Current distribution during galvanic corrosion of carbon steel welded with type-309 stainless steel in NaCl solution

Galvanic corrosion of carbon steel welded with type-309 stainless steel in NaCl solution was tentatively evaluated with a newly developed multi-channel electrode technique in which the welded specimen was divided into nine working electrodes (WEs), reconstructed in resin, and connected individually to an imaginary ground level of an electric circuit via relay switches. This allows the WEs to join a galvanic couple and simultaneous measurement of participating current or open circuit potential of each WE. WEs were immersed together in 5.1 × 10² mol dm⁻³ or 2.1 × 10⁻⁴ mol dm⁻³ NaCl solutions, and spatial distribution of participating currents and open circuit potentials were monitored as a function of immersion time. The WE of the weldment acted as a cathode throughout the immersion period, while the other WEs of base steel became anodes or cathodes depending on their location, immersion time and concentration of the electrolyte solution. The ability of zinc-rich paint to protect the welded specimen as sacrificial anode was also investigated.     

Controlled experiments to study corrosion effects due to external varying fields in embedded pipelines

We present controlled laboratory tests carried out to study corrosion effects due to induction currents on pipes embedded in environments with electrical resistance lateral discontinuities. Sacrificial anodes were connected to underground pipes, and corrosion rates were estimated by measuring the mass loss in each anode. We considered 1 Hz and 50 Hz inducting fields, and the effects produced on the pipes were compared with cases without an external field. The results indicated an increase in the corrosion rate when the pipe was under the effect of induction currents, particularly where there was a change of electrical resistance in the soil.     

The effect of magnesium additions on the microstructure and cut edge corrosion resistance of zinc aluminium alloy galvanised steel

The magnesium levels in 20 μm thick 4.5% Al/Zn galvanising coatings applied to 0.7 mm gauge steel under continuous galvanising conditions were altered from 0.0% to 0.05%. The additions result in an increase in the zinc dendrites (volume fraction from 6% to 22% and number from 150 to 325 mm⁻²) since magnesium depresses the eutectic temperature increasing the freezing range. The microstructural modification results in increasing cut edge corrosion determined using a scanning vibrating electrode technique for 24 h exposure to 5% NaCl. The Mg additions result in an increase in zinc loss (from 80 to 185 μg), an increase in active anode numbers (from 600 to 1700 m⁻¹ cut edge) and an increase in the number of long lived anodes.     

Corrosion and metal release rates of Ni substrates under a porous gold coating

Noble metal coatings intended to protect devices from corrosion may have small porosity that allows corrosive fluid to attack the substrate alloy. A technique combining electrochemical tests and chemical analysis is described that measures low levels of porosity and low corrosion product release rates from the substrate. The technique has been applied to an electrodeposited gold coating on a nickel substrate. The results yielded a porosity of 1.8 × 10⁻³, defined as the area of substrate exposed to corrosion/area of the coating. Galvanic coupling between gold and nickel was found to increase the rate of nickel corrosion by about a factor of 10. A simplified model showed that if the substrate alloy does not passivate, the corrosion product release rate is expected to increase with exposure time.     

Activation of aluminium alloy sacrificial anodes by selenium

Several studies have focussed on alloying and structural modifications of aluminium alloy sacrificial anodes using different activators. The present work explores the feasibility of effective aluminium activation by selenium incorporation. The electrochemical performance of these anodes is evaluated by galvanic and galvanostatic polarization, OCP and CCP measurements etc. The selenium incorporated anode showed improved galvanic efficiency of around 70%. High performed anodes were developed by incorporating other activators of Sn and Bi along with Se in aluminium alloy anodes. The best activator combination was found to be 0.5%Se + 0.1%Sn + 0.1%Bi. This combination of activator in aluminium alloy anodes shows a galvanic efficiency of 90%.     

