Increase In Corrosion Potential Research Articles

Microstructure, mechanical and corrosion properties of TiN/Ni nanomultilayered films

Nanomultilayered TiN/Ni thin films with different bilayer periods (57.8–99.7 nm) and Ni single-layer thickness (3.9–19.2 nm) were prepared by alternatively sputtering Ti and Ni targets in N2 gas atmosphere. The microstructure, mechanical and corrosion properties of the multilayer films were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), nanoindenter and electrochemical technologies. The multilayer films are fine with a mean grain size of ~ 8–9 nm independent of the bilayer period. However, the smoothness and compactness seem to decrease with the bilayer period increasing. The hardness (H) and elastic modulus (E) of the multilayer films gradually decrease as the bilayer period increases, and the multilayer film with bilayer period of 57.8 nm exhibits higher H, ratios of $$ (H/E^{*} \,\,{\text{and}}\,\,H^{3} /E^{*2} ) $$ ( $$ E^{*} $$ is effective Young’s modulus) than the monolithic TiN film and the other multilayers. The multilayer films exhibit an obvious passivation phenomenon in 10% H2SO4 solution, and the passive current and corrosion current densities decrease, whereas the corrosion potential increases when the bilayer period or Ni single-layer thickness decreases. It is found that the passivating behavior and corrosion potential of the multilayers are more sensitive to Ni single-layer thickness than the bilayer period. More corrosion pits and lamellar flaking could be found on the films with larger bilayer period or Ni single-layer thickness.

Cathodic electrophoretic deposition (EPD) of phenylenediamine-modified graphene oxide (GO) for anti-corrosion protection of metal surfaces

Anti-corrosion metal protection of the 2D structured graphene oxide (GO) was investigated in this study using its intrinsic impermeability against reactive molecules stemming from the small geometric pore size and π-orbital repelling fields of graphene. The electrophoretic deposition (EPD) of GO sheets on metals is an attractive coating method but the negatively-charged GO only allows the anodic EPD process, which makes it difficult to achieve high-quality coating layers due to gas bubbling and electrochemical oxidation of metals. Thus, we imposed the positive charge to GO sheets using p-phenylenediamine (PPD) and successfully carried out the cathodic EPD in the ethanol aqueous solution. The cathodic EPD of GO on cupper provided a linear growth rate with both deposition time and voltage providing the thickness over 6.0 μm in a void-free and robust feature, which could hardly be achieved by other coating methods. Converting the GO coating to the reduced GO (RGO) by thermal reduction, we successfully increased the RGO adhesion strength up to the highest adhesion grade of 5B in the cross-cut adhesion test. An excellent anti-corrosion protection capability of the developed RGO coating was demonstrated by a decreased corrosion current density and increased corrosion potential in potentiodynamic polarization analysis.

Multi-response optimization of mechanical properties for ZrWN films grown using grey Taguchi approach

ZrWN nitride films are prepared using direct current (dc) reactive magnetron sputtering. Grey Taguchi analysis is used to determine the effect of deposition parameters (substrate plasma etching time, N2/(N2+Ar) flow rates, deposition time, and substrate temperature) on the microstructure and the tribological properties. An orthogonal array, signal-to-noise ratio and analysis of variance are used to determine the effects of deposition parameters. The substrates are pretreated using oxygen plasma etching. The resulting ZrWN coatings are homogeneous, very compact and completely adhered to the substrate. In the confirmation runs, using grey Taguchi analysis, the coefficient of friction decreases from 0.45 ± 0.02 to 0.35 ± 0.02, the corrosion potential increases from − 0.201 ± 0.01 to − 0.072 ± 0.01 V, the Vickers hardness increases from 23.63 ± 0.07 to 24.65 ± 0.05 GPa, and reduced modulus increases from 115.82 ± 1.13 to 136.17 ± 1.18 GPa. The ZrWN films are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rockwell C indentation and scratch testing. The TEM pattern for the ZrWN films corresponds to the (111), (200) and (220) planes of the face center cubic structure. Samples with a ZrWN film coating are classified as HF1 and exhibit good adhesive strength. The signal of friction and the associated acoustic emission signal are analyzed, and the scratch profile is analyzed using an optical microscope. Results show that the adhesive force for the critical load Lc2 is about 76.2 ± 0.5 N.

