Polarization Curve Test Research Articles

Electrochemical corrosion behavior of HVOF sprayed WC–12Co coating on H13 hot work mould steel

Purpose This study aims to investigate the electrochemical corrosion performance of high velocity oxygen fuel (HVOF) sprayed WC–12Co coating in 3.5 Wt.% NaCl solution, which provided a guiding significance on the corrosion resistance of H13 hot work mould steel. Design/methodology/approach A WC–12Co coating was fabricated on H13 hot work mould steel using a HVOF, and the electrochemical corrosion behaviors of WC–12Co coating and substrate in 3.5 Wt.% NaCl solution was measured using open circuit potential (OCP), potentiodynamic polarization curve (PPC) and electrochemical impedance spectroscopy (EIS) tests. Findings The OCP and PPC of WC–12Co coating positively shift than those of substrate, its corrosion tendency and corrosion rate decrease to enhance its corrosion resistance. The curvature radius of capacitance curve on the WC–12Co coating is larger than that on the substrate, and the impedance and polarization resistance of WC–12Co coating increase faster than those of substrate, which reduces the corrosion process. Originality/value The electrochemical corrosion behaviors of WC–12Co coating and substrate in 3.5 Wt.% NaCl solution is first measured using OCP, PPC and EIS tests, which improve the electrochemical corrosion resistance of H13 hot work mould steel.

The corrosion behavior of chromated AA2024 aluminum alloy in 3.5% NaCl solution

PurposeA chromate conversion coating was prepared on the surface of bare AA2024 aluminum alloy by direct immersion in the chromating treatment bath, and the corrosion behavior of chromated AA2024 aluminum alloy in 3.5 per cent NaCl solution was studied by electrochemical measurement and microstructural observation.Design/methodology/approachAccording to the polarization curve test and the scanning electron microscope observation, the corrosion evolution of chromated AA2024 in 3.5 per cent NaCl solution was divided into the following three stages: coating failure, pitting corrosion and intergranular corrosion (IGC).FindingsIn the first stage, the chromate coating degraded gradually due to the combined action of chloride anions and water molecules, resulting in the complete exposure of AA2024 substrate to 3.5 per cent NaCl solution. Subsequently, in the second stage, chloride anions adsorbed at the sites of θ phase (Al2Cu) and S phase (Al2CuMg) on the AA2024 surface preferentially, and some corrosion pits initiated at the above two sites and propagated towards the deep of crystal grains. However, the propagation of a pit terminated when the pit front arrived at the adjacent grain boundary, where the initiation of IGC occurred.Originality/valueFinally, in the third stage, the corrosion proceeded along the continuous grain boundary net and penetrated the internal of AA2024 substrate, resulting in the propagation of IGC. The related corrosion mechanisms for the bare and the chromated AA2024 were also discussed.

High sensitivity and fast response sensor based on sputtering Au tuned ZnFe2O4-SE for low concentration NH3 detection

The NH3 sensitivity of a potentiometric YSZ-based planar sensor utilizing ZnFe2O4 sensing electrode (SE) was tuned by sputtering Au on the SE. ZnFe2O4 was prepared by sol-gel method and calcined at 900 °C. ZnFe2O4-SE was prepared by screen printing and sintered at 1100 °C for 3 h. SEM results show that Au is uniformly distributed in the network structure of the ZnFe2O4-SE. The response characteristics of the sensor to 5–80 ppm NH3 were evaluated between 650 °C and 750 °C, and it was found that the response rate and response signal increased significantly after gold sputtering on SE. The performance improvement by gold sputtering may originate from enhanced catalytic activity of the anodic electrode reaction, which was observed by the polarization curve test. At 700 °C, the sensor exhibited the largest sensitivity with the slope of −31.3 mV/decade, and its response to 80 ppm NH3 was −42.3 mV, and it has relatively short response and recovery time of 25 s and 49 s for 80 ppm NH3, respectively. It could even displayed a considerable signal for 5 ppm NH3 at each temperature. The oxygen concentration had non-negligible influence on the NH3 response signal. It showed tiny cross sensitivities toward NOx and C3H8, but weak CO cross sensitivity. When the water vapor concentration is within 10%, the water vapor has a small influence on the response signal. The sensor also displayed slight signal drifts in weekly tests in six weeks, which showed that ZnFe2O4 had a good long-term stability.

