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Instrumentation for potentiostatic corrosion studies with distilled water  

NASA Technical Reports Server (NTRS)

Corrosion is studied potentiostatically in the corroding environment of distilled water with an instrument that measures the potential of the corroding specimen immediately after interruption of the polarizing current. No current is flowing. The process permits compensation for IR drops when potentiostatic control is used in high resistance systems.

Loess, R. E.; Youngdahl, C. A.



A CMOS Potentiostat for Control of Integrated MEMS Actuators  

E-print Network

. The fabricated chip has been employed for the control of off-chip electroactive polymer films and micro-actuatorsA CMOS Potentiostat for Control of Integrated MEMS Actuators Somashekar Bangalore Prakash, Pamela-- We describe a potentiostat designed for in situ electrochemical control of MEMS actuators

Maryland at College Park, University of


Development of a low cost potentiostat using ATXMEGA32  

NASA Astrophysics Data System (ADS)

Potentiostat is principal devices in modern electrochemical research especially in the investigation of mechanism reaction which associated with the redox chemistry reaction and other chemical phenomena. Several applications measurement is developed based on this tool such as measurement of sample concentrations, quality test of food and medicine, environmental monitoring and biosensors or development of a protein sensor. We have developed a low cost, simple and portable potentiostat with a relatively small dimension. TLC2264 op-amp and ATMEGA32 microcontroller is used to build controller circuit system. Range potential measurement of this tool is between -1600mV and +1600mV within frequency range 1Hz - 1 kHz. The developed instrument has been tested for measuring samples using different voltammetry techniques, like cyclic, square wave, and linear sweep with relative error under 2.5%.

Muid, Abdul; Djamal, Mitra; Wirawan, Rahadi



Design of a CMOS Potentiostat Circuit for Electrochemical Detector Arrays  

PubMed Central

High-throughput electrode arrays are required for advancing devices for testing the effect of drugs on cellular function. In this paper, we present design criteria for a potentiostat circuit that is capable of measuring transient amperometric oxidation currents at the surface of an electrode with submillisecond time resolution and picoampere current resolution. The potentiostat is a regulated cascode stage in which a high-gain amplifier maintains the electrode voltage through a negative feedback loop. The potentiostat uses a new shared amplifier structure in which all of the amplifiers in a given row of detectors share a common half circuit permitting us to use fewer transistors per detector. We also present measurements from a test chip that was fabricated in a 0.5-?m, 5-V CMOS process through MOSIS. Each detector occupied a layout area of 35?m 15?m and contained eight transistors and a 50-fF integrating capacitor. The rms current noise at 2kHz bandwidth is ? 110fA. The maximum charge storage capacity at 2kHz is 1.26 106 electrons. PMID:20514150

Ayers, Sunitha; Gillis, Kevin D.; Lindau, Manfred; Minch, Bradley A.



Localized corrosion of container materials under potentiodynamic and potentiostatic controls  

SciTech Connect

Potentiodynamic and potentiostatic polarization experiments were performed on ten candidate waste package container materials to evaluate their pitting tendency at ambient and elevated temperatures in aqueous environments relevant to the potential underground nuclear waste repository. Results indicate that of all the materials tested, Alloys G-30, C-4 and C-22, and Ti Gr-12 exhibited the maximum corrosion resistance, showing no pitting or observable dissolution in any environment tested. These experimental results will be used in identifying a group of potential container materials having the desired corrosion resistance.

Roy, A.K. [Framatome Cogema Fuels, Livermore, CA (United States); Fleming, D.L.; Gordon, S.R. [Lawrence Livermore National Lab., CA (United States)




E-print Network

VLSI POTENTIOSTAT FOR AMPEROMETRIC MEASUREMENTS FOR ELECTROLYTIC REACTIONS Harpreet S. Narula and John G. Harris Computational Neuro-Engineering Lab University of Florida, Gainesville, FL, USA harpreet, 1. ABSTRACT This paper describes a CMOS integrated potentiostatic con- trol circuit. The design

Harris, John G.


Potentiostatic Start-Up of PEMFCs from Subzero Temperatures Fangming Jiang* and Chao-Yang Wang**,z  

E-print Network

of membrane and rising cell temperature, potentiostatic start-up features a drastic increase in current. Quick start-up of a proton exchange membrane fuel cell PEMFC engine from subzero temperatures remainsPotentiostatic Start-Up of PEMFCs from Subzero Temperatures Fangming Jiang* and Chao-Yang Wang


Integrated VLSI Potentiostat For Cyclic Voltammetry In Electrolytic Reactions Harpreet S. Narula and John G. Harris  

E-print Network

Integrated VLSI Potentiostat For Cyclic Voltammetry In Electrolytic Reactions Harpreet S. Narula and John G. Harris Computational Neuro-Engineering Lab University of Florida, Gainesville, FL, USA harpreet. The design maintains a constant bias po- tential between the reference and working electrodes

Harris, John G.


A compact hybrid-multiplexed potentiostat for real-time electrochemical biosensing applications.  


The architecture and design of a compact, multichannel, hybrid-multiplexed potentiostat for performing electrochemical measurements on continuously-biased electrode arrays is presented. The proposed architecture utilises a combination of sequential and parallel measurements, to enable high performance whilst keeping the system low-cost and compact. The accuracy of the signal readout is maintained by following a special multiplexing approach, which ensures the continuous biasing of all the working electrodes of an array. After sampling the results, a digital calibration technique factors out errors from component inaccuracies. A prototype printed circuit board (PCB) was designed and built using off-the-shelf components for the real-time measurement of the amperometric signal of 48 electrodes. The operation and performance of the PCB was evaluated and characterised through a wide range of testing conditions, where it exhibited high linearity (R(2)>0.999) and a resolution of 400pA. The effectiveness of the proposed multiplexing scheme is demonstrated through electrochemical tests using KCl and [Fe(CN)6](3-) in KCl solutions. The applicability of the prototype multichannel potentiostat is also demonstrated using real biosensors, which were applied to the detection of IgA antibodies. PMID:23624017

Ramfos, Ioannis; Vassiliadis, Nikolaos; Blionas, Spyridon; Efstathiou, Konstantinos; Fragoso, Alex; O'Sullivan, Ciara K; Birbas, Alexios



Fabrication of triazinedithiol functional polymeric nanofilm by potentiostatic polymerization on aluminum surface  

NASA Astrophysics Data System (ADS)

The functional polymeric nanofilm of 6-(N-allyl-1,1,2,2-tetrahydroperfluorodecyl)amino-1,3,5-triazine-2,4-dithiol monosodium (AF17N) was prepared on pure aluminum surface by potentiostatic polymerization at different potentials. The thickness and weight of polymeric nanofilm increased proportionally to electro-polymerization potential following linear equation. The chemical structure of nanofilm was characterized by Fourier transform-infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Adsorption peaks in FT-IR and C1s, N1s, S2p, F1s and Al2p peaks in XPS spectra indicated that the polymeric nanofilm was poly(6-(N-allyl-1,1,2,2-tetrahydroperfluorodecyl)amino-1,3,5-triazine-2,4-disulfide) (PAF17). The morphologies of polymeric nanofilm were also observed by atomic force microscopy (AFM). All the results showed that the optimal electro-polymerization potential and time were 8 V and 20 s, respectively. Uniform and compact nanofilm of PAF17 could be obtained under these conditions. It is expected that this technique will be applied in the preparation of lubricating, dielectric and hydrophobic surface on aluminum substrate.

Wang, Fang; Wang, Yabin; Li, Yanni; Wang, Qian



Potentiostatic control of ionic liquid surface film formation on ZE41 magnesium alloy.  


The generation of potentially corrosion-resistant films on light metal alloys of magnesium have been investigated. Magnesium alloy, ZE41 [Mg-Zn-Rare Earth (RE)-Zr, nominal composition approximately 4 wt % Zn, approximately 1.7 wt % RE (Ce), approximately 0.6 wt % Zr, remaining balance, Mg], was exposed under potentiostatic control to the ionic liquid trihexyl(tetradecyl)phosphonium diphenylphosphate, denoted [P(6,6,6,14)][DPP]. During exposure to this IL, a bias potential, shifted from open circuit, was applied to the ZE41 surface. Electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) were used to monitor the evolution of film formation on the metal surface during exposure. The EIS data indicate that, of the four bias potentials examined, applying a potential of -200 mV versus OCP during the exposure period resulted in surface films of greatest resistance. Both EIS measurements and scanning electron microscopy (SEM) imaging indicate that these surfaces are substantially different to those formed without potential bias. Time of flight-secondary ion mass spectrometry (ToF-SIMS) elemental mapping of the films was utilized to ascertain the distribution of the ionic liquid cationic and anionic species relative to the microstructural surface features of ZE41 and indicated a more uniform distribution compared with the surface following exposure in the absence of a bias potential. Immersion of the treated ZE41 specimens in a chloride contaminated salt solution clearly indicated that the ionic liquid generated surface films offered significant protection against pitting corrosion, although the intermetallics were still insufficiently protected by the IL and hence favored intergranular corrosion processes. PMID:20433137

Efthimiadis, Jim; Neil, Wayne C; Bunter, Andrew; Howlett, Patrick C; Hinton, Bruce R W; MacFarlane, Douglas R; Forsyth, Maria



Ionic motion in polypyrrole-cellulose composites: trap release mechanism during potentiostatic reduction.  


This work investigates the movement of anions during potentiostatic controlled reduction of novel composite materials consisting of high surface area cellulose substrates, extracted from the Cladophora sp. algae, coated with thin ( approximately 50 nm) layers of the intrinsically conducting polymer (ICP) polypyrrole. The coating was achieved by chemical polymerization of pyrrole on the cellulose fibers with iron(III) chloride and phosphomolybdic acid, respectively. The composites are in the form of paper sheets and can be directly immersed into an electrolyte solution for ion absorption/desorption. The motion of glutamate and aspartate anions during cathodic polarization was investigated as a function of preceding anodic polarization at various potentials. The composite was found to exhibit memory effect as the response to a cathodic polarization of constant magnitude produced different responses depending on the magnitude of the preceding anodic potential. After the application of a cathodic potential to the composite, the reduction current curvesgenerated by anions leaving the compositewere found to initially increase in magnitude followed by a monotonic decay. A similar response has not been described and analyzed for electrochemical reduction of anion containing ICP materials earlier. A theoretical model was developed to aid the analysis of the experimental data. The model accounts for both freely mobile anions and anions that may be temporarily trapped in a contracting PPy network during cathodic polarization. By fitting the recorded reduction current curves to this model, detailed information about the ionic movement in the composite could be obtained, which may be used to further optimize the materials properties of conducting polymer systems aimed for specific electrochemical ion exchange processes. PMID:19338363

Strmme, Maria; Frenning, Gran; Razaq, Aamir; Gelin, Kristina; Nyholm, Leif; Mihranyan, Albert



Integrated potentiostat for electrochemical sensing of urinary 3-hydroxyanthranilic acid with molecularly imprinted poly(ethylene-co-vinyl alcohol).  


Changing demographics, the rise of personalized medicine and increased identification of biomarkers for diagnosis and management of chronic disease have increased the demand for portable bioanalytical instrumentation and point-of-care. The recent development of molecularly imprinted polymers enables production of low cost and highly stable sensing chips; however, the commercially available and full functional instruments employed for electrochemical analysis have shortcomings in actual homecare applications. In this work, integrated circuits (ICs) for monolithic implementation of voltammeter potentiostat with a large dynamic current range (5nA to 1.2mA) and short conversion time (10ms) were fabricated in a 0.35?m complementary metal-oxide-semiconductor (CMOS) process. The new instrumentation was tested with molecular imprinted sensors for 3-hydroxyanthranilic acid (3HAA) in urine. The sensor consisted of molecular imprinted of poly(ethylene-co-vinyl alcohol)s (abbreviated as EVALs) for implementation in a flow injection analysis system. The EVAL containing 32 ethylene mol% had the highest imprinting effectiveness for the target molecules. Fit-for-purpose figures of merit were achieved with a limit-of-detection (LOD) of 3.06pg/mL. The measurements obtained in real undiluted urine samples fell within the reference concentration range of 50-550ng/mL. PMID:25175746

Huang, Chun-Yueh; O'Hare, Danny; Chao, I-Jen; Wei, Hung-Wei; Liang, Yi-Fan; Liu, Bin-Da; Lee, Mei-Hwa; Lin, Hung-Yin



Re-passivation Potential of Alloy 22 in Chloride plus Nitrate Solutions using the Potentiodynamic-Galvano-static-Potentiostatic Method  

SciTech Connect

In general, the susceptibility of Alloy 22 to suffer crevice corrosion is measured using the Cyclic Potentiodynamic Polarization (CPP) technique. This is a fast technique that gives rather accurate and reproducible values of re-passivation potential (ER1) in most cases. In the fringes of susceptibility, when the environment is not highly aggressive, the values of re-passivation potential using the CPP technique may not be highly reproducible, especially because the technique is fast. To circumvent this, the re-passivation potential of Alloy 22 was measured using a slower method that combines Potentiodynamic-Galvano-static-Potentiostatic steps (called here the Tsujikawa-Hisamatsu Electrochemical or THE method). The THE method applies the charge to the specimen in a more controlled way, which may give more reproducible re-passivation potential values, especially when the environment is not aggressive. The values of re-passivation potential of Alloy 22 in sodium chloride plus potassium nitrate solutions were measured using the THE and CPP methods. Results show that both methods yield similar values of re-passivation potential, especially under aggressive conditions. (authors)

Evans, Kenneth J. [Lawrence Livermore National Laboratory, Livermore, CA, 94550 (United States); Rebak, Raul B. [Chemistry and Materials Science, Lawrence Livermore National Laboratory, 7000 East Ave, L- 631, Livermore, CA, 94550 (United States)



Potentiostatic pulse-deposition of calcium phosphate on magnesium alloy for temporary implant applications - An in vitro corrosion study.  


In this study, a magnesium alloy (AZ91) was coated with calcium phosphate using potentiostatic pulse-potential and constant-potential methods and the in vitro corrosion behaviour of the coated samples was compared with the bare metal. In vitro corrosion studies were carried out using electrochemical impedance spectroscopy and potentiodynamic polarization in simulated body fluid (SBF) at 37C. Calcium phosphate coatings enhanced the corrosion resistance of the alloy, however, the pulse-potential coating performed better than the constant-potential coating. The pulse-potential coating exhibited ~3 times higher polarization resistance than that of the constant-potential coating. The corrosion current density obtained from the potentiodynamic polarization curves was significantly less (~60%) for the pulse-deposition coating as compared to the constant-potential coating. Post-corrosion analysis revealed only slight corrosion on the pulse-potential coating, whereas the constant-potential coating exhibited a large number of corrosion particles attached to the coating. The better in vitro corrosion performance of the pulse-potential coating can be attributed to the closely packed calcium phosphate particles. PMID:25427473

Kannan, M Bobby; Wallipa, O



Finite element analysis of lithium insertion-induced expansion of a silicon thin film on a rigid substrate under potentiostatic operation  

NASA Astrophysics Data System (ADS)

Diffusion-induced stress and volumetric expansion under potentiostatic operation are investigated with an axisymmetric finite element model taking account of plastic yielding, coupling effects between diffusion and stress, diffusion from the edge surface, and concentration dependence of material properties. Significant differences on stresses, displacements, and fracture energies between purely elastic and elastic-plastic materials are found. Plasticity based on von-Mises criterion has no effect on concentration variation. The critical regions for fracture are the edge surface, and the regions near the edges on both the top surface and the interface.

Liu, Ming



Evaluation of in-channel amperometric detection using a dual-channel microchip electrophoresis device and a two-electrode potentiostat for reverse polarity separations.  


In-channel amperometric detection combined with dual-channel microchip electrophoresis is evaluated using a two-electrode isolated potentiostat for reverse polarity separations. The device consists of two separate channels with the working and reference electrodes placed at identical positions relative to the end of the channel, enabling noise subtraction. In previous reports of this configuration, normal polarity and a three-electrode detection system were used. In the two-electrode detection system described here, the electrode in the reference channel acts as both the counter and reference. The effect of electrode placement in the channels on noise and detector response was investigated using nitrite, tyrosine, and hydrogen peroxide as model compounds. The effects of electrode material and size and type of reference electrode on noise and the potential shift of hydrodynamic voltammograms for the model compounds were determined. In addition, the performance of two- and three-electrode configurations using Pt and Ag/AgCl reference electrodes was compared. Although the signal was attenuated with the Pt reference, the noise was also significantly reduced. It was found that lower LOD were obtained for all three compounds with the dual-channel configuration compared to single-channel, in-channel detection. The dual-channel method was then used for the detection of nitrite in a dermal microdialysis sample obtained from a sheep following nitroglycerin administration. PMID:25256669

Meneses, Diogenes; Gunasekara, Dulan B; Pichetsurnthorn, Pann; da Silva, Jos A F; de Abreu, Fabiane C; Lunte, Susan M



The cell-impedance-controlled lithium transport through LiMn 2O 4 film electrode with fractal surface by analyses of ac-impedance spectra, potentiostatic current transient and linear sweep voltammogram  

Microsoft Academic Search

Lithium transport through the fractal LiMn2O4 film electrode under the cell-impedance-controlled constraint was investigated by employing ac-impedance spectroscopy, potentiostatic current transient technique and linear sweep voltammetry. For this purpose, the flat and fractal LiMn2O4 film electrodes were prepared on the as-deposited Pt\\/polished Al2O3 substrate and the surface modified Pt\\/unpolished Al2O3 substrate, respectively. From the analysis of the ac-impedance spectra obtained

Kyu-Nam Jung; Su-Il Pyun



Communication: Coordination structure of bromide ions associated with hexyltrimethylammonium cations at liquid/liquid interfaces under potentiostatic control as studied by total-reflection X-ray absorption fine structure  

NASA Astrophysics Data System (ADS)

Total-reflection X-ray absorption fine structure (TR-XAFS) technique was applied for the first time to an interface between two immiscible electrolyte solutions under potentiostatic control. The hydration structure of bromide ions was investigated at polarized 2-octanone/water interfaces. TR-XAFS spectra at Br K-edge measured in the presence of hexyltrimethylammonium bromide (C6TAB) were slightly modified depending on the Galvani potential difference ({? }_o^w ?). The extended X-ray absorption fine structure analysis exposed hydration structure changes of bromide ions at the polarized interface. The coordination structure of bromide ions at the interface could be analyzed as compared with bromide ions dissolved in aqueous solution and Br--exchanged resin having quaternary ammonium groups. The results indicated that bromide ions were associated with C6TA+ at the polarized interface. The relative contribution of ion association form of bromide ions with quaternary ammonium groups was enhanced at a potential close to the ion transfer of C6TA+, where the interfacial concentration of C6TA+ is increased as a function of {? }_o^w ?.

Nagatani, Hirohisa; Harada, Makoto; Tanida, Hajime; Sakae, Hiroki; Imura, Hisanori



An investigation of the potentiostatic current oscillation during the anodic dissolution of iron in sulfuric acid  

NASA Astrophysics Data System (ADS)

A dynamical system analysis is presented to disclose the origin of current oscillation during the anodic dissolution of iron in sulfuric acid. The threshold of the electrochemical oscillatory dynamical regime is discussed in the parameter plane. The necessary electrode potential for oscillation increases as the stirring speed of the electrolyte solution increases and there is a critical stirring speed above which stable limit cycle oscillation cannot appear. The polarization curve is calculated and there is a limiting current plateau. There is an electrode potential interval within which the non-equilibrium steady state is unstable and the system oscillates before the potential reaches the limiting current plateau region. The limiting current increases with increasing stirring speed.

Hua, Dayin; Luo, Jiuli



Study of Metal-NH[subscript 3] Interfaces (Metal= Cu, Ni, Ag) Using Potentiostatic Curves  

ERIC Educational Resources Information Center

Experiment is conducted to determine the kinetic parameters of metal-solution interfaces. During the experiment the kinetic parameters for the interfaces Cu-NH[subscript 3], Ag-NH[subscript 3] and Ni-NH[subscript 3] is easily determined.

Nunes, Nelson; Martins, Angela; Leitao, Ruben Elvas



VLSI Potentiostat Array with Oversampling Gain Modulation for Wide-Range Neurotransmitter  

E-print Network

spanning over six orders of magnitude from picoamperes to microamperes. The array offers 100fA input. INTRODUCTION STUDIES of neural pathways and the etiology of neuro- logical diseases, like epilepsy and stroke. Stana´cevi´c is with the Department of Electrical and Computer Engineering, Stony Brook University

Stanacevic, Milutin


Potentiostatic reversible photoelectrochromism: an effect appearing in nanoporous TiO2/Ni(OH)2 thin films.  


In the field of energy saving, finding composite materials with the ability of coloring upon both illumination and change of the applied electrode potential keeps on being an important goal. In this context, chemical bath deposition of Ni(OH)2 into nanoporous TiO2 thin films supported on conducting glass leads to electrodes showing both conventional electrochromic behavior (from colorless to dark brown and vice versa) together with photochromism at constant applied potential. The latter phenomenon, reported here for the first time, is characterized by fast and reversible coloration upon UV illumination. The bleaching kinetics shows first order behavior with respect to the Ni(III) centers in the film, and an order 1.2 with respect to electrons in the TiO2 film. From a more applied point of view, this study opens up the possibility of having two-mode smart windows showing not only conventional electrochromism but also reversible darkening upon illumination. PMID:24926989

Cibrev, Dejan; Jankulovska, Milena; Lana-Villarreal, Teresa; Gmez, Roberto



Photoinduced Thermal Copper Reduction onto Gold Nanocrystals under Potentiostatic Peter L. Redmond,* Erich C. Walter, and Louis E. Brus  

E-print Network

the pattern at a deposition rate of 0.1 nm of laser intensity and increases sharply with cathodic voltage in the underpotential deposition region+ reduction, leading to particle growth.1 The irradiation wave- length controls the particle shape. Plasmon



E-print Network

of the input current spanning over six orders of magnitude from picoamperes to microamperes. The array offers. INTRODUCTION STUDIES of neural pathways and the etiology of neurolog- ical diseases, like epilepsy and stroke. Thakor are with the Department of Biomedical Engineering, Johns Hopkins School of Medicine, Baltimore, MD

Fainman, Yeshaiahu


An investigation on the optimum corrosion protection potential for minimization of cavitation damage using the potentiostatic method in seawater.  


In this study, we replaced the expensive blade material with an aluminum-bronze alloy that has excellent corrosion resistance and cavitation characteristics and developed the corrosion protection method to improve durability using an electrochemical method. The objective of this study was to identify the electrochemical corrosion protection conditions to minimize cavitation damage due to generating hydrogen gas (2H?O + 2e? ? 2OH? + H?) by means of hydrogen overvoltage before the impact pressure of the cavity is transferred to the surface. In the constant potential experiment under the cavitation environment, the energy was reflected or cancelled out by collision of the cavities with the hydrogen gas generated by the hydrogen overvoltage. As a result, the optimal corrosion prevention potential in the dynamic state is assumed to be the range of -1.4 to -1.7 V, which is the range at which active polarization took place. PMID:23920179

Kim, Seong-Jong; Jang, Seok-Ki; Park, Jae-Cheul



Aerated Shewanella oneidensis in Continuously-fed Bioelectrochemical Systems for Power and Hydrogen Production  

Technology Transfer Automated Retrieval System (TEKTRAN)

We studied the effects of aeration of Shewanella oneidensis on potentiostatic current production, iron(III) reduction, hydrogen production in a microbial electrolysis cell, and electric power generation in a microbial fuel cell. The potentiostatic performance of aerated S. oneidensis was considerab...


Electrochemical characterization of various metal foils as a current collector of positive electrode for rechargeable lithium batteries  

Microsoft Academic Search

Electrochemical characterization of various metal foils as a current collector of the positive electrode for rechargeable lithium batteries was carried out by cyclic voltammetry, potentiostatic electrolysis and a.c. impedance measurement. Products of the potentiostatic electrolysis were determined by atomic absorption spectroscopy and gas chromatography\\/mass spectrometry. As a result, it was found that an aluminum foil seems to be the most

Chiaki Iwakura; Yuko Fukumoto; Hiroshi Inoue; Syunpei Ohashi; Satoshi Kobayashi; Hiroshi Tada; Masaaki Abe




EPA Science Inventory

An instrument has been designed, constructed, and evaluated for electrochemical measurements in flow streams. The instrument is basically a computer-controlled potentiostat with features that are necessary for measurements in flow streams. These features include real-time graphic...



Microsoft Academic Search

The recycling process studied deals with cobalt electrolytic recovery from Li-ion batteries by means of both galvanostatic and potentiostatic electrowinning followed by an electrochemical purification of the exhausted electrolyte. A good Co metal deposit with a purity of 99.95% was produced by working at 250 A\\/m 2 current density and 50 C temperature, while working in potentiostatic conditions (-0.9V vs.

L. Criscuoli; C. Lupi; M. Pasquali


A Study on Stress Corrosion Cracking of X70 Pipeline Steel in Carbonate Solution by EIS  

NASA Astrophysics Data System (ADS)

In this study, electrochemical impedance spectroscopy (EIS) simultaneously with the slow strain rate testing were used to investigate the stress corrosion cracking (SCC) behavior of X70 pipeline steel in high pH bicarbonate solution at different applied potentials. Potentiostatic EIS tests were also conducted at certain times to determine the changes associated with the SCC. Circuit models for the cracking were proposed by the use of the potentiostatic EIS measurements at different applied potentials. Finally, the results of the potentiostatic EIS tests and the SSR tests showed the decline of the circuit element resistance by increasing the stress which was related to the cracking. It was also observed that the X70 pipeline steel was most susceptible to SCC at potential of -650 mV versus SCE.

Shahriari, A.; Shahrabi, T.; Oskuie, A. A.



Effect of fcc-hcp phase transformation produced by isothermal aging on the corrosion resistance of a Co27Cr5Mo0.05C alloy  

Microsoft Academic Search

The corrosion resistance of two-phase (fcc-hcp) Co-27Cr-5Mo-0.05C alloys produced by isothermal aging at 800 C was studied\\u000a using potentiostatic polarization tests in Ringers solution. Critical pitting potentials were estimated from the potentiostatic\\u000a polarization curves and were found superior to that exhibited by the conventional ASTM-F75 cast alloy used for the manufacture\\u000a of orthopedic implants. Formation of suitable distributions of hcp

C. Montero-Ocampo; R. Juarez; A. Salinas Rodriguez



A Real Time Measuring Method for Complex Impedance in Biomedical Instrumentations  

NASA Astrophysics Data System (ADS)

The author proposes a measuring method of complex bioimpedance in real time by using a potentiostat circuit and LabVIEW programming tools. In the system, 4-electrode method is applied on the dc-coupled potentiostat. Complex impedance is calculated from the frequency response function in LabVIEW. The resolutions of the resistive and reactive components are about 0.005% respectively. As a preliminary experiment, the complex impedance on a middle finger at 1kHz is measured with sampling time of 10ms. Pulse waves of resistive components which are synchronizing with ECG are clearly observed and very small reactive components.

Dendo, Isao


Apparatus for use in rapid and accurate controlled-potential coulometric analysis  


An apparatus for controlled-potential coulometric analysis of a solution includes a cell to contain the solution to be analyzed and a plurality of electrodes to contact the solution in the cell. Means are provided to stir the solution and to control the atmosphere above it. A potentiostat connected to the electrodes controls potential differences among the electrodes. An electronic circuit connected to the potentiostat provides analog-to-digital conversion and displays a precise count of charge transfer during a desired chemical process. This count provides a measure of the amount of an unknown substance in the solution.

Frazzini, Thomas L. (Frankfort, IL); Holland, Michael K. (LaGrange Park, IL); Pietri, Charles E. (Downers Grove, IL); Weiss, Jon R. (Downers Grove, IL)



r XXXX American Chemical Society 1176 DOI: 10.1021/jz100188d |J. Phys. Chem. Lett. 2010, 1, 11761180  

E-print Network

electrodes with very high rate capability. SECTION Energy Conversion and Storage W hile commercial lithium graphite (HOPG). The results reveal inherent high lithium ion diffusivity in the direction parallel of reliable theoretical and experimental methods. Impedance spectroscopy,5-8 potentiostatic intermittent titra

Ceder, Gerbrand


In situ monitoring of the Li-O2 electrochemical reaction on nanoporous gold using electrochemical AFM.  


The lithium-oxygen (Li-O2) electrochemical reaction on nanoporous gold (NPG) is observed using in situ atomic force microscopy (AFM) imaging coupled with potentiostatic measurement. Dense Li2O2 nanoparticles form a film at 2.5 V, which is decomposed at 3.8-4.0 V in an ether-based electrolyte. PMID:24469227

Wen, Rui; Byon, Hye Ryung



Formation of Surface Oxides on 13% Chromium Stainless Steel  

Microsoft Academic Search

The objective with this work was to get a better understanding of the formation of protective surface oxides on 13% chromium steel in formation water. Formation of oxide was studied by an electrochemical quartz crystal micro balance (EQCM) and dynamic and potentiostatic polarization. The EQCM samples were produced by pulse laser deposition (PLD) of about 200 nm alloy on the

Ole ystein KNUDSEN; Thomas M. DEVINE


Electrochemical approach for passivating steel and other metals and for the simultaneous production of a biocide to render water potable  

NASA Technical Reports Server (NTRS)

Potentiostatic polarization curves indicated that the cathodic reactions in deaerated KI-I2 water solutions were due to iodine reduction and hydrogen evolution. In the presence of oxygen an additional reduction wave appeared. Anodic polarization curves revealed that iodine could be produced in the region of potential from +600 to +1000 nv vs. SCE.



Affordable Cyclic Voltammetry  

ERIC Educational Resources Information Center

Cyclic voltammetry is an important component of the undergraduate chemical curriculum. Unfortunately, undergraduate students rarely have the opportunity to conduct experiments in cyclic voltammetry owing to the high cost of potentiostats, which are required to control these experiments. By using MicroLab data acquisition interfaces in conjunction

Stewart, Greg; Kuntzleman, Thomas S.; Amend, John R.; Collins, Michael J.



Application of Bacterial Biocathodes in Microbial Fuel Cells Zhen He, Largus T. Angenent*  

E-print Network

Review Application of Bacterial Biocathodes in Microbial Fuel Cells Zhen He, Largus T. Angenent breakthroughs are made. Keywords: Microbial fuel cell, Biofuel cell, Biocathode, Potentiostat-poised half cell, microbial fuel cells (MFCs) are special types of biofuel cells, producing electric power by utilizing


Toward developing long-life water quality sensors for the ISS using planar REDOX and conductivity sensors  

NASA Technical Reports Server (NTRS)

REDOX and conductivity sensors are metal electrodes that are used to detect ionic species in solution by measuring the electrochemical cell current as the voltage is scanned. This paper describes the construction of the sensors, the potentiostat electronics, the measurement methodology, and applications to water quality measurements.

Buehler, M. G.; Kuhlman, G. M.; Keymeulen, D.; Myung, N.; Kounaves, S. P.



Cybernetic Control of an Electrochemical Repertoire.  

ERIC Educational Resources Information Center

Describes major features of a computer-operated, cybernetic potentiostat and the development, design, and operation of the software in ROM. The instrument contains control circuitry and software making it compatible with the static mercury drop electrode produced by EG&G Princeton Applied Research Corporation. Sample results using the instrument

He, Peixin; And Others



Voltammetry at the Thin-Film Mercury Electrode (TFME).  

ERIC Educational Resources Information Center

Reviewed is the use of the Thin-Film Mercury Electrode for anodic stripping voltammetry, simple voltammetry of solution cations and cathodic stripping voltammetry for the determination of an environmentally important molecule, thiourea. The construction of a simple potentiostat and applications for student laboratory courses are included. (CW)

Pomeroy, R. S.; And Others



Graphite electrodes as electron donors for anaerobic respiration  

Microsoft Academic Search

Summary It has been demonstrated previously that Geobacter species can transfer electrons directly to electrodes. In order to determine whether electrodes could serve as electron donors for microbial respiration, enrich- ment cultures were established from a sediment inoc- ulum with a potentiostat-poised graphite electrode as the sole electron donor and nitrate as the electron acceptor. Nitrate was reduced to nitrite

Kelvin B. Gregory; Daniel R. Bond; Derek R. Lovley



Silver nanowire arrays electrochemically grown into nanoporous anodic alumina templates  

Microsoft Academic Search

Silver nanowire arrays with high aspect ratios have been prepared using potentiostatic electrodeposition within the confined nanochannels of a commercial porous anodic aluminium oxide template. The nucleation and growth processes are intensively studied by current versus time transients. Scanning electron microscopy results show that the nanowires have a highly anisotropic structure with diameters and lengths of 170 nm and 58

G. Riveros; S. Green; A. Cortes; H. Gmez; R. E. Marotti; E. A. Dalchiele



Analysis of Cold Start in Polymer Electrolyte Fuel Cells Leng Mao and Chao-Yang Wang*,z  

E-print Network

-Emmett-Teller BET porosity analysis upon thermal cycling from 80 to - 10°C.2 They found that freezing-thawing leads al. used CV and BET to investigate MEA degradation in isothermal potentiostatic cold start.4,5 Cold


Surface pK(sub a) of Self-Assembled Monolayers  

ERIC Educational Resources Information Center

The difference between solution and surface properties such as pK(sub a) is illustrated enabling students to understand the differences between nanoscale and macroscopic systems. Details regarding the usage of electrochemical instrumentation, such as a potentiostat, and of the technique such as cyclic voltammetry are given.

Hale, Penny S.; Maddox, Leone M.; Shapter, Joe G.



Electroetching of Dental Amalgam  

Microsoft Academic Search

Application of the potentiostatic polarization technique to the metallographic etching of set dental amalgam is described. Etching studies of amalgam prepared from a lathe-cut, a spherical, and a silver-copper dispersed-phase amalgam alloy are reported. The ?2 phase in set dental amalgam can be characterized by this electrochemical technique.

P. J. Staheli; J. A. Von Fraunhofer



Preparation and dispersion of NiCu composite nanoparticles Yu-Guo Guo,y Li-Jun Wan,* Jian-Ru Gong and Chun-Li Bai*  

E-print Network

- cally in Fig. 1. The porous anodic aluminum oxide (AAO) templates were grown by potentiostatically properties, and their applica- tions in building advanced materials as nanoscale building blocks.1-controlled composite nanoparticles with special properties and high efficiency. Here we report a novel method

Gong, Jian Ru


Platinum particles deposited on synthetic boron-doped diamond surfaces. Application to methanol oxidation  

Microsoft Academic Search

Two methods have been used for the deposition of Pt particles on synthetic boron-doped diamond (BDD) surfaces: chemical deposition and electrodeposition under potentiostatic conditions. However, electrodeposition leads much higher platinum dispersion than chemical deposition. The mechanism of nucleation and growing of the electrodeposited platinum was investigated by means of chronoamperometric studies in acid medium. The electrodeposition on diamond surfaces shows

F. Montilla; E. Morallon; I. Duo; Ch. Comninellis; J. L. Vazquez




EPA Science Inventory

A low power, hand-held system has been developed for the measurement of heavy metal ions in aqueous solutions. The system consists of an electrode array sensor, a high performance single chip potentiostat and a microcontroller circuit. The sensor is a microfabricated array of ...


Talanta 58 (2002) 2331 Voltammetric measurement of arsenic in natural waters  

E-print Network

to contain arsenic at levels higher than the maximum contaminant level (MCL), on-site screening and a field portable potentiostat, at an arsenic contaminated site in southern New Jersey. © 2002 Elsevier arsenic and concludes with a report on the field analysis of arsenic at a contaminated site in southern

Kounaves, Samuel P.



E-print Network

Integrated Potentiostat for Neurotransmitter Sensing A High Sensitivity, Wide Range VLSI Design and Chip neurochemicals can be detected using electrochemi- cal principles but require a highly sensitive measurement-order single-bit delta-sigma modulator architecture with a digitally configurable oversampling ratio (OSR

Stanacevic, Milutin


Electrochemical behaviour of iron and copper in a culture solution for Spirulina platensis  

Microsoft Academic Search

Cyclic voltammograms of iron and copper electrodes were run in sodium hydroxide, carbonatebicarbonate buffer and culture media for Spirulina platensis at 30C. Potentiostatic steady state polarisation curves for both electrode surfaces in these electrolytes were performed in the presence and the absence of S. platensis at fixed temperature. Corrosion potential and corrosion current density values of iron and copper were

R. Malgor; G. Heijo; L. Romero; C. F. Zinola



Improvement in the Corrosion Resistance of Austenitic Stainless Steel 316L by Ion Implantation  

NASA Astrophysics Data System (ADS)

In the present work, austenitic stainless steel 316L (SS316L) samples were implanted with Ni and Ni-Cr. A nickel-rich layer about 100 nm in thickness and a Ni-Cr enriched layer about 60 nm thick are formed on the surface of SS316L. The effects of ion implantation on the corrosion performance of SS316L are investigated in a 0.5 M H2SO4 with 2 ppm HF solution at 80C by open circuit potential (OCP), potentiodynamic and potentiostatic tests. The samples after the potentiostatic test are analyzed by XPS. The results indicate that the composition of the passive film change from a mixture of Fe oxides and Cr oxide to a Cr oxide dominated passive film after the potentiostatic test. The solutions after the potentiostatic test are analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). The results reveal that Fe is selectively dissolved in all cases and a proper Ni and Ni-Cr implant fluence can greatly improve the corrosion resistance of SS316L in the simulated polymer electrolyte membrane fuel cells (PEMFCS) environment. They are in agreement with the electrochemical test results that the bare SS316L has the highest dissolution rate in both cathode and anode environments and the Ni and Ni-Cr implantation reduce markedly the dissolution rate. After the potentiostatic test the interfacial contact resistance (ICR) values are also measured. Ni and Ni-Cr are enriched in the passive film formed in the simulated PEMFC cathode environment after ion implantation thereby providing better conductivity than that formed in the anode one. A significant improvement of ICR is achieved for the SS316L implanted with Ni and Ni-Cr as compared to the bare SS316L, which is attributed to the reduction in passive layer thickness caused by Ni and Ni-Cr implantation. The ICR values for implanted specimens increase with increasing dose.

Cai, Xun; Feng, Kai


Design and Fabrication of Complementary Metal-Oxide-Semiconductor Sensor Chip for Electrochemical Measurement  

NASA Astrophysics Data System (ADS)

An electrochemical sensor has been developed on a single chip in which potentiostat and sensor electrodes are integrated. Sensor chips were fabricated using 5.0 ?m complementary metal-oxide-semiconductor (CMOS) technology. All processes including the CMOS process, postprocessing for fabricating sensor electrodes and passivation layers, and packaging were performed at Toyohashi University of Technology. The integration makes it possible to measure electrochemical signals without having to use a bulky external electrochemical system. The potential between the working electrode and the reference electrode was controlled using an on-chip potentiostat composed of CMOS transistors. The chip characteristics were verified by electrochemical measurement, namely, by cyclic voltammetry. Potassium ferricyanide solution was measured to obtain results that fit well to the theoretical formula. A clear proportional relationship between peak height and the concentration of the sample solution was obtained using the proposed sensor chip, and the dynamic range obtained was 0.10 to 8.0 mM.

Tomoyuki Yamazaki,; Takaaki Ikeda,; Yoshiko Kano,; Hidekuni Takao,; Makoto Ishida,; Kazuaki Sawada,



Design and Fabrication of Complementary Metal-Oxide-Semiconductor Sensor Chip for Electrochemical Measurement  

NASA Astrophysics Data System (ADS)

An electrochemical sensor has been developed on a single chip in which potentiostat and sensor electrodes are integrated. Sensor chips were fabricated using 5.0 m complementary metal-oxide-semiconductor (CMOS) technology. All processes including the CMOS process, postprocessing for fabricating sensor electrodes and passivation layers, and packaging were performed at Toyohashi University of Technology. The integration makes it possible to measure electrochemical signals without having to use a bulky external electrochemical system. The potential between the working electrode and the reference electrode was controlled using an on-chip potentiostat composed of CMOS transistors. The chip characteristics were verified by electrochemical measurement, namely, by cyclic voltammetry. Potassium ferricyanide solution was measured to obtain results that fit well to the theoretical formula. A clear proportional relationship between peak height and the concentration of the sample solution was obtained using the proposed sensor chip, and the dynamic range obtained was 0.10 to 8.0 mM.

Yamazaki, Tomoyuki; Ikeda, Takaaki; Kano, Yoshiko; Takao, Hidekuni; Ishida, Makoto; Sawada, Kazuaki



Selective dissolution in copper-tin alloys: Formation of corrosion- resistant patina on ancient Chinese bronze mirrors  

SciTech Connect

Many ancient Chinese bronze mirrors have survived with a patina that leaves the delicate relief surface decorations intact. The microstructure of these ancient mirrors is two-phase and consists of acicular {alpha}-phase (Cu-rich) regions encased in a {delta}-phase (Sn-rich) matrix. At the surface, there is evidence of selective dissolution of the ct phase; the cc-phase regions are replaced pseudomorphically by a mineral product with the {delta} phase remaining metallic. Electrochemical polarization has been used to drive the copper dealloying process in modem, cast bronze. Synchrotron x-ray diffraction was employed to compare the ancient samples with those that were prepared potentiostatically. Poorly crystallized tin oxide (SnO{sub 2}) was found in the {alpha} replacement products of both sample types. The corrosion-resistance of the potentiostatically-treated bronze samples was tested by atmospheric exposure. Comparison with exposed, untreated samples indicated that the treatment was protective.

Taube, M. [State Univ. of New York, Stony Brook, NY (United States). Dept. of Materials Science and Engineering]|[Brookhaven National Lab., Upton, NY (United States); Davenport, A.J. [Brookhaven National Lab., Upton, NY (United States); King, A.H. [State Univ. of New York, Stony Brook, NY (United States). Dept. of Materials Science and Engineering; Chase, T. III [Smithsonian Institution, Washington, D.C. (United States) Freer Gallery of Art, Dept. of Conservation and Scientific Research



Template-assisted electrodeposition of indium-antimony nanowires - Comparison of electrochemical methods  

NASA Astrophysics Data System (ADS)

Indium antimonide (InSb) is a III-V compound semiconductor that in a form of nanowires can possess improved thermoelectrical and optical properties compared to the corresponding bulk crystal. Here, we applied three electrodeposition techniques for a fast and inexpensive template-assisted fabrication of InSb nanowires from a sodium citrate-citric acid solution at room temperature. The home-made anodic aluminum oxide (AAO) templates with the pore diameter of 100 nm were used. InSb nanowires were synthesized by potentiostatic, galvanostatic and periodic pulse reverse techniques. The morphology, composition and crystallinity of as-obtained and annealed nanowires were investigated and compared with the literature data. It was found that the potentiostatic and pulse reverse methods gave crystalline nanowires. On the other hand, the constant current density deposition results in a partially amorphous nanowire material.

Hnida, Katarzyna; Mech, Justyna; Sulka, Grzegorz D.



Proton transfer in oxidized adenosine self-aggregates  

NASA Astrophysics Data System (ADS)

The UV-vis and the IR spectra of derivativized adenosine in dichloromethane have been recorded during potentiostatic oxidation at an optically transparent thin layer electrode. Oxidized adenosine shows a broad Zundel like absorption extending from 2800 up to 3600 cm-1, indicating that a proton transfer process is occurring. Theoretical computations predict that proton transfer is indeed favored in oxidized 1:1 self-association complexes and allow to assign all the observed transient spectroscopic signals.

