bluuebunny/crossref_metadata_2025 huggingface dataset:
Internal Reforming Kinetics in SOFC-Anodes
Authors: Kromp Alexander , Leonide André , Timmermann Henrik , Weber André , Ivers-Tiffée Ellen
Published: October 2010

The internal reforming of methane in a solid oxide fuel cell (SOFC) has been modeled for operation conditions relevant to both stationary and auxiliary power unit (APU) applications. A 2D-FEM model was developed in COMSOL Multiphysics. Aim of this model is the space-resolved prediction of the gas composition in the anode side of planar anode supported single cells. The isothermal model accounts for the mass transport phenomena in the fuel-gas channel and the anode substrate. A global rate expression is applied to model the gas conversion caused by the internal reforming reactions. The kinetic parameters were fitted to experimental data. In the investigated parameter range, the model shows good correlation with experimental data. As the model is capable to coherently calculate the complex species transport phenomena and the kinetics of the chemical reactions, the limitation of pore transport on the effective chemical reaction kinetics can be reproduced with the model.
Anchoring of Infiltrated Nickel Electro-Catalyst by Addition of Aluminum Titanate
Authors: Law Cameron , Sofie Stephen W.
Published: October 2010

Solid oxide fuel cell electrodes based on catalyst coatings offer substantial potential for creating more effective anode and cathode structures. Infiltrated anodes based on nickel metal can yield finer catalyst phase distribution at volumetric concentrations well below percolation for traditional cermets. The coarsening of nickel after high temperature thermal treatment poses substantial degradation to the deposited structure, therefore, methods of anchoring the nickel metal to the yttria-stabilized zirconia (YSZ) scaffold have been evaluated to stabilize fine scale electro-catalyst particles. Aluminum titanate was introduced into the porous YSZ anode scaffold to facilitate a step-wise chemical reaction to anchor the nickel metal catalyst as determined by XRD. SEM observation of thermally treated nickel infiltrated scaffolds indicates excellent preservation of the nickel network at 800 C for 72 hrs. Electrochemical tests show not only decreased degradation rates, but also increased initial performance levels due to the additive.
Enhanced Performance of the GdBaCo2O5+δ Cathode with Active Ce0.8Sm0.2O1.9 Nanoparticles
Authors: Wei Bo , Lü Zhe , Wei Tianshi , Jia Dechang , Huang Xiqiang , Zhang Yaohui , Su Wenhui
Published: October 2010

Cathodic polarization resistance (Rp) critically limits the performance of intermediate temperature solid oxide fuel cell (IT-SOFC). In this paper, high performance GdBaCo2O5+delta - Ce0.8Sm0.2O1.9 (GBCO-SDC) nano-composite cathodes were fabricated via an ion-infiltration method and their chemical compatibility, microstructures and electrochemical properties were evaluated. Good chemical compatibility was found between GBCO and SDC components. Active SDC nano-particles (40nm) formed continuous ionic-conducting phase on the surface of GBCO backbone, which significantly enhanced the electrocatalytic activity for oxygen reduction reaction. The composite cathode with 3.3mg•cm-2 SDC loading showed encouragingly low polarization resistance values of 0.55Ohm•cm2 and 0.096Ohm•cm2 at 500 degree C and 600 degree C, respectively, which implies their promising application for cathodes of IT-SOFC.
Identification of the Charge Carriers in Cerium Phosphate Ceramics
Authors: Ray Hannah L. , De Jonghe Lutgard C.
Published: October 2010

The total conductivity of Sr-doped cerium orthophosphate changes by nearly two orders of magnitude depending on the oxygen and hydrogen content of the atmosphere. The defect model for the system suggests that this is because the identity of the dominant charge carrier can change from electron holes to protons when the sample is in equilibrium with air vs. humidified hydrogen. In this work are presented some preliminary measurements that can help to clarify this exchange between carriers. The conduction behavior of a 2% Sr-doped CePO4 sample under symmetric atmospheric conditions is investigated using several techniques, including AC impedance, H/D isotope effects, and chronoamperometry.
Phase Transition Behavior of Proton Conducting Oxides, Sr1-xBaxZrO3
Authors: Sugimoto Takayuki , Hasegawa Shinya , Hashimoto Takuya
Published: October 2010

Phase diagram of Sr1-xBaxZrO3, which is a mother phase of high proton conducting oxide, has been established by using high temperature X-ray diffraction, DSC and dilatometry. The temperature, jump of specific heat and variation of enthalpy of three kinds of phase transitions detected in SrZrO3 decreased with increasing Ba content. The phase boundaries among primitive orthorhombic, body-centered orthorhombic, tetragonal and cubic phase have been determined.
Phase Stability and Electrochemical Analysis of Nb Doped BaCe0.9Y0.1O3-x Electrolyte for IT-SOFCs
Authors: Di Bartolomeo Elisabetta , D'Epifanio Alessandra , Pugnalini Chiara , Zunic Milan , D'Ottavi Cadia , Licoccia Silvia
Published: October 2010

Barium cerate-based electrolytes containing different amounts of Nb5+ as a dopant were investigated with the aim of attaining materials with improved chemical stability. BaCe0.9-xNbxY0.1O3-x (BCYN) powders with different compositions (0 {less than or equal to} x {less than or equal to} 0.20) were synthesized by citrate-nitrate auto-combustion method and pure single phases were obtained at 1000 {degree sign}C. Dense pellets were obtained using sintering a temperature of 1450 {degree sign}C for 10 hours. The chemical stability was evaluated by XRD analysis after CO2 exposure at 700{degree sign}C for 3 hours. To investigate the effect of Nb5+ doping on conductivity, electrochemical impedance spectroscopy (EIS) measurements were carried out in the 400-700 {degree sign}C temperature range in different atmospheres.
Synthesis and Li-Ion Transport Mechanism of Li1.4[M0.4N1.6](PO4)3 Electrolyte
Authors: Rao R. Prasada , Adams Stefan
Published: October 2010

