Cl- on initial electrochemical corrosion of steel

A deeper understanding of the effect of chloride on the process of iron initial corrosion could reveal the detailed mechanism of the Cl--induced acceleration corrosion of steel. In light of the difficulty to unravel the intricacies of H2O-O2-Cl- interactions in experiments, this study conducted the molecular study on the effect of H2O, O2 and Cl- coadsorption and interactions on the electrochemical corrosion process of Fe (100) surface by DFT method, and the electron-correlation functional is GGA-PW91. It is discovered that the adsorption of H2O, O2 and Cl- all promote the electrochemical corrosion of iron. The electrochemical corrosion rate of iron surface rises as the Cl-/H2O concentration ratio increasing, while decrease with the Cl-/O2 concentration ratio increasing. The transition state search found that the presence of Cl- assists the dissociation of H2O on the iron surface, while the interaction between Cl- and O2 could be ignored. Moreover, the successive reaction of Cl-, H2O and O2 with iron surface were further investigated. When the Cl- reacts with H2O ahead of O2, the Cl- promotes the iron oxidation via promoting the dissociation of H2O. While O2 and Cl- firstly coadsorb on iron surface, Cl- accelerates iron oxidation by exacerbating the iron surface losing electrons. These findings could facilitate the development of anti-corrosion techniques for steel in chloride environment.

Texture and surface morphology influence of A106 carbon steel pipe on mechanical properties and corrosion resistance after welding process

The surface morphology influenced the corrosion resistance, which depended on the welding process and its parameters. In this study, we investigated the relevance of the welding process that produces excellent mechanical properties and corrosion resistance, which gives the best working performance for carbon steel pipes that transfer refined oil products in an Iraq oil refinery. AISI 1020-A106 carbon steel pipes are welded using shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW). Electrochemical corrosion tests were performed in 3.5% NaCl and immersion tests in heavy Naphtha at 50, 75, and 100 °C. The results show that retained austenite, ferrite, pearlite, and martensite phases are produced after the SMAW process. In contrast, ferrite, pearlite, and a small amount of martensite are produced after GTAW. The ultimate tensile strength of the SMAW samples was higher than those of the GTAW samples, but the GTAW samples had higher fracture elongation, and all samples had no cracks in the welding area during the bending test. The electrochemical and immersion corrosion rates of the samples welded with SMAW are higher than those welded with GTAW. The corrosion rate increases when the naphtha temperature increases and has a higher and unacceptable value at 100 °C.

Investigation of the Microstructure, Mechanical Properties, in Vitro Degradation Behavior, and Biocompatibility of Newly Developed Zn‐0.6%Li Alloy

Zn–Li alloys are considered as one of the promising materials in biodegradable bone implants because they have excellent biocompatibility and high strength. This study examines the extrusion deformation effects on the microstructure, mechanical characteristics, in vitro degradation behavior, and biocompatibility of Zn‐0.6Li alloy. It is shown that primary α‐Zn and LiZn4 precipitates of as‐extruded Zn‐0.6Li alloy are significantly refined. The dendritic primary α‐Zn is refined into fine equiaxed grains. The eutectic (α‐Zn + LiZn4) lamellar spacing distributed in dendrites are refined from 0.86 ± 0.5 to 0.57 ± 0.4 μm. The extruded Zn‐0.6Li alloy of the yield strength, ultimate tensile strength, and elongation are significantly enhanced, reaching 365, 498 MPa, and 13.55%, respectively. In Hanks’ solution, the electrochemical corrosion rate and immersion corrosion rate of extruded Zn‐0.6Li alloy are 1.479 ± 0.061 and 0.878 ± 0.006 mm year−1. In addition, the cytotoxicity test and CCK‐8 evaluation demonstrate that the extruded Zn‐0.6Li alloy displays a good biocompatibility.