Effect of Si Addition on Mechanical and Electrochemical Properties of Al-Fe-Cu-La Alloy for Current Collector of Lithium Battery

The increasing demand for high-performance current collectors of lithium ion secondary batteries requires that the employed aluminum alloys have better mechanical properties and superior electrochemical performance. The effect of Si addition on the microstructure, tensile and electrochemical performance of Al-Fe-Cu-La alloy was investigated by optical microscopy, X-ray diffraction, scanning electron microscopy, a tensile test, conductivity test and Tafel polarization curve test. Experimental results indicated that Si addition to the Al-Fe-Cu-La alloy helped to refine the longitudinal grain size of the alloy. The Si-containing phase (AlFeSi) nucleated and grew along the surface of the AlFeLa phase. The Si addition to the Al-Fe-Cu-La alloy could greatly increase the tensile strength in the temperature range of −20 °C to 50 °C and improve high temperature stability of the alloy. Also, the addition of Si promoted the formation of the AlFeSi ternary phase, which helped to improve the corrosion resistance of the alloy.

Study on the corrosion mechanism of the oxide scale on hot rolled steel in an atmospheric environment

Purpose The purpose of this paper is to understand the process of failure of scale and the corrosion resistance of scale to the substrate in an atmospheric environment. Design/methodology/approach The corrosion behaviour of X65 pipeline steel with different types of oxide scale was analysed using the natural environment exposure corrosion test, scanning electron microscopy analysis, electrochemical corrosion polarization curve test and other methods in a warehouse environment. Findings The results of this research show that one type of oxide scale, which is rough, has an uneven microstructure, and exhibits weak adhesion to the matrix, does not protect the substrate from corrosion. Conversely, the uniform, dense oxide scale, which exhibits strong adhesion to the matrix, provides effective protection to the steel. However, as the corrosion develops, the corrosion rate of the substrate tends to accelerate, especially when the structure of the oxide scale is damaged to a certain extent. Originality/value The corrosion mechanism of the oxide scale on hot rolled steel in an atmospheric environment has been proposed.

Corrosion resistance of composite coating used for fastener protection

Purpose The purpose of this paper is to examine the performance of a fastener composite coating system, sherardized (SD) coating/zinc-aluminum (ZA) coating whether it has good performance in marine environment. Design/methodology/approach In this paper, SD coating was fabricated on fastener surface by solid-diffusion method. ZA coating was fabricated by thermal sintering method. Corrosion behaviours of the composite coating were investigated with potentiodynamic polarization curves, open circuit potential and electrochemical impedance spectroscopy methods. Findings Neutral salt spray (NSS) and deep sea exposure tests revealed that the composite coating had excellent corrosion resistance. Polarization curve tests showed that corrosion current density of the sample with composite coating was significantly decreased, indicating an effective corrosion protection of the composite coating. OCP measurement of the sample in NaCl solution demonstrated that the composite coating had the best cathodic protection effect. The good corrosion resistance of the composite coating was obtained by the synergy of SD and ZA coating. Practical implications SD/ZA coating can be used in marine environment to prolong the life of carbon steel fastener. Social implications SD/ZA composite coating can reduce the risk and accident caused by failed fastener, avoid huge economic losses. Originality/value A new kind of composite coating was explored to protect the carbon steel fastener in marine environment. And the composite coating has the long-term anti-corrosion performance both in simulated and marine environment test.

