Polarization Curve Test Research Articles

Water Management Capacity of Metal Foam Flow Field for PEMFC under Flooding Situation.

Porous metal foam with complex opening geometry has been used as a flow field to enhance the distribution of reactant gas and the removal of water in polymer electrolyte membrane fuel cells. In this study, the water management capacity of a metal foam flow field is experimentally investigated by polarization curve tests and electrochemical impedance spectroscopy measurements. Additionally, the dynamic behavior of water at the cathode and anode under various flooding situations is examined. It is found that obvious flooding phenomena are observed after water addition both into the anode and cathode, which are alleviated during a constant-potential test at 0.6 V. Greater abilities of anti-flooding and mass transfer and higher current densities are found as the same amount of water is added at the anode. No diffusion loop is depicted in the impedance plots although a 58.3% flow volume is occupied by water. The maximum current density of 1.0 A cm-2 and the lowest Rct around 17 mΩ cm2 are obtained at the optimum state after 40 and 50 min of operation as 2.0 and 2.5 g of water are added, respectively. The porous metal pores store a certain amount of water to humidify the membrane and achieve an internal "self-humidification" function.

Effect of Tropical Marine Atmospheric Environment on Corrosion Behaviour of the 7B04-T74 Aluminium Alloy

In this work, the effects of the tropical marine atmospheric environment on the corrosion behaviour of the 7B04-T74 aluminium alloy were systematically investigated by using accelerated testing, together with corrosion kinetic analysis, microstructure observation, product composition analysis, and potentiodynamic polarization curve tests. The weight loss method was used for the corrosion kinetics analysis. The surface morphology and corrosion products transformation law were investigated by OM, SEM, EDS, and XPS. The electrochemical characteristics were studied using potentiodynamic polarization curves. The research indicated that the 7B04-T74 aluminium alloy has eminent corrosion resistance in the tropical marine atmospheric environment. Localized pitting corrosion occurred rapidly in the tropical marine atmosphere. In the later stage of corrosion, the corrosion of aluminium alloy did not become serious. Specifically, no obvious intergranular corrosion was found, which is related to the thermal treatment method. Corrosion products included Al(OH)3, Al2O3, and AlCl3, of which Al(OH)3 is the most notable.

Analysis of heat exchanger corrosion failure in 800,000 light hydrocarbon plant in Liaohe Oilfield

Heat exchangers, as the major equipment for forced heat exchange, are now widely utilized in all areas of life, however in real usage, corrosion failure can frequently occur and cause catastrophic mishaps. In this study, the composition of the corrosion products in the heat exchanger's head section was examined using XRF and XRD, and the corrosion of Q345D steel in the head section was examined using the dynamic potential polarization curve test method in conjunction with SEM under various CO2 and O2 partial pressure and temperature conditions. Fluent simulation software was also used to simulate the impact of erosion corrosion on the heat exchanger's head section. Results indicate that the main corrosion products in the regenerative heat exchanger E-303 are Fe3O4, with minor amounts of Fe2O3 and FeOOH; in terms of temperature, CO2 and O2, these three influencing factors on the heat exchanger head Q345D steel corrosion results, the temperature on the steel corrosion damage is significantly greater than the local corrosion caused by CO2 and O2, but when the temperature is higher than the solution boiling point of its corrosion in and out will occur. The flow rate scouring on the heat exchanger head high temperature inlet that is caused by the damage is much greater than the head low temperature outlet, corrosion damage is primarily concentrated in the lower inlet baffle, which is also consistent with the actual conditions of the site heat exchanger.

Self-repairing functionality and corrosion resistance of in-situ Mg-Al LDH film on Al-alloyed AZ31 surface

A novel Mg-Al LDH film was in-situ prepared hydrothermally in an alkaline aqueous solution on an Al-alloyed AZ31 substrate. The structural, chemical and functional characteristics of the film were explored by means of scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), polarization curve, AC impedance and salt immersion tests, respectively. The anti-corrosion results indicated that the Mg-Al LDH film on the Al-alloyed AZ31 surface could effectively protect the AZ31 from corrosion attack even after 90 days of immersion in 3.5 wt.% NaCl solution. The protection performance is surprisingly better than most of the reported coatings on Mg alloys. More interestingly, when the Mg-Al LDH film was scratched, the exposed Al-alloyed surface might gradually release metal ions and re-generate dense LDH nano-sheets in the corrosive environment to inhibit the further corrosion there, exhibiting a self-repairing behavior. The combination of the benign long-term protection and desirable self-repairing performance in this new process of surface-alloying and LDH-formation may significantly extend the practical application of magnesium alloys.