The durability of different elements doped manganese dioxide-coated anodes for oxygen evolution in seawater electrolysis

Manganese-molybdenum (Mn-Mo), manganese-molybdenum-vanadium (Mn-Mo-V), manganese-molybdenum-iron (Mn-Mo-Fe) and manganese-iron-vanadium (Mn-Fe-V) anodes were prepared by anodic electrodeposition on iridium oxide-coated titanium substrates for oxygen evolution in seawater electrolysis. XRD, FESEM, EDX and oxygen evolution efficient analysis revealed that the prepared anodes had a γ-MnO₂ structure and show a unique mesh-like nanostructure. Oxygen evolution efficiencies were all measured to be more than 99%. The durability tests were performed at 1000 A·m^− 2 in 3.5 wt% NaCl solution at pH 12 and 90 °C. The Mn-Fe-V anode was the most stable electrode during the sea water electrolysis, and maintained an oxygen evolution efficiency of 87.96% even after 500 h. It has been found that the main reason for the eventual decrease in oxygen evolution efficiency was partly because of the peeling and electrochemical dissolution of the oxide layer after electrolysis. Also, it was found that the addition of iron and vanadium would maintain a high level of oxygen evolution efficiency during electrolysis.     

Effects of the nickel-coated ferritic stainless steel for solid oxide fuel cells interconnects

In this study, a protective nickel layer was prepared on the SUS430 alloy substrate by the atmospheric plasma spraying technology (APS). Oxidation kinetics, area specific resistance (ASR) and interfacial microstructure of the SUS430 alloy with nickel layers as well as its elemental composition were studied under the flowing humidified hydrogen atmosphere at 800 °C to evaluate the effectiveness of the protective nickel layer. The current collector between the interconnect and the anode was optimized in this paper. Results showed that the oxide growth rate constant of the SUS430 alloy with the APS nickel layer was 1.99 × 10⁻¹⁴ g² cm⁻⁴ s⁻¹, which was only one fiftieth of that of the alloy without a protective layer. The ASR of the SUS430 alloy with the APS nickel layer was 12 mΩ cm² after being oxidized under the simulated SOFC anode operating atmosphere at 800 °C for 250 h. With the optimized structure of current collector, the contact ASR between the nickel-coated interconnect and the Ni-YSZ anode was only 3 mΩ cm² after being oxidized at 800 °C for 100 h.     

Revealing the effect of aluminum content on the electrochemical performance of magnesium anodes for aqueous batteries

Al is one of the principal alloying elements for Mg anodes. In this study, a series of Mg–Al alloys has been evaluated as anode materials for optimizing the Al addition amount in Mg anodes with the intention of improving the discharge performance in aqueous batteries. The effect of Al content on the discharge potential and corrosion resistance of the Mg anode has been investigated through microstructure characterization, electrochemical measurements in a half-cell, discharge morphology analysis, and Mg–water battery tests. The results show that the Mg–1Al alloy possesses a larger corrosion resistance during discharge, with significant increase of the anode utilization efficiency at 1 and 5 mA/cm² compared with pure Mg. However, a further increase of Al content does not continuously improve the discharge performance of the Mg anode with the decline of utilization efficiency due to the influence of the precipitated phase. This study contributes to a better understanding about the effect of Al on anodic dissolution and corrosion kinetics of the Mg anode.     

Preparation and performance of 3D-Pb anodes for nonferrous metals electrowinning in H2SO4 aqueous solution

The effects of Pb²⁺ concentration, current density, deposition time and temperature on Pb deposit structure were investigated. In lower Pb²⁺ concentration (∼0.15 mol/L), carambola-like 3D-Pb structure was constructed, while in higher Pb²⁺ concentration (≥0.30 mol/L), Pb deposits exhibited pyramid-like structure. Furthermore, the oxide layer and anodic potential of carambola-shaped 3D-Pb (Cara-Pb) and pyramid-shaped 3D-Pb (Pyra-Pb) anodes were investigated and compared with those of fresh Pb anode. After 72 h galvanostatic electrolysis (50 mA/cm²) in 160 g/L H₂SO₄ solution, the oxide layer on Pyra-Pb was much thicker than that on Cara-Pb and Pb anodes, which remarkably relieved intercrystalline corrosion of the metallic substrate. Additionally, the oxide layer on Pyra-Pb anode presented a larger surface area and higher PbO₂ content. Hence, Pyra-Pb anode showed a 40 mV lower anodic potential compared to Cara-Pb and Pb anodes. In sum, Pyra-Pb anode had a potential to decrease energy consumption and prolong the life span of traditional Pb anode.     

