bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Durability of Direct Methanol Fuel Cells
Authors: Zelenay Piotr
Published: November 2006

This paper addresses various routes for performance losses in single direct methanol fuel cells and DMFC stacks. The study identifies recoverable (reversible) and unrecoverable (irreversible) sources of DMFC performance degradation during single-cell operation for up to 3000 hours and short stack operation for up to 850 hours. Single-cell test data focus on two otherwise identical MEAs, of which one was prepared by a standard low-temperature approach (Standard MEA) whereas the other was made by high-temperature method to improve anode durability (Novel MEA). Thanks to the approach taken in the preparation of the Novel MEA, the unrecoverable DMFC performance loss was reduced to 10 mV over 3000 hours, relative to a 60-mV loss incurred by the Standard MEA over the same period of time. Both single-cell MEAs exhibited much lower performance loss than individual cells in a six-cell stack, which lost 40-80 mV per cell during only 850 hours of stack testing.
Modeling Nanocrystalline Grain Growth during the Pulsed Electrodeposition of Gold-Copper
Authors: Jankowski Alan
Published: November 2006

The process parameters of current density, pulse duration, and cell potential affect both the structure and composition of electrodeposits. The mechanism for nucleation and growth as determined from current transients yield relationships for nucleus density and nucleation rate. To develop an understanding of the role of the process parameters on grain size - as a design structural parameter to control strength for example, a formulation is presented to model the affects of the deposition energy on grain size and morphology. An activation energy for the deposition process is modeled that reveals different growth mechanisms, wherein nucleation and diffusion effects are each dominant as dependent upon pulse duration. A diffusion coefficient common for each of the pulsed growth modes demarcates an observed transition in growth from smooth to rough surfaces.
Diameter Dependent Optical Constants of Gold Meso-particles Electrodeposited on Aluminum Films Containing Copper
Authors: Brevnov Dmitri A. , Bungay Corey
Published: November 2006

Electrodeposition of Au meso-particles on anodized and chemically etched Al-Cu films deposited on Si wafers proceeds by instantaneous nucleation and with no diffusion limitations. Both of these phenomena favor the formation of relatively mono-dispersed Au particles. The mean particle diameter varies a function of electrodeposition time in the range of 40-80 nm. Optical constants of Au meso-particles are determined by spectroscopic ellipsometry. A two layer optical model is suggested to determine both extinction coefficients and refractive indexes of Au meso-particles as a function of the mean particle diameter. The absorption peak, associated with surface plasmons, is modeled with two Lorentz oscillators. The maximum of extinction coefficient shifts from 610 to 675 nm as the mean particle diameter increases from 42 to 74 nm.
A Novel Approach to Deposit Compositionally Modulated Zn-Ni Multilayer as a Replacement for Cadmium Coating
Authors: Popov Branko N. , Kumaraguru Swaminatha , Ganesan Prabhu
Published: November 2006

Compositionally Modulated multilayer Zn-Ni deposits were electrodeposited from acidic electrolytes (pH=4.7) by using a potentiostatic sequence. The Zn and Ni composition in the alloy is tailored as a function of distance from the steel substrate. The kinetic parameters controlling the processes at the deposit electrolyte interface were estimated by using electrochemical corrosion techniques in 5% NaCl solution. Open Circuit Potential (OCP), Tafel Polarization (LP) and Electrochemical Impedance Spectroscopy (EIS) studies were used to characterize the deposits.
Synthesis of Birnessite-Type Layered Manganese Oxide and their Composites for Supercapacitors
Authors: Favier Fred , Zhou Yingke , Fournier Claire , Dorval-Douville G. , Shanley Samantha , Jones Deborah , Mula Bernard , Roziere Jacques , Brousse Thierry , Belanger Daniel
Published: November 2006

Birnessite-type layered manganese oxides were prepared using various approaches for the design and fabrication of supercapacitor electrodes: (i) Oxidized carbon-MnO2 nanocomposites were obtained from birnessite precipitated in the presence of the oxidized forms of four different carbon types: graphite, acetylene black, high surface area active carbon and fullerene. (ii) films were anodically deposited at the surface of inexpensive stainless steel foils. MnSO4 plating solutions were electrolyzed at various potentials and for various durations. Preparation conditions are shown to affect the oxide structure, morphology (surface area), and chemical composition (content of Mn3+, Mn4+). Consequently, they also greatly affect the electrochemical capacitance performances of the prepared electrode materials.
The Effect on In-Cell Measurements from Water and Methanol Transport in Direct Methanol Proton Exchange Membrane Fuel Cells
Authors: Lefebvre Mark , Olmeijer David
Published: November 2006

This submission relates to direct methanol fuel cells (DMFCs) and to a method for the determination, simultaneously, of in-cell methanol crossover and water diffusion coefficients. Preliminary experimental results are presented describing an extension of the electrochemical methanol crossover technique in a fuel cell. A purge gas flow rate dependence is shown to arise in the methanol crossover current when that cathode purge gas is not humidified and it is suggested that this flow rate dependence drives water flux across the cell. At limiting flow, conditions prevail that allow the determination of trans-membrane water diffusion coefficient. This offers the possibility of deriving this important water transport parameter from a simple and near ubiquitously used electrochemical method. Beyond this, our experiments have suggested that the use of zero-flow purge for methanol permeation current measurement gives rapid and reliable results.
Hydrogen Production from Mill-Scale via Metal-Steam Reforming
Authors: Kesavan Sathees Kumar , Azad Abdul-Majeed
Published: November 2006