Open circuit potential and leaching rate of pyrite in cupric chloride solution

ABSTRACTAs a refractory gold mineral, pyrite needs to be oxidised prior to gold leaching. In this study, the effect of [Cl−] concentration (40.6–149.8 g/L), [Cu2+] concentration (0.8–31.6 g/L), pH (1.5–2.5) and temperature (25–90 –C) on the pyrite leaching rate was investigated. In addition, the open circuit potential (OCP) values of pyrite in cupric chloride solution were investigated. A linear regression model was constructed to predict pyrite dissolution rate i.e. corrosion current density. It was shown that the temperature had a significant positive effect on pyrite dissolution, while increased cupric ion concentration was also shown to provide some dissolution enhancement. According to the regression analysis, pH had no effect on the corrosion current density at OCP. Dissolution rates of pyrite varied between 0.05 and 2.9 µm/h. The activation energy values varied from 20 to 90 kJ/mol, indicated that the pyrite dissolution reaction rate was controlled by the chemical reaction or mixed mechanism rather than diffusion alone. The simultaneous increase in corrosion potential and corrosion current density indicated that the anodic pyrite dissolution reaction was rate determining at OCP.

Effect of iron content on the corrosion of pure magnesium: Critical factor for iron tolerance limit

The present work investigates the corrosion behaviour of magnesium with different Fe contents. It is found that the micro-galvanic coupling between Fe-rich particles and magnesium matrix results in surface film formation and decrease in anodic reaction rate, consequently, increase of corrosion potential. Depending on the population density of Fe-rich particle, if the corrosion potential increases to the breakdown potential of surface film, localized corrosion initiates at the sites of breakdown. It is observed that Mg with different Fe contents exhibit the same critical potential value for corrosion initiation. Thus, corrosion potential is a critical factor for the corrosion tolerance limit of Fe in Mg.

Long-Term Behavior of Carbon Steel in Alkaline Nitrate Solutions Related to Radioactive Waste Storage

Radioactive wastes from the processing of nuclear materials used for weapons production have been stored in underground carbon steel tanks for the past several decades. The waste solutions are a complex mixture of a variety of anionic and cationic species, dominated by sodium nitrates, nitrites, and hydroxide. It has been well established that localized corrosion and stress corrosion cracking of carbon steel can occur in these solutions above certain critical potentials that are determined by the anionic species and temperature. Recent studies have shown that the corrosion potential increases significantly over a period of weeks to months, such that there is a concern about exceeding the critical potentials under natural conditions of exposure. This paper discusses the evolution of the corrosion potential of steel in alkaline solutions (pH >11) in comparison to the critical potentials. The impedance behavior of the steel in these solutions shows changes in the semi-conductive behavior over time as well as the density of charge carriers that may influence the evolution of corrosion potential. The effect of the changes in corrosion potential on localized corrosion and stress corrosion cracking is discussed.

Effect of laser shock peening on electrochemical corrosion resistance of IN718 superalloy.

The effects of laser shock peening (LSP) treatment with different impacts on surface roughness, micro-hardness, microstructural observations, residual stress, and electrochemical corrosion resistance of IN718 superalloy were investigated. Results show that the corrosion potential increases to -0.4863 V, -0.2956 V, and -0.3578 V, and the corrosion rate reduces 66.10%, 79.08%, and 84.07% for 2 LSP impacts, 4 LSP impacts, and 6 LSP impacts, respectively, compared with the untreated one. In addition, LSP treatment has an important influence on grain refinement, which increases micro-hardness, reduces roughness of a surface, and also results in a compressive residual stress on a surface, both of which can be responsible for the electrochemical corrosion improvement. Finally, corrosion morphology under scanning electron microscopy demonstrates that LSP is an effective method to prevent the corrosion micro-crack propagation and improve the corrosion resistance. Also, with an increase in laser impacts, the electrochemical corrosion resistance will be further improved.

Corrosion behaviour of low temperature nitrided nickel-free, AISI 200 and AISI 300 series austenitic stainless steels in NaCl solution

Low temperature plasma nitriding was performed on CrNi-based (AISI 316L), CrMn-based (AISI 202) and nickel-free (P558) austenitic stainless steels. For all the used steels modified surface layers consist mainly of S phase without the precipitation of large amounts of nitrides, and they show enhanced surface microhardness and corrosion resistance in NaCl acqueous solution. The different electrochemical corrosion testing techniques evidence that the increase of corrosion potential may be ascribed mainly to nitrogen addition, while regarding the increase of potential, at which localized corrosion phenomena occur, also alloy elements, and in particular Mo, play an important role.