Capobianco, Amedeo; Caruso, Tonino; Celentano, Maurizio; La Rocca, Mario Vincenzo; Peluso, Andrea



Caustic Stress Corrosion Cracking of Mild Steel  

Microsoft Academic Search

The stress corrosion cracking (SCC) behavior of cold worked mild steel in hot, aqueous, 33 pct NaOH solutions was studied\\u000a with prefatigue cracked double cantilever beam specimens. SCC kinetics were studied under freely corroding potentials (E\\u000a corr ? ?1.00 VSHE) and potentiostatic potentials of ?0.76 VSHE near the active-passive transition. The pH of the liquid within the crack was determined

Douglas Singbeil; Desmond Tromans



Corrosion Inhibition of Copper with Benzotriazole and Other Organic Surfactants  

Microsoft Academic Search

The corrosion behavior of copper with various organic inhibitors in aerated solutions at pH 1 to pH 2 was studied using a potentiostat. The inhibitors studied included benzotriazole (BTAH), hydroxy benzophenoximes, L-hydroxy-5-nonylacetophenone oxime, and sodium octyl hydroxamate (SOH). BTAH was shown to be the most effective of the inhibitors tested. Morphology of the copper substrate after corrosion in the presence

Y. Ling; K. N. Han; Y. Guan



Corrosion Inhibition of a Mild Steel by Aniline and Alkylamines in Acidic Solutions  

Microsoft Academic Search

Corrosion inhibition of a mild steel in acid solutions by alkylamines (ALK-AM) and aniline hydrochloric (ANL-HCl) salts was investigated in the presence of sodium sulfate (NaSO) and sodium chloride (NaCl) using a potentiostat, a contact-angle goniometer, a scanning electron microscope (SEM), a Fourier transform infrared spectrometer (FTIR), and an atomic force microscope (AFM). Results showed chloride ions (Cl⁻) had a

H. Luo; K. N. Han; Y. C. Guan



Structure and magnetism of electrodeposited ZnSe-Co granular films  

NASA Astrophysics Data System (ADS)

ZnSe-Co granular films have been electrodeposited under potentiostatic condition on polished stainless steel substrates. X-ray diffraction and transmission electron microscopy measurements indicate the formation of polycrystalline granular films with Co particles dispersed in an ZnSe matrix without evidence of intermediate compound formation. Magnetic measurements reveal low values of coercive field and remanence, indicating that the overall magnetic response of the deposited films is determined by multidomain nanosized particles.

de Moraes, A. R.; Mosca, D. H.; Mattoso, N.; Schreiner, W. H.; de Oliveira, A. J. A.; Ortiz, W. A.



Structure and magnetism of electrodeposited ZnSeCo granular films  

Microsoft Academic Search

ZnSeCo granular films have been electrodeposited under potentiostatic condition on polished stainless steel substrates. X-ray diffraction and transmission electron microscopy measurements indicate the formation of polycrystalline granular films with Co particles dispersed in an ZnSe matrix without evidence of intermediate compound formation. Magnetic measurements reveal low values of coercive field and remanence, indicating that the overall magnetic response of the

A. R de Moraes; D. H Mosca; N Mattoso; W. H Schreiner; A. J. A de Oliveira; W. A Ortiz



Development of a distributed, fully automated, bidirectional telemetry system for amperometric microsensor and biosensor applications  

Microsoft Academic Search

A new bidirectional telemetry system for amperometric sensor applications has been developed. A fully automated peripheral unit (PU), constituted by a potentiostat, a two-channel I\\/V converter, a microcontroller unit (MCU) and a signal transmitter, was designed, constructed, and tested. A peripheral interface controller (PIC) MCU drives a digital-to-analog converter (DAC), which polarized the sensor, while the resulting anodic current is

Gaia Rocchitta; Rossana Migheli; Sonia Dedola; Giammario Calia; Maria S. Desole; Egidio Miele; John P. Lowry; Robert D. ONeill; Pier A. Serra



Synthesis of gold nanowires with controlled crystallographic characteristics  

Microsoft Academic Search

The controlled fabrication of poly- and single-crystalline Au nanowires is reported. In polycarbonate templates, prepared by heavy-ion irradiation and subsequent etching, Au nanowires with diameters down to 25nm are electrochemically synthesized. Four-circle X-ray diffraction and transmission electron microscopy measurements demonstrate that wires deposited potentiostatically at a voltage of -1.2V at 65C are single-crystalline and oriented along the [110] direction. By

S. Karim; M. E. Toimil-Molares; F. Maurer; G. Miehe; W. Ensinger; J. Liu; T. W. Cornelius; R. Neumann



5-(Phenyl)-4H-1,2,4-triazole-3-thiol as a corrosion inhibitor for copper in 3.5% NaCl solutions  

Microsoft Academic Search

5-(Phenyl)-4H-1,2,4-triazole-3-thiol (PTAT) was synthesized and tested as a corrosion inhibitor for copper in stagnant and stirred 3.5% NaCl solutions using potentiodynamic polarization, potentiostatic current time, weight loss and pH measurements along with Fourier transform infrared spectroscopy (FT-IR) investigation. Potentiodynamic polarization measurements indicated that the presence of PTAT in both stagnant and stirred solutions decreases cathodic, anodic and corrosion currents, polarization

El-Sayed M. Sherif; A. M. El Shamy; Mostafa M. Ramla; Ahmed O. H. El Nazhawy



Preferential dissolution behaviour in Ni-Cr dental cast alloy  

Microsoft Academic Search

A Ni-Cr-Mo dental alloy was fabricated by three different casting methods, viz. centrifugal casting, high frequency induction\\u000a casting and vacuum pressure casting. The dependence of cast microstructure on the electrochemical corrosion behaviour was\\u000a investigated using potentiodynamic cyclic and potentiostatic polarization techniques, impedance spectroscopy and scanning\\u000a electron microscopy. The experimental results were compared and discussed with those obtained for a Co-Cr-Mo

Viswanathan S. Saji; Han Cheol Choe



Characterization and corrosion behavior of injection molded 17-4 PH steel electrochemically coated with poly[ trans -dichloro(4-vinylpyridine)ruthenium  

Microsoft Academic Search

The present study describes preliminary results on the corrosion resistance of injection molded 17-4 PH stainless steel potentiostatically\\u000a coated with poly {trans-[RuCl2(vpy)4]}, where vpy (4-vinylpyridine) acts as a ligand. The coated electrodes were characterized by scanning electron microscopy\\u000a and energy dispersive spectroscopy, as well as by electrochemical techniques. The microstructural analysis indicated that\\u000a the films reached up to 100??m thickness.

A. V. C. Sobral; W. Ristow Jr.; S. C. Domenech; C. V. Franco



Evaluation of a diffusion\\/trapping model for hydrogen ingress in high-strength alloys. Final technical report, November 1988November 1990  

Microsoft Academic Search

The objective of this research was to obtain the hydrogen ingress and trapping characteristics for a range of microstructures and so identify the dominant type of irreversible trap in different alloys. A diffusion\\/trapping model was used in conjunction with a potentiostatic pulse technique to study the ingress of hydrogen in three precipitation-hardened alloys (Inconel 718, Incoloy 925, and 18Ni maraging




The kinetics of lithium transport through a composite electrode made of mesocarbon-microbeads heat-treated at 800C investigated by current transient analysis  

Microsoft Academic Search

\\u000a Lithium transport through a mesocarbon-microbeads composite electrode was investigated in a 1M LiPF6 solution in ethylene carbonate\\/diethyl carbonate (1:1 by vol%) using a galvanostatic intermittent titration technique and\\u000a a potentiostatic current transient technique. From analysis of the anodic current transient it is recognized that when the\\u000a potential step is small enough for the lithium extraction potential to be below

Seung-Bok Lee; Su-Il Pyun



Investigation of lithium transport through LiMn 2O 4 film electrode in aqueous LiNO 3 solution  

Microsoft Academic Search

Lithium transport through LiMn2O4 film electrode was investigated in aqueous saturated LiNO3 solution by analyses of the potentiostatic current transient and ac-impedance spectra. It was found that the current transient hardly shows the Cottrell behaviour, and the initial current is linearly proportional to the potential step. This strongly suggests that lithium transport through the film electrode proceeds in aqueous LiNO3

Jong-Won Lee; Su-Il Pyun



Poly(3,4-ethylenedioxithiophene)\\/MnO 2 composite electrodes for electrochemical capacitors  

Microsoft Academic Search

Composite electrodes of poly(3,4-ethylenedioxithiophene) and manganese oxide (PEDOT\\/MnO2) have been prepared by electrodeposition of manganese oxide over PEDOT-modified titanium substrate. The PEDOT layers are deposited on titanium by potentiostatic deposition at 1.4V and at two different temperatures: 5 and 25C (named PEDOT(5) and PEDOT(25), respectively). The electrodes are characterized by field emission gun scanning electron microscopy (FEG-SEM) and their electrochemical

Emerson C. Rios; Alessandra A. Correa; Fernando H. Cristovan; Leandro A. Pocrifka; Adriane V. Rosario


Cavitation erosion and pitting corrosion behaviour of laser surface-melted martensitic stainless steel UNS S42000  

Microsoft Academic Search

Surface modification of martensitic stainless steel UNS S42000 was achieved by laser surface-melting using a 3.5-kW continuous wave CO2 laser. The cavitation erosion and corrosion characteristics of laser surface-melted specimens in 3.5% NaCl solution at 23C were studied by means of a 20-kHz ultrasonic vibrator at a peak-to-peak amplitude of 30 ?m and a potentiostat, respectively. In a series of

C. T Kwok; H. C Man; F. T Cheng



A Scanning Auger Microprobe analysis of corrosion products associated with sulfate reducing bacteria  

SciTech Connect

A Scanning Auger Microprobe analysis was performed on the corrosion products of an austenitic AISI type 304 SS after a potentiostatic polarization of one volt for ten minutes in a modified Postgate`s C media containing sulfate reducing bacteria. The corrosion products were characterized and mapped in local regions where pitting was observed. A critical evaluation of the applicability of this technique for the examination of microbially influenced corrosion (MIC) is presented.

Sadowski, R.A.; Chen, G.; Clayton, C.R.; Kearns, J.R. [State Univ. of New York, Stony Brook, NY (United States). Dept. of Materials Science and Engineering; Gillow, J.B.; Francis, A.J. [Brookhaven National Lab., Upton, NY (United States). Biosystems and Process Sciences Div.



Lead-based systems as suitable anode materials for Li-ion batteries  

Microsoft Academic Search

Three lead-based materials formed by PbO2, PbO and Pb as main phases were prepared by following different synthetic procedures and tested as anodic materials in Li-ion batteries by using potentiostatic and galvanostatic methods. While the reduction of Pb(IV) to Pb(II) takes place in a single step, that of Pb(II) to Pb is a complex process involving several steps. Both reduction

M. Martos; J. Morales; L. Snchez



Fabrication and nanostructure study of ultra thin electroplating constantan film on GaAs as a thermopower sensor  

Microsoft Academic Search

Ultra thin film of constantan was potentiostatically electrodeposited on n-type GaAs (111) from a citrate electrolyte containing both copper and nickel ions. SEM and EDX analyses were used to determine the film quality and composition. In order to fabricate high quality constantan alloy the optimum values of deposition potential and solution temperature were respectively found -1.45 V and 22-26 C

I. Kazeminezhad; E. Khoshbakht; M. Farbod



Electroplating and Nanostructure Study of Ultra Thin Cu\\/Constantan Bilayer on GaAs from Citrate and Sulphamate Electrolytes  

Microsoft Academic Search

In this research, ultra thin film of constantan was potentiostatically electrodeposited on n-type GaAs from a citrate and sulphamate electrolytes containing both copper and nickel ions. In order to remove the oxide layers on GaAs all substrates were rinsed in 10%NH3 aqueous solution. SEM and EDX analysis were respectively used to determine the film morphology and composition. With using CV

I. Kazeminezhad; E. Khoshbakht; M. Farbod


Preparation and characterization of polyaniline film on stainless steel by electrochemical polymerization as a counter electrode of DSSC  

Microsoft Academic Search

Polyaniline (PANI) films were electrodeposited on stainless steel 304 (SS) from 0.5M H2SO4 solution containing 0.3M aniline by potentiostatic techniques to prepare a low cost and non-fragile counter electrode in dye-sensitized solar cell (DSSC). The compact layer, micro-particles, nanorods and fibrils were observed on the top of PANI films with different applied potentials (Eappl) by SEM. Then the conductivity and

Qi Qin; Jie Tao; Yan Yang



Magnetic hybrid modified electrodes, based on magnetite nanoparticle containing polyaniline and poly(3,4-ethylenedioxythiophene)  

Microsoft Academic Search

In this paper, we report on the direct electrodeposition of magnetic hybrids based on magnetite nanoparticle containing poly(3,4-ethylenedioxythiophene)\\u000a (PEDOT) and polyaniline (PANI) in the presence of magnetite and the special conducting electrolyte, potassium tetraoxalate.\\u000a The optimal electropolymerization processes (monitored by scanning electron microscopy) were performed potentiostatically,\\u000a and the incorporation of the iron oxide into the polymeric film was demonstrated by

Csaba Janky; Attila Kormnyos; Csaba Visy


The electrochemical behaviour of polycrystalline nickel electrodes in different carbonate-bicarbonate ion-containing solutions  

Microsoft Academic Search

The dissolution and passivation of polycrystalline nickel in carbonate-bicarbonate ion-containing solutions covering wide ranges of pH and electrolyte concentration were investigated by employing voltammetric, galvanostatic and potentiostatic transient techniques. Results obtained with a rotating disc electrode allow the competing reactions related to the active-passive transition to be distinguished through the influence of the potential sweep rate and the rotation speed

A. E. Boh; J. R. Vilche; A. J. Arvia



Pretreatment effects on the electrochemical responses for aluminiummagnesium alloy AA5083 corrosion behaviour  

Microsoft Academic Search

Electrochemical investigations on aluminium alloy corrosion in a sodium chloride solution have been performed by potentiostatic\\u000a and potentiodynamic (electrochemical impedance spectroscopy) methods. Measurements have been obtained after mechanical polishing\\u000a or electrochemical stripping in deaerated or not solution. All the results are strongly depending on the pretreatments that\\u000a are undergone in the laboratory before the experimental measurements. Mechanical polishing induces huge

Nacer Zazi; Ahcne Bouabdallah; Omar Aaboubi; J.-P. Chopart



Effect of chemical etching and aging in boiling water on the corrosion resistance of Nitinol wires with black oxide resulting from manufacturing process.  


The effect of chemical etching in a HF/HNO(3) acid solution and aging in boiling water on the corrosion resistance of Nitinol wires with black oxide has been evaluated with the use of potentiodynamic, modified potentiostatic ASTM F746, and scratch tests. Scanning-electron microscopy, elemental XPS, and Auger analysis were employed to characterize surface alterations induced by surface treatment and corrosion testing. The effect of aging in boiling water on the temperatures of martensitic transformations and shape recovery was evaluated by means of measuring the wire electroresistance. After corrosion tests, as-received wires revealed uniformly cracked surfaces reminiscent of the stress-corrosion-cracking phenomenon. These wires exhibited negative breakdown potentials in potentiostatic tests and variable breakdown potentials in potentiodynamic tests (- 100 mV to + 400 mV versus SCE). Wires with treated surfaces did not reveal cracking or other traces of corrosion attacks in potentiodynamic tests up to + 900-1400-mV potentials and no pitting after stimulation at + 800 mV in potentiostatic tests. They exhibited corrosion behavior satisfactory for medical applications. Significant improvement of corrosion parameters was observed on the reverse scans in potentiodynamic tests after exposure of treated wires to potentials > 1000 mV. In scratch tests, the prepared surfaces repassivated only at low potentials, comparable to that of stainless steel. Tremendous improvement of the corrosion behavior of treated Nitinol wires is associated with the removal of defect surface material and the growth of stable TiO(2) oxide. The role of precipitates in the corrosion resistance of Nitinol-scratch repassivation capacity in particular-is emphasized in the discussion. PMID:12808592

Shabalovskaya, S; Rondelli, G; Anderegg, J; Simpson, B; Budko, S



Convection of tin in a Bridgman system. II - An electrochemical method for detecting flow regimes  

NASA Technical Reports Server (NTRS)

An ampoule was designed in order to obtain local flow behavior of the flow fields for convection of tin in a vertical Bridgman configuration. Multiple electrochemical cells were located along the periphery of the ampoule. Oxygen was titrated into the ampoule at one of the cell locations using a potentiostat and the concentration of oxygen was monitored at the other cell locations by operating the cells in a galvanic mode. Onset of oscillations were detected by means of thermocouples. We conclude that the flows are generally three dimensional for an aspect ratio of 5. Results on oscillations concurred with those of earlier workers. Suggestions for improved designs were made.

Sears, B.; Fripp, A. L.; Debnam, W. J., Jr.; Woodell, G. A.; Anderson, T. J.; Narayanan, R.



Local probing of ionic diffusion by electrochemical strain microscopy: Spatial resolution and signal formation mechanisms  

SciTech Connect

Electrochemical insertion-deintercalation reactions are typically associated with significant change in molar volume of the host compound. This strong coupling between ionic currents and strains underpins image formation mechanisms in electrochemical strain microscopy (ESM), and allows exploring the tip-induced electrochemical processes locally. Here we analyze the signal formation mechanism in ESM, and develop the analytical description of operation in frequency and time domains. The ESM spectroscopic modes are compared to classical electrochemical methods including potentiostatic and galvanostatic intermittent titration, and electrochemical impedance spectroscopy. This analysis illustrates the feasibility of spatially resolved studies of Li-ion dynamics on the sub-10-nm level using electromechanical detection.

Morozovska, A.; Eliseev, E.; Balke, N.; Kalinin, S. V.



Over 95% of large-scale length uniformity in template-assisted electrodeposited nanowires by subzero-temperature electrodeposition  

PubMed Central

In this work, we report highly uniform growth of template-assisted electrodeposited copper nanowires on a large area by lowering the deposition temperature down to subzero centigrade. Even with highly disordered commercial porous anodic aluminum oxide template and conventional potentiostatic electrodeposition, length uniformity over 95% can be achieved when the deposition temperature is lowered down to -2.4C. Decreased diffusion coefficient and ion concentration gradient due to the lowered deposition temperature effectively reduces ion diffusion rate, thereby favors uniform nanowire growth. Moreover, by varying the deposition temperature, we show that also the pore nucleation and the crystallinity can be controlled. PMID:21781335



Anodic behaviour of a metallic U-Pu-Zr alloy during electrorefining process  

NASA Astrophysics Data System (ADS)

Electrorefining tests of the non-irradiated U-Pu-Zr alloy were performed in LiCl-KCl-UCl 3-PuCl 3-ZrCl 4 melts at 773 K, aiming at reduced Zr dissolution. The tests were carried out both using potentiostatic electrolysis at -1.0 V (vs. Ag +/Ag), i.e. at a more negative potential than the Zr dissolution potential, and galvanostatic electrolysis with a limited amount of Zr dissolution. The ICP-AES analysis of the anode residues confirmed that a high dissolution yield of actinides (U: >99.6%, Pu: 99.9%) was successfully demonstrated for both electrolyses.

Murakami, T.; Sakamura, Y.; Akiyama, N.; Kitawaki, S.; Nakayoshi, A.; Fukushima, M.



Specific features of formation and growth mechanism of multilayered quasi-one-dimensional (Co-Ni-Fe)/Cu systems in pores of anodic alumina matrices  

NASA Astrophysics Data System (ADS)

A method for fabricating multilayered quasi-one-dimensional ferromagnet-diamagnet systems is described by the example of Co-Ni-Fe/Cu nanowires. The fabrication is implemented in a unified technological cycle from a combined electrolyte by pulsed potentiostatic electrodeposition. Regimes of the formation of layers of different systems, from pure ferromagnetic metals to alloys on their basis, are described. Mechanisms of nanowire growth are proposed. The distribution of chemical elements in the layers is investigated as a function of the electrolyte composition and the fabrication conditions. The nanowire microstructure is investigated by high-resolution scanning electron microscopy.

Trukhanov, A. V.; Grabchikov, S. S.; Vasiliev, A. N.; Sharko, S. A.; Mukhurov, N. I.; Gasenkova, I. V.



Electrochemical behaviour of uranium (IV) in DMF at vitreous carbon  

Microsoft Academic Search

The electrochemical behaviour of UCl4 (0.01molL?1 up to 0.05molL?1) in 0.1molL?1 TBAPF6\\/DMF solution at vitreous carbon was studied, at room temperature, by cyclic voltammetry and potentiostatic techniques. The electrolytic solutions were analyzed by UV spectroscopy (UV), and the electrodeposited films were characterized by Rutherford Backscattering Spectroscopy (RBS) and X-ray diffraction (XRD). The cyclic voltammetric results, at low UCl4 concentrations (0.01molL?1),

M. L. Afonso; A. Gomes; A. Carvalho; L. C. Alves; F. Wastin; A. P. Gonalves



Electrochemical Reactions During Ru Chemical Mechanical Planarization and Safety Considerations  

NASA Astrophysics Data System (ADS)

We analyzed electrochemical reactions during ruthenium (Ru) chemical mechanical planarization (CMP) using a potentiostat and a quartz crystal microbalance, and considered the potential safety issues. We evaluated the valence number derived from Faraday's law using the dissolution mass change of Ru and total coulomb consumption in the electrochemical reactions for Ru in acidic solution and slurry. The valence numbers of dissolved Ru ions were distributed in the range of 2 to 3.5. As toxic ruthenium tetroxide (RuO4) has a valence number of 8, we were able to conclude that no toxic RuO4 was produced in the actual Ru CMP.

Shima, Shohei; Wada, Yutaka; Tokushige, Katsuhiko; Fukunaga, Akira; Tsujimura, Manabu



Inhibitive Effect of L-Oh on the Corrosion of Austenitic Chromium-Nickel Steel in H2SO4 Solution  

Microsoft Academic Search

The corrosion behavior of the austenitic chromium-nickel steel in different concentrations (0.001, 0.002, 0.005, and 0.01 M) of dimethyl 2-(2-hydroxy phenyl amino)-3-(triphenyl phosphoranilidin) butane dioate (L-OH) in 0.5 M H2SO4 was investigated by potentiostatic polarization measurements. The effect of concentration and temperature on inhibition properties was determined. It was found that the presence of L-OH reduces markedly the corrosion rate

S. M. A. Hosseini; M. Amiri; A. Momeni



Comparative study on corrosion behaviour of Nitinol and stainless steel orthodontic wires in simulated saliva solution in presence of fluoride ions.  


Localized corrosion and effects of pre-passivation treatment of Nitinol and SS304 orthodontic wires in simulated saliva solution in the presence and absence of fluoride ions were investigated by means of potentiodynamic and potentiostatic polarisations. Results revealed that Nitinol does not show pitting corrosion in saliva solution however, SS304 shows pitting corrosion. Meanwhile fluoride ion has deteriorative effect on pitting corrosion of Nitinol, while its effect on SS304 was marginally constructive. Additionally, the presence of artificial crevice has no effect on corrosion behaviour in the presence of fluoride. Pre-passivation treatment has positive influence on pitting corrosion of both alloys in the presence of F(-) ions. PMID:23498236

Mirjalili, M; Momeni, M; Ebrahimi, N; Moayed, M H



Cooperative stochastic behavior in localized corrosion. 1: Model  

SciTech Connect

A stochastic model for localized corrosion is investigated both analytically and numerically. A feature of the model is that each metastable pitting event can influence subsequent events, although the influence of an individual event decays with time. The model describes an abrupt, cooperative transition from metastable to stable pitting, both under constant, e.g., potentiostatic conditions, and under conditions corresponding to an anodic scan. The model accounts for several commonly observed distributions in pitting parameters. Histograms for the induction times for transition to stable pitting and for stable pitting potentials are presented.

Wu, B.; Scully, J.R.; Hudson, J.L. [Univ. of Virginia, Charlottesville, VA (United States); Mikhailov, A.S. [Max-Planck-Gesellschaft, Berlin (Germany). Fritz-Haber Institut



Fabrication and nanostructure study of ultra thin electroplating constantan film on GaAs as a thermopower sensor  

NASA Astrophysics Data System (ADS)

Ultra thin film of constantan was potentiostatically electrodeposited on n-type GaAs (111) from a citrate electrolyte containing both copper and nickel ions. SEM and EDX analyses were used to determine the film quality and composition. In order to fabricate high quality constantan alloy the optimum values of deposition potential and solution temperature were respectively found -1.45 V and 22-26 C using the SEM analyses. The SEM images also showed that the grain size of the alloy extremely increases for the films with thickness of above 400 nm.

Kazeminezhad, I.; Khoshbakht, E.; Farbod, M.



Study of the corrosion behavior of titanium and some of its alloys for biomedical and dental implant applications  

Microsoft Academic Search

The influence of alloying elements and the potential on the corrosion resistance of Ti and other Ti-based biomedical implant alloys under simulated physiological conditions is presented. Ti and its following alloys: Ti?10Mo, Ti?10Mo?10Al, Ti?7Al?4.5V and Ti?5Al?4.5V and Ti?5Al?2.5Fe were studied. Electrochemical impedance spectroscopy was used and the experimental results were compared with those obtained by potentiostatic and potentiodynamic techniques. All

J. E. G Gonzlez; J. C Mirza-Rosca



Patterned electrochemical deposition of copper using an electron beam  

SciTech Connect

We describe a technique for patterning clusters of metal using electrochemical deposition. By operating an electrochemical cell in the transmission electron microscope, we deposit Cu on Au under potentiostatic conditions. For acidified copper sulphate electrolytes, nucleation occurs uniformly over the electrode. However, when chloride ions are added there is a range of applied potentials over which nucleation occurs only in areas irradiated by the electron beam. By scanning the beam we control nucleation to form patterns of deposited copper. We discuss the mechanism for this effect in terms of electron beam-induced reactions with copper chloride, and consider possible applications.

Heijer, Mark den [Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden (Netherlands); Shao, Ingrid; Reuter, Mark C.; Ross, Frances M., E-mail: [IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, New York 10598 (United States); Radisic, Alex [IMEC, Kapeldreef 75, B-3001 Leuven (Belgium)



Integrated Nanopore Detectors in a Standard Complementary Metal-Oxide-Semiconductor Process  

NASA Astrophysics Data System (ADS)

High-bandwidth and low-noise nanopore sensor and detection electronics are crucial in achieving single-DNA base resolution. A potential way to accomplish this goal is to integrate solid-state nanopores within a CMOS platform, in close proximity to the biasing electrodes and custom-designed amplifier electronics. Here we report the development of solid-state nanopore devices in a commercial CMOS potentiostat chip implemented in On-Semiconductor's 0.5 micron technology. By using post-CMOS micromachining, a free-standing oxide membrane and electrodes are fabricated utilizing the N+ polysilicon/oxide/N+ polysilicon capacitor structure available in the aforementioned process. Nanopores with sub-5 nm diameter are drilled in the membrane using a Transmission Electron Microscope. The integrity of pores is validated by measuring current-voltage and noise characteristics. DNA translocation experiments are also performed utilizing these on-chip pores. In addition, electrical tests performed on the CMOS potentiostat circuitry show that the post-CMOS micromachining process does not have any detrimental effect on the CMOS circuitry.

Uddin, Ashfaque; Chen, Chin-Hsuan; Yemenicioglu, Sukru; Milaninia, Kaveh; Corigliano, Ellie; Varma, Madoo; Theogarajan, Luke



Amperometric measurements of ethanol on paper with a glucometer.  


Recent advances in electrochemical analysis on filter paper exemplify the versatility of this substrate for high performance testing. Its low-cost, light-weight, and environmentally friendly properties make it particularly attractive for applications in addressing health and environmental safety needs in low-resource settings and developing countries. However, the main drawback to sensitive electrochemical testing is the use of a potentiostat, a bench-top instrument that is extremely expensive, thereby negating the some of the benefits of paper-based devices. Hence there is a need to develop paper-devices for use with handheld, portable device readers that can extract quantitative readouts. In this study, we developed a method to use micro-paper electrochemical devices, or PEDs, with a glucose meter, which are used for personal monitoring of blood glucose levels. Ethanol was chosen as a model target analyte due to its importance in the global issue of road safety. PEDs were simple in design and could be tested with a potentiostat. We observed that inclusion of the stabilizer trehalose was critical to preparing PEDs for later analysis. In addition, an NAD(+)-dependent enzyme was used to impart selectivity to the biosensor, which also represents a class of enzymes with targets relevant to the health and food industry. PMID:25618657

Wu, Grace; Zaman, Muhammad H



Analytical modeling of dislocation effect on diffusion induced stress in a cylindrical lithium ion battery electrode  

NASA Astrophysics Data System (ADS)

This paper is theoretically suggested to describe the combined effects of diffusion induced stress and dislocation induced stress in a cylinder lithium ion battery electrode on the nucleation and propagation of cracks under galvanostatic or potentiostatic solute insertion and extraction. By the conventional assumption, we develop this model accounting for dislocation mechanics in a cylindrical electrode under axisymmetric diffusion induced stress, focusing on the dislocation and size effects on the magnitude and distribution of the combined DIS during galvanostatic or potentiostatic condition. The results show that dislocation induced stress can decrease tensile stress, and converts the state of stress from tensile to compressive. The trend of the crack nucleation and propagation can be prevented as the cylindrical particle radius drops down to nanoscale range. Dislocation induced stress suppressing the crack nucleation, however, provides a novel way of mitigating internal damage in a cylindrical lithium ion battery during cycling. It may be used in conjunction with the methods of nano-engineering to create microstructures tailored to maximize suppressing the crack nucleation, yielding new strategy to improve battery life and avoid failure.

Li, Jia; Fang, Qihong; Liu, Feng; Liu, Youwen



Growth and Etch Rate Study of Low Temperature Anodic Silicon Dioxide Thin Films  

PubMed Central

Silicon dioxide (SiO2) thin films are most commonly used insulating films in the fabrication of silicon-based integrated circuits (ICs) and microelectromechanical systems (MEMS). Several techniques with different processing environments have been investigated to deposit silicon dioxide films at temperatures down to room temperature. Anodic oxidation of silicon is one of the low temperature processes to grow oxide films even below room temperature. In the present work, uniform silicon dioxide thin films are grown at room temperature by using anodic oxidation technique. Oxide films are synthesized in potentiostatic and potentiodynamic regimes at large applied voltages in order to investigate the effect of voltage, mechanical stirring of electrolyte, current density and the water percentage on growth rate, and the different properties of as-grown oxide films. Ellipsometry, FTIR, and SEM are employed to investigate various properties of the oxide films. A 5.25?/V growth rate is achieved in potentiostatic mode. In the case of potentiodynamic mode, 160?nm thickness is attained at 300?V. The oxide films developed in both modes are slightly silicon rich, uniform, and less porous. The present study is intended to inspect various properties which are considered for applications in MEMS and Microelectronics. PMID:24672287

Ashok, Akarapu; Pal, Prem



Polarization characteristics of novel molten carbonate fuel cell anodes and cathodes using three-dimensional electrodes  

SciTech Connect

The electrode performance of molten carbonate fuel cell anode and cathode using three-dimensional electrodes has been examined experimentally with the low Btu gas containing H{sub 2}S. A three-dimensional electrode half-cell of 42 mm inside diameter and 500 mm in height was used with an air/CO{sub 2}/gold reference electrode at 923 K. Nickel and copper particles were used as the electrode particles in the anode and cathode, respectively. Fuel gas containing H{sub 2}S with levels of 0-200 ppm was fed into the anode at a velocity of 7.7 mm/s. Oxidant gas was fed into the cathode at a velocity between 1.5 - 7.0 mm/s. Steady-state polarization curves for anodes and cathodes were measured potentiostatically using a potentiostat. Degradation of electrode performance by H{sub 2}S in the fuel gas was studied at various concentration of H{sub 2}S. It was found that the fluidized-bed electrode MCFC can tolerate high level of H2S for a long period of operation time. 6 refs., 7 figs., 1 tab.

Matsuno, Yasunari; Tsutsumi, Atsushi; Yoshida, Kunio [Univ. of Tokyo (Japan)



An approach to an inhibition electronic tongue to detect on-line organophosphorus insecticides using a computer controlled multi-commuted flow system.  


An approach to an inhibition bioelectronic tongue is presented. The work is focused on development of an automated flow system to carry out experimental assays, a custom potentiostat to measure the response from an enzymatic biosensor, and an inhibition protocol which allows on-line detections. A Multi-commuted Flow Analysis system (MCFA) was selected and developed to carry out assays with an improved inhibition method to detect the insecticides chlorpyrifos oxon (CPO), chlorfenvinfos (CFV) and azinphos methyl-oxon (AZMO). The system manifold comprised a peristaltic pump, a set of seven electronic valves controlled by a personal computer electronic interface and software based on LabView to control the sample dilutions into the cell. The inhibition method consists in the injection of the insecticide when the enzyme activity has reached the plateau of the current; with this method the incubation time is avoided. A potentiostat was developed to measure the response from the enzymatic biosensor. Low limits of detection of 10 nM for CPO, CFV, and AZMO were achieved. PMID:22163822

Alonso, Gustavo A; Dominguez, Rocio B; Marty, Jean-Louis; Muoz, Roberto



Waste Water Derived Electroactive Microbial Biofilms: Growth, Maintenance, and Basic Characterization  

PubMed Central

The growth of anodic electroactive microbial biofilms from waste water inocula in a fed-batch reactor is demonstrated using a three-electrode setup controlled by a potentiostat. Thereby the use of potentiostats allows an exact adjustment of the electrode potential and ensures reproducible microbial culturing conditions. During growth the current production is monitored using chronoamperometry (CA). Based on these data the maximum current density (jmax) and the coulombic efficiency (CE) are discussed as measures for characterization of the bioelectrocatalytic performance. Cyclic voltammetry (CV), a nondestructive, i.e. noninvasive, method, is used to study the extracellular electron transfer (EET) of electroactive bacteria. CV measurements are performed on anodic biofilm electrodes in the presence of the microbial substrate, i.e. turnover conditions, and in the absence of the substrate, i.e. nonturnover conditions, using different scan rates. Subsequently, data analysis is exemplified and fundamental thermodynamic parameters of the microbial EET are derived and explained: peak potential (Ep), peak current density (jp), formal potential (Ef) and peak separation (?Ep). Additionally the limits of the method and the state-of the art data analysis are addressed. Thereby this video-article shall provide a guide for the basic experimental steps and the fundamental data analysis. PMID:24430581

Gimkiewicz, Carla; Harnisch, Falk



Nanopore formation on the surface oxide of commercially pure titanium grade 4 using a pulsed anodization method in sulfuric acid.  


Titanium and its alloys form a thin amorphous protective surface oxide when exposed to an oxygen environment. The properties of this oxide layer are thought to be responsible for titanium and its alloys biocompatibility, chemical inertness, and corrosion resistance. Surface oxide crystallinity and pore size are regarded to be two of the more important properties in establishing successful osseointegration. Anodization is an electrochemical method of surface modification used for colorization marking and improved bioactivity on orthopedic and dental titanium implants. Research on titanium anodization using sulphuric acid has been reported in the literature as being primarily conducted in molarity levels 3 M and less using either galvanostatic or potentiostatic methods. A wide range of pore diameters ranging from a few nanometers up to 10 ?m have been shown to form in sulfuric acid electrolytes using the potentiostatic and galvanostatic methods. Nano sized pores have been shown to be beneficial for bone cell attachment and proliferation. The purpose of the present research was to investigate oxide crystallinity and pore formation during titanium anodization using a pulsed DC waveform in a series of sulfuric acid electrolytes ranging from 0.5 to 12 M. Anodizing titanium in increasing sulfuric acid molarities showed a trend of increasing transformations of the amorphous natural forming oxide to the crystalline phases of anatase and rutile. The pulsed DC waveform was shown to produce pores with a size range from ?0.01 to 1 ?m(2). The pore size distributions produced may be beneficial for bone cell attachment and proliferation. PMID:23807314

Williamson, R S; Disegi, J; Griggs, J A; Roach, M D



Corrosion resistance of stressed NiTi and stainless steel orthodontic wires in acid artificial saliva.  


The purpose of this study was to investigate the corrosion resistance of stressed NiTi and stainless steel orthodontic wires using cyclic potentiodynamic and potentiostatic tests in acid artificial saliva at 37 degrees C. An atomic force microscope was used to measure the 3-D surface topography of as-received wires. Scanning electron microscope observations were carried out before and after the cyclic potentiodynamic tests. The surface chemical analysis was characterized using X-ray photoelectron spectroscopy and Auger electron spectroscopy after the potentiostatic tests. The cyclic potentiodynamic test results showed that the pH had a significant influence on the corrosion parameters of the stressed NiTi and stainless steel wires (p < 0.05). The pitting potential, protection potential, and passive range of stressed NiTi and stainless steel wires decreased on decreasing pH, whereas the passive current density increased on decreasing pH. The load had no significant influence on the above corrosion parameters (p > 0.05). For all pH and load conditions, stainless steel wire showed higher pitting potential and wider passive range than NiTi wire (p < 0.001), whereas NiTi wire had lower passive current density than stainless steel wire (p < 0.001). The corrosion resistance of the stressed NiTi and stainless steel wires was related to the surface characterizations, including surface defect and passive film. PMID:12926035

Huang, Her-Hsiung



Passive film formation on 316L stainless steel  

SciTech Connect

The polarization behavior of 316L stainless steel has been studied in deaerated sodium sulfate solutions of various pH values. Potentiodynamic, potentiostatic and galvanostatic methods were used for a kinetic study of the formation and growth of passive films. For the film composition analysis, Auger Electron Spectroscopy (AES) and ESCA techniques were also employed. Anodic polarization curves show that current increases as pH decreases and temperature increases. The activation energy for the reaction in the active region was determined to be 10.8 Kcal/mole. From potentiostatic experiments, three stages for passive film formation were observed: the initial active-passive transition, the logarithmic growth of the film and the parabolic growth of the film. The logarithmic relation is expressed and the parabolic relation written. The depth profile concentration of elements in the film by AES showed chromium enrichment at the surface except for the specimen treated at 0.9V (SCE), where iron was the dominant element in the film. The relative amount of Fe/sup 2 +/ and Fe/sup 3 +/ on the film surface analyzed by ESCA was not different for specimens anodized at 0.18V and 0.58V.

Lee, S.; Pitt, C.H.; Wadsworth, M.E.



In situ electrochemical investigation of tungsten electrochemical behavior during chemical mechanical polishing  

SciTech Connect

The electrochemical behavior of tungsten during chemical mechanical polishing (CMP) was observed in order to investigate a proposed blanket passivation and abrasion mechanism for tungsten removal. The experiments were performed in a cell that allowed electrochemical measurements to be made during polish. Polish rates were determined from the same samples used in the cell. Alumina-based polish slurries containing potassium iodate, ferric nitrate, or ammonium persulfate were used. DC polarization experiments show no evidence of passive film formation on the tungsten during polish. Tungsten oxidation rates measured during polish account for removal rates that are 1 to 2 orders of magnitude below the measured polish rate. Values of the charge-transfer resistance (measured by ac impedance spectroscopy) during polish are 1 to 2 orders of magnitude higher than expected from the polish rate, thus corroborating the dc-based data. Polish rates under potentiostatic conditions were also measured. The current required to maintain the metal anodic of the open-circuit potential is well below the current expected from measured polish rates, assuming complete oxidation of the tungsten. The polish rate during cathodic potentiostatic conditions ({minus}0.5 V with regard to the open-circuit potential) was similar to the polish rate at open circuit. The authors conclude that the formation of a blanket passive layer does not significantly contribute to tungsten removal during CMP.

Stein, D.J.; Cecchi, J.L. [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Chemical and Nuclear Engineering; Hetherington, D.; Guilinger, T. [Sandia National Labs., Albuquerque, NM (United States)



Post-CMOS fabrication of Working Electrodes for On-Chip Recordings of Transmitter Release  

PubMed Central

The release of neurotransmitters and hormones from secretory vesicles plays a fundamental role in the function of the nervous system including neuronal communication. High-throughput testing of drugs modulating transmitter release is becoming an increasingly important area in the fields of cell biology, neurobiology, and neurology. Carbon-fiber amperometry, provides high-resolution measurements of amount and time course of transmitter release from single vesicles, and their modulation by drugs and molecular manipulations. However, such methods do not allow the rapid collection of data from a large number of cells. To allow such testing, we have developed a CMOS potentiostat circuit that can be scaled to a large array. In this paper, we present two post-CMOS fabrication methods to incorporate the electrochemical electrode material. We demonstrate by proof of principle the feasibility of on-chip electrochemical measurements of dopamine, and catecholamine release from adrenal chromaffin cells. The measurement noise is consistent with the typical electrode noise in recordings with external amplifiers. The electronic noise of the potentiostat in recordings with 400 ?s integration time is ~0.11 pA and is negligible compared to the inherent electrode noise. PMID:20514361

Ayers, Sunitha; Berberian, Khajak; Gillis, Kevin D.; Lindau, Manfred; Minch, Bradley A.



Pharmacokinetic study of medicinal polymers: models based on dextrans  

SciTech Connect

The authors study the pharmacokinetics of dextrans with various molecular masses modified by fluorescein isothiocyanate (FITC) using a radioisotope method. The radionuclide /sup 125/I was selectively bound to a FITC residue attached to the polysaccharide by electrochemical iodination under potentiostatic conditions. In the experiments, dextrans modified by FITC were labeled with /sup 125/I (DF-/sup 125/I) by electrochemical iodination. The separation of DF-/sup 125/I and FITC from ionic forms of the radionuclide not bound to the polymer was carried out. The properties of the samples obtained are presented. The radioactivity accumulated in the rate organs and urine studied are shown. The features of DF-/sup 125/I behavior in the blood and liver are examined.

Kulakov, V.N.; Pimenova, G.N.; Matveev, V.A.; Sedov, V.V.; Vasil'ev, A.E.



Alginate electrodeposition onto three-dimensional porous Co-Ni films as drug delivery platforms.  


Three-dimensional porous Co-Ni films/alginate hybrid materials have been successfully prepared by electrodeposition to be used as a steerable magnetic device for drug delivery. Firstly, 3D porous Co-Ni films were prepared as substrates for the subsequent electrodeposition of the alginate biopolymer. Cyclic voltammetry, galvanostatic and potentiostatic studies were performed to establish the best conditions to obtain porous Co-Ni films. The electrochemical experiments were carried out in an electrolyte containing the metal salts and ammonium chloride at low pHs. In a second stage, the electrochemical deposition of alginate as a biocompatible polymer drug delivery carrier was performed. The characteristics of the alginate matrix were investigated in terms of electrochemical properties, morphology and drug release. The hybrid material obtained showed soft-magnetic behavior and drug release indicating its suitability to be used as a steerable magnetic drug delivery device. PMID:25437927

Garca-Torres, J; Gispert, C; Gmez, E; Valls, E



Electrochemical behavior of 0.2 to 3 molar ferrous chloride-ferric chloride mixtures on edge-on pyrolytic graphite rotated disk electrodes  

NASA Technical Reports Server (NTRS)

Potentiostatic determinations in various mixtures of FeCl2-FeCl3 with excess HCl show rest potentials that are 0.1 V less electropositive than the theoretical values from the formulated ratios of FeII to FeIII (probably as a result of complexing). The standard rate constant sub s. ranges between 0.0001 and 0.000 cm/sec. Tafel slopes b of roughly 0.12V per decade indicate single-electron exchange kinetics. No significant trend in either b or sub s was attributed to mixture composition. The higher sub s. values occurred with and edge-on pyrolytic graphite that had undergone a permanent surface change.

Miller, R. O.



Power dependent effects in the luminescence decay of GaAs/electrolyte contacts at the flat band potential  

SciTech Connect

Saturation of surface traps has been observed in the GaAs/Na{sub 2}-S photoelectrochemical system under modest excitation conditions. Saturation is shown to result in a surface minority trapping velocity that is dependent on time as well as laser excitation power. These saturation effects are observed by studying the luminescence decays of GaAs as a function of excitation pulse power under potentiostatic control at the flat band potential. The decays also indicate that surface minority carrier trapping is fast compared with processes which remove minority carriers from trap states. These results suggest that time-resolved experiments under high injection open circuit conditions may underestimate the surface minority trapping rate under typical solar conditions. 21 refs., 2 figs., 1 tab.