Mill-scale wastes from steel industry have been successfully reduced to pure metallic iron via hydrogen and carbothermic reduction. Use of high temperature and H2 gas has been eliminated by a novel solution-based room temperature reduction technique whereby nanoscale iron powder is produced. This new scheme totally obviates the issue of sintering of the iron/iron oxide and hence the deactivation during the cyclic operation of metal-steam reforming. Some of the preliminary results of this investigation are discussed.
Hybrid Supercapacitors with Ionic Liquid Electrolytes
Authors: Mastragostino Marina , Arbizzani Catia , Balducci Andrea , Passerini Stefano , Simon Patrice , Soavi Francesca
Published: November 2006

We developed a hybrid supercapacitor with N-butyl-N- methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) ionic liquid electrolyte, activated carbon (AC) as the negative electrode and poly(3-methylthiophene) (pMeT) as the positive which provides at 60{degree sign}C maximum cell voltages higher than 3.4 V as well as long cycling stability over 15,000 cycles. In the present paper we present and discuss the results of our study as well as the strategies for materials and cell design optimization in view of the development of 2kF- 3.9 V AC/PYR14TFSI/pMeT supercapacitors operating at 60{degree sign}C.
Electrochemical Properties Carbon Derived from Sol-Gel Catechol-Formaldehyde Gels
Authors: Nagireddy Ravinder Reddy , Reddy Ramana
Published: November 2006

Catechol-formaldehyde (CF) polymer was prepared from catechol and formaldehyde at pH conditions of 3, 6 and 7.5 employing Na2CO3 catalyst. Thermogravimetric studies were done on prepared CF polymers to know the carbon yield. Carbons were prepared from theses polymers by pyrolyzing 750 åC temperatures. Thus prepared carbons were characterized using XRD, SEM and EDAX. Their surface areas were measured using BET method. Cyclic voltammetric studies (CV) were done on these carbons to evaluate them as electrode material for electrochemical double layer capacitors. CV was performed using by a three electrode method, and H2SO4 solution was used as electrolyte. Carbon obtained at pyrolyzing CF polymer that was prepared at 750 åC at pH 6 showed highest capacitance of 109 F/g.
Electronic Properties and Performance upon Lithium Intercalation of MoO3 Thin Films Grown by PLD
Authors: Julien C. M. , Ramana C. , Hussain Mohamad
Published: November 2006

Over a wide range of growth temperature, 25-500 {degree sign}C, structural and optical characteristics of a series of MoO3 films prepared by PLD technique are studied. It is found that the growth temperature strongly influences the surface morphology, local atomic structure, and optical properties of PLD MoO3 thin films. The compositional stability was found to be well maintained up to a temperature on the order of 400 {degree sign}C, at which point the formation of compositional defects introduces structural disorder and changes in the optical characteristics. The electrochemical features of the insertion of Li ion into the MoO3 host lattice are also considered for various deposition temperature. Performance of Li//MoO3 thin film batteries are evaluated.
Studies on the Electrochromic Behavior of Lithium and Proton Based Solid State Devices
Authors: Somasundaram Gunasekaran , Subrahmanyam A. , Suresh Kumar C. , Muthu Karuppasamy
Published: November 2006

In the present investigation, two types of DC magnetron sputtered tungsten oxide (WO3) solid state electrochromic devices: one with lithium and the other using protons as intercalating ions have been prepared and analyzed. The lithium based device consisting of lithium aluminum fluoride (electrolyte ~ 500nm) and vanadium oxide (storage layer ~100 nm) has color/bleach cycle of about 10s and the transmittance variation of 40%. The proton device consisting of: Ta2O5 (electrolyte ~300nm) and NiOx (storage layer ~100nm) has a coloration time of few milliseconds and the transmittance variation is about 60%; the top electrode for these devices is semitransparent gold of thickness 10nm. The stability of the proton device has been found to be quite satisfactory for thermal cycling and X-ray dosage of 11.7R. The change in contact potential difference of WO3 during coloration has been measured using Kelvin probe technique for the first time to understand the electrochromic behavior.
Numerical Calculation for Fuel Depletion State of SOFCs
Authors: Yakabe Hisataka , Fujita Kenjiro , Sakurai Teruhiro
Published: November 2006

Fuel depletion states under cell operations of SOFCs were simulated. Three dimensional calculations for the cell operations were carried out using a commercial computational fluid dynamics code. Using a simple geometry model of an anode-supported cell, effects of a gas diffusion in a porous anode, a current density, and a fuel utilization on the fuel depletion state were studied. A local fuel depletion resulting in a large concentration overpotential and thus a steep drop of the electromotive force was figured out and discussed. The study made clear that the planar SOFC is robust against the fuel depletion state.
Computational Modeling of the Stability of Crevice Corrosion of Wetted SS316L
Authors: Kelly Robert , Cui Fushuang , Presuel-Moreno Francisco
Published: November 2006

The stability of localized corrosion sites on SS 316L exposed to atmospheric conditions was studied computationally by considering the wetted cathode and the crevice anode separately and linking them via a constant potential boundary condition at the mouth of the crevice. The limitations on the ability of the cathode that are inherent due to the restricted geometry were assessed in terms of the dependence on physical and electrochemical parameters (temperature, electrolyte layer thickness, solution conductivity, and the size of the cathode). An analysis of variance showed that the solution conductivity and the length of the cathode were the most important parameters in determining the total cathodic current capacity of the external surface. A semi-analytical equation was derived for the total current from a restricted geometry held at a constant potential at one end.
Modeling the Cathodic Region in Crevice Corrosion under a Thin Electrolyte Film Including Particulates
Authors: Agarwal Arun S. , Landau Uziel , Shan Xi , Payer Joe
Published: November 2006

