Cathodic Polarization Measurements Research Articles

Catalytic Activity Evaluation of Molten Salt-Treated Stainless Steel Electrodes for Hydrogen Evolution Reaction in Alkaline Medium

The goal of this research is to fabricate a novel type of highly active porous electrode material, based on stainless steel and dedicated to water electrolyzers. The main novelty of the presented work is the innovative application of the molten salts treatment, which allows the design of a highly developed porous structure, which characterizes significantly higher catalytic activity than untreated steel substrates. The equimolar mixture of NaCl and KCl with 3.5 mol% AlF3 was used as the molten salt. The surface modification procedure includes the deposition of an Al layer with application at the potential of −1.8 V and following dissolution at −0.9 V, to create a porous alloy surface. The cathodic polarization measurements of the prepared porous stainless steel electrodes were measured in a 10 mass% KOH solution. Moreover, the amount of hydrogen generated during constant voltage electrolysis with a hydrogen sensor in situ was also measured. The porous stainless steel alloy showed higher current density at lower potentials in the cathodic polarization compared to untreated stainless steel. The cathodic polarization measurements in alkaline solution showed that the porous 304 stainless steel alloy is an excellent cathode material.

(Digital Presentation) Fabrication of AA7075 Containing Mn-Rich Phases By Spark Plasma Sintering and Evaluation of the Pitting Corrosion Resistance

Aluminum alloy 7075 (AA7075) is known as a light-weight and high strength material. AA7075 mainly contains alloying elements such as Zn, Mg, Cu, and Fe to increase strength by intermetallic particles (IMPs). Cu-containing and Fe-containing IMPs in aluminum alloys act as initiation sites of localized corrosion such as pitting in chloride solutions1-3). These IMPs in aluminum alloys show higher potential relative to the Al-matrix and act as cathodic reaction sites4). As for AA7075, it was reported that an increase in pH by the oxygen reduction reaction around Cu-containing IMPs contributes to the dissolution of Al-matrix, followed by pitting3). Therefore, it would appear that the inhibition of the oxygen reduction reaction on the IMPs prevents the pitting corrosion of AA7075.Spark plasma sintering (SPS) is a sintering technique which has been applied to fabricate various materials. When stainless steel powders and pure Mo powders are mixed and sintered by SPS, stainless steel containing Mo-rich phases was fabricated5).In this study, AA7075 containing Mn-rich phases was fabricated by SPS. Gas-atomized AA7075 powders and pure Mn powders were mixed and sintered at 773 K for 15 min. After sintering, hot-forging was conducted at 773 K. After hot-forging, heat-treatment was conducted at 688 K for 2 h, followed by furnace-cooling. After that, the specimens were polished with a diamond paste down to 0.25 µm. AA7075 was fabricated same procedure as AA7075 containing Mn-rich phases. The surface of specimens was observed using an optical microscope and a field emission scanning electron microscope (FE-SEM) equipped with energy dispersive X-ray spectroscopy system (EDS). Electrochemical measurements were performed in 0.1 M NaCl at pH 6.0 adjusted with NaOH. With the exception of the electrode area, the surfaces of specimens were coated with an epoxy resin. The size of the exposed electrode area was ca. 5 mm × 5 mm or 100 µm × 100 µm. Surface treatment of AA7075 was performed in 0.1 M MnSO4. The specimens were polarized in the solution at -0.9 V vs. Ag/AgCl (3.33 M KCl) for 5 hours. A dip-dry corrosion test was conducted to evaluate the corrosion resistance of the specimens. The specimens were dipped in 0.1 M NaCl (pH 6.0) for 20 min and dried at 298 K and 50%RH for 60 min.Al- and Mn-containing films were formed on Cu-containing IMPs by surface treatment in 0.1 M MnSO4. In the 20 cycles of dip-dry corrosion test, MnSO4-treated specimen showed less discoloration than non-treated specimen. It was found that the Al- and Mn-containing films inhibited the oxygen reduction reaction by cathodic polarization measurements. Mn-rich phases were detected in Mn-added AA7075. Mn-rich phases consisted of Mn, Al-Mn, and Al-Mn-Cu intermetallic phases. The size of Mn-rich phases was ca. 20 - 150 µm. In the dip-dry corrosion test, mass-loss decreased with Mn content. After 40 cycles, mass-loss of 5.0 mass% Mn-added AA7075 was twice as lower as that of Mn-free AA7075. After the dip-dry corrosion test, pitting corrosion of the matrix was observed and Mn phases were dissolved. Al- and Mn-containing films were formed on Cu-containing IMPs around the Mn-rich phases after the corrosion test. It was found that the Al- and Mn-containing films inhibited the oxygen reduction reaction by cathodic polarization measurements.