Improved mechanical and corrosion properties through high-pressure phase transition in a biodegradable Zn-1.5Mn alloy

Zn-Mn alloys are considered promising biodegradable metals for orthopedic applications due to their large elongation and favorable osteogenicity. However, the corrosion rate of Zn-Mn alloys could be improved to meet the degradation requirement for orthopedic implants. In this study, a Zn-1.5Mn alloy was prepared via high-pressure solid-solution (HPSS) treatment at 5 GPa and 380 °C for 1 h to cast ingots. Microstructural evaluation revealed the HPSS treatment caused a phase transition from a ζ-MnZn13 phase to an ε-MnZn3 phase. The electrode potential difference between the ε-MnZn3 and the α-Zn was significantly larger than between the ζ-MnZn13 and the α-Zn, leading to an accelerated corrosion rate of the HPSS-treated alloy. It showed an electrochemical corrosion rate of 0.343 mm/y and an immersion degradation rate of 0.028 mm/y, while the as-cast (AC) Zn-1.5Mn displayed an electrochemical corrosion rate of 0.216 mm/y and an immersion degradation rate of 0.026 mm/y. Further, the HPSS-treated Zn-1.5Mn exhibited a compressive yield strength of 202 MPa and a microhardness of 83.48 HV. In addition, the HPSS-treated Zn-1.5Mn exhibited a cell viability toward human umbilical vein endothelial cells (HUVEC) comparable to its AC and atmospheric pressure solid-solution-treated (APSS-treated) counterparts toward HUVEC, along with improved antibacterial activity.

Corrosion performance of naval brass in a simulated ocean water environment under different aqueous conditions

This study assesses the corrosion response of naval brass (NB) (Cu-39.0Zn-1.0Sn-3.5Pb wt.%) with ocean water salt mixture added in distilled water (DW), tap water (TW), and 50%Tap water + 50%Rain water (TW + RW) conditions. The NB in DW exhibited reduced weight loss and corrosion rate compared to TW and TW + RW conditions, which was maximum in TW condition. The electrochemical corrosion rates increased to 168 h and declined at 336 h, with higher corrosion rates witnessed in TW and lowest in DW conditions. The corrosion rate after 168 h in TW was 32 % higher than in DW condition. The corrosion products on NB include cuprite, atacamite, brochantite, and simonkolleite, more prevalent in TW conditions. The dezincification was minimal in DW but increased in TW and TW + RW conditions, peaking in TW condition. Pit number and size were smaller in DW but larger in TW and TW + RW conditions, with TW exhibiting the most extensive and deeper pits, indicating heightened corrosion from localized Zn dissolution. Zn removal from α and β′ phases was lower initially in DW while escalating in TW and TW + RW conditions over time. The NB in the TW condition showed prominent Zn removal than in DW condition, especially after 336 h.

Electrochemical Characteristics and Corrosion Mechanisms of High-Strength Corrosion-Resistant Steel Reinforcement under Simulated Service Conditions

Long-term steel reinforcement corrosion greatly impacts reinforced concrete structures, particularly in marine and coastal settings. Concrete failure leads to human casualties, requiring extensive demolition and maintenance, which represents an inefficient use of energy and resources. This study utilizes microscopic observation, atomic force microscopy (SKPM), electrochemical experiments, and XPS analysis to investigate the corrosion behavior of 500CE and 500E under identical conditions. We compared 500E with 500CE, supplemented with 0.94% Cr, 0.46% Mo, 0.37% Ni, and 0.51% Cu through alloying element regulation to obtain a finer ferrite grain and lower pearlitic content. The results indicate that 500CE maintains a stable potential, whereas 500E exhibits larger grain sizes and significant surface potential fluctuations, which may predispose it to corrosion. In addition, despite its more uniform microstructure and stable electrochemical activity, 500E shows inferior corrosion resistance under prolonged exposure. The electrochemical corrosion rate of 500CE in both the pristine and passivated states and for various passivation durations is slower than that of 500E, indicating superior corrosion performance. Notably, there is a significant increase in the corrosion rate of 500E after 144 h of exposure. This study provides valuable insights into the chloride corrosion phenomena of low-alloy corrosion-resistant steel reinforcement in service, potentially enhancing the longevity of reinforced concrete structures.

