bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase Reactions of Ceria in LPS SiC
Authors: Pan Zhu , Seifert Hans J. , Fabrichnaya Olga , Baney Ronald , Tulenko James
Published: August 2009

SiC was densified by liquid phase sintering using additives (Y2O3, Al2O3) and (Y2O3, Al2O3 and CeO2), respectively. Maximum sintering temperature was 1925 oC at 80 bar Ar pressure. The total amount of additives (Al2O3 + Y2O3) was fixed as 10 wt.%. The molar ratio of Al2O3:Y2O3 additives were changed in a systematic way from 1Al2O3:1Y2O3 to 5Al2O3:3Y2O3. The CeO2 amount was varied from 0 to 5 mass percent. Both influence of different of Al2O3: Y2O3 and amount of CeO2 on sintering behaviour were investigated. The products and microstructure were investigated by X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) techniques. Due to Al2O3 vaporization only the Al2Y4O9(YAM) phase was found in the remarkable amounts. The CeO2 dissolves in Y4Al2O9 (YAM) phase. The Ce3+ ions (i.e. Ce4+ to Ce3+ valence change) occupy Y3+ positions, causing a lattice parameter increase of Y4Al2O9 (YAM) with CeO2 content raise. A formula Y4(1-x)Ce4xAl2O9 is assigned to the solid solution. Ceria is proofed as an excellent sintering aid.
Steam Oxidation and Chromia Evaporation in Ultra-Supercritical Steam Boilers and Turbines
Authors: Holcomb Gordon R.
Published: August 2009

U.S. Department of Energy's goals include power generation from coal at 60% efficiency, which requires steam conditions of up to 760 {degree sign}C and 340 atm, so called ultra-supercritical (USC) conditions. Evaporation of protective chromia scales is expected to be a primary corrosion mechanism. A methodology to calculate Cr evaporation rates from chromia scales was developed and combined with Cr diffusion calculations within the alloy (with a constant flux of Cr leaving the alloy from evaporation) to predict Cr concentration profiles and to predict the time until breakaway oxidation. At the highest temperatures and pressures, the time until breakaway oxidation was predicted to be quite short for the turbine blade, and of concern within the steam pipe and the higher temperature portions of the superheater tube. Alloy additions such as Ti may allow for a reduction in evaporation rate with time, mitigating the deleterious effects of chromia evaporation.
High Temperature Erosion-Corrosion Resistance of TiB2-Stainless Steel Cermets for Refinery Process Applications
Authors: Chun Charlie , Bangaru Rao , Peterson John R. , Ramanarayanan Trikur
Published: August 2009

Refinery process vessel internal walls and related piping exposed to aggressive fluids containing hard, solid particles such as catalyst particles are subject to both erosion and corrosion. The protection of these vessels and piping against erosion and corrosion induced material degradation especially at high temperatures is a technological challenge. The life span of the state­of-the-art monolithic refractory liners currently in use is limited by excessive mechanical recession of the liner from high velocity solid particle impingement, mechanical cracking and spalling. In order to overcome this challenge, advanced TiB2-stainless steel cermets were designed for high fracture toughness and the chemical stability required for the long term service. In this paper, we present a class of TiB2-stainless steel cermets exhibiting an order of magnitude higher erosion resistance and superior corrosion resistance compared to state­of-the-art materials.
The Phenomena of Adherence of a Growing Scale with Inert Materials Under Given Reaction Conditions
Authors: Werber Teodor , Zurek Zbigniew , Jaron Artur
Published: August 2009

During the oxidation of metals at high temperatures, the growing scale can sometimes form an adhesive bond with solid substances. This phenomenon has been observed on copper and iron scales formed in air at high temperature in contact with inert materials. The adhesive bond was also formed during the sulphurisation of copper in liquid sulphur at a temperature of 445 ºC, when the growing sulphide scale came into contact with graphite, quartz glass, platinum and mica. The created adhesive connections are tough and equal to or even greater in strength than the cohesion forces of scale and solid phase, with which they came into contact. The formation of adhesive connections occurs when the product of the metal oxidation reaction grows on the external surface of the scale, i.e. when the process of outward diffusion of metal through scale occurs.
Oxidation of Carbon/Carbon through Coating Cracks
Authors: Jacobson Nathan , Roth Don , Rauser Richard , Cawley James , Curry Donald
Published: August 2009

Reinforced carbon/carbon (RCC) is used to protect the wing leading edge and nose cap of the Space Shuttle Orbiter on re-entry. It is composed of a lay-up of carbon/carbon fabric protected by a SiC conversion coating. Due to the thermal expansion mismatch of the carbon/carbon and the SiC, the SiC cracks on cool-down from the processing temperature. The cracks act as pathways for oxidation of the carbon/carbon. A model for the diffusion controlled oxidation of carbon/carbon through machined slots and cracks is developed and compared to laboratory experiments. A symmetric cylindrical oxidation cavity develops under the slots, confirming diffusion control. Comparison of cross sectional dimensions as a function of oxidation time shows good agreement with the model. A second set of oxidation experiments was done with samples with only the natural craze cracks, using weight loss as an index of oxidation. The agreement of these rates with the model is quite reasonable.
Oxidation of ZrB2 and ZrB2-SiC Ceramics with Tungsten Additions
Authors: Zhang Shi C. , Fahrenholtz William G. , Hilmas Gregory E.
Published: August 2009