Experimental and theoretical studies of acridine orange as corrosion inhibitor for copper protection in acidic media

The corrosion process commonly limits the use of copper in practical applications. The use of corrosion inhibitors is one of the effective methods to reduce the corrosion rate of copper. In this research, the inhibition effect of acridine orange (3,6-bis(dimethylamine)acridine) (AcO) for the protection of copper in 0.5 ​M ​H2SO4 solution was studied. For this aim, the change of open circuit potential with exposure time (Eocp-t), electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), anodic and cathodic potentiodynamic polarization measurements (PP) and chronoamperometry (CA) techniques were used. Some quantum chemical parameters (EHOMO, ELUMO and dipole moment) were calculated and discussed. The AcO film formed over the copper surface was examined by SEM, EDX, AFM and contact angle measurements. The electrochemical data showed that AcO is an effective corrosion inhibitor even at low concentrations (ranging between 99.1% and %99.4 ​at concentrations from 0.01 ​mM to 1 ​mM). The corrosion rate of copper decreases in the presence of the inhibitor by reducing both anodic and cathodic rates, which is depended on its concentration. This compound behaves as mixed-type corrosion inhibitors with predominantly cathodic type. Its adsorption on the copper surface obeys Langmuir adsorption isotherm. The value of adsorption equilibrium constant (Kads) and the standard free energy of adsorption were ΔGads 1.298 x 103 ​M−1 and -27.71 ​kJ/mol in the case of 0.5 ​M ​H2SO4 solution containing 1.0 ​mM AcO, which shows the adsorption is high and spontaneous. The adsorbed inhibitor film over the metal increase contact angle of the surface, which suggests the more hydrophobic properties of the surface are increasing coming from the orientation of hydrophobic sites to the electrolyte. The zero charge potential (Epzc) studies showed that the surface charge of the metal is positive in the corrosive media containing the inhibitor. Quantum chemical calculations showed that the binding of inhibitor molecules to the metal surface takes place through N atoms of the inhibitor.

Effects of number of substituents and molecular weight of polyamines on the non-cyanide alkaline zinc plating process

The effects of the number of substituents and molecular weight of polyamines in the non-cyanide alkaline plating bath on the morphology, brightness and bright ranges of zinc electrodeposited coating and cathodic polarization, cyclic voltammogram on the non-cyanide alkaline zinc plating process were investigated. Cathodic polarization measurements showed that the polyamines all increased cathodic polarization of the plating process and shifted the zinc reduced potential to a more negative direction. However, cycle voltammogram curves of the 5 continuous cycles shows that the quaternary polyamine Q7-20 has a more stable adsorption and desorption processes than the secondary polyamine Bt18 has.

Separation of Uranium and Zirconium in Alkali Chloride Melts Using Liquid Metal Cathodes

Cyclic voltammetry and cathodic polarization measurements were employed to study zirconium and uranium electrochemical behavior in LiCl–KCl eutectic based melts on solid (tungsten) and liquid (zinc, gallium, indium, Gz–Zn eutectic alloy) working electrodes. Deposition potentials of zirconium and uranium were determined. Ga–Zn alloy showed a difference of ca. 0.9 V in U and Zr deposition potentials. Thermodynamically achievable Zr/U separation factor in a “LiCl–KCl salt melt – liquid Ga–Zn alloy” system was experimentally determined.