Kauffman, J.F.; Balko, B.A.; Richmond, G.L. [Univ. of Oregon, Eugene, OR (United States)



Relation between energetic and utilization coefficients in the positive plates of automotive lead/acid batteries  

NASA Astrophysics Data System (ADS)

A new experimental method to distinguish between energetic and structural materials and to characterize the manufacturing technology for positive plates in lead/acid batteries is discussed. This new method proposes the evaluation of the energetic ?-coefficient from plots of capacity versus very low current densities under galvanostatic conditions and using real-size positive plates in 2.3-6.9 M H 2SO 4 solutions. The results are identical to those obtained previously from potentiostatic measurements, and they fit a new equation as opposed to Peukert's equation. The independence of the ?-coefficient with H 2SO 4 concentration indicates that the discharge of PbO 2 to its products proceeds via a solid-state reaction mechanism.

D'Alkaine, C. V.; Carubelli, A.; Fava, H. W.; Sanhueza, A. C.


Novel Pt nanowires modified screen-printed gold electrode by electrodeposited method  

NASA Astrophysics Data System (ADS)

In this work, the preparation and characterization of novel Pt nanowires (Pt NWs) on the screen-printed gold electrode (SPGE) surface are reported. Firstly the mesoporous template was prepared by the electro-assisted self-assembly (EASA) method on the manual SPGE. Then, in the potentiostatic condition, Pt NWs were electrodeposited in the meosoporous channel on the Au electrode surface using the chronopotentiometry (CP) method at room temperature. The synthesized Pt NWs were characterized by cyclic voltammetry (CV), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) spectrometer. The results indicated that Pt NWs were successfully electrodeposited on the SPGE substrate, even the diameter of each Pt NWs could reach 3.2 nm. Furthermore, the SPGE could be mass produced conveniently and cost low which had very promising application prospect. And it is significant that the Pt NWs modified SPGE could function as an electrode in an electrochemical biosensor.

Zhao, Hongli; Zhou, Changxiang; Teng, Yuanjie; Chen, Chen; Lan, Minbo



Light addressable potentiometric sensor with an array of sensing regions  

NASA Astrophysics Data System (ADS)

This paper describes the mechanism of light addressable poteniometric sensors (LAPS) from the viewpoints of Semiconductor Physics, and introduces the fabrication of a multi-parameter LAPS chip. The MEMS technology is applied to produce a matrix of sensing regions on the wafer. By doing that, the cross talk among these regions is reduced, and the precision of the LAPS is increased. An IR-LED matrix is used as the light source, and the flow-injection method is used to input samples. The sensor system is compact and highly integrated. The measure and control system is composed of a personal computer, a lock-in amplifier, a potentiostat, a singlechip system, and an addressing circuit. Some experiments have been done with this device. The results show that this device is very promising for practical use.

Liang, Weiguo; Han, JingHong; Zhang, Hong; Chen, Deyong



Permeability improvements of electropolymerized polypyrrole films using dissolvable nano-CaCO3 particle templates.  


The electropolymerisation of N-substituted pyrroles on a dissolvable calcium carbonate nanoparticle template was investigated in order to improve the film permeabilities in aqueous solution. After deposition of CaCO3 nanoparticles on the electrode surface, poly(pyrrole-ammonium) or poly(pyrrole-NTA) (NTA: nitrilotriacetic acid) were electrogenerated around the template structures of the electrodes using potentiostatic methods. The dissolution of nanoparticles in acidic medium leads to the formation of nano-porous structures increasing, therefore, the polypyrrole permeability in aqueous solutions. Histidine-tagged glucose oxidase, chosen as an enzyme model, was immobilised on the modified polypyrrole-NTA via the NTA-Cu(2+)-histidine interactions to validate the proposed method. The described setup led to a twofold increase in the maximum current density from 5 to 10 ?A cm(-2) after template dissolution. PMID:24481549

Popescu Mandoc, Luisa-Roxana; Gorgy, Karine; Ungureanu, Eleonora-Mihaela; Buica, George-Octavian; Holzinger, Michael; Cosnier, Serge



Studies on the electrodeposition of tin from acidic chloride-gluconate solutions  

NASA Astrophysics Data System (ADS)

Electrodeposition of tin from acidic chloride-gluconate baths was investigated. Equilibrium distribution of tin(II) species showed domination of Sn(II)-gluconate complexes, but for Sn2+ concentrations 50 mM or higher increased percentage of Sn(II)-chloride complexes was found. Cyclic voltammetry, anodic stripping analysis and potentiostatic measurements indicated that rate of the cathodic process is determined by the release of metal cations from gluconate complexes in diluted bath (5 mM), but for more concentrated solutions reduction of Sn(II) ions run under diffusion control. Studies of anodic response showed that it depends on the Sn(II)/Glu ratio in the bath and deposition potential due to development of different planes of metal crystal. Average effective diffusion coefficients of metal species were determined. Morphology and structure tin deposits were also presented.

Rudnik, Ewa; W?och, Grzegorz



The alkaline zinc electrode as a mixed potential system  

NASA Technical Reports Server (NTRS)

Cathodic and anodic processes for the alkaline zinc electrode in 0.01 molar zincate electrolyte (9 molar hydroxide) were investigated. Cyclic voltammograms and current-voltage curves were obtained by supplying pulses through a potentiostat to a zinc rotating disk electrode. The data are interpreted by treating the system as one with a mixed potential; the processes are termed The zincate and corrosion reactions. The relative proportions of the two processes vary with the supplied potential. For the cathodic region, the cathodic corrosion process predominates at higher potentials while both processes occur simultaneously at a lower potential (i.e., 50 mV). For the anodic region, the anodic zincate process predominates at higher potentials while the anodic corrosion process is dominant at lower potential (i.e., 50 mV) if H2 is present.

Fielder, W. L.



Electrochemical Polishing Applications and EIS of a Novel Choline Chloride-Based Ionic Liquid  

SciTech Connect

Minimal surface roughness is a critical feature for high-field superconducting radio frequency (SRF) cavities used to engineer particle accelerators. Current methods for polishing Niobium cavities typically utilize solutions containing a mixture of concentrated sulfuric and hydrofluoric acid. Polishing processes such as these are effective, yet there are many hazards and costs associated with the use (and safe disposal) of the concentrated acid solutions. An alternative method for electrochemical polishing of the cavities was explored using a novel ionic liquid solution containing choline chloride. Potentiostatic electrochemical impedance spectroscopy (EIS) was used to analyze the ionic polishing solution. Final surface roughness of the Nb was found to be comparable to that of the acid-polishing method, as assessed by atomic force microscopy (AFM). This indicates that ionic liquid-based electrochemical polishing of Nb is a viable replacement for acid-based methods for preparation of SRF cavities.

Wixtrom, Alex I. [Christopher Newport University, Newport News, VA (United States); Buhler, Jessica E. [Christopher Newport University, Newport News, VA (United States); Reece, Charles E. [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Abdel-Fattah, Tarek M. [Christopher Newport University, Newport News, VA (United States)



Magnetic behavior of as-deposited and annealed CoFe and CoFeCu nanowire arrays by ac-pulse electrodeposition  

NASA Astrophysics Data System (ADS)

CoFe and CoFeCu self-organized alloy nanowires were grown into anodic aluminum oxide template by potentiostatic mode of ac-pulse electrodeposition technique and subsequently annealed at 580 C. The influence of bath composition, off-time between pulses and annealing treatment on the Cu content, microstructure and magnetic properties of CoFeCu nanowire arrays have been discussed. Increasing the off-time between pulses decreased the coercivity and saturation magnetization of the CoFeCu nanowires due to substitution of Co and Fe with Cu atoms which resulted in electroless process. Coercivity and squareness of the annealed samples increased due to improvement of samples crystallinity. Magnetic measurements showed high perpendicular magnetic anisotropy of the nanowires with easy axis parallel to nanowires axis. X-ray diffraction results indicated that annealed CoFeCu nanowires were polycrystalline with two distinct CoFe and Cu phases.

Ramazani, A.; Almasi-Kashi, M.; Golafshan, E.; Arefpour, M.



Large-diameter titanium dioxide nanotube arrays as a scattering layer for high-efficiency dye-sensitized solar cell  

PubMed Central

Large-sized titanium dioxide (TiO2) nanotube arrays with an outer diameter of approximately 500nm have been successfully synthesized by potentiostatic anodization at 180V in a used electrolyte with the addition of 1.5M lactic acid. It is found that the synthesized large-diameter TiO2 nanotube array shows a superior light scattering ability, which can be used as a light scattering layer to significantly enhance the efficiency of TiO2 nanoparticle-based dye-sensitized solar cells from 5.18% to 6.15%. The remarkable light scattering ability makes the large-diameter TiO2 nanotube array a promising candidate for light management in dye-sensitized solar cells (DSSCs). PMID:25114652



Elucidation of charge storage characteristics of conducting polymer film using redox reaction  

E-print Network

A general technique to investigate charge storage characteristics of conducting polymer films has been developed. A redox reaction is conducted on a polymer film on a rotating disk electrode under potentiostatic condition so that the rate of charging of the film equals the rate of removal of the charge by the reaction. In an experiment on polyaniline film deposited on platinum substrate, using Fe2+/Fe3+ in HCl as the redox system, the voltammogram shows five distinct linear segments (bands) with discontinuity in the slope at specific transition potentials. These bands are the same as those indicated by ESR/Raman spectroscopy with comparable transition potentials. From the dependence of the slopes of the bands on concentration of ferrous and ferric ions, it was possible to estimate the energies of the charge carrier in different bands. It is shown that the charge storage in the film is capacitive.

Contractor, Asfiya Q



Photoelectrochemical and Electrochemical Characterization of Sub-Micro-Gram Amounts of Organic Semiconductors Using Scanning Droplet Cell Microscopy.  


A model organic semiconductor (MDMO-PPV) was used for testing a modified version of a photoelectrochemical scanning droplet cell microscope (PE-SDCM) adapted for use with nonaqueous electrolytes and containing an optical fiber for localized illumination. The most attractive features of the PE-SDCM are represented by the possibility of addressing small areas on the investigated substrate and the need of small amounts of electrolyte. A very small amount (ng) of the material under study is sufficient for a complete electrochemical and photoelectrochemical characterization due to the scanning capability of the cell. The electrochemical behavior of the polymer was studied in detail using potentiostatic and potentiodynamic investigations as well as electrochemical impedance spectroscopy. Additionally, the photoelectrochemical properties were investigated under illumination conditions, and the photocurrents found were at least 3 orders of magnitude higher than the dark (background) current, revealing the usefulness of this compact microcell for photovoltaic characterizations. PMID:25101149

Kollender, Jan Philipp; Gasiorowski, Jacek; Sariciftci, Niyazi S; Mardare, Andrei I; Hassel, Achim Walter



Single-step electrochemical nanolithography of metal thin films by localized etching with an AFM tip  

NASA Astrophysics Data System (ADS)

This work introduces electrochemical nanolithography (ENL), a single-step method in which a metal thin film is locally etched without application of a mask on a 100 nm length scale with an electrochemical atomic force microscope (AFM). The method requires the application of ultra-short voltage pulses on the tip (nanosecond range duration, 2-4 V amplitude), while both the sample and the metalized tip are under independent potentiostatic control for full control of interface reactions in an AFM electrochemical cell. It is demonstrated that Cu films as well as Co and Cu/Co sandwich magnetic films can be patterned if negative voltage pulses are applied to the tip. This method also applies to films deposited on an insulating substrate. Moreover the lateral dimension of lithographed structures is tunable, from a few micrometers down to 150 nm, by appropriate choice of ENL conditions. Simulation of the dissolution process is discussed.

de Abril, O.; Gndel, A.; Maroun, F.; Allongue, P.; Schuster, R.



Preparation of Mo nanopowders through electroreduction of solid MoS2 in molten KCl-NaCl.  


Electrolysis of MoS2 to produce Mo nanopowders and elemental sulfur has been studied in an equimolar mixture of NaCl and KCl at 700 C. The reduction mechanism was investigated by cyclic voltammetry (CV), potentiostatic and constant voltage electrolysis together with spectroscopic and scanning electron microscopic analyses. The reduction pathway was identified to be MoS2 ? LxMoS2 (x ? 1, L = Na or K) ? L3Mo6S8 and LMo3S3 ? Mo, and the last step to format metallic Mo was found to be relatively slow in kinetics. Electrolysis at a cell voltage of 2.7 V has led to a rapid reduction of MoS2 to nodular Mo nanoparticles (50-100 nm), with the current efficiency and energy consumption being about 92% and 2.07 kW h kg(-1)-Mo, respectively. PMID:25105181

Gao, Haiping; Tan, Mingsheng; Rong, Liangbin; Wang, Zhiyong; Peng, Junjun; Jin, Xianbo; Chen, George Z



Influence of poly(3,4-dioctyloxythiophene) and carbon nanotubes on photoelectrochemical properties of CdS nanostructures  

NASA Astrophysics Data System (ADS)

In this work we present a hybrid electrode, composed of conducting polymer and nanosized CdS, of an enhanced photoactivity in comparison with that of the pure CdS. Poly(3,4-dioctyloxythiophene) (PDOT) was electrosynthesized on Pt or Au substrates by the cyclic voltammetry, whereas CdS was obtained by chemical transformation of Cd nanostructures deposited potentiostatically on the polymer-modified electrode. Photoelectrochemical properties of PDOT/CdS and CdS electrodes were studied in aqueous solution of 0.1 M Na2S. The improved photoactivity of the PDOT/CdS system in comparison with that of the pure CdS is discussed in terms of composition of the hybrid electrode and hole-mediating ability of PDOT. An enhancement of the photocurrent stability of Pt/PDOT-CdS hybrid electrode was accomplished by modification of Pt substrate with carbon nanotubes.

Refczy?ska, Monika; Skompska, Magdalena



High frequency reference electrode  


A high frequency reference electrode for electrochemical experiments comprises a mercury-calomel or silver-silver chloride reference electrode with a layer of platinum around it and a layer of a chemically and electrically resistant material such as TEFLON around the platinum covering all but a small ring or halo' at the tip of the reference electrode, adjacent to the active portion of the reference electrode. The voltage output of the platinum layer, which serves as a redox electrode, and that of the reference electrode are coupled by a capacitor or a set of capacitors and the coupled output transmitted to a standard laboratory potentiostat. The platinum may be applied by thermal decomposition to the surface of the reference electrode. The electrode provides superior high-frequency response over conventional electrodes. 4 figs.

Kronberg, J.W.



Simplified Electrochemically Mediated Atom Transfer Radical Polymerization using a Sacrificial Anode.  


Simplification of electrochemically mediated atom transfer radical polymerization was achieved efficiently under either potentiostatic or galvanostatic conditions using an aluminum wire sacrificial anode (seATRP) immersed directly into the reaction flask without separating the counter electrode. seATRP polymerizations were carried out under different applied potentials, Eapp s=E1/2 , Epc , Epc -40?mV, and Epc -80?mV. As the rate of polymerization (Rp ) can be modulated by applying different Eapp potentials, more reducing conditions resulted in faster Rp . The polymerization results showed similar narrow molecular-weight distribution throughout the reactions, similar to results observed for n-butyl acrylate (BA) polymerization under conventional eATRP. High-molecular-weight PBA and diblock copolymers were synthesized by seATRP with more than 90?% monomer conversion. Furthermore, galvanostatic conditions were developed for synthesizing PBA with the two-electrode system. PMID:25565188

Park, Sangwoo; Chmielarz, Pawe?; Gennaro, Armando; Matyjaszewski, Krzysztof



Electrochemical formation of uranium-zirconium alloy in LiCl-KCl melts  

NASA Astrophysics Data System (ADS)

Since zirconium is considered an electrochemically active species under practical conditions of the electrorefining process, it is crucial to understand the electrochemical behavior of zirconium in LiCl-KCl melts containing actinide ions. In this study, the electrochemical codeposition of uranium and zirconium on a solid cathode was performed. It was found that the ?-(U, Zr) phase, which is the only intermediate phase of the uranium-zirconium binary alloy system, was deposited on a tantalum substrate by potentiostatic electrolysis at -1.60 V (vs. Ag +/Ag) in LiCl-KCl melts containing 0.13 in mol% UCl 3 and 0.23 in mol% ZrCl 4 at 773 K. To our knowledge, this is the first report on the electrochemical formation of the ?-(U, Zr) phase. The relative partial molar properties of uranium in the ?-(U, Zr) phase were evaluated by measuring the open-circuit-potentials of the electrochemically prepared ?-phase electrode.

Murakami, Tsuyoshi; Kato, Tetsuya; Kurata, Masaki; Yamana, Hajimu



Rapid fabrication of bimetallic spherical motors.  


Catalytic bimetallic nanomotors can swim at 100 body lengths per second as well as pick up, haul, and release micrometer-scale cargo. The electrokinetic locomotion of bimetallic nanomotors is driven by the electrocatalytic decomposition of hydrogen peroxide. The motors are typically fabricated by electrodeposition-based template synthesis techniques that result in heterogeneous samples and require specialized knowledge of electrochemistry, a three-electrode potentiostat setup, cyanide-based chemistry, and porous membranes. This paper presents a rapid and facile method for fabrication of spherical bimetallic motors that only requires access to metal deposition equipment and commercially available microspheres. The resulting spherical motors swim at speeds comparable to rod-shaped motors with the same dimensions and composition. The spherical motors' velocity increases with fuel concentration and decreasing diameter. PMID:20695541

Wheat, Philip M; Marine, Nathan A; Moran, Jeffrey L; Posner, Jonathan D



Correlation between electronic and corrosion properties of the passive oxide film on nitinol.  


The oxide film (TiO(2)) was formed on Nitinol potentiostatically in an acetic acid solution. Deep understanding of electronic properties of this film is needed to predict long-term corrosion properties of Nitinol implant material in simulated body fluid conditions. The capacitance measurements were performed under depletion conditions to study electronic (semiconducting) properties. The space charge, formed at the solid|liquid interface, creates the barrier for the corrosion processes in aggressive (bio)environment. According to the results of electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis (MS), the passive film on Nitinol behaves as amorphous highly-doped n-type semiconductor. The values of electronic structure parameters (the flat-band potential, E(fb) and the carrier (donor) density, N(D)) were corrected for frequency dispersion. PMID:25125118

Kati?, Jozefina; Metiko-Hukovi?, Mirjana



Fabrication of Cu2O/?-FeOOH heterojunction solar cells using electrodeposition  

NASA Astrophysics Data System (ADS)

Cu2O/?-FeOOH heterojunction solar cells were fabricated using galvanostatic-potentiostatic electrodeposition methods. The ?-FeOOH films showed n-type conductivity with a band gap of 2.2 eV. The electrodeposited Cu2O/?-FeOOH heterojunction exhibited photovoltaic characteristics with a short-circuit current density of 0.95 mA/cm2 and open-circuit voltage of 0.11 V. Using core-level spectroscopy, it was demonstrated that the Cu2O/FeOOH heterostructure exhibited a type II junction with a valence band offset of 0.8 eV. The conduction band minimum of Cu2O was predicted to be higher than that of ?-FeOOH by 0.7 eV. This finding indicates that the ?-FeOOH material can be regarded as a suitable hetero-partner of other p-type absorbers.

Vequizo, Junie Jhon M.; Ichimura, Masaya



Use of cyclic current reversal polarization voltammetry for investigating the relationship between corrosion resistance and heat-treatment induced variations in microstructures of 400 C martensitic stainless steels  

NASA Technical Reports Server (NTRS)

Software for running a cyclic current reversal polarization voltammagram has been developed for use with a EG&G Princeton Applied Research Model 273 potentiostat/galvanostat system. The program, which controls the magnitude, direction and duration of an impressed galvanostatic current, will produce data in ASCII spreadsheets (Lotus, Quattro) for graphical representation of CCRPV voltammograms. The program was used to determine differences in corrosion resistance of 440 C martenstic stainless steel produced as a result of changes in microstructure effected by tempering. It was determined that tempering at all temperatures above 400 F resulted in increased polarizability of the material, with the increased likelihood that pitting would be initiated upon exposure to marine environments. These results will be used in development of remedial procedures for lowering the susceptibility of these alloys toward the stress corrosion cracking experienced in bearings used in high pressure oxygen turbopumps used in the main engines of space shuttle orbiters.

Ambrose, John R.



The inhibition effects of some cyclic nitrogen compounds on the corrosion of the steel in NaCl mediums  

NASA Astrophysics Data System (ADS)

Corrosion inhibition efficiencies of 3-amino-1,2,4-triazole (3-ATA), 2-amino-1,3,4-thiadiazole (2-ATDA), 5-( p-tolyl)-1,3,4-triazole (TTA), 3-amino-5-methylmercapto-1,2,4-triazole (3-AMTA) and 2-aminobenzimidazole (2-ABA) on steel in sodium chloride media were investigated using Tafel extrapolation method. Potentiostatic current-potential curves were utilized to derive corrosion potentials ( Ecorr), corrosion current densities ( icorr), surface coverage degrees ( ?) and corrosion inhibition efficiencies ( ?, %). 2-ABA was found to have the highest inhibition efficiency in both, 2.5 and 3.5% aqueous NaCl media. For all the inhibitors studied, surface coverage and inhibition efficiency values were found to increase with increasing concentration of the compound concerned. Inspection of the ? values indicate that the adsorption process obeys the Temkin isotherm for TTA and 2-ABA, but the Langmuir isotherm is followed by 3-ATA, 2-ATDA and 3-AMTA.

?ahin, M.; Bilgi, S.; Y?lmaz, H.



In vitro biocompatibility response of Ti-Zr-Si thin film metallic glasses  

NASA Astrophysics Data System (ADS)

In this study, the bio-electrochemical response of the Ti-Zr-Si thin film metallic glasses (TFMGs) in simulated body fluid with different contents of titanium is measured via potentiostat. According to the results of bio-corrosion potential and current, as well as the polarization resistance, it is concluded that the Ti66Zr25Si9 TFMGs possess the highest bio-electrochemical resistance. With increasing content of titanium, the corrosion resistance becomes progressively higher. The passive current results reveal that amorphous alloys can form a more protective and denser passive film on the metallic glass surface than the crystalline materials. In addition, the mechanical performance of the Ti-Zr-Si TFMGs is better than the crystalline counterparts. As a result, the Ti-based TFMGs are considered to be potential materials for bio-coating applications.

Ke, J. L.; Huang, C. H.; Chen, Y. H.; Tsai, W. Y.; Wei, T. Y.; Huang, J. C.



Novel integrated and portable endotoxin detection system based on an electrochemical biosensor.  


This paper describes the design, implementation and validation of a sensitive and integral technology solution for endotoxin detection. The unified and portable platform is based on the electrochemical detection of endotoxins using a synthetic peptide immobilized on a thin-film biosensor. The work covers the fabrication of an optimized sensor, the biofunctionalization protocol and the design and implementation of the measuring and signalling elements (a microfluidic chamber and a portable potentiostat-galvanostat), framed ad hoc for this specific application. The use of thin-film technologies to fabricate the biosensing device and the application of simple immobilization and detection methods enable a rapid, easy and sensitive technique for in situ and real time LPS detection. PMID:25431806

Zuzuarregui, Ana; Souto, David; Prez-Lorenzo, Eva; Arizti, Fernando; Snchez-Gmez, Susana; Martnez de Tejada, Guillermo; Brandenburg, Klaus; Arana, Sergio; Mujika, Maite



Electrodeposited Ag nanoparticles on TiO2 nanorods for enhanced UV visible light photoreduction CO2 to CH4  

NASA Astrophysics Data System (ADS)

We employed the double-potentiostatic methodology to electrodeposit Ag nanoparticles on oriented single-crystalline rutile TiO2 nanorods synthesized by hydrothermal method. The synthesized composites were used as the photocatalyst to reduce CO2 to CH4 under UV irradiation, and tested by SEM, XRD, TEM, XPS, UV-vis and photoluminescence. Deposition with Ag nanoparticles was observed to enhance the photocatalytic activity (?1.5-2.64 ?mol (gcatal h)-1) up to 5 times with respect to undecorated TiO2 nanorods (?0.5 ?mol (gcatal h)-1). The increase in the CH4 yield was correlated with the surface morphology and structure of TiO2 nanorods.

Kong, Dan; Tan, Jeannie Ziang Yie; Yang, Fei; Zeng, Jieliang; Zhang, Xiwen



Distinguishing nanowire and nanotube formation by the deposition current transients  

PubMed Central

High aspect ratio Ni nanowires (NWs) and nanotubes (NTs) were electrodeposited inside ordered arrays of self-assembled pores (approximately 50?nm in diameter and approximately 50??m in length) in anodic alumina templates by a potentiostatic method. The current transients monitored during each process allowed us to distinguish between NW and NT formation. The depositions were long enough for the deposited metal to reach the top of the template and form a continuous Ni film. The overfilling process was found to occur in two steps when depositing NWs and in a single step in the case of NTs. A comparative study of the morphological, structural, and magnetic properties of the Ni NWs and NTs was performed using scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometry, respectively. PMID:22650765



Distinguishing nanowire and nanotube formation by the deposition current transients  

NASA Astrophysics Data System (ADS)

High aspect ratio Ni nanowires (NWs) and nanotubes (NTs) were electrodeposited inside ordered arrays of self-assembled pores (approximately 50 nm in diameter and approximately 50 ?m in length) in anodic alumina templates by a potentiostatic method. The current transients monitored during each process allowed us to distinguish between NW and NT formation. The depositions were long enough for the deposited metal to reach the top of the template and form a continuous Ni film. The overfilling process was found to occur in two steps when depositing NWs and in a single step in the case of NTs. A comparative study of the morphological, structural, and magnetic properties of the Ni NWs and NTs was performed using scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometry, respectively.

Proenca, Mariana P.; Sousa, Clia T.; Ventura, Joo; Vazquez, Manuel; Araujo, Joo P.



Adhesion and proliferation of osteoblast-like cells on anodic porous alumina substrates with different morphology.  


We have fabricated nanoporous alumina surfaces by means of anodization in oxalic acid in different conditions and used them as the substrates for the growth of cells from a human osteoblast-like cell line. The rough nanoporous alumina substrates have been compared both with smooth standard Petri dishes used as the control and with commercial substrates of similar material. The viability of the cells has been assessed at different culture times of 4, 11, 18, and 25 days in vitro. It turned out that the porous side of the galvanostatically fabricated alumina performed similar to the control and better than the commercial porous alumina, whereas the potentiostatically fabricated porous alumina performed better than all the other substrates at all times, and in particular at the two shortest time periods of 4 and 11 days in vitro. The best performance of the substrates is associated with intermediate surface roughness and feature spacing. PMID:23722279

Salerno, Marco; Caneva-Soumetz, Federico; Pastorino, Laura; Patra, Niranjan; Diaspro, Alberto; Ruggiero, Carmelina



High frequency reference electrode  


A high frequency reference electrode for electrochemical experiments comprises a mercury-calomel or silver-silver chloride reference electrode with a layer of platinum around it and a layer of a chemically and electrically resistant material such as TEFLON around the platinum covering all but a small ring or "halo" at the tip of the reference electrode, adjacent to the active portion of the reference electrode. The voltage output of the platinum layer, which serves as a redox electrode, and that of the reference electrode are coupled by a capacitor or a set of capacitors and the coupled output transmitted to a standard laboratory potentiostat. The platinum may be applied by thermal decomposition to the surface of the reference electrode. The electrode provides superior high-frequency response over conventional electrodes.

Kronberg, James W. (Aiken, SC)



Synthesis and microstructural studies of annealed Cu(2)O/Cu(x)S bilayer as transparent electrode material for photovoltaic and energy storage devices.  


Cu2 O thin film and a transparent bilayer have been fabricated by electrodeposition method. The growths were obtained in potentiostatic mode with gradual degradation of anodic current. X-ray diffraction (XRD) study showed that the bilayer is polycrystalline and it possesses mixture of different crystallite phases of copper oxides. Surface morphology of the films was investigated by scanning electron microscopy (SEM). The SEM images revealed that the films were uniformly distributed and the starting material (Cu2 O) had cubical structure. Grains agglomeration and crystallinity were enhanced by annealing. Optical studies indicated that all the samples have direct allowed transition. Energy band gap of the bilayer film was reduced by annealing treatment thus corroborating quantum confinement upshot. PMID:25088932

Taleatu, B A; Arbab, E A A; Omotoso, E; Mola, G T



Electrochemical nanoneedle biosensor based on multiwall carbon nanotube.  


We report the fabrication and analytical functions of a biosensor based on a nanoneedle consisting of a multiwall carbon nanotube attached to the end of an etched tungsten tip. The devised electrode is the smallest needle-type biosensor reported to date. The nanoneedles prepared in this work are 30 nm in diameter and 2-3 microm in length. Dopamine and glutamate, which are physiologically important neurotransmitters, were successfully detected using these nanoneedles. Bare nanoneedles detected dopamine in the range from 100 to 1000 microM by differential pulse voltammetry, and enzyme-modified nanoneedles were able to respond to glutamate in the 100-500 microM range by potentiostatic amperometry. PMID:16408948

Boo, Hankil; Jeong, Ran-A; Park, Sejin; Kim, Keun Soo; An, Kay Hyeok; Lee, Young Hee; Han, Ji Hyung; Kim, Hee Chan; Chung, Taek Dong



Microdialysis Sampling Coupled to Microchip Electrophoresis with Integrated Amperometric Detection on an All Glass Substrate  

PubMed Central

The development of an all-glass separation-based sensor using microdialysis coupled to microchip electrophoresis with amperometric detection is described. The system includes a flow-gated interface to inject discrete sample plugs from the microdialysis perfusate into the microchip electrophoresis system. Electrochemical detection was accomplished with a platinum electrode in an in-channel configuration using a wireless electrically isolated potentiostat. To facilitate bonding around the in-channel electrode, a fabrication process was employed that produced a working and a reference electrode flush with the glass surface. Both normal and reversed polarity separations were performed with this sensor. The system was evaluated in vitro for the continuous monitoring of the production of hydrogen peroxide from the reaction of glucose oxidase with glucose. Microdialysis experiments were performed using a BASi loop probe with an overall lag time of approximately five minutes and a rise time of less than 60 seconds. PMID:23794474

Scott, David E.; Grigsby, Ryan; Lunte, Susan M.



Electrochemical and surface studies of zinc in alkaline solutions containing organic corrosion inhibitors  

NASA Astrophysics Data System (ADS)

The electrochemical behavior of zinc in strong alkaline solutions containing 8.5 M of potassium hydroxide (KOH) and polymeric organic inhibitors was evaluated. The concentrations of the organic inhibitors studies were in the range of 400-4000 ppm and included polyethylene glycol (PEG), with a molecular weight of 600, and polyoxyethylen alkyl phosphate ester acid form (GAFAC RA600). The electrochemical studies included anodic, cathodic, and linear polarization along with potentiostatic studies. It was found that the inhibition properties of PEG, in the strong alkaline solution, are by far much more efficient than the inhibition capability of GAFAC RA600. Surface analysis obtained with the use of high resolution scanning electron microscopy (HRSEM) revealed different morphology characteristic developed at the zinc surface in the presence of the two inhibitors. A methodology employing electrochemical tests is proposed to quickly and conveniently evaluate inhibitors for Zn in alkaline media.

Ein-Eli, Y.; Auinat, M.; Starosvetsky, D.


Photoelectrochemical and Electrochemical Characterization of Sub-Micro-Gram Amounts of Organic Semiconductors Using Scanning Droplet Cell Microscopy  

PubMed Central

A model organic semiconductor (MDMO-PPV) was used for testing a modified version of a photoelectrochemical scanning droplet cell microscope (PE-SDCM) adapted for use with nonaqueous electrolytes and containing an optical fiber for localized illumination. The most attractive features of the PE-SDCM are represented by the possibility of addressing small areas on the investigated substrate and the need of small amounts of electrolyte. A very small amount (ng) of the material under study is sufficient for a complete electrochemical and photoelectrochemical characterization due to the scanning capability of the cell. The electrochemical behavior of the polymer was studied in detail using potentiostatic and potentiodynamic investigations as well as electrochemical impedance spectroscopy. Additionally, the photoelectrochemical properties were investigated under illumination conditions, and the photocurrents found were at least 3 orders of magnitude higher than the dark (background) current, revealing the usefulness of this compact microcell for photovoltaic characterizations. PMID:25101149



The capacitive characteristics of supercapacitors consisting of activated carbon fabric-polyaniline composites in NaNO 3  

NASA Astrophysics Data System (ADS)

A sandwich-type supercapacitor consisting of two similar activated carbon fabric-polyaniline (ACF-PANI) composite electrodes was demonstrated to exhibit excellent performance (i.e., highly reversibility and good stability) in NaNO 3. Polyaniline with the charge density of polymerization less than or equal to 9 C cm -2 synthesized by means of a potentiostatic method showed a high specific capacitance of 300 F g -1. Influences of the polymerization charge density (i.e., the polymer loading) on the capacitive characteristics of ACF-PANI composites were compared systematically. The capacity of an ACF-PANI electrode reach ca. 3.4 F cm -2 (a 100% increase in total capacity) when the charge density of polymerization is equal to 9 C cm -2. The surface morphology of these ACF-PANI composites was examined by a scanning electron microscope (SEM).

Hu, Chi-Chang; Li, Wen-Yar; Lin, Jeng-Yan


Relaxation phenomena in lithium ion insertion cells and simulation of the Sony cell  

SciTech Connect

Relaxation phenomena in lithium-ion-insertion cells are modeled. Simulation results are presented for a dual lithium-ion-insertion cell and for a cell using a lithium-foil negative electrode. A period of relaxation after a charge or discharge can cause appreciable changes in the distribution of material in the insertion electrodes. Local concentration cells in the solution phase and an open-circuit potential that depends on state of charge for the solid phase drive the redistribution of material. Concentration profiles in solid and solution phases during relaxation are analyzed, and the consequences for cell performance are discussed. The model predicts the effects of relaxation time on multiple charge-discharge cycles and on peak power. Galvanostatic and potentiostatic charging are simulated; the results are compared to experimental data for a commercial battery.

Fuller, T.F.; Doyle, M.; Newman, J. [Univ. of California, Berkeley, CA (United States). Dept. of Chemical Engineering; [Lawrence Berkeley Lab., CA (United States). Materials Sciences Division



One-step through-mask electrodeposition of a porous structure composed of manganese oxide nanosheets with electrocatalytic activity for oxygen reduction  

SciTech Connect

Potentiostatic electrolysis of a mixed aqueous solution of Bu{sub 4}NBr and MnSO{sub 4} at +1.0 V (vs. Ag/AgCl) on Pt electrode led to the oxidation of Br{sup -} and Mn{sup 2+} ions. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and X-ray diffraction (XRD) revealed that this anodic process was followed by the deposition of insulating crystals of bromide salt of Bu{sub 4}N{sup +} and the subsequent formation of layered manganese oxide in the interstitial spaces of the bromide grains already grown. Dissolution of the bromide crystals in water left a well-dispersed porous texture composed of manganese oxide nanosheets. The resulting MnO{sub x}-modified electrode exhibited a larger catalytic current for the reduction of oxygen in alkaline solution, compared to the bare Pt electrode.

Fukuda, Masaki; Iida, Chihiro [Department of Applied Chemistry, Yamaguchi University, 2-16-1 Tokiwadai, Ube 755-8611 (Japan); Nakayama, Masaharu, E-mail: [Department of Applied Chemistry, Yamaguchi University, 2-16-1 Tokiwadai, Ube 755-8611 (Japan)



Influence of monomer concentration on polycarbazole-polyindole (PCz-PIn) copolymer properties: Application in Schottky diode  

NASA Astrophysics Data System (ADS)

Copolymerization of carbazole (Cz) and indole (In) is successfully performed through potentiostatic polymerization; and the influence of the monomer concentrations ratio on copolymer formation, is investigated. It is found that 1:2 ratio of Cz to In monomer is optimum for the synthesis of a copolymer with high electroactivity. The structural, optical, thermal and morphological analysis of the copolymers are carried out with UV-vis, FT-IR spectroscopy, differential scanning coulometry (DSC) and scanning electron microscopic (SEM) technique. Electrochemical and thermal studies, further support better redox activity and thermal stability of the copolymer, respectively. We also report fabrication and characterizations of the electrochemically synthesized copolymer in organic Schottky diode with configuration metal Al/copolymer/indium tin oxide coated glass (ITO). The current density-voltage (J-V) characteristic of the Schottky diode is consequential in extracting the electronic parameters and the charge transport mechanism of the devices.

Gupta, Bhavana; Singh, Arun Kumar; Melvin, Ambrose A.; Prakash, Rajiv



Cooperative stochastic behavior in localized corrosion. 2: Experiments  

SciTech Connect

Two types of experiments on metastable pitting are carried out in NaCl solutions, one with galvanically coupled Al-2% Cu and the second with 316L stainless steel under potentiostat control; the time dependence of the current is compared to simulated time series developed from the model of Part 1 of these two papers. The experimental and simulated time series are analyzed by several methods in order to extract defining characteristics, and specifically the degree to which interactions among metastable pitting events are present. The similarity between the model and the experiment, particularly of the stainless steel data, is strong, most important when the intermittent transitions between low and high activity metastable pitting regions are considered. Depending on the experimental conditions, large deviations from the Poissonian statistics are observed which agree with the predictions of the model.

Lunt, T.T.; Pride, S.T.; Scully, J.R.; Hudson, J.L. [Univ. of Virginia, Charlottesville, VA (United States); Mikhailov, A.S. [Max-Planck-Gesellschaft, Berlin (Germany). Fritz-Haber-Institut



Electrochemical flowcell for in-situ investigations by soft x-ray absorption and emission spectroscopy  

SciTech Connect

A new liquid flow-cell designed for electronic structure investigations at the liquid-solid interface by soft X-ray absorption and emission spectroscopy is presented. A thin membrane serves simultaneously as a substrate for the working electrode and solid state samples as well as for separating the liquid from the surrounding vacuum conditions. In combination with counter and reference electrodes this approach allows in-situ studies of electrochemical deposition processes and catalytic reactions at the liquid-solid interface in combination with potentiostatic measurements. As model system in-situ monitoring of the deposition process of Co metal from a 10 mM CoCl{sub 2} aqueous solution by X-ray absorption and emission spectroscopy is presented.

Schwanke, C.; Lange, K. M., E-mail: [Helmholtz-Zentrum Berlin fr Materialien und Energie, Institute of Solar Fuels, Albert-Einstein-Strae 15, 12489 Berlin (Germany); Golnak, R.; Xiao, J. [Helmholtz-Zentrum Berlin fr Materialien und Energie, Institute of Methods for Material Development, Albert-Einstein-Strae 15, 12489 Berlin (Germany)



Electrodeposition of indium on molybdenum studied with optical second harmonic generation and electrochemical impedance spectroscopy  

NASA Astrophysics Data System (ADS)

In this work, we study kinetics of indium deposition onto a molybdenum substrate under electrochemical control. We show that mass transfer limited slow electrode position of In on Mo cannot be detected with traditional cyclic voltammetry. However, the In-deposited surface modifications of Mo are readily detected with optical second harmonic generation (SHG). By analyzing potentiostatic current transients, we show that the adsorption kinetics of In on Mo are dominated by 3D progressive nucleation. The SHG results provide further support to this conclusion. We also examine the relative roles of In-deposition and anion coadsorption under diffusion control by using fast Fourier transform electrochemical impedance spectroscopy (FFT-EIS). The results demonstrate how the process of surface modification by electrodeposition can be studied by combining SHG with FFT-EIS.

Pettit, C. M.; Garland, J. E.; Etukudo, N. R.; Assiongbon, K. A.; Emery, S. B.; Roy, D.



Electrochemical removal of tannins from aqueous solutions  

SciTech Connect

The application of electrochemical methods to remove tannins from wastewater was investigated. Gallotannic acid was used as the reference substance. Electrochemical experiments were performed using platinum electrodes. Macroscale potentiostatic or galvanostatic electrolyses were carried out with sodium sulfate or sodium chloride as supporting electrolytes, to analyze direct and indirect oxidation processes. Operating variables such as pH and chloride concentration were considered to determine their influence on the efficiency and energy consumption of the process. The simulation of a pilot plant was carried out with a mathematical model, the parameters of which were determined by fitting of experimental profiles. The results of a preliminary investigation on the oxidation-coagulation process using sacrificial electrodes are also reported.

Buso, A.; Balbo, L.; Giomo, M.; Farnia, G.; Sandona, G.



Preselection of Ni-Cr(-Mo) alloys as potential canister materials for vitrified high active nuclear waste by electrochemical testing  

NASA Astrophysics Data System (ADS)

Several Ni-Cr(-Mo) alloys (Hastelloy C4, Inconel 625, Sanicro 28, Incoloy 825, Inconel 690) were tested by electrochemical methods to characterize their corrosion behavior in chloride containing solutions at various temperatures and pH-values in respect to their application as canister materials for final radioactive waste storage. Especially, Hastelloy C4 was tested by potentiodynamic, potentiostatic and galvanostic measurements. As electrolytes H 2SO 4 solutions were used, as parameters temperature, chloride content and pH-value were varied. All tested alloys showed a clearly limited resistance against pitting corrosion phenomena; under severe conditions even crevice corrosion phenomena were observed. The best corrosion behavior, however, is shown by Hastelloy C4, which has the lowest passivation current density of all tested alloys and the largest potential region with protection against local corrosion phenomena.

Bort, H.; Wolf, I.; Leistikow, S.



Anodic growth of highly ordered TiO2 nanotube arrays to 134 microm in length.  


Described is the fabrication of self-aligned highly ordered TiO(2) nanotube arrays by potentiostatic anodization of Ti foil having lengths up to 134 mum, representing well over an order of magnitude increase in length thus far reported. We have achieved the very long nanotube arrays in fluoride ion containing baths in combination with a variety of nonaqueous organic polar electrolytes including dimethyl sulfoxide, formamide, ethylene glycol, and N-methylformamide. Depending on the anodization voltage, pore diameters of the resulting nanotube arrays range from 20 to 150 nm. Our longest nanotube arrays yield a roughness factor of 4750 and length-to-width (outer diameter) aspect ratio of approximately 835. The as-prepared nanotubes are amorphous but crystallize with annealing at elevated temperatures. In initial measurements, 45 mum long nanotube-array samples, 550 degrees C annealed, under UV illumination show a remarkable water photoelectrolysis photoconversion efficiency of 16.25%. PMID:16913737

Paulose, Maggie; Shankar, Karthik; Yoriya, Sorachon; Prakasam, Haripriya E; Varghese, Oomman K; Mor, Gopal K; LaTempa, Thomas J; Latempa, Thomas A; Fitzgerald, Adriana; Grimes, Craig A



Synthesis and thermoelectric/electrical characterization of electrodeposited Sb{sub x}Te{sub y} thin films  

SciTech Connect

Sb{sub x}Te{sub y} films were potentiostatically electrodeposited from acidic nitric baths at room temperature by controlling the applied potential. Near-stoichiometric Sb{sub 2}Te{sub 3} thin films were obtained at applied potentials between ?0.15 and ?0.30 V vs. saturated calomel electrode (SCE). Post-annealing in a reducing environment resulted in an improvement in the crystal structure without the evaporation of the Te element. This result was indicated by a significant reduction in the electrical resistance and decrease in the FWHM of the main diffraction peaks. The power factor (?S{sup 2}) increased from 44.2 to 372.1 ?W/m K{sup 2} after annealing at 473 K.