Study on Corrosion Fatigue Properties of the Welded Joints of SMA490BW Weathering Steel

The polarization curve test and corrosion fatigue test of SMA490BW weathering steel welded joints for high-speed train bogies were carried out by electrochemical workstation and fatigue testing machine, respectively, and the fatigue fractures were observed and analyzed by scanning electron microscope (SEM). The results show that: The mechanical properties of the SMA490BW weathering steel welded joints welded by MAG welding are good, the tensile strength is 519MPa, and the elongation after fracture is 26.67%. In 3.5wt% sodium chloride solution, the self-corrosion potential of the heat-affected zone is the lowest, the self-corrosion current density is the largest, and the corrosion resistance is the worst, the weld is in the middle, and the base metal is the best. The corrosion fatigue limit of SMA490BW weathering steel welded joints in 3.5wt% sodium chloride (NaCl) solution is 236.55MPa, which is much lower than the fatigue limit of 335.22MPa in air. SEM fracture analysis showed that the fatigue cracks of the joints in the air originated from the weld pores, while the corrosion fatigue cracks originated from the pitting pits on the surface of the specimens.

Influence of Li+/Al3+ on the corrosion behavior of Li-Al layered double hydroxides (LDHs) film on LA51 magnesium alloys

A hierarchical superhydrophobic Al-Li layered double hydroxide (LDH) films with different Li + /Al 3+ molar ratios of 1:1, 1:2, 2:1, pH value of 11.5 and reaction temperature of 125 °C, have been fabricated on the surface of Mg-5Li-1Al (LA51) alloys by hydrothermal method following the characteristics of controllable cation structure and exchangeable anion between layers. The properties of the films were investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). XRD and SEM results indicate that the Al-Li LDH films are successfully prepared on LA51 alloys. The contact angle (CA) was measured to be about 100.7°, indicating that the surface wettability of the film converted from hydrophilic to hydrophobic by surface modification. The corrosion resistance of Al-Li LDH films was evaluated by Tafel polarization curve and electrochemical impedance spectroscopy (EIS). Surprisingly, Tafel polarization curve and EIS test reveal that the Al-Li LDH films prepared at the molar ratio of Li + /Al 3+ 1:2, pH 11.5 and temperature 125 °C have better corrosion resistance in 0.1 M NaCl neutral solution. In addition, the formation mechanism and corrosion mechanism of the films on the surface of LA51 alloy are also proposed. It provides innovative synthetic materials and novel design ideas for the preparation of high-efficiency anti-corrosion coatings on LA51 alloys, whose application can be extended in industrial fields.

Effect of Nanoscale W Coating on Corrosion Behavior of Diamond/Aluminum Composites

The stability of diamond/aluminum composite is of significant importance for its extensive application. In this paper, the interface of diamond/aluminum composite was modified by adding nanoscale W coating on diamond surface. We evaluated the corrosion rate of nanoscale W-coated and uncoated diamond/aluminum composite by a full immersion test and polarization curve test and clarified the corrosion products and corrosion mechanism of the composite. The introduction of W nanoscale coating effectively reduces the corrosion rate of the diamond/aluminum composite. After corrosion, the bending strength and thermal conductivity of the nanoscale W-coated diamond/aluminum composite are considerably higher than those of the uncoated diamond/aluminum composite. The corrosion loss of the material is mainly related to the hydrolysis of the interface product Al4C3, accompanied by the corrosion of the matrix aluminum. Our work provides guidance for improving the life of electronic devices in corrosive environments.

Enhanced corrosion resistance and hardness of CoCrCuFeNi alloy under high-pressure solidification

This study adopts a high-pressure method to prepare a CoCrCuFeNi high-entropy alloy (HEA). The effects of high pressure on the microstructure, phase composition, hardness, and corrosion resistance of the alloy are studied. The Vickers hardness of the CoCrCuFeNi HEA solidified under ambient pressure and 4 GPa is determined to be 203.4 HV and 822.4 HV, respectively. This presents an approximately three-fold increase in hardness. The nanohardness of the matrix is also increased three-fold, and the value of the intergranular phase is increased by 0.2 times, which is attributed to the precipitation of a finer nano Cu-rich phase and nano Fe–Cr phase under high pressure. A more complete, dense, and uniform CoCrCuFeNi HEA passive film is obtained under high pressure, and the passivation film resistance (Rpass) is increased by 1.3 times. From a polarization curve test, the corrosion rates of the CoCrCuFeNi HEA solidified under ambient pressure and 4 GPa are 0.0209 mm/a and 0.0076 mm/a, respectively. Thus, the corrosion rate is reduced by 64%.