A review analysis of corrosion rate on stainless steel pipe in sea water media

Regarding providing energy, few sectors are as massive as the oil and gas business. One of the most crucial parts of oil and gas production is the distribution pipes or pipelines that transport the production fluids, which include oil and gas, from one distribution point to another. The corrosion of A316 material, which can lead to holes or pitting, and the damage it causes in most industrial operations, particularly in the oil and gas industry, has resulted in substantial losses at high prices over an extended period of time. In the study, we will quickly examine what corrosion is, the different kinds of corrosion, inhibitors, and how to assess the corrosion rate of A316 stainless steel in salt water. Analysis of the electrochemical corrosion rate of Inconel 600 nickel alloy and stainless steel 316L subjected to varying amounts of saltwater (freshwater, seawater, mixed water). Because chlorine speeds up corrosion, alloys like Inconel 600 and 316L undergo pitting corrosion. The molybdenum component gives 316 stainless steel its superior corrosion resistance. That's why it works well for gas and oil pipelines that go through saltwater. Nevertheless, materials exposed to maritime environments must have cathodic protection or coating to prolong their life and stop the pipe from continuously corroding.

Study on the crystallographic orientation dependent electrochemical corrosion rates of aluminum and its binary alloys

This paper provides a study for crystallographic orientation-dependent corrosion rate of aluminum employing an ab initio model with inputs from first-principles calculations. Results showed that the sequence of corrosion rate is in the order of (111) < (410) < (331) < (221) < (321) < (211) < (110) < (100) < (210) < (320) < (310) < (311) for aluminum. The predicted corrosion current densities for (111), (110), and (100) surfaces are in general agreement with the experimental results. The alloying effects were further investigated employing this model with results validated via the polarization curves of alloyed aluminum.

Mechanical properties, corrosion behavior, and in vitro and in vivo biocompatibility of hot-extruded Zn-5RE (RE = Y, Ho, and Er) alloys for biodegradable bone-fixation applications

Biodegradable Zn alloys have significant application potential for hard-tissue implantation devices owing to their suitable degradation behavior and favorable biocompatibility. Nonetheless, pure Zn and its alloys in the as-cast state are mechanically instable and low in strength, which restricts their clinical applicability. Here, we report the exceptional mechanical, corrosion, and biocompatibility properties of hot-extruded Zn-5RE (wt.%, RE = rare earth of Y; or Ho; or Er) alloys intended for use in biodegradable bone substitutes. The microstructural characteristics, mechanical behavior, corrosion resistance, cytocompatibility, osteogenic differentiation, and capacity of osteogenesis in vivo of the Zn-5RE alloys are comparatively investigated. The Zn-5Y alloy demonstrates the best tensile properties, encompassing a 138 MPa tensile yield strength, a 302 MPa ultimate tensile strength, and 63% elongation, while the Zn-5Ho alloy shows the highest compression yield strength of 260 MPa and Vickers hardness of 104 HV. The Zn-5Er alloy shows a 126 MPa tensile yield strength, a 279 MPa ultimate tensile strength, 52% elongation, a 196 MPa compression yield strength, and a 101 HV Vickers microhardness. Further, the Zn-5Er alloy has a 130 µm per year corrosion rate in electrochemical tests and a 26 µm per year degradation rate in immersion tests, which is the lowest among the tested alloys. It also has the best in vitro osteogenic differentiation ability and capacity for osteogenesis and osteointegration in vivo after implantation in rat femurs among the Zn-5RE alloys, indicating promising potential in load-bearing biodegradable internal bone-fixation applications. Statement of significanceThis work reports the exceptional mechanical, corrosion, and biocompatibility properties of hot-extruded (HE) Zn-5 wt.%–rare earth (Zn-5RE) alloys using single yttrium (Y), holmium (Ho), and erbium (Er) alloying for biodegradable bone-implant applications. Our findings demonstrate that the HE Zn-5Er alloy showed σuts of 279 MPa, tensile yield strength of 126 MPa, elongation of 51.6%, compression yield strength of 196 MPa, and microhardness of 101.2 HV. Further, HE Zn-5Er showed the lowest electrochemical corrosion rate of 130 µm/y and lowest degradation rate of 26 µm/y, and the highest in vitro osteogenic differentiation ability, in vivo osteogenesis, and osteointegration ability after implantation in rat femurs among the Zn-5RE alloys, indicating promising potential in load-bearing biodegradable internal bone-fixation applications.