Li1.4N1.6M0.4(PO4)3 with M = Al, Ga, N = Ti, Ge were prepared by annealing of the mixtures at 800°C. X-ray diffraction showed the formation of NASICON phase with space group R-3c along with a minor impurity second phase. Rietveld refinement of the X-ray data was performed to identify the structural variation. The compound with N = Ti and M = Al exhibited lattice parameters a = 8.5015 Aå and c = 20.820 Aå, slightly lower than for the undoped Ti compound (N = M = Ti). Measurements of σionic were carried out on sintered pellets by impedance spectroscopy at 30°C, highest ionic conductivity 2.57 x 10-4 S/cm among the prepared samples was observed when N = Al and M = Ti, two orders of magnitude higher than for the undoped case. Bond valence approach was applied to visualize the migration pathways of Li+ ion and barrier energies were estimated. Obtained Li site energy landscapes indicate the continuous Li transport pathway accessible with activation energy of 0.45eV for undoped Li1Ti2(PO4)3 and 0.42 eV for N = Al and M = Ti doped compound.
Ultrafast Lithium Migration by Heterogeneous Doping in Surface Modified LixFePO4
Authors: Adams Stefan , Prasada Rao R. , Choo Haiping
Published: October 2010

Molecular dynamics (MD) simulations with a dedicated force-field in combination with our bond valence (BV) pathway analysis have been employed to reproduce and explain the experimentally observed ultrafast Li+ transport in surface modified LixFePO4-δ as a consequence of heterogeneous doping, i.e. the Li+ redistribution in the vicinity of the interface between LixFePO4 and a pyrophosphate glass surface layer. Over the usual working temperature range of LIBs Li+ ion conductivity in the surface modified LixFePO4 phase is enhanced by 2-3 orders of magnitude, while the enhancement practically vanishes for T > 700K. Simulations for the bulk phase reproduce the experimental conductivities and the activation energy of 0.57eV (for x ≈ 1). A layer-by-layer analysis of structurally relaxed multilayer systems indicates a continuous variation of Li+ mobility with the distance from the interface and the maximum mobility close to the interface, but Li+ diffusion rate remains enhanced (compared to bulk values) even at the center of the simulated cathode material crystallites. Our BV migration pathway analysis in the dynamic local structure models shows that the ion mobility is related to the extension of unoccupied accessible pathway regions. The change in the extent of Li redistribution across the interface with the overall Li content constitutes a fast pseudo-capacitive (dis)charging contribution.
Interaction of Intercalated Li+ Ions with Oxygen Vacancies in Rutile TiO2
Authors: Sushko Peter V. , Rosso Kevin M. , Abarenkov Igor V.
Published: October 2010

Point defects are known to affect transport properties of materials. The effect of oxygen vacancies on the diffusion of Li+ ions in rutile TiO2 is investigated using an embedded cluster method. The calculated Li+ diffusion pathway in vacancy-containing lattice is similar to that found for the ideal lattice. However, vacancies strongly modify the shape of the Li+ potential energy surface and increase the diffusion activation energies by the factor of two.
Characterization of Conductivity in Single Crystal TlBr
Authors: Bishop Sean R. , Higgins William , Churilov Alexei , Ciampi Guido , Kim Hadong , Cirignano Leonard , Biteman V. , Tower Josh , Shah Kanai , Tuller Harry
Published: October 2010

TlBr is an ionic material with good potential for use in high energy radiation detectors because of its relatively large band gap and heavy elements. In these sensors, incident radiation excites electron hole pairs that are collected as the response, and the mobility-lifetime product for electrons and holes, as well as low dark current are common figures of merit. TlBr reportedly displays ionic conductivity that leads to undesirable leakage, or dark current thereby reducing sensor response. This work focuses on the development of a defect and transport model appropriate to TlBr. The derived enthalpies of migration and Schottky defect formation are compared with literature values.
Long Term Testing of Solid Oxide Fuel Cell Stacks with Yttria Stabilized Zirconia Electrolyte in the H2O Electrolysis Mode
Authors: Schefold Josef , Brisse Annabelle , Zahid Mohsine
Published: October 2010

A fairly broad experimental basis exists for solid oxide fuel cells reversibly operated as H2O electrolyser cells (SOECs), notably for classical cells with Ni based anodes, YSZ electrolytes, and LSM cathodes. High electrical-to-chemical energy conversion efficiencies are achieved at such cells. Results from the long-term SOEC testing of two 5-cell stacks are compared, stack I with (H2) electrode and stack II with electrolyte supported cells. Operation times were 2600 h and 2000 h, respectively, under current densities between -0.4 and -0.6 Acm-2, 90% feed gas humidity, and 40 to 60 % steam conversion. The voltage degradation under constant current operation amounts to 3% (stack I) and 4.6% (stack II) per 1000 h. The evaluation is complicated by instabilities arising from poor endplate contacts and also by initial passivation/activation at stack I. Faradaic efficiencies are close to 100%. Electronic conduction in the electrolyte limits the cell voltage under current flow without steam supply.
Grain Size Dependence Characteristic of Nanocrystalline ZnO-Channel Thin Film Transistors
Authors: Ebrahimi Takalloo Saeedeh , Asl Soleimani Ebrahim
Published: October 2010