The Durability of an Organic-Inorganic Sol-Gel Interlayer in Al-GFRP-CFRP Laminates in a Saline Environment.

The aim of the study was to assess the selected properties of a hybrid organic–inorganic silane sol–gel coating (HSG) used in hybrid fiber metal laminates (FML) in a corrosion environment. The HSG coating on the aluminum alloy was produced using 3M™ AC130-2 formulation consisting of 3-glycidoxypropyl-trimethoxysilane (GPTMS) and tetra-n-propoxyzirconium (zirconium(IV) propoxide) (TPOZ). Laminates consisted of aluminum alloy AA2024-T3 sheets, with carbon fiber reinforced polymers (CFRPs) and a glass fiber reinforced metal–composite structure (GFRP). Potentiodynamic and polarization curve and impedance (EIS) tests were carried out on HSG at ambient temperatures after 1 h and 150 h of soaking. Neutral 0.5 M NaCl and 0.8 M NaCl solutions were used for open circuit potential (OCP) and potentiodynamic tests, and 0.5 NaCl was used for the EIS test. A neutral salt spray (NSS) test was applied to laminates with a 12 week exposure period. The results obtained revealed that the HSG coating did not provide sufficient protection against corrosion of the aluminum alloy in direct contact with an aggressive environment but was effective as an interlayer. Local aluminum sheet perforation did not lead to delamination at the metal–composite interface regardless of the type or configuration of the composite. This confirms the durability of HSG used in FMLs.

Fracture location transition in constant load tests of a NiCrMoV steel welded joint

The fracture location transition of the NiCrMoV steel welded joints induced by different tensile loads has been investigated through the constant load tests in 3.5 wt% NaCl at 180 °C. The mechanical properties of different zones in the welded joints were measured by the hardness measurement and localized tensile tests in air at room temperature. The corrosion properties were characterized by potentiodynamic polarization curve tests and scanning vibrating electrode technique (SVET) tests. The results reveal that the most susceptive corrosion zone and the weakest strength zone do not locate in same zone of the welded joint. This mismatch leads to the rupture locations of the welded joints change with the applied load in the constant load tests. For the applied load larger than or equal to 765 MPa, the rupture section locates in the middle of WM due to its weakest strength. But the fracture position shifts to the fusion zone for the applied load less than or equal to 760 MPa, which is attributed to stress corrosion cracking (SCC) originating from the pits under the combined effect of galvanic and stress-assisted corrosion.

One-step hydrothermal synthesis of In2.77S4 nanoparticles doped graphene oxide hybrids as efficient counter electrodes in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) have become a potential alternative to photovoltaic devices, which can convert solar energy into electrical energy. As an essential component of DSSCs, counter electrode (CE) materials play an important role in determining the performance of DSSCs. Thus, research should seek for a cost-effective and high-activity CE materials. In this work, we explored an efficient, low-cost (platinum (Pt)-free) CE made of hybrids of In2.77S4 nanoparticles and reduced graphene oxide (RGO) for DSSCs. In2.77S4-RGO hybrids were facilely synthesized via a one-step hydrothermal approach without template or complicated precursor. Especially during synthesis, glacial acetic acid was added to prevent the precipitation of In3+ ions. Thus, free In3+ and S2− ions can readily absorb onto the graphene oxide (GO) surface by electrostatic forces. Finally, In2.77S4 nanoparticle-doped GO hybrids were obtained under hydrothermal conditions. Based on electrochemical measurement in cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel polarization curve tests, the as-prepared mesoporous In2.77S4-RGO hybrids exhibited remarkable electrocatalytic properties, charge–transfer capabilities, and electrochemical stabilities. As a result, the DSSCs assembled with In2.77S4-RGO hybrid CE exhibited a powder conversion efficiency of 6.72%, which is superior to that with Pt CE (6.30%). These findings suggest that In2.77S4-RGO hybrids can be used as a promising alternative CE in DSSCs.