The effect of tungsten additions on the oxidation behavior of zirconium diboride-based ceramics was studied. Four mole percent tungsten carbide was added to ZrB2. The oxidation behavior was studied using thermal gravimetric analysis and isothermal testing in flowing air. Upon heating to 1500{degree sign}C, the mass gain decreased from ~14 mg/cm2 for nominally pure ZrB2 to ~4.5 mg/cm2 for tungsten containing ZrB2. After heating to 1500{degree sign}C for three hours, the scale thickness on nominally pure ZrB2 was ~500 µm compared to ~100 µm for tungsten containing ZrB2. Tungsten additions improved the oxidation resistance of ZrB2 by modifying the morphology of the ZrO2 scale by liquid phase sintering, providing an improved barrier to oxygen diffusion.
Microstructural Observations on Oxidized Ni-Based Superalloy TMS-75 and PGM-doped Derivatives
Authors: Pruessner Karin , Harada Hiroshi
Published: August 2009

The isothermal oxidation behavior of experimental 3rd and 4th generation Ni-based superalloys was studied at temperatures between 900 and 1100ºC. It was found that the lower Cr-concentration in 3rd and 4th generation alloys compared to 2nd generation alloys negatively affects the ability of the alloy to form and maintain a protective alumina scale esp. at lower temperatures. An extensive internal reaction zone comprised of oxide and nitride phases is observed underneath a non-protective external scale. At higher temperatures, a continuous alumina scale forms underneath (Ni,Co)O and spinel layers. Due to the low level of reactive element additions in these experimental alloys, scale adhesion is not good though. Increased Cr content is necessary to ensure formation of a protective alumina scale at lower temperatures. Addition of Y and or Zr is recommended for improved oxide adhesion resulting in better overall oxidation performance.
Oxidation Behavior of Nb-20Mo-15Si-5B-20Cr and Nb-20Mo-15Si-5B-20Ti Alloys Up To 1300{degree sign}C
Authors: Ventura Julieta A. , Portillo Benedict I. , Varma Shailendra K. , Mahapatra Rabindra N.
Published: August 2009

Nb-20Mo-15Si-5B-20Cr (Cr alloy) and Nb-20Mo-15Si-5B-20Ti (Ti alloy) alloys have been subjected to oxidation in air for 24 hours in a range of temperatures from 700 to 1300{degree sign}C. As cast structures contain Nbss, Nb5Si3, and Nb3Si in both alloys but Cr alloy also contains NbCr2. Cr alloy exhibits better oxidation resistance than Ti alloy. Oxidation characterization has been carried out for samples heated in 700-1300{degree sign}C temperature range. Large number of oxides of Nb, Mo, Si, Cr, and Ti has been observed as characterized by XRD, x-ray mapping, and EDS on SEM. The scale in immediate contact with the alloy substrate has been found to usually contain Mo oxides. Swollen oxide/metal mixture appears at 900, 1200 and 1300{degree sign}C for Ti alloys and between 1100 and 1300{degree sign}C for Cr alloy.
Oxidation Behavior of F-treated TiAl Alloys in SO2-Containing High Temperature Environments
Authors: Masset Patrick J. , Schütze Michael
Published: August 2009

The surface of TNBV5 alloys was treated using fluorine based polymer which improves the oxidation resistance of titanium aluminides. This work shows that the controlled fluorination of a TiAl alloy surface improves the oxidation resistance even in the presence of 0.1 v/o SO2 in the environment. Contrary to thermodynamic predictions no sulfides were found in the oxide scale. Diffusion of oxygen and nitrogen into the alloy during oxidation seems to be reduced in the presence of sulfur dioxide.
Tie-Line Compositions of the σ and (γ, γ', β) phases in the Ni-Al-Re-Cr System at 1423K
Authors: Saito Shigeru , Kurokawa Kazuya , Hayashi Shigenari , Takashima Toshiyuki , Narita T.
Published: August 2009

Compositions with tie-lines between the σ and γ, γ', β phases in a quaternary Ni-Al-Re-Cr system were investigated by heat-treating various quaternary Ni-Al-Re-Cr alloys in vacuum at 1423 K for a variety of times up to 2500 h. It was found that a very long heat treatment was required to obtain equilibrium compositions of arc-melted Ni-Al-Re-Cr alloys. The tie-lined compositionsat%of each phase at 1423 K were experimentally determined as follows. The σ phase tie-lined with the γ phase73.5Ni, 14.6Al, 2.9Re, and 9.0Cr) consists of 56.7Re, 25.0Cr, 18.1Ni, and 0.2Al. The σ phase tie-lined with the γ' phase73.6Ni, 21.0Al, 1.2Re, and 4.2Cr) consists of 58.3Re, 25.0Cr, 16.6Ni, and 0.1Al. The σ phase tie-lined with the β phase50.2Ni, 48.7Al, 0.3Re, and 0.8Cr) consists of 61.1Re, 32.5Cr, 5.2Ni, and 1.2Al.
Resistance to Active Oxidation of Sol-Gel HfO2 Coated SiC Polycrystal
Authors: Akashi Takaya , Kasajima Miho , Kiyono Hajime
Published: August 2009