Bottom gate ZnO-Channel test structure thin film Transistors are fabricated on 100 p-type silicon wafers. ZnO is deposited by RF sputtering in different powers of 100, 150, 200, 250 and 300W. We showed that Ion to Ioff ratio of transistors has a reverse trend as grain size of ZnO channel. The transistor which the channel is fabricated in power of 150W has the lowest logarithm of Ion to Ioff ratio of 2.5 and the related channel layer has the largest grains and the one which its channel is fabricated in power of 300W has the highest value of about 6 and the smallest channel grain size. This transistor has also the highest field effect mobility of 0.5 VS/cm2 and the highest Vth of 20V among all. The subthreshold slope of this transistor is calculated 3V/dec which is the lowest among all.
CO-Stripping at Ru Nanoparticles
Authors: Ochal Piotr , Gomez de la Fuente Jose Luis , Tsypkin Mikhail , Garcia-Rodriguez S. , Seland Frode , Sunde Svein
Published: October 2010

The paper reports synthesis and characterization of electrocatalyst composed of Ru nanoparticles (NPs). The catalysts were prepared by a polyol process and deposited on carbon (Vulcan XC72) support and employed PVP as a stabilizer. The as-prepared sample did not show any diffraction peaks, suggesting an amorphous structure, and was highly active for oxidation of CO. Heating of the catalyst in an inert atmosphere, however, resulted in the crystallization of the particles. The heat treatment resulted in significant drops in the electrocatalytic activity, tentatively ascribed to carbonaceous deposits at the catalyst surface. The results demonstrate that stabilisers such as PVP will not pose a significant hindrance for low-temperature electrochemical reactions at these catalysts.
Automated Printing of Electrochemical Immunoassay Microarrays: Studies of Conditions Affecting Alkaline Phosphatase Enzyme Label Activity
Authors: Williams Caitlin R. , Fritsch Ingrid
Published: October 2010

Microarray printing of components of an enzyme-linked immunosorbant assay (ELISA) is attractive for constructing miniaturized platforms to simultaneously and quantitatively analyze multiple chemical species in clinical, environmental, and forensic applications. A truncated version of an electrochemical ELISA was used to address a major challenge of this approach, namely the effect of evaporation on assay activity. An antibody-alkaline phosphatase conjugate (Ab-AP) was printed with a microarrayer onto an N-hydroxysuccinimide-ester-terminated self-assembled monolayer on gold. The activity of the enzyme label AP to convert the substrate p-aminophenyl phosphate to electroactive p-aminophenol was followed as a function of different conditions via detection by cyclic voltammetry at microband electrodes. It was found that enzyme activity decreased by 60% from 30 min to 4 h after evaporation. However, printing in ambient humidity ("dry") as opposed to printing in a humidified chamber, resulted in the highest assay signals observed and low nonspecific adsorption.
The Effect of the Oxygen-Containing Functional Groups on the Electrochemical Reduction of Oxygen of Multi-Walled Carbon Nanotubes in Acid Media
Authors: Matsubara Kenji , Waki Keiko
Published: October 2010

The effect for oxygen reduction characteristics of O-functionalities formed on the edge planelike defects at the open ends of multiwalled carbon nantoubes (MWCNTs) and on the hole defects at the tube walls was investigated by means of the rotating disk electrode method. The onset potential of the electrochemical reduction of oxygen for MWCNTs shifts to the positive direction of 0.19V, while the O-functionalities were removed from the defect sites. This result suggests that the control of functional groups is important for the control of the oxygen reduction catalyst activity.
Effect of Sulfur Incorporation on Coercivity in CoFe Nanowires
Authors: Kola Avinash , Davis Despina
Published: October 2010

In this study we report for the first time the effect of sulfur incorporation on coercivity in CoFe nanowires. The CoFe alloys were deposited from a sulfate bath with varying concentrations of thiourea in polycarbonate membranes. The physical incorporation of sulfate anions from the electrolyte was also taken into account as a source of sulfur which was not considered earlier. The deposition was done potentiostatically to control the composition of the CoFe nanowires. A low coercivity (soft nanowire) in the range of 120-130 oersteds was obtained for samples containing low S at%. Also the amount of sulfur seemed to have an effect on the microstructure of the deposits. A low thiourea concentration was determined to be ideal to achieve low coercivities. Composition and surface morphology was studied using EDAX and SEM respectively. Coercivity was studied using an Alternating Gradient Magnetometer (AGM) with fields applied upto 1Tesla.
Nitrogen Doped Carbon Nanotubes Based Non-Precious Metal Catalysts for Oxygen Reduction Reaction at Alkaline Fuel Cell Cathode
Authors: Chen Zhu , Chen Zhongwei
Published: October 2010

Alkaline fuel cell is a highly efficient and environmentally friendly energy conversion device showing great potential for sustainable development. However, to realize the commercialization of alkaline fuel cell, many obstacles must be overcome. The biggest challenge is perhaps to improve the oxygen reduction reaction (ORR) at the alkaline fuel cell cathode. Platinum based catalyst remained to be the most effective catalyst for ORR, but the scarcity and high cost prohibit large scale application in alkaline fuel cell. Nitrogen doped carbon materials have showed great potential for ORR, making these catalysts desirable replacements for platinum based catalysts. In this paper, nitrogen doped carbon nanotube exhibiting high ORR activity is presented. Through material characterizations, the various factors affecting the activity of nitrogen doped carbon nanotube are elaborated as well.
Diagnostic Methods of Solar Cell Based on Temperature Dependence
Authors: Dolensky Jan , Vesely Ales , Vanek Jiri , Hrozek Jan
Published: October 2010