Nanocrystalline Ni–Cu Electroplated Alloys Cathodes for Hydrogen Generation in Phosphate-Buffered Neutral Electrolytes

The use of hydrogen as a green fuel alongside an environmentally friendly electrolyte is the most promising technology required for the conversion and storage of renewable energies and the transition to a low carbon future. Nanocrystalline Ni–Cu alloys have been electroplated onto copper electrodes and characterized via scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The electrocatalytic performance of the electroplated Ni–Cu alloys cathodes for the hydrogen evolution reaction (HER) was investigated using cyclic voltammetry, electrochemical impedance spectroscopy and cathodic polarization measurements in the PBNE. The results demonstrate that the nanocrystalline Ni–Cu alloys cathodes have high electrocatalytic efficiency for HER. The overpotential of HER required to reach a catalytic current density of 10.0 mA/cm2 was 284 mV vs. RHE. The most active cathode was a 30:70 (Atom ratio) Ni:Cu alloy in the PBNE and had 1.5 times higher than standard Pt/C which can be applied as a cathode for H2 production in the industrial water electrolyzer, potentially increasing the efficiency of devices and thus lowering the cost of green hydrogen production.

Catalytic Activity of Lanthanide-Doped Sr2PdO3 for the Hydrogen Evolution Reaction in Fuel Cells

The electrocatalytic activity of Ln0.3Sr1.7PdO3 (Ln = La, Nd, or Gd) perovskites prepared by the citrate combustion method for the hydrogen evolution reaction (HER) was examined by electrochemical techniques. The X-ray diffraction data indicate the formation of Sr2PdO3 and SrPd3O4 as primary and secondary phases, respectively, with the LnPd alloy only appearing in the Gd3+-doped sample. Transmission electron microscopy images clearly show the orthorhombic geometry of Sr2PdO3 in all samples, and the particle size decreased and the Brunauer–Emmett–Teller surface area increased as the dopant ionic size decreased. Potentiodynamic cathodic polarization measurements show that lanthanide doping at the Sr2+ site increased the catalytic activity toward the HER compared to that of the undoped binary perovskite, Sr2PdO3, except for the La3+-doped sample. The order of catalytic activity is Gd0.3Sr1.7PdO3 > Nd0.3Sr1.7PdO3 ≈ Sr2PdO3 > La0.3Sr1.7PdO3, which is consistent with the impedance data and activation energy calculations. This order is probably related to the amount of the secondary phase, SrPd3O4, contained in each sample, which not only contributes to the activity but also prevents the catalyst from being deactivated. Of all the prepared ternary perovskites, Ln0.3Sr1.7PdO3 shows considerable operational stability, making it a promising HER catalyst.

Theoretical and experimental studies of dried marjoram leaves extract as green inhibitor for corrosion protection of steel substrate in acidic solution

ABSTRACTDried marjoram leaves (DML) aqueous extract solution was prepared and characterized by Fourier transform infrared spectroscopy (FTIR) and cyclic voltammetry (CV). The effect of DML solution concentration on corrosion protection of mild steel in 0.5 M H2SO4 at different temperatures was studied using anodic and cathodic polarization and electrochemical impedance spectroscopy (EIS) measurements. It was determined from the polariazation curves that the DML acts as a mixed type inhibitor since, both the cathodic and anodic reactions of mild steel corrosion were inhibited. The protection efficiency increases with increasing concentration of DML and decreasing temperatures. The surface morphology was investigated before and after adsorption of DML molecules on the steel surface using scanning electron microscope (SEM). The activation and adsorption parameters were calculated and discussed. The results were supported using density functional theory (DFT), and the quantum chemical parameters were estimated. These parameters reveal the effect of the electronic structure of Thymol, the main component of DML, on its electron donating ability at the B3LYP/6-311 + G (d, p) level.