Crevice corrosion may be limited by the capacity of the external cathodic region to support anodic dissolution currents within the crevice. The analysis here focuses on behavior of metal surfaces covered by a thin (~microns) layer of the electrolyte film including particulates. The particulates can affect the cathode current capacity (Itotal) by increasing the solution resistance (volume effect) and by decreasing the electrode area (surface effect). This work simulates and characterizes the effect of a uniform particulate monolayer on the cathode current capacity for steady state conditions in the presence of a thin electrolyte film. Particulate configurations with varying particle size, shape, arrangement, volume fraction, and electrode area coverage were numerically modeled as a function of the properties of the system. It is observed that the effects of particles can be fully accounted for in terms of two corrections: the volume blockage effect on the electrolyte resistivity can be correlated using Bruggeman's equation, and the electrode coverage effect can be modeled in terms of a simple area correction to the kinetics expression. For the range of parameters analyzed, applying these two correction factors, cathodes covered with thin electrolyte films that contain particles can be represented in terms of equivalent homogenous electrolytes that can then be analyzed using simpler approaches. Continuing work will examine the effects of greater volume fractions of particles and multiple particle layers.
Electroless and Electrodeposition of Tin on Gold Surfaces Sputtered onto Aluminum Nitride Substrates: A Comparison
Authors: Djokic Stojan
Published: November 2006

The experimental results obtained on electroless and electrodeposition of tin on gold surfaces sputtered onto aluminum nitride substrates are comparatively discussed. Electroless deposition of tin on gold surfaces sputtered onto AlN substrates was carried out from a solution containing NaOH. While it resulted in tin coatings with a desirable thickness, uniform appearance and a desirable surface morphology, problems related to the dissolution of aluminum nitride in alkaline solutions were observed during the course of work. The solderability of the electroless deposited tin onto gold surfaces was excellent. To overcome problems related to the dissolution of aluminum nitride in strong alkaline solutions, the future work was concentrated to the electrodeposition of tin from various solutions. The successful results were obtained with tin borofluoride solutions. The conditions leading to a production of a uniform tin coating with excellent solderabilty were determined.
Hydrotalcite Mineral Stabilization of Titanium Dioxide Photocatalyzed Degradation of Unplasticized Poly(vinylchloride)
Authors: Worsley David A. , Martin Glyn , Robinson Andrew
Published: November 2006

Hydrotalcite additions (up to 10 PHR) can stabilize un- plasticized-poly-vinyl-chloride against TiO2 photo-catalyzed degradation. Without stabilization, hydrogen chloride, produced through de-hydrochlorination, catalyses the TiO2 sensitized degradation after a set period of reaction leading to an increase in rate from 13 mu-mol m-2 min-1 to 32 mu-mol m- 2 min-1. Hydrotalcite removes chloride by anion exchange releasing carbonate ions in the PVC removing this autocatalytic pathway. Hydrotalcite performs very well in comparison to commercial Barium/Zinc salt stabilizers.
Voltammetric Study of Titanium Chlorides in the Ionic Liquid 1-Ethyl-3-methylimidazolium Tetrafluoroborate
Authors: Cheek Graham T. , Canby Dana , O'Grady William
Published: November 2006

The electrochemical characteristics of TiCl3 and TiCl4 hve been studied in the room-temperature ionic liquid 1-ethyl-3- methylimidazolium tetrafluoroborate. The Ti3+/Ti4+ couple is observed at +0.30V vs Ag/AgCl, shifting to 0.00V upon addition of chloride ion. Reduction of the Ti3+ species is not well- defined; however, reduction to the +2 state, and possibly to titanium metal, is observed from -1 V to -2 V. Comparison studies of Ti(NO3)4 have shown that the electrochemical processes are very poorly-defined, implying that the presence of some chloride is necessary for well-characterized voltammetric processes.
A New Graph Language for Representing the Macroscopic Formalism in Physicochemistry and Physics
Authors: Vieil Eric
Published: November 2006

A new way for representing algebraic equations used in macroscopic physics and physico-chemistry is proposed. Based on oriented graph built in accordance with the properties of energy in a system, it uses state variables as nodes and constitutive system properties as connections, together with space-time properties. The ordering introduced by topology reveals common structures between mechanics, electrodynamics, physico-chemistry and all domains in which energy is quantified. Among numerous interesting consequences, two new concepts, energetic path and energetic mode, shed interesting physical meaning on transfer processes: The energetic path conveys the nature, conserved and/or dissipated, of transferred energy in a process. The energetic mode depicts the proportion of conserved vs. dissipated energy. Semi- infinite transient diffusion appears as an equilibrated process conserving fifty percent and dissipating the other part of its energy, while fractal or anomalous diffusion, identified with a fractional exponent, can be seen as conserving the energy in the proportion given by this exponent.
Acoustoelectric Effect in Hydrogen Surface Acoustic Wave Sensors with Phthalocyanine-Palladium Sensing Bi-layers
Authors: Jakubik Wieslaw , Urbanczyk Marian , Cular Stefan , Bhethanabotla Venkat
Published: November 2006