Relation between corrosion behavior and microstructure of Mg-Zn-Y alloys prepared by rapid solidification at various cooling rates

The relation between corrosion resistance and microstructure of Mg-Zn-Y alloys with a long period stacking ordered (LPSO) phase has been investigated. In order to clarify the influence of microstructure evolution by rapid solidification on the occurrence of localized corrosion such as filiform corrosion, several Mg_97.25Zn_0.75Y₂ (at. %) alloys with different cooling rates were fabricated by the gravity casting, copper mould injection casting and melt-spinning techniques and their corrosion behavior and microstructures were examined by the salt immersion tests, electrochemical measurements, XRD and TEM. When the cooling rate was less than 3 × 10⁴ K s⁻¹, filiform corrosion propagated in the early stage of salt immersion test, due to formation of a massive block-shaped LPSO phase during casting. On the other hand, when the cooling rate was increased up to 3 × 10⁴ K s⁻¹, rapidly solidified (RS) alloys exhibited excellent corrosion resistance because of grain refinement and formation of a supersaturated single-phase solid solution. Large-sized Mg_97.25Zn_0.75Y₂ alloys fabricated by consolidation of the RS ribbons also exhibited excellent corrosion resistance with passivity. Enhancement of microstructural and electrochemical homogeneities in the Mg-Zn-Y alloys by rapid solidification techniques results in the passivity of substrate materials.     

Microstructural changes in zinc aluminium alloy galvanising as a function of processing parameters and their influence on corrosion

The effect of cooling rate and substrate gauge upon the microstructure and corrosion resistance of Galfan (Zn-4.5 wt.%Al) coated steels is presented. The coatings, applied to steel of gauges 0.47 mm (light gauge) and 0.67 mm (heavy gauge) on a coil coating line, were subjected to three different cooling rates by increasing output from 55% to 100% of the total power from a high powered cooling rig. The increase in cooling rate did not significantly alter the volume fraction of the primary zinc, this remaining at ∼20%. However, the size and number of the primary zinc dendrites were altered. The fast cooled samples contained small but numerous (∼3000 mm⁻² in the heavy gauge and ∼2850 mm⁻² in the light gauge) dendrites as opposed to the slow cooled samples where there were fewer (∼1850 mm⁻² for the heavy gauge and ∼1500 mm⁻² in the light gauge) dendrites of greater size. Characterisation of the surface revealed a reduction in eutectic cell size (∼1.8 mm to ∼0.8 mm on the heavy gauge and ∼2.1 mm to ∼1.2 mm on the light gauge) with increasing cooling rate. This leads to an increased unit length of depressed boundary between the eutectic cells. The eutectic microstructure is also finer (with reduced inter-lamella spacing) in the fast cooled samples again reflecting the more rapid nucleation of the coating.The scanning vibrating electrode technique (SVET) has been used to quantify the effects of these microstructural changes upon the surface and cut edge corrosion performance. There is an increase in corrosion activity on the surface of the fast cooled samples (metal loss 150 μg to 260 μg on the heavy gauge and 50 μg to 80 μg on the light gauge) primarily due to the increased length of depressed boundaries. Applying the same analysis to the cut edge, a decrease in corrosion occurs upon the faster cooled specimens. Metal loss calculations show a decrease (140 μg to 75 μg on the heavy gauge and 190 μg to 115 μg on the light gauge) as the cooling rate is increased. The higher intensity long lived anodes at the cut edge in the slower cooling rate samples are directly related to the increase in zinc dendrite size within the coating as nucleation rates are reduced.     

Effect of Zn/Mg ratio on cathodic protection of carbon steel using Al−Zn−Mg sacrificial anodes

Al−Zn−Mg alloys with different Zn/Mg mass ratios were evaluated as sacrificial anodes for cathodic protection of carbon steel in 3.5 wt.% NaCl solution. The anodes were fabricated from pure Al, Zn and Mg metals using casting technique. Optical microscopy, SEM−EDS, XRD and electrochemical techniques were used. The results indicated that with decreasing Zn/Mg mass ratio, the grain size of α(Al) and the particle size of the precipitates decreased while the volume fraction of the precipitates increased. The anode with Zn/Mg mass ratio >4.0 exhibited the lowest corrosion rate, while the anode with Zn/Mg mass ratio <0.62 gave the highest corrosion rate and provided the highest cathodic protection efficiency for carbon steel (AISI 1018). Furthermore, the results showed that the anode with Zn/Mg mass ratio <0.62 exhibited a porous corrosion product compared to the other anodes.     