This study is focused on testing methods determining quality of solar cells. Non-destructive methods are used for correct determination of defects by using of recombination effect of charge carrier in PN junction. Due to these methods can be the solar cell diagnosed and described. By using of various temperatures during the testing we can receive more objective results thanks to simulated operation conditions. Peltier cells are used for graditional change of temperature. Diagnostic and testing methods described in this study are based on emission of light and the recombination processes in PN junction. It is especially electroluminescence and photoluminescence method. For comparison it is used the observation of emitted light from microplasma method. Described methods detect materials and process defects due to use of lownoise and very sensitive CCD camera.
A Study of Properties of F- Removal in Dilute Solutions Using Mesoporous Carbon Electrodes
Authors: Hamada Mitsuhiro , Yoshida Sayuki , Nakagawa Kiyoharu , Oda Hirokazu
Published: October 2010

A mesoporous carbon material, Resorcinol-Formaldehyde Carbon Cryogel (RFCC), was used as an electrode of water treatment technologies applied principle of electric double layer (EDL). And the electrode performance of RFCC was compared with that of microporous materials, such as MSC10 and ACo. The efficiency of ion removal of RFCC was the highest of the three electrodes and carbon electrodes with a large mesopore (> 20nm) was formed an ideal EDL in the dilute solution.
The Reliability of LTPS-TFTs Alternately Stressed in OFF Region
Authors: Liu Han-Wen , Chiou Si-Ming , Wang Fang-Hsing
Published: October 2010

The reliability of n-channel low temperature poly-Si thin film transistors (LTPS TFTs), which are dynamically stressed in OFF region with drain zero biased and source grounded, is investigated. Rectangular pulses with different parameters such as rising time, falling time or frequency are imposed to the gate electrode to examine the degradation. It is observed that the degradation depends strongly on the rising time and frequency of ac signal. As the gate voltage switches in the rising period, the accumulated holes should be swept out and flow into source or drain terminals, owing to the floating body structure of TFTs. Therefore, there is high electric field at the rising period of transient stress, which enhances the degradation. A degradation model is proposed to explain the degradation mechanism of LTPS TFTs on the basis of the flowing direction of the sampling current Id, and demonstrated by two electrical measuring items, saturation forward & reverse Id-Vg transfer curves and C-V curves.
Surface Modification of Nanocarbon Materials for Electrochemical Capacitors
Authors: Akter Tahmina , Lian Keryn K.
Published: October 2010

Multi-walled carbon nanotubes (MWCNT) modified by pseudocapacitive polyoxometalates (POM) have been investigated as electrode materials for high rate electrochemical capacitors (EC). Layer-by-Layer deposition method was utilized in this study. Even with merely a single-layer of POM, the modified MWCNT exhibited over 50% increase in capacitance compared with that of bare nanotubes. The deposition sequence of the POM layers was also optimized to further enhance the electrochemical performances of these MWCNT for fast charge delivery.
Effect of Carbonate on Anion Exchange Membrane Conductivity and Hydrogen Oxidation for AEMFCs
Authors: Vega Jose A. , Smith Shawna , Chartier Casey , Mustain W.
Published: October 2010

A commercially available anion exchange membrane, Ralex AMH-PAD, was exposed to hydroxide and alkaline environments over a 30 day period. Exposure to hydroxide caused a 26% conductivity decrease over the experimental period, which was attributed to the Hofmann elimination and nucleophilic attack degradation mechanisms. Exposure to carbonate environments did not cause any measurable effect on the ionic conductivity. Also, hydrogen oxidation was studied in carbonate environments. The reaction followed a 2-electron pathway, analogous to the reaction with hydroxide. The exchange current density was unchanged for the oxidation with carbonate compared to hydroxide.
Enhancement of ORR by Electrodeposited CoFePt Multilayered Alloys
Authors: Avekians Alex , Podlaha-Murphy Elizabeth
Published: October 2010

Ternary FeCoPt alloys have been electrodeposited as thin films and in a multilayer fash-ion for ORR studies. X-ray fluorescent (XRF) was used to characterize the composition and voltammetry was used to assess the deposit's catalytic behavior. Fe and Co deposited at potentials more positive than their equilibrium potentials and only the Co partial cur-rent density was affected by changes in Co(II) ion concentration. In the OPD region a first order Co partial current density behavior was observed. The thin film deposition results also were used to determine conditions for multilayer deposition. At potentials of -300 and -800 mV vs. Ag/AgCl, Pt-rich and FeCo-rich films are formed, respectively. Voltammetry experiments, conducted in aerated 0.5 H2SO4, found that multilayer thin films have improved catalytic activity with respect to its identical thin film counterparts.
Synergistic Effect of Different Salts on the Inhibition Efficiency of a Cationic Surfactant on Steel Corrosion in Acid Medium
Authors: Asefi Dourna , Arami Mokhtar , Mahmoodi Niyaz Mohammad
Published: October 2010