Electrocatalytic Properties of Vanadate Glass for Metal-Air Rechargeable Battery

A metal-air battery has a high energy density because they can use atmospheric oxygen as the electrode active material. It is expected that the battery could be used for the electric vehicle which demands power sources with a high energy-density. This rechargeable battery needs bifunctional catalytic materials, which involve effective oxygen reduction/evolution at the air electrode at the discharge/charge process. In this study, a new bifunctional catalytic material for the air electrode has been developed using a conductive vanadate glass. Conductivity of vanadate glass, 20BaO·10Fe2O3·70V2O5, was reported to be easily tunable over a wide range (10-7 - 10-1 S･cm-1) when the local distortion of the glass skeleton was removed by means of the annealing [1]. Utilizing these characteristics, new catalytic materials have been prepared by adding MnO2 and NiO for the oxygen reduction and evolution, respectively. 20BaO·5MnO2·5NiO·70V2O5 glass was synthesized by melting the mixture composed of BaCO3, MnO2, NiO, and V2O5 at 1100 °C for 2 hours. The vanadate glass was annealed at 450 °C for various times (0, 30, 60, and 300 min.). Pulverized vanadate glass was utilized for the preparation of the air electrode by mixing the powder with 7.5 mass% of poly (tetrafluoroethylene) (PTFE), which was hot-pressed on a gas diffusion layer over a Ni metal mesh. The electrode connected to a Cu wire was mounted onto the window of Teflon-made cell. 8M KOH aqueous solution and a Pt mesh were placed inside the Teflon cell as the electrolyte and the counter electrode, respectively. The temperature of the Teflon cell was held constant by soaking it into a water tank kept at 60 °C. Anodic and cathodic polarization measurements were carried out using a potentiostat. An Hg/HgO electrode was used as the reference electrode. The electrical conductivity of the as-prepared vanadate glass was 5.4 × 10 -6 S cm-1 at RT. After the annealing at 450 oC for 300 min, it increased to 1.1 × 10 -2 S cm-1. Figure shows the anodic and cathodic polarization curves of 20BaO·5MnO2·5NiO·70V2O5 glass electrodes. The vanadate electrode showed an excellent bifunctional oxygen reduction/evolution activity, being comparable to that of the materials reported in the literature, like polycrystalline LaNiO3 [2]. This vanadate glass could be a highly potential candidate for the bifunctional catalytic material for the rechargeable metal-air battery.

Cathodic activation of titanium-supported gold nanoparticles: An efficient and stable electrocatalyst for the hydrogen evolution reaction

As-polished titanium (Ti) substrates decorated with dispersed gold nanoparticles (Au NPs/Ti) of various sizes and densities were prepared here to effectively catalyze hydrogen evolution reaction (HER) in 0.5 M H2SO4. These materials were synthesized adopting a facile one-step wet chemical method without using reducing agents, stabilizers, or any chemical pre-treatment, where Ti acts as both the reducing agent and support. This was achieved via soaking the Ti substrates for 30 min in a gold precursor bath as a function of temperature (5–65 °C). Morphological characterizations of the synthesized Au NPs/Ti catalysts indicated a size decrease and density increase of loaded Au NPs with the rise of temperature. Cathodic polarization measurements revealed that the catalyst loaded with the highest density of Au NPs exhibited the best HER activity with onset potential (EHER), exchange current density (jo), and Tafel slope (βc) of −44 mV (RHE), 6.0 × 10−3 mA cm−2, and 40 mV decade−1, respectively. This activity has markedly increased upon cathodic activation (cathodic pre-polarization treatment at −2 V (SCE) for 12 h) that yielded a Ti substrate with a porous-like network structure decorated with highly dispersed Au NPs. In addition, a catalytically active TiH2 phase was formed (as evidenced from XRD and XPS) on such a porous substrate. Such cathodically pre-treated catalyst recorded HER electrochemical parameters of −18 mV (RHE), 0.117 mA cm−2, and 38 mV decade−1, thus approaching the commercial Pt/C catalyst (EHER: 0.0 mV, jo: 0.78 mA cm−2, and βc: 31 mV dec−1). The stability of the best catalyst was assessed employing cyclic polarization and chronoamperometry measurements. It exhibited a good stability with improved activity during stability testing.

Corrosion and microstructural characterization of martensitic stainless steels submitted to industrial thermal processes for use in surgical tools

INTRODUCTION: The mechanical properties and corrosion resistance of a material are dependent on its microstructure and can be modified by phase transformation. When a phase transformation occurs in a material it usually forms at least one new phase, with physical-chemical characteristics that differ from the original phase. Moreover, most phase transformations do not occur instantly. This paper presents an evaluation of the phase transformation of martensitic stainless steels ASTM 420A and ASTM 440C when submitted to different thermal processes. METHODS: Dilatometry tests were performed with several continuous heating and cooling rates in order to obtain the profiles of the continuous heating transformation (CHT) and continuous cooling transformation (CCT) diagrams for these two types of steel. Also, the temperature ranges for the formation of the different phases (ferrite and carbides; ferrite; austenite and carbides; non-homogeneous and homogeneous austenite phases) were identified. Rockwell hardness (HRC) tests were performed on all thermally treated steels. Anodic and cathodic potential dynamic polarization measurements were carried out through immersion in enzymatic detergent as an electrolyte for different samples submitted to the thermal processes in order to select the best routes for the heat treatment and to recommend steels for the manufacture of surgical tools. RESULTS: The martensitic transformation temperature tends to increase with increasing temperature for the initiation of cooling. The 440C steel had a higher hardness value than the 420A steel at the austenitizing temperature of 1100 °C. Above the austenitizing temperature of 1100 °C, the material does not form martensite at the cooling rate used, which explains the sharp decline in the hardness values. CONCLUSION: The study reported herein achieved its proposed objectives, successfully investigating the issues and indicating solutions to the industrial problems addressed, which are frequently encountered in the manufacture of surgical instruments.