Parametric study of nitrided AISI 304 austenite stainless steel prepared by plasma immersion ion implantation

This paper investigates the characteristics of plasma immersion nitrogen-ion implanted AISI 304 austenite stainless steel against such processing parameters as bias voltage (5-20 kV), substrate temperature (300-500 °C), and implantation fluence (1.4 × 10¹⁸-4.2 × 10¹⁸ cm^− 2). Characteristics of the as-implanted specimens under investigation included elemental depth profile, hardness depth profile, crystallographic structure, and corrosion behavior and were determined using glow discharge spectrometry (GDS), the Vickers hardness tester, X-ray diffractometry (XRD), and the potentiodynamic polarization test, respectively. The results show that nitrogen depth profiles strongly depend on these processing parameters and closely relate to the corresponding chromium depth profiles. The hardness depth profiles increase and widen as substrate temperature, bias voltage, and implantation fluence increase. In particular, an improvement in hardness is accompanied by a reduction in corrosion resistance when substrate temperature reaches 500 °C. The corrosion-resistance degrader, CrN, precipitates as substrate temperature exceeds 450 °C, a phenomenon which is clearly evident in the chromium depth profiles as well as the XRD results.     

The corrosion performance of anodised magnesium alloys

The corrosion performance of anodised magnesium and its alloys, such as commercial purity magnesium (CP-Mg) and high-purity magnesium (HP-Mg) ingots, magnesium alloy ingots of MEZ, ZE41, AM60 and AZ91D and diecast AM60 (AM60-DC) and AZ91D (AZ91D-DC) plates, was evaluated by salt spray and salt immersion testing. The corrosion resistance was in the sequential order: AZ91D ≈ AM60 ≈ MEZ ? AZ91D-DC ? AM60-DC > HP-Mg > ZE41 > CP-Mg. It was concluded the corrosion resistance of an anodised magnesium alloy was determined by the corrosion performance of the substrate alloy due to the porous coating formed on the substrate alloy acting as a simple corrosion barrier.     

Nano-pit corrosion of the tabs in aluminum electrolytic capacitor: Polarization characteristics of the tabs in ethyleneglycol-borate solution with chloride ions

To evaluate the corrosion behavior of the anode tab in aluminum electrolytic capacitor, we performed some electrochemical and morphology analysis using the polarization curves in conjunction with atomic force microscope (AFM), scanning electronic microscope (SEM) and optical microscope (OM). The results suggest that the current oscillation was found to be associated with nano-pit, which is defined as the rectangular pit (β) with a depth less than 55 nm and a width no more than 100 nm. Furthermore, elevation of Cl⁻ concentration widened the crevices caused by electrolytic tension, enlarged the nano-pit area, and accelerated the electrochemical reaction rate of the anode tab in ethyleneglycol-borate solution. These findings may have implications for the failure of aluminum electrolytic capacitor.     

Al and Zn film deposition using a vacuum arc plasma source with a refractory anode

The radially expanding plasma plume generated in a Hot Refractory Anode Vacuum Arc was used to deposit thin Al and Zn films on glass substrates. The electrode separation was 10 mm, arc time varied up to 165 s, and current (I) was 100-225 A. The cathode was a water-cooled Al or Zn cylinder. A graphite anode with 9 or 30 mm height was used with the Al cathode, and 10 or 30 mm height Mo anode was used with the Zn cathode. A mechanical shutter controlled the substrate exposure onset and duration (15 s) to the anodic plasma. The distance from the arc axis to the substrate (L) was varied between 80 and 165 mm. The film thickness was measured with a profilometer, and macroparticle (MP) presence on the coating surface was examined by optical microscopy.It was found that the deposition rate increased as a function of time to a peak, and then decreased to a steady-state value. The peak occurred sooner using the 9 mm anode than with the 30 mm anode. The peak deposition rate increased and the peak time decreased with I. The steady-state deposition rate was larger for Zn (~ 2 μm/min) than for Al cathodes (~ 1 μm/min) at I = 225 A and L = 110 mm. The arc voltage for Al was ~ 20-22 V and for Zn it was 11 V. The deposition rate peak appeared due to MPs evaporating from the hot anode, where they had initially condensed during the conventional arc stage when the anode was still cold. This effect was significant with low melting temperature Al and Zn cathodes, and negligible with Cu and Ti cathodes studied previously.     