Influence of polyethylene glycol inhibitors on properties of electroplated copper layer

Inhibitor is one of the important additive components in electrodeposited copper. As a common inhibitor, the concentration of PEG8000 has an important effect on electrodeposited copper. In this article, different concentrations of polyethylene glycol-based organic additives were added to the acidic electrolyte, and their effects on the electrochemical behavior of copper electrodeposition were investigated by galvanostatic test, cathodic polarization curve test, and cyclic voltammetry test. In addition, the surface morphology and crystallographic orientation of the obtained copper layers were analyzed by SEM and XRD. The results show that with the increase of PEG8000 concentration in the electroplating solution system, the inhibitory effect of PEG8000 on electroplating copper becomes stronger, and the copper surface density obtained by electroplating is better.

Study on preparation and anticorrosive performance of a new high hydrophobic anticorrosive coating

AbstractWater‐based anticorrosive coatings have poor water resistance, which easily lead to coating deterioration and metal corrosion. In order to improve the anticorrosion performance of waterborne coating, herein, the polytetrafluoroethylene/dimethyl siloxane/epoxy resin (PTFE/PDMS/EP) hydrophobic anticorrosive coating was prepared by layer‐by‐layer construction. The spatial structure and microscopic morphology of the hydrophobic coating were analyzed by XRD, FTIR, and SEM. The hydrophobicity and corrosion resistance of the composite coating were analyzed by hydrophobicity test, electrochemical polarization curve, hydrophobicity and corrosion resistance test of the mixed layer, Tafel polarization curves, and AC impedance spectrum. The results showed that the water contact angle of PTFE/PDMS/EP coating reached 141° and the protection efficiency of PTFE/PDMS/EP coating was 98.62%. After soaking for 7 days, the corrosion process still stays at the initial stage, which was mainly due to the good sealing and barrier properties and high anticorrosion efficiency of PTFE/PDMS/EP coating. The coating has high corrosion protection efficiency and long service life, which is of great significance to metal corrosion protection in harsh marine environments.

Microstructure Evolution and Performance of Laser-Remelted Ti-6Al-4V Alloy

Herein, Ti-6Al-4V alloy was remelting by high-energy laser, the influence of laser energy density of mobile laser source on the evolution of solidification structure of Ti-6Al-4V alloy was studied, and the changes of relevant service performance of Ti-6Al-4V alloy after laser-remelting were explored. The results showed that there were four distinct regions: overheated zone, melting zone, heat-affected zone and substrate zone in Ti-6Al-4V alloy after laser remelting. The overheated zone and melting zone were dominated by primary α phase and secondary α phase, and a heat-affected zone was dominated by β phase. With the increase of laser energy density, the depth of molten pool and the range of melting zone in Ti-6Al-4V alloy increased, and the crystal phase distribution and grain size changed significantly. Laser-remelting Ti-6Al-4V alloy could still maintain a good passive state in the potentiodynamic polarization curve test, and the optimal laser power during remelting was 1200 W. This study proved that the crystal phase composition and grain size during the solidification process after laser-remelting were a key factor affecting the service performance of Ti-6Al-4V alloy.

Effect of Cu addition on phase fraction, mechanical properties and corrosion properties of Fe–Cr–Mn–Al duplex stainless steel

In recent years, Cu has been regarded as an important element to improve the corrosion resistance of stainless steels. For duplex stainless steels, especially those obtained by cold rolling and annealing, at present, little is known about the role mechanism of Cu addition. Therefore, on the basis of a new type of Fe–Cr–Mn–Al duplex stainless steel designed by the author, the effects of Cu on phase fraction, mechanical properties and corrosion resistance were studied in detail through tensile tests, electron backscattering diffraction (EBSD), polarization curve test and laser scanning confocal microscopy. The results show that the addition of 0.5% Cu to Fe–Cr–Mn–Al system increases the volume fraction of austenite and its stability, greatly improving the strength and ductility of steels due to the TRIP effect occurring in a wider strain range. In addition, the addition of Cu increases the content of Cr in austenite, improving the pitting resistance of duplex stainless steels. After annealing at 860 °C, the Cu-added duplex stainless steel exhibits superior mechanical and corrosive properties, i.e. the yield strength, tensile strength, elongation and pitting potential are 520 MPa, 760 MPa, 42.5% and 260 mV, respectively. In view of obvious advantages in mechanical properties and corrosion resistance, the present developed Cu-added Fe–Cr–Mn–Al duplex stainless steel is expected to replace the conventional 304 stainless steel for some applications.

