Improvement of La0.8Sr0.2MnO3−δ Cathode Material for Solid Oxide Fuel Cells by Addition of YFe0.5Co0.5O3

The high efficiency of solid oxide fuel cells with La0.8Sr0.2MnO3−δ (LSM) cathodes working in the range of 800–1000 °C, rapidly decreases below 800 °C. The goal of this study is to improve the properties of LSM cathodes working in the range of 500–800 °C by the addition of YFe0.5Co0.5O3 (YFC). Monophasic YFC is synthesized and sintered at 950 °C. Composite cathodes are prepared on Ce0.8Sm0.2O1.9 electrolyte disks using pastes containing YFC and LSM powders mixed in 0:1, 1:19, and 1:1 weight ratios denoted LSM, LSM1, and LSM1, respectively. X-ray diffraction patterns of tested composites reveal the presence of pure perovskite phases in samples sintered at 950 °C and the presence of Sr4Fe4O11, YMnO3, and La0.775Sr0.225MnO3.047 phases in samples sintered at 1100 °C. Electrochemical impedance spectroscopy reveals that polarization resistance increases from LSM1, by LSM, to LSM2. Differences in polarization resistance increase with decreasing operating temperatures because activation energy rises in the same order and equals to 1.33, 1.34, and 1.58 eV for LSM1, LSM, and LSM2, respectively. The lower polarization resistance of LSM1 electrodes is caused by the lower resistance associated with the charge transfer process.

Corrosion Activity of Carbon Steel B450C and Low Chromium Ferritic Stainless Steel 430 in Chloride-Containing Cement Extract Solution

The carbon steel B450C and low chromium SS 430 ferritic samples were exposed for 30 days to chloride-containing (5 g L−1 NaCL) cement extract solution. The initial pH ≈ 13.88 decreased to pH ≈ 9.6, associated mainly with the consumption of OH− ions and the formation of γ-FeOOH, α-FeOOH, Fe3O4 and Cr(OH)3, as suggested by XRD and XPS analysis, in the presence of CaCO3 and NaCl crystals. The deep corrosion damages on B450C were observed around particles of Cu and S as local cathodes, while the first pitting events on the SS 430 surface appeared after 30 days of exposure. The change in the activity of each type of steel was provided by the potentiodynamic polarization curves (PDP). Two equivalent electrical circuits (EC) were proposed for quantitative analysis of EIS (Nyquist and Bode diagrams). The calculated polarization resistance (Rp), as an indicator of the stability of passive films, indicated that SS 430 presented relatively constant values, being two-three orders of magnitude higher than those of the carbon steel B450C. The calculated thickness (d) of the SS 430 passive layers was ≈0.5 nm and, in contrast, that of the B450C passive layers tends to disappear after 30 days.

In Situ Monitoring of Corrosion under Insulation Using Electrochemical and Mass Loss Measurements

Corrosion under insulation (CUI) refers to the external corrosion of piping and vessels when they are encapsulated in thermal insulation. To date, very limited information (especially electrochemical data) is available for these “difficult-to-test” CUI conditions. This study was aimed at developing a novel electrochemical sensing method for in situ CUI monitoring and analysis. Pt-coated Ti wires were used to assemble a three-electrode electrochemical cell over a pipe surface covered by thermal insulation. The CUI behavior of X70 carbon steel (CS) and 304 stainless steel (SS) under various operating conditions was investigated using mass loss, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) measurements. It was found that both the consecutive wet and dry cycles and cyclic temperatures accelerated the progression of CUI. LPR and EIS measurements revealed that the accelerated CUI by thermal cycling was due to the reduced polarization resistance and deteriorated corrosion film. Enhanced pitting corrosion was observed on all tested samples after thermal cycling conditions, especially for CS samples. The proposed electrochemical technique demonstrated the ability to obtain comparable corrosion rates to conventional mass loss data. In addition to its potential for in situ CUI monitoring, this design could be further applied to rank alloys, coatings, and inhibitors under more complex exposure conditions.

Oxygen Diffusion and Surface Exchange Coefficients of Porous La0.6Sr0.4Co0.2Fe0.8O3-δ Decorated with Co3O4 Nanoparticles

This work presents a comparative study of the diffusion (Dchem) and surface exchange coefficients (kchem) of porous La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and Co3O4 nanoparticles decorated LSCF electrodes. The study was carried out using the 3DT-EIS method, which combines Electrochemical Impedance Spectroscopy experiments with FIB-SEM tomography data through an adapted Transmission Line - Adler Lane Steele electrochemical model. A reduction of the polarization resistance of about 60% was measured for the Co3O4 decorated LSCF respect to the reference LSCF cathode, in air at 700 °C. The Co3O4 decoration was found to modify the ORR surface reaction limiting mechanism from O2 dissociation to O-ion incorporation, whereas the diffusion coefficient was not modified by the decoration, which represents a surface diffusion process for both electrodes. After the EIS measurements, the Co3O4 particles were almost no longer visible by Field-Emission SEM on the surface of the decorated sample, but signs that these particles play an active role in Sr Segregation were observed by STEM-EDS, in particular by concentrating the segregated SrO in the surroundings of the decorated particles.