Lim, Jae-Hong; Park, MiYeong; Lim, Dong-Chan [Materials Processing Division, Korea Institute of Materials Science, 66, Sangnam-dong, Changwon 641-010 (Korea, Republic of)] [Materials Processing Division, Korea Institute of Materials Science, 66, Sangnam-dong, Changwon 641-010 (Korea, Republic of); Myung, Nosang V. [Department of Chemical and Environmental Engineering, University of California-Riverside, Riverside, CA 92521 (United States)] [Department of Chemical and Environmental Engineering, University of California-Riverside, Riverside, CA 92521 (United States); Lee, Jung-Ho [Division of Materials and Chemical Engineering, Hanyang University, Kyeonggi 426-791 (Korea, Republic of)] [Division of Materials and Chemical Engineering, Hanyang University, Kyeonggi 426-791 (Korea, Republic of); Jeong, Young-Keun [Hybrid Materials Solution NCRC, Pusan National University, Busan 609-735 (Korea, Republic of)] [Hybrid Materials Solution NCRC, Pusan National University, Busan 609-735 (Korea, Republic of); Yoo, Bongyoung, E-mail: [Division of Materials and Chemical Engineering, Hanyang University, Kyeonggi 426-791 (Korea, Republic of)] [Division of Materials and Chemical Engineering, Hanyang University, Kyeonggi 426-791 (Korea, Republic of); Lee, Kyu Hwan, E-mail: [Materials Processing Division, Korea Institute of Materials Science, 66, Sangnam-dong, Changwon 641-010 (Korea, Republic of)



Electro-Mechanical Actuation of Carbon Nanotube Yarns, Sheets, Composites  

NASA Astrophysics Data System (ADS)

We report preparation of highly conductive carbon nanotube yarns and sheets. The materials aim at such applications as electronic textiles, electro-mechanical actuators, and conductive coatings. The electro-mechanical response of the specimens was measured using custom made force transducer operating in an isometric mode. The measurements were carried out at room temperature in aqueous and organic electrolytes; square-wave potential of variable amplitude was applied with a potentiostat. It was found that the maximum isometric stress generated by nanotube actuators could be as large as 12 MPa. This approaches the stress generation capability of commercial ferroelectrics and is significantly larger than that of natural muscles. A variety of applications of the materials is discussed.

Oh, Jiyoung; Kozlov, Mikhail; Zhang, Mei; Fang, Shaoli; Baughman, Ray



Kinetic model of the electrochemical oxidation of graphitic carbon in acidic environments.  


The electrochemical oxidation of graphitic carbon results in the performance decay of electrochemical systems such as aqueous, acidic fuel cells, redox-flow batteries, and supercapacitors. An electrochemical mechanism and numerical model is proposed to explain long-standing questions. The model predicts carbon weight loss and surface oxide growth as a function of time, temperature, and potential. Experimentally observed phenomena are discussed and analyzed using the numerical model. Three mechanisms are concluded to contribute to the current decay commonly observed during electrochemical oxidation: mass loss, reversible passive oxide formation, and irreversible oxide formation. Although reversible passive oxide formation governs the current decay under potentiostatic oxidation, a reduction in the equilibrium catalytic oxide is the most significant decay mechanism under potential cycling. Finally, the model is used to determine the change in active site concentration resulting from high-temperature heat treatment of carbon black. PMID:20024428

Gallagher, Kevin G; Fuller, Thomas F



An electronic pollen detection method using Coulter counting principle  

NASA Astrophysics Data System (ADS)

A method for detecting and counting pollen particles based on Coulter counting principle is presented. This approach also provides information on the size and surface charges of the micro particles, allowing for preliminary differentiation of pollens from other micro particles. Three samples are studied: polymethyl methacrylate particles, tree pollens from Juniperus Scopulorum and grass pollens from Secale Cerale. The samples, suspended in diluted KCl aqueous solutions in an electrochemical cell, were allowed to pass through a microchannel and the conductance of the microchannel was sampled with a Gamry Potentiostat. The changes in the conductance due to the passing of the micro particles was thus recorded and analyzed. The experimental results showed that tree pollens and grass pollens display distinctive behaviors. The phenomena may be attributed to the differences in the surface characteristics of the pollens and is potentially useful for counting and differentiating different micro particles.

Zhang, Zheng; Zhe, Jiang; Chandra, Santanu; Hu, Jun


Electrochemical Behavior of Epinephrine at a Glassy Carbon Electrode Modified by Electrodeposited Films of Caffeic Acid  

PubMed Central

A stable electroactive thin film of poly(caffeic acid) has been deposited on the surface of a glassy carbon electrode by potentiostatic technique in an aqueous solution containing caffeic acid. The voltammetric behavior of epinephrine (EP) at the poly(caffeic acid) modified glassy carbon electrode was studied by cyclic voltammetry. The poly(caffeic acid) modified electrode exhibited a promotion effect on the oxidation of EP. In a pH 7.4 phosphate buffer, the anodic current increased linearly with the concentration of EP in the range from 2.0 10?6 to 3.0 10?4 mol L?1 and the detection limit for EP was 6.0 10?7 mol L?1. The proposed method can be applied to the determination of EP in practical injection samples with simplicity, rapidness and accurate results.

Ren, Wang; Luo, Hong Qun; Li, Nian Bing



Effects of TiN coating on the corrosion of nanostructured Ti-30Ta-xZr alloys for dental implants  

NASA Astrophysics Data System (ADS)

Electrochemical characteristics of a titanium nitride (TiN)-coated/nanotube-formed Ti-Ta-Zr alloy for biomaterials have been researched by using the magnetic sputter and electrochemical methods. Ti-30Ta-xZr (x = 3, 7 and 15 wt%) alloys were prepared by arc melting and heat treated for 24 h at 1000 C in an argon atmosphere and then water quenching. The formation of oxide nanotubes was achieved by anodizing a Ti-30Ta-xZr alloy in H3PO4 electrolytes containing small amounts of fluoride ions at room temperature. Anodization was carried out using a scanning potentiostat, and all experiments were conducted at room temperature. The microstructure and morphology of nanotube arrays were characterized by optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The TiN coatings were obtained by the radio-frequency (RF) magnetron sputtering technique. The depositions were performed from pure Ti targets on Ti-30Ta-xZr alloys substrates. The corrosion properties of the specimens were examined using potentiodynamic test in a 0.9% NaCl solution by using potentiostat. The microstructures of Ti-30Ta-xZr alloys were changed from an equiaxed to a needle-like structure with increasing Zr content. The interspace between the nanotubes was approximately 20, 80 and 200 nm for Zr contents of 3, 7 and 15 wt%, respectively. The corrosion resistance of the TiN-coated on the anodized Ti-30Ta-xZr alloys was higher than that of the untreated Ti alloys, indicating a better protective effect.

Kim, Won-Gi; Choe, Han-Cheol



Electrochemically and bioelectrochemically induced ammonium recovery.  


Streams such as urine and manure can contain high levels of ammonium, which could be recovered for reuse in agriculture or chemistry. The extraction of ammonium from an ammonium-rich stream is demonstrated using an electrochemical and a bioelectrochemical system. Both systems are controlled by a potentiostat to either fix the current (for the electrochemical cell) or fix the potential of the working electrode (for the bioelectrochemical cell). In the bioelectrochemical cell, electroactive bacteria catalyze the anodic reaction, whereas in the electrochemical cell the potentiostat applies a higher voltage to produce a current. The current and consequent restoration of the charge balance across the cell allow the transport of cations, such as ammonium, across a cation exchange membrane from the anolyte to the catholyte. The high pH of the catholyte leads to formation of ammonia, which can be stripped from the medium and captured in an acid solution, thus enabling the recovery of a valuable nutrient. The flux of ammonium across the membrane is characterized at different anolyte ammonium concentrations and currents for both the abiotic and biotic reactor systems. Both systems are compared based on current and removal efficiencies for ammonium, as well as the energy input required to drive ammonium transfer across the cation exchange membrane. Finally, a comparative analysis considering key aspects such as reliability, electrode cost, and rate is made. This video article and protocol provide the necessary information to conduct electrochemical and bioelectrochemical ammonia recovery experiments. The reactor setup for the two cases is explained, as well as the reactor operation. We elaborate on data analysis for both reactor types and on the advantages and disadvantages of bioelectrochemical and electrochemical systems. PMID:25651406

Gildemyn, Sylvia; Luther, Amanda K; Andersen, Stephen J; Desloover, Joachim; Rabaey, Korneel



The electrochemical behavior and surface analysis of Ti49.6Ni45.1Cu5Cr0.3 alloy for orthodontic usage.  


The aim of this study was to investigate the electrochemical behavior of Ti(49.6)Ni(45.1)Cu(5)Cr(0.3) (TiNiCuCr) alloy in artificial saliva solutions with a wide rage of pH values and to characterize the surface passive film after polarization tests. This article represents the ideal, static environment and associated electrochemical response and comparison values. The corrosion behavior of TiNiCuCr alloy was systematically studied by open circuit potential, potentiodynamic, potentiostatic, and electrochemical impedance techniques. Potentiodynamic and potentiostatic test results showed that the corrosion behavior of TiNiCuCr was similar to that of NiTi alloy. Both corrosion potential (E(corr)) and pitting corrosion potential (E(b)) showed a pH-dependent tendency that E(corr) and E(b) decreased with the increase of the pH value. X-ray photoelectron spectroscopy results revealed the composition of the passive film consisted mainly of TiO(2) with a little amount of Ni oxides (NiO/Ni(2)O(3)) that was identical with NiTi alloy. Besides Ni, a Cu enriched sub-layer was also found. The nickel ion release rate showed a typical time-related decrease as examined by ICP/OES. In conclusion, the addition of Cu and Cr had little effect on the corrosion behavior of NiTi or on the composition and the structure of the passive film. PMID:18161810

Zheng, Y-F; Wang, Q Y; Li, L



Prediction of Failure Due to Thermal Aging, Corrosion and Environmental Fracture in Amorphous and Titanium Alloys  

SciTech Connect

DARPA is exploring a number of advanced materials for military applications, including amorphous metals and titanium-based alloys. Equipment made from these materials can undergo degradation due to thermal aging, uniform corrosion, pitting, crevice corrosion, denting, stress corrosion cracking, corrosion fatigue, hydrogen induced cracking and microbial influenced corrosion. Amorphous alloys have exceptional resistance to corrosion, due in part to the absence of grain boundaries, but can undergo crystallization and other phase instabilities during heating and welding. Titanium alloys are extremely corrosion resistant due to the formation of a tenacious passive film of titanium oxide, but is prone to hydrogen absorption in crevices, and hydrogen induced cracking after hydrogen absorption. Accurate predictions of equipment reliability, necessary for strategic planning, requires integrated models that account for all relevant modes of attack, and that can make probabilistic predictions. Once developed, model parameters must be determined experimentally, and the validity of models must be established through careful laboratory and field tests. Such validation testing requires state-of-the-art surface analytical techniques, as well as electrochemical and fracture mechanics tests. The interaction between those processes that perturb the local environment on a surface and those that alter metallurgical condition must be integrated in predictive models. The material and environment come together to drive various modes of corrosive attack (Figure 1). Models must be supported through comprehensive materials testing capabilities. Such capabilities are available at LLNL and include: the Long Term Corrosion Test Facility (LTCTF) where large numbers of standard samples can be exposed to realistic test media at several temperature levels; a reverse DC machine that can be used to monitor the propagation of stress corrosion cracking (SCC) in situ; and banks of potentiostats with temperature controlled cells for potentiostatic and potentiodynamic testing (Figure 2).

Farmer, J C



Power management systems for sediment microbial fuel cells in high power and continuous power applications  

NASA Astrophysics Data System (ADS)

The objective of this dissertation was to develop power management systems (PMS) for sediment microbial fuel cells (SFMCs) for high power and continuous applications. The first part of this dissertation covers a new method for testing the performance of SMFCs. This device called the microbial fuel cell tester was developed to automatically test power generation of PMS. The second part focuses on a PMS capable of delivering high power in burst mode. This means that for a small amount of time a large amount of power up to 2.5 Watts can be delivered from a SMFC only generating mW level power. The third part is aimed at developing a multi-potentiostat laboratory tool that measures the performance at fixed cell potentials of microbial fuel cells so that I can optimize them for use with the PMS. This tool is capable of controlling the anode potential or cathode potential and measuring current of six separate SMFCs simultaneously. By operating multiple potentiostats, I was able to run experiments that find ideal operating conditions for the sediment microbial fuel cells, and also I can optimize the power management system for these conditions. The fourth part of the dissertation is targeting a PMS that was able to operate a sensor continuously which was powered by an SMFC. In pervious applications involving SMFCs, the PMS operated in batch mode. In this PMS, the firmware on the submersible ultrasonic receiver (SUR) was modified for use with my PMS. This integration of PMS and SUR allowed for the continuous operation of the SUR without using a battery. Finally, the last part of the dissertation recommends a scale-up power management system to overcome the linearity scale up issue of SMFCs as future work. Concluding remarks are also added to summarize the goal and focus of this dissertation.

Donovan, Conrad Koble


Analysis of electrochemical noise from metastable pitting in aluminum, aged Al-2%Cu, and AA 2024-T3  

SciTech Connect

The authors compare methods of analyzing electrochemical current (ECN) and potential (EPN) noise data associated with metastable pitting and the transition from metastable to stable pitting. Various analysis methods were applied to electrochemical noise data associated with metastable pit events on aluminum, aged Al-2%Cu, and AA 2024-T3 ST. Two experimental approaches were used. High-purity Al, roughly simulating copper-depleted grain boundary zones in aged Al-Cu alloys, was potentiostatically polarized so that current spikes associated with individual pitting events could be analyzed. Second, the coupling current between nominally identical galvanically coupled Al, aged Al-2%Cu, and AA 2024-T3 ST electrodes was recorded in conjunction with couple potential using a saturated calomel reference electrode. Pit stabilization occurred when individual pits exceeded a threshold of I{sub pit}/r{sub pit} > 10{sup {minus}2} A/cm at all times during pit growth as established from potentiostatic measurements. The magnitude of this ratio is linked directly to the concentration of the aggressive solution within pits. Two related statistical pit stabilization factors (I{sub rms}/r{sub pit total} from ECN data and the mean of (I{sub peak}-I{sub ox})/r{sub pit} values from each pit current spike) were obtained from galvanic ECN data containing a large number of pit current spikes. These parameters provided a better indication of the transition to stable pitting than the pitting index or noise resistance but also had shortcomings. Spectral analysis using current and potential spectral power density (SPD) data provided qualitative information on pit susceptibility. However, the transition to stable pitting could not be accurately defined because of a lack of information on pit sizes in spectral data.

Pride, S.T.; Scully, J.R.; Hudson, J.L. [Univ. of Virginia, Charlottesville, VA (United States)



Statistic analysis of operational influences on the cold start behaviour of PEM fuel cells  

NASA Astrophysics Data System (ADS)

For portable fuel cell systems a multitude of applications have been presented over the past few years. Most of these applications were developed for indoor use, and not optimised for outdoor conditions. The key problem concerning this case is the cold start ability of the polymer electrolyte membrane fuel cell (PEMFC). This topic was first investigated by the automotive industry, which has the same requirements for alternative traction systems as for conventional combustion engines. The technical challenge is the fact that produced water freezes to ice after shut-down of the PEMFC and during start-up when the temperature is below 0 C. To investigate the basic cold start behaviour isothermal, potentiostatic single cell experiments were performed and the results are presented. The cold start behaviour is evaluated using the calculated cumulated charge transfer through the membrane which directly corresponds with the amount of produced water in the PEMFC. The charge transfer curves were mathematically fitted to obtain only three parameters describing the cold start-up with the cumulated charge transfer density and the results are analysed using the statistical software Cornerstone 4.0. The results of the statistic regression analyses are used to establish a statistic-based prediction model of the cold start behaviour which describes the behaviour of the current density during the experiment. The regression shows that the initial start current mainly depends on the membrane humidity and the operation voltage. After the membrane humidity has reached its maximum, the current density drops down to zero. The current decay also depends on the constant gas flows of the reactant gases. Ionic conductivity of the membrane and charge transfer resistance were investigated by a series of ac impedance spectra during potentiostatic operation of the single cell at freezing temperatures. Cyclic voltammetry and polarisation curves between cold start experiments show degradation effects by ice formation in the porous structures which lead to significant performance loss.

Oszcipok, M.; Riemann, D.; Kronenwett, U.; Kreideweis, M.; Zedda, M.


Real-time telemetry system for amperometric and potentiometric electrochemical sensors.  


A real-time telemetry system, which consists of readout circuits, an analog-to-digital converter (ADC), a microcontroller unit (MCU), a graphical user interface (GUI), and a radio frequency (RF) transceiver, is proposed for amperometric and potentiometric electrochemical sensors. By integrating the proposed system with the electrochemical sensors, analyte detection can be conveniently performed. The data is displayed in real-time on a GUI and optionally uploaded to a database via the Internet, allowing it to be accessed remotely. An MCU was implemented using a field programmable gate array (FPGA) to filter noise, transmit data, and provide control over peripheral devices to reduce power consumption, which in sleep mode is 70 mW lower than in operating mode. The readout circuits, which were implemented in the TSMC 0.18-?m CMOS process, include a potentiostat and an instrumentation amplifier (IA). The measurement results show that the proposed potentiostat has a detectable current range of 1 nA to 100 ?A, and linearity with an R2 value of 0.99998 in each measured current range. The proposed IA has a common-mode rejection ratio (CMRR) greater than 90 dB. The proposed system was integrated with a potentiometric pH sensor and an amperometric nitrite sensor for in vitro experiments. The proposed system has high linearity (an R2 value greater than 0.99 was obtained in each experiment), a small size of 5.6 cm 8.7 cm, high portability, and high integration. PMID:22164093

Wang, Wei-Song; Huang, Hong-Yi; Chen, Shu-Chun; Ho, Kuo-Chuan; Lin, Chia-Yu; Chou, Tse-Chuan; Hu, Chih-Hsien; Wang, Wen-Fong; Wu, Cheng-Feng; Luo, Ching-Hsing



Utilization of subsurface microbial electrochemical systems to elucidate the mechanisms of competition between methanogenesis and microbial iron(III)/humic acid reduction in Arctic peat soils  

NASA Astrophysics Data System (ADS)

High-latitude peat soils are a major carbon reservoir, and there is growing concern that previously dormant carbon from this reservoir could be released to the atmosphere as a result of continued climate change. Microbial processes, such as methanogenesis and carbon dioxide production via iron(III) or humic acid reduction, are at the heart of the carbon cycle in Arctic peat soils [1]. A deeper understanding of the factors governing microbial dominance in these soils is crucial for predicting the effects of continued climate change. In previous years, we have demonstrated the viability of a potentiostatically-controlled subsurface microbial electrochemical system-based biosensor that measures microbial respiration via exocellular electron transfer [2]. This system utilizes a graphite working electrode poised at 0.1 V NHE to mimic ferric iron and humic acid compounds. Microbes that would normally utilize these compounds as electron acceptors donate electrons to the electrode instead. The resulting current is a measure of microbial respiration with the electrode and is recorded with respect to time. Here, we examine the mechanistic relationship between methanogenesis and iron(III)- or humic acid-reduction by using these same microbial-three electrode systems to provide an inexhaustible source of alternate electron acceptor to microbes in these soils. Chamber-based carbon dioxide and methane fluxes were measured from soil collars with and without microbial three-electrode systems over a period of four weeks. In addition, in some collars we simulated increased fermentation by applying acetate treatments to understand possible effects of continued climate change on microbial processes in these carbon-rich soils. The results from this work aim to increase our fundamental understanding of competition between electron acceptors, and will provide valuable data for climate modeling scenarios. 1. Lipson, D.A., et al., Reduction of iron (III) and humic substances plays a major role in anaerobic respiration in an Arctic peat soil. Journal of Geophysical Research-Biogeosciences, 2010. 115. 2. Friedman, E.S., et al., A cost-effective and field-ready potentiostat that poises subsurface electrodes to monitor bacterial respiration. Biosensors and Bioelectronics, 2012. 32(1): p. 309-313.

Friedman, E. S.; Miller, K.; Lipson, D.; Angenent, L. T.



Corrosion resistance, chemistry, and mechanical aspects of Nitinol surfaces formed in hydrogen peroxide solutions  

SciTech Connect

Ti oxides formed naturally on Nitinol surfaces are only a few nanometers thick. To increase their thickness, heat treatments are explored. The resulting surfaces exhibit poor resistance to pitting corrosion. As an alternative approach to accelerate surface oxidation and grow thicker oxides, the exposure of Nitinol to strong oxidizing H2O2 aqueous solutions (3 and 30%) for various periods of time was used. Using X-Ray Photoelectron Spectroscopy (XPS) and Auger spectroscopy, it was found that the surface layers with variable Ti (615 at %) and Ni (513 at %) contents and the thickness up to 100 nm without Ni-enriched interfaces could be formed. The response of the surface oxides to stress in superelastic regime of deformations depended on oxide thickness. In the corrosion studies performed in both strained and strain-free states using potentiodynamic and potentiostatic polarizations, the surfaces treated in H2O2 showed no pitting in corrosive solution that was assigned to higher chemical homogeneity of the surfaces free of secondary phases and inclusions that assist better biocompatibility of Nitinol medical devices. 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 100B: 14901499, 2012

Shabalovskay, Svetlana A.; Anderegg, James W.; Undisz, Andreas; Rettenmayr, Markus; Rondelli, Gianni C.



STM-SEM combination study on the electrochemical growth mechanism and structure of gold overlayers. A quantitative approach to electrochemical metal surface roughening  

NASA Astrophysics Data System (ADS)

The growth mode and structure of gold overlayers resulting from the electroreduction of thick oxide films are studied using potentiodynamic and potentiostatic techniques combined with ex-situ STM and SEM. Electroreduction of the thick gold oxide at low overpotentials, that is slowly grown gold overlayers, results in a close-packed array of grains exhibiting a low roughness factor. Grains in the order of 100 nm of radii are formed by aggregation of small monomers. At higher overpotentials, fast grown gold overlayers, we suggest that the monomer growth results in a columnar structure terminated on rounded domes with radii ranging between 10 and 20 nm. This overlayer exhibits a roughness factor which increases according to electrodeposit height. The columnar structure is unstable decreasing its surface free energy by coalescence of small columns to form large units leading to a drastic decrease in the surface area with ageing time. A mechanism for the growth mode is proposed where the crystallite size depends on the diffusion length of the electrodepositing particles which is controlled by the applied overpotential.

Vazquez, L.; Bartolome, A.; Baro, A. M.; Alonso, C.; Salvarezza, R. C.; Arvia, A. J.



Low-melting-point titanium-base brazing alloyspart 2: Characteristics of brazing Ti-21Ni-14Cu on Ti-6Al-4v substrate  

NASA Astrophysics Data System (ADS)

Filler metal of a low-melting-point (917 C) Ti-21Ni-14Cu was brazed onto the substrate of Ti-6Al-4V alloy at 960 C for 2,4, and 8 h to investigate the microstructural evolution and electrochemical characteristics of the brazed metal as a function of the period of brazing time. Optical microscopy, scanning and transmission electron microscopy, and x-ray diffractometry were used to characterize the microstructure and phase of the brazed metal; also, the potentiostat was used for corrosion study. Experimental results indicate that diffusion of copper and nickel from the filler metal into the equiaxed a plus intergranular ? structure of Ti-6Al-4V substrate causes the lamellar Widmansttten structure to form. The intermetallic Ti2Ni phase existing in the prior filler metal diminishes, while the Ti2Cu phase can be identified for the metal brazed at 960 C for 2 h, but the latter phase decreases with time. Advantage might be taken from the evidence of faster diffusion of nickel than copper along the ? phase to the substrate. In deaerated Hanks solution, corrosion potential, corrosion current density, and critical potential for active-to-passive transition decrease while the passivation range broadens with the period of brazing time. However, all the brazed metals, immersed for different periods in oxygen-saturated Hanks solution, show similar corrosion behavior, irrespective of the brazing time.

Chang, E.; Chen, C.-H.



Experimental and Quantum Studies on Adsorption and Corrosion Inhibition Effect of Imidazole Derivatives on N80 Steel in Hydrochloric Acid  

NASA Astrophysics Data System (ADS)

The inhibition effect of synthesized N?-(phenylmethylidene)-2-(2-methyl-1H-benzimidazol-1-yl)acetohydrazides, N?-(4-methylphenylmethylidene)-2-(2-methyl-1H-benzimidazol-1-yl)acetohydrazides, and N?-(4-methoxyphenylmethylidene)-2-(2-methyl-1H-benzimidazol-1-yl)acetohydrazides on the corrosion behaviour of N80 steel in 15% hydrochloric acid solution was investigated using weight loss, potentiostatic polarization and electrochemical impedance spectroscopy methods. The inhibition efficiency increased as the concentration of the inhibitors was increased. The effect of temperature on corrosion inhibition was investigated by weight loss method and thermodynamic parameters were calculated. Potentiodynamic polarization measurements show that all the three studied inhibitors act as mixed inhibitor. The adsorption of inhibitors on N80 steel surface obeys Langmuir adsorption isotherm. The structure of inhibitors was optimized using semiemperical AM1 method. Theoretical parameters such as the highest occupied molecular orbital (EHOMO), lowest unoccupied molecular orbital (ELUMO) energy levels, energy gap (?E = ELUMO - EHOMO), dipole moment (?), global hardness (?), softness (?), binding energy, molecular surface area and the fraction of electrons transferred (?N) were calculated and the adsorption mechanism was discussed. Scanning electron microscopy was used to characterize the surface marphology of the N80 steel.

Yadav, M.; Kumar, Sumit; Sharma, Dipti; Yadav, P. N.



Development of Amperometric Biosensors Based on Nanostructured Tyrosinase-Conducting Polymer Composite Electrodes  

PubMed Central

Bio-composite coatings consisting of poly(3,4-ethylenedioxythiophene) (PEDOT) and tyrosinase (Ty) were successfully electrodeposited on conventional size gold (Au) disk electrodes and microelectrode arrays using sinusoidal voltages. Electrochemical polymerization of the corresponding monomer was carried out in the presence of various Ty amounts in aqueous buffered solutions. The bio-composite coatings prepared using sinusoidal voltages and potentiostatic electrodeposition methods were compared in terms of morphology, electrochemical properties, and biocatalytic activity towards various analytes. The amperometric biosensors were tested in dopamine (DA) and catechol (CT) electroanalysis in aqueous buffered solutions. The analytical performance of the developed biosensors was investigated in terms of linear response range, detection limit, sensitivity, and repeatability. A semi-quantitative multi-analyte procedure for simultaneous determination of DA and CT was developed. The amperometric biosensor prepared using sinusoidal voltages showed much better analytical performance. The Au disk biosensor obtained by 50 mV alternating voltage amplitude displayed a linear response for DA concentrations ranging from 10 to 300 ?M, with a detection limit of 4.18 ?M. PMID:23698270

Lupu, Stelian; Lete, Cecilia; Balaure, Paul C?t?lin; Caval, Dan Ion; Mihailciuc, Constantin; Lakard, Boris; Hihn, Jean-Yves; del Campo, Francisco Javier



Joint mapping of mobility and trap density in colloidal quantum dot solids.  


Field-effect transistors have been widely used to study electronic transport and doping in colloidal quantum dot solids to great effect. However, the full power of these devices to elucidate the electronic structure of materials has yet to be harnessed. Here, we deploy nanodielectric field-effect transistors to map the energy landscape within the band gap of a colloidal quantum dot solid. We exploit the self-limiting nature of the potentiostatic anodization growth mode to produce the thinnest usable gate dielectric, subject to our voltage breakdown requirements defined by the Fermi sweep range of interest. Lead sulfide colloidal quantum dots are applied as the active region and are treated with varying solvents and ligands. In an analysis complementary to the mobility trends commonly extracted from field-effect transistor studies, we focus instead on the subthreshold regime and map out the density of trap states in these nanocrystal films. The findings point to the importance of comprehensively mapping the electronic band- and gap-structure within real quantum solids, and they suggest a new focus in investigating quantum dot solids with an aim toward improving optoelectronic device performance. PMID:23786265

Stadler, Philipp; Sutherland, Brandon R; Ren, Yuan; Ning, Zhijun; Simchi, Arash; Thon, Susanna M; Hoogland, Sjoerd; Sargent, Edward H



Effects of dilution on methane entering an SOFC anode  

NASA Astrophysics Data System (ADS)

Methane and other hydrocarbons such as propane and butane are ideal fuels for SOFCs operating in portable devices for domestic or leisure use [J. Power Sources 71 (1998) 268]. This paper addresses the fuel entry conditions necessary for such devices. A gas manifold system was connected to a micro-tubular zirconia cell 2 mm diameter with lanthanum strontium manganite cathode and nickel/zirconia/ceria anode. Wire current collectors were used to obtain electrochemical performance data via a potentiostat system. The reaction products from the anode were analysed by mass spectroscopy to elucidate the reaction mechanism, and temperature programmed oxidation allowed the carbon deposition to be evaluated [Proceedings of the 4th European Solid Oxide Fuel Cell Forum, Luzern, July 2001, p.151]. Carbon deposition was substantial near open circuit voltage, when little oxygen was flowing to the anode. Dilution with inert gas or with CO 2 caused a significant change in the reaction mechanism. The conclusion was that diluted methane could be fed directly into the SOFC, and that particular compositions (e.g. biogas at 30% methane and 70% carbon dioxide) gave optimum performance with little carbon fouling.

Kendall, K.; Finnerty, C. M.; Saunders, G.; Chung, J. T.


Seed layer-free electrodeposition of well-aligned ZnO submicron rod arrays via a simple aqueous electrolyte  

SciTech Connect

A potentiostatic electrodeposition technique was used to directly fabricate large-scale, well-aligned, and single-crystalline submicron ZnO rod arrays on tin doped indium oxide glass substrate without a pre-prepared seed layer of ZnO from an aqueous solution only containing zinc nitrate. The effects of electrochemical parameters, such as electrodeposition potential, electrodeposition duration, solution temperature, and precursor concentration, on the orientation, morphology, aspect ratio, and growth rate of ZnO rod arrays were systematically investigated. Results show that submicron ZnO rod arrays with (0 0 0 2) preferred orientation and perfect crystallization were obtained when electrodeposition potential was in the range from -0.6 to -1.1 V and solution temperature was controlled above 60 deg. C. Both high solution temperature and low precursor concentration resulted in the decrease in rod diameters. Photoluminescence measures showed that small diameter and nanotips of ZnO rod arrays should be responsible for strong and sharp ultraviolet emission in the room temperature photoluminescence spectra.

Xu Feng [State Key Laboratory of Materials-Oriented Chemical Engineering, College of Materials Science and Engineering, Nanjing University of Technology, No. 5 Xinmofan Road, Nanjing 210009 (China); Lu Yinong, E-mail: [State Key Laboratory of Materials-Oriented Chemical Engineering, College of Materials Science and Engineering, Nanjing University of Technology, No. 5 Xinmofan Road, Nanjing 210009 (China); Xia Lili; Xie Yan; Dai Min; Liu Yunfei [State Key Laboratory of Materials-Oriented Chemical Engineering, College of Materials Science and Engineering, Nanjing University of Technology, No. 5 Xinmofan Road, Nanjing 210009 (China)



Electrochemical generation of oxygen. 1: The effects of anions and cations on hydrogen chemisorption and anodic oxide film formation on platinum electrode. 2: The effects of anions and cations on oxygen generation on platinum electrode  

NASA Technical Reports Server (NTRS)

The effects were studied of anions and cations on hydrogen chemisorption and anodic oxide film formation on Pt by linear sweep voltammetry, and on oxygen generation on Pt by potentiostatic overpotential measurement. The hydrogen chemisorption and anodic oxide film formation regions are greatly influenced by anion adsorption. In acids, the strongly bound hydrogen occurs at more cathodic potential when chloride and sulfate are present. Sulfate affects the initial phase of oxide film formation by produced fine structure while chloride retards the oxide-film formation. In alkaline solutions, both strongly and weakly bound hydrogen are influenced by iodide, cyanide, and barium and calcium cations. These ions also influence the oxide film formation. Factors considered to explain these effects are discussed. The Tafel slope for oxygen generation was found to be independent on the oxide thickness and the presence of cations or anions. The catalytic activity indicated by the exchange current density was observed decreasing with increasing oxide layer thickness, only a minor dependence on the addition of certain cations and anions was found.

Huang, C. J.; Yeager, E.; Ogrady, W. E.



Comparison of Pt and Pd catalysts for hydrogen pump separation from reformate  

NASA Astrophysics Data System (ADS)

Hydrogen recovery from CO2/H2 reformate mixtures by selective electrochemical pumping was compared from carbon supported Pt and Pd catalysts. Catalyst coated membranes were prepared by air-brushing a suspension of commercially available 20wt% Pt/C or 20wt% Pd/C catalysts and solubilized Nafion in methanol onto Nafion 115 membranes. Electrochemical activity and separation efficiency for the different catalyst layer formulations were evaluated by cyclic voltammetry, polarization and potentiostatic hydrogen pumping. The effective membrane-electrode-assembly (MEA) resistance increased due to dilution of H2 by CO2; the effective MEA resistance was greater for Pd/C catalysts than for Pt/C catalysts. CO2 adsorbed more strongly to Pd catalysts than Pt catalysts reducing the electrochemical active surface area available for hydrogen oxidation/reduction. Pd/C catalysts had an energy efficiency for hydrogen recovery from reformate mixtures approximately 80% that of Pt catalysts. Because Pd is ten times less costly than Pt the results presented here suggest that Pd/C catalysts would be a promising candidate for hydrogen pumps to recover H2 from reformate mixtures.

Wu, Xuemei; Benziger, Jay; He, Gaohong



Fabrication of CIGS Films by Electrodeposition Method for Photovoltaic Cells  

NASA Astrophysics Data System (ADS)

Cu(InGa)Se2 (CIGS) thin films were fabricated by electrochemical deposition in a single bath containing Cu, In, Ga, and Se ions. The electrolyte was prepared by dissolving CuCl2, InCl3, GaCl3, H2SeO3, and LiCl in deionized water. The potentiostatic deposition process was achieved by applying a voltage ranging from -0.5 V to -0.8 V versus Ag/AgCl. The effects of different chemical bath concentrations on the film composition and morphology were investigated. Stoichiometric CIGS film composition could be achieved by controlling the chemical compositions of the bath and the voltage. Gelatin was added to the solution to improve the surface and microstructures of the CIGS film. The as-deposited films were annealed at 500C in Ar atmosphere for crystallization. The structural, morphological, and compositional properties of the CIGS thin films before and after annealing were examined by x-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. This study showed that the composition of the CIGS films is dependent on the bath concentration, whereas the applied potential had relatively less effect on the CIGS film composition. In addition, the use of gelatin helped in the fabrication of crack-free CIGS thin films with greatly improved surface morphology.

Lee, Hyunju; Yoon, Hyukjoo; Ji, Changwook; Lee, Dongyun; Lee, Jae-Ho; Yun, Jae-Ho; Kim, Yangdo



Electrochemical Polishing Applications and EIS of a Vitamin B{sub 4}-Based Ionic Liquid  

SciTech Connect

Modern particle accelerators require minimal interior surface roughness for Niobium superconducting radio frequency (SRF) cavities. Polishing of the Nb is currently achieved via electrochemical polishing with concentrated mixtures of sulfuric and hydrofluoric acids. This acid-based approach is effective at reducing the surface roughness to acceptable levels for SRF use, but due to acid-related hazards and extra costs (including safe disposal of used polishing solutions), an acid-free method would be preferable. This study focuses on an alternative electrochemical polishing method for Nb, using a novel ionic liquid solution containing choline chloride, also known as Vitamin B{sub 4} (VB{sub 4}). Potentiostatic electrochemical impedance spectroscopy (EIS) was also performed on the VB4-based system. Nb polished using the VB4-based method was found to have a final surface roughness comparable to that achieved via the acid-based method, as assessed by atomic force microscopy (AFM). These findings indicate that acid-free VB{sub 4}-based electrochemical polishing of Nb represents a promising replacement for acid-based methods of SRF cavity preparation.

Wixtrom, Alex I. [Christopher Newport University, Newport News, VA (United States); Buhler, Jessica E. [Christopher Newport University, Newport News, VA (United States); Reece, Charles E. [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Abdel-Fattah, Tarek M. [Christopher Newport University, Newport News, VA (United States)



Electrosynthesis of polyanilinemutilwalled carbon nanotube nanocomposite films in the presence of sodium dodecyl sulfate for glucose biosensing  

NASA Astrophysics Data System (ADS)

Polyanilinemutilwalled carbon nanotube (PANiMWCNT) nanocomposites were electropolymerized in the presence of sodium dodecyl sulfate (SDS) onto interdigitated platinum-film planar microelectrodes (ID?E). The MWCNTs were first dispersed in SDS solution then mixed with aniline and H2SO4. This mixture was used to electro-synthesize PANiMWCNT films with potentiostatic method at E = + 0.90 V (versus SCE). The PANiMWCNT films were characterized by cyclic voltammetry (CV) and scanning electron microscopy (SEM). The results show that the PANiMWCNT films have a high electroactivity, and a porous and branched structure that can increase the specific surface area for biosensing application. In this work the PANiMWCNT films were applied for covalent immobilization of glucose oxidase (GOx) via glutaraldehyde agent. The GOx/PANiMWCNT/ID?E was studied using cyclic voltammetric and chronoamperometric techniques. The effect of several interferences, such as ascorbic acid (AA), uric acid (UA), and acetaminophen (AAP) on the glucosensing at +0.6 V (versus SCE) is not significant. The time required to reach 95% of the maximum steady-state current was less than 5 s. A linear range of the calibration curve for the glucose concentration lies between 1 and 12 mM which is a suitable level in the human body.

Huyen Le, Trong; Thang Trinh, Ngoc; Nguyen, Le Huy; Binh Nguyen, Hai; Nguyen, Van Anh; Tran, Dai Lam; Dung Nguyen, Tuan



Synthesis and magnetic properties of Ni nanocylinders in self-aligned and randomly disordered grown titania nanotubes  

NASA Astrophysics Data System (ADS)

A novel ferromagnetic/semiconductor oxide nanocomposite formed by arrays of Ni nanocylinders grown by the electrodeposition technique in a semiconductor oxide matrix of self-aligned and randomly disordered titanium dioxide nanotubes has been synthesized. X-ray diffraction, EDX, SEM, AFM, rf-GDOES and VSM magnetometry techniques have been used to investigate the structural, compositional and morphological properties, as well as its specific magnetic behaviour. Titania nanotubes have been grown through a single anodization process, by using HF acidic electrolytes in a potentiostatic mode. The thus-obtained titanium dioxide nanotube outer diameter ranges between 90 and 150 nm, wall thickness about 25-40 nm and 300 nm in depth. The electrodeposited Ni nanocylinders reach above 100 nm diameter and 240 nm length, giving rise to coercive fields of 98 and 200 Oe, well within the hysteresis loops perpendicular or parallel to the nanocylinder axis, respectively, which could be ascribed to the formation of magnetic vortex domain states. It is expected that this novelty nanocomposite, based on ferromagnetic Ni nanocylinders embedded in a semiconductor titanium dioxide nanotube template, will become a promising candidate for many applications in a broad range of scientific and technological areas, such as ultrahigh density magnetic storage media or spin-based electronic devices.

Prida, V. M.; Hernndez-Vlez, M.; Pirota, K. R.; Menndez, A.; Vzquez, M.



Low modulus Ti-Nb-Hf alloy for biomedical applications.  


?-Type titanium alloys with a low elastic modulus are a potential strategy to reduce stress shielding effect and to enhance bone remodeling in implants used to substitute failed hard tissue. For biomaterial application, investigation on the mechanical behavior, the corrosion resistance and the cell response is required. The new Ti25Nb16Hf alloy was studied before and after 95% cold rolling (95% C.R.). The mechanical properties were determined by tensile testing and its corrosion behavior was analyzed by potentiostatic equipment in Hank's solution at 37C. The cell response was studied by means of cytotoxicity evaluation, cell adhesion and proliferation measurements. The stress-strain curves showed the lowest elastic modulus (42GPa) in the cold worked alloy and high tensile strength, similar to that of Ti6Al4V. The new alloy exhibited better corrosion resistance in terms of open circuit potential (EOCP), but was similar in terms of corrosion current density (iCORR) compared to Ti grade II. Cytotoxicity studies revealed that the chemical composition of the alloy does not induce cytotoxic activity. Cell studies in the new alloy showed a lower adhesion and a higher proliferation compared to Ti grade II presenting, therefore, mechanical features similar to those of human cortical bone and, simultaneously, a good cell response. PMID:25063170

Gonzlez, M; Pea, J; Gil, F J; Manero, J M



Packaged Au-PPy valves for drug delivery systems  

NASA Astrophysics Data System (ADS)

The most common methods for the drug delivery are swallowing pills or receiving injections. However, formulations that control the rate and period of medicine (i.e., time-release medications) are still problematic. The proposed implantable devices which include batteries, sensors, telemetry, valves, and drug storage reservoirs provide an alternative method for the responsive drug delivery system [1]. Using this device, drug concentration can be precisely controlled which enhances drug efficiency and decreases the side effects. In order to achieve responsive drug delivery, a reliable release valve has to be developed. Biocompatibility, low energy consumption, and minimized leakage are the main requirements for such release method. A bilayer structure composed of Au/PPy film is fabricated as a flap to control the release valve. Optimized potentiostatic control to synthesize polypyrrole (PPy) is presented. The release of miniaturize valve is tested and showed in this paper. A novel idea to simultaneously fabricate the device reservoirs as well as protective packaging is proposed in this paper. The solution of PDMS permeability problem is also mentioned in this article.

Tsai, Han-Kuan A.; Ma, Kuo-Sheng; Zoval, Jim; Kulinsky, Lawrence; Madou, Marc



Mitigating Electronic Current in Molten Flux for the Magnesium SOM Process  

NASA Astrophysics Data System (ADS)

The solid oxide membrane (SOM) process has been used at 1423 K to 1473 K (1150 C to 1200 C) to produce magnesium metal by the direct electrolysis of magnesium oxide. MgO is dissolved in a molten MgF2-CaF2 ionic flux. An oxygen-ion-conducting membrane, made from yttria-stabilized zirconia (YSZ), separates the cathode and the flux from the anode. During electrolysis, magnesium ions are reduced at the cathode, and Mg(g) is bubbled out of the flux into a separate condenser. The flux has a small solubility for magnesium metal which imparts electronic conductivity to the flux. The electronic conductivity decreases the process current efficiency and also degrades the YSZ membrane. Operating the electrolysis cell at low total pressures is shown to be an effective method of reducing the electronic conductivity of the flux. A two steel electrode method for measuring the electronic transference number in the flux was used to quantify the fraction of electronic current in the flux before and after SOM process operation. Potentiodynamic scans, potentiostatic electrolyses, and AC impedance spectroscopy were also used to characterize the SOM process under different operating conditions.

Gratz, Eric S.; Guan, Xiaofei; Milshtein, Jarrod D.; Pal, Uday B.; Powell, Adam C.



Electrochemical nucleophilic synthesis of di-tert-butyl-(4-[18F]fluoro-1,2-phenylene)-dicarbonate.  