Cobalt, Ferrum Co-Doped Ni3Se4 Nano-Flake Array: An Efficient Electrocatalyst for the Alkaline Hydrogen Evolution and Overall Water Splitting

Herein, Co, Fe co-doped Ni3Se4 nano-flake array (Ni0.62Co0.35Fe0.03)3Se4) was prepared on conductive carbon cloth by a two-step hydrothermal method. XRD and EDX analysis show that the nanosheets are monoclinic Ni3Se4, and Co, and Fe were doped into the lattice of Ni3Se4. Electrochemical tests showed that Co, Fe co-doping can effectively improve the hydrogen evolution activity of Ni3Se4 in acidic and alkaline environment. When the current density of (Ni0.62Co0.35Fe0.03)3Se4/CC is 10 mA/cm2 in 1 M KOH solution, the overpotentials of hydrogen evolution and oxygen evolution are 87 mV and 53.9 mV, respectively, and the Tafel slopes are 122.6 and 262 mV/dec. The electrochemical active area test (ECSA) and the polarization curve test further show that (Ni0.62Co0.35Fe0.03)3Se4/CC has a larger electrochemical active area (34.8 mF/cm2), lower electrolytic potential (0.9 V at 10 mA/cm2) and better stability. Therefore, the novel bifunctional catalyst synthesized by a simple method is a promising candidate for large-scale industrial water electrolysis.

Proton exchange membrane fuel cell performance investigation considering internal heterogeneity of current density – A novel method study

The remaining useful lifetime (RUL) of proton exchange membrane fuel cell (PEMFC) has been influenced by the heterogeneous distribution. In this presented paper, a novel method considering the internal heterogeneity is proposed and investigated to manage the proton exchange membrane fuel cell (PEMFC) operation thus prolonging the remaining useful lifetime. This method including the mathematic steps of quantification, normalization, and coordinate transformation, converts the conventional power-current density curve into a novel power-heterogeneity curve. The electro-thermal mapping device is applied to measure the physical-field heterogeneity of a single cell during the polarization curve tests under different temperature conditions. This method is validated by the results in the current region of 750–860 mA cm−2 of the polarization curves under temperature conditions of 50 °C and 60 °C. The novel method shows the effectiveness to make the fuel cell operate at a lower heterogeneity extent meanwhile a similar performance.

Performance improvement of air-breathing proton exchange membrane fuel cell (PEMFC) with a condensing-tower-like curved flow field

Air-breathing proton exchange membrane fuel cells (PEMFCs) are very promising portable energy with many advantages. However, its power density is low and many additional supporting parts affect its specific power. In this paper, we aim to improve the air diffusion and fuel cell performance by employing a novel condensing-tower-like curved flow field rather than an additional fan, making the fuel cell more compact and has less internal power consumption. Polarization curve test and galvanostatic discharge test are carried out and proved that curved flow field can strengthen the air diffusion into the PEMFC and improve its performance. With appropriate curved flow field, the fuel cell peak power can be 55.2% higher than that of planar flow field in our study. A four-layer stack with curved cathode flow field is fabricated and has a peak power of 2.35 W (120 W/kg).

Long-Term Potentiodynamic Testing and Tribometric Properties of Amorphous Alloy Coatings under Saline Environment.

Protective coatings for harsh environments are always welcome, but they must overcome profound challenges, including corrosion and wear resistance. The purpose of this study is to look into the long-term potentiodynamic polarization measurements and dry tribometric behavior of plasma-sprayed amorphous coatings on AISI 1035 mild steel. To investigate the impact of unique active polarization potentials on the electrochemical studies of the iron-based amorphous layer, which compares favorably to AISI 1035 mild steel, the active potential polarization curve and friction coefficient tests were performed. Scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) analyses were used to investigate the coating’s corrosion behavior. Their mechanical (Tribometric tests at higher sliding speeds) and chemical properties (electrochemical potentiodynamic polarization investigations) have also been thoroughly investigated. There is enough validation that these protective coatings can be used in hostile environments. The effects of long-term corrosion for 24 and 48 h were thoroughly examined. Tribometric examinations revealed that amorphous layers are highly resistant under dry conditions, as they offered a very low and stable friction coefficient less than 4 μ with micro Vickers hardness 1140 ± 22.14 HV, which is more than twice as compared to mild steel AISI 1035. The corrosion resistance of coatings in 3.5 wt % NaCl solution displays active transition characteristics of activation, passivation, over passivation, and pitting, as shown by the potentiodynamic polarization curves.