Corrosion inhibition effect of cationic surfactant DTAB (Dodecyl Threemethyl Ammonium Bromide) on low carbon steel in 1M HCl was studied using weight loss and OCP (Open Circuit Potential) methods. Inhibition efficiency increases with increasing of surfactant concentration. Also synergistic effect between surfactant and different alkaline metals salts (KCl, NaCl, NaBr, NaI, LiCl, Na2SO4, and NaNO3) in 1 M HCl is investigated. The effect of different anions and different metal cations on inhibition efficiency is discussed. The inhibition efficiency increases with increasing of salts concentration and reaches the maximum value near 0.1 M. The results show that the synergistic effects of salts are in this order Na2SO4 >NaI > LiCl > NaCl > KCl > NaBr > NaNO3. This inhibitor system containing cationic surfactant and an alkaline metal salt is efficient and low-cast for steel corrosion inhibition in HCl medium, even when the concentration of DTAB is as low as 0.5 × 10-4 M.
Studies on the Stability of Zn and Zn-TiO2 Nanocomposite Coatings Prepared by Pulse Reverse Current
Authors: Gomes Anabela , Frade Tânia , Da Silva Pereira M. Isabel
Published: October 2010

The stability of the metal matrix nanocomposites Zn-TiO2, has been investigated with the aim of using them as catalysts and electrocatalysts for the degradation of pharmaceutical compounds. Nanocomposite thin films were obtained from the occlusion electrodeposition method, using pulsed reverse current electrolysis, from acidic zinc sulphate solutions, on a Ti support. The stability of the films is strongly dependent on the morphologic and structural characteristics of the materials. The formation of a protective layer, mainly composed of Zn4SO4(OH)6 and ZnSO4, is easier on the Zn-TiO2 films than on Zn electrodeposits and acts as barrier against further metal dissolution, proved by the absorption atomic analysis of the solution.
"Chemical Effect" Head Loss Pressure Drop for the Nuclear Power Plant Safety
Authors: Choromokos Robert , Mast Pete , Park Jong-Hee M.
Published: October 2010

This paper has shown the progresses and evaluations on the chemical effect headloss pressure drop causing factors for the post loss of coolant accident (LOCA) nuclear power plant safety concerns. The 'chemical effect head loss pressure drop' tests were performed by simulating power plant input parameters post-LOCA 30-days period. The following various factors have to be evaluated to find out the chemical effect head loss causing factors, i) released Al from metallic corrosion and/or insulators which plays major role in the AlOOH, NAS (sodium aluminum silicate) precipitates, ii) particles size, debris bed pore size, iii) electrostatic and chemical interaction between precipitates and debris bed short and longer times for the Ostwald ripening, iv) flow patterns (laminar/turbulent), v) dissolved gas phases impregnation in the debris bed, vi) viscosity, vii) fiber strength, viii) solubility (T, pH), and ix) composition of debris bed such as glass fiber with dust, dirts, iron oxide, etc.
Performance of Alloy 625 under Combustion Gas Environments: A Review
Authors: Cuevas-Arteaga Cecilia , Verhelst D. , Alfantazi A.
Published: October 2010

The nickel-based alloy 625 in the form of thermal sprayed coatings, as weld overlay, and as an alloyed material has been used extensively to minimize high temperature oxidation and hot corrosion in incinerators, supercritical water oxidation processes, biomass-fired plants, and other industries. Corrosion in these applications occurs due to the combination of gaseous species in the form of CO2, O2, SO2, and HCl; and solid impurities which form chlorides and sulphates of alkali and heavy metals (K, Na, Zn, Pb, Sn, etc) with low melting points. Even though alloy 625 has some shortcomings under certain conditions at high temperatures, the alloy from its beginning has had significant success, and its production has increased considerably worldwide. This paper will review some aspects for which alloy 625 is the material of choice and explain its unique features in many applications.
Constant-Phase-Element Behavior Caused by Resistivity Distributions in Films
Authors: Hirschorn Bryan , Orazem Mark E. , Tribollet Bernard , Vivier Vincent , Frateur Isabelle , Musiani Marco
Published: October 2010

CPE behavior may be attributed to the distribution of physical properties in films, in the direction normal to the electrode surface. Numerical simulations were used to show that, under assumption that the dielectric constant is independent of position, a normal power-law distribution of local resistivity is consistent with the Constant-Phase Element (CPE). An analytic expression for the impedance corresponding to a power-law distribution of resistivity was developed and used to establish a relationship between parameters for the CPE and physical properties of the film. The resulting impedance response was compared to that obtained from the Young resistivity distribution.
Corrosion Performance of Carbon Steel in Micelle-Containing Cement Extract
Authors: Hu Jie , Koleva Dessi , De Wit J. H. W. , Petrov Petar , Van Breugel Klaas
Published: October 2010

This study presents the results from a preliminary investigation on the corrosion behavior of low carbon steel in cement extract (CE) in the presence of very low concentration polymeric nano-aggregates (PEO113-b-PS70 micelles). The steel electrodes were investigated in Cl--containing CE as corrosion medium, compared to chloride-free CE as a reference case. The results from the electrochemical measurements indicate that the presence of micelles leads to increased corrosion resistance of the steel, but pronounced only at early stages (1h and 3h), whereas no significant influence was observed within longer immersion periods (5d). To some extent, this result was as expected, considering the used low concentration of micelles for this test. The surface analysis however, shows that the presence of the micelles in the cement extract, results in a more homogeneous and compact layer on the steel surface, compared to the steel immersed in the micelles-free solutions.
The Point Defect Model for Bi-Layer Passive Films
Authors: Macdonald Digby , Englehardt George
Published: October 2010