An electrochemical method with the ability to conduct (18)F-fluorination of aromatic molecules through direct nucleophilic fluorination of cationic intermediates is presented in this paper. The reaction was performed on a remote-controlled automatic platform. Nucleophilic electrochemical fluorination of tert-butyloxycarbonyl (Boc) protected catechol, an intermediate model molecule for the positron emission tomography (PET) probe (3,4-dihydroxy-6-[(18)F]fluoro-L-phenylalanine), was performed. Fluorination was achieved under potentiostatic anodic oxidation in acetonitrile containing Et3N3HF and other supporting electrolytes. Radiofluorination efficiency was influenced by a number of variables, including the concentration of the precursor, concentration of Et3N3HF, type of supporting electrolyte, temperature and time, as well as applied potentials. Radio-fluorination efficiency of 10.40.6% (n=4) and specific activity of up to 43GBq/mmol was obtained after 1h electrolysis of 0.1M of 4-tert-butyl-diboc-catechol in the acetonitrile solution of Et3N3HF (0.033M) and NBu4PF6 (0.05M). Density functional theory (DFT) was employed to explain the tert-butyl functional group facilitation of electrochemical oxidation and subsequent fluorination. PMID:25000498

He, Qinggang; Wang, Ying; Alfeazi, Ines; Sadeghi, Saman



Electrochemical Fractionation of Molybdenum Stable Isotopes  

NASA Astrophysics Data System (ADS)

Stable isotope signatures were measured from Molybdenum (Mo) electrodeposited from aqueous solution. As potential varied from -1.35 V to -2.00 V (relative to Ag/AgCl), fractionation decreases from ?97/95Mo = -1.3 to -0.9 (?97/95Mo defined as the difference in the 97Mo/95Mo ratio of deposited Mo relative to aqueous Mo). Natural variations of ?97/95Mo span a range of ~ 3 [Barling, J. and Anbar, A. D., EPSL. 2004, 217: 315], therefore, charge transfer driven fractionation may be responsible for some of the observed variation in Mo stable isotope geochemistry. Following previous approaches with Fe and Zn [Kavner, A. et al. Geochim. Cosmochim. Acta. 2005, 69: 2971; 2008, 72: 1731], Mo was plated in a three-electrode cell from a neutral to slightly alkaline solution (pH ~ 8.7). Voltage was held constant during electrodeposition using an Autolab Potentiostat. In all experiments, less than 0.5 % of the Mo was deposited, which insures that the plating reservoir remains at an approximately constant isotopic composition. Plated Mo was then recovered in acid, and the isotopic composition of samples and stock solutions were measured using a Thermo Scientific Neptune MC-ICP-MS. These experiments show that the redox process induces an isotopic signature with respect to the starting material, with a trend showing that fractionation decreases as a function of applied voltage.

Crawford, J.; Black, J.; Wasylenki, L.; Gordon, G.; Anbar, A.; Kavner, A.



Highly crystalline WO3 thin films with ordered 3D mesoporosity and improved electrochromic performance.  


WO3 thin layers with nanometer-scale periodicity were prepared by evaporation-induced self-assembly (EISA) using a novel amphiphilic block-copolymer template (poly(ethylene-co-butylene)-block-poly(ethylene oxide)). The evolution of the mesoporous ordered network and the crystallinity of the framework were monitored by 2D-SAXS, WAXS, SEM, XPS, and porosimetry. By annealing the films, the pore-wall crystallinity is adjusted between fully amorphous and highly crystalline without mesostructural degradation. Thus, the crystalline-film framework is composed of phase-pure monoclinic WO3 nanoparticles (12-14 nm in size). Furthermore, heat treatment transforms the originally spherical mesopores into ellipsoids, resulting in a unidirectionally shrunken, but still well-defined and fully accessible bcc mesopore architecture. The influence of mesoporosity and crystallinity on electrochemical/electrochromic characteristics was addressed by monitoring electrochemical features and the absorption changes during Li insertion/extraction (repetitive potentiostatic cycling). Both the amorphous and crystalline mesoporous films possess electrochromic response times on the order of only seconds, which are attributable to the facilitated insertion of guest ions due to shortening of the diffusion path lengths. Also, the insertion/extraction reversibility of crystalline WO3 layers with 3D mesoporosity is improved compared to amorphous ones and reaches values close to 100%. PMID:17193590

Brezesinski, Torsten; Rohlfing, Dina Fattakhova; Sallard, Sbastien; Antonietti, Markus; Smarsly, Bernd M



Photoelectrochemical behavior of nanostructured WO3 thin-film electrodes: The oxidation of formic acid.  


Nanostructured tungsten trioxide thin-film electrodes are prepared on conducting glass substrates by either potentiostatic electrodeposition from aqueous solutions of peroxotungstic acid or direct deposition of WO3 slurries. Once treated thermally in air at 450 degrees C, the electrodes are found to be composed of monoclinic WO3 grains with a particle size around 30-40 nm. The photoelectrochemical behavior of these electrodes in 1 M HClO4 apparently reveals a low degree of electron-hole recombination. Upon addition of formic acid, the electrode showed the current multiplication phenomenon together with a shift of the photocurrent onset potential toward less positive values. Photoelectrochemical experiments devised on the basis of a kinetic model reported recently [I. Mora-Ser, T. Lana-Villarreal, J. Bisquert, A. Pitarch, R. Gmez, P. Salvador, J. Phys. Chem. B 2005, 109, 3371] showed that an interfacial mechanism of inelastic, direct hole transfer takes place in the photooxidation of formic acid. This behavior is attributed to the tendency of formic acid molecules to be specifically adsorbed on the WO3 nanoparticles, as evidenced by attenuated total reflection infrared spectroscopy. PMID:17072939

Monllor-Satoca, Damin; Borja, Luis; Rodes, Antonio; Gmez, Roberto; Salvador, Pedro



Electrodeposited ZnO films with high UV emission properties  

SciTech Connect

Highlights: {yields} Electrodeposition of ZnO from nitrate baths is investigated. {yields} The influence of process parameters on morphological and optical properties is studied. {yields} Experimental conditions to fabricate ZnO films with high UV emission were found. -- Abstract: We report here our results in the preparation of ZnO films with high UV band to band characteristic luminescence emission by potentiostatic electrodeposition. Zinc nitrate aqueous baths with different concentration and additives were employed for the preparation of the films on platinum substrates. We focused our research in determining how the electrodeposition bath composition, i.e. zinc nitrate concentration and addition of KCl or polyvinyl pyrolidone and applied overpotential influence the morphological and optical properties of the oxide films. Scanning electron microscopy was employed for characterizing the films in terms of morphology. Optical reflection, photoluminescence spectroscopy and cathodoluminescence were used for determining the optical characteristics of the samples. The morphology of the deposit varies from hexagonal prisms to platelets as a function of the deposition rate. This experimental parameter also influences the luminescence properties. We found that at low deposition rates high UV luminescent material is obtained.

Matei, Elena [National Institute of Materials Physics, PO Box MG 7, 77125 Magurele, Ilfov (Romania)] [National Institute of Materials Physics, PO Box MG 7, 77125 Magurele, Ilfov (Romania); Enculescu, Ionut, E-mail: [National Institute of Materials Physics, PO Box MG 7, 77125 Magurele, Ilfov (Romania)] [National Institute of Materials Physics, PO Box MG 7, 77125 Magurele, Ilfov (Romania)



Corrosion inhibitor storage and release property of TiO{sub 2} nanotube powder synthesized by rapid breakdown anodization method  

SciTech Connect

Graphical abstract: Display Omitted Highlights: ? TiO{sub 2} nanotube powders were synthesized by rapid breakdown anodization method. ? Benzotriazole was loaded into the TiO{sub 2} nanotube powders. ? Low pH induced release of benzotriazole from TiO{sub 2} nanotube powders was proved. -- Abstract: Titanium dioxide (TiO{sub 2}) is one of the most studied substances in material science due to its versatile properties and diverse applications. In this study titanium dioxide nanotube powder were synthesized by rapid breakdown anodization (RBA) method. The synthesis involved potentiostatic anodization of titanium foil in 0.1 M HClO{sub 4} electrolyte under an applied voltage of 20 V and rapid stirring. The morphology and the phase of titanium dioxide nanotube powder were studied using field emission scanning electron microscopy, laser Raman spectroscopy and high resolution transmission electron microscopy. Benzotriazole was chosen as model inhibitor to evaluate TiO{sub 2} nanotube powder's corrosion inhibitor loading and releasing properties. The storage and release properties of TiO{sub 2} nanotube powder were studied using UVvisible spectroscopy and thermogravimetric analysis.

Arunchandran, C.; Ramya, S.; George, R.P. [Corrosion Science and Technology Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India)] [Corrosion Science and Technology Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India); Kamachi Mudali, U., E-mail: [Corrosion Science and Technology Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India)



Ultrathin, Stretchable, Multiplexing pH Sensor Arrays on Biomedical Devices With Demonstrations on Rabbit and Human Hearts Undergoing Ischemia  

PubMed Central

Stable pH is an established biomarker of health, relevant to all tissues of the body, including the heart. Clinical monitoring of pH in a practical manner, with high spatiotemporal resolution, is particularly difficult in organs such as the heart due to its soft mechanics, curvilinear geometry, heterogeneous surfaces and continuous, complex rhythmic motion. The results presented here illustrate that advanced strategies in materials assembly and electrochemical growth can yield interconnected arrays of miniaturized IrOx pH sensors encapsulated in thin, low-modulus elastomers to yield conformal monitoring systems capable of non-invasive measurements on the surface of the beating heart. A thirty channel custom data acquisition system enables spatiotemporal pH mapping with a single potentiostat. In-vitro testing reveals super-Nernstian sensitivity with excellent uniformity (69.9 2.2 mV/pH), linear response to temperature (?1.6 mV/C), and minimal influence of extracellular ions (< 3.5 mV). Device examples include sensor arrays on balloon catheters and on skin-like stretchable membranes. Real-time measurement of pH on the surfaces of explanted rabbit hearts and a donated human heart during protocols of ischemia-reperfusion illustrate some of the capabilities. Envisioned applications range from devices for biological research, to surgical tools and long-term implants. PMID:23868871

Chung, Hyun-Joong; Sulkin, Matthew S.; Kim, Jong-Seon; Goudeseune, Camille; Chao, Hsin-Yun; Song, Joseph W.; Yang, Sang Yoon; Hsu, Yung-Yu; Ghaffari, Roozbeh



Recreation of Marine Atmospheric Corrosion Condition on Weathering Steel in Laboratory  

NASA Astrophysics Data System (ADS)

Salt spray test, autoclave corrosion test, SO2 salt spray test, and Relative humidity test are generally used to assess atmospheric corrosion in laboratories at accelerated rates. However, no test can absolutely simulate the service condition. One can get only approximate corrosion rates using the aforesaid tests which serve as an indicative of corrosion behavior of the material in a service condition. The present work is aimed at creating specific environmental condition in laboratory to get the corrosion test done in short duration to compare with on field exposure test which would otherwise take years to complete. In this work recreation of atmospheric environment of Digha was tried and it was simulated in such a manner that the results of laboratory test could be compared with long time field exposure at Digha. Weathering steel (WS) was taken for experimentations. Potentiostatic electrochemical tests route was adopted to simulate atmospheric condition of Digha. Laboratory test results compared well with 18 month field exposure data in terms of corrosion rate, SEM and Ramon Spectroscopy matching.

Guchhait, S. K.; Dewan, S.; Saha, J. K.; Mitra, P. K.



UV/Vis/NIR Spectroelectrochemistry  

NASA Astrophysics Data System (ADS)

Voltammetric techniques used in electrochemistry monitor the flow of current as a function of potential, time, and mass transport. A huge variety of different experiments are possible, giving information about reaction energies, reaction intermediates, and the kinetics of a process [1-4]. However, additional data are often required and are accessible, in particular, via in situ spectroelectrochemical approaches. By coupling a spectroscopic technique such as UV/Vis/NIR spectroscopy [5, 6] to an electrochemical experiment, a wealth of complementary information as a function of the potential, time, and mass transport is available. In a recently published book dedicated to spectroelectrochemical techniques [7] the diversity of methods and new chemical information obtained is apparent. Both spectroscopic information about short-lived unstable intermediates and spectroscopic information disentangling the composition of complex mixtures of reactants can be obtained. Figure II.6.1 shows a schematic diagram for the case of a computer-controlled potentiostat system connected to a conventional electrochemical cell (working electrode WE, reference electrode RE, counter electrode CE) and simultaneously controlling the emitter and detector of a spectrometer. This kind of experimental arrangement allows the electrochemical and the spectroscopic data to be recorded simultaneously and, therefore, in contrast to the analysis of two independent data sets, direct correlation of data as a function of time and potential is possible.

Neudeck, Andreas; Marken, Frank; Compton, Richard G.


Environmental factors affecting corrosion of munitions  

SciTech Connect

Spent small arms munitions have accumulated for years at outdoor firing ranges operated by the DoD and other groups. Used bullets are often subjected to moisture sources. There is increasing concern that accumulations of lead-based munitions represent potential sources of water and soil pollution. To understand both the severity of and solutions to this problem, it is necessary to measure how rapidly bullets corrode and to determine the soil variables affecting the process. In this study M16 bullets were buried in samples of soil taken from Louisiana army firing ranges. Four environmental conditions were simulated; rain water, acid rain, sea water, and 50% sea water/50% acid rain. The three electrode technique was used to measure the bullet corrosion. Graphite rods served as counter electrodes. A saturated calomel reference electrode was used along with a specially constructed salt bridge. Electrochemical measurements were conducted using a computer-controlled potentiostat to determine corrosion potential, soil resistance, and corrosion current. The rate of corrosion was found to markedly increase with decreasing soil pH and increasing chloride and moisture contents, with the chloride content being the most influential variable. High soil resistance and noble corrosion potential were found to be associated with low corrosion rates. This is important since both parameters can be readily measured in the field.

Bundy, K. [Tulane Univ., New Orleans, LA (United States); Bricka, M.; Morales, A. [Army Engineer Waterways Experiment Station, Vicksburg, MS (United States)



The effect of oxidizing water on metallic restorations in the mouth: in vitro reduction behavior of oxidizing water.  


Mouth-rinsing with oxydized water which contains electrolytically generated chlorine is known to hinder dental plaque formation and growth, but it also accelerates the deterioration of metallic restorations in the mouth. The present work consists of an in vitro study to elucidate the electrochemical reactions involved in the reduction of oxydized water on dental alloys through a systematic investigation of the potentiostatic polarization behavior of dental alloy electrodes. The five dental alloys selected for investigation were gold alloy, gold alloy containing platinum, silver-palladium-gold alloy, conventional amalgam and high copper amalgam. The corrosion potentials of all dental alloy electrodes were shown to be more noble in oxydized water than in 0.1N sodium chloride solution. The potential differences between the corrosion potentials were relatively small in the case of amalgam electrodes. The polarization curves for all of the dental alloy electrodes in oxydized water revealed reduction currents of chlorine, hypochlorous acid, dissolved oxygen and oxonium ion. The reduction of chlorine and hypochlorous acid started at a more noble potential than that of dissolved oxygen. The dental alloys studied, except the amalgams, did not dissolve excessively at the corrosion potentials in oxydized water. PMID:9198335

Nishida, T



Potential COntrol Under Thin Aqueous Layers Using a Kelvin Probe  

SciTech Connect

Kelvin Probes can be modified to control as well as monitor potential. The design and operation of two different Kelvin Probe Potentiostats (KPPs) are described in this paper. One approach uses a permanent magnet and double coil to oscillate the needle at a fixed frequency, an AC backing potential, and software analysis and control schemes. This technique can also control the distance between the tip and sample, thereby tracking the topography of the sample. Both KPPs were used to make measurements on Type 304L stainless steel under thin layers of electrolyte. Cathodic polarization curves exhibited a limiting current density associated with oxygen reduction. The limiting current density varied with solution layer thickness over a finite range of thickness. Anodic polarization curves on 304L in a thin layer of chloride solution resulted in pitting corrosion. The breakdown potential did not vary with solution layer thickness. However, the thin layer was observed to increase in volume remarkably during pit growth owing to the absorption of water from the high humidity environment into the layer with ionic strength increased by the pit dissolution. The open circuit potential (OCP) and solution layer thickness were monitored during drying out of a thin electrolyte layer. Pitting corrosion initiated, as indicated by a sharp drop in the OCP, as the solution thinned and increased in concentration.

G.S. Frankel; B. Maier; M. Stratman; M. Rohwerder; A. Michalik; J. Dora; M. Wicinski



Halogen-free boron based electrolyte solution for rechargeable magnesium batteries  

NASA Astrophysics Data System (ADS)

All halogen containing electrolytes for Mg battery are apt to corrode conventional metal current collectors. In this paper, a new type of halogen-free boron based electrolyte (Mg[Mes3BPh]2/THF) is designed and prepared. Electrochemical tests show that this electrolyte system possesses high ion conductivity (1.5נ10-3Scm-1) and good Mg deposition-dissolution reversibility. More importantly, the same electrochemical window (2.6V vs. Mg RE) of the electrolyte on Pt and stainless steel electrodes indicates that halogen-free electrolyte indeed lessens the corrosion to conventional metal current collectors. The surface morphologies of stainless steel, aluminum and copper are further observed after their anodic potentiostatic polarization in 0.25molL-1 Mg[Mes3BPh]2/THF electrolyte solution for 2 days. A comparison with halogen containing electrolytes proves that the presence of halogen in electrolyte is the reason for corrosion. This work provides a stepping stone for developing new halogen-free electrolyte systems for rechargeable Mg batteries.

Zhu, Jinjie; Guo, Yongsheng; Yang, Jun; Nuli, Yanna; Zhang, Fan; Wang, Jiulin; Hirano, Shin-ichi



Properties of electrodeposited CoFe/Cu multilayers: The effect of Cu layer thickness  

NASA Astrophysics Data System (ADS)

CoFe/Cu multilayers were potentiostatically electrodeposited on Ti substrates as a function of different non-magnetic (Cu) layer thicknesses, and their characterizations were investigated. The compositional analysis performed by energy dispersive X-ray spectroscopy disclosed that the Cu content in the multilayers increased and the Co content decreased as non-magnetic layer was increased. However, the Fe content was almost stable. The scanning electron microscopy studies showed that the surface morphology of the films is strongly affected by the non-magnetic layer thickness, and X-ray diffraction was used to analyse the structural properties of the multilayers and revealed that the multilayers have face-centred cubic (fcc) structure and their preferred orientations change depending on the Cu layer thickness. In the case of magnetoresistance measurements of the multilayers performed at room temperature, the highest giant magnetoresistance (GMR) values exhibited for the films with the Cu layer thickness (6.0 nm) whereas the lowest GMR magnitudes were observed for the films without Cu layer. Therefore, the variations of the Cu layer thicknesses were observed to have a significant effect on the GMR of multilayers. The differences observed in the magnetotransport properties were attributed to the microstructural changes caused by the Cu layer thickness.

Sahin, Turgut; Kockar, Hakan; Alper, Mursel



Comparison of Electrochemical Methods to Determine Crevice Corrosion Repassivation Potential of Alloy 22 in Chloride Solutions  

SciTech Connect

Alloy 22 (N06022) is a nickel-based alloy highly resistant to corrosion. In some aggressive conditions of high chloride concentration, temperature and applied potential, Alloy 22 may suffer crevice corrosion, a form of localized corrosion. There are several electrochemical methods that can be used to determine localized corrosion in metallic alloys. One of the most popular for rapid screening is the cyclic potentiodynamic polarization (CPP). This work compares the repassivation potentials obtained using CPP to related repassivation potential values obtained using the Tsujikawa-Hisamatsu Electrochemical (THE) method and the potentiostatic (POT) method. Studied variables included temperature and chloride concentration. The temperature was varied from 30 C and 120 C and the chloride concentration was varied between 0.0005 M to 4 M. Results show that similar repassivation potentials were obtained for Alloy 22 using CPP and THE methods. Generally, under more aggressive conditions, the repassivation potentials were more conservative using the CPP method. POT tests confirmed the validity of the repassivation potential as a threshold below which localized corrosion does not nucleate. The mode of attack in the tested specimens varied depending if the test method was CPP or THE; however, the repassivation potential remained the same.

K. Evans; A. Yilmaz; S. Day; L. Wong; J. Estill



Electrochemical Testing of Ni-Cr-Mo-Gd Alloys  

SciTech Connect

The waste package site recommendation design specified a boron-containing stainless steel, Neutronit 976/978, for fabrication of the internal baskets that will be used as a corrosion-resistant neutron-absorbing material. Recent corrosion test results gave higher-than-expected corrosion rates for this material. The material callout for these components has been changed to a Ni-Cr-Mo-Gd alloy (ASTM-B 932-04, UNS N06464) that is being developed at the Idaho National Laboratory. This report discusses the results of initial corrosion testing of this material in simulated in-package environments that could contact the fuel baskets after breach of the waste package outer barrier. The corrosion test matrix was executed using the potentiodynamic and potentiostatic electrochemical test techniques. The alloy performance shows low rates of general corrosion after initial removal of a gadolinium-rich second phase that intersects the surface. The high halide-containing test solutions exhibited greater tendencies toward initiation of crevice corrosion.

T. E. Lister; R. E. Mizia; H. Tian



Virtual electrochemical nitric oxide analyzer using copper, zinc superoxide dismutase immobilized on carbon nanotubes in polypyrrole matrix.  


In this work, we have designed and developed a novel and cost effective virtual electrochemical analyzer for the measurement of NO in exhaled breath and from hydrogen peroxide stimulated endothelial cells using home-made potentiostat. Here, data acquisition system (NI MyDAQ) was used to acquire the data from the electrochemical oxidation of NO mediated by copper, zinc superoxide dismutase (Cu,ZnSOD). The electrochemical control programs (graphical user-interface software) were developed using LabVIEW 10.0 to sweep the potential, acquire the current response and process the acquired current signal. The Cu,ZnSOD (SOD1) immobilized on the carbon nanotubes in polypyrrole modified platinum electrode was used as the NO biosensor. The electrochemical behavior of the SOD1 modified electrode exhibited the characteristic quasi-reversible redox peak at the potential, +0.06 V vs. Ag/AgCl. The biological interferences were eliminated by nafion coated SOD1 electrode and then NO was measured selectively. Further, this biosensor showed a wide linear range of response over the concentration of NO from 0.1 ?M to 1 mM with a detection limit of 0.1 ?M and high sensitivity of 1.1 ?A ?M(-1). The electroanalytical results obtained here using the developed virtual electrochemical instrument were also compared with the standard cyclic voltammetry instrument and found in agreement with each other. PMID:23141325

Madasamy, Thangamuthu; Pandiaraj, Manickam; Balamurugan, Murugesan; Karnewar, Santosh; Benjamin, Alby Robson; Venkatesh, Krishna Arun; Vairamani, Kanagavel; Kotamraju, Srigiridhar; Karunakaran, Chandran



Development of an amperometric sulfite biosensor based on SO(x)/PBNPs/PPY modified ITO electrode.  


A sulfite oxidase (SO(x)) (EC purified from Syzygium cumini leaves was immobilized onto prussian blue nanoparticles/polypyrrole composite (PBNPs/PPY) electrodeposited onto the surface of indium tin oxide (ITO) electrode. An amperometric sulfite biosensor was fabricated using SO(x)/PBNPs/PPY/ITO electrode as working electrode, Ag/AgCl as standard and Pt wire as auxiliary electrode connected through a potentiostat. The working electrode was characterized by Fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry (CV), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) before and after immobilization of SO(x). The biosensor showed optimum response within 2s, when operated at 20 mV s? in 0.1M Tris-HCl buffer, pH 8.5 and at 35 C. Linear range and minimum detection limit were 0.5-1000 ?M and 0.12 ?M (S/N=3) respectively. There was good correlation (r=0.99) between red wine samples sulfite value by standard DTNB method and the present method. The sensor was evaluated with 97% recovery of added sulfite in red wine samples and 2.2% and 4.3% within and between batch coefficients of variation respectively. The sensor was employed for determination of sulfite level in red and white wine samples. The enzyme electrode was used 200 times over a period of 3 months when stored at 4 C. PMID:22705572

Rawal, Rachna; Pundir, C S



Nucleation and growth of zinc from chloride concentrated solutions  

SciTech Connect

The electrodeposition of metals is a complex phenomenon influenced by a number of factors that modify the rates of nucleation and growth and determine the properties of the deposits. In this work the authors study the influence of the zinc chloride (ZnCl{sub 2}) concentration on the zinc nucleation process on glassy carbon, in a KCl electrolyte under conditions close to those employed in commercial acid deposition baths for zinc. The electrochemical study was performed using cyclic voltammetry and potentiostatic current-time transients. The charge-transfer coefficient and the formal potential for ZnCl{sub 2} reduction were evaluated from cyclic voltammetry experiments. The nucleation process was analyzed by comparing the transients obtained with the known dimensionless (i/i{sub m}){sup 2} vs. t/t{sub m} response for instantaneous or progressive nucleation. The results show that the nucleation process and the number density of sites are dependent on ZnCl{sub 2} concentration. Scanning electron microscopy analysis of the deposits shows that the deposits are homogeneous and compact although a change in the morphology is observed as a function of ZnCl{sub 2} concentration. Evaluation of the corrosion resistance reveals the influence of the nucleation process on the subsequent corrosion resistance of the zinc deposits.

Trejo, G.; Ortega B, R.; Meas V, Y. [Parque Tecnologico Queretaro-Sanfandila, Pedro Escobedo (Mexico). Centro de Investigacion y Desarrollo Tecnologico en Electroquimica; Ozil, P.; Chainet, E.; Nguyen, B. [Ecole Nationale Superieure d`Electrochimie et d`Electrometallurgie de Grenoble, Saint Martin d`Heres (France). Lab. d`Electrochimie et Physicochimie de Materiaux et Interfaces



Improvement in direct methanol fuel cell performance by treating the anode at high anodic potential  

NASA Astrophysics Data System (ADS)

This work investigates the effect of a high anodic potential treatment protocol on the performance of a direct methanol fuel cell (DMFC). DMFC membrane electrode assemblies (MEAs) with PtRu/C (Hi-spec 5000) anode catalyst are subjected to anodic treatment (AT) at 0.8V vs. DHE using potentiostatic method. Despite causing a slight decrease in the electrochemical surface area (ECSA) of the anode, associated with ruthenium dissolution, AT results in significant improvement in DMFC performance in the ohmic and mass transfer regions and increases the maximum power density by ?15%. Furthermore, AT improves the long-term DMFC stability by reducing the degradation of the anode catalyst. From XPS investigation, it is hypothesized that the improved performance of AT-treated MEAs is related to an improved interface between the catalyst and Nafion ionomer. Among potential explanations, this improvement may be caused by incorporation of the ionomer within the secondary pores of PtRu/C agglomerates, which generates a percolating network of ionomer between PtRu/C agglomerates in the catalyst layer. Furthermore, the decreased concentration of hydrophobic CF2 groups may help to enhance the hydrophilicity of the catalyst layer, thereby increasing the accessibility of methanol and resulting in better performance in the high current density region.

Joghee, Prabhuram; Pylypenko, Svitlana; Wood, Kevin; Corpuz, April; Bender, Guido; Dinh, Huyen N.; O'Hayre, Ryan



Niobized AISI 304 stainless steel bipolar plate for proton exchange membrane fuel cell  

NASA Astrophysics Data System (ADS)

AISI 304 stainless steel (SS) has been niobized by a plasma surface diffusion alloying method. A 3 ?m niobized layer with dominant niobium elements has been formed on the 304 SS surface and the performances of the niobized 304 SS has been examined and evaluated as bipolar plate for proton exchange membrane fuel cell (PEMFC). Results show that the average contact angle with water for the niobized 304 SS is about 90.4, demonstrating better hydrophobicity as compared with the untreated 304 SS (68.1). The corrosion resistance of the 304 SS is considerably improved by the niobized layer with the corrosion current densities decreased at 0.2 and 0.4 ?A cm-2 in simulated PEMFC anode purged with hydrogen and the cathode purged with air condition (0.05 M H2SO4 + 2 ppm F- solution at 70 C), respectively. The interfacial contact resistance (ICR) for the as-prepared niobized 304 SS is 10.53 m? cm2 at the compaction of 140 N cm-2. Furthermore, after 4 h potentiostatic tests, the niobizied specimens exhibit much lower ICR than that for the untreated ones. Thus, the niobized layer can act as a conductively protective layer of the 304 SS bipolar plate for PEMFC.

Wang, Lixia; Sun, Juncai; Li, Pengbin; Jing, Bo; Li, Song; Wen, Zhongsheng; Ji, Shijun



Coupling EELS/EFTEM Imaging with Environmental Fluid Cell Microscopy  

SciTech Connect

Insight into dynamically evolving electrochemical reactions and mechanisms encountered in electrical energy storage (EES) and conversion technologies (batteries, fuel cells, and supercapacitors), materials science (corrosion and oxidation), and materials synthesis (electrodeposition) remains limited due to the present lack of in situ high-resolution characterization methodologies. Electrochemical fluid cell microscopy is an emerging in-situ method that allows for the direct, real-time imaging of electrochemical processes within a fluid environment. This technique is facilitated by the use of MEMS-based biasing microchip platforms that serve the purpose of sealing the highly volatile electrolyte between two electron transparent SiNx membranes and interfacing electrodes to an external potentiostat for controlled nanoscale electrochemislly experiments [!]. In order to elucidate both stmctural and chemical changes during such in situ electrochemical experiments, it is impmtant to first improve upon the spatial resolution by utilizing energy-filtered transmission electron microscopy (EFTEM) (to minimize chromatic aben ation), then to detennine the chemical changes via electron energy loss spectroscopy (EELS). This presents a formidable challenge since the overall thickness through which electrons are scattered through the multiple layers of the cell can be on the order of hundreds of nanometers to microns, scattering through which has the deleterious effect of degrading image resolution and decreasing signal-to noise for spectroscopy [2].

Unocic, Raymond R [ORNL; Baggetto, Loic [ORNL; Veith, Gabriel M [ORNL; Dudney, Nancy J [ORNL; More, Karren Leslie [ORNL



Recycling of Magnesium Alloy Employing Refining and Solid Oxide Membrane (SOM) Electrolysis  

NASA Astrophysics Data System (ADS)

Pure magnesium was recycled from partially oxidized 50.5 wt pct Mg-Al scrap alloy and AZ91 Mg alloy (9 wt pct Al, 1 wt pct Zn). Refining experiments were performed using a eutectic mixture of MgF2-CaF2 molten salt (flux). During the experiments, potentiodynamic scans were performed to determine the electrorefining potentials for magnesium dissolution and magnesium bubble nucleation in the flux. The measured electrorefining potential for magnesium bubble nucleation increased over time as the magnesium content inside the magnesium alloy decreased. Potentiostatic holds and electrochemical impedance spectroscopy were employed to measure the electronic and ionic resistances of the flux. The electronic resistivity of the flux varied inversely with the magnesium solubility. Up to 100 pct of the magnesium was refined from the Mg-Al scrap alloy by dissolving magnesium and its oxide into the flux followed by argon-assisted evaporation of dissolved magnesium and subsequently condensing the magnesium vapor. Solid oxide membrane electrolysis was also employed in the system to enable additional magnesium recovery from magnesium oxide in the partially oxidized Mg-Al scrap. In an experiment employing AZ91 Mg alloy, only the refining step was carried out. The calculated refining yield of magnesium from the AZ91 alloy was near 100 pct.

Guan, Xiaofei; Zink, Peter A.; Pal, Uday B.; Powell, Adam C.



Effect of microstructure and strain on the degradation behavior of novel bioresorbable iron-manganese alloy implants.  


Advancing the understanding of microstructural effects and deformation on the degradability of Fe-Mn bioresorbable alloys (specifically, Fe-33%Mn) will help address the current problems associated with designing degradable fracture fixation implants for hard tissues. Potentiostatic polarization tests were conducted on a wide variety of metal samples to examine how different deformation processes affect the instantaneous rate of degradation of Fe-Mn alloys. Large-strain machining (LSM), a novel severe plastic deformation (SPD) technique was utilized during these experiments to modify the degradation properties of the proposed Fe-Mn alloy. It was discovered that Fe-33%Mn after LSM with a rake angle of 0 (effective strain?=?2.85) showed the most promising increase in degradation rate compared to as-cast, annealed, and additional deformation conditions (rolled and other LSM parameters) for the same alloy. The mechanisms for enhancement of the corrosion rate are discussed. 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2014. PMID:24825402

Heiden, Michael; Kustas, Andrew; Chaput, Kevin; Nauman, Eric; Johnson, David; Stanciu, Lia



SEM method for direct visual tracking of nanoscale morphological changes of platinum based electrocatalysts on fixed locations upon electrochemical or thermal treatments.  


A general method for tracking morphological surface changes on a nanometer scale with scanning electron microscopy (SEM) is introduced. We exemplify the usefulness of the method by showing consecutive SEM images of an identical location before and after the electrochemical and thermal treatments of platinum-based nanoparticles deposited on a high surface area carbon. Observations reveal an insight into platinum based catalyst degradation occurring during potential cycling treatment. The presence of chloride clearly increases the rate of degradation. At these conditions the dominant degradation mechanism seems to be the platinum dissolution with some subsequent redeposition on the top of the catalyst film. By contrast, at the temperature of 60C, under potentiostatic conditions some carbon corrosion and particle aggregation was observed. Temperature treatment simulating the annealing step of the synthesis reveals sintering of small platinum based composite aggregates into uniform spherical particles. The method provides a direct proof of induced surface phenomena occurring on a chosen location without the usual statistical uncertainty in usual, random SEM observations across relatively large surface areas. PMID:24662366

Zorko, Milena; Jozinovi?, Barbara; Bele, Marjan; Hodnik, Nejc; Gaber?ek, Miran



Electrochemical sensing method for point-of-care cortisol detection in human immunodeficiency virus-infected patients  

PubMed Central

A novel electrochemical sensing method was devised for the first time to detect plasma cortisol, a potential psychological stress biomarker, in human immunodeficiency virus (HIV)-positive subjects. A miniaturized potentiostat (reconfigured LMP91000 chip) interfaced with a microfluidic manifold containing a cortisol immunosensor was employed to demonstrate electrochemical cortisol sensing. This fully integrated and optimized electrochemical sensing device exhibited a wide cortisol-detection range from 10 pg/mL to 500 ng/mL, a low detection limit of 10 pg/mL, and sensitivity of 5.8 ?A (pg mL)?1, with a regression coefficient of 0.995. This cortisol-selective sensing system was employed to estimate plasma cortisol in ten samples from HIV patients. The electrochemical cortisol-sensing performance was validated using an enzyme-linked immunosorbent assay technique. The results obtained using both methodologies were comparable within 2%5% variation. The information related to psychological stress of HIV patients can be correlated with disease-progression parameters to optimize diagnosis, therapeutic, and personalized health monitoring. PMID:25632229

Kaushik, Ajeet; Yndart, Adriana; Jayant, Rahul Dev; Sagar, Vidya; Atluri, Venkata; Bhansali, Shekhar; Nair, Madhavan



Catalytic activity of platinum nanoparticles on highly boron-doped and 100-oriented epitaxial diamond towards HER and HOR.  


Platinum nanoparticles supported on boron-doped single-crystalline diamond surfaces were used as a model system to investigate the catalytic activity with respect to the influence of particle morphology, particle density and surface preparation of the diamond substrates. We report on the preparation, characterization and activity regarding hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) of these Pt/diamond electrodes. Two kinds of diamond layers with boron doping above 10(20) cm(-3) were grown epitaxially on (100)-oriented diamond substrates; post-treatments of wet chemical oxidation and radio frequency (rf) oxygen plasma treatments were applied. Electrochemical deposition of Pt was performed using a potentiostatic double-pulse technique, which allowed variation of the particle size in the range between 1 nm and 15 nm in height and 5 nm and 50 nm in apparent radius, while keeping the particle density constant. Higher nucleation densities on the plasma processed surface at equal deposition parameters could be related to the plasma-induced surface defects. Electrochemical characterization shows that the platinum particles act as nanoelectrodes and form an ohmic contact with the diamond substrate. The catalytic activity regarding HER and HOR of the platinum nanoparticles exhibits no dependence on the particle size down to particle heights of ?1 nm. The prepared Pt on diamond(100) samples show a similar platinum-specific activity as bulk platinum. Therefore, while keeping the activity constant, the well-dispersed particles on diamond offer an optimized surface-to-material ratio. PMID:21687867

Brlle, Tine; Denisenko, Andrej; Sternschulte, Hadwig; Stimming, Ulrich



The Electrochemical Formation of Ni-Tb Intermetallic Compounds on a Nickel Electrode in the LiCl-KCl Eutectic Melts  

NASA Astrophysics Data System (ADS)

The work presents an electrochemical study on the formation of Ni-Tb intermetallic compounds in the LiCl-KCl-TbCl3 melts on tungsten and nickel electrodes at 773 K (500 C) by electrochemical techniques. For a tungsten electrode, cyclic voltammetry and square-wave voltammetry showed that the electrochemical reduction of Tb(III) proceeded in a one-step process involving three electrons at -2.06 V ( vs Ag/AgCl). For a nickel electrode, the reduction potential of Tb(III)/Tb was observed at more positive values than those on W electrode by cyclic voltammetry, due to the formation of Ni-Tb intermetallic compounds. Square-wave voltammetry and open-circuit chronopotentiometry put into evidence the formation of intermetallic compounds at around -1.27, -1.63, and -1.88 V, respectively. Three alloy samples were obtained by potentiostatic electrolysis on a Ni electrode at various potentials and analyzed by X-ray diffraction, scanning electron micrograph, and energy-dispersive spectrometry. The analysis results confirmed the formation of Ni17Tb2, Ni5Tb, and Ni2Tb alloy compounds.

Han, Wei; Sheng, Qingnan; Zhang, Milin; Li, Mei; Sun, Tingting; Liu, Yaochen; Ye, Ke; Yan, Yongde; Wang, Yingcai



Degradation of SS316L bipolar plates in simulated fuel cell environment: Corrosion rate, barrier film formation kinetics and contact resistance  

NASA Astrophysics Data System (ADS)

A potentiostatic polarization method is used to evaluate the corrosion behavior of SS316L in simulated anode and cathode environments of polymer electrolyte fuel cells. A passive barrier oxide film is observed to form and reach steady state within ?10 h of polarization, after which time the total ion release rates are low and nearly constant at ?0.4 ?g cm-2 h-1 for all potentials investigated. The equilibrium film thickness, however, is a function of the applied potential. The main ionic species dissolved in the liquid are predominately Fe followed by Ni, that account for >90% of the steady-state corrosion current. The dissolution rate of Cr is low but increases systematically at potentials higher than 0.8 V. The experimental ion release rates can be correlated with a point defect model using a single set of parameters over a broad range of potentials (0.2-1 V) on the cathode side. The interfacial contact resistance measured after 48 h of polarization is observed to increase with increase in applied potential and can be empirically correlated with applied load and oxide film thickness. The oxide film is substantially thicker at 1.5 V possibly because of alteration in film composition to Fe-rich as indicated by XPS data.

Papadias, Dionissios D.; Ahluwalia, Rajesh K.; Thomson, Jeffery K.; Meyer, Harry M.; Brady, Michael P.; Wang, Heli; Turner, John A.; Mukundan, Rangachary; Borup, Rod



Coatings on NiTi Alloy  

NASA Astrophysics Data System (ADS)

Atomic layer deposition is introduced as a method suitable for preparation of Al2O3 layers on the surface of NiTi medical devices such as stents because of the excellent thickness control and conformal protective coating on complex structures. The corrosion properties of NiTi plates with Al2O3 coatings of various thicknesses in an environment similar to that occurring in the human body were studied using open circuit potential, potentiostatic electrochemical impedance spectroscopy, and cyclic polarization tests. It shows that the layer thickness plays a key role in the inhibition of corrosion. The thinner layers are more diffuse and make it easier for anodic reaction of passive NiTi with protective TiO2 underneath of Al2O3, while the thicker layers have the barrier effect with local pores initiating pitting corrosion. The results of our electrochemical experiments consistently show that corrosion properties of thick Al2O3 coatings on NiTi plate are inferior compared to the thin layers.

Kei, C. C.; Yu, Y. S.; Racek, J.; Vokoun, D.; ittner, P.



Electrochemical preparation of nanostructured lanthanum using lanthanum chloride as a precursor in 1-butyl-3-methylimidazolium dicyanamide ionic liquid.  


Nanostructured lanthanum was electrochemically prepared on a platinum (Pt) substrate in the room temperature ionic liquid 1-butyl-3-methylimidazolium dicyanamide (BMI-DCA) containing anhydrous LaCl3 at 333 K. The electrochemical reduction behavior of La(iii) was investigated using cyclic voltammetry and chronoamperometry techniques. Cyclic voltammogram revealed that the reduction of La(iii) in BMI-DCA involved an irreversible process controlled by diffusion. Chronoamperometric transient analysis confirmed the diffusion controlled electrodeposition process with the diffusion coefficient of La(iii) species in the range of 10(-10) cm(2) s(-1). The strong complexing capability of DCA(-) anions facilitated the displacement of chloride ligands and induced the solubility of LaCl3. The subsequent coordination of La(iii) and DCA(-) anions forming [La(DCA)4](-) complex anions was monitored by designing amperometric titration experiments. Potentiostatically deposited La-deposits with different nanostructures were characterized by SEM, XRD and XPS analyses. The electrodeposition potential was found to play an important role in controlling the nucleation and growth kinetics of the nanocrystal during the electrodeposition process. Depending on the deposition potential, metallic lanthanum with either nanoparticles or nanoporous structures was obtained. PMID:25589210

Zhang, Q B; Yang, C; Hua, Y X; Li, Y; Dong, P



Electrodeposited NiFeCu/Cu multilayers: Effect of Fe ion concentration on properties  

NASA Astrophysics Data System (ADS)

A series of 125[NiFeCu(3 nm)/Cu(1 nm)] multilayers were electrodeposited on strong (110) textured Cu substrates from electrolytes containing different Fe ion concentrations under potentiostatic control. The compositional analysis by energy dispersive X-ray spectroscopy demonstrated that as the Fe ion concentration in the electrolyte is increased, the Fe content of the multilayers increased. X-ray diffraction measurements indicated that all samples exhibited a face-centred cubic structure with a strong (110) texture as their substrates. The surface images obtained by scanning electron microscopy disclosed that all films have smooth surfaces. Magnetoresistance measurements were carried out at room temperature with magnetic fields up to 12 kOe. All samples exhibited giant magnetoresistance (GMR) and the maximum GMR value of 5% was obtained in the multilayer grown from the electrolyte containing 0.0036 M Fe ion concentration. The GMR magnitude changed depending on the film contents arising from the variation of the Fe ion concentration in the electrolyte. The magnetic properties studied with the vibrating sample magnetometer showed that the saturation magnetisation changed, and the coercivities decreased with varying Fe ion concentration in the electrolyte. The changes observed in the properties were ascribed to the variations observed in the film composition caused by the Fe ion concentration of the electrolyte.

Kuru, Hilal; Kockar, Hakan; Alper, Mursel



Evaluation of a diffusion/trapping model for hydrogen ingress in high-strength alloys. Final technical report, November 1988-November 1990  

SciTech Connect

The objective of this research was to obtain the hydrogen ingress and trapping characteristics for a range of microstructures and so identify the dominant type of irreversible trap in different alloys. A diffusion/trapping model was used in conjunction with a potentiostatic pulse technique to study the ingress of hydrogen in three precipitation-hardened alloys (Inconel 718, Incoloy 925, and 18Ni maraging steel), two work-hardened alloys (Inconel 625 and Hastelloy C-276), titanium (pure and grade 2), and copper-enriched AISI 4340 steel in 1 mol/L acetic acid-1 mol/L sodium acetate containing 15 ppm arsenic oxide. In all cases except pure titanium, the data were shown to fit the interface-control form of the model and values were determined for the irreversible trapping constants (k) and the flux of hydrogen into the alloys. The density of irreversible trap defects were calculated from k and generally found to be in close agreement with the concentration of a specific heterogeneity in each alloy. Moreover, the trapping constants for the alloys were found to be consistent with their relative susceptibilities to hydrogen embrittlement.

Pound, B.G.



Influence of the sliding velocity and the applied potential on the corrosion and wear behavior of HC CoCrMo biomedical alloy in simulated body fluids.  