Efficient fabrication and characterization of Ni-Fe-WC composite coatings with high corrosion resistance

Nickel-iron alloy is broadly utilized in the industrial field due to its fabulous mechanical properties. How to prepare nickel-iron alloy with better corrosion resistance more efficiently is an important concern. Based on this, the WC particles enhanced nickel-iron coatings were fabricated by jet electrodeposition (JED) at a high current density of 100A/dm2. It was found that increasing the deposition temperature appropriately during JED is beneficial to obtain Ni-Fe-WC coating with the higher number of hard particles. Specifically, the maximum WC particles proportion reaches 4.47 wt% at 55 °C. The electrochemical corrosion behavior of coating was measured by polarization curve and electrochemical impedance spectroscopy (EIS). The polarization curve test results displayed that the Ecorr positively shifted from −0.402 to −0.281 V and the icorr reduced from 25.13 to 7.05 μA/cm2 with the increase of WC particles proportion. Meanwhile, the EIS test results exhibited that the impedance of coating enhanced from 12,720 to 59,140 Ω cm2. The neutral salt spray test (NSS) was used to simulate the corrosion of coating in a seawater environment. The NSS results showed that with the increase of WC particles, the corrosion products decreased gradually and the degree of corrosion decreased. The analysis showed that WC particles can help the grain growth and release the internal stress in the coating. Larger grain sizes reduces intergranular corrosion and smaller internal stress help to alleviate stress corrosion cracking. The above research can provide theoretical support for the efficient preparation of particle enhanced composite coating with strong corrosion resistance.

Corrosion Performance and Rust Conversion Mechanism of Graphene Modified Epoxy Surface Tolerant Coating

A graphene modified epoxy surface tolerant coating was prepared, and the corrosion performance and rust conversion mechanism of the prepared composite coating on rusty carbon steel substrate was investigated. Scanning electron microscope (SEM), X-ray powder diffractometer (XRD), and infrared (IR) spectrum were used to confirmed the iron rust conversion performance by the reaction of phytic acid and rust. electrochemical impedance spectroscopy (EIS), polarization curve, and salt spray test were used to evaluate the corrosion resistance of low surface treatment coatings. Results indicated most of the rust were dissolved and transformed with the reaction of phytic acid and rust on the rusty carbon steel; graphene could effectively improve the compactness and protective performance of the epoxy surface tolerant coating.

Proposal of a New Technique to Obtain Some Fuel Cell Internal Parameters Using Polarization Curve Tests and EIS Results

Nowadays, fuel cells are becoming a real alternative to power several applications, from portable electronic devices to cars, buses, or stationary facilities. Usually, a basic analysis of a fuel cell includes polarization curve test, as this method is excellent to characterize the behavior of a fuel cell as a whole, because it integrates all the different physical process that happens inside in current and voltage signals. On the other hand, it does not provide accurate information of these physical processes as individual. In this research, we relate the results of polarization curve test and EIS (Electrochemical Impedance Spectroscopy) test through two mathematical expressions. Then, using equivalent electrical circuit elements to model EIS curves, and applying the developed expressions, we correlate the EIS and polarization curve results, allowing us to interpret the physical meaning of these circuit elements and obtain a deeper vision of the internal processes that happen.

Mechanical and corrosion resistance of cold sprayed zinc (CSZ) nano composite coating enhanced by SiO2-GO hybrid material

The purpose of this study is to provide an effective solution for improving the mechanical strength and corrosion resistance of cold sprayed zinc (CSZ) coating. In this paper, a convenient method to prepare SiO2-GO hybrid material by surface modification of GO with SiO2 is introduced, so as to improve the dispersibility of GO in CSZ coating and the hydrophobic performance of the coating. Characterization of GO and SiO2-GO by XRD, FT-IR spectrum, Raman spectrum and SEM proves the success of hybridization. The surface state, physical properties and electrochemical properties of the SiO2-GO/CSZ composite coating were studied. The SiO2-GO in the CSZ coating has good dispersion. Composite coating has low surface energy and hydrophobic effect, and the contact angle reaches 125.78°. Compared with GO/CSZ coating, the tensile adhesion of SiO2-GO/CSZ coating was significantly enhanced, reaching 0.7 MPa. Tafel polarization curve and electrochemical impedance test showed that the addition of 0.4 wt% SiO2-GO can greatly improve the barrier time and cathodic protection cycle of CSZ coating under the protection of topcoat. The initial corrosion resistance of 0.4 wt% SiO2-GO/CSZ improved by 24%. After soaking in 3.5 wt% NaCl solution for 50 days, it still had good coating structure and corrosion resistance.