Improving Corrosion Resistance of 316L Austenitic Stainless Steel Using ZrO2 Sol-Gel Coating in Nitric Acid Solution

In this study, thin-film coating of zirconium oxide (ZrO2) was prepared by sol-gel method and subsequent heat treatment process. The sol was prepared by controlled hydrolysis of zirconium tetrapropoxide using acetic acid and ethanol/acetylacetone mixture as catalyst and chelating agent, respectively, and finally deposited onto the 316L austenitic stainless steel (316L SS) using dip coating method in order to improve its corrosion resistance in nitric acid medium. The composition, structure, and morphology of the coated surface were investigated by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The obtained results from XRD and FTIR state the formation of tetragonal and monoclinic ZrO2 phase. Also, the obtained results from surface morphology investigation by SEM and AFM indicate the formation of smooth, homogeneous and uniform coatings on the steel substrate. Then, the corrosion behavior of stainless steel was investigated in a 1 and 10 M nitric acid solutions using electrochemical impedance spectroscopy and linear polarization test. The obtained results from these tests for ZrO2-coated specimens indicated a considerable improvement in the corrosion resistance of 316L stainless steel by an increase in corrosion potential and transpassive potential, and a decrease in passive current density and corrosion current density. The decrease in passive current density in both the concentration of solutions was two orders of magnitude from bare to coated specimens.

Corrosion behavior of ultrafine-grained AA2024 aluminum alloy produced by cryorolling

The objectives of this study were to produce ultrafine-grained (UFG) AA2024 aluminum alloy by cryorolling followed by aging and to evaluate its corrosion behavior. Solutionized samples were cryorolled to ~85% reduction in thickness. Subsequent aging resulted in a UFG structure with finer precipitates of Al2CuMg in the cryorolled alloy. The (1) solutionized and (2) solutionized and cryorolled samples were uniformly aged at 160°C/24 h and were designated as CGPA and CRPA, respectively; these samples were subsequently subjected to corrosion studies. Potentiodynamic polarization studies in 3.5wt% NaCl solution indicated an increase in corrosion potential and a decrease in corrosion current density for CRPA compared to CGPA. In the case of CRPA, electrochemical impedance spectroscopic studies indicated the presence of two complex passive oxide layers with a higher charge transfer resistance and lower mass loss during intergranular corrosion tests. The improved corrosion resistance of CRPA was mainly attributed to its UFG structure, uniform distribution of fine precipitates, and absence of coarse grain-boundary precipitation and associated precipitate-free zones as compared with the CGPA alloy.

Anodic plasma electrolytic nitrocarburising of VT22 titanium alloy in carbamide and ammonium chloride electrolyte

The structure of alpha- and beta-titanium alloy VT22, its microhardness, surface roughness, wear and corrosion resistance after anodic plasma electrolytic nitrocarburising in an electrolyte containing carbamide and ammonium chloride were investigated. An X-ray diffractometer and a scanning electron microscope were used to characterize the phase composition and structure of the modified surface. Tribological properties of the treated titanium alloy were evaluated using a ball-on-disc tribometer under lubricated testing conditions. The effect of processing temperature on corrosion resistance of the plasma electrolytic nitrocarburising samples was examined by means of potentiodynamic polarization in Ringer’s solution. It was shown that the anodic nitrocarburising provides saturation of the titanium alloy with oxygen, nitrogen and carbon and the formation of TiO2 with a rutile structure and a nitrogen/carbon solid solution in titanium. The anodic plasma electrolytic nitrocarburising at all treatment temperatures diminishes the wear rate of the titanium alloy samples and the surface roughness. Friction coefficient of treated samples can be reduced by 4.7 times. The anodic nitrocarburising results in an enhanced corrosion resistance since the corrosion potential increases by an order of magnitude.

Mechanical Properties and Corrosion Behavior of Hot Extruded Mg 99.2 Ca 0.6 Mn 0.2 Alloy in SBF Solution

Abstract The tensile and compression properties of hot extruded Mg99.2Ca0.6Mn0.2 (at%) alloy were tested, and the cyclic polarization curves and impedance spectroscopy of the alloy soaked in SBF solutions with various pH values were measured by electrochemical method so that the corrosion behavior of the alloy can be evaluated and the experimental foundation for preparation of magnesium implant materials was provided. The results show that the tensile failure of the alloy appears to be characteristic of quasi-cleavage fracture. The tensile strength, yield strength, compressive strength and elongation are 279 MPa, 251 MPa, 330 MPa and 11% at room temperature, respectively. The pH value of the solution has prominent effect on corrosion behavior. As the pH value increases, the arc radius of impedance spectroscopy and corrosion potential increase remarkably, whereas the corrosion current density decreases, and thus the corrosion resistance of the alloy is strengthened. There is only one time constant which appears at low frequency in phase angle plot. The corrosion rate can be significantly reduced by increasing pH value of the solution. The instantaneous corrosion rates of the alloy immersed in the solutions with pH value of 7.2 and 10.0 are 4.1 mm/a and 0.2 mm/a, respectively.