Bi-layer structures with two thicknesses of metal-free phthalocyanine (~80 and ~120 nm) but the same thickness of palladium (~20 nm), have been studied for hydrogen and carbon monoxide gas-sensing applications at ~30 {degree sign}C and ~50 {degree sign}C temperatures. The structures were fabricated in two different vacuum deposition processes (first the H2Pc film and followed by the Pd) onto a LiNbO3 Y-cut Z-propagating substrate for a SAW method. Additionally, using the same deposition techniques, the bilayer structure was deposited onto a glass substrate with a planar microelectrode array for simultaneously monitoring of the planar resistance of the structure. A good correlation has been observed between these two methods; frequency changes for SAW method correlate with decreases of the bilayer structure resistance. These measurements can give information about the acousto-electric interactions between SAW and charge carriers in the bi-layer structure.
Measurements of Particles in Liquid Using Shear-Horizontal Surface Acoustic Wave Sensor
Authors: Kondoh Jun , Oyama Taichi , Shiokawa Showko
Published: November 2006

In this paper, we present interaction between a shear horizontal surface acoustic wave (SH-SAW) and particles in liquid. As the SH-SAW sensor can detect mechanical and electrical perturbations, a three-channel SH-SAW sensor is used in the experiments. The three-channel SH-SAW sensor simultaneously detects the mechanical and electrical perturbations. The SH-SAW sensor for the electrical perturbation detection is influenced by the particles in liquid. Therefore, it has high potential for detecting particles in liquid. On the other hand, the SH-SAW sensor for mechanical perturbation detection does not detect the particles in liquid. To detect the particles based on the mechanical perturbation, influence of viscous penetration is discussed.
A 3-D Finite Element Model of Surface Acoustic Wave Sensor Response
Authors: Sankaranarayanan Subramanian , R. Bhethanabotla Venkat , Joseph Babu
Published: November 2006

In this work, 3-D finite element models (FEM) based on a ~100 MHz YZ-LiNbO3 piezoelectric substrate coated with a thin Pd sensing layer was simulated to gain insights into the H2 sensor response. Literature suggests that structural and morphological changes due to gas absorption occurring at the molecular scale affect the material properties of the sensing layer which in turn affects the wave propagation at macro- scale. The changes in the material properties of the sensing layer on gas exposure were used to simulate the behavior of a SAW sensor. Frequency responses of the displacement and voltage waveforms generated at the output IDT nodes were used to quantify the effects of gas interaction. Additionally, 2-D FEM simulations of modified sensing layers involving micron- sized gratings have also been carried out and compared with results obtained using thin films. This study demonstrates the effectiveness of finite element models in understanding gas sensor response.
Pit Initiation on Partially Amorphous Alloys with Solute-Lean Nanocrystals
Authors: Scully J. R. , Lucente Ashley , Shiflet Gary
Published: November 2006

The good global pitting resistance of amorphous Al90Fe5Gd5 in 0.6 M NaCl solution is maintained upon partial devitrification to form solute lean crystals in an amorphous matrix. The focus of this paper is to distinguish whether this can be explained by decreased pit initiation or hindered pit growth and stabilization. The metastable pitting properties of Al90Fe5Gd5 were investigated at the nanometer (nm) and micrometer (μm) scales. The fully amorphous alloy, versions of the alloy containing a high volume fraction of isolated 5-15 nm diameter Al-rich crystals embedded within the amorphous matrix, and versions containing ~500 nm transitional phases in a remaining amorphous-nanocrystalline matrix were compared to a fully crystallized condition and pure polycrystalline Al. Nanocrystals and transitional phases embedded in an amorphous Al-Fe-Gd matrix do not promote pit initiation at the nm-scale in NaCl solution under the same electrochemical conditions where the bulk equivalent of Al-rich f.c.c. nanocrystals do initiate sub-μm sized pits. The number and size of sub-micrometer pit initiation events is similar for the fully amorphous and amorphous-nanocrystalline alloys under the same conditions.
Oxidation and Vacuum Degassing Behavior of Rapidly Solidified Al Alloy Powders
Authors: Yamasaki Michiaki , Iwamoto Kotaro , Kawamura Yoshihito
Published: November 2006

In the rapidly solidified powder metallurgy processing of aluminum alloys, vacuum degassing is one of the important process steps. The aim of the degassing is removing the adsorbed gaseous species from powder surface, and transforming the ductile hydrated alumina and aluminum hydroxide into brittle g-alumina in order to realize the formation of metal- to-metal bonding between powder particles during consolidation. Temperature-programmed desorption measurement on powders exposed to humid air, dry air and pure argon gas was performed to determine the gas species evolved during degassing for powders of Al-Ti-Fe-Cr and Al-Zn-Mg-Cu-Ag alloys. The surface composition and processing atmosphere significantly influenced degassing behavior of the powders. The su rface oxide of Al- Zn-Mg-Cu-Ag powder was more prone to hydration than that of Al- Ti-Fe-Cr powder. Accordingly, the formation of fresh Al2O3 on the Al-Zn-Mg-Cu-Ag powder occurred at low temperature during vacuum degassing by the reaction, Al + 3H2O = Al2O3 + 3H2.
Polarization Behavior of Powder Consolidated Zr Base Amorphous Alloy with Culturing Fibroblasts
Authors: Hiromoto Sachiko , Hanawa T. , Maruyama Norio , Yamamoto Akiko
Published: November 2006