Spinodal Zr–Nb alloys with ultrahigh elastic admissible strain and low magnetic susceptibility for orthopedic applications

Metallic biomaterials, such as stainless steels, cobalt–chromium–molybdenum (Co–Cr–Mo) alloys, and titanium (Ti) alloys, have long been used as load-bearing implant materials due to their metallic mechanical strength, corrosion resistance, and biocompatibility. However, their magnetic susceptibility and elastic modulus of more than 100 GPa significantly restrict their therapeutic applicability. In this study, spinodal Zr60Nb40, Zr50Nb50, and Zr40Nb60 (at.%) alloys were selected from the miscibility gap based on the Zr–Nb binary phase diagram and prepared by casting, cold rolling, and aging. Their microstructure, mechanical properties, corrosion resistance, magnetic susceptibility, and biocompatibility were systematically evaluated. Spinodal decomposition to alternating nanoscale Zr-rich β1 and Nb-rich β2 phases occurred in the cold-rolled Zr–Nb alloys during aging treatment at 650 °C. In addition, a minor amount of α phase was precipitated in Zr60Nb40 due to the thermodynamic instability of the Zr-rich β1 phase. Spinodal decomposition significantly improved the mechanical strength of the alloys due to nanosized dual-cubic reinforcement. The Zr–Nb alloys showed an electrochemical corrosion rate of 94–262 nm per year in Hanks’ solution because of formation of dense passive films composed of ZrO2 and Nb2O5 during the polarization process. The magnetic susceptibilities of the Zr–Nb alloys were significantly lower than those of commercial Co–Cr–Mo and Ti alloys. The cell viability of the Zr–Nb alloys was more than 98 % toward MC3T3-E1 cells. Overall, the spinodal Zr–Nb alloys have enormous potential as bone-implant materials due to their outstanding overall mechanical properties, extraordinary corrosion resistance, low magnetic susceptibility, and sufficient bicompatibility. Statement of significanceThis work reports on spinodal Zr–Nb alloys with heterostructure. Spinodal decomposition significantly improved their mechanical strength due to the nanosized dual-cubic reinforcement. The Zr–Nb alloys showed large corrosion resistance in Hanks’ solution because of formation of dense passivation films composed of ZrO2 and Nb2O5 during the polarization process. The magnetic susceptibilities of the Zr–Nb alloys were significantly lower than those of commercial Co–Cr–Mo and Ti alloys. The cell viability of the Zr–Nb alloys was more than 98 % toward MC3T3-E1 cells. The results demonstrate that spinodal Zr–Nb alloys have enormous potential as bone-implant materials due to their outstanding overall mechanical properties, high corrosion resistance, low magnetic susceptibility, and sufficient biocompatibility.

Monitoring and Evaluation of the Corrosion Behavior in Seawater of the Low-Alloy Steels BVDH36 and LRAH36.

The purpose of this study is to evaluate the corrosion resistance in natural seawater (Năvodari area) of two types of low-alloy carbon steels BVDH36 and LRAH36 by electrochemical methods. The electrochemical methods used were the evolution of the free potential (OCP), electrochemical impedance spectroscopy (EIS), polarization resistance (Rp) and corrosion rate (Vcorr), potentiodynamic polarization (PD), and cyclic voltammetry (CV). The studies were completed by ex situ characterization analyzes of the studied surfaces before and after corrosion such as: optical microscopy, scanning electron microscopy and X-ray diffraction analysis. The results of the study show us that the polarization resistance of the low-alloy carbon steel BVDH36 is higher compared to the polarization resistance of the low-alloy carbon steel LRAH36. It is also observed that with the increase in the immersion time of the samples in natural seawater, the polarization resistance of the BVDH36 alloy increases over time and finally decreases, and for the carbon steel LRAH36 the polarization resistance increases.