The Point Defect Model (PDM) has been shown to accurately describe the properties of passive films that form on metal surfaces in contact with aggressive environments under both open circuit and anodic polarization conditions. However, the commonly-employed PDM, known henceforth as PDM-II assumes that passivity arises from the properties of the barrier layer and that the outer layer, if present, contributes negligibly to the interfacial impedance. In this paper, we describe PDM-III, in which a resistive outer layer exists on the surface and contributes substantially to the impedance of the interface. The outer layer is shown to have a profound impact on the properties of the barrier layer and under certain circumstances the barrier layer is predicted to disappear. This new form of depassivation has been observed experimentally. The use of electrochemical impedance spectroscopy to characterize passive films having resistive outer layers is describe and illustrated with reference to the passive state on zirconium in simulated PWR (Pressurized Water Reactor) primary coolant.
Progress towards a Unified Model of Corrosion with Porous Oxides
Authors: Venkatraman Murali S. , Cole Ivan S. , Emmanuel Bosco
Published: October 2010

The oxide that develops on the surface of the metals like zinc is usually porous. Any further oxidation of the metal can happen only if the electrolyte percolates through the oxide and comes in contact with the metal and also if there is a provision for the cathodic reaction to happen elsewhere. The oxide layer thus changes the conditions of corrosion of a metal surface. Three different electrochemical models for atmospheric corrosion of a metal under an aerosol solution are described. The models described are part of the holistic approach to model corrosion where multiple scales of time and space occur due to the various physical phenomena. When coupled with the macroscopic holistic model of production, transport, and deposition of aerosols these models are expected to comprehensively predict the corrosion rates and state of surfaces over a wide range of conditions. Some representative results of the models are presented and important assumptions underlying the models are stated. Also conditions leading to passivation are identified by all the three models.
High Temperature Corrosion of 625 Supperalloy under Iron-Zinc-Lead Oxide/Sulfate/Chloride Salt Mixtures
Authors: Mohammadi Zahrani E. , Cuevas-Arteaga Cecilia , Verhelst D. , Alfantazi A.
Published: October 2010

The corrosion resistance and degradation mechanisms of 625 supperalloy at 800 oC under three molten salt compositions containing PbSO4, PbO, PbCl, ZnO, Fe2O3 and CdO in air atmosphere were studied. The concentrations of Fe2O3 and CdO were varied to evaluate the effect of these compounds on the corrosion reaction. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization technique were applied to evaluate the degradation mechanisms and corrosion properties of the alloy. Corrosion products and surface layer of the corroded specimens were studied by SEM/EDX and X-ray map analyses. Electrochemical evaluation confirmed that increasing the concentration of CdO in the molten phase could increase the corrosion rate of the alloy and in this condition the corrosion phenomena occurred under the control of charge transfer effect. The presence of a Cr-depleted layer on the surface of the alloy was the reason for the formation of an internally attacked area at the alloy/oxide interface.
Corrosion Protection of Cerium-Based Conversion Coatings with Subsurface Crevices
Authors: Pinc William , Maddela Surender , Fahrenholtz William G. , O'Keefe Matthew J.
Published: October 2010

The corrosion protection of electrodeposited cerium-based conversion coatings (CeCCs) on AA 2024-T3 with and without subsurface crevices was investigated. Coatings that were otherwise identical provided significant corrosion protection with or without crevices, as long as a post-treatment was employed after crevice formation. During salt spray exposure, impedance of crevice-free coatings increased from an initial value of ~50 kΩ-cm2 to ~60 kΩ-cm2 after 96 hours of exposure. In contrast, the impedance of coatings containing crevices doubled after 24 hours to ~100 kΩ-cm2. The impedance increase for crevice-containing coatings was associated with the build up of oxides / hydroxides in the crevices, which limited direct contact between the electrolyte solution and the substrate. Crevice-free coatings exhibited active corrosion protection even though no oxide build up was observed. For CeCCs with or without crevices, corrosion protection appeared to occur due to the formation of an interfacial layer between the coating and the substrate.
Directly Deposited Cerium Phosphate Coatings for the Corrosion Protection of Al 2024-T3
Authors: Heller Daimon K. , Fahrenholtz William G. , Fair Geoff E. , O'Keefe Matthew J.
Published: October 2010

Cerium phosphate coatings were directly deposited onto Al 2024-T3 substrates by precipitation from aqueous solution containing cerium citrate and phosphoric acid. These coatings were characterized and compared to post-treated, cerium-based conversion coatings (CeCCs). Directly deposited CePO4 coatings exhibited corrosion current densities of 2 - 4 µA/cm2, compared to ≈0.45 µA/cm2 for CeCCs. Analysis revealed that directly deposited CePO4 coatings did not significantly impact the electrochemical properties of bare Al 2024 T3, an indication that deposition was independent of the local galvanic activity utilized to deposit CeCCs. After salt spray exposure, cross-sectional analyses showed that directly deposited coatings acted as a static barrier to corrosion, allowing the formation of pits at crack/substrate interfaces, which were not observed in similar regions of post-treated CeCCs. Instead, an interfacial reaction layer had formed at the CeCC/substrate interface, revealing that the CeCC exhibited an active response to the salt spray environment that influenced corrosion protection.
Effect of Humidity on Cerium-based Conversion Coatings on Al 7075-T6
Authors: Joshi Simon , Fahrenholtz William G. , O'Keefe Matthew J.
Published: October 2010