Polarisation test and impedance measurement were performed on powder consolidated Zr-Al-Ni-Cu amorphous alloy with and without fibroblast L929 cells incubated in medium for 7 d. L929 cells show well extended morphology, indicating that the surface of the alloy dose not show toxicity. L929 does not influence the values of cathodic and passive current densities and pitting potential of the alloy. Also, impedance behaviour is not changed with L929 cells. Those results indicate that the corrosion resistance of the powder consolidated Zr base amorphous alloy is not influenced with L929 cells. However, the pitting potential varies in the wide potential range regardless of the existence of L929 cells. Significant uniform corrosion sometimes occurs under impedance measurement at open circuit potential. It is supposed that the alloy becomes sensitive to electrochemical stimulation during the immersion in solution probably due to the defects such as grain boundary between original amorphous alloy powders.
Purification of Tannery Effluent by Electrolytic Corrosion of Aluminum
Authors: Mathieson Grant A. , Langdon Alan , Jamieson Graham
Published: November 2006

Tannery Effluent is noxious because tanning process chemicals are preservatives, including chromium, and the pH is high. Electrolytic processing is feasible because the high salt content gives a high electrical conductivity. While research on the subject dates back to early in the 20th Century, commercialization has not occurred, perhaps due to excessive power consumption. Other researchers have produced promising results with rendering plant effluent (Tetrault 2003). During 2005 a specialised proprietary prototype with a novel anode design was trialed extensively at a Tannery site in New Zealand and produced good results during continuous inline operation despite wide variation in the inflow. Greater than 90% removal of chromium from solution with similar reductions in turbidity were achieved at lower operating cost, residual aluminum and total aluminum addition than by dosing with usual commercial aluminum based flocculants. Results from the field trials are shown and discussed.
Interfacial Structure and Composition as Controlling Factors in Void Formation at the Passive Oxide Aluminum Interface
Authors: Zavadil Kevin R. , Kotula Paul , Ohlhausen James
Published: November 2006

Galvanostatic polarization of aluminum thin films capped with an anhydrous oxide can be used to control a resulting interfacial void population formed in an aqueous chloride electrolyte. The potential-time profiles generated by polarization are consistent with a high initial barrier to ion transport through the oxide, followed by defect introduction and accentuated transport. Void nucleation and growth occur during these latter stages. Void nucleation preferentially occurs in regions of high terrace step densities indicating that oxide-metal interfacial structure plays a critical role in vacancy trapping and coalescence. The growth and hydration induced morphological changes of the oxide are quite different for planar facets and facet edges plus boundaries suggesting that local variation in the oxide my also play a role in dictating void nucleation sites.
Electrochemical Behavior of Titanium in NaOH Solutions
Authors: Moon Sungmo , Jeong Chanyoung , Byon Eungsun , Jeong Yongsoo
Published: November 2006

The electrochemical behavior of commercially pure titanium was investigated as a function of NaOH concentration by open- circuit potential (OCP) transients, cyclic voltammograms and galvanostatic method. The OCP value was observed to decrease with increasing NaOH concentration, and the magnitude of the anodic current peaks in cyclic voltammograms becomes higher with increasing NaOH concentration. These results indicate easier anodic dissolution of Ti in more concentrated alkaline solutions in active potential region. The cyclic voltammograms and galvanostatic potential transient curves of Ti showed that protective anodic oxide films are formed on Ti in the passive potential region in all the concentrations of NaOH up to 10 M. The surface film formed anodically on Ti becomes less protective with increasing NaOH concentration up to 3M but it becomes more protective with increasing NaOH concentration above 3M NaOH.
Initial Stage of Localized Corrosion on Titanum in Phosphate Buffer Solutions by Photon Rupture
Authors: Sakairi Masatoshi , Miyata Hiroomi , Takahashi Hideaki
Published: November 2006

A photon rupture method, by which oxide film can be removed by focused, pulsed Nd-YAG laser beam irradiation, applied to investigate localized repair of passive oxide films of titanium. The specimens were irradiated with a focused pulse of a pulsed Nd - YAG laser beam at a constant potential in 8.1 mol/m3 Na2HPO4/ 5 mol/m3 KH2PO4 solutions with 140 mol/m3 NaCl + 50 mol/m3 KCl (PBS) or with different chloride concentrations, and the current transients were monitored. The current increases with increasing applied potential and chloride concentration. The oxide film, however, repairs in all experimental conditions. The oxide film formation kinetics did not follow the inverse logarithmic law according to Cabrera- Mott theory.
Atmospheric Corrosion of Electroplated Cu Thin Film in Moist Oxygen Environment
Authors: Fujimoto Shinji , Umemura Hiroto , Shibata Toshio
Published: November 2006

Atmospheric corrosion of electrodeposited Cu thin film in water vapour with oxygen was studied using a quartz crystal microbalance. The adsorption of water with N2 carrier gas without oxygen was reversible and roughly proportional to the relative humidity. The corrosion weight gain exhibited an initial linear rate law region followed by a parabolic rate law one. The rate for both regions was influenced by both relative humidity and O2 partial pressure. The electrochemical oxidation process of Cu might occur under an adsorbed water layer. It is considered that the water adsorbed as clusters and corrosion progressed under the water cluster, the thickness and surface coverage of which varied with relative humidity. The rough estimation revealed that the kinetic constants for both first linear rate and parabolic rate laws is proportional to the ratio of surface coverage by water cluster. However, the rate constant is independent of R.H., if normalized by the area of water clusters.
Parametric Aqueous Electrodeposition Studies of Co-Sm Alloys
Authors: Wei J. C. , Schwartz Morton , Nobe K.
Published: November 2006