Study on the structure, growth pattern and corrosion behavior of CoCrFeNiAl high entropy alloy coatings - base on hollow cathode effect

The surface of TC18 titanium alloy was coated with a CoCrFeNiAl HEA coating using double-glow plasma surface metallurgy. The structure, phase, and growth mode of the coating were investigated, along with its electrochemical corrosion behavior. The prepared HEA coating, under the influence of the hollow cathode effect and non-equilibrium diffusion, exhibits a composite structure consisting of a deposited layer and an interdiffused layer. It demonstrates robust metallurgical bonding with the substrate, and it exhibits a hardness of 12.66 GPa and an elastic modulus of 158.52 GPa, along with exceptional hardness and high elastic modulus. The primary phase of the coating consists of an FCC solid solution, with a minor presence of Ni3Al and Al8Cr5 phases. TEM results demonstrate that hollow cathode enhanced sputtering effectively refines the grain structure on the substrate surface. The high entropy alloy coating, characterized by a significant abundance of nanocrystalline and amorphous structures, is obtained under the bombardment of high-energy particles. Gradually increasing from the interface to the deposited layer, there is an augmentation in the content of nanocrystals. The transition from the substrate to the sedimentary layer comprises three distinct regions: a surface fine crystal region, a nanocrystalline structure region, and a nanocrystalline and amorphous precipitated phase-rich region. In 3.5 wt% NaCl solution, the electrochemical corrosion rate of the coating is 1.36 × 10−1 μm·year−1, which is about ten times lower than that of the substrate. Moreover, pre-soaking forms a stable oxide film on the coating's surface, effectively preventing corrosion and demonstrating its remarkable corrosion resistance.

Effects of Li addition on the properties of biodegradable Zn–Fe–Li alloy: Microstructure, mechanical properties, corrosion behavior, and cytocompatibility

Biodegradable Zn-based alloys have excellent mechanical properties, a good corrosion rate, and favorable biocompatibility, which have broad application prospects. In this study, new biodegradable Zn-0.5Fe-xLi (x = 0, 0.2, 0.5, 0.8 wt%) alloys were successively prepared by melting and hot extrusion, and the effects of Li content on the microstructure, mechanical properties, corrosion behavior, and biocompatibility of the alloys were investigated. The formation of FeZn13 and eutectic LiZn4 phases in the Zn-0.5Fe-xLi alloys and the grain size of the Zn-0.5Fe-0.5Li alloys significantly reduced with an increase in Li content. The synergistic effect of solid solution and grain refinement of Li significantly improved the strength of the Zn-0.5Fe-0.5Li alloy and ensured the ductility of the alloy, which resulted in its optimum overall performance. The yield strength was 353.6 ± 6.8 MPa, the ultimate tensile strength was 441.9 ± 2.6 MPa, and the elongation was 26.8 ± 0.8%. In addition, the Zn-0.5Fe-0.5Li alloy showed excellent corrosion properties. The electrochemical corrosion rate was 0.735 mm/year, and the surface corrosion degradation morphology was uniform after immersion. The Zn-0.5Fe-0.5Li alloy also demonstrated the most favorable in vitro cytocompatibility in cellular experiments. Overall, the extruded Zn-0.5Fe-0.5Li alloy is a promising biodegradable implant material with excellent mechanical properties, a suitable corrosion rate, and good cytocompatibility.

A biodegradable Zn-5Gd alloy with biomechanical compatibility, cytocompatibility, antibacterial ability, and in vitro and in vivo osteogenesis for orthopedic applications