Carboxylic Acids: Pitting Corrosion Inhibitors for Carbon Steel in Alkaline Medium and in the Presence of Chlorides

The effect of phthalic acid, salicylic acid, benzoic acid, o-aminobenzoic acid, and oxalic acid on pitting corrosion of carbon steel in a 0.01 M NaOH solution in the presence of NaCl is evaluated using potentiodynamic anodic and cathodic polarization measurements. The results show that the carboxylic acids shift the pitting corrosion potential toward more positive values, indicating that they have an inhibiting effect. Of the studied acids, phthalic acid has the greatest inhibiting effect and oxalic acid has the lowest inhibiting effect. All the carboxylic acids are mixed corrosion inhibitors, with predominantly anodic inhibition. We discuss the pitting corrosion inhibition mechanism, taking into account the structure of the acid molecules, their behavior in alkaline medium, and the electron density on the COO– group.

Evaluation of Nitrate and Nitrite Reduction Kinetics Related to Liquid-Air-Interface Corrosion

Liquid-air interface (LAI) corrosion has been a concern for causing leaks in the carbon steel tanks used for holding high-level radioactive liquid waste. To assist in understanding the mechanism of LAI corrosion, the kinetics of nitrate and nitrite reduction reactions were investigated electrochemically. Cyclic voltammetry and cathodic polarization measurements indicated that the nitrite reduction reaction exhibited faster kinetics than the nitrate reduction reaction at higher cathodic overpotential. However, the primary reduction reaction at the open circuit potential under aerated conditions was the oxygen reduction reaction. The reduction of residual oxygen was also the dominant cathodic reaction at open circuit potential in deaerated conditions. Moreover, the kinetics of oxygen reduction on steel electrodes were significantly influenced by the sample immersion conditions (partial vs. full) for aerated liquid nuclear waste simulants, but not for deaerated conditions. Lastly, the gaseous products formed during LAI corrosion were analyzed using the gas detector tube method and gas chromatography-mass spectrometry and found to contain NH3, NO2 and NO. However, the results suggested that these products were caused by the local acidification generated by the hydrolysis of cations after LAI corrosion underwent extensive propagation, instead of being directly reduced in alkaline conditions. Thus, the results in this work showed that the kinetics of nitrate and nitrite reduction could not generate a salt concentration cell in the meniscus region to cause LAI corrosion.

Towards a Physical Description for the Origin of Enhanced Catalytic Activity of Corroding Magnesium Surfaces

The so-called “negative difference effect” (NDE) exhibited by corroding magnesium (Mg) surfaces, where the rate of hydrogen evolution increases with the extent of anodic polarization, has been well documented. Recently this behaviour has been explained by a theory involving an increase in the cathodic exchange current density that occurs during anodic polarization, rather than the popular theory involving the formation of a univalent Mg+ ion and its subsequent chemical reaction with water to produce hydrogen. The present study reports on the results of transmission electron microscopy (TEM) conducted on focused ion beam (FIB) prepared cross-section lamellae of the dark film formed on a corroding area of a Mg surface from which hydrogen evolved. The film was found to consist of an outer columnar mixed magnesium oxide-hydroxide layer on top of a magnesium oxide-rich inner layer. X-ray energy dispersive spectroscopy (EDS) reveals iron (Fe)-rich particles embedded in the columnar outer layer. Subsequent cathodic polarization measurements showed that the corroded surface became cathodically activated relative to a non-corroded surface. These observations demonstrate that a surface film enriched in more noble metals can catalyze the cathodic process, provide physical evidence towards support of the enhanced catalytic surface theory explaining the NDE, and validate the chemistry and structure of the surface film that forms upon corroding regions during anodic polarization.