Sintered SiC substrate was coated with HfO2 by a sol-gel process using Hf(OEt)2, diethanol-amine, and ethanol. The HfO2-coated SiC specimen was oxidized isothermally in high purity Ar gas flow at 1873 K for 36 ks and the weight change was monitored by an electro-microbalance. The weight of the un-coated SiC specimen decreased significantly due to the active oxidation, while the weight losses of HfO2-coated SiC specimens after the isothermal oxidation for 36 ks were smaller than that of un-coated specimen. TEM image of HfO2-coated SiC specimen after oxidation depicted that thick SiO2 layer (~800 nm) with a small amount of Hf elements formed on the surface of the specimen. XRD analysis indicated that HfC formed during the isothermal oxidation of HfO2-coated SiC specimen.
Oxygen Nonstoichiometry and Defect Equilibrium in La2-xSrxNiO4+δ
Authors: Nakamura Takashi , Yashiro Keiji , Sato Kazuhisa , Mizusaki Junichiro
Published: August 2009

Oxygen nonstoichiometry of La2-xSrxNiO4+δ (x = 0, 0.1, 0.2, 0.3, 0.4) were measured by high temperature gravimetry and coulometric titration. La2-xSrxNiO4+δ shows oxygen deficient and oxygen excess compositions depending on the Sr content, temperature, and oxygen partial pressure.
Grain Growth Behavior of La0.6Sr0.4CoO3-δ Film Dispersed with a Second Phase
Authors: Sawada Takeyuki , Akashi Takaya
Published: August 2009

La0.6Sr0.4CoO3-δ (LSC) film and Co3O4-dispersed La0.6Sr0.4CoO3-δ (LSC+Co3O4) film were prepared by a sol-gel process. The film thickness and average grain size were 100 nm and 50nm. The obtained films were annealed at 1273 K for 1-20 h under the oxygen partial pressure between 3.4 and 81 kPa. The grain size increased with increasing isothermal annealing time and decreasing oxygen partial pressure. No significant differences in the grain growth were observed between LSC films and LSC+Co3O4 films. The oxygen partial pressure dependence of the grain growth suggested that the grain growth was not controlled by the cation diffusion, implying that the grain growth was controlled by transport of ions across the grain boundary.
High-Temperature Gravimetric Study on the Kinetics of the Formation of SrTiO3 by Solid State Reaction of SrCO3 and TiO2
Authors: Niwa Eiki , Sato Kazuhisa , Yashiro Keiji , Mizusaki Junichiro
Published: August 2009

SrTiO3-based perovskite-type oxides are used in various fields because these oxides have high chemical stability and many functions. In this study, a trial was made to find the best conditions for the preparations of the single phase SrTiO3. Two kinds of powder mixtures, SrCO3/TiO2(anataze) and SrCO3/TiO2(rutile), were prepared and the reaction behavior, the formation energy to SrTiO3, the reaction rate constant and the activation energy were compared to elucidate the mechanism and the condition for single phase formation.
A Quantitative Study on the Effects of Environment and Microstructure on Pit Initiation in Al-alloys
Authors: Cavanaugh Mary K. , Birbilis Nick , Buchheit Rudy
Published: August 2009

Potentiostatic testing was employed to examine pit initiation on AA7075-T651 exposed to chloride solutions. The influence of chloride concentration, potential, and temperature on pit initiation was studied. An automated method for counting current transients is presented, and the applicability of potentiostatic testing in Al alloys is generally discussed.
An EQCM Study of the Corrosion of Synthetic Aluminium Alloys
Authors: Schneider Oliver
Published: August 2009

Thin film aluminum electrodes were sputter-deposited onto quartz resonators for the electrochemical quartz crystal microbalance technique. The aluminum electrodes were then photolithographically patterned and decorated with arrays of Cu islands or Al-Cu-Mg islands mimicking cathodic and anodic phases in commercial Al alloys. Open circuit exposure to 0.5 M NaCl of different pH was performed, and the resonance frequency of the quartz measured in parallel. In the beginning of the experiments a frequency increase due to loss of Al by corrosion was observed. Later on the deposition of corrosion products with a large roughness caused the frequency to decrease.
Localized Approach of Galvanic Coupling on Aluminum-Magnesium Systems
Authors: Lacroix Loïc , Blanc Christine , Pébère Nadine , Tribollet Bernard , Vivier Vincent
Published: August 2009

The corrosion behavior of a pure aluminum/pure magnesium couple in a weakly conductive sodium sulfate solution was investigated. Potential and current distributions on the surface of the model couple at the beginning of immersion were obtained by solving the Laplace equation using a finite element method (FEM) algorithm. It was shown that magnesium was the anode of the system while both oxygen and water reduced on aluminum. Calculations predicted a large current peak at the Al/Mg interface related to a local increase of both Mg dissolution and oxygen and water reduction on aluminum. This led to a local pH increase. Optical and scanning electron microscope observations confirmed a strong dissolution of magnesium combined with depassivation of aluminum at the Al/Mg interface. Local electrochemical impedance spectroscopy showed the detrimental effect of the galvanic coupling both on aluminum and magnesium.
Galvanic Corrosion and Localized Degradation of Aluminum-Matrix Composites Reinforced with Boron Carbide Particulates
Authors: Ding Hongbo , Hihara Lloyd H.
Published: August 2009

Galvanic corrosion of a 6092-T6 Al metal-matrix composite (MMC) reinforced with boron carbide (B4C) particulates was examined through electrochemical characterization of the MMC as well as a monolithic B4C. The results were interpreted based on a recently proposed electronic model for B4C that emphasizes a conventional non-degenerate p-type semiconductor band structure with high density of gap states. A combination of scanning vibration electrode technique and scanning ion-selective electrode technique revealed that localized anodic and cathodic sites of over 200 μm in diameter co-existed on the surface of the MMC during immersion of the MMC in an air-exposed 3.15 wt% NaCl solution.
Anodic Activation of Aluminum by Trace Element Tin
Authors: Graver Brit , Pedersen Anne M. , Nisancioglu Kemal
Published: August 2009