Zinc (Zn) and some of its alloys are recognized as promising biodegradable implant materials due to their acceptable biocompatibility, facile processability, and moderate degradation rate. Nevertheless, the limited mechanical properties and stability of as-cast Zn alloys hinder their clinical application. In this work, hot-rolled (HR) and hot-extruded (HE) Zn-5 wt.% gadolinium (Zn-5Gd) samples were prepared by casting and respectively combining with hot rolling and hot extrusion for bone-implant applications. Their microstructure evolution, mechanical properties, corrosion behavior, cytotoxicity, antibacterial ability, and in vitro and in vivo osteogenesis were systematically evaluated. The HR and HE Zn-5Gd exhibited significantly improved mechanical properties compared with those of their pure Zn counterparts and the HR Zn-5Gd showed a unique combination of tensile properties with an ultimate tensile strength of ∼311.6 MPa, yield strength of ∼236.5 MPa, and elongation of ∼40.6%, all of which are greater than the mechanical properties required for bone-implant materials. The HR and HE Zn-5Gd showed higher corrosion resistance than their pure Zn counterpart in Hanks’ solution and the HE Zn-5Gd had the lowest corrosion rate of 155 µm/y measured by electrochemical corrosion and degradation rate of 26.9 µm/y measured by immersion testing. The HR and HE Zn-5Gd showed high cytocompatibility toward MC3T3-E1 and MG-63 cells, high antibacterial effects against S. aureus, and better in vitro osteogenic activity than their pure Zn counterparts. Furthermore, the HE Zn-5Gd exhibited better in vivo biocompatibility, osteogenesis, and osteointegration ability than pure Zn and pure Ti. Statement of significanceThis work reports the mechanical properties, corrosion behaviors, cytocompatibility, antibacterial ability, in vitro and in vivo osteogenesis of biodegradable Zn–Gd alloy for bone-implant applications. Our findings demonstrate that the hot-rolled (HR) Zn–5Gd showed a unique combination of tensile properties with an ultimate tensile strength of ∼311.6 MPa, yield strength of ∼236.5 MPa, and elongation of ∼40.6%. The HR and HE Zn-5Gd showed higher corrosion resistance than their pure Zn counterpart in Hanks’ solution. The HR and HE Zn-5Gd showed high cytocompatibility toward MC3T3-E1 and MG-63 cells, good antibacterial effects against S. aureus, and better in vitro osteogenic activity. Furthermore, the HE Zn-5Gd exhibited better in vivo biocompatibility, osteogenesis, and osteointegration ability than pure Zn and pure Ti.

Degradable Zn–5Ce alloys with high strength, suitable degradability, good cytocompatibility, and osteogenic differentiation fabricated via hot-rolling, hot-extrusion, and high-pressure torsion for potential load-bearing bone-implant application

Zinc (Zn)-based alloys are considered the next-generation biodegradable material for promising bone-implant devices due to their good degradability, formability, and functionality. Nevertheless, the as-cast Zn alloys showed a low strength-toughness, making it challenging to meet the mechanical properties requirements for high-load-bearing bone implants due to their hexagonal close-packed structure, coarse grain size, and less sliding system. Herein, we have developed biodegradable Zn–5Ce alloys by cerium (Ce) alloying followed by hot-rolling, hot-extrusion, and high-pressure torsion (HPT), respectively, for potential bone-implant application. Mechanical testing revealed that the HPT sample exhibited the best mechanical performance matching among the Zn–5Ce samples with a high ultimate tensile strength of ∼345 MPa, yield strength of ∼230 MPa, a moderate elongation of ∼11.4%, and macro-hardness of ∼96.6 HB. Electrochemical corrosion and static immersion testing revealed that the HPT sample showed the highest electrochemical corrosion rate of ∼416 μm/y and degradation rate of ∼43.8 μm/y in Hanks' solution among the Zn–5Ce samples, which is suitable for degradation rate requirements for bone-implant application. Bio-tribological testing revealed that the HPT sample showed high bio-tribological properties matching in Hanks’ solution with the lowest friction coefficients of ∼0.530 and moderate wear loss of ∼2.2 mg. Cytocompatibility and osteogenic differentiation assessment revealed that the diluted extract of the HPT sample showed the highest cytocompatibility towards 3T3 and MG-63 cells and osteogenic differentiation performance towards 3T3 cells among the most diluted extracts. Accordingly, the HPT Zn–5Ce sample is expected to be used for high-load-bearing degradable bone-implant devices, including bone fixation and guided bone regeneration systems.