Polyphenol-reduced graphene oxide toward high-performance corrosion inhibitor

Graphene as a physical barrier in organic coating exhibits good anticorrosion property, whereas its agglomeration would greatly debase such performance. Here, functionalized graphene was prepared via a green/facile method with tea polyphenol as reductant and graphene oxide (GO) as precursor. The anticorrosion performance of polyphenol-reduced graphene oxide (T-rGO) in waterborne epoxy coating was evaluated according to the electrochemical impedance spectroscopy, polarization curve, water absorption and salt spray test. Results indicate that the T-rGO/epoxy coating has the largest impedance modulus and corrosion potential, and the corrosion current density is an order of magnitude lower than that of pure epoxy coating. The T-rGO/epoxy coating displays excellent corrosion protection under continuous high salt spray environment, with pure epoxy coating as a comparison. T-rGO greatly enhances the corrosion resistance of waterborne epoxy coating, which is attributed to its good dispersibility and intrinsic characteristics.

Preparation of graphene/polyaniline nanocomposite by in situ intercalation polymerization and their application in anti-corrosion coatings

This study reports a strategy for further simplifying the synthesis process of polyaniline-modified graphene (An/G) nanocomposite. For this purpose, the An/G nanocomposite was prepared by expanded graphite (EG) and aniline (An) via in situ polymerization. The structures and morphologies of the An/G nanocomposite were examined by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, ultraviolet–visible spectroscopy and atomic force microscopy. The results show that the An/G nanocomposite was synthesized successfully. The coatings were prepared using polyaniline (PANI) and An/G as the fillers and epoxy resin as the matrix. The anti-corrosion performance was evaluated by electrochemical impedance spectroscopy, Tafel polarization curve and salt immersion test. When An/G100 nanocomposite with a mass ratio of An to EG of 100:1 as a filler is used, the coating on the steel exhibited superior anti-corrosion effect. In particular, the impedance at 0.01 Hz of the coating with the An/G100 nanocomposite at a low loading of 2 wt% (An/G100-2) remained constant above 1 × 1010 Ω·cm2 for up to 35 days in 3.5 wt% sodium chloride solution. The Tafel plots reveal that the undamaged zone of the An/G100-2 coating possessed a high corrosion potential of −0.16 V, and the corrosion current density was only 1.5 × 10−11 A cm−2. The protective mechanism of graphene and PANI is discussed.

Anticorrosive epoxy coatings based on polydopamine modified molybdenum disulfide

Introducing inorganic layered nanomaterials into polymer arrays is one of the important methods to improve the anti-corrosion performance of epoxy coatings, but the compatibility between them is the first problem to be solved. In this study, lamellar molybdenum disulfide (MoS2) is modified by polydopamine (PDA) to improve its dispersibility and anti-corrosion properties in epoxy resin coatings. PDA is firstly coated onto the surface of MoS2 successfully, which can be proved by FT-IR, Raman and SEM. Then, the PDA modified MoS2 (MoS2 @ PDA) is introduced into epoxy resin system to prepare a new epoxy resin coatings (MoS2 @ PDA/EP). The anticorrosive performance of EP (pure epoxy coatings), MoS2/EP and MoS2 @ PDA /EP coatings are evaluated by electrochemical impedance spectroscopy spectra (EIS), polarization curve and pull-off adhesion tests. Compared to EP coating, the corrosion resistance of MoS2 @ PDA/EP coating has increased nearby three orders amount and the adhesion strength of MoS2 @ PDA/EP coating has increased nearby 3 Mpa. So, polydopamine modified MoS2 (MoS2 @ PDA) is an effective nanocomposite for preparing high-peroformane anticorrosion epoxy coatings.