Trace elements in Group IIIA-VA activate aluminum alloys anodically in chloride environment. The present focus is on trace element Sn. Surface segregation by heat treatment and resulting surface activation on model AlSn alloys, containing 30 to 1000 ppm of Sn, were characterized, respectively, by use of surface-analytical and electrochemical techniques. Tin segregated by annealing for 1 h annealing at 300ºC, thereby causing significant activation, as characterized by pitting potential depression and high anodic currents produced. Activation was attributed to the segregated submicron particles. By increasing the annealing temperature to 600ºC, tin was incorporated in solid solution. This reduced surface activation to an insignificant level for the AlSn alloy containing 30 ppm Sn. However, alloy containing 1000 ppm Sn remained active. Removal of the active surface layers resulting from the segregation of the activating metals passivated the surface. However, Sn in solid solution affected the entire material.
The Aqueous Corrosion Behavior of Plutonium Metal and Plutonium-Gallium Alloys Exposed to Aqueous Nitrate and Chloride Solutions
Authors: Kolman David , Colletti Lisa
Published: August 2009

Previous work in this laboratory examined the polarization behavior of high-purity plutonium metal exposed to various solutions, however, the polarization behavior of plutonium-gallium alloys has not been studied. The objective of this work is to establish the effect of gallium on the electrochemical behavior of plutonium metal exposed to nitric acid, sodium nitrate, and sodium chloride solutions. Results indicated that plutonium-gallium alloys were not passive in HNO3 solutions, unlike unalloyed plutonium. The dissolution of 0.5 and 1 wt % Ga alloys exposed to HNO3, and all materials exposed to NaCl, was found to be controlled by the presence of a corrosion product film. Relative oxide thickness measurements of unalloyed Pu exposed to HNO3 were obtained. Chloride was found to aggressively attack Pu and its alloys with increasing chloride concentration resulting in increased corrosion. Nitrate ions were shown to have a weak effect on the corrosion behavior of Pu, as compared to protons and chloride ions.
The Effect of Alloy Composition on the Metastable Pitting Behavior of Ni-Cr-Mo Alloys in Hot Dilute Chloride Solution
Authors: Wong Fariaty , Buchheit Rudy
Published: August 2009

The effect of Cr and Mo in on the metastable pitting behavior of Ni-Cr-Mo alloys of various compositions was studied through analysis of transients captured in current-time records produced during potentiostatic polarization in hot chloride solutions. It was found that the total number of metastable pitting events decreases with an increasing amount of Cr and Mo, with Mo exerting a more potent effect. As Mo concentration increases, the peak current of metastable pits decreases. Additionally, the growth rate of the fastest growing pits was slowed as alloying Mo content increased. Chromium additions, on the other hand, were found to act in suppressing pitting by increasing pit repassivation rates.
Stress Corrosion Cracking of Zirconium in Boiling Nitric Acid Solution at Potentiostatic Condition
Authors: Yamamoto Masahiro , Kato Chiaki , Ishijima Yasuhiro , Kano Youichi , Ebina Tetsunari
Published: August 2009

Zirconium has been utilized in reprocessing plant because of its superior corrosion resistance. But Stress corrosion cracking (SCC) susceptibility had been reported in some conditions. In order to clarify the SCC occurrence criteria of Zr in boiling nitric acid solution, constant load tests at potentiostatic condition were conducted. From the results, SCC of Zr in nitric acid solution occurred only at transpassive region. And it is attributes to tarnish rupture model. From the observation of intermediate samples, many cracks initiate under oxide film and then the maximum crack grown to rupture. If the reprocessing plant operates in the potential of passivity region, SCC of Zr will not occur.
Anodic Behavior of Nickel in Acidic Perchlorate Solution Containing Pb2+
Authors: Seo Masahiro , Kikuchi Naoki , Fushimi Koji , Habazaki Hiroki , Narita T. , Nakayama Takenori
Published: August 2009

The anodic behavior of nickel has been investigated in deaerated acidic perchlorate solution containing 10-4 M Pb2+ at room temperature. The addition of Pb2+ in solution shifted the corrosion potential or the potential of anodic current peak to the more noble direction and suppressed the anodic dissolution of nickel. The Tafel slope of anodic dissolution decreased from 37 mV decade-1 to 13 mV decade-1 due to the addition of Pb2+. The uderpotential deposition (UPD) of Pb on nickel was discussed with relation to the effect of Pb2+ on anodic behavior of nickel.
The Influence of the Semiconducting Properties of Passive Films on Localized Corrosion Rates
Authors: Harrington Scott P. , Devine Thomas
Published: August 2009

A passive film with a high electrical resistance can lead to a small cathodic current and repassivation of metastable pits and crevices. Many passive films behave as semiconductors and cathodic current magnitudes can be related to the semiconducting properties of the films. In this study, Alloy C22 was investigated with Mott-Schottky (MS) tests in neutral and acidic solutions. The passive film forming on Alloy C22 was found to be n-type with measured charge carrier densities and flatband potentials that were frequency dependent. An expression developed by Brug et al.(1) was found to calculate flatband potentials consistent with polarization scans. Using this expression the charge carrier density was calculated to be 1021 cm-3 and the flatband potential was found to be pH dependent, but close to the hydrogen redox couple. Alloy's C22's low flatband potential may increase its resistance to stable localized corrosion in ambient environments.
In-situ Raman Spectroscopy for the Passive Oxide Film on Iron in Neutral Borate Solution
Authors: Ohtsuka Toshiaki , Taneda Kento
Published: August 2009