Cerium-based conversion coatings and Al 7075-T6 were exposed to 85% relative humidity at 40 °C to simulate ASTM B117 corrosion testing without NaCl. As-deposited coatings with cracks >0.5 µm wide showed a significant increase in impedance from ~5 kΩ-cm2 before exposure to ~95 kΩ-cm2 after 168 hours of exposure compared to phosphate post-treated coatings (from ~60 to 90 kΩ-cm2) with cracks <0.5 µm. The impedance of bare Al 7075-T6 increased from ~10 kΩ-cm2 before exposure to ~275 kΩ-cm2 after 168 hours of exposure. The increase in impedance in all cases was due to an altered layer containing Al and O on exposed alloy surfaces. X-ray photoelectron spectroscopy indicated that exposure to humidity reduced Ce(IV) to Ce(III) on as-deposited coatings, whereas post-treated coatings did not show any change in Ce oxidation state. Despite the increase in impedance, only post-treated coatings were able to inhibit corrosion in salt spray testing.
Characterization of Transport Processes in a Praseodymium-Containing Coating
Authors: Treu Becky L. , Pinc William , Fahrenholtz William G. , O'Keefe Matthew J. , Morris Eric , Albers Richard
Published: October 2010

The electrochemical response of Pr-containing epoxy-polyamide primers on aluminum alloy 2024-T3 substrates was investigated. The effect of electrolyte pHs on corrosion behavior was studied before and after salt spray exposure. X-ray diffraction analysis confirmed that the praseodymium phase that was added to the primer converted into Pr(OH)3 in the as-deposited coating and remained present in the primer up to 3000 hours of salt spray exposure. Examination of panels prior to salt spray testing indicated that Pr was not detected in the scribes; however, following salt spray testing, Pr-rich species were found in localized clusters in scribes. Electrochemical tests were performed on test panels with machined defects using electrolyte pHs ranging from 5 to 8. The largest change in passivation range occurred at pH=8, and was two times higher than the change observed for bare Al 2024-T3. Corrosion protection of Pr-based primers is due to the ability of Pr-rich species to dissolve from coatings during exposure to corrosive environment and is influenced by pH.
Coatings for Early Corrosion Detection
Authors: Liu Guangjuan , Wheat Harovel G.
Published: October 2010

Corrosion of metal alloys can sometimes be detected based on coatings that incorporate corrosion indicators. The indicators may change color or fluorescence depending on pH or they may change fluorescence based on changes in oxidation state. The investigators have examined aluminum alloys and steels and used positive or negative indicators. The positive indicators for steel are initially non-fluorescent upon application, but glow over areas of corrosion. While microscopic and electrochemical results have demonstrated some success in early corrosion detection in aluminum alloy specimens, several challenging issues were noted for steel alloys. For example, coating degradation was observed by EIS as a function of exposure to saltwater. Moreover, in some cases, increases in fluorescence were also observed as a function of exposure. However, these incidents did not occur simultaneously and the fluorescent locations changed with time and did not grow with time. This paper will explore some of the possible reasons for this behavior.
Review of Studies on Corrosion of Electrodeposited Nanocrystalline Metals and Alloys
Authors: Nik Masdek Nik Rozlin , Alfantazi A.
Published: October 2010

Nanocrystalline materials are now gaining vast interest due to their outstanding physical, mechanical and chemical properties. Electrodeposition is an economical, reliable and viable technique in producing nanostructured materials as compared to other available methods. Recently, due to the high potential of nanocrystalline materials in anti-wear and corrosion resistance coating applications, the interest to develop better nanostructured materials as well as to improve the understanding of their corrosion behaviour has gained much attention. However, studies on the corrosion behaviour of electrodeposited nanocrystalline materials are rather limited. Hence, the corrosion performance of nanostructured materials in various electrochemical conditions will be addressed here. This review will provide a survey of existing literature on corrosion behaviour of electrodeposited nanostructured pure metals and its alloys as well as composites.
Surface Modification of Heteropolyacids (HPAs) for Proton Exchange Membrane Fuel Cells (PEMFCs)
Authors: Sutrisno Joko , Fuchs Alan
Published: October 2010

Novel composite proton exchange membranes have been prepared from surface modification of heteropolyacids, namely: silicotungstic acid (SiWA), and sulfonated poly(ether ether ketone) (SPEEK) as a polymer matrix. Atom transfer radical polymerization (ATRP) has been used for surface polymerization of sodium 4-vinyl benzene sulfonate (S4VBS) on SiWA. PEEK has been sulfonated using chlorosulfonic acid. The major outcome of this work was surface coated SiWA-poly(S4VBS) which resulted in homogenous composite membranes as compared with non-surface coated SiWA. The thermal properties of surface polymerized S4VBS have been characterized using differential scanning calorimetry (DSC). The SiWA particles and cross section of the composite membrane have been imaged using DSC. Composite membrane conductivity has been characterized using electrochemical impedance spectroscopy. This route was expected to provide a membrane with high conductivity because of the presence of sulfonic acid groups on the grafted polymer backbone, and to avoid "washing out" of HPA in the fuel cell.
Nanocomposite Ternary Acid-Base Blend Based Polymer Electrolyte Membranes for Fuel Cells
Authors: Stewart Kerrilee S. , Missan Harinder Pal Singh
Published: October 2010