The corrosion and tribocorrosion behavior of an as-cast high carbon CoCrMo alloy immersed in phosphate buffered solution (PBS) and phosphate buffered solution with bovine serum albumin (PBS+BSA) have been analyzed by electrochemical techniques and surface microscopy. After the electrochemical characterization of the alloy in both solutions, the sample was studied tribo-electrochemically (by open circuit potential, OCP measurements, potentiodynamic curves and potentiostatic tests) in a ball-on-disk tribometer rotating in different sliding velocities. The influence of solution chemistry, sliding velocity and applied potential on the corrosion and tribocorrosion behavior of the CoCrMo alloy has been studied. Anodic current density increases with sliding velocity but wear rate does not change at an applied anodic potential; on the other hand, BSA modifies the wear debris behavior (by agglomerating the debris formed by mechanical removal of particles) thus increasing the mechanical wear volume. Under cathodic conditions, cathodic current density also increases during mechanical contact while the wear rate decreases with sliding velocity and BSA lubricates the contact thus reducing the total wear volume with respect to the non-containing BSA solution. The work shows how the electrode potential critically affects the corrosion and tribocorrosion rates by increasing the wear coefficients at applied anodic potentials due to severe wear accelerated corrosion. PMID:22098909

Gil, Roberto Alonso; Muoz, Anna Igual



Effects of electrolytes and electrochemical pretreatments on the capacitive characteristics of activated carbon fabrics for supercapacitors  

NASA Astrophysics Data System (ADS)

The capacitive characteristics of activated carbon fabrics (ACFs) coated on the graphite substrates were systematically investigated by means of cyclic voltammetry and the galvanostatic charge-discharge technique. Effects of the PVDF contents in the electronically conductive binder, electrochemical pretreatments, and the electrolytes on the capacitive performance of ACFs were compared in aqueous media. These ACF-pasted electrodes showed the more ideally capacitive responses in 1 M NaNO 3 with a specific capacitance of 76 F g -1 when the electronically conductive binder contained 40 wt.% PVDF. The specific capacitance of ACF-pasted electrodes reached a maximum in 0.5 M H 2SO 4 (about 153 F g -1 measured at 25 mV s -1), due to the presence of a suitable density of oxygen-containing functional groups, when they were subjected to the potentiostatic polarization at 1.8 V (versus reversible hydrogen electrode (RHE)) or potentio-dynamic polarization between 1.3 and 1.8 V in NaNO 3 for 20 min. The oxygen-containing functional groups within the electrochemically pretreated ACFs were identified by means of X-ray photoelectron spectroscopy (XPS).

Hu, Chi-Chang; Wang, Chen-Ching


Influence of post-treatment temperature of TNTa photoelectrodes on photoelectrochemical properties and photocatalytic degradation of 4-nonylphenol  

NASA Astrophysics Data System (ADS)

TiO2/Ti Nanotube array (TNTa) photoelectrodes were prepared by galvanostatic and potentiostatic anodization technique, and annealed at different temperature. The morphology and structure were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectra. Optical properties and photoelectrochemical (PECH) properties were investigated by surface photovoltage (SPV), ultra UV-vis diffuse reflectance spectra (UV/vis/DRS), open-circuit potential (OCP) and transient photocurrent. Photodecomposition performances were evaluated by the yield of OH radicals and photocatalytic (PC) degradation rate of 4-nonylphenol (4-NP) under xenon light. The results showed that with the increase of post-treatment temperature, PECH and PC properties increased gradually and then decreased. The photocurrent densities, yield of *OH radicals and photodecomposition rates of 4-NP were following the trend of TNT-823>TNT-873>TNT-773>TNT-673>TNT-973>TNT-298. When the annealing temperature was 823 K, the photoelectrodes were composed of mixed crystal structure and ordered nanotube array, which exhibited superior PECH properties. When the annealed temperature arrived to 973 K, the nanotube collapsed and the PECH and PC properties of TNTa photoelectrodes decreased. For TNT-823 photoelectrodes, after the assistant potential was applied, the degradation rate of 4-NP increased significantly from 77% to 97% after 120 min illumination.

Xin, Yanjun; Liu, Huiling; Li, Junjing; Chen, Qinghua; Ma, Dong



Cobalt extraction in ammoniacal solution: Electrochemical effect of metallic iron  

NASA Astrophysics Data System (ADS)

The dissolution behavior of iron and cobalt in ammoniacal ammonium carbonate solution has been investigated with the aid of Eh-pH diagrams for the Fe-NH3-H2O-CO3 and Co-NH3-H2O-CO3 systems, and electrochemical techniques such as open circuit potential measurements and potentiostatic and potentiodynamic polarization experiments. The polarization measurements indicate that both Fe and Co electrodes show active and passive behavior, and that Co dissolves at a more oxidizing potential than does Fe (e.g., E = -0.34 V (SHE) for Co and E = -0.52 V for Fe at a dissolution rate of 1 mA cm-2). The active and passive current densities for Co are both greater than for Fe. In sintered Fe-Co mixtures, the presence of Fe shifts the potential of the maximum current to less noble values and also lowers the magnitude of this current. In addition there is practically no cobalt dissolution when the potential exceeds 0.6 V (SHE). It is suggested that the well-known poor recovery of cobalt from reductive-roasted ferruginous oxide ores may be partly related to the dissolution behavior of a metallic alloy phase containing both iron and cobalt.

Osseo-Asare, K.; Lee, J. W.; Kim, H. S.; Pickering, H. W.



Exchange bias, training effect, and bimodal distribution of blocking temperatures in electrodeposited core-shell nanotubes  

NASA Astrophysics Data System (ADS)

Co nanotubes (NTs) were electrodeposited inside nanoporous alumina templates by a potentiostatic method and then left in air for the natural oxidation of their inner walls. Temperature-dependent magnetic measurements evidenced the existence of exchange-bias (EB) coupling between the Co ferromagnetic (FM) outer wall and the CoO antiferromagnetic (AFM) inner wall of the NTs. The values of the EB field measured at 6 K were found in the same order of magnitude as those already reported for Co/CoO bilayer thin films and core-shell nanoparticles. The effect of temperature and cooling field on the EB effect between the Co/CoO walls of the NTs is here reported. The training effect of the EB in the Co/CoO NT arrays, measured at 6 K, suggests the existence of a stronger coupling between the AFM and the FM layers that are shaped into a core-shell nanotubular structure, when compared with flat interfaces. A bimodal distribution of blocking temperatures is also found when applying the magnetic field parallel and perpendicular to the NTs axis.

Proenca, M. P.; Ventura, J.; Sousa, C. T.; Vazquez, M.; Araujo, J. P.



Magnetic interactions and reversal mechanisms in Co nanowire and nanotube arrays  

NASA Astrophysics Data System (ADS)

Ordered hexagonal arrays of Co nanowires (NWs) and nanotubes (NTs), with diameters between 40 and 65 nm, were prepared by potentiostatic electrodeposition into suitably modified nanoporous alumina templates. The geometrical parameters of the NW/NT arrays were tuned by the pore etching process and deposition conditions. The magnetic interactions between NWs/NTs with different diameters were studied using first-order reversal curves (FORCs). From a quantitative analysis of the FORC measurements, we are able to obtain the profiles of the magnetic interactions and the coercive field distributions. In both NW and NT arrays, the magnetic interactions were found to increase with the diameter of the NWs/NTs, exhibiting higher values for NW arrays. A comparative study of the magnetization reversal processes was also performed by analyzing the angular dependence of the coercivity and correlating the experimental data with theoretical calculations based on a simple analytical model. The magnetization in the NW arrays is found to reverse by the nucleation and propagation of a transverse-like domain wall; on the other hand, for the NT arrays a non-monotonic behavior occurs above a diameter of 50 nm, revealing a transition between the vortex and transverse reversal modes.

Proenca, M. P.; Sousa, C. T.; Escrig, J.; Ventura, J.; Vazquez, M.; Araujo, J. P.



Temperature dependence of the training effect in electrodeposited Co/CoO nanotubes  

NASA Astrophysics Data System (ADS)

High aspect ratio Co/CoO nanotubes (NTs) were obtained by potentiostatic electrodeposition of Co inside nanoporous alumina templates followed by the natural oxidation of their inner walls. Magnetic measurements performed at low temperatures after field cooling the samples from above its blocking temperature (TB220 K), evidenced the existence of exchange bias (EB) coupling between the Co ferromagnetic outer wall and the CoO antiferromagnetic inner wall of the NTs. A decrease in the magnitude of the EB field was measured at T

Proenca, M. P.; Ventura, J.; Sousa, C. T.; Vazquez, M.; Araujo, J. P.



Effect of Fluid Flow on Zinc Electrodeposits from Acid Chloride Electrolytes. M.S. Thesis  

NASA Technical Reports Server (NTRS)

Zinc was deposited potentiostatically from acid chloride baths. Once bath chemistry and electrochemistry were controlled, the study was focused on convective mass transfer at horizontal electrodes and its effect on cell performance. A laser schlieren imaging technique allowed in situ observations of flow patterns and their correlation with current transients. Convection was turbulent and mass transfer as a function of Rayleigh number was well correlated by: Sh = 0.14 R to the 1/3 power. Similarly, convection initiation time was correlated by DT/d squared = 38 Ra to the -2/3 power. Time scale of fluctuations was about half the initiation time. Taking the boundary layer thickness as a characteristic length, a critical Rayleigh number for the onset of convection was deduced: Ra sub CR = 5000. Placing the anode on the top of the cathode completely changed the flow pattern but kept the I-t curves identical whereas the use of a cathode grid doubled the limiting current. A well defined plateau in the current voltage curves suggested that hydrogen evolution has been successfully inhibited. Finally, long time deposition showed that convection at horizontal electrodes increased the induction time for dentrite growth by at least a factor of 2 with respect to a vertical wire.

Abdelmassir, A. A.



Evidence of surface migration and formation of catalytically inactive Pt in corrosion studies of Pt+ implanted Ti  

SciTech Connect

This investigation is part of an ongoing research project directed at applying the techniques of ion implantation doping and ion scattering analysis to identify the mechanisms associated with the anodic dissolution of Ti-Pt alloys. The Ti-Pt alloys produced by ion implantation were electrochemically examined in hydrogen saturated 1 N H/sub 2/SO/sub 4/ by both potentiostatic polarization and open-circuit potential methods. In this study, Ti samples implanted to relatively high doses (5.4 x 10/sup 15/ to 2.9 x 10/sup 16/ atoms/cm/sup 2/) were examined by ion scattering analysis at various stages in the electrochemical measurements. Quantitative measurements showed that the majority of the implanted Pt accumulated on the surface during anodic dissolution and underwent large scale surface migration. Evidence is also presented for the transition of the Pt on the surface from a catalytically active to inactive state. Possible mechanisms for the observed catalytically inactive Pt are discussed.

Appleton, B.R.; Kelly, E.J.; White, C.W.; Thompson, N.G.; Lichter, B.D.



Electrochemically modulated liquid-liquid extraction of ions.  


The development of ion extraction methods under electrochemical control via electrochemistry at the interface between two immiscible electrolyte solutions is discussed. A hydrodynamic flow injection system was used for the potentiostatic extraction of non-redox-active species from a flowing aqueous phase into a stationary organogel phase. The ions tetraethylammonium, 4-octylbenzenesulfonate (4-OBSA-), and p-toluenesulfonate (p-TSA-) were studied as model analytes. The extraction study comprised examination of the influence of extraction potentials, aqueous-phase flow rate, and target species concentration. The extraction process can be monitored in situ by means of the ion-transfer current, which has opposing signs for anions and cations. Hydrodynamic voltammograms were obtained from these experiments. The selective extraction of 4-OBSA-, from its mixture with p-TSA-, as well as coextraction of both anions is shown. The results demonstrate the utility of electrochemical modulation for the controlled extraction of ions from an aqueous phase into an organogel electrolyte phase. This offers potential benefits for various analytical processes including sample preparation and cleanup. PMID:16285680

Berduque, Alfonso; Sherburn, Amanda; Ghita, Mihaela; Dryfe, Robert A W; Arrigan, Damien W M



Porphyrin-cobaloxime complexes for hydrogen production, a photo- and electrochemical study, coupled with quantum chemical calculations.  


Two porphyrin-cobaloxime complexes; [{Co(dmgH)2Cl}{MPyTPP}] () and [{Co(dmgH)2Cl}{ZnMPyTPP}] () (dmgH = dimethylglyoxime, MPyTPP = 5-(4-pyridyl)-10,15,20-triphenylporphyrin) have been synthesised as model systems for the generation of hydrogen from water. Although initially envisaged as photocatalytic systems neither complex catalysed the reduction of water to hydrogen following irradiation. However, both complexes are molecular precursors for hydrogen evolution under electrochemical conditions. Turnover numbers for hydrogen production of 1.8 10(3) and 5.1 10(3) were obtained for and respectively following potentiostatic electrolysis at -1.2 V vs. Ag/AgCl while cobaloxime alone produced a turnover-number of 8.0 10(3). The photophysical properties of and were examined to provide an explanation for the lack of photochemical activity. These results, coupled with quantum chemical calculations, confirm that porphyrins fail to act as light-harvesting units for these systems and that the lowest energy excited states are in fact cobaloxime-based rather than porphyrin based. PMID:24399269

Manton, Jennifer C; Long, Conor; Vos, Johannes G; Pryce, Mary T



A liquid-junction-free reference electrode based on a PEDOT solid-contact and ionogel capping membrane.  


Liquid-junction-free reference electrodes have been prepared on screen printed substrates using poly-3,4-ethylenedioxythiophene (PEDOT) as solid-contact and novel ionogels as capping membrane. The chemico-physical properties of the PEDOT layer were tuned by changing the electropolymerization media and the electrodeposition technique. Electrodepositing PEDOT films potentiostatically or potentiodynamically were found to have a significant impact on the stability of the electrodes during the conditioning step. Optimization of the capping membrane formulation, e.g., acrylate monomers, ionic liquid, cross-linkers and photo-initiators, produced electrodes with properties almost equivalent with a commercial reference electrode. Thus, calibration plots of Na(+) ion-selective electrodes against the optimized solid-contact ionogel reference electrodes (SCI-REs) or against a double-liquid junction Ag/AgCl electrode did not present any significant difference. Such SCI-REs may provide an effective route to the generation of future low-cost components for potentiometric sensing strips. PMID:24840415

Zuliani, Claudio; Matzeu, Giusy; Diamond, Dermot



A photo- and electrochemical investigation of BODIPY-cobaloxime complexes for hydrogen production, coupled with quantum chemical calculations.  


Two BODIPY-cobaloxime complexes; [{Co(dmgH)2Cl}{3-[bis-(4-ethyl-3,5-dimethyl-1H-pyrrol-2-yl)-methyl]-pyridine-borondiflouride}] (1a) and [{Co(dmgH)2Cl}{4-[bis-(4-ethyl-3,5-dimethyl-1H-pyrrol-2-yl)-methyl]-pyridine-borondiflouride}] (2a) (BODIPY = boron dipyrromethene), (dmgH = dimethylglyoxime) have been synthesised and studied as model catalytic systems for the generation of hydrogen gas in aqueous media. Under photochemical conditions, neither complex catalysed the reduction of water to hydrogen. However, both complexes showed considerable activity under electrochemical conditions. Turn-over-numbers for hydrogen production of 1.65 10(4) and 1.08 10(4) were obtained for 1a and 2a respectively following potentiostatic electrolysis at -1.2 V vs. Ag/AgCl after 1 hour. Quantum chemical calculations were performed to provide an explanation for the lack of photochemical activity. PMID:24487702

Manton, Jennifer C; Long, Conor; Vos, Johannes G; Pryce, Mary T



Electrical pH control in aqueous solutions  

NASA Astrophysics Data System (ADS)

This paper describes a method and instrumentation for electrical pH control in aqueous solutions. It is targeted to environmental and industrial on-line chemical and optic fiber sensors measurement, calibration and process control. The method is an alternative to the existing automatic pH controllers based on correction chemical addition. The on- line measurement of dissolved gaseous species which produce acidic and basic waters is of great concern for environmental monitoring applications. Such measurements are maintained by using preconditioned water samples and ion- selective electrodes or absorption spectrometry. A gas- permeable membrane can be used to allow only the transport of the molecular form of the measured species where the solution pH is controlled to ensure the reversible transition of the species of interest from ionic to molecular form and to allow their permeation through the membrane. An electrochemical instrument for electrolysis- based feedback controlled pH regulation has been attempted. The choice of galvanostatic, potentiostatic and combined methods of modulation electrodes biasing with their speed, settling time and accuracy are discussed. Different feedback control approaches, involving electrochemical and optical sensors, are compared.

Bourilkov, Jordan; Belz, Mathias; Boyle, William J. O.; Grattan, Kenneth T. V.



Amperometric determination of acetylcholine-A neurotransmitter, by chitosan/gold-coated ferric oxide nanoparticles modified gold electrode.  


An amperometric acetylcholine biosensor was constructed by co-immobilizing covalently, a mixture of acetylcholinesterase (AChE) and choline oxidase (ChO) onto nanocomposite of chitosan (CHIT)/gold-coated ferric oxide nanoparticles (Fe@AuNPs) electrodeposited onto surface of a Au electrode and using it as a working electrode, Ag/AgCl as reference electrode and Pt wire as auxiliary electrode connected through potentiostat. The biosensor is based on electrochemical measurement of H2O2 generated from oxidation of choline by immobilized ChO, which in turn is produced from hydrolysis of acetylcholine by immobilized AChE. The biosensor exhibited optimum response within 3s at +0.2V, pH 7.0 and 30C. The enzyme electrode had a linear working range of 0.005-400 M, with a detection limit of 0.005 M for acetylcholine. The biosensor measured plasma acetylcholine in apparently healthy and persons suffering from Alzheimer's disease. The enzyme electrode was unaffected by a number of serum substances but lost 50% of its initial activity after its 100 uses over a period of 3 months, when stored at 4C. PMID:24836212

Chauhan, Nidhi; Pundir, C S



A soft/hard magnetic nanostructure based on multisegmented CoNi nanowires.  


In this paper we have introduced a new soft/hard nanostructure based on multisegmented CoNi nanowire arrays having diameters of around 110 nm and made of five segments with nominal compositions of Co, Co66Ni33, Co50Ni50, Co33Ni66 and Ni, each of which has a length of 800 nm, so that the total length of the multisegmented nanowire is 4 ?m. These arrays have been synthesized by means of potentiostatic electrodeposition into the pores of hard-anodic alumina templates. The morphology, chemical composition and microstructure of the multisegmented CoNi nanowires were determined by high-resolution scanning electron microscopy, energy dispersive X-ray microanalysis, and powder X-ray diffraction method, respectively. The room temperature magnetic behavior of the multisegmented nanowire arrays is also studied and compared with CoNi nanowire arrays with homogeneous composition (non-segmented nanowires), synthesized in the same templates and having the same dimensions as the segmented ones. These nanostructures could be used to control the movement of magnetic domain walls. In this way, these nanostructures can be an alternative to store information or even perform logic functions. PMID:25597517

Pereira, A; Palma, J L; Vzquez, M; Denardin, J C; Escrig, J



Effect of Non-ionic Surfactants and Its Role in K Intercalation in Electrolytic Manganese Dioxide  

NASA Astrophysics Data System (ADS)

The effect of non-ionic surface active agents (surfactants) Triton X-100 (TX-100) and Tween-20 (Tw-20) and their role in potassium intercalation in electrolytic manganese dioxide (EMD) produced from manganese cake has been investigated. Electrosynthesis of MnO2 in the absence or presence of surfactant was carried out from acidic MnSO4 solution obtained from manganese cake under optimized conditions. A range of characterization techniques, including field emission scanning electron microscopy, transmission electron microscopy (TEM), Rutherford back scattering (RBS), and BET surface area/porosity studies, was carried out to determine the structural and chemical characteristics of the EMD. Galvanostatic (discharge) and potentiostatic (cyclic voltammetric) studies were employed to evaluate the suitability of EMD in combination with KOH electrolyte for alkaline battery applications. The presence of surfactant played an important role in modifying the physicochemical properties of the EMD by increasing the surface area of the material and hence, enhancing its electrochemical performance. The TEM and RBS analyses of the discharged EMD (?-MnO2) material showed clear evidence of potassium intercalation or at least the formation of a film on the MnO2 surface. The extent of intercalation was greater for EMD deposited in the presence of TX-100. Discharged MnO2 showed products of Mn2+ intermediates such as MnOOH and Mn3O4.

Biswal, Avijit; Tripathy, B. C.; Subbaiah, T.; Meyrick, D.; Ionescu, Mihail; Minakshi, Manickam



Inhibitive Effect of L-Oh on the Corrosion of Austenitic Chromium-Nickel Steel in H2SO4 Solution  

NASA Astrophysics Data System (ADS)

The corrosion behavior of the austenitic chromium-nickel steel in different concentrations (0.001, 0.002, 0.005, and 0.01 M) of dimethyl 2-(2-hydroxy phenyl amino)-3-(triphenyl phosphoranilidin) butane dioate (L-OH) in 0.5 M H2SO4 was investigated by potentiostatic polarization measurements. The effect of concentration and temperature on inhibition properties was determined. It was found that the presence of L-OH reduces markedly the corrosion rate of steel in the acid solution. The inhibition efficiency increases as the L-OH concentration is increased. Maximum inhibition efficiency (95%) was obtained for alloy in acid solution containing 0.01 M of L-OH. Thermodynamic parameters for adsorption of L-OH are calculated. It was found that the inhibitor is adsorbed on the steel surface and the experimental results are in agreement with Timken's isotherm. Negative values of the free energy of adsorption were obtained indicating the spontaneity of adsorption process. Scanning electron microscopy was done from the surface of exposed sample indicating uniform film on the surface of the alloy.

Hosseini, S. M. A.; Amiri, M.; Momeni, A.


Oriented electrophoretic deposition of GdOCl nanoplatelets.  


Electrophoretic deposition has emerged as a versatile and precisely tunable approach for the rapid deposition of conformal thin films of colloidal nanocrystals. The electrophoretic deposition of phosphor particles has assumed special significance in recent years as a commercially viable means toward the fabrication of large-area, ultrathin high-resolution emissive display screens. Here, we demonstrate that the anisotropic shape of colloidal ligand-passivated GdOCl nanoplatelets enables their assembly with remarkable substrate alignment and a high packing density upon electrophoretic deposition. GdOCl nanocrystals are promising candidates for phosphor applications given their low maximum phonon cutoff energy, robust chemical stability over prolonged periods of operation, and ability to promote efficacious phonon energy transfer to dopant ions. Potentiostatic deposition of GdOCl nanoplatelets from cyclohexane dispersions allows the deposition of individual nanoplatelets with their basal planes parallel to the electrode surface. Tuning the applied voltage and solution concentration allows control of film thickness, ranging up to several tens of micrometers. The high degree of particle alignment is attributed to anisotropic charge distribution and entrainment within electroosmotic flows established in the vicinity of the electrode surface. The oriented high-particle-density GdOCl nanoplatelet thin films are possible candidates for phosphor applications, which is illustrated by the green emission from a Tb-doped GdOCl thin film on indium tin oxide (ITO)-coated glass. PMID:22963367

Kort, Kenneth R; Banerjee, Sarbajit



Submicron patterned metal hole etching  


A wet chemical process for etching submicron patterned holes in thin metal layers using electrochemical etching with the aid of a wetting agent. In this process, the processed wafer to be etched is immersed in a wetting agent, such as methanol, for a few seconds prior to inserting the processed wafer into an electrochemical etching setup, with the wafer maintained horizontal during transfer to maintain a film of methanol covering the patterned areas. The electrochemical etching setup includes a tube which seals the edges of the wafer preventing loss of the methanol. An electrolyte composed of 4:1 water: sulfuric is poured into the tube and the electrolyte replaces the wetting agent in the patterned holes. A working electrode is attached to a metal layer of the wafer, with reference and counter electrodes inserted in the electrolyte with all electrodes connected to a potentiostat. A single pulse on the counter electrode, such as a 100 ms pulse at +10.2 volts, is used to excite the electrochemical circuit and perform the etch. The process produces uniform etching of the patterned holes in the metal layers, such as chromium and molybdenum of the wafer without adversely effecting the patterned mask.

McCarthy, Anthony M. (Menlo Park, CA); Contolini, Robert J. (Lake Oswego, OR); Liberman, Vladimir (Needham, MA); Morse, Jeffrey (Martinez, CA)



Synthesis and enhanced electrochemical performance of Li2CoPO4F cathodes under high current cycling.  


Lithium cobalt fluorophosphate, Li(2)CoPO(4)F, is successfully synthesized by a solid state reaction under Ar flow at 700 C. X-ray diffraction and scanning electron microscopic studies are utilized to analyze the structural and morphological features of the synthesized materials, respectively. The presence of fluorine is also supported by energy-dispersive X-ray spectroscopy. The electrochemical properties are evaluated by means of Li/Li(2)CoPO(4)F half-cell configurations in both potentiostatic and galvanostatic modes. The Li/Li(2)CoPO(4)F cell delivers an initial discharge capacity of 132 mA h g(-1) at a current density of 0.1 mA cm(-2) between 2.0 and 5.1 V at room temperature. Due to the higher operating potential of the Co(2+/3+) couple in the fluorophosphate matrix, this cell shows a capacity retention of only 53% after 20 cycles, still the material delivered 108 mA h g(-1) at a high current rate of 1 C. Cyclic voltammetric studies corroborate the insertion and extraction of Li(+) ions by a single phase reaction mechanism during cycling. PMID:22832971

Amaresh, S; Kim, G J; Karthikeyan, K; Aravindan, V; Chung, K Y; Cho, B W; Lee, Y S



A low power sensor signal processing circuit for implantable biosensor applications  

NASA Astrophysics Data System (ADS)

A low power sensor read-out circuit has been implemented in 0.35 m CMOS technology that consumes only 400 W of power and occupies an area of 0.66 mm2. The circuit is capable of converting the current signal from any generic biosensor into an amplitude shift keying (ASK) signal. The on-chip potentiostat biases the chemical sensor electrodes to create the sensor current which is then integrated and buffered to generate a square wave with a frequency proportional to the sensor current level. A programmable frequency divider is incorporated to fix the ASK envelope frequency to be inbetween 20 Hz and 20 kHz, which is within the audible range of human hearing. The entire transmitter block operates with a supply voltage as low as 1.5 V, and it can be easily powered up by an external RF source. Test results emulate the simulation results with good agreement and corroborate the efficacy of the designed system.

Zhang, Mo; Haider, Mohammad R.; Huque, Mohammad A.; Adeeb, Mohammad A.; Rahman, Shaela; Islam, Syed K.



Corrosion resistance studies on grain-boundary etched drug-eluting stents.  


In this paper we compare the influence of different microstructures on the corrosion resistance of new drug-eluting stainless steel stents, which have been produced by grain-boundary-selective electrochemical etching processes. The morphology of the stent surfaces was analysed by scanning electron microscopy (SEM), and the surface composition was investigated with Auger electron spectroscopy (AES) as well as with energy dispersive X-ray analysis (EDX). The passivity of the different microstructured stents was studied by cyclovoltammetry in Ringer solution. Release of nickel and chromium was assessed after potentiostatic experiments in Ringer solution by analysing the collected electrolyte with AAS. For stents produced by different two-step etching procedures bringing about ideal morphologies regarding the mechanical and biological properties of the surface, no significant differences in the passivation behaviour could be observed. A two-step process using first nitric acid and oxalic acid in a second step produces stent surfaces with very good corrosion properties: electrochemical analysis shows that the range of stable passivity is the same as for conventional stent surfaces, and low rates of nickel and chromium release are observed. The etching procedures do not seem to change the surface oxide layer composition. PMID:17277971

Rettig, Ralf; Kunze, Julia; Stver, Michael; Wintermantel, Erich; Virtanen, Sannakaisa



Effect of gelling on the impedance parameters of Pb/PbSO 4 electrode in maintenance-free lead-acid batteries  

NASA Astrophysics Data System (ADS)

The impedance parameters of Pb/PbSO 4 electrode in 4.8 M sulfuric acid have been measured potentiostatically under open-circuit conditions over a wide range of frequencies (10 -2 to 10 4 Hz) under both deep-discharged (state-of-charge, SoC=0) and fully charged (SoC=1) conditions. Immobilization of the electrolyte by adding sodium silicate (5 g/l) on the impedance of Pb/PbSO 4 electrode shows significant difference in comparison with the flooded system. Four equivalent circuits have been formulated for overcharged and deep-discharged electrodes in gelled and flooded electrolytes, respectively. Impedance parameters are calculated using a phenomenological model, which indicates that in the case of gelled electrolytes, the electrochemical reactions are mass-transfer controlled, in contrast to the flooded electrolyte cells, where the process is known to be charge-transfer controlled. The study provides a non-destructive investigation of the effect of gelling on the electrical performance of sealed maintenance-free lead-acid batteries.

Vinod, M. P.; Vijayamohanan, K.


Tuning the electrochemical swelling of polyelectrolyte multilayers toward nanoactuation.  


We discuss physicochemical determinants of electrochemical polyelectrolyte multilayer swelling that are relevant to actuator usage. We used electrochemical quartz crystal microbalance with dissipation monitoring (EC-QCM-D) and cyclic voltammetry to compare the electrochemical swelling of two types of ferrocyanide-containing polyelectrolyte multilayers, poly(l-glutamic acid)/poly(allylamine hydrochloride) (PGA/PAH), and carboxymethyl cellulose/poly(diallyldimethylammonium chloride) (CMC/PDDA). We showed that ferrocyanide oxidation causes the swelling of PGA/PAH multilayers whereas it results in the contraction of CMC/PDDA multilayers. This behavior can be attributed to the presence of a positive and a negative Donnan potential in the case of PGA/PAH and CMC/PDDA multilayers, respectively. Using multilayers consisting of PGA and poly(allylamine) ferrocene (PGA/PAH-FC), we applied EC-QCM-D and demonstrated potentiostatic thickness control with nanometer precision and showed that the multilayer's thickness depends linearly on the applied potential within a certain potential range. PMID:25229875

Zahn, Raphael; Vrs, Jnos; Zambelli, Tomaso



Wafer Scale Integration of CMOS Chips for Biomedical Applications via Self-Aligned Masking  

PubMed Central

This paper presents a novel technique for the integration of small CMOS chips into a large area substrate. A key component of the technique is the CMOS chip based self-aligned masking. This allows for the fabrication of sockets in wafers that are at most 5 m larger than the chip on each side. The chip and the large area substrate are bonded onto a carrier such that the top surfaces of the two components are flush. The unique features of this technique enable the integration of macroscale components, such as leads and microfluidics. Furthermore, the integration process allows for MEMS micromachining after CMOS die-wafer integration. To demonstrate the capabilities of the proposed technology, a low-power integrated potentiostat chip for biosensing implemented in the AMI 0.5 m CMOS technology is integrated in a silicon substrate. The horizontal gap and the vertical displacement between the chip and the large area substrate measured after the integration were 4 m and 0.5 m, respectively. A number of 104 interconnects are patterned with high-precision alignment. Electrical measurements have shown that the functionality of the chip is not affected by the integration process. PMID:22400126

Uddin, Ashfaque; Milaninia, Kaveh; Chen, Chin-Hsuan; Theogarajan, Luke



Electrochemical corrosion behavior of modified 9Cr-1Mo alloy  

SciTech Connect

The electrochemical corrosion behavior of modified 9Cr-1Mo alloy was studied in aqueous sulfate solution, with emphasis on the active dissolution, active-passive transition and passive film growth as a function of electrode potential, electrolyte pH and temperature. The primary electrochemical techniques employed were potentiodynamic, potentiostatic and galvanostatic polarization measurements supplemented by ESCA measurements of the anodic oxide film formed at various potentials. Passivation potential and critical current density of modified 9Cr-1Mo alloy were found to be significantly lower than those of pure iron, indicating alloying iron with chromium facilitates passivation. The oxidative dissolution of chromium oxide, the secondary passivation, and oxygen evolution were observed at the relatively higher oxidizing potentials. The anodic current under conditions of controlled constant potential decreased with increasing pH. Evidenced by ESCA, the excellent corrosion resistance of the iron-chromium alloy is strongly believed to be due to the enrichment of chromium on the surface which blocks the dissolution of iron.

Ahn, J.H.



Corrosion resistance, chemistry, and mechanical aspects of Nitinol surfaces formed in hydrogen peroxide solutions.  


Ti oxides formed naturally on Nitinol surfaces are only a few nanometers thick. To increase their thickness, heat treatments are explored. The resulting surfaces exhibit poor resistance to pitting corrosion. As an alternative approach to accelerate surface oxidation and grow thicker oxides, the exposure of Nitinol to strong oxidizing H(2)O(2) aqueous solutions (3 and 30%) for various periods of time was used. Using X-Ray Photoelectron Spectroscopy (XPS) and Auger spectroscopy, it was found that the surface layers with variable Ti (6-15 at %) and Ni (5-13 at %) contents and the thickness up to 100 nm without Ni-enriched interfaces could be formed. The response of the surface oxides to stress in superelastic regime of deformations depended on oxide thickness. In the corrosion studies performed in both strained and strain-free states using potentiodynamic and potentiostatic polarizations, the surfaces treated in H(2)O(2) showed no pitting in corrosive solution that was assigned to higher chemical homogeneity of the surfaces free of secondary phases and inclusions that assist better biocompatibility of Nitinol medical devices. PMID:22689286

Shabalovskaya, Svetlana A; Anderegg, James W; Undisz, Andreas; Rettenmayr, Markus; Rondelli, Gianni C



Applications of Planar ITO Electrodes for Studying of Some Biochemical Activities  

NASA Astrophysics Data System (ADS)

Trends in disposable and handheld biosensors have called for miniaturized and planar electrodes in the place of conventional bulky ones. In this work, thin tin-doped indium oxide (ITO) film coated on glass were used as a based electrode in a three-electrode electrochemical system to follow some biochemical activities, such as NADH and phenol activity. The reference electrode is made on ITO layer by electro-deposition of thin nickel layer and silver layer, consecutively, followed by chlorination of silver surface by electrochemical potentiostatic method. The plain planar ITO-coated glasses were used as both counter electrode and working electrodes. Cyclic-voltammetry measurements; which follow an oxidation of 200 ?M nicotinamide adenine dinucleotide (NADH) in 0.1 M KCl, show current peak of 8.5 ?A. Another case was also to follow the NADH oxidation but in competition with its coupling activity with flavin mononucleotide (FMN). In this case, cyclic-voltammetry measurements were carried out of 200 ?M NADH in 50 mM sodium phosphate; current peak of 1.3 ?A was observed.

Learngarunsri, P.; Chaiyen, P.; Srikhirin, T.; Veerasai, W.; Dangtip, S.


Ultramicroband array electrode. 1. Analysis of mercury in contaminated soils and flue gas exposed samples using a gold-plated iridium portable system by anodic stripping voltammetry.  


The applicability of a gold-plated iridium Nano-Band array ultramicroelectrode (6 microm by 0.2 microm, 64-microm interspacing, 100 electrode bands) in the analysis of mercury using a portable system is demonstrated by anodic stripping voltammetry in real-life samples. Optimized measurement parameters, 0.1 M HCl electrolyte, plating potential of 0 mV, and staircase scan mode were identified. The dynamic linear range is 10-180 ppb at 5-s deposition time with 1.5 microC of gold plated. The experimental detection limit for Hg2+ in 0.1 M HCl was 0.5 ppb at a deposition time of 4 min and a scan rate of 10 V/s. Real-life samples, such as flue gas exposed samples from flue gas simulators could be analyzed within 5 min using the method of standard additions. We identified a field-portable extraction procedure for soil samples using 1:1 concentrated HNO3/30% H2O2 mixture, compatible with ASV and the iridium electrode. The detection limit for soils is 1 ppm. The results obtained using ASV are in good agreement with reference values using cold vapor atomic absorption for the sample matrixes studied here. To our knowledge, this is the first mercury application using a reusable iridium array ultramicroelectrode. The portable potentiostat is less than 500 g, and together with the portable digestion method, makes the Nano-Band Explorer system field applicable. PMID:16841944

Xiao, Li; Dietze, William; Nyasulu, Frazier; Mibeck, Blaise A F



Amperometric Sensor for Detection of Chloride Ions  

PubMed Central

Chloride ion sensing is important in many fields such as clinical diagnosis, environmental monitoring and industrial applications. We have measured chloride ions at a carbon paste electrode (CPE) and at a CPE modified with solid AgNO3, a solution of AgNO3 and/or solid silver particles. Detection limits (3 S/N) for chloride ions were 100 ?M, 100 ?M and 10 ?M for solid AgNO3, solution of AgNO3 and/or solid silver particles, respectively. The CPE modified with silver particles is the most sensitive to the presence chloride ions. After that we approached to the miniaturization of the whole electrochemical instrument. Measurements were carried out on miniaturized instrument consisting of a potentiostat with dimensions 35 166 125 mm, screen printed electrodes, a peristaltic pump and a PC with control software. Under the most suitable experimental conditions (Britton-Robinson buffer, pH 1.8 and working electrode potential 550 mV) we estimated the limit of detection (3 S/N) as 500 nM.

Trnkova, Libuse; Adam, Vojtech; Hubalek, Jaromir; Babula, Petr; Kizek, Rene



New Secondary Batteries Utilizing Electronically Conductive Polypyrrole Cathode. Ph.D. Thesis  

NASA Technical Reports Server (NTRS)

To gain a better understanding of the dynamic behavior in electronically conducting polypyrroles and to provide guidance toward designs of new secondary batteries based on these polymers, two mathematical models are developed; one for the potentiostatically controlled switching behavior of polypyrrole film, and one for the galvanostatically controlled charge/discharge behavior of lithium/polypyrrole secondary battery cell. The first model is used to predict the profiles of electrolyte concentrations, charge states, and electrochemical potentials within the thin polypyrrole film during switching process as functions of applied potential and position. Thus, the detailed mechanisms of charge transport and electrochemical reaction can be understood. Sensitivity analysis is performed for independent parameters, describing the physical and electrochemical characteristic of polypyrrole film, to verify their influences on the model performance. The values of independent parameters are estimated by comparing model predictions with experimental data obtained from identical conditions. The second model is used to predict the profiles of electrolyte concentrations, charge state, and electrochemical potentials within the battery system during charge and discharge processes as functions of time and position. Energy and power densities are estimated from model predictions and compared with existing battery systems. The independent design criteria on the charge and discharge performance of the cell are provided by studying the effects of design parameters.

Yeu, Taewhan



Thermoelectric properties of electrodeposited CuNi alloys on Si  

NASA Astrophysics Data System (ADS)

Thin films with the composition of the constantan alloy (a solid solution with 35 to 50 wt. % of Ni in Cu) have a high-thermoelectric power, which allows the fabrication of very sensitive heat-flux sensors based on planar technology. In this article, the thermoelectric properties of CuxNi100-x thin films electrodeposited on silicon were studied as a function of the composition, temperature, and thickness. The electrodeposition of thin layers on silicon is an important step for the integration of thermal sensors with semiconductor technology. The CuxNi100-x alloys were electrodeposited potentiostatically at room temperature, from a citrate electrolyte containing both copper and nickel sulfates. The layer composition was controlled by the applied potential in the range from pure copper (at -0.4 V/SCE) up to a solid solution of about 25 wt. % Cu in Ni (at -1.2 V/SCE). Extremely high values of thermoelectric power were measured for very thin layers of Cu40Ni60 on Si, showing a strong influence of the substrate. By considering the system as a thermoelectric bilayer and extracting the contribution of the semiconductor, thermopower values for the Cu40Ni60 alloys comparable to the expected ones for constantan wires were obtained.

Delatorre, R. G.; Sartorelli, M. L.; Schervenski, A. Q.; Pasa, A. A.; Gths, S.



Corrosion of Carbon Steel and Corrosion-Resistant Rebars in Concrete Structures Under Chloride Ion Attack  

NASA Astrophysics Data System (ADS)

Corrosion of reinforced concrete is the most challenging durability problem that threatens reinforced concrete structures, especially structures that are subject to severe environmental conditions (i.e., highway bridges, marine structures, etc.). Corrosion of reinforcing steel leads to cracking and spalling of the concrete cover and billions of dollars are spent every year on repairing such damaged structures. New types of reinforcements have been developed to avoid these high-cost repairs. Thus, it is important to study the corrosion behavior of these new types of reinforcements and compare them to the traditional carbon steel reinforcements. This study aimed at characterizing the corrosion behavior of three competing reinforcing steels; conventional carbon steel, micro-composite steel (MMFX-2) and 316LN stainless steel, through experiments in carbonated and non-carbonated concrete exposed to chloride-laden environments. Synthetic pore water solutions have been used to simulate both cases of sound and carbonated concrete under chloride ions attack. A three-electrode corrosion cell is used for determining the corrosion characteristics and rates. Multiple electrochemical techniques were applied using a Gamry PC4 potentiostat manufactured by Gamry Instruments (Warminster, PA). DC corrosion measurements were applied on samples subjected to fixed chloride concentration in the solution.

Mohamed, Nedal; Boulfiza, Mohamed; Evitts, Richard



Electrodeposition of polycrystalline and amorphous silicon for photovoltaic applications  

NASA Astrophysics Data System (ADS)

Plating experiments with SiHCl3 solutions in propylene carbonate with 0.1 M tetrabutylammonium tetrafluoroborate are described. Silicon was deposited on ITO glass (Nesatron) as well as Mo substrates at temperatures from 25-80 C. Both potentiostatic and galvanostatic conditions were used. The high resistance of the films limited the thickness which could be deposited by either method to less than 5 micrometers. Deposition beyond this limit resulted in a deterioration of the film quality. X-ray analysis of the films confirmed that they were amorphous. SEM analysis of the films revealed a very porous structure with nodules about 1 micrometer in diameter. Annealing the deposit at 400 C in an Ar:H2 atmosphere resulted in a slightly smoother surface but the nodules remained. The films deposited on ITO glass had a band gap of about 1.0 eV and an EO4 value of 1.5-2.0 eV. The Auger analysis of the films showed the presence of large amounts of oxygen in the samples that had been exposed to air.

Rauh, R. D.



SEMICONDUCTOR MATERIALS: Effect of bath temperature on the properties of CuInxGa1-x Se2 thin films grown by the electrodeposition technique  

NASA Astrophysics Data System (ADS)

Electrodeposition is a promising and low cost method to synthesize CuInx Ga1-x Se2 (CIGS)thin films as an absorber layer for solar cells. The effect of bath temperature on the properties of CIGS thin films was investigated in this paper. CIGS films of 1 ?m thickness were electrodeposited potentiostatically from aqueous solution, containing trisodium citrate as a complexing agent, on Mo/glass substrate under a voltage of -0.75 V, and bath temperatures were varied from 20 to 60C. The effects of bath temperature on the properties of CIGS thin films were characterized by X-ray diffraction (XRD) and scanning electron microscopy. XRD revealed the presence of the CuIni0.7Ga0.3 Se2 phase, the optimal phase for application in solar cells. The grain dimensions and crystallizability increase along with the increase of the bath temperature, and the films become stacked and homogeneous. There were few changes in surface morphology and the composition of the films.

Jie, Cao; Shengchun, Qu; Kong, Liu; Zhanguo, Wang



Preparation of CuInSe2 film with electrodeposition  

NASA Astrophysics Data System (ADS)

CuInSe2(CIS) films directly electrodeposited on sputtered Mo-glass, sprayed SnO2-glass substrates had been accomplished at room temperature in the potentiostatic mode from a bath containing CuCl, InCl3(DOT)4H2O and SeO2. The acidity of bath was adjusted to 1PH. Energy dispersive spectrometry, atomic force microscopy (AFM), x- ray diffraction and hot-probe method was utilized to characterize the CIS films. The key factor for preparing single-phase CuInSe2 is the proportion of CuCl, InCl3(DOT)4H2O and SeO2. The CIS films are nearly stoichiometry of CuInSe2 and polycrystalline on Mo- glass. The Cu excess films are p-type semiconductor, and the In excess films n-type. The deposition potential obviously affects the surface morphology of CIS films. AFM results had indicated that the CIS films on Mo-glass grow in layer and on SnO2 glass in island.