In-situ Raman spectra of the passive oxide film in neutral borate solution at pH 8.4 was measured without any enhancement such as surface enhanced Raman scattering or resonance Raman scattering. To measure the Raman spectra of the surface thin film on the electrode, we introduced a confocal collection system to reject the scattering signal from the electrolytes surrounding the surface in front of the spectrometer. The background signal is still high, and it is more intensive by 100 times than the Raman signal from the passive film. The difference Raman signal between the surfaces of the passivated iron and the reduced bare iron reveals a peak at about 670 cm-1. When we measured the passivated iron surface soon after transfer from the electrolytes to air, we observed another broad and faint peak at 320 cm-1. From these peaks, we assume that the passive oxide film on iron is composed of Fe3O4 and γ-Fe2O3.
The Effect of Metal Texture on Depassivation-repassivation Behavior of Iron in Borate Buffer Solution Investigated by Micro-indentation
Authors: Yamamoto Takatoshi , Fushimi Koji , Habazaki Hiroki , Konno Hidetaka , Miura Seiji
Published: August 2009

The effects of grain orientation and cold-rolling on the depassivation-repassivation behavior of polycrystalline irons were examined in pH8.4 borate buffer solution using in-situ micro-indentation technique. The depassivation rate on the passive iron surface during the downward drive of the indenter (penetration of an indenter tip into iron surface) depended on the grain orientation; the highest rate was obtained on {100} surface, on which a possible main slip plane of {110} was normal to the surface. In contrast, the total electric charge required for repassivation during the downward and subsequent upward drives was not influenced by the grain orientation. The electric charge for repassivation was strongly influenced by the rolling reduction that changed the dislocation density at the specimen surface. There was a linear correlation between the electric charge normalized by residual dent area and the square root of the dislocation density.
Passivity and Pit Stability Behavior of Copper as a Function of Selected Water Chemistry Variables
Authors: Cong Hongbo , Michels Harold , Scully John R.
Published: August 2009

The electrochemical pitting behavior of UNS C11000 copper was investigated in a synthetic potable water found to cause pitting. Tests were also conducted in several other HCO3-, SO42- and Cl- containing-waters. Studies of the effect of water chemistry on passivity, uniform corrosion, and pitting were accomplished using the cyclic voltammetry method. Certain water chemistry concentrations promote pitting. High [SO42-]/[OH-],[SO42-]/[HCO3-] and [Cl-]/[HCO3-] ratios lower pitting potentials while an increase in alkalinity improves passivity and raises pitting potentials. HCO3-/CO32- can protect copper surfaces by forming carbonate containing minerals. However, carbonated species are less beneficial towards passivity compared to OH- with respect to passivation efficiency. Empirical equations that forecast pitting and repassivation potentials as a function of selected water chemistry variables were developed by linear regression analysis based on experimental pitting and repassivation potential trends with HCO3-, Cl- and SO42- content. The origins of the trends with water chemistry variables are discussed.
Corrosion Behaviour of New PVD Coatings on Steel
Authors: Warren David J. , McMurray Hamilton , De Vooys Arnoud
Published: August 2009

Coating pinhole defects produce a corrosion related problem for barrier coated steel products. Due to this it is important to be able to identify the levels of pinholes in a coating and relate this to how it will corrode. The technique of Electrogenerated Chemiluminescence (ECL) is applied to this problem and provides a useful option for detecting pinholes through the localised production of visible light. It is shown that the technique can identify pinholes in coatings which can then be related to corrosion behaviour through the use of the Scanning Vibrating Electrode Technique (SVET). Both techniques have then been applied to assess the effect of forming has on coating defect distribution and therefore the induced corrosion properties.
Self-healing Ability of Conductive Polypyrrole Coating with Artificial Defect
Authors: Kowalski Damian , Ueda Mikito , Ohtsuka Toshiaki
Published: August 2009

A bi-layered PPy film consisting of an inner layer doped with Keggin-structure anions of PMo12O403- and HPO42- (PPy-PMo12) and an outer layer doped with organic anions of dodecyl sulfate (PPy-DoS) exhibited a self-healing property when coated on steel. When a defect was introduced into the PPy-coated steel immersed in 3.5% NaCl aqueous solution, the potential initially decreased and activation of the coated steel occurred. After a few hours, the potential was recovered to the passive region, and the passivation continued for another 20 hours. Without any damage, the release of PMo12 doped in the inner layer was inhibited by the outer PPy layer doped with DoS. When a defect was introduced into the PPy film, the inner PPy layer released phosphate and molybdate anions to the damaged zone due to their decomposition via hydrolysis. Both anions work as passivation inhibitors and helped to repassivate the damaged zone on the steel.
Neutral and n-Doped Conjugated Polymers for Corrosion Control of Aluminum Alloys
Authors: Yan Maocheng , He Jie , Tallman Dennis E. , Rasmussen Seth , Bierwagen Gordon
Published: August 2009