Synthesis and characterization of spray deposited PdO-NiO-SDC composite anode material for potential application in IT-SOFC

The synthesis of mixed conducting PdO-NiO-SDC composite films has been reported for the first time by a simple and cost effective spray pyrolysis technique. The films were deposited at low substrate and annealing temperatures of 350 °C and 500 °C, respectively. The structure, morphology and electrical properties of the films were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX), atomic force microscopy (AFM) and impedance spectroscopy (IS). The substrate and annealing temperatures were optimized for obtaining nano-crystalline, porous, adherent and composite films with PdO, NiO and SDC phases. Films showed good microstructure with sufficient porosity and good connectivity of the deposited material. Crystallite size of the deposited material was found to be in the range of 7-9 nm. The deposited film showed high oxygen ion conductivity, 3.94 × 10⁻¹ S cm⁻¹ at 350 °C. Due to their nano-crystalline, porous and composite nature the spray deposited PdO-NiO-SDC films may have high three phase boundary area and hence can be considered as an anode for intermediate temperature solid oxide fuel cells.     

Langmuir-Blodgett films of dococyltriethylammonium bromide and octadecanol on iron. Deposition and corrosion inhibitor performance in CO2 containing brine

The stability and compressibility of Langmuir films of dococyltriethylammonium bromide (C₂₂TAB) and 1-octadecanol (C₁₈OH) and their mixtures on water surfaces were first investigated. Langmuir-Blodgett films were transferred onto iron substrate. Their effect on corrosion of iron in carbon dioxide containing brine were investigated by electrochemical methods. The C₁₈OH formed a thin homogenous film with molecular area 19.4 Å² at 36 mN m⁻¹ at water surface. The films of C₂₂TAB and C₂₂TAB/C₁₈OH mixtures were less dense, with 31 Å² molecular area at 36 mN m⁻¹ at water surface. The corrosion rate of iron substrate was reduced by 95% by deposition film of C₁₈OH, while the corrosion rate of iron was reduced by 60% for films of C₂₂TAB and C₂₂TAB/C₁₈OH mixtures.     

Development of nano cerium oxide incorporated aluminium alloy sacrificial anode for marine applications

Aluminium-zinc alloy sacrificial anodes are extensively used for cathodic protection. The performance of the sacrificial anodes can be significantly improved by incorporation of microalloying elements in the aluminium matrix. In the present work nano cerium oxide particles of different concentrations, ranging from 0 to 1 wt% were incorporated for activating and improving the performance of the anode. The electrochemical test results revealed the increased efficiency of the anode. The electrochemical impedance spectroscopy revealed the information that the presence of nano cerium oxide in the anode matrix caused effective destruction of the passive alumina film, which facilitated enhancement of galvanic performance of the anode. Moreover, the biocidal activity of cerium oxide prevented the bio accumulation considerably which enables the anodes to be used in aggressive marine conditions.     

Numerical evaluation of the capacity of galvanic anode systems for patch repair of reinforced concrete structures

Cathodic protection (CP) is an electrochemical repair or corrosion prevention technique for steel structures exposed to a corrosive environment. For reinforced concrete (RC) usually impressed current CP is used, due to the comparably high resistivity of the concrete, serving as electrolyte. Nevertheless, the market provides a wide range of galvanic anode systems for RC structures. Their most common use is the application within the framework of partial concrete replacement due to chloride-induced corrosion. This patch repair is often accompanied by the so-called anode ring effect, causing accelerated corrosion of the rebar in the substrate concrete in the vicinity of repair patches. This is caused by the cathodic capabilities of the repassivated rebar. Galvanic anodes are reported to prevent this effect. In this paper, a numerical model is proposed, which is capable of determining the effectiveness of the method dependent on, for example, the type and quantity of anodes, rebar content, and geometry or climatic conditions. The method is presented for a specific set of input parameters and the applicability is discussed against the background of different protection criteria.