Copper, Iron and Aluminium Electrochemical Corrosion Investigation during Electrolysis and Temperature Increasing

An experimental method to calculate average charge of metal ions by electrolysis at different temperatures is proposed. Aluminium undergoes dissolution to the Al3+ ions at all temperatures. Iron undergoes dissolution to the Fe2+ or the Fe3+ ions and copper undergoes dissolution to the Cu+ or the Cu2+. It depends on temperature and electric current density. Direct electric current value and anode mass decreasing were measured during electrolysis into concentrated NaCl solution in water (5 mol/kg or 23.1%, freezing point equals -22°C, pH 6.5–7.5) at room temperature and 100°C. The average charges of copper, iron, and aluminium ions were calculated using Faraday’s law of electrolysis at electric current density 3,000 A/m2 (or 30 A/dm2): +3 for aluminium; +2 for iron; and +1 for copper at room temperature, and +3 for aluminium; +2 for iron; and +1.5 for copper at temperature 100°C. The main condition was zAl=3. We concluded that calculations of the average metal ions charges, zFe and zCu, were correct since zAl=3. The result is as follows: the Al3+, the Fe2+, and the Cu+ ions dissolve into concentrated NaCl solution in water at room temperature; the Al3+, the Fe2+, the Cu+ and the Cu2+ ions (50%/50%) dissolve into the solution at temperature 100°C. We have obtained experimentally and by mathematical modelling that aluminium anodes (cylindrical or spherical) dissolve into the solution more rapidly with temperature increasing during electrolysis accordingly to the Arrhenius law, while copper anodes (cylindrical or spherical) dissolve more slowly with temperature increasing from room temperature to temperature 180°C like “inverse Arrhenius law”. Iron electrochemical corrosion rate practically does not depend on temperature below 100°C (and, obviously, up to 180°C) like “zeroth Arrhenius law”. The spherical anode effect is greater than the cylindrical anode effect in 1.5 times.

Computational Prediction of Electrochemical Corrosion Rates of Copper in the Presence of Corrosion Inhibitors

Computational prediction of corrosion rates is still a challenging issue in the field of metal corrosion. In this study, we proposed a computational model to predict the corrosion rates of copper in the presence of adsorption-type corrosion inhibitors using density functional theory calculations, microkinetic simulation, and machine learning. The model-calculated corrosion current and potential of clean copper are close to values obtained in available experiments. The copper corrosion rates in the presence of inhibitors were further predicted using the adsorption free energy of adsorbed inhibitors and the inhibitor concentration in solution to describe the effects of inhibitors. The proposed model was applied to predict corrosion inhibition efficiency by combining it with a machine learning model. The combining model exhibited that it was more interpretative and accurate than a machine-learning-only model in predicting corrosion inhibition efficiencies of organic compounds on copper.

Iron, copper, and aluminium electrochemical corrosion in motionless and moving electrolytes investigation during electrolysis

An experimental method to calculate average charge of metal ions by electrolysis at different temperatures is proposed. Aluminium undergoes dissolution to the Al3+ ions at all temperatures. Iron undergoes dissolution to the Fe2+ or the Fe3+ ions and copper undergoes dissolution to the Cu+ or the Cu2+. It depends on temperature and electric current density. Direct electric current value and anode mass decreasing were measured during electrolysis into concentrated NaCl solution in water (5 mol/kg or 23.1 %, freezing point equals −22 °C, pH 6.5–7.5) at room temperature and 100 °C. The average charges of copper, iron, and aluminium ions were calculated using Faraday's law of electrolysis at electric current density 3000 A/m2 (or 30 A/dm2 = 3 mA/mm2): +3 for aluminium; +2 for iron; and +1 for copper at room temperature, and +3 for aluminium; +2 for iron; and +1.5 for copper at temperature 100 °C. The main condition was zAl = 3. We concluded that calculations of the average metal ions charges, zFe and zCu, were correct since zAl = 3. The result is as follows: the Al3+, the Fe2+, and the Cu+ ions dissolve into concentrated NaCl solution in water at room temperature; the Al3+, the Fe2+, the Cu+ and the Cu2+ ions (50 %/50 %) dissolve into the solution at temperature 100 °C. We have obtained experimentally and by mathematical modelling that aluminium anodes (cylindrical or spherical) dissolve into the solution more rapidly with temperature increasing during electrolysis accordingly to the Arrhenius law, while copper anodes (cylindrical or spherical) dissolve more slowly with temperature increasing from room temperature to temperature 180 °C like “inverse Arrhenius law”. Iron electrochemical corrosion rate practically does not depend on temperature below 100 °C (and, obviously, up to 180 °C) like “zeroth Arrhenius law”. The spherical anode effect is practically the same as the cylindrical anode effect. The galvanic current dependence on ratio of cathodic surface area to anodic surface area in the system Fe-chromium (Cr) stainless steel and the time of the iron anodes dissolution in motionless electrolyte and in moving electrolyte are also analysed using literature experimental data.