Fabrication of hydrophobic coating on electrolytic manganese surface for enhancing corrosion resistance

Two kinds of hydrophobic coating, lauric diethanolamide (LDEA) hydrophobic coating, lauric diethanolamide and stearic acid (LDEA-SA) hydrophobic coating were fabricated on electrolytic manganese by immersion method. Studies of experimental variables, such as immersion time and solution concentration, had been performed to better optimize hydrophobic coatings with the desired corrosion resistance. The wettability, morphology and composition of the hydrophobic coatings were characterized by contact angle measurement (CA), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The corrosion behavior of the samples was investigated by polarization curve test and electrochemical impedance spectroscopy (EIS). The results revealed that the LDEA-SA hydrophobic coating showed better corrosion resistance and hydrophobicity. Compared with the manganese substrate, the corrosion current density of the LDEA-SA hydrophobic coating decreased from 3.782 × 10−4 to 1.153 × 10-5 A/cm2, and the contact angle increased from 41° to 124°. The complete coating morphology was more conducive to enhancing the corrosion resistance of the sample.

A novel diagnostic methodology for fuel cell stack health: Performance, consistency and uniformity

Internal heterogeneity is a significant challenge to the service life of large-format commercial fuel cell stacks. Methods for diagnosing fuel cell stack health, however, are still lacking. This paper proposes a novel diagnostic methodology for analyzing the performance, the consistency between cells and the uniformity within individual cells of fuel cell stacks. Specifically, this three-step methodology can comprehensively analyze the internal heterogeneity of large-format multi-cell stacks. First, a polarization curve test is conducted to provide a quick qualitative performance analysis. Then, the quantitative parameters consistency decline is analyzed by galvanostatic charging and electrochemical impedance spectroscopy methods. Finally, a novel multi-point voltage monitoring method is applied to rule out possible misdiagnoses and to qualitatively analyze cell uniformity. This degradation diagnostic methodology is applied to analyze degradation in several fuel cell stacks, revealing high potential in practice.

Corrosion Behavior of Pipeline Steel with Different Microstructures Under AC Interference in Acid Soil Simulation Solution

Corrosion behavior of X65 pipeline steels with different microstructures under alternating current (AC) interference was investigated in acid soil simulation solution by potentiodynamic polarization curve, potentiostatic polarization curve and immersion test. The results show that superimposed AC causes a sharp increase in corrosion current density of X65 steel. With the increase in iAC, the corrosion current densities of steels with various microstructures increase, especially at high iAC. Hot-rolled steel mainly experiences uniform corrosion, with very slight pit corrosion. Serious corrosion degrees with intensive corrosion pits can be observed on the surfaces of normalized and quenched microstructure steels. The annealed steel exhibits the feature of non-uniform corrosion with some pitting. The steels with various microstructures applied with AC have different corrosion resistance. The normalized steel shows the worst corrosion resistance, then the quenched microstructure, and the hot-rolled steel displays the optimum corrosion resistance. The difference in the microstructure can result in difference in corrosion degree and occurrence position of pitting corrosion of X65 steel. The normalized microstructure composed of polygonal ferrite and a large amount of pearlite and bainite is the most susceptible to AC corrosion.

How semiconductor transition metal dichalcogenides replaced graphene for enhancing anticorrosion

Influences of semiconductor transition metal dichalcogenides on the corrosion behavior of metals under epoxy nanocomposite coatings.

Enhanced Galvanic Corrosion Phenomenon in the Welded Joint of NiCrMoV Steel by Low-Cycle Fatigue Behavior

The effect of microstructural changes on the corrosion of a NiCrMoV steel welded joint induced by low-cycle fatigue behavior in chloride solution has been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), potentiodynamic polarization curve tests and scanning vibrating electrode technique (SVET) tests. During the low-cycle fatigue tests, cyclic softening takes place in the three zones (base metal, BM/weld metal, WM/heat affected zone, HAZ) of the welded joint due to the decrease of dislocation density or the formation of low-energy structures. Compared to the as-received specimens, the corrosion potential of each zone in the low-cycle fatigue damage specimens moves to the positive direction and the corrosion current density decreases. The corrosion resistance of the individual zone increases, which is related to the reduction of dislocation density or the formation of low-energy structures. However, the difference of corrosion potential between base metal and weld metal in the low-cycle fatigue welded joints becomes lager, which means that the galvanic corrosion susceptibility of the low-cycle fatigue welded joint increases. This may be caused by the difference of microstructural changes in the various regions of welded joints during cyclic plastic deformation.