Effect of Microstructure of 304L SS and Thermal Aging of 304L SS Weld on the Corrosion Behavior in Simulated High Level Waste

The effect of oxidizing ions present in simulated high level liquid waste (HLW) on the corrosion behaviour of solution annealed, sensitized 304L SS and 304L SS weld was investigated by potentiodynamic anodic polarization technique. Potentiodynamic anodic polarization studies showed a higher passivation current density and increased corrosion potential (Ecorr) in simulated HLW when compared to 3 M HNO3 in all the specimen mentioned above. In addition, the effect of microstructure of thermally aged 304L SS weld on the corrosion behavior was investigated in simulated HLW medium. Thermal ageing of 304L SS weld was carried out at 1023 K/100 h. Optical microscopy confirmed step microstructure for solution annealed and ditch microstructure for the sensitized specimens. The weld region was found to possess delta-ferrite distributed in austenite matrix. Thermal ageing resulted in fragmentation/dissolution of delta-ferrite and transformation of delta-ferrite to carbides and sigma phases. The thermally aged 304L SS weld specimen showed only a marginal decrease in corrosion resistance in simulated HLW when compared to the 304L SS weld.

The Effect of Surfactant Content over Cu-Ni Coatings Electroplated by the sc-CO₂ Technique.

Co-plating of Cu-Ni coatings by supercritical CO2 (sc-CO2) and conventional electroplating processes was studied in this work. 1,4-butynediol was chosen as the surfactant and the effects of adjusting the surfactant content were described. Although the sc-CO2 process displayed lower current efficiency, it effectively removed excess hydrogen that causes defects on the coating surface, refined grain size, reduced surface roughness, and increased electrochemical resistance. Surface roughness of coatings fabricated by the sc-CO2 process was reduced by an average of 10%, and a maximum of 55%, compared to conventional process at different fabrication parameters. Cu-Ni coatings produced by the sc-CO2 process displayed increased corrosion potential of ~0.05 V over Cu-Ni coatings produced by the conventional process, and 0.175 V over pure Cu coatings produced by the conventional process. For coatings ~10 µm thick, internal stress developed from the sc-CO2 process were ~20 MPa lower than conventional process. Finally, the preferred crystal orientation of the fabricated coatings remained in the (111) direction regardless of the process used or surfactant content.

Effect of crack openings on carbonation-induced corrosion

Reinforced concrete is widely used in the construction of buildings, historical monuments, infrastructures and nuclear power plants. For a variety of reasons, many concrete structures are subject to unavoidable cracks that accelerate the diffusion of atmospheric carbon dioxide to the steel/concrete interface. Carbonation at the interface induces steel corrosion that could cause the development of new cracks in the structure, a determining factor for its durability. The aim of this article is to study the effect of existing cracks on the development of carbonation-induced corrosion. The results indicate that, after the initiation phase, the corrosion kinetics decreases with time and the free corrosion potential increases independently of the crack opening. In addition, the corroded zone matches the carbonated one. The interpretation of these results allows the authors to conclude that, during the corrosion process, corrosion products seal the crack and act as a barrier to oxygen and water diffusion. Consequently, the influence of crack opening on corrosion development is masked and the corrosion development is limited.

Erratum to: Thermal stability, mechanical properties and corrosion behavior of a Mg–Cu–Ag–Gd metallic glass with Nb addition

By the minor addition of Nb to a Mg–Cu–Ag–Gd alloy, a Mg–Cu–Ag–Gd–Nb bulk metallic glass (BMG) with improved thermal stability and corrosion resistance as well as good mechanical properties was developed. Mg54Cu26.5Ag8.5Gd11−x Nb x (x = 0, 1) BMGs with a diameter of 2 mm were fabricated by copper-mold casting. The Mg54Cu26.5Ag8.5Gd10Nb1 BMG exhibits enlarged supercooled liquid region of 58 K. Electrochemical measurements indicate that the addition of Nb improves the corrosion resistance of the Mg-based BMG in NaCl solution evidenced by the increased corrosion potential, though no significant effect of Nb on the corrosion behavior of the BMG in NaOH solution is observed. The Mg–Cu–Ag–Gd–Nb BMG also shows high compressive strength up to 890 MPa and elastic strain of about 1.9%.