Conjugated polymers (CPs) continue to be of interest for use as components of corrosion control coatings. For aluminum alloys, however, there is controversy and uncertainty regarding the protection mechanism(s), or indeed even whether corrosion protection by a CP is possible. Recent results from our laboratory indicate that, for an aluminum alloy coated with the oxidized form of polypyrrole, a passivation mechanism is not likely and that the dopant release mechanism may not be effective, especially in the presence of oxygen. An alternative approach is to utilize the neutral or reduced (n-doped) form of a conjugated polymer to cathodically protect the alloy and/or to serve as an oxygen scavenging coating. The CP coatings and alloy studied were neutral polypyrrole and neutral and n-doped poly(2,3-dihexylthieno[3,4-b]pyrazine) on AA 2024-T3. Results from the scanning vibrating electrode technique and galvanic coupling measurements are presented to demonstrate the efficacy of this approach.
Lift Off Strategies for Self-Organized TiO2 Nanotube Layers
Authors: Albu Sergiu P. , Ghicov Andrei , Schmuki P.
Published: August 2009

The present work describes the fabrication of lift-off layers of self-assembled TiO2 nanotubular films. Anodization of Ti in a F-containing ethylene glycol electrolyte can be used to form TiO2 nanotubes. Such layers can be detached from the metallic substrates by chemical means. As a result, detached nanotubular layers (membranes) with thicknesses in the range of 1 and 250 µm were obtained. The length of these nanotube layers is an important parameter which affects the transparency of the entire layers or diffusion of species through.
Pitting of Passivated Cadmium Monocrystals
Authors: Tromans Desmond
Published: August 2009

A combination of aqueous thermodynamics, anodic polarization tests and scanning electron microcopy was used to study the pitting behavior of Cd monocrystals in a phosphate buffered (pH 11.2) solution of 0.1 M NaCl. Pitting occurred in the passive region where the most stable passive film was Cd (OH)2. The initial film thickness was estimated to be ~4 x 10-9 m. Pitting potentials were not reproducible, being variable within surfaces of the same orientation and between different orientations. Variability was attributed to structural defects in the passive film playing a major role in pit site nucleation. Early stages of pitting produced crystallographic facets consistent with (0001), and planes, the morphology becoming increasingly complex with pit growth. The pH decreased in the growing pit and increased the influence of chloride species on localized dissolution behavior.
Chloride Ion Effects in the Corrosion Kinetics of Intermetallics in Acidic Solutions
Authors: Ito Chris R. , Nobe Ken
Published: August 2009

The electrodissolution rates of polycrystalline Sb and InSb in Cl--free acid perchlorate and acid chloride solutions have been investigated. The rest potentials of Sb and InSb in these solutions were linear functions of pH and chloride ions. Furthermore, Tafel behavior was observed for both Sb and InSb in these solutions and electrodissolution rates increased with increase in pH and Cl-. Reaction orders of the electrodissolution rates with respect to pH (or H+) and Cl- were determined. Solution analyses indicate that within the Tafel region InSb electrodissolution is non-selective.
Initial Stage of SCC of Type 316L Stainless Steel in High Temperature and High Pressure Aqueous Solution
Authors: Masaki Hiroya , Saito Tomo , Mukhlis Fahmi , Fujimoto Shinji
Published: August 2009

Stress corrosion cracking (SCC) of Type316L stainless steel initiated by a slow strain rate test (SSRT) in a dilute sodium sulphate solution at 288{degree sign}C containing 8 ppm dissolved oxygen. Intergranular stress corrosion cracking (IGSCC) and Transgranular stress corrosion cracking (TGSCC) was observed from Surface of sample after SSRT. Orientation measurements of Type316L were performed by electron backscatter diffraction (EBSD) in a scanning electron microscope (SEM) before SSRT. EBSD analysis was also performed after SSRT. An EBSD map was obtained even after SSRT. A relation between crystal orientation and crack initiation of IGSCC and TGSCC was characterized from EBSD data before SSRT. This demonstrates that the procedure proposed in this work can be of great use for obtaining crystallographic characteristics of crack initiation.
Localized Corrosion Behavior of Austenitic Stainless Steels under Stress Loading Environment
Authors: Noda Kazuhiko , Suzuki Keita
Published: August 2009

Three elements (the material, the environment, and the stress) relate closely to the occurrence of the stress corrosion cracking (SCC). SCC can occur in austenitic stainless steels during operation under tensional stress in chloride environment. And it is important to evaluate the passivation behavior of the stainless steels that has high corrosion resistance by a passive film under the stress loading environment, because it is assumed that the stress have a effect in the passivation, breakdown of the passive film and repassivation. In this present work, the corrosion behavior of type 304 and 316 stainless steels in sodium chloride solutions using a constant strain is measured by the electrochemical measurement. On the basis of the results that the polarization curve measurement and the potentiostatic polarization curve measurement obtained, the localized corrosion sensitivity was increased in stress loading environment.
Initiation of SCC on SUS304 Stainless Steel without Corrodent on Surface
Authors: Masuda Hiroyuki
Published: August 2009

We have developed a new SCC test method that enables the super Kelvin force microscope (SKFM) and the Kelvin force microscope (KFM) observations. By using this test device, the crack tip deformation and surface potential distribution were observed by SKFM under various loading conditions. At the same time, the distribution of hydrogen was examined by the silver decoration method with combining the EDX image mapping analysis. The results showed that large amount of hydrogen existed near the crack tip and caused a crack. Hydrogen moves to the maximum stressed part, so corrosion on the back of the specimen might affect the initiation of SCC. To clarify this, SCC test was done at 343K and 30%RH with attaching MgCl2 droplets on the back of the specimen (compressive site). Crack was detected in 1 and 2 weeks at the specimen thickness of 0.07mm. Large amount of Ag precipitated near the crack even the crack was too small to detect the color laser microscope. Large region of less noble potential was detected even before the crack initiation. This can be used as a monitoring of SCC.
Critical Potential for Propagation of Stress Corrosion Cracking
Authors: Shinohara Tadashi , Brunk Jon
Published: August 2009