Electrodeposition of SmCo alloys from an aqueous solutions has been studied at various current densities, temperatures and bath compositions. Magnetic properties, such as both parallel and perpendicular coercivities, and magnetic saturation, have been measured. Higher bath temperatures lead to metallic deposits at higher current densities resulting in larger deposit Sm content. 33 at% Sm have been obtained at 500 mA/cm2 from bath temperatures of 60oC. The absence of the conducting salt (NH4 sulfamate) leads to higher deposit Sm content. XRD of these deposits shows the presence of Sm2Co17 (200) and SmCo5 (201) phases. Current efficiencies were below 20%. Magnetic saturation of SmCo electrodeposits were close to those obtained by sputtering. Heat treatment of the deposits should increase the perpendicular coercivities to the 2-10 kOe range.
Developing Concepts of Passivity and Passivity Breakdown to Improve Alloy Performance
Authors: Shifler David A.
Published: November 2006

Understanding the nature of the passive oxide film and the mechanisms and processes that influence the breakdown of passivity of metallic materials is necessary to formulate strategies for effective corrosion control. The interactions of surfaces, interfaces, grain boundaries, inclusions, intermetallics and other second phase particles, coating integrity, structural defects, enrichment-segregation phenomena, and transport properties are also essential towards understanding passivation and corrosion degradation mechanisms. Corrosion is known to initiate at sulfide inclusions in many alloys when exposed in aqueous solutions and in aprotic, nonaqueous solvents. Sulfides may lower the effective solvent oxidation potential at the alloy surface and decrease the anodic potential at which breakdown initially occurs at these surface sites in pure solvents. Sulfides also may influence the kinetics of repassivation above the oxidation potential of water and aprotic solvents when passivation is provided by several mechanisms. Sulfides also affect the performance of high-temperature superalloys.
Effects of Manganese on the Passivity of Fe-18Cr-xMn (x = 0, 6, 12)
Authors: Kwon Hyuksang , Park Kyungjin
Published: November 2006

Effects of Mn on the passivity of Fe-18Cr-xMn(x=0, 6, 12) were examined by various electrochemical tests including potentiodynamic test, micro-droplet cell test and photoelectrochemical test. With an increase in Mn content of Fe-18Cr-xMn(x=0, 6, 12) alloys, passivity of the alloys was significantly degraded in an acidified chloride solution. It was demonstrated through the micro-droplet cell tests conducted in 0.1 M NaCl solution that Mn decreased considerably the resistance to pitting corrosion of Fe-18Cr alloys even if any nonmetallic inclusions (NMI) was not included in the observed region. Passive film formed on Fe-18Cr-6Mn alloy in pH 8. 5 buffer solution is found to be composed of Cr-substituted gamma-Fe2O3 containing nano-sized Mn-oxide particles. The significant degradation in the resistance to localized corrosion of Fe-18Cr alloy, even if any NMI is absent in the alloy, appears to be associated with the nano-sized Mn-oxide particles present in the passive film.
Copper Surface Oxidation Induced by a Local Alkalization
Authors: Vasiljevic Natasa , Viyannalage L.T. , Dimitrov Nikolay , Missert Nancy A. , Copeland Robert
Published: November 2006

In this work we present the first and comprehensive electrochemical in-situ Scanning Tunneling Microscopy (STM) study of locally induced oxidation of the Cu(100) surface in naturally aerated 0.1 M NaClO4 solutions acidified to pH <= 4. The oxygen reduction reaction (ORR) induces a near electrode alkalization by a steady OH- generation, thus setting a decaying pH gradient from the surface toward the bulk of the solution. The pH gradient profile and the concomitant surface processes are dependent upon the bulk solution pH, polarization potential and polarization time. The local alkalization in the presence of dissolved oxygen in the solution influences the surface properties and morphology. This is manifested by very distinctive electrochemical behavior and by in-situ STM in solutions with different bulk pH values.
Growth and Properties of Self-Organized TiO2 Nanotube Layers
Authors: Schmuki P. , Tsuchiya Hiroaki , Macak Jan , Taveira Luciano , Ghicov Andrei , Balaur Eugeniu , Bauer Sebastian
Published: November 2006

The present paper summarizes recent progress on the formation of TiO2 nanotubes and briefly reports unique and enhanced properties of TiO2 related to the morphology. The morphology and thickness of TiO2 nanotube layers have been developed by tailoring electrochemical conditions, that is, tuning the tube growth rate and the dissolution rate. By suppressing pH variations (due to current fluctuations) lead to thicker TiO2 nanotubes with extremely smooth and homogeneous walls. Clearly the photoelectrochemical responses and contact angles on the nanotube layers are strongly altered by the presence of nanotubes compared to flat TiO2 surfaces.
Field Crystallization of Anodic Niobia on Nb-O Substrates
Authors: Habazaki H. , Ogasawara Takeru , Konno Hidetaka , Shimizu Ken-Ichi , Asami Katsuhiko , Nagata Shinji , Takayama Koichi , Skeldon Peter , Thompson George
Published: November 2006