Li, Wenyi; Yu, Jian; Yu, Xuebin; Chen, Qiulong; Cai, Xun



Electrodeposition of polycrystalline and amorphous silicon for photovoltaic applications  

NASA Astrophysics Data System (ADS)

Electrochemical measurements were made on SHCl3 and (CH3)3SiCl to determine if they were suitable precursors for electrodepositing silicon from organic solvents. The precursors were dissolved in solutions of propylene carbonate containing 0.1M tetrabutylammonium tetrafluoroborate (TBATFB). Cyclic voltammograms of the systems were run at 25 C and 70 C using Pt as the reference electrode and Pt, Al, or Mo wires as the working electrode. The results showed that the two peaks appearing between 0 and -1.0V could be attributed to impurities made electroactive by addition of the silicon precursor. Reduction to silicon occurred with SHCl3 between -1.0 to -2.8V; however, for (CH3)3SiCl, no reduction leading to silicon deposition was observed in this region. Several deposits of silicon were done potentiostatically on Mo, Al, and Ni discs. The thickness, surface finish and color of the amorphous deposits were dependent on the precursor concentration, temperature and material, and surface finish of the metal working electrode.

Rauh, R. D.; Hoover, T. G.; Natwig, D. L.



Role of surfactant-mediated electrodeposited titanium oxide substrate in improving electrocatalytic features of supported platinum particles  

NASA Astrophysics Data System (ADS)

A new hybrid system with improved photocatalytic and electrocatalytic performances was obtained by two-step potentiostatic deposition on highly boron-doped diamond (BDD) substrate. First, hydrated TiO2 was anodically deposited from a TiCl3 aqueous solution, both in the presence and in the absence of sodium dodecyl sulfate (SDS). The study of the UV irradiation effect evidenced that titanium oxide coatings obtained by surfactant-assisted electrodeposition (TiO2:SDS) exhibit enhanced photocurrent, due to its very rough texture and presumably to better efficiency of charge carrier separation. Electrochemical deposition of platinum on the oxide-coated BDD was carried out in a second step and AFM, SEM and XPS measurements have shown that, on the TiO2:SDS substrate, Pt particles are smaller, more uniformly distributed, and tend to form clusters, leading to a specific surface area of the electrocatalyst of ca. 6.55 m2 g-1. Carbon monoxide stripping experiments demonstrated that, when deposited on TiO2:SDS, Pt particles are also less sensitive to CO-poisoning during methanol anodic oxidation.

Sp?taru, Tan?a; Preda, Loredana; Osiceanu, Petre; Munteanu, Cornel; Anastasescu, Mihai; Marcu, Maria; Sp?taru, Nicolae



Change of electrochemical impedance spectra (EIS) with time during CO-poisoning of the Pt-anode in a membrane fuel cell  

NASA Astrophysics Data System (ADS)

This paper focuses on the electrochemical characterisation, e.g. current-voltage-measurement and time resolved electrochemical impedance spectroscopy (TREIS) of polymer electrolyte fuel cells (PEFCs) during operation of the fuel cell with oxygen and H 2+100 ppm CO respectively. Due to the poisoning effect of carbon monoxide, the system changes its state during the experiment. The reconstruction of quasi-causal impedance spectra was made by using enhanced numerical procedures. The reconstructed impedance spectra recorded at constant load, in galvanostatic mode of operation of the fuel cell show a strong time dependence and exhibit pseudo-inductive contributions at the low frequency part of the spectra which increase during the experiment. The analysis of the spectra suggests that the pseudo-inductive behaviour can be attributed to a surface relaxation process of the anode. Furthermore, the influence of the carbon monoxide on the electrochemical behaviour of the contaminated fuel cell may be interpreted by means of a Faraday impedance in addition with a potential-dependent hindrance of the charge transfer. Otherwise, the impedance spectra recorded during CO poisoning of the anode at constant cell voltage, in the potentiostatic mode of operation of the fuel cell, show also a strong time dependence, but no pseudo-inductive contribution in the low frequency part of the spectra.

Wagner, N.; Glzow, E.


Preliminary corrosion studies of candidate materials for supercritical water oxidation reactor systems. Master's thesis  

SciTech Connect

An experimental test facility has been designed and constructed for investigation of the corrosion behavior of candidate materials in a supercritical water oxidation environment. The high temperatures (500 deg C) and high pressures (300 atm) required in this process, made the experimental apparatus construction and control a complex engineering problem. The facility consists of two systems. The first is an exposure autoclave internal volume 850 ml, with associated monitoring and control systems for conducting long term exposure testing of test coupons and U-bends. The second is an electrochemical cell with a potentiostat and frequency response analyzer for conducting Electronic Impedance Spectroscopy (EIS) in the supercritical water environment. Exposure testing of three candidate materials; Inconel 625, Hastelloy C-276 and 316 stainless steel was conducted at three temperature regimes corresponding to three locations in a SCWO waste treatment system. Preliminary results are presented in an environment of demineralized water as a control. Experimental results indicate evidence of a film on the materials characterized by slight weight gain. Light and confocal laser light microscopic evaluations revealed the presence of localized pitting corrosion on the Inconel 625.

Orzalli, J.C.



Growth and characterization of electrodeposited Cu2O thin films  

NASA Astrophysics Data System (ADS)

This work demonstrates the electrodeposition of cuprous oxide (Cu2O) thin films onto a fluorine-doped tin oxide (FTO)-coated conducting glass substrates from Cu(II) sulfate solution with C6H8O7 chelating agent. During cyclic voltammetry experiences, the potential interval where the electrodeposition of Cu2O is carried out was established. The thin films were obtained potentiostatically and were characterized through different techniques. From the Mott-Schottky measurements, the flat-band potential and the acceptor density for the Cu2O thin films are determined. All the films showed a p-type semiconductor character with a carrier density varying between 2.41 1018 cm-3 and 5.38 1018 cm-3. This little difference is attributed to the increase of the stoichiometric defects in the films with the deposition potential. Atomic force microscopy analysis showed that the Cu2O thin films obtained at high potential are more homogenous in appearance and present lower crystallites size. X-ray diffraction measurements indicate a cubic structure with good crystallization state and the deposition potential was found to have an influence on the size of the crystallites. The optical measurements show a direct band gap between 2.07-2.49 eV depending on the applied potential.

Laidoudi, S.; Bioud, A. Y.; Azizi, A.; Schmerber, G.; Bartringer, J.; Barre, S.; Dinia, A.



Solid-state electrochemical kinetics of Li-ion intercalation into Li{sub 1{minus}x}CoO{sub 2}: Simultaneous application of electroanalytical techniques SSCV, PITT, and EIS  

SciTech Connect

The electroanalytical behavior of thin Li{sub 1{minus}x}CoO{sub 2} electrodes is elucidated by the simultaneous application of three electroanalytical techniques: slow-scan-rate cyclic voltammetry (SSCV), potentiostatic intermittent titration technique, and electrochemical impedance spectroscopy. The data were treated within the framework of a simple model expressed by a Frumkin-type sorption isotherm. The experimental SSCV curves were well described by an equation combining such an isotherm with the Butler-Volmer equation for slow interfacial Li-ion transfer. The apparent attraction constant was {minus}4.2, which is characteristic of a quasi-equilibrium, first-order phase transition. Impedance spectra reflected a process with the following steps: Li{sup +} ion migration in solution, Li{sup +} ion migration through surface films, strongly potential-dependent charge-transfer resistance, solid-state Li{sup +} diffusion, and accumulation of the intercalants into the host materials. An excellent fit was found between these spectra and an equivalent circuit, including a Voigt-type analog (Li{sup +} migration through multilayer surface films and charge transfer) in series with a finite-length Warburg-type element (Li{sup +} solid-state diffusion), and a capacitor (Li accumulation). In this paper, the authors compare the solid-state diffusion time constants and the differential intercalation capacities obtained by the three electroanalytical techniques.

Levi, M.D.; Salitra, G.; Markovsky, B.; Teller, H.; Aurbach, D. [Bar-Ilan Univ., Ramat-Gan (Israel). Dept. of Chemistry] [Bar-Ilan Univ., Ramat-Gan (Israel). Dept. of Chemistry; Heider, U.; Heider, L. [Merck KGaA, Darmstadt (Germany)] [Merck KGaA, Darmstadt (Germany)



Disposable electrochemical sensor to evaluate the phytoremediation of the aquatic plant Lemna minor L. toward Pb(2+) and/or Cd(2+).  


In this work a miniaturized and disposable electrochemical sensor was developed to evaluate the cadmium and lead ion phytoremediation potential by the floating aquatic macrophyte Lemna minor L. The sensor is based on a screen-printed electrode modified "in-situ" with bismuth film, which is more environmentally friendly than the mercury-based sensor usually adopted for lead and cadmium ion detection. The sensor was coupled with a portable potentiostat for the simultaneous measurement of cadmium and lead ions by stripping analysis. The optimized analytical system allows the simultaneous detection of both heavy metals at the ppb level (LOD equal to 0.3 and 2 ppb for lead and cadmium ions, respectively) with the advantage of using a miniaturized and cost-effective system. The sensor was then applied for the evaluation of Pb(2+) or/and Cd(2+) uptake by measuring the amount of the heavy metals both in growth medium and in plant tissues during 1 week experiments. In this way, the use of Lemna minor coupled with a portable electrochemical sensor allows the set up of a model system able both to remove the heavy metals and to measure "in-situ" the magnitude of heavy metal removal. PMID:24899412

Neagu, Daniela; Arduini, Fabiana; Quintana, Josefina Calvo; Di Cori, Patrizia; Forni, Cinzia; Moscone, Danila



High-accuracy oxygen polarograph for photosynthetic systems  

NASA Astrophysics Data System (ADS)

A new system is presented here, whose design is based on the electrochemical phenomena occurring on the platinum electrode that we examined before [P. Meunier and R. Popovic (unpublished)]. The architecture of the system is articulated around an IBM-PC computer which controls the polarization of the electrodes, the triggering of the flash lamp, and the acquisition of data. The potentiostat circuit and new electrode design improve the response of the electrode to a rise time of 4 ms and a decay time constant of 21 ms, without the signal being distorted by filters and without using the first derivative of the signal. This polarograph shows a 50-dB signal-to-noise ratio (0.3% error) during experiments with the motile algae Dunaliella tertiolecta. The determination of amplitudes of oxygen production is performed with third-order cubic spline interpolations, after subtraction of the current base line. The resulting accuracy and reproducibility will enable researchers to attain a higher degree of refinement in the quantification of properties of the oxygen evolving complex.

Meunier, P. C.; Popovic, R.



Photoelectrocatalytic oxidation of glucose at a ruthenium complex modified titanium dioxide electrode promoted by uric acid and ascorbic acid for photoelectrochemical fuel cells  

NASA Astrophysics Data System (ADS)

The simultaneous presence of uric acid (UA) and ascorbic acid (AA) is first found to largely promote the photoelectrocatalytic oxidation of glucose (GLU) at an indium-tin oxide (ITO) or TiO2 nanoparticles/ITO electrode modified with [Ru(tatp)3]2+ (tatp = 1,4,8,9-tetra-aza-triphenylene) possessing good redox activity and nanoparticle size distribution. A well-defined electrocatalytic peak for GLU oxidation is shown at 0.265 V (vs. SCE) under approximate physiological conditions upon incorporation of UA and AA. The [Ru(tatp)3]2+/ITO electrode exhibits attractive amperometric oxidation responses towards GLU, UA and AA, while controlled potentiostatically at 0.3 V, 0.7 V and 1.0 V, respectively, indicating high sensitivity and excellent reproducibility. On basis of the photoelectrocatalysis of [Ru(tatp)3]2+/TiO2/ITO anode, a GLU concentration-dependent photoelectrochemical fuel cell vs. SCE is elaborately assembled. The proposed free-enzyme photoelectrochemical fuel cell employing 0.1 M GLU associated with 0.01 M UA and 0.01 M AA as fuel shows open-circuit photovoltage of 0.608 V, short-circuit photocurrent density of 124.5 ?A cm-2 and maximum power density of 21.75 ?W cm-2 at 0.455 V, fill factor of 0.32 and photoenergy conversion efficiency of 36.65%, respectively.

Lu, Shuo-Jian; Ji, Shi-Bo; Liu, Jun-Chen; Li, Hong; Li, Wei-Shan



Evaluation on the Corrosion of the Three Ni-Cr Alloys with Different Composition  

PubMed Central

Dental casting alloys are widely used in contact with oral tissue for many years now. With the development of new dental alloys over the past 15 years, many questions remain unanswered about their biologic safety. Concepts and current issues concerning the response to the biologic effects of dental casting alloys are presented. In this paper, samples of three commercially available nickel-chrome (Ni-cr) casting alloys (Dentaurum, Bego, Sankin) were taken to assess their corrosion behavior, using potentiodynamic polarization method (electrochemical method) with fusayama artificial saliva as an electrolyte medium to check for their biocompatibility. The parameters for corrosion rate and corrosion resistance were obtained from computer-controlled corrosion schematic instrument, namely, potentiostat through corrosion software (power CV). The results obtained were analyzed by classic Tafel analysis. Statistical analysis was done by Student's t-test and ANOVA test. It was concluded that Dentarum and Bego showed satisfactory corrosive behavior, with exception of Sankin which depicted higher corrosion rate and least resistance to corrosion. Thus, the selection of an alloy should be made on the basis of corrosion resistance and biologic data from dental manufactures. PMID:21461232

Rao, Srinivasa B.; Chowdhary, Ramesh



Flow microcapillary plasma mass spectrometry-based investigation of new Al-Cr-Fe complex metallic alloy passivation.  


Al-Cr-Fe complex metallic alloys are new intermetallic phases with low surface energy, low friction, and high corrosion resistance down to very low pH values (0-2). Flow microcapillary plasma mass spectrometry under potentiostatic control was used to characterize the dynamic aspect of passivation of an Al-Cr-Fe gamma phase in acidic electrolytes, allowing a better insight on the parameters inducing chemical stability at the oxyhydroxide-solution interface. In sulfuric acid pH 0, low element dissolution rates (in the g cm(-2) range after 60 min) evidenced the passive state of the Al-Cr-Fe gamma phase with a preferential over-stoichiometric dissolution of Al and Fe cations. Longer air-aging was found to be beneficial for stabilizing the passive film. In chloride-containing electrolytes, ten times higher Al dissolution rates were detected at open-circuit potential (OCP), indicating that the spontaneously formed passive film becomes unstable. However, electrochemical polarization at low passive potentials induces electrical field generated oxide film modification, increasing chemical stability at the oxyhydroxide-solution interface. In the high potential passive region, localized attack is initiated with subsequent active metal dissolution. PMID:24468364

Ott, N; Beni, A; Ulrich, A; Ludwig, C; Schmutz, P



A micro flow injection electrochemical biosensor for organophosphorus pesticides.  


We describe a disposable, amperometric micro flow injection electrochemical biosensor that can be applied to the identification and quantification of highly toxic organophosphorus (OP) compounds in the environment, on the spot and in a short time. The system traces very small quantities of OP by monitoring the enzymatic reaction of acetylcholine esterase (AChE) and its inhibition. The sensor is sensitive, rapid, small, inexpensive, disposable and can be operated by non-professional technicians. The electrochemical cell consists of screen-printed electrodes covered with an enzymatic membrane and placed in a home-made flow cell. The electrodes are connected to a computer-controlled potentiostat. We quantitatively detected the OP compound, dimethyl 2,2-dichlorovinyl phosphate (DDVP), by monitoring the OP induced decrease in enzymatic degradation of the substrate, acetylthiocholine chloride (ATCh), to thiocholine and acetic acid. Thiocholine reacts with hexacyanoferrate ion in the working solution and the reduction of [Fe(CN)6](-3) to [Fe(CN)6](-4) and its subsequent reoxidization by the electrode generates very sharp, rapid and reproducible electric signals. The ability to detect low quantities is extremely important when dealing with hazardous environmental pollutants. PMID:11219744

Neufeld, T; Eshkenazi, I; Cohen, E; Rishpon, J



Seasonal and spatial variation in soil chemistry and anaerobic processes in an Arctic ecosystem  

NASA Astrophysics Data System (ADS)

Drained thaw lake basins (DTLB) are the dominant landform in the Arctic coastal plain near Barrow, Alaska. Our previous work in a DTLB showed that Fe(III) and humic substances are important electron acceptors in anaerobic respiration, and play a significant role in the C cycle of these organic-rich soils. In the current study, we investigated seasonal and spatial patterns of availability of electron acceptors and labile substrate, redox conditions and microbial activity. Landscapes within DTLB contain complex, fine-scale topography arising from ice wedge polygons, which produce raised and lowered areas. One goal of our study was to determine the effects of microtopographic variation on the potential for Fe(III) reduction and other anaerobic processes. Additionally, the soil in the study site has a complex vertical structure, with an organic peat layer overlying a mineral layer, overlying permafrost. We described variations in soil chemistry across depth profiles into the permafrost. Finally, we installed an integrated electrode/potentiostat system to electrochemically monitor microbial activity in the soil. Topographically low areas differed from high areas in most of the measured variables: low areas had lower oxidation-reduction potential, higher pH and electrical conductivity. Soil pore water from low areas had higher concentrations of Fe(III), Fe(II), dissolved organic C (DOC), and aromaticity (UV absorbance at 260nm, A260). Low areas also had higher concentrations of dissolve CO2 and CH4 in soil pore water. Laboratory incubations of soil showed a trend toward higher potentials for Fe(III) reduction in topographically low areas. Clearly, ice wedge-induced microtopography exerts a strong control on microbial processes in this DTLB landscape, with increased anaerobic activity occurring in the wetter, depressed areas. Soil water extracted from 5-15 cm depth had higher concentrations of Fe(III), Fe(II), A260, and DOC compared to soil water sampled from 0-5cm. The soil depth profile showed highest concentrations of acid-extractable Fe in the mineral layer and permafrost, though Fe(III) was highest in the surface layer. Total and soluble C increased with depth, as did the potential for CO2 and CH4 production in anaerobic incubations. Thus, the mineral layer may be a significant source of Fe for oxidation-reduction reactions that occur at shallower depths, though methanogenesis dominates in the mineral layer, while Fe(III) reduction dominates in the organic layer. Most of the ions measured in the soil pore water (Fe(III), DOC, A260) showed the same general seasonal pattern: high concentrations soon after soils thawed, declining over time until mid-August. Concentrations of Fe(II) in soil pore water were fairly stable over time. There was a significant positive relationship between A260 and Fe(III) concentrations, possibly indicating the presence of microbially-produced aromatic chelating molecules. Potentiostat measurements confirmed the presence of an electrochemically active microbial community in the soil.

Lipson, D.; Mauritz, M.; Bozzolo, F.; Raab, T. K.; Santos, M. J.; Friedman, E. F.; Rosenbaum, M.; Angenent, L.



Degradation mechanisms of carbon-based electrocatalyst support materials and development of an advanced support based on electrically conducting diamond  

NASA Astrophysics Data System (ADS)

In this dissertation, the degradation mechanisms of sp 2-bonded carbon electrocatalyst supports were studied under potential and temperature conditions relevant to the polymer electrolyte membrane fuel cell (PEMFC). In addition, an alternative support was fabricated in two forms: electrically conducting diamond powder and paper to overcome current material stability issues in the PEMFC. Two structurally well-characterized sp2-bonded carbon powders, graphite (structurally well-ordered) and glassy carbon (GC, structurally disordered) were studied under potentiostatic polarization from 1.0 to 1.6 V vs. Ag/AgCl at 25, 50, and 80C. Characterization of the surface oxidation and microstructural changes (i.e., increase in the exposed edge plane density) provided evidence for the so-called order/disorder mechanism where structurally disordered carbons corrode more severely because of oxidation and gasification of the exposed edge plane. Microstructural changes for graphite were heterogeneously distributed across the electrode surface. This is indicative of a nucleation and growth process, where disordered regions and defects serve as active sites for electrochemical corrosion, while other, more structurally ordered regions do not corrode. Preliminary results for a high-surface-area carbon black, Vulcan XC-72, are presented that show changes in the surface oxide content and also discuss the effect of polarization potential on Pt activity. The physical and electrochemical properties of two commercial boron-doped diamond thin-film electrodes were compared with microcrystalline and nanocrystalline boron-doped diamond thin film deposited in our laboratory. The electrochemical response for Fe(CN)63-/4-, Ru(NH3)6 3+/2+, IrCl62-/3-, 4-methylcatechol, and Fe3+/2+ was quite reproducible from electrode type-to-type and from film-to-film for a given type. DeltaEp, ipox, and ip red values for Fe(CN)63-/4-, Ru(NH 3)63+/2+ on all electrodes were relatively unaffected by pH. Electrically conducting diamond powder was prepared by coating insulating diamond powder (8-12 mum diam) with a thin boron-doped diamond layer using microwave-assisted chemical vapor deposition (CVD). Increases in the electrical conductivity after growth confirmed that a conductive diamond overlayer formed. The charge passed during anodic polarization at 1.6 V vs. Ag/AgCl and 25C for 1 h was largest for GC powder (0.88 C/cm2) and smallest for conductive diamond powder (0.18 C/cm2), illustrating the dimensional stability of diamond powder compared to sp2-bonded carbon powder. Boron-doped nanocrystalline diamond (BND) was coated on Toray RTM carbon paper (TCP) via microwave-assisted CVD. Pt nanoparticles were deposited on TCP and BND using a pulsed galvanostatic method. The stability of the bare TCP and BND substrates and the composite Pt/TCP and Pt/BND electrodes were studied using potentiostatic polarization in 0.1 M HClO4. The BND electrode exhibited superior morphological and microstructural stability over TCP at 1.6 V vs. Ag/AgCl. Evidence was found for dissolution and redeposition of Pt on composite electrodes, particularly for Pt/TCP.

Fischer, Anne Elizabeth



Electrochemical and Structural Study of the Layered, 'Li-Excess' Lithium-Ion Battery Electrode Material Li[Li[subscript 1/9]Ni[subscript 1/3]Mn[subscript 5/9  

SciTech Connect

The overcapacity mechanism and high voltage process of the Li-excess electrode material Li[Li{sub 1/9}Ni{sub 1/3}Mn{sub 5/9}]O{sub 2} are studied by solid-state NMR, X-ray diffraction, X-ray absorption spectroscopy, transmission electron microscopy, combined with galvanostatic and potentiostatic intermittent titration electrochemical measurements. The cycling performance is improved noticeably when the material is cycled between potential windows of 5.3-2.5 V compared to 4.6-2.5 V. Diffraction data show that structural changes occur at high voltages, the solid-state NMR data of the same samples indicating that the high voltage processes above 4.4 V are associated with Li removal from the structure, in addition to electrolyte decomposition. The NMR spectra of the discharged samples show that cation rearrangements in the transition metal layers have occurred. The XAS spectra confirm that the Mn oxidation state remains unchanged at 4+, whereas Ni{sup 2+} is oxidized to Ni{sup 4+} on charging to 4.4 V, returning to Ni{sup 2+} on discharge, independent of the final charge voltage. A significant change of the shape of the Ni edge is observed in the 4.6-5.3 V potential range on charge, which is ascribed to a change in the Ni local environment. No O{sub 2} evolution was detected based on ex situ analysis of the gases evolved in the batteries, the TEM data showing that thick passivating films form on the electrodes. The results suggest that at least some of the oxygen loss from these lithium-excess materials occurs via a mechanism involving electrolyte decomposition.

Jiang, Meng; Key, Baris; Meng, Ying S.; Grey, Clare P.; (SBU); (Florida)



Nanotubular oxide surface and layer formed on the Ti-35Ta-xZr alloys for biomaterials.  


Titanium and its alloys are widely used as a dental implant material in clinical dentistry and as an orthopedic implant materials due to their good mechanical properties, corrosion resistance, and biocompatibility. In this study, nanotubular oxide surface and layer formed on the Ti-35Ta-xZr alloys for biomaterials have been investigated by using electrochemical methods. Ti-35Ta-xZr alloys were prepared by arc melting and heat treated for 24 hr at 1000 degrees C in argon atmosphere, and then water quenching. Ti oxide nanotubes were formed on the Ti-35Ta-xZr alloys by anodizing in H3PO4 containing 0.8 wt% NaF solution at 25 degrees C. Anodization was carried out using a scanning potentiostat. Microstructures of the alloys and nanotube surface were examined by FE-SEM, EDX, and XRD. Crystallization treatment of nanotube surface was carried out for 3 hr at 450 degrees C. Microstructures of the Ti-35Ta-xZr alloys were changed from beta phase to alpha'' phase, and changed from an equiaxed to a needle-like structure with increasing Zr content. Nanotubular oxide surface and layers consisting of highly ordered nanotubes with a wide range of diameters (approximately 150-200 nm) and lengths (approximately 4-10 microm) can be formed on alloys in the Ti-35Ta-xZr alloys with Zr content. As the Zr content increased from 3% to 15%, length of step between the bamboo knob-like had increasing values of approximately 50 nm, 80 nm, and 140 nm, respectively. The nanotubes formed on the Ti-35Ta-xZr alloy surface were amorphous structure before heat treatment, but oxide surface had mainly an anatase structure by heat treatment. PMID:22103213

Kim, Eun-Ju; Kim, Won-Gi; Jeong, Yong-Hoon; Choe, Han-Cheol



Nature and extent of electrogenic microbial communities recovered from Juan de Fuca hydrothermal sulfides  

NASA Astrophysics Data System (ADS)

Microbes have evolved a variety of metabolic strategies to survive in anaerobic environments, including extracellular electron transfer (EET). Here we present laboratory and in situ experiments revealing that hydrothermal vent microbes employ and depend upon EET to access spatially remote oxidants via semi-conductive pyrite. To simulate the physical and electrochemical conditions in vent sulfides, we constructed a two-chamber flow-through bioelectrochemical reactor in which a pyrite electrode was enclosed in one chamber and subject to simulated hydrothermal conditions. Electroactive biofilms formed solely on pyrite in electrical continuity with oxygenated water. Phylogenetic and metagenomic analyses revealed a diversity of autotrophic and heterotrophic archaea and bacteria, markedly different in composition from the control (pyrite without electrical continuity). To further characterize this phenomenon, we deployed a bioelectrochemical experiment in situ at the hydrothermal vent sulfide "Roane" (2200 m water depth, at the Mothra hydrothermal field, Juan de Fuca ridge). A graphite anode was inserted into a borehole drilled into the base of a hydrothermal sulfide, and connected through a potentiostat to a carbon-fiber cathode on the outside of the vent structure. The in situ experiment produced sustained current and enriched for a distinct microbial community likely associated with EET. The data presented herein reveal the nature and extent of microbial communities that use conductive minerals such as pyrite, though fully reduced, to facilitate the reduction of spatially remote oxidants while maintaining chemical discontinuity. Thus EET, by enabling sustained access to terminal electron acceptors while maintaining the functioning of strictly anaerobic metabolisms, may alleviate the limitations commonly associated with anaerobic environs, namely the depletion of oxidants.

Girguis, P. R.; Nielsen, M. E.



Maximizing flow velocities in redox-magnetohydrodynamic microfluidics using the transient faradaic current.  


There is a need for a microfluidic pumping technique that is simple to fabricate, yet robust, compatible with a variety of solvents, and which has easily controlled fluid flow. Redox-magnetohydrodynamics (MHD) offers these advantages. However, the presence of high concentrations of redox species, important for inducing sufficient convection at low magnetic fields for hand-held devices, can limit the use of redox-MHD pumping for analytical applications. A new method for redox-MHD pumping is investigated that takes advantage of the large amplitude of the transient portion of the faradaic current response that occurs upon stepping the potential sufficiently past the standard electrode potential, E, of the pumping redox species at an electrode. This approach increases the velocity of the fluid for a given redox concentration. An electronic switch was implemented between the potentiostat and electrochemical cell to alternately turn on and off different electrodes along the length of the flow path to maximize this transient electronic current and, as a result, the flow speed. Velocities were determined by tracking microbeads in a solution containing electroactive potassium ferrocyanide and potassium ferricyanide, and supporting electrolyte, potassium chloride, in the presence of a magnetic field. Fluid velocities with slight pulsation were obtained with the switch that were 70% faster than the smooth velocities without the switch. This indicates that redox species concentrations can be lowered by a similar amount to achieve a given speed, thereby diminishing interference of the redox species with detection of the analyte in applications of redox-MHD microfluidics for chemical analysis. PMID:23057608

Weston, Melissa C; Nash, Christena K; Homesley, Jerry J; Fritsch, Ingrid



Interaction of progenitor bone cells with different surface modifications of titanium implant.  


Changes in the physical and chemical properties of Ti surfaces can be attributed to cell performance, which improves surface biocompatibility. The cell proliferation, mineralization ability, and gene expression of progenitor bone cells (D1 cell) were compared on five different Ti surfaces, namely, mechanical grinding (M), electrochemical modification through potentiostatic anodization (ECH), sandblasting and acid etching (SLA), sandblasting, hydrogen peroxide treatment, and heating (SAOH), and sandblasting, alkali heating, and etching (SMART). SAOH treatment produced the most hydrophilic surface, whereas SLA produced the most hydrophobic surface. Cell activity indicated that SLA and SMART produced significantly rougher surfaces and promoted D1 cell attachment within 1 day of culturing, whereas SAOH treatment produced moderate roughness (Ra=1.26?m) and accelerated the D1 cell proliferation up to 7 days after culturing. The ECH surface significantly promoted alkaline phosphatase (ALP) expression and osteocalcin (OCN) secretion in the D1 cells compared with the other surface groups. The ECH and SMART-treated Ti surfaces resulted in maximum ALP and OCN expressions during the D1 cell culture. SLA, SAOH, and SMART substrate surfaces were rougher and exhibited better cell metabolic responses during the early stage of cell attachment, proliferation, and morphologic expressions within 1 day of D1 cell culture. The D1 cells cultured on the ECH and SMART substrates exhibited higher differentiation, and higher ALP and OCN expressions after 10 days of culture. Thus, the ECH and SMART treatments promote better ability of cell mineralization in vitro, which demonstrate their great potential for clinical use. PMID:24582253

Chen, Wen-Cheng; Chen, Ya-Shun; Ko, Chia-Ling; Lin, Yi; Kuo, Tzu-Huang; Kuo, Hsien-Nan



Self-discharge of electrochemical double layer capacitors.  


Spontaneous voltage drop between EDLC electrodes, when it is kept under the open-circuit condition, is commonly called 'self-discharge' and is interpreted as a result of energy loss by the device. Three mechanisms of self-discharge were proposed: due to a leakage-current, faradaic reactions and charge redistribution. According to the law of energy preservation, if the voltage drop is associated with the energy loss, the energy would more likely be exchanged with the environment. While heat generation was measured during EDLC charging and discharging, the corresponding effect during storage under open-circuit conditions has not been reported. This may support the conclusion that voltage changes during 'self-discharge' are not related to a considerable energy loss. Moreover, it has been shown that a two-stage charging process, i.e. first galvanostatic charging followed by a potentiostatic charge redistribution, resulted in considerably slower potential changes when the device was switched to the open circuit. All discussed models were based on the assumption that the energy accumulated by EDLCs is proportional to the voltage in the second power, with capacitance (C/2) as the proportionality constant. However, it has been shown that during EDLC charging or discharging through a resistance R, equations valid for 'dielectric' and electrolytic capacitors, do not hold in the case of EDLCs. Consequently, the assumption that the energetic state of the EDLC is proportional at any time to the voltage in the second power may not be valid due to considerable variability of the 'constant' C. Therefore, voltage changes may not reflect the energetic state of the device. PMID:23640679

Lewandowski, Andrzej; Jakobczyk, Pawel; Galinski, Maciej; Biegun, Marcin



Characterization of anodized titanium for hydrometallurgical applicationsEvidence for the reduction of cupric on titanium dioxide  

NASA Astrophysics Data System (ADS)

Anodic oxide films (AOFs) were potentiostatically formed on commercially pure titanium in 0.5 M sulfuric acid solutions at various anodizing voltages (up to 80 V) at room temperature. The subject of this study was the corrosion resistance of the AOFs in synthetic copper sulfide leaching solutions containing 30 g L-1 sulfuric acid as well as 12 g L-1 Cl-, 15 g L-1 Cu2+ and 1 g L-1 Fe3+. Open circuit potential (OCP) measurement, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) were used to study the corrosion response of the AOFs in copper sulfide leaching solutions up to 85 C. Scanning electron microscopy (SEM) was used to investigate the morphology of the AOFs before and after 12 h of immersion at 85 C. X-ray photoelectron spectroscopy (XPS) was used to examine the surface chemistry of the AOFs after immersion. OCP measurements showed that the final failure of the AOFs occurred in 2 h in de-aerated 30 g L-1 H2SO4 and 12 g L-1 Cl- solutions at 85 C. Both LPR and EIS results showed a significant increase in the corrosion resistance of the anodized titanium versus that of freshly polished titanium. Electrochemical results were confirmed by SEM analysis, where the AOF formed at 80 V lead to the best improvement in corrosion resistance. XPS measurements revealed that Cu2+ was reduced to Cu or Cu+ within the titanium oxide film. It was further confirmed that the presence of leaching oxidants would inhibit the reduction of Cu2+ on titanium dioxide in chloride containing copper sulfide leaching solutions.

Liu, Jing; Alfantazi, Akram; Asselin, Edouard



Nanostructuring effect of multi-walled carbon nanotubes on electrochemical properties of carbon foam as constructive electrode for lead acid battery  

NASA Astrophysics Data System (ADS)

In the present study, nanostructuring effect of multi-walled carbon nanotubes (MWCNTs) on electrochemical properties of coal tar pitch (CTP) based carbon foam (CFoam) was investigated. The different weight fractions of MWCNTs were mixed with CTP and foam was developed from the mixture of CTP and MWCNTs by sacrificial template technique and heat treated at 1,400 and 2,500 C in inert atmosphere. These foams were characterized by scanning electron microscopy, X-ray diffraction, and potentiostat PARSTAT for cyclic voltammetry. It was observed that, bulk density of CFoam increases with increasing MWCNTs content and decreases after certain amount. The MWCNTs influence the morphology of CFoam and increase the width of ligaments as well as surface area. During the heat treatment, stresses exerting at MWCNTs/carbon interface accelerate ordering of the graphene layer which have positive effect on the electrochemical properties of CFoam. The current density increases from 475 to 675 mA/cm2 of 1,400 C heat treated and 95 to 210 mA/cm2 of 2,500 C heat-treated CFoam with 1 wt% MWCNTs. The specific capacitance was decreases with increasing the scan rate from 100 to 1,000 mV/s. In case of 1 % MWCNTs content CFoam the specific capacitance at the scan rate 100 mV/s was increased from 850 to 1,250 ?F/cm2 and 48 to 340 ?F/cm2 of CFoam heat treated at 1,400 C and 2,500 C respectively. Thus, the higher value surface area and current density of MWCNTs-incorporated CFoam heat treated to 1,400 C can be suitable for lead acid battery electrode with improved charging capability.

Kumar, Rajeev; Kumari, Saroj; Mathur, Rakesh B.; Dhakate, Sanjay R.



Determination of arsenic by galvanostatic stripping analysis and its application to steels.  


Arsenic can be determined by galvanostatic stripping analysis with a modified gold-film electrode, prepared by simultaneous electro-deposition of gold and arsenic on a glassy-carbon support. This initially deposited arsenic is stripped from the film before the electrode is used for the analysis, but its presence during the formation of the film apparently leads to uniformly distributed crystallization sites for the subsequent determination of arsenic, so that the precision of the determination is better than that obtained with an unmodified gold-film electrode. The pre-electrolysis is performed potentiostatically in a stirred solution of 7M hydrochloric acid, at a potential from -0.10 to -0.35 V (vs. Ag/AgCl). If the galvanostatic stripping step is performed in quiescent solution after a 6-sec rest-period, at a current of 2-12 muA, then for a 100-sec pre-electrolysis time the calibration curve is linear up to an arsenic concentration of about 2mug ml and the limit of determination is 8 ng ml . In the analysis of steel, the arsenic must first be separated by selective extraction of arsenic(III) bromide into toluene and back-extraction into the supporting electrolyte. A single extraction is virtually 100% quantitative. The relative error of the determination in steels is a few per cent and the results are in good agreement with the certified values for reference materials and with the results obtained by X-ray fluorescence analysis. PMID:18963479

Lexa, J; Stulk, K



Dye-sensitized solar cells based on free-standing titanium dioxide nanotube arrays  

NASA Astrophysics Data System (ADS)

Dye-sensitized solar cells (DSSCs) are photoelectrochemical cells using wide band gap nanoporous oxide semiconductors sensitized by dey molecules. DSSCs generally consist of photosensitive dye molecules and a titanium dioxide (TiO2) nanoparticle network. DSSCs convert light energy to electrical energy through photo-excitation of dye molecules anchored to the surface of TiO2 nanoparticles, electron injection and transport in the TiO 2 nanoparticle network. DSSCs attracted great attention due to their respectable efficiency with very low fabrication cost, good performance under diffuse light conditions, semi-transparency and multi color range possibilities, and the ability to be fabricated on flexible substrates. Its main efficiency limiting factor is the random hopping of electrons within the TiO2 nanoparticle network, which causes carrier trapping and recombination. The charge transport and collection can be enhanced by employing ordered nanostructures such as nanowire or nanotube arrays. However, DSSCs based on nanowire or nanotube arrays with power conversion efficiency higher than 11.18% achieved from the conventional DSSCs have yet to be demonstrated. This dissertation focuses on the development of DSSCs using highly crystalline free-standing TiO2 nanotube (FSTNT) arrays to enhance charge transport and collection, and hence, power conversion efficiency. TiO2 nanotube arrays were obtained by potentiostatic anodization of titanium foil in fluoride-based ethylene glycol electrolyte. TiO2 nanotube arrays were detached from the titanium foil by chemical etching and annealed at high temperatures to obtain highly crystalline anatase phase FSTNT arrays. DSSCs based on FSTNT arrays revealed high power conversion efficiency of 13.2% and short-circuit photocurrent density comparable to that of monocrystalline silicon solar cell.

Kim, Chaehyun


Nanostructuring effect of multi-walled carbon nanotubes on electrochemical properties of carbon foam as constructive electrode for lead acid battery  

NASA Astrophysics Data System (ADS)

In the present study, nanostructuring effect of multi-walled carbon nanotubes (MWCNTs) on electrochemical properties of coal tar pitch (CTP) based carbon foam (CFoam) was investigated. The different weight fractions of MWCNTs were mixed with CTP and foam was developed from the mixture of CTP and MWCNTs by sacrificial template technique and heat treated at 1,400 and 2,500 C in inert atmosphere. These foams were characterized by scanning electron microscopy, X-ray diffraction, and potentiostat PARSTAT for cyclic voltammetry. It was observed that, bulk density of CFoam increases with increasing MWCNTs content and decreases after certain amount. The MWCNTs influence the morphology of CFoam and increase the width of ligaments as well as surface area. During the heat treatment, stresses exerting at MWCNTs/carbon interface accelerate ordering of the graphene layer which have positive effect on the electrochemical properties of CFoam. The current density increases from 475 to 675 mA/cm2 of 1,400 C heat treated and 95 to 210 mA/cm2 of 2,500 C heat-treated CFoam with 1 wt% MWCNTs. The specific capacitance was decreases with increasing the scan rate from 100 to 1,000 mV/s. In case of 1 % MWCNTs content CFoam the specific capacitance at the scan rate 100 mV/s was increased from 850 to 1,250 ?F/cm2 and 48 to 340 ?F/cm2 of CFoam heat treated at 1,400 C and 2,500 C respectively. Thus, the higher value surface area and current density of MWCNTs-incorporated CFoam heat treated to 1,400 C can be suitable for lead acid battery electrode with improved charging capability.

Kumar, Rajeev; Kumari, Saroj; Mathur, Rakesh B.; Dhakate, Sanjay R.



Electrochemical photovoltaic cells. Project 65021 quarterly technical progress report, October 15, 1979-January 15, 1980  

SciTech Connect

During the third quarter of this program, liquid junction devices based upon the semiconductors MoSe/sub 2/, MoS/sub 2/, GaAs, and CdSe have been evaluated. Lifetime testing of MoSe/sub 2/ and MoS/sub 2/ materials in acidic halogen electrolytes at constant current densities of 5 mA/cm/sup 2/ have shown excellent stability to date. For MoSe/sub 2/ single crystals in the electrolyte 1M HBr + 1M Br/sub 2/, short-circuit currents of 63 mA/cm/sup 2/ were achieved with a power conversion efficiency of 6.7% for 200 mW/cm/sup 2/ xenon light illumination. Transient potentiostatic measurements made on MoSe/sub 2/ in this electrolyte indicated little diffusion control, with exchange currents being of the order of 1 to 10 mA/cm/sup 2/. Good photoresponse of MoS/sub 2/ has been observed in 1M HBr + 1M Br/sub 2/. The performance of the natural crystal is comparable to the performance of a single-crystal MoS/sub 2/ in this electrolyte. CdSe thermally evaporated onto porous titanium gave efficiencies of about 4% with 100 mW/cm/sup 2/ xenon illumination. Experimental work was initiated on the dye sensitization of Fe/sub 2/O/sub 3/ and TiO/sub 2/ materials. Of the twelve dyes evaluated, little enhancement of the photoresponse of these materials was noted. Solid-state photoelectrochemical cells have been fabricated, based upon LiI. Cells of the configuration - cond. glass CdSe/LiI + PbI/sub 2//LiI/LiI + C + PbI/sub 2//cond. glass - were fabricated. Photoresponses up to 150 mV were observed.

Ang, P.G.P.; Remick, R.J.; Sammells, A.F.



The effect of grain boundary chemistry on Intergranular stress corrosion cracking of Ni-Cr-Fe alloys in 50 Pct NaOH at 140 C  

NASA Astrophysics Data System (ADS)

The role of chromium, carbon, chromium carbides, and phosphorus on the intergranular stress corrosion cracking (IGSCC) resistance of Ni-Cr-Fe alloys in 50 pct NaOH at 140 C is studied using controlled-purity alloys. The effect of carbon is studied using heats in which the carbon level is varied between 0.002 and 0.063 wt pct while the Cr level is fixed at 16.8 wt pct. The effect of Cr is studied using alloys with Cr concentrations between 5 and 30 wt pct. The effect of grain boundary Cr and C together is studied by heat-treating the nominal alloy composition of Ni-16Cr-9Fe-0.035C, and the effect of P is studied using a high-purity, P-doped alloy and a carbon-containing, P-doped alloy. Constant extension rate tensile (CERT) results show that the crack depth increases with decreasing alloy Cr content and increasing alloy C content. Crack- ing severity also correlates inversely with thermal treatment time at 700 C, during which the grain boundary Cr content rises and the grain boundary C content falls. Phosphorus is found to have a slightly beneficial effect on IG cracking susceptibility. Potentiodynamic polarization and potentiostatic current decay experiments confirm that Cr depletion or grain boundary C enhances the dissolution at the grain boundary. Results support a film rupture-anodic dissolution model in which Cr depletion or grain boundary C (independently or additively) enhances dissolution of nickel from the grain boundary region and leads to increased IG cracking.

Sung, J. K.; Koch, J.; Angeliu, T.; Was, G. S.