Critical potentials for initiation and propagation of stress corrosion cracking, SCC, were investigated with creviced round bar specimens in various concentrations of NaCl solutions at 80åC. After critical potentials for crevice corrosion, ER,CREV, were measured, two types of SCC tests - that is SCC test without pretreatment, Test-1, and with pretreatment, Test-2 - were performed. It was confirmed that ER,CREV is the critical potential for initiation of both crevice corrosion and SCC. After SCC initiation condition was determined, stepwise polarization measurement with stress was performed to determine the repassivation potential for the crack propagation, ER,CRACK. The ER,CRACK values were lower than ER,CREV and they became lower with increasing test duration, and reached to the specific value. It indicates that the stress corrosion crack works as severer crevice.
Microelectrochemistry on CrS and MnS Inclusions and Its Relation with Pitting Potentials of Stainless Steels
Authors: Muto Izumi , Kurokawa Shimpei , Hara Nobuyoshi
Published: August 2009

The anodic dissolution behavior of CrS inclusions was compared with that of MnS inclusions containing around 10 at% Cr, (Mn,Cr)S, using a microelectrochemical cell in NaCl solutions. CrS inclusions were resistant to pit initiation compared with (Mn,Cr)S inclusions. The dissolution potential of CrS inclusions was found to be in the transpassive region of stainless steels. Stable pits were initiated in this potential region. (Mn,Cr)S inclusions dissolved in the passive region of stainless steels, providing lower pitting potentials than those of CrS-containing stainless steels. AES analysis of the surface films on CrS inclusions indicated that chromium-containing oxide films were formed on the CrS inclusions and grew with electrode potential, which suggested the oxide films on CrS inclusions prevented the anodic dissolution of the inclusions, thereby leading to an increased resistance to pit initiation.
Electrochemical Noise Analysis of 13 mass% Cr Stainless Steel HAZ by Solution Flow Type Micro-droplet Cell-Effect of Solution Concentration-
Authors: Sakairi Masaotoshi , Nakayama Toshiya , Kikuchi Tatsuya , Hashizume Shuji , Fushimi Koji
Published: August 2009

Low Carbon- 13 mass% Cr martensitic stainless steels have been widely used for line pipe application because of their high strength and excellent corrosion resistance in corrosive conditions. Newly developed solution flow type micro-droplet cell was applied to investigate electrochemical behavior of heat affected zone (HAZ) of 13 mass% Cr stainless steel. This technique makes it possible to measure electrochemical behavior of very narrow area of HAZ. Effects of solution pH and stress on corrosion potentials, and current at constant potential for HAZ portion of welded joints were focused. The corrosion potentials at HAZ and base metal show almost same tendency, however, current change shows clear difference of corrosion resistance at HAZ and base metal.
Depassivation pH of Austenitic Stainless Steels in NaCl Aqueous Solution
Authors: Fushimi Koji , Takakura Ko-hei , Habazaki Hiroki , Konno Hidetaka , Azumi Kazuhisa , Tsuri Shiro
Published: August 2009

The combination of the potentiometric pH measurement and potentiostatic polarization was carried out for the type-312L and 316L austenitic stainless steels during decreasing pH by dropping hydrochloric acid in sodium chloride solution. The acidification changed the surface condition of the austenitic stainless steels. The significant acidity of the solution induced a rapid increase in the anodic current passing through the steel at a critical pH, pHdepass. The value of pHdepass was increased by elevating the solution temperature or concentrating the chloride ions in solution. In the potential - pHdepass diagram, the surface condition could be classified into four domains; immunity, active, passive and transpassive/pitting states. The boundary between the active and passive states was strongly dependent on solution pH but independent of potential, indicating that the depassivation of the steel surface proceeded with a chemical reaction participating protons rather than the electrochemical one.
Critical Pitting Temperature of a 22-05 Duplex Stainless Steel and Pitting Potential Statistics
Authors: Dussart Capucine , Peguet Lionel , Gaugain Alain , Baroux Bernard
Published: August 2009

The Critical Pitting Temperature of a 22-05 type duplex stainless is investigated using both potentiodynamic and potentiostatic techniques. The potentiodynamic technique leads to a lower CPT value than the potentiostatic one. The pitting potential distribution near the CPT is determined using a multichannel device. A 10{degree sign}C transition temperature interval is evidenced in which pitting probability gradually increases from 0 to 1. A conservative CPT should then be defined as the lowest boundary of this temperature interval.
Characterization of Boundwater in Passive Film of Type 304 Stainless Steel Formed in H2SO4 and NaCl Solutions
Authors: Haruna Takumi , Sanuki Toshiaki , Nishiuma Yu
Published: August 2009