Solid-solution Nb-O films, containing up to 50 at% oxygen, prepared by magnetron sputtering were used to investigate the influence of the oxygen on field crystallization during anodizing at 100 V in 0.1 mol dm-3 ammonium pentaborate electrolyte at 333 K. The findings reveal that field crystallization is hindered dramatically by addition of 20 at% oxygen to the substrate, while no crystallization occurs for an Nb-50 at% O substrate. Prior thermal treatment accelerates field crystallization of niobium, but not of the Nb-50 at% O substrate. The thermal treatment is considered to promote generation of pre-cursor sites for crystal nucleation. However, sufficient oxygen in the substrate may restrict pre- cursor development and/or reduce the compressive stresses in the amorphous anodic niobia that can facilitate crystal growth.
Formation of Self-Organized Zirconia Nanostructure
Authors: Schmuki P. , Tsuchiya Hiroaki , Macak Jan , Taveira Luciano
Published: November 2006

The present work investigates the anodic formation of a self- organized high-aspect-ratio zirconia nanotube layer on Zr. Under specific electrochemical conditions anodization of Zr in (NH4)2SO4/NH4F electrolyte results in arrays of individual nanotubes with a diameter of 50 nm and a length of 17 μm - the aspect ratio is estimated as more than 300. The tube walls where extremely straight and smooth - this morphology is significantly different from a nanotubular zirconia shapes formed in acidic electrolytes. SAD pattern reveals that the nanotubes have a crystalline structure already after anodization, that is, without any further annealing. The nanotube growth features are similar to that of HfO2 nanotubes, but is different from that of TiO2.
The Role of Metallic Bonding in the Crystallographic Pitting of Magnesium
Authors: Lillard R. Scott , Wang Guofeng , Baskes Mike
Published: November 2006

The role of metallic bonding in the crystallographic pitting of magnesium (Mg) has been investigated using atomistic simulations. To assess the degree of metallic bonding in Mg and surfaces the modified embedded atom method (MEAM) has been used. The inter atomic potentials developed with MEAM were then used by a Monte Carlo MC code, standard Metropolis algorithm, to calculate atom removal probabilities. Simulations for the Mg surface found that atom removal formed geometric surface structures, the orientation of which where always at a 58o or 116o angle with respect to the direction or 90o with respect to . These results are identical to experimental results from Mg single crystals. Simulations of Mg surfaces found no preferred orientations similar to experimental results.
Effects of Cr2N on the Pitting Corrosion of High Nitrogen Stainless Steel Investigated by Micro-droplet Cell
Authors: Kwon Hyuksang , Ha Heonyoung
Published: November 2006

Effects of nitrogen (N) content on the precipitation behavior of Cr2N with its relevant influences on the resistance to localized corrosion of high nitrogen stainless steels (HNSs) were examined using a capillary based micro-droplet cell. HNS of 18Cr-20Mn-3Mo-1.07N was highly resistant to pitting corrosion. With aging the alloy at 900 °C, Cr2N precipitated initially along grain boundaries, then within grain, and eventually formed a lamellar structure, accompanied with a drastic decrease in the resistance to pitting corrosion. It was found from the micro-droplet cell tests that the lamellar Cr2N was the most susceptible site for pitting corrosion when compared with any other heterogeneity such as a (Mn, Cr)-oxide or a Cr2N precipitated along grain boundaries.
Effect of Sensitization on Stress Corrosion Cracking of Type 316 Austenitic Stainless Steel in Sulfuric Acid Solution
Authors: Nishimura Rokuro , Sulaiman Achmad
Published: November 2006

The stress corrosion cracking (SCC) of a commercial austenitic stainless steel type 316 was investigated as functions of applied stress, sensitizing temperature and sensitizing time in 0.82 kmol/m3 sulphuric acid solution by using a constant load method. The applied stress dependence of the three parameters (lss, steady state elongation rate, tss, transition time, tf , time to failure) showed three regions irrespective of sensitizing temperature and sensitizing time; the stress- dominated, SCC- dominated and corrosion- dominated regions. In the SCC- dominated region, the logarithm of lss was a linear function of the logarithm of tf for each sensitized specimens, showing that lss became a relevant parameter for prediction of tf, although the slope depended upon sensitizing temperature and sensitizing time. At a sensitizing time of more than 360 ks, the SCC susceptibility was found to reduce because of Cr healing. Sulphate ions became more aggressive to SCC than chloride ions for the specimens with the severest sensitization. The effect of sensitization on SCC and the role of sulphate ions were discussed and further a qualitative IGSCC mechanism was proposed.
Sn-P Alloys for Rapid and Stable Production of Tin Solution for Tin Plating
Authors: Hashimoto Koji , Kato Zenta , Kumagai Naokazu , Kamio Keiji , Hirose Keisuke
Published: November 2006

For fast preparation of tin solution for electrodeposition, the dissolution characteristics controlled by oxygen reduction were investigated for Sn metal and Sn-P alloys containing cathodic inclusions using electrochemical measurement in p- phenolsulfonic acid. The dissolution rate of tin increased with phosphorus content of the alloys due to faster oxygen reduction and showed the maximum at about 1 at % phosphorus. The cathodic inclusions were dispersed in the Sn matrix by water quenching of molten mixture of Sn and Sn-50at%P, and were identified as the Sn4P3 phase by X-ray diffraction. The Sn4P3 compound has the higher activity for oxygen reduction than Sn metal and platinized platinum. The mechanism for the cathodic reduction of dissolved oxygen on Sn metal and Sn-P alloys was investigated in p-phenolsulfonic acid. Increasing phosphorus content of Sn-P alloys resulted in an increase in the limiting oxygen reduction current density which was proportional to the partial pressure of oxygen, but independent of pH. It was concluded that the rate-determining process of oxygen reduction was adsorption of oxygen molecule on the Sn metal and Sn-P alloys.
Thermodynamic Phase Modeling in the Ce-O System
Authors: Seifert Hans J. , Nerikar Pankaj , Lukas Hans Leo
Published: November 2006