Wear and Corrosion Resistance of Al0.5CoCrCuFeNi High-Entropy Alloy Coating Deposited on AZ91D Magnesium Alloy by Laser Cladding.

In order to improve the wear and corrosion resistance of an AZ91D magnesium alloy substrate, an Al0.5CoCrCuFeNi high-entropy alloy coating was successfully prepared on an AZ91D magnesium alloy surface by laser cladding using mixed elemental powders. Optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction were used to characterize the microstructure of the coating. The wear resistance and corrosion resistance of the coating were evaluated by dry sliding wear and potentiodynamic polarization curve test methods, respectively. The results show that the coating was composed of a simple FCC solid solution phase with a microhardness about 3.7 times higher than that of the AZ91D matrix and even higher than that of the same high-entropy alloy prepared by an arc melting method. The coating had better wear resistance than the AZ91D matrix, and the wear rate was about 2.5 times lower than that of the AZ91D matrix. Moreover, the main wear mechanisms of the coating and the AZ91D matrix were different. The former was abrasive wear and the latter was adhesive wear. The corrosion resistance of the coating was also better than that of the AZ91D matrix because the corrosion potential of the former was more positive and the corrosion current was smaller.

Mass preparation and anticorrosion mechanism of highly triple-effective corrosion inhibition performance for co-modified zinc phosphate-based pigments

The benzotriazole and GO co-modified zinc phosphate (ZP/BTA/GO) pigments with chemically oriented laminated structure are synthesized massively by in situ self-heating method for the first time. The heat released from the formation of ZP increases the solubility of BTA achieving the self-sufficiency of system energy in one step. After modification by BTA, the anticorrosive blind region of ZP pigments in the initial corrosion stage is repaired. With the co-modification by BTA and GO, the strong interaction among ZP, BTA and GO makes the compact laminated structure of ZP/BTA/GO pigments more stable, exerting bidirectional shielding effect on the penetration of corrosive medium. Meanwhile, the electrochemical impedance spectroscopy (EIS) and polarization curve tests reveal that the anticorrosion performance of ZP/BTA/GO pigments is increased by 366.1% compared to ZP pigments. The remarkable improvement of corrosion inhibition is attributed to the synergistic complementary anticorrosion mechanism containing the extension of electrons transport path, the deviation of electrons transfer and the formation of diversified passive films. The formation of zinc phosphate-based laminated pigments with full-covered anticorrosion time and excellent corrosion inhibition performance promotes the industrial production and development of anticorrosion materials.

Anticorrosion Performance of LDH Coating Prepared by CO2 Pressurization Method

Many surface treatment methods are used to improve the corrosion resistance of magnesium alloys. LDH (layered double hydroxides) conversion coatings are currently found in the most environmentally friendly and pollution-free coatings of magnesium alloy. In this study, the CO2 pressurization method was applied to the preparation of LDH coating on magnesium alloy for the first time. The effect of CO2 pressurization on the formation and corrosion resistance of LDH coating on AZ91D alloy was investigated. The hardness and adhesion were significantly higher on LDH coating in the case of CO2 pressurization than it is in atmospheric pressure. The surface and cross-sectional morphologies show that LDH coating is more compact in the case of CO2 pressurization than with atmospheric pressure. The results of the polarization curve, hydrogen evolution, and immersion tests indicate that the corrosion resistance of the LDH coating prepared by the CO2 pressurization method was significantly improved.