Electrochemical analysis of the degradation of lead alloy organ-pipes due to acetic acid

Abstract Lead is commonly used for making small size organ-pipes instead of using tin alloys. In fact, when the organ-pipes are small enough to avoid collapsing due to room temperature creep, lead can be used instead of other alloys with superior mechanical properties, because it is relatively cheap, it is easy to form into different shapes, the tonality of the obtained sounds are acceptable and the corrosion resistance is quite good. However, organic substances such as organic acids released from the wood made support of the organ-pipes and organic contaminations of the air pumped through the pipes may lead to a rapid degradation of lead. In this study, the effect of organic acids, such as acetic acid, on the degradation of lead-made organ-pipes was investigated. Lead made specimens obtained from real organ-pipes were exposed to organic-acid rich environments and the induced degradation was monitored by means of electrochemical techniques. In literature, it was evidenced that the degradation promoted by the organic acids leads to the formation of lead oxides and carbonates characterized by a very high volume, which promotes a quick degradation of the lead specimens. The effect of different concentrations of acetic acid on the degradation rate of the organ pipes was investigated by means of electrochemical impedance spectroscopy (EIS). The effect of the acid concentration on the corrosion process occurring on lead surface was evaluated by means of cathodic and anodic polarization measurements in both aerated and degassed conditions. The morphology of the degradation products was investigated by means of SEM during exposure time in the aggressive environment.

Electrochemical behavior of gold (III) in cyanide-free bath with 5,5′-dimethylhydantoin as complexing agent

Gold electrodeposits are prepared in a cyanide-free bath with 5,5′-dimethylhydantoin (DMH) as complexing agent. The electrochemical behavior of the electrodeposition is then investigated together with the influence of additive A (pyridyl-compound) as an additive on the nucleation and growth of gold using electrochemical techniques on gold working electrode at different temperatures. Cyclic voltammogram consists of a single cathodic reduction wave at −0.62 V which corresponds to the reduction of Au(III) to Au without anodic oxidation wave observed. The diffusion coefficient of Au(III) in the bath is found to be ∼10 −6 cm 2/s and the energy of activation (43 kJ/mol) is deduced from the cyclic voltammograms at different temperatures. The nucleation and growth of gold on gold working electrode is investigated by chronoamperometry. The progressive nucleation mechanism is found for gold deposition using Scharifker–Hills’ model with three-dimensional (3D) diffusion-controlled growth nucleation. The introduction of the additive A does not influence this mechanism. The gold electrodeposits are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and cathodic polarization measurements. Experimental results indicate that additive A increases the cathodic polarization of bath, refines the grains of electrodeposit and changes the preferred orientation of electrodeposit from [1 1 1] direction to [2 0 0] direction.

Chemical compatibility, thermal expansion matches and electrochemical performance of SrCo 0.8Fe 0.2O 3− δ–La 0.45Ce 0.55O 2− δ composite cathodes for intermediate-temperature solid oxide fuel cells

The chemical compatibility, thermal expansion and electrochemical property measurements of the SrCo 0.8Fe 0.2O 3− δ (SCF)–La 0.45Ce 0.55O 2− δ (LDC) composite cathodes for solid oxide fuel cells (SOFCs) were investigated by X-ray diffraction (XRD), thermal expansion coefficients (TECs) and cathodic polarization measurements together with electrochemical impedance spectroscopy (EIS). The results indicated that LDC had good chemical compatibility with SCF and La 0.9Sr 0.1Ga 0.8Mg 0.2O 3− δ (LSGM), and the addition of LDC to SCF markedly reduced the polarization resistance. When the content of LDC reached 50 wt%, the SCF50 cathode showed the best electrochemical performance, with a cathodic overpotential of 0.1 V at the current density of 1102.0 mA cm −2, together with a polarization resistance of 0.149 Ω cm 2 at 800 °C. The improved electrochemical performance was attributed to the expansion of the electrochemical reaction region into the electrode, and offering an easier path for the oxygen ion transport. Furthermore, the SCF–LDC composite cathodes match better with the LSGM electrolyte.