The thermodynamic modeling for the phases of the Ce-O system is presented. The central part of the Ce-O system, covering the range between Ce2O3 and CeO2 up to about 2000 K, was tken into account. The calculated phase diagram, the heat capacities, the chemical potentials of oxygen and the partial enthalpies of oxygen are presented. The diagrams reproduce fairly well the experimental data from literature.
J.B. Wagner Award Address- Mixed Potential Sensors: From Understanding to Applications
Authors: Mukundan R. , Brosha Eric L. , Garzon F. H.
Published: November 2006

Mixed potential sensors have been studied at Los Alamos National Laboratory (LANL) over the past decade for various gas sensing applications. In this paper we outline this research with specific emphasis on the sensing mechanism and how it relates to the design of robust, stable and reproducible sensors. The importance of the oxygen reduction kinetics on the sensor response was ascertained by the use of 4 electrode devices with dual air-reference electrodes. The unstable and irreproducible response of previous mixed-potential devices is attributable to changes in the gas/electrode/electrolyte interface with time. Improved sensor designs use dense electrodes and porous and/or thin film electrolytes to produce morphologically stable devices. The electrode composition and mode of operation of these sensors was then varied to design sensors for specific applications including carbon monoxide, hydrocarbon and nitrogen oxide sensing.
Optimization of La2CuO4 Sensing Electrodes for a NOx Potentiometric Sensor
Authors: Macam Eric R. , Van Assche Frederick M. , Yoo Jiho , Wachsman E. D.
Published: November 2006

Lanthanum Copper Oxide (La2CuO4) was previously studied as a sensing electrode for a potentiometric sensor. In those studies, we have shown that as the particle size of La2CuO4 decreases, the sensitivity to NO and NO2 increases. In order to determine whether or not this phenomena is due to the relative surface to volume ratio or to total surface area of the electrode, this study aims at examining the effect of the varying sensing and counter electrode areas has on the sensitivity of the electrode. The effect of area in this study has shown that Mixed Potential Theory cannot completely explain NOx sensing behavior and confirms that semiconducting properties of the electrode must be considered.
CO Gas Sensing Characteristics of ITO Electrode Coupled with Sc2O3-ZrO2 Solid Electrolyte
Authors: Kale Girish M. , Li Xiaogan
Published: November 2006

Tin-doped indium oxide (ITO) is an important industrial material, which was extensively studied as an electrode material for optoelectronic devices and semiconductor gas sensors. However, its application as an oxide electrode material in mixed-potential gas sensor has not been explored so far. In this report, the sensing properties of the planar scandia-stabilized zirconia based mixed potential gas sensor coupled with hydrothermally-obtained nano-sized ITO as an electrode material have been investigated. The planar sensor has shown good sensitivity to low-level of CO concentrations (16~500ppm) in a lower oxygen ambient (4 vol.%) in terms of the high magnitude of the signal and fast response (<5s). A possible sensing mechanism of the planar sensor for rapidly detecting CO has also been discussed. The fast response feature of the fabricated sensor could be attributed to the porous nanocrystalline ITO employed as a thick film electrode in the CO sensor.
Potentiometric NOx Sensing Behavior of Cr2O3-Based Sensor and TPR of the Sensor Element
Authors: Yoo Jiho , Wachsman E. D.
Published: November 2006

The NO2 and NO sensing behavior of a Cr2O3/YSZ/Pt potentiometric sensor was studied in 3 - 21% O2 at 450 - 700 ºC and compared with that of a WO3-based potentiometric sensor. A positive voltage response is shown for NO2 and negative for NO, and a linear relationship is generally attained in the plot of the emf vs. the logarithm of NO2 and NO concentration. The Cr2O3 sensor shows very similar tendency in NO2 selectivity to the WO3 sensor, but their NO selectivities are different from each other. The selective NO2 detection is commonly achieved against CO and CO2, being consistent with a CO- and CO2-independent NO2 profile in the TPR results. In contrast, the Cr2O3 sensor is not NO selective against CO. The NO+CO+O2 TPR profile showing no gas concentration changes up to 800 ºC indicates that the CO- induced change in the NO sensitivity is seemingly adsorption- related.
Synthesis and Characterization of Y2Ru2O7 and Y2-XPrXRu2O7 for Cathode Application in Intermediate Temperature Solid Oxide Fuel Cells
Authors: Abate Chiara , Duncan Keith , Esposito Vincenzo , Traversa E. , Wachsman E. D.
Published: November 2006

Nanocrystalline powders of Y2Ru2O7 and Y2-xPrxRu2O7 were prepared by a co-precipitation method. Pr was chosen as the A- site dopant in order to increase the electrical conductivity of Y2Ru2O7. Phase and morphology were studied by XRD and FE- SEM, which showed both systems exhibit a particle size of about 100 nm, and the doped powders were single pyrochlore phase. The electrical conductivity of a dense bar of Y2- xPrxRu2O7 was measured at several temperatures by d.c. 4-probe method, while the electrochemical properties of Y2-xPrxRu2O7 pyrochlores were tested in contact to ESB electrolytes, using Electrochemical Impedance Spectroscopy (EIS) in air. The Y2- xPrxRu2O7 on ESB electrolyte solid-state cells presents a significant decrease of electrodes impedance.