Biodegradable iron-based foams prepared by the space holder technique using urea

Iron-based degradable biomaterials have attracted much attention as next-generation bone implants due to their excellent mechanical properties and good biocompatibility. Many studies are now focusing on the preparation and detailed study of porous versus non-porous degradable materials. Porous degradable biomaterials have many advantages over the non-porous ones owing to their structure, which allows easier bone tissue ingrowth. The aim of this work was to prepare Fe-based biodegradable porous materials in a cost-effective way via powder metallurgy technique using urea space holders. Five different samples with increasing space holder weight ratio (up to 20 wt%) were prepared. Surface morphology and sample structure were studied using the optical microscopy, Raman spectroscopy, and scanning electron microscopy (SEM) with energy-dispersive X-ray analysis (EDX). Electrochemical corrosion rate analysis confirmed that the samples corroded faster with increasing number of pores. With an increasing amount of urea, the number of pores increased proportionally, which can potentially be used to tune the corrosion rate. However, mechanical integrity of the samples was not maintained when more than 10 wt% of space holder was used.Graphical abstract

Mechanical properties, corrosion and degradation behaviors, and in vitro cytocompatibility of a biodegradable Zn-5La alloy for bone-implant applications.

Zinc (Zn) and its alloys are used in bone-fixation devices as biodegradable bone-implant materials due to their good biosafety, biological function, biodegradability, and formability. Unfortunately, the clinical application of pure Zn is hindered by its insufficient mechanical properties and slow degradation rate. In this study, a Zn-5 wt.% lanthanum (Zn-5La) alloy with enhanced mechanical properties, suitable degradation rate, and cytocompatibility was developed through La alloying and hot extrusion. The hot-extruded (HE) Zn-5La alloy showed ultimate tensile strength of 286.3MPa, tensile yield strength of 139.7MPa, elongation of 35.7%, compressive yield strength of 262.7MPa, and microhardness of 109.7 HV. The corrosion resistance of the HE Zn-5La in Hanks' and Dulbecco's modified Eagle medium (DMEM) solutions gradually increased with prolonged immersion time. Further, the HE Zn-5La exhibited an electrochemical corrosion rate of 36.7μm/y in Hanks' solution and 11.4μm/y in DMEM solution, and a degradation rate of 49.5μm/y in Hanks' solution and 30.3μm/y in DMEM solution, after 30 d of immersion. The corrosion resistance of both HE Zn and Zn-5La in DMEM solution was higher than in Hanks' solution. The 25% concentration extract of the HE Zn-5La showed a cell viability of 106.5%, indicating no cytotoxicity toward MG-63 cells. We recommend the HE Zn-5La alloy as a promising candidate material for biodegradable bone-implant applications. STATEMENT OF SIGNIFICANCE: This work reports the mechanical properties, corrosion and degradation behaviors, in vitro cytocompatibility and antibacterial ability of biodegradable Zn-5La alloy for bone-implant applications. Our findings demonstrate that the hot-extruded (HE) Zn-5La alloy showed an ultimate tensile strength of 286.3MPa, a yield strength of 139.7MPa, an elongation of 35.7%, compressive yield strength of 262.7MPa, and microhardness of 109.7 HV. HE Zn-5La exhibited appropriate degradation rates in Hanks' and DMEM solutions. Furthermore, the HE Zn-5La alloy showed good cytocompatibility toward MG-63 and MC3T3-E1 cells and greater antibacterial ability against S. aureus.