Electrochemical formation of Dy alloy films in a molten LiCl-KCl-DyCl3 system  

NASA Astrophysics Data System (ADS)

As to the electrochemical formation of Dy-Ni alloy films in a molten LiCl-KCl-DyCl3 system at 700 K, the growth of DyNi2 film and behavior of anodic dissolution of Dy from the formed DyNi2 film were investigated. The DyNi2 films were formed by potentiostatic electrolysis at 0.55, 0.62 and 0.70 V with Ni electrodes. The growth rates of DyNi2 films are higher at less noble potential, i.e., 0.47 8m min-1 at 0.55 V, 0.32 8m min-1 at 0.62 V and 0.14 8m min-1 at 0.70 V. From RBS analysis, it was suggested that the Dy-Ni alloy film was formed for 10 or 30 s during electrodepositing Dy at 0.30 V with a Ni electrode. Moreover, the growth rate of Dy-Ni alloy film was faster than that of Dy-Fe alloy film. Anodic electrolysis of the formed DyNi2 film with thickness of 15 ?m was conducted at 0.90 V, 1.30 V and 1.90 V, respectively. The formed DyNi2 were transformed to other phases, i.e., DyNi3, DyNi5 and Ni, by selective anodic dissolution of Dy. The transformed Ni film was about 10 ?m in thickness and had a porous structure with a pore diameter of 1~2 ?m.

Konishi, H.; Usui, T.; Nohira, T.; Ito, Y.



Automated Controlled-Potential Coulometer for the IAEA  

SciTech Connect

An automated controlled-potential coulometer has been developed at the Savannah River Site (SRS) for the determination of plutonium for use at the International Atomic Energy Agency`s (IAEA) Safeguards Analytical Laboratory in Siebersdorf, Austria. The system is functionally the same as earlier systems built for use at the Savannah River Site`s Analytical Laboratory. All electronic circuits and printed circuits boards have been upgraded with state-of-the-art components. A higher amperage potentiostat with improved control stability has been developed. The system achieves electronic calibration accuracy and linearity of better than 0.01 percent, with a precision and accuracy better than 0.1 percent has been demonstrated. This coulometer features electrical calibration of the integration system, electrolysis current background corrections, and control-potential adjustment capabilities. These capabilities allow application of the system to plutonium measurements without chemical standards, achieving traceability to the international measurement system through electrical standards and Faraday`s constant. the chemist is provided with the capability to perform measurements without depending upon chemical standards, which is a significant advantage for applications such as characterization of primary and secondary standards. Additional benefits include reducing operating cost to procure, prepare and measure calibration standards and the corresponding decrease in radioactive waste generation. The design and documentation of the automated instrument are provided herein. Each individual module`s operation, wiring, layout, and alignment are described. Interconnection of the modules and system calibration are discussed. A complete set of prints and a list of associated parts are included.

Cordaro, J.V. [Westinghouse Savannah River Company, AIKEN, SC (United States); Holland, M.K.; Fields, T.



Formation mechanisms and characterization of black and white cobalt electrodeposition onto stainless steel  

SciTech Connect

Cobalt electrodeposition onto a stainless steel substrate from 1.17 M Co(II) aqueous solution containing 0.98 M H{sub 2}SO{sub 4}, 0.56 M KCl, and 0.2 M H{sub 3}BO{sub 3} was evaluated in the absence (1) and presence (2) of 0.1 M KNO{sub 3}. Cobalt electrodeposited from the electrolytic bath (1) was white-gray colored, whereas deposition from bath (2) formed a black-colored surface. SEM-WDX, AFM, and XRD analysis of the steel surfaces covered with these two deposits revealed distinct characteristics for black and white cobalt films. Although both deposits were composed of metallic cobalt, the white cobalt deposit was a smooth, 2D film while the black deposit consisted of many dispersed, nano-sized clusters of 150 to 250 nm in diameter. Analysis of potentiostatic current transients (I-t curves) indicated that formation of white cobalt was carried out by multiple 3D nucleation limited by lattice incorporation of cobalt adatoms to the growth centers. Formation of black cobalt was shown to involve the simultaneous processes of 3D nucleus formation and growth, limited by mass transfer, and the reduction of nitrates in the medium onto the surfaces of these nuclei. It is shown that, beside this cobalt-nitrate interaction, NO{sub 3}{sup {minus}} ions in solution can block active sites for cobalt reduction and the effect of this phenomenon strongly depends on the nitrate concentration. These facts could explain the observed dispersion of the black cobalt coating.

Barrera, E.; Pardave, M.P.; Batina, N.; Gonzalez, I.



Reversible detection of heparin and other polyanions by pulsed chronopotentiometric polymer membrane electrode.  


The first fully reversible polymeric membrane-based sensor for the anticoagulant heparin and other polyanions using a pulsed chronopotentiometry (pulstrode) measurement mode is reported. Polymeric membranes containing a lipophilic inert salt of the form R(+)R(-) (where R(+) and R(-) are tridodecylmethylammonium (TDMA(+)) and dinonylnaphthalene sulfonate (DNNS(-)), respectively) are used to suppress unwanted spontaneous ion extractions under zero-current equilibrium conditions. An anodic galvanostatic current pulse applied across the membrane perturbs the equilibrium lipophilic ion distribution within the membrane phase in such a way that anions/polyanions are extracted into the membrane from the sample. The membrane is then subjected to an open-circuit zero current state for a short period, and finally a 0 V vs reference electrode potentiostatic pulse is applied to restore the membrane to its initial full equilibrium condition. Potentials are sampled as average values during the last 10% of the 0.5 s open circuit phase of the measurement cycle. Fully reversible and reproducible electromotive force (emf) responses are observed for heparin, pentosan polysulfate (PPS), chondroitin sulfate (CS), and oversulfated chondroitin sulfate (OSCS), with the magnitude of the potentiometric response proportional to charge density of the polyanions. The sensor provides an emf response related to heparin concentrations in the range of 1-20 U/mL. The responses to variations in heparin levels and toward other polyanions of the pulstrode configuration are analogous to the already established single-use, nonreversible potentiometric polyion sensors based on membranes doped only with the lipophilic anion exchanger TDMA(+). PMID:20121058

Gemene, Kebede L; Meyerhoff, Mark E



Hydrophobic ionic liquids based on the 1-butyl-3-methylimidazolium cation for lithium/seawater batteries  

NASA Astrophysics Data System (ADS)

Two hydrophobic ionic liquids (room temperature molten salts) based on 1-butyl-3-methylimidazolium cation (BMI +), BMI +PF 6- and BMI +Tf 2N -, were used in developing a highly efficient lithium anode system for lithium/seawater batteries. The lithium anode system was composed of lithium metal/ionic liquid/Celgard membrane. Both BMI +PF 6-and BMI +Tf 2N - maintained high apparent anodic efficiency (up to 100%) under potentiostatic polarization (at +0.5 V versus open-circuit potential (OCP)) in a 3% NaCl solution. Eventually, traces of water contaminated the ionic liquid and a bilayer film (LiH and LiOH) on the lithium surface was formed, decreasing the rate of lithium anodic reaction and hence the discharge current density. BMI +Tf 2N - prevented traces of water from reaching the lithium metal surface longer than BMI +PF 6- (60 h versus 7 h). However, BMI +PF 6- was better than BMI +Tf 2N - in keeping a constant current density (0.2 mA cm -2) before the traces of water contaminated the lithium surface due to the non-reactivity of BMI +PF 6- with the lithium metal that kept the bare lithium surface. During the discharge process, BMI +PF 6- and BMI +Tf 2N - acted as ion transport media of Li +, Cl -, OH - and H 2O, but did not react with them because of the excellent chemical stability, high conductivity, and high hydrophobicity of these two ionic liquids. Both BMI +PF 6- and BMI +Tf 2N - gels were tentative approaches used to delay the traces of water coming in contact with the lithium surface.

Zhang, Yancheng; Urquidi-Macdonald, Mirna


Part I. Carbon and mercury-carbon optically transparent electrodes. Part II. Investigation of redox properties of technetium by cyclic voltammetry and thin layer spectroelectrochemistry  

SciTech Connect

A carbon optically transparent electrode (C OTE) has been prepared by vapor-deposithing a thin carbon film (150 to 310 A thick) on glass and quartz. Optical transparency is good throughout the ultraviolet-visible region. Electrochemical and spectroelectrochemical measurements were made with ferricyanide and o-tolidine respectively. The C OTE serves as a good substrate for deposition of a thin mercury film to form a mercury film transparent electrode (Hg-C OTE). The Hg-C OTE exhibits electrochemical properties of conventional mercury film electrodes as evidenced by Pb/sup 2 +/ cyclic voltammograms. The Hg-C OTE exhibits electrochemical properties of conventional mercury film electrodes as evidenced by Pb/sup 2 -/ cyclic VOHammograms. The Hg-C OTE enabled the spectrochemical characterization of cysteine oxidation, which was shown to involve the oxidation of mercury to form mercurous cysteinate. An 8080 based microcomputer has been interfaced with a Harrick oscillating mirror rapid scanning uv-visible spectrophotometer. Two different approaches are compared for controlling the galvanometer. The first utilizes the digital hardware on the Harrick processing module to derive the mirror drive waveform, while the second creates the waveform under direct software control. A potentiostat is also interfaced and the system is demonstrated by the spectroelectrochemical determination of the redox potential of o-tolidine. Redox potentials are also determined for a series of technetium complexes by the spectropotentiostatic technique. These include hexahalogens, ditertiary arsine, and 1,2-bis(diphenylphosphino) ethane complexes of technetium. Transient hexavalent technetium is produced, detected, and characterized in aqueous alkaline media by pulse radiolysis and very fast scan cyclic voltammetry. The lifetime is of the order of milliseconds. This species is potentially useful in the preparation of technetium radiopharmaceuticals.

Hurst, R.W.



Corrosion behaviour of high copper dental amalgams.  


This study evaluated the corrosion behaviour of two high copper dental amalgam alloys [Dispersalloy (Dentsply-Caulk) and Tytin (Kerr)] in different electrolytes. Amalgam specimens were prepared, coupled to a copper wire, cemented into glass tubes and polished to a 600-grit finish. A corrosion cell was prepared using a carbon counter-electrode, a standard calomel electrode as the reference and amalgam as the working electrode. The alloys were tested in the following mediums at 37 degrees C: (i) artificial saliva based on Fusayama's solution (FS), (ii) artificial saliva with citric acid adjusted to pH 4.0 (FC) and (iii) 1% sodium chloride solution (SC). Corrosion potentials (E(corr)) and corrosion rates (I(corr)) were determined using potentiostatic and impedance spectroscopy methods. Data was subjected to anova/Scheffe's post hoc test at 0.05 significance level. For both alloys, the corrosion potential in FS was significantly greater than in SC. Corrosion potential of Tytin in FS and SC was also significantly greater than in FC. The corrosion rate of Dispersalloy in FC was significantly greater than in FS and SC. For Tytin, corrosion rate in SC was significantly greater than in FS and FC. Although no significant difference in corrosion potential/rate was observed between the alloys when tested in FS, significant differences were observed when electrochemical testing was carried out in FC and SC. The corrosion behaviour of high copper amalgam alloys are both material and environment dependent. Certain food substances may increase the corrosion of high copper amalgams. PMID:15189319

Yap, A U J; Ng, B L; Blackwood, D J



Corrosion probes for fireside monitoring in coal-fired boilers  

SciTech Connect

Corrosion probes are being developed and combined with an existing measurement technology to provide a tool for assessing the extent of corrosion of metallic materials on the fireside in coal-fired boilers. The successful development of this technology will provide power plant operators the ability to (1) accurately monitor metal loss in critical regions of the boiler, such as waterwalls, superheaters, and reheaters; and (2) use corrosion rates as process variables. In the former, corrosion data could be used to schedule maintenance periods and in the later, processes can be altered to decrease corrosion rates. The research approach involves laboratory research in simulated environments that will lead to field tests of corrosion probes in coal-fired boilers. Laboratory research has already shown that electrochemically-measured corrosion rates for ash-covered metals are similar to actual mass loss corrosion rates. Electrochemical tests conducted using a potentiostat show the corrosion reaction of ash-covered probes at 500?C to be electrochemical in nature. Corrosion rates measured are similar to those from an automated corrosion monitoring system. Tests of corrosion probes made with mild steel, 304L stainless steel (SS), and 316L SS sensors showed that corrosion of the sensors in a very aggressive incinerator ash was controlled by the ash and not by the alloy content. Corrosion rates in nitrogen atmospheres tended to decrease slowly with time. The addition of oxygen-containing gases, oxygen and carbon dioxide to nitrogen caused a more rapid decrease in corrosion rate, while the addition of water vapor increased the corrosion rate.

Covino, Bernard S., Jr.; Bullard, Sophie J.; Ziomek-Moroz, M.; Holcomb, Gordon R.



Electrochemical growth and studies of CuInSe2 thin films  

NASA Astrophysics Data System (ADS)

Thin films of CuInSe2 were grown on fluorine doped tin oxide (<10 ?/?) coated glass using the electrodeposition technique. The electrodeposition was carried out potentiostatically using an aqueous bath consisting of solutions of CuCl2, InCl3 and SeO2 with ethylenediamine-dihydrochloride (EDC) added for complexation. CuInSe2 films were also deposited without using any complexing agent in the bath. To improve the crystallinity the CuInSe2 films were annealed in vaccum at 300 C for one hour. The annealed films were analyzed by x-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive analysis of x-rays (EDAX), atomic force microscopy (AFM) and optical spectra. The results obtained in this work show that by adding a suitable complexing agent to the electrochemical bath, nanocrystalline CuInSe2, 20 nm to 30 nm in size, can be grown. The composition of the CuInSe2 films can be controlled by means of the bath composition and stoichiometric films can be obtained for a bath with ionic Cu:In:Se composition close to 1:4:2. AFM micrographs show that the particles are generally oval shaped for near stoichiometric compositions. However for extreme copper rich layers, the morphology is completely different, the particles in this case appearing in the form of nanoflakes. Each flake has a thickness in the nano range, but the surface extends to a length of several microns.

Prasher, Dixit; Chandel, Tarun; Rajaram, Poolla



Model for anodic film growth on aluminum with coupled bulk transport and interfacial reactions.  


Films grown through the anodic oxidation of metal substrates are promising for applications ranging from solar cells to medical devices, but the underlying mechanisms of anodic growth are not fully understood. To provide a better understanding of these mechanisms, we present a new 1D model for the anodization of aluminum. In this model, a thin space charge region at the oxide/electrolyte interface couples the bulk ionic transport and the interfacial reactions. Charge builds up in this region, which alters the surface overpotential until the reaction and bulk fluxes are equal. The model reactions at the oxide/electrolyte interface are derived from the Vland-Heusler model, with modifications to allow for deviations from stoichiometry at the interface and the saturation of adsorption sites. The rate equations and equilibrium concentrations of adsorbed species at the oxide/electrolyte interface are obtained from the reactions using Butler-Volmer kinetics, whereas transport-limited reaction kinetics are utilized at the metal/oxide interface. The ionic transport through the bulk oxide is modeled using a newly proposed cooperative transport process, the counter-site defect mechanism. The model equations are evolved numerically. The model is parametrized and validated using experimental data in the literature for the rate of ejection of aluminum species into the electrolyte, embedded charge at the oxide/electrolyte interface, and the barrier thickness and growth rate of porous films. The parametrized model predicts that the embedded charge at the oxide/electrolyte interface decreases monotonically for increasing electrolyte pH at constant current density. The parametrized model also predicts that the embedded charge during potentiostatic anodization is at its steady-state value; the embedded charge at any given time is equal to the embedded charge during galvanostatic anodization at the same current. In addition to simulations of anodized barrier films, this model can be extended to multiple dimensions to simulate anodic nanostructure growth. PMID:24739021

DeWitt, Stephen; Thornton, Katsuyo



Liquid infused porous surfaces for mineral fouling mitigation.  


Prevention of mineral fouling, known as scale, is a long-standing problem in a wide variety of industrial applications, such as oil production, water treatment, and many others. The build-up of inorganic scale such as calcium carbonate on surfaces and facilities is undesirable as it can result in safety risks and associated flow assurance issues. To date the overwhelming amount of research has mainly focused on chemical inhibition of scale bulk precipitation and little attention has been paid to deposition onto surfaces. The development of novel more environmentally-friendly strategies to control mineral fouling will most probably necessitate a multifunctional approach including surface engineering. In this study, we demonstrate that liquid infused porous surfaces provide an appealing strategy for surface modification to reduce mineral scale deposition. Microporous polypyrrole (PPy) coatings were fabricated onto stainless steel substrates by electrodeposition in potentiostatic mode. Subsequent infusion of low surface energy lubricants (fluorinated oil Fluorinert FC-70 and ionic liquid 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIm)) into the porous coatings results in liquid-repellent slippery surfaces. To assess their ability to reduce surface scaling the coatings were subjected to a calcium carbonate scaling environment and the scale on the surface was quantified using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). PPy surfaces infused with BMIm (and Fluorinert to a lesser extent) exhibit remarkable antifouling properties with the calcium carbonate deposition reduced by 18 times in comparison to untreated stainless steel. These scaling tests suggest a correlation between the stability of the liquid infused surfaces in artificial brines and fouling reduction efficiency. The current work shows the great potential of such novel coatings for the management of mineral scale fouling. PMID:25585291

Charpentier, Thibaut V J; Neville, Anne; Baudin, Sophie; Smith, Margaret J; Euvrard, Myriam; Bell, Ashley; Wang, Chun; Barker, Richard



Corrosion in stainless-steel and nickel-titanium files.  


This study evaluated and compared the corrosion susceptibility of stainless-steel and nickel-titanium (NiTi) endodontic files immersed in sodium hypochlorite. For each of the stainless-steel files (Kerr K-Flex, Caulk Flex-O, and Union Broach Flex-R) plus the NiTi files (Union Broach NiTi and Tulsa NiTi), the cutting flutes of 24 ISO size 20 files were immersed into 5.25% sodium hypochlorite. Their open circuit potential (OCP) was recorded for 1 h on a strip chart with high impedance. The strip chart recording for each file was classified into a stability score: (i) stable, (ii) unstable, or (iii) erratic. The OCP was measured by a potentiostat and a standard calomel electrode reference. The OCP classification of unstable and erratic for the files evaluated were as follows: K-Flex (16%), Flex-R (12%), Flex-O (75%), Union Broach NiTi (62%), and Tulsa NiTi (0%). After OCP testing, each of the 120 files was inspected by light microscopy at x 25. The frequencies of visually observed corrosion were detected as follows: K-Flex (2/24), Flex-R (1/24), Flex-O (6/24), Union Broach NiTi (2/24), and Tulsa NiTi (0/24). There was a significant difference in corrosion frequency between brands when evaluated by OCP and light microscopy; however, there was no significant difference between stainless steel and NiTi. PMID:10196837

Stokes, O W; Fiore, P M; Barss, J T; Koerber, A; Gilbert, J L; Lautenschlager, E P



The effect of dopant concentration on properties of transparent conducting Al-doped ZnO thin films for efficient Cu2ZnSnS4 thin-film solar cells prepared by electrodeposition method  

NASA Astrophysics Data System (ADS)

Al-doped ZnO (AZO) thin films were potentiostatically deposited on indium tin oxide substrates. The influence of the doping level of the ZnO:Al films was investigated. The results of the X-ray diffraction and scanning electron microscopy analysis revealed that the structural properties of the AZO films were found polycrystalline with a hexagonal wurtzite-type structure along the (002) plane. The grain size of the AZO films was observed as approximately 3 ?m in the film doping with 4 mol% ZnO:Al concentration. The thin films also exhibited an optical transmittance as high as 90 % in the wavelength range of 100-1,000 nm. The optical band gap increased from 3.33 to 3.45 eV. Based on the Hall studies, the lowest resistivity (4.78 10-3 ? cm) was observed in the film doping with 3 mol% ZnO:Al concentration. The sheet resistant, carrier concentration and Hall mobility values were found as 10.78 ?/ square, 9.03 1018 cm-3 and 22.01 cm2/v s, respectively, which showed improvements in the properties of AZO thin films. The ZnO:Al thin films were used as a buffer layer in thin-film solar cells with the structure of soda-lime glass/Mo/Cu2ZnSnS4/ZnS/ZnO/Al grid. The best solar cell efficiency was 2.3 % with V OC of 0.430 V, J SC of 8.24 mA cm-2 and FF of 68.1 %.

Mkawi, E. M.; Ibrahim, K.; Ali, M. K. M.; Farrukh, M. A.; Mohamed, A. S.



Effect of bicarbonate ion additives on pitting corrosion of type 316L stainless steel in aqueous 0.5 M sodium chloride solution  

SciTech Connect

The effect of bicarbonate ions (HCO{sub 3}{sup {minus}}) on pitting corrosion of type 316L stainless steel (SS, UNS S3 1603) was investigated in aqueous 0.5 M sodium chloride (NaCl) solution using potentiodynamic polarization, the abrading electrode technique, alternating current (AC) impedance spectroscopy combined with x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Addition of HCO{sub 3}{sup {minus}} ions to NaCl solutions extended the passive potential region in width and, at the same time, raised the pitting potential in value on the potentiodynamic polarization curve. Potentiostatic current transients obtained from the moment just after interrupting the abrading action showed the repassivation rate of propagating pits increased and that the pit growth rate decreased with increasing HCO{sub 3}{sup {minus}} ion concentration. Over the whole applied potential, the oxide film resistance was higher in the presence of HCO{sub 3}{sup {minus}} ions. The pit number density decreased with increasing HCO{sub 3}{sup {minus}} ion concentration. Moreover, addition of HCO{sub 3}{sup {minus}} ions to NaCl solutions retarded lateral pit growth, while promoting downward pit growth from the surface. The bare surface of the specimen repassivated preferentially along the pit mouth and walls, compared to the pit bottom, as a result of formation of a surface film with a high content of protective mixed ferrous-chromous carbonate ([Fe,Cr]CO{sub 3}) that formed from preferential adsorption of HCO{sub 3}{sup {minus}} ions.

Park, J.J.; Pyun, S.I.; Lee, W.J. [Korea Advanced Inst. of Science and Technology, Taejon (Korea, Republic of). Dept. of Materials Science and Engineering; Kim, H.P. [Korea Atomic Energy Research Inst., Taejon (Korea, Republic of)



Electrochemical incineration of wastes  

NASA Technical Reports Server (NTRS)

The novel technology of waste removal in space vehicles by electrochemical methods is presented to convert wastes into chemicals that can be eventually recycled. The important consideration for waste oxidation is to select a right kind of electrode (anode) material that should be stable under anodic conditions and also a poor electrocatalyst for oxygen and chlorine evolution. On the basis of long term electrolysis experiments on seven different electrodes and on the basis of total organic carbon reduced, two best electrodes were identified. The effect of redox ions on the electrolyte was studied. Though most of the experiments were done in mixtures of urine and waste, the experiments with redox couples involved 2.5 M sulfuric acid in order to avoid the precipitation of redox ions by urea. Two methods for long term electrolysis of waste were investigated: (1) the oxidation on Pt and lead dioxide electrodes using the galvanostatic methods; and (2) potentiostatic method on other electrodes. The advantage of the first method is the faster rate of oxidation. The chlorine evolution in the second method is ten times less then in the first. The accomplished research has shown that urine/feces mixtures can be oxidized to carbon dioxide and water, but current densities are low and must be improved. The perovskite and Ti4O7 coated with RuO2 are the best electrode materials found. Recent experiment with the redox agent improves the current density, however, sulphuric acid is required to keep the redox agent in solution to enhance oxidation effectively. It is desirable to reduce the use of acid and/or find substitutes.

Bhardwaj, R. C.; Sharma, D. K.; Bockris, J. OM.



Electrochemically assisted self-assembly of ordered and functionalized mesoporous silica films: impact of the electrode geometry and size on film formation and properties.  


Surfactant-templated mesoporous silica thin films can be deposited onto solid electrode surfaces by electrochemically assisted self-assembly (EASA). The method involves a cathodically triggered self-assembly of cationic surfactants (cetyltrimethyl ammonium bromide, CTAB) and local pH increase leading to the polycondensation of silica precursors (i.e., tetraethoxysilane, alone or in the presence of (3-mercaptopropyl) trimethoxysilane (MPTMS)) and concomitant growth of the ordered mesoporous silica or organosilica film. The present work shows that the EASA method can be applied to film deposition on electrode supports of various morphologies, geometries and sizes (large and flat discs or non-flat streaked supports, i.e., gold CD-trodes, as well as several kinds of ultramicroelectrodes, including carbon fibers, platinum wires, and platinum microdiscs). Galvanostatic conditions were mainly preferred to potentiostatic conditions to avoid problems related to various overpotentials and surface areas experienced with the various working electrodes used here. The results indicate that film deposition was possible on each electrode support but also that both the film formation and properties were dependent on the experimental conditions for EASA. For example, passing from large electrodes to ultramicroelectrodes required the application of larger current densities to ensure film deposition, which can be due to faster loss of the hydroxyl species in solution in the case of radial or spherical diffusion, in comparison to the linear. Highly porous deposits were obtained after template removal, as ascertained by cyclic voltammetry using Ru(NH3)6(3+) as a redox probe. The advantage of better signal-to-background current ratios for ultramicroelectrodes relative to the macroscopic ones was maintained after film deposition, also resulting in higher sensitivity when used in conditions of preconcentration electroanalysis (using silver(I) or mercury(II) as a probe being accumulated by complexation to MPTMS-based films). PMID:24466668

Herzog, Grgoire; Sibottier, Emilie; Etienne, Mathieu; Walcarius, Alain



A comparison of hydrogen ingress behavior in alloys 625 and 716  

SciTech Connect

Microstructural heterogeneities in alloys provide trapping sites for diffusing hydrogen and so strongly affect the susceptibility of the alloys to hydrogen embrittlement (HE). These traps are able to be classified as reversible or irreversible, according to their energy for trapping hydrogen. Irreversible traps can be highly detrimental to the performance of an alloy in a hydrogen environment. So identification of the dominant types of irreversible traps is crucial to characterizing the susceptibility to HE. Hydrogen trapping has been studied previously for a wide range of alloys using a technique referred to as hydrogen ingress analysis by potentiostatic pulsing (HIAPP). The alloy is charged with hydrogen at a constant potential (E[sub c]) for a time (t[sub c]), after which the potential is stepped anodically, resulting in a current transient with a charge q[sub a]. For all the alloys studied to date, the transients could be analyzed in terms of a diffusion/trapping model involving a constant entry flux; that is, the rate of ingress was found to be controlled by diffusion under the influence of kinetically-limited entry. HIAPP has previously been applied to nickel-base alloys of age-hardened types (718 and 925) and work-hardened types (625 and C-276). In the present study, HIAPP was used to investigate hydrogen ingress in Custom Age 625 PLUS (UNS N07716), which was developed as an age-hardenable alternative to alloy 625. The hydrogen entry and trapping characteristics were obtained for alloy 716 and compared with those for alloy 615, with the objective of relating these characteristics to their HE susceptibilities.

Pound, B.G. (SRI International, Menlo Park, CA (United States). Materials Research Center)



Environment-assisted cracking of a nickel-based superalloy in hydrogen-producing solutions  

NASA Astrophysics Data System (ADS)

The environment assisted cracking (EAC) of nickel-based superalloy 718 was characterized in acidic chloride solutions under hydrogen-producing conditions using a rising-load fracture mechanics method. The stress intensity at the onset of crack growth (KTH) was used to measure EAC susceptibility as a function of applied electrode potential and solution chemistry. For all test conditions KTH was reduced from the air fracture initiation toughness (KICi). EAC susceptibility depended on both the electrode potential and solution pH. When the electrode potential was constant, susceptibility increased as the solution pH decreased. When the solution pH was constant, there was a minimum in KTH at intermediate electrode potentials. The appearance of the fracture surface gradually changed from voids and transgranular facets to voids with transgranular and intergranular facets as KTH decreased. The amount of plasticity associated with the voids and transgranular facets decreased as KTH decreased. Transgranular cracking dominated the onset of crack growth and occurred primarily by slip band fracture. A ductile fracture model, based on a critical fracture strain as measured by void growth, accurately predicted KTH and microstructure effects, suggesting that absorbed hydrogen lowered KTH from K ICi by promoting secondary microvoid nucleation which lead to intravoid strain localization and transgranular cracking. An empirical model of hydrogen production and absorption, based on a local crack chemistry that was less acidic than the bulk, was developed and used to predict the pH dependence of KTH at -1.0 VSCE . Gaseous hydrogen embrittlement data from the literature, hydrogen charging results, potentiostatic and potentiodynamic polarization data, and data from a buffered solution were combined to predict KTH of Alloy 718 as a function of solution pH at -1.0 VSCE in acidic chloride environments. The model accurately predicted KTH over the pH range studied.

Lillard, Jennifer Anne


Characterization of hydrogen ingress in high-strength alloys. Final report, 15 September 1993-14 September 1995  

SciTech Connect

The ingress of hydrogen (H) in various high-strength alloys was investigated with a view to characterizing their susceptibility to hydrogen embrittlement (HE). A potentiostatic pulse technique was applied to three Fe-base alloys (AerMet 100, H11, and A-286), two Cu-containing alloys (Be-Cu and alloy K-500), a superferritic stainless steel (Sea-Cure), and three Beta-Ti alloys (Ti-15V-3Cr-3Al-3Sn, Beta-21S, and Beta-C) in 1 mol/L acetic acid-1 mol/L sodium acetate. The data were analyzed using a diffusion/trapping model to obtain the irreversible trapping constant (k) and H entry flux for each alloy. The order of the k values for AerMet 100, H11, and two high-strength steels previously studied (4340 and 18Ni) inversely parallels their threshold stress intensities for stress corrosion cracking. Likewise, the k values for the other alloys can be correlated with their observed resistances to HE according to the following groups: (1) alloy A-286,18Ni steel, H11, Be-Cu, and also alloy 718 from earlier work; (2) annealed/aged and direct aged alloy K-500; and (3) Ti alloys. The trapping characteristics of Sea-Cure could not be determined. However, the propensity of the S44660 alloy to undergo HE at cathodic protection potentials can be attributed to changes in the oxide that lead to a less restricted entry of H.

Pound, B.G.



Evaluation of a diffusion/trapping model for hydrogen ingress in high-strength alloys. Annual report, 15 September 1993-14 September 1994  

SciTech Connect

The ingress of hydrogen in various high-strength alloys was investigated with a view to characterizing their susceptibility to hydrogen embrittlement (HE). A potentiostatic pulse technique was applied to two precipitation-hardened iron-base alloys (AerMet 100 and alloy A-286), two Cu-containing alloys (Be-Cu and alloy K-500), and a superferritic stainless steel (UNS 544660) in 1 mol/L acetic acid-1 mol/L sodium acetate. The data were analyzed using a diffusion/trapping model to obtain the irreversible trapping constant (k) and hydrogen entry flux for each alloy. Irreversible trapping was negligible in overaged AerMet 100 but pronounced in the aged alloy. The order of the k values for AerMet 100 and two steels (4340 and 1 18Ni) previously studied inversely parallels their threshold stress intensities for stress corrosion cracking. Likewise, the k values of alloy A-286, 18Ni steel, and also alloy 718 from earlier work are consistent with test data for their relative resistance to HE. The results for AerMet 100 and alloy A-286 extend the previously reported correlation between k and HE resistance. Unaged Be-Cu is intrinsically more susceptible to HE than unaged alloy K- 500. The type of heat treatment has a marked effect on the rapping behavior of alloy K-500. The intrinsic susceptibility of the annealed and aged alloy is twice that or the direct-aged alloy. The propensity of the S44660 alloy to undergo HE at cathodic protection potentials can be attributed to the absence of an oxide and hence the relatively unrestricted entry of H.

Pound, B.G.



Synthesis and structural characterization of polyoxometalates incorporating with anilinium cations and facile preparation of hybrid film  

NASA Astrophysics Data System (ADS)

The self-assembly reaction of tungstate and copper(II) in the presence of aniline (ANI) and phosphoric acid led to the formation of an anilinium (ANIH +) salt of mono-substituted Keggin-type polyoxotungstophosphate (ANIH) 5[PCu(H 2O)W 11O 39](ANI)8H 2O ( 1), while the reaction of heptamolybdate in the coexistence of copper(II), phosphoric acid and ANI yielded an ANIH + salt of Strandberg-type pentamolybdodiphosphate, (ANIH) 2[(PO 4) 2Mo 5O 15{Cu(ANI) 2(H 2O)} 2](ANI)2H 2O ( 2). These compounds were characterized by elemental analysis, infrared spectroscopy and X-ray single-crystal analysis. The compound 1, crystallizing in trigonal, P3,a = 13.883(4), c = 10.187(3) , Z = 1, consists of copper mono-substituted Keggin-typed [PCu(H 2O)W 11O 39] 5- anion surrounded by six ANI molecules, of which five are protonated (ANIH +). The compound 2, crystallizing in triclinic, P1,a = 13.98(2), b = 14.73(1), c = 16.24(1) , ? = 111.27(3), ? = 97.42(3), ? = 99.54(4), Z = 2, consists of Strandberg-type pentamolybdodiphospate [(PO 4) 2Mo 5O 15] 6- anions interconnected by two Cu(ANI) 2(H 2O) linkers to form a 1D-chain structure. A potentiostatic electrolysis of 1 in aqueous solution gave rise to electropolymerization of the ANIH + cations (and ANI) and deposition with the [PCu(H 2O)W 11O 39] 5- anion on an ITO electrode, forming a nano-structured polyaniline/[PCu(H 2O)W 11O 39] 5- hybrid thin film.

Fukaya, Keisuke; Srifa, Atthapon; Isikawa, Eri; Naruke, Haruo



Carbon Nanotube Microwell Array for Sensitive Electrochemiluminescent Detection of Cancer Biomarker Proteins  

PubMed Central

This paper describes fabrication of a novel electrochemiluminescent (ECL) immunosensor array featuring capture-antibody-decorated single-wall carbon nanotube forests (SWCNT) residing in the bottoms of 10 L wells with hydrophobic polymer walls. Silica nanoparticles containing [Ru(bpy)3]2+ and secondary antibodies (RuBPY-silica-Ab2) are employed in this system for highly sensitive two-analyte detection. Antibodies to PSA and IL-6 were attached to the same RuBPY-silica-Ab2 particle. The array was fabricated by forming the wells on a conductive pyrolytic graphite chip (1 1 in.) with a single connection to a potentiostat to achieve ECL. The sandwich immunoassay protocol employs antibodies attached to SWCNTs in the wells to capture analyte proteins. Then RuBPY-silica-Ab2 is added to bind to the captured proteins. ECL is initiated in the microwells by electrochemical oxidation of tripropyl amine (TprA), which catalytically reduces [Ru(bpy)3]2+ in the 100 nm particles, and is measured with a coupled charged device (CCD) camera. Separation of the analytical spots by the hydrophobic wall barriers enabled simultaneous immunoassays for two proteins in a single sample without cross-contamination. Detection limit (DL) for prostate specific antigen (PSA) was 1 pg mL?1 and for interleukin-6 (IL-6) was 0.25 pg mL?1 (IL-6) in serum. Array determinations of PSA and IL-6 in patient serum were well-correlated with single-protein ELISAs. These microwell SWCNT immunoarrays provide a simple, sensitive approach to detection of two or more proteins. PMID:21728322

Sardesai, Naimish P.; Barron, John C.; Rusling, James F.



Measurements and mechanisms of localized aqueous corrosion in aluminum-lithium-copper alloys  

NASA Technical Reports Server (NTRS)

Summary information is included for electrochemical aspects of stress corrosion cracking in alloy 2090 and an introduction to the work to be initiated on the new X2095 (Weldalite) alloy system. Stress corrosion cracking (SCC) was studied in both S-T and L-T orientations in alloy 2090. A constant load TTF test was performed in several environments with a potentiostatically applied potential. In the same environments the electrochemical behavior of phases found along subgrain boundaries was assessed. It was found that rapid failure due to SCC occurred when the following criteria was met: E(sub BR,T1) is less than E(sub applied) is less than E(sub Br, matrix phase). Although the L-T orientation is usually considered more resistant to SCC, failures in this orientation occurred when the stated criteria was met. This may be due to the relatively isotropic geometry of the subgrains which measure approximately 12 to 25 microns in diameters. Initial studies of alloy X2095 includes electrochemical characterization of three compositional variations each at three temperatures. The role of T(sub 1) dissolution in SCC behavior is addressed using techniques similar to those used in the research of 2090 described. SCC susceptibility is also studied using alternate immersion facilities at Reynolds Metals Corporation. Pitting is investigated in terms of stability, role of precipitate phases and constituent particles, and as initiation sites for SCC. In all research endeavors, attempts are made to link electrochemistry to microstructure. Previous work on 2090 provides a convenient basis for comparison since both alloys contain T(sub 1) precipitates but with different distributions. In 2090 T(sub 1) forms preferentially on subgrain boundaries whereas in X2095 the microstructure appears to be more homogeneous with finer T(sub 1) particles. Another point for comparison is the delta prime strengthening phase found in 2090 but absent in X2095.

Wall, Douglas; Stoner, Glenn E.



A miniaturized transcutaneous system for continuous glucose monitoring.  


Implantable sensors for continuous glucose monitoring hold great potential for optimal diabetes management. This is often undermined by a variety of issues associated with: (1) negative tissue response; (2) poor sensor performance; and (3) lack of device miniaturization needed to reduce implantation trauma. Herein, we report our initial results towards constructing an implantable device that simultaneously address all three aforementioned issues. In terms of device miniaturization, a highly miniaturized CMOS (complementary metal-oxide-semiconductor) potentiostat and signal processing unit was employed (with a combined area of 0.665mm(2)). The signal processing unit converts the current generated by a transcutaneous, Clark-type amperometric sensor to output frequency in a linear fashion. The Clark-type amperometric sensor employs stratification of five functional layers to attain a well-balanced mass transfer which in turn yields a linear sensor response from 0 to 25mM of glucose concentration, well beyond the physiologically observed (2 to 22mM) range. In addition, it is coated with a thick polyvinyl alcohol (PVA) hydrogel with embedded poly(lactic-co-glycolic acid) (PLGA) microspheres intended to provide continuous, localized delivery of dexamethasone to suppress inflammation and fibrosis. In vivo evaluation in rat model has shown that the transcutaneous sensor system reproducibly tracks repeated glycemic events. Clarke's error grid analysis on the as-obtained glycemic data has indicated that all of the measured glucose readings fell in the desired Zones A & B and none fell in the erroneous Zones C, D and E. Such reproducible operation of the transcutaneous sensor system, together with low power (140?W) consumption and capability for current-to-frequency conversion renders this a versatile platform for continuous glucose monitoring and other biomedical sensing devices. PMID:22992979

Croce, Robert A; Vaddiraju, SanthiSagar; Kondo, Jun; Wang, Yan; Zuo, Liang; Zhu, Kai; Islam, Syed K; Burgess, Diane J; Papadimitrakopoulos, Fotios; Jain, Faquir C



A mechanistic study of copper electropolishing in phosphoric acid solutions  

NASA Astrophysics Data System (ADS)

The microelectronics industry is using copper as the interconnect material for microchips. A study of copper electropolishing is important for the process development of a new, low downforce approach, which is being developed to replace chemical mechanical polishing (CMP) of the copper overburden. A promising technology is a combination of electropolishing with conventional CMP. Electropolishing of copper in phosphoric acid has been studied for, more than 70 years. Previous work has shown that the polishing rate, as measured by current density is directly related to the viscosity of the electrolyte. Also, the limiting species is water. In this study, a multidimensional design of experiments was performed to develop an in-depth model of copper electropolishing. Phosphoric acid was mixed with alcohols of different molecular weight and related viscosity to investigate how the solvents' properties affected polishing. The alcohols used were methanol, ethanol, isopropanol, butanol, ethylene glycol, and glycerol. The limiting current densities and electrochemical behavior of each solution was measured by potentiodynamic and potentiostatic experiments. Also, the kinematic viscosity and density were measured to determine the dynamic viscosity to investigate the relationship of current density and viscosity. Water, methanol, ethanol, and isopropanol solutions were also examined at 20C to 60C. Next, the relative percentage of dissociated phosphoric acid was measured by Raman spectroscopy for each polishing solution. Raman spectroscopy was also used to measure the relative dissociation of phosphoric acid inside the polishing film. Additionally, wafers were electropolished and electrochemical mechanically polished to investigate the effects of the different solvents, fluid flow, current, and potential. The results of these experiments have shown that the molecular mass and the ability of the solvent to dissociate phosphoric acid are the primary electrolyte properties that control copper electropolishing. The dependence of the polishing rate on viscosity seen in previous studies is purely consequential. Therefore, by controlling the type and concentration of alcohol in the electropolishing solution the polishing rate can be controlled.

Mansson, Andrew


Characterization of native and anodic oxide films formed on commercial pure titanium using electrochemical properties and morphology techniques  

NASA Astrophysics Data System (ADS)

Potentiostatically anodized oxide films on the surface of commercial pure titanium (cp-Ti) formed in sulfuric (0.5 M H 2SO 4) and in phosphoric (1.4 M H 3PO 4) acid solutions under variables anodizing voltages were investigated and compared with the native oxide film. Potentiodynamic polarization and electrochemical impedance spectroscopy, EIS, were used to predicate the different in corrosion behavior of the oxide film samples. Scanning electron microscope, SEM, and electron diffraction X-ray analysis, EDX, were used to investigate the difference in the morphology between different types of oxide films. The electrochemical characteristics were examined in phosphate saline buffer solution, PSB (pH 7.4) at 25 C. Results have been shown that the nature of the native oxide film is thin and amorphous, while the process of anodization of Ti in both acid solutions plays an important role in changing the properties of passive oxide films. Significant increase in the corrosion resistance of the anodized surface film was recorded after 3 h of electrode immersion in PSB. On the other side, the coverage ( ?) of film formed on cp-Ti was differed by changing the anodized acid solution. Impedance results showed that both the native film and anodized film formed on cp-Ti consist of two layers. The resistance of the anodized film has reached to the highest value by anodization of cp-Ti in H 3PO 4 and the inner layer in the anodized film formed in both acid solutions is also porous.

Fadl-allah, Sahar A.; Mohsen, Q.



Properties of an Au/Pt bilayered counter electrode in dye sensitized solar cells  

NASA Astrophysics Data System (ADS)

A 0.45 cm2 dye-sensitized solar cell (DSSC) device with glass/FTO/blocking layer/TiO2/dye/electrolyte/50 nm Pt/50 nm Au/glass was prepared to improve the energy conversion efficiency by applying an Au/Pt bilayer to the flat glass substrate of the counter electrode (CE). For comparison, Au and Pt CEs, 100 nm in thickness, on flat glass substrates were also prepared using the same method. The photovoltaic properties, such as the short circuit current density ( J sc ), open circuit voltage ( V oc ), fill factor ( FF) and energy conversion efficiency (ECE), were checked using a solar simulator and potentiostat. The strain of a Pt thin film was examined by x-ray diffraction. The sheet resistance and interface resistance were examined using a four point probe and impedance measurements. The measured energy conversion efficiencies of the dye-sensitized solar cell devices with Pt only and Au/Pt bilayer counter electrodes were 4.60% and 5.28%, respectively. The Au/Pt bilayer was confirmed by XRD, which also revealed a large compressive strain of -6.66 10-3 in the Pt layer. The interface resistance at the interface between the counter electrode and electrolyte decreased when an Au/Pt bilayered thin film was applied. The increase in efficiency at the Au/Pt bilayered counter electrode was attributed to the effect of a compressive strain field formed at the Pt layer and the low resistive Au layer used.

Noh, Yunyoung; Song, Ohsung



Electrochemical incineration of wastes  

NASA Astrophysics Data System (ADS)

The novel technology of waste removal in space vehicles by electrochemical methods is presented to convert wastes into chemicals that can be eventually recycled. The important consideration for waste oxidation is to select a right kind of electrode (anode) material that should be stable under anodic conditions and also a poor electrocatalyst for oxygen and chlorine evolution. On the basis of long term electrolysis experiments on seven different electrodes and on the basis of total organic carbon reduced, two best electrodes were identified. The effect of redox ions on the electrolyte was studied. Though most of the experiments were done in mixtures of urine and waste, the