Boundwater in the passive film on Type 304 stainless steel was characterized using a thermal desorption gas analyzer. The passive film was produced electrochemically in a H2SO4 solution and was modified electrochemically in an NaCl solution. In case of producing the passive film in the H2SO4 solution, total amount of the boundwater was relatively large in the initial stage, and then decreased as the passivation time elapsed. In addition, it was found that the boundwater was classified into three types of binding states in the passive film. When the passive film was modified in the NaCl solution, the boundwater, especially of the second type, increased.
Effect of Alloying Elements on Electrochemical Behavior of Fe-18Cr Alloy
Authors: Tsuchiya Hiroaki , Fujimoto Shinji , Shibata Toshio
Published: August 2009

The present work reports electrochemical behavior of Fe-18Cr alloy thin films with various alloying elements prepared by ion beam sputtering technique. Polarization curves measured in H2SO4 solution reveal that active dissolution is effectively suppressed by the addition of Mo, Cu, Ni, Nb or Ti whereas the addition of Al, Si or Mn do not affect the active dissolution. Except for Zr, Al and Si, most of alloying elements suppress pitting corrosion in severe chloride solution. In particular, Nb is very effective and the small amount of Nb completely inhibits pitting corrosion. Reactivation behavior of passive films on Fe-18Cr alloys in H2SO4 solution is strongly affected by alloying elements. Nb, Mo, Ti and Ni shift the reactivation potential in less noble direction, meaning that they stabilize passivity of Fe-18Cr. On the other hand, Mn and Si deteriorate the passivity.
Effect of the Passive Film on the Crevice Corrosion of Stainless Steels Experimental and Modeling Approaches
Authors: Souier Tewfik , Berthome Gregory , Malki Brahim , Baroux Bernard
Published: August 2009

We investigate the crevice corrosion resistance of bright annealed (BA) or pickled (2B) AISI 430 type industrial stainless steel sheets. An artificial crevice is electrochemically coupled to a crevice free specimen through a low impedance ammeter measuring the crevice corrosion current at rest potential . After exposure the specimen show a corroded zone around the crevice bottom and a remaining passive zone at the crevice mouth. The active area and the corrosion current are much smaller for BA than for 2B but the average crevice current density does not depend on the surface condition. Modeling ionic concentrations and flows in the crevice allows determining the transition pH between active and passive zones, giving respectively 2.6 and 2.8 for BA and 2B. It fairly accounts for the better corrosion resistance of BA surface, as observed in practice. This coupled experimental and modeling approach provides a powerful tool for further crevice corrosion investigation.
JAK redux: a second look at the regulation and role of JAKs in the heart
Authors: Kurdi Mazen , Booz George W.
Published: August 2009

A number of type 1 receptor cytokine family members protect the heart from acute and chronic oxidative stress. This protection involves activation of two intracellular signaling cascades: the reperfusion injury salvage kinase (RISK) pathway, which entails activation of phosphatidylinositol 3-kinase (PI3-kinase) and ERK1/2, and JAK-STAT signaling, which involves activation of transcription factor signal transducer and activator of transcription 3 (STAT3). Obligatory for activation of both RISK and STAT3 by nearly all of these cytokines are the kinases JAK1 and JAK2. Yet surprisingly little is known about how JAK1 and JAK2 are regulated in the heart or how they couple to PI3-kinase activation. Although the JAKs are linked to antioxidative stress programs in the heart, we recently reported that these kinases are inhibited by oxidative stress in cardiac myocytes. In contrast, others have reported that cardiac JAK2 is activated by acute oxidative stress by an undefined process. Here we summarize recent insights into the regulation of JAK1 and JAK2. Besides oxidative stress, inhibitory regulation involves phosphorylation, nitration, and intramolecular restraints. Stimulatory regulation involves phosphorylation and adaptor proteins. The net effect of stress on JAK activity in the heart likely represents the sum of both inhibitory and stimulatory processes, along with their dynamic interaction. Thus the regulation of JAKs in the heart, once touted as the paragon of simplicity, is proving rather complicated indeed, requiring a second look. It is our contention that a better understanding of the regulation of this kinase family that is implicated in cardiac protection could translate into effective therapeutic strategies for preventing myocardial damage or repairing the injured heart.
Regulation of central angiotensin type 1 receptors and sympathetic outflow in heart failure
Authors: Zucker Irving H. , Schultz Harold D. , Patel Kaushik P. , Wang Wei , Gao Lie
Published: August 2009

Angiotensin type 1 receptors (AT1Rs) play a critical role in a variety of physiological functions and pathophysiological states. They have been strongly implicated in the modulation of sympathetic outflow in the brain. An understanding of the mechanisms by which AT1Rs are regulated in a variety of disease states that are characterized by sympathoexcitation is pivotal in development of new strategies for the treatment of these disorders. This review concentrates on several aspects of AT1R regulation in the setting of chronic heart failure (CHF). There is now good evidence that AT1R expression in neurons is mediated by activation of the transcription factor activator protein 1 (AP-1). This transcription factor and its component proteins are upregulated in the rostral ventrolateral medulla of animals with CHF. Because the increase in AT1R expression and transcription factor activation can be blocked by the AT1R antagonist losartan, a positive feedback mechanism of AT1R expression in CHF is suggested. Oxidative stress has also been implicated in the regulation of receptor expression. Recent data suggest that the newly discovered catabolic enzyme angiotensin-converting enzyme 2 (ACE2) may play a role in the modulation of AT1R expression by altering the balance between the octapeptide ANG II and ANG- (1–7). Finally, exercise training reduces both central oxidative stress and AT1R expression in animals with CHF. These data strongly suggest that multiple central and peripheral influences dynamically alter AT1R expression in CHF.