Corrosion Properties of S-Phase/Cr2N Composite Coatings Deposited on Austenitic Stainless Steel

In order to study the suitability of the S-phase layers as the interlayer for Cr2N chromium nitride coatings, a number of composite coatings were deposited by the reactive magnetron sputtering (RMS) method on austenitic steel substrates with various initial surface conditions (as delivered and polished) and their corrosion resistance was assessed. Coatings with S-phase interlayer were deposited at three different nitrogen contents in the working atmosphere (15%, 30%, and 50%), which influenced the nitrogen concentration in the S-phase. Coatings with chromium, as a traditional interlayer to improve adhesion, and uncoated austenitic stainless steel were used as reference materials. Detailed microstructural and phase composition studies of the coatings were carried out by means of scanning electron microscopy (SEM), optical microscopy (LM), and X-ray diffraction (XRD) and were discussed in the context of results of corrosion tests carried out with the use of the potentiodynamic polarization method conducted in a 3% aqueous solution of sodium chloride (NaCl). The performed tests showed that the electrochemical potential of the S-phase/Cr2N composite coatings is similar to that of Cr/Cr2N coatings. It was also observed that the increase in the nitrogen content in the S-phase interlayer causes an increase in the polarization resistance of the S-phase/Cr2N composite coating. Moreover, with a higher nitrogen content in the S-phase interlayer, the polarization resistance of the S-phase/Cr2N coating is higher than for the Cr/Cr2N reference coating. All the produced composite coatings showed better corrosion properties in relation to the uncoated austenitic stainless steel.

Insulative Phase Formation and Polarization Resistance of PrBaCo2−xCuxO5+δ under Thermal Stress

The degradation behavior of PrBaCo2−xCuxO5+δ (x = 0, 0.2, 0.5) under thermal stress was investigated in terms of phase formation and polarization resistance. The tetragonal phase was indexed in all compositions of PBCCux, and the secondary phase, BaO, was identified after thermal degradation in the crystal structure analysis. BaO formation is induced by the nature of perovskite to terminate the surface with AO layer. For pristine specimens, the oxygen vacancy peak ratio was increased from 57% to 60% according to the decrease in the average oxidation number of the B-site ion with Cu doping. After thermal deterioration, the oxidation number of B-site ions was increased, and the M = O bonding peak increased due to the decrease in oxygen vacancies and BaO formation according to the thermal stress. In all compositions, the electrical conductivity decreased from 1000 S/cm to 17 S/cm, and the polarization resistance increased approximately 200 times. These results are considered to be related to the increase in the oxidation number of B-site ions along with the formation of secondary phases.

Assessment of physical, chemical, and tribochemical properties of biomedical alloys used in explanted modular hip prostheses

During their service life, modular interfaces experience tribological, and corrosion phenomena that lead to deterioration, which in turn can cause a revision procedure to remove the failed prosthesis. To achieve a clearer understanding of the surface performance of those biomedical alloys and the role of the surface properties in the mechanical and chemical performance, samples were taken from retrieval implants made of Ti6Al4V and Co28Cr6Mo alloys. Polarization resistance and pin-on-disk tests were performed on these samples. Physical properties such as contact angle, roughness, microhardness, and Young’s modulus were determined. A correlation between surface energy and evolution of the tribological contact was observed for both biomedical alloys. In tribocorrosion tests, titanium particles seem to remain in the surface, unlike what is observed in CoCr alloys. These metallic or oxidized particles could cause necrosis or adverse tissue reactions.

Heat Treatment Effect in the Corrosion Resistance of the Al-Co-Mn Alloys Immersed in 3 M KOH

Al-based alloys named M1, M2, M3, M4, and M5 doped with different atomic percentage (at%) of cobalt and manganese as cast and submitted at two heat treatments (600°C and 1100°C) were analyzed by using electrochemical techniques to evaluate their corrosion resistance immersed in 3 M KOH. With the heat treatments applied to the alloys, the sample M2 (65% Al, 20% Co, and 15% Mn) observed the highest corrosion resistance with R p values of 3.0 × 10 2 , 6.2 × 10 2 , and 1.61 × 10 3 Ω · c m 2 as cast, 600°C, and 1100°C, respectively. The latter was in agreement with the I corr calculated from the polarization curves where the values decrease based on the heat treatment applied as follows: 1.60 × 10 3 > 6.16 × 10 2 > 3.07 × 10 2 mA / c m 2 for 1100, 600, and as cast, respectively. Co concentration above 20% increases the corrosion current ( I corr ) and decreases the polarization resistance of the remain samples. The chemical analysis done with EDS and X-ray diffraction made confirmed the presence of compounds such as CoAl, Co2Al5, Co2Al9, MnAl4, and MnAl6.

Study on anode material of CoδFe1-δOx-Sm0.2Ce0.8O1.9 for solid oxide fuel cell

This paper mainly explores the anode properties of CoδFe1-δOx-Sm0.2Ce0.8O1.9 (SDC) (δ=0, 0.2, 0.5, 0.8, and 1) for solid oxide fuel cell (SOFC). The composite anode materials were synthesized by sol-gel method, and the XRD technique was used to characterize structural properties. After H2 reduction at 700 oC, the CoδFe1-δOx oxides were reduced to Co, Fe metal or Co-Fe alloy. The symmetric cells were fabricated with CoδFe1-δOx-SDC as the electrodes and SDC-carbonate as the electrolyte. At 700 oC, the symmetric cell with Co0.5Fe0.5Ox-SDC electrodes showed the lowest polarization resistance and the symmetric cell with Co0.2Fe0.8Ox-SDC showed the largest polarization resistance.

Poisoning Effect of CO: How It Changes Hydrogen Electrode Reaction and How to Analyze It Using Differential Polarization Curve

The hydrogen electrode reaction (HER) on Pt electrode in a H2SO4 solution when CO gas was injected/stopped was studied using polarization resistance curve [...]