Nitrate reduction and its effects on trichloroethylene degradation by granular iron

Laboratory column experiments and reactive transport modeling were performed to evaluate the reduction of nitrate and its effects on trichloroethylene (TCE) degradation by granular iron. In addition to determining degradation kinetics of TCE in the presence of nitrate, the columns used in this study were equipped with electrodes which allowed for in situ measurements of corrosion potentials of the iron material. Together with Raman spectroscopic measurements the mechanisms of decline in iron reactivity were examined. The experimental results showed that the presence of nitrate resulted in an increase in corrosion potential and the formation of thermodynamically stable passive films on the iron surface which impaired iron reactivity. The extent of the decline in iron reactivity was proportional to the nitrate concentration. Consequently, significant decreases in TCE and nitrate degradation rates and migration of degradation profiles for both compounds occurred. Furthermore, the TCE degradation kinetics deviated from the pseudo-first-order model. The results of reactive transport modeling, which related the amount of a passivating iron oxide, hematite (α-Fe2O3), to the reactivity of iron, were generally consistent with the patterns of migration of TCE and nitrate profiles observed in the column experiments. More encouragingly, the simulations successfully demonstrated the differences in performances of three columns without changing model parameters other than concentrations of nitrate in the influent. This study could be valuable in the design of iron permeable reactive barriers (PRBs) or in the development of effective maintenance procedures for PRBs treating TCE-contaminated groundwater with elevated nitrate concentrations.

Corrosion protection and electrical conductivity of copper coatings deposited by low-pressure cold spraying

Aluminium/copper contacts occur in power networks made of aluminium alloy busbars. Bolted joints of aluminium and copper cause galvanic corrosion of aluminium in the presence of electrolyte. The paper focuses on the effect of different powder morphology and the addition of ceramics on coating porosity and consequently on corrosion resistance and electrical conductivity behaviour. In this work, corrosion protection of copper coatings deposited by low-pressure cold spraying (LPCS) onto AA 1350 aluminium alloy is examined. The coatings were sprayed using two copper powders of different morphology, namely spherical and dendritic ones. These powders were mixed with alumina before spraying in a 50:50 weight ratio and composite coatings were deposited. The coating microstructures were characterized by the scanning electron microscopy (SEM). The measurements of coating hardness in the middle of the coating thickness were carried out. The coating corrosion protection was analysed by polarization measurements. All coatings showed increased corrosion potential as compared to the substrate. The electrical conductivity of coatings was determined by eddy-current measurements and showed coating conductivity up to 63% IACS. Moreover, coatings heat treatment was conducted to further increase electrical conductivity.

Imidazole based compounds as copper corrosion inhibitors in seawater

The effects of imidazole and its structural derivatives: purine, adenine and 6-benzylaminopurine, on copper corrosion in seawater were investigated. Electrochemical methods were chosen for this purpose and the results show that they all act as mixed-type corrosion inhibitors under tested conditions. According to the potentiodynamic polarization results inhibition efficiency at corrosion potential increases in the following order imidazole<purine<adenine<6-benzylaminopurine, which is in agreement with the expectation that the increase of molecular weight and number of heteroatoms in the molecule leads to the increase of inhibition efficiency degree. In the broader potential range, adenine is more efficient. The mechanism of inhibitor action includes adsorption on copper surface that fits the Langmuir adsorption isotherm. Quantum mechanical calculations indicate that there is a correlation between energy gap and inhibition efficiency.

Chemical mechanical planarization of Al alloy in alkaline slurry at low down pressure

Effects of hydrogen peroxide and inhibitors (sodium benzoate, NaNO3, sodium lauryl sulfate) on material removal at low down pressure for chemical mechanical planarization of Al alloy were investigated in alkaline slurry by using atomic force microscope, electrochemical polarization tests, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The material removal rate initially increases with concentration of H2O2 owing to the increase in corrosion potential and in thickness of oxidization layer, and then reaches a constant value. Additionally, surface scratch and orange peel disappear with H2O2. Sodium lauryl sulfate (SLS) reduces the surface roughness while maintaining a reasonable material removal rate in comparison with sodium benzoate and NaNO3 due to decrease in passive current density and increase in thickness of passive layer. A weak passive layer is generated on Al alloy surface by adhesive of SLS with H2O2, which is easily removed at low mechanical abrasion. The chemical composition of the film layer is dominated by the Al oxide rather than sulfate though the thickness of the passive layer is increased with SLS concentration.