Evaluation of mechanically treated cerium (IV) oxides as corrosion inhibitors for galvanized steel

The use of cerium salts as corrosion inhibitors for hot dip galvanized steel has been object of a numerous studies in the last few years. The role of cerium ions as corrosion inhibitors was proved: cerium is able to block the cathodic sites of the metal, forming insoluble hydroxides and oxides on the zinc surface. This fact leads to a dramatic decrease of the cathodic current densities and, therefore, to a reduction the overall corrosion processes. On the other hand, the potential of cerium oxides as corrosion inhibitors was also proposed. However, the real effectiveness of this kind of anticorrosive pigments has not been clarified yet. In this work cerium (IV) oxides are considered as corrosion inhibitors for galvanized steel. The corrosion inhibition mechanism of mechanically treated (milled) CeO 2 alone and in combination with milled SiO 2 nanoparticles was investigated. For this purpose milled CeO 2, CeO 2 and SiO 2 milled together and milled SiO 2 particles were studied as corrosion inhibitors in water solution. Therefore, the different mechanically treated particles were dispersed in 0.1 M NaCl solution to test their effectiveness as corrosion inhibitors for galvanized steel. The galvanized steel was immersed in the different solutions and the corrosion inhibition efficiency of the different particles was measured by means of electrochemical techniques. For this purpose, electrochemical impedance spectroscopy (EIS) measurements were carried out, monitoring the evolution of the corrosion processes occurring at the metal surface with the immersion time in the solution. The effect of the different pigments was also investigated by carrying out anodic and cathodic polarization measurements. The polarization curves were acquired under conditions of varied pH. The experimental measurements suggest that the mechanical treatment performed on the SiO 2 and CeO 2 particles promote the formation of an effective corrosion pigment. The tests evidence also the beneficial effect of the CeO 2 milled particles when used in combination with the mechanically treated SiO 2 particles. It was proved that in alkaline conditions the effect of the mechanically treated CeO 2 and SiO 2 particles is dramatically increased.

Study on the Electrodeposition of Ni-P Nanowires and Their Electrocatalytic Properties

The anodized aluminum oxide (AAO) template was used in the electrodeposition of Ni-P alloy in this study. The fabricated Ni-P wires were 70 to 80 nm in diameter and 15 to 20 μm in length. The analyses employing a field-emission scanning electron microscope, X-ray diffraction, transmission electron microscope, and X-ray photoelectron spectrometer (XPS) showed these nanowires were amorphous structure mixed with nanosized grains and had preferred orientation along its length. From the cathodic polarization measurements in 0.5M H2SO4 electrolyte, it was found that the Ni-P nanowires demonstrated a nearly double magnitude in the current at –0.75 VSCE compared with its solid film counterpart. Thus, the enhancement of the electrocatalytic activity due to the increase in the surface area of the nanowired structure was demonstrated and discussed. However, the formation of oxide film on the surface of the nanowire was discovered after cathodic polarization. The effect of the oxide film was also discussed in this article.

Electrochemical properties of La 0.8Sr 0.2FeO 3-δ based composite cathode for intermediate temperature SOFC

La 0.8 Sr 0.2FeO 3-δ is a new kind of cathode material for intermediate SOFC, but its electrochemical activity is relative poor for the lanthanum gallate based solid oxide fuel cell. In this paper, a novel composite cathode of La 0.8Sr 0.2FeO 3-δ/La 0.9Sr 0.1 Ga 0.8Mg 0.2O 3-δ was prepared on the LSGM electrolyte substrate by screen-printing method. The results of cathodic polarization measurements show that the overpotential decreases significantly when the composite cathode is used instead of the La 0.8Sr 0.2 FeO 3-δ single layer cathode. The cathodic overpotential of the composite La 0.8Sr 0.2FeO 3-δ/La 0.9Sr 0.1Ga 0.8Mg 0.2O 3-δ cathode is 150 mV at the current density of 0.2 A·cm −2 at 800 °C, while the cathodic overpotential of the La 0.8Sr 0.2 FeO 3-δ single layer cathode is higher than 260 mV at the same condition. The electrochemical impedance spectroscopy was employed to investigate the polarization resistance of the cathode. The polarization resistance of the composite cathode is 1.20 ω·cm 2 in open circuit condition, while the value of the single La 0.8 Sr 0.2FeO 3-δ cathode is 1.235 ω·cm 2.