The recognition that the world now needs a renewable energy source is fuelling scientific research in many areas of renewable energy. One of the most promising of these sources of renewable energy is the fuel cell. One of the major areas of development in polymer electrolyte membrane fuel cells (PEMFC's) lies in one of the most fundamental parts, the membrane itself. As such Poly(1-vinylimidazole) (PVIm) polymer was synthesized in order to make polymer electrolyte membranes and to use the well known ability of imidazole compounds to conduct via grotthus mechanism. A ternary composition has been developed utilizing PVdF-HFP, triflic acid, and PVIm and high conductivities has been observed. Nanocomposite blend and ternary membranes has also been synthesized in situ by the addition of nanotubular titania. Morphological as well as electrical, thermal and mechanical properties of these membranes have been studied. The membrane exhibited good properties making them suitable for application in fuel cells.
Nafion/Sulfonated Silica Composite Membranes for PEM Fuel Cells
Authors: De Almeida Nicole E. , Easton E. Bradley
Published: October 2010

Nafion/sulfonated silica (NSS) composite membranes were prepared from 2-(4-chlorosulfonylphenyl)trimethoxysilane in a one step process. Proton conductivity measurements were made at various temperature and relative humidity conditions. The NSS composite membranes exhibited higher proton conductivities than unmodified Nafion under all conditions, with highest conductivity and fuel cell performance being achieved with NSS membranes with lower sulfonated silica loadings. This was explained in terms of enhanced proton conductivity from the presence of SS and the large free pore within the pores of Nafion to accommodate the required water content.
Proton Conductivity within Fuel Cell Electrodes Containing a Sulfonated Carbon Support
Authors: Pedersen Andrew W. , Pauric Allen D. , Eastcott Jennie I. , Easton E. Bradley
Published: October 2010

Sulfonic acid functionalities were grafted onto the surface of Pt/Vulcan XC72 electrocatalysts via the thermal decomposition of ammonium sulfate method. Electrochemical impedance spectroscopy was used to investigate its impact on catalyst utilization and proton conductivity as a function of depth within the catalyst layer. Catalysts prepared from sulfonated carbon supports displayed higher electrochemically active surface areas at lower Nafion contents than those prepared from untreated carbons. This enhanced conductivity and active area was explained in terms of an increased concentration and more effective deployment of sulfonic acid groups.
Effect of Spray Parameters on Electrode Surface and Performance
Authors: Brooker Robert P. , Rodgers Marianne P. , Bonville Leonard J. , Kunz H. Russell , Slattery Darlene K. , Fenton James M.
Published: October 2010

PEM fuel cell electrode performance is shown to be influenced by catalyst ink application methods in a spray-type setup. As the spray parameters are varied, diffusion resistance changes significantly. SEM images reveal particles of ionomer and catalyst are formed with different sizes. Larger particles are formed when the ink has a greater amount of solvent evaporation between the gun and the membrane. These particles appear to be connected to the diffusion resistance of the electrode, with a greater number of particles leading to a lower diffusion resistance.
Investigation of the Presence of a Saturating Media during Hot Pressing of Proton Exchange Membranes to Improve Performance
Authors: Rodgers Marianne P. , Pearman Benjamin P. , Mohajeri Nahid , Bonville Leonard J. , Slattery Darlene K. , Kunz H. Russell , Fenton James M.
Published: October 2010

To circumvent conductivity and therefore performance losses due to hot pressing, proton exchange membranes (PEMs) were immersed in high-boiling point solvents prior to hot pressing. It was hypothesized that the presence of the high boiling point solvents during hot pressing would prevent collapse of the hydrophilic domains because, unlike water, they would remain in the membranes even at temperatures above 100 oC. The presence of high-boiling point solvents during hot pressing improved the conductivity of the membranes 20-30%. The water contents of the membranes also increased and the dry densities of the membranes decreased when the high boiling point solvents were used during hot pressing. It is hypothesized that this increase in water content and conductivity and decrease in membrane density is due to the high boiling point solvents preventing the collapse of the hydrophilic pore walls during hot pressing, creating void spaces and therefore allowing more room for water.
The Analysis of Performance Loss with Low Platinum Loaded Cathode Catalyst Layers
Authors: Ono Yoshitaka , Mashio Tetsuya , Takaichi Satoshi , Ohma Atsushi , Kanesaka Hiroyuki , Shinohara Kazuhiko
Published: October 2010

An analysis of performance loss with low platinum loaded cathode catalyst layers (CCLs) was conducted. A modified 1-D calculation model in the CCL was developed in this study, where newly developed oxygen transport resistance in the direction from pores in the CCL to platinum surface (RO2,CCL-micro) and the effect of platinum oxide coverage on RO2,CCL-micro were taken into account. The analysis results indicated that the oxygen transport loss caused by RO2,CCL-micro became a dominant factor of the performance loss with the low platinum loaded CCLs.
Atomic Force Microscopy Investigation of Polymer Fuel Cell Gas Diffusion Layers before and after Operation
Authors: Hiesgen Renate , Wehl Ines , Friedrich K. Andreas , Schulze Mathias , Haug Andrea , Bauder Alexander , Carreras Alejo , Yuan Xiao-Zi , Wang Haijang
Published: October 2010

The ageing of microporous layers (MPL) of fuel cell gas diffusion layers has been analyzed using a special atomic force microscopy technique. The mean local adhesion force on the surface as well as the energy dissipation on the same area has been used as a measure for changes of surface properties corresponding to ageing of the MPL. The samples have been studied before and after fuel cell operation. In all cases, the changes due to operation are stronger on the cathode compared to the anode. The results from measurements under comparably dry and wet conditions are consistent with an increased loss of polytetrafluoroethylene (PTFE) at the cathode which leads to a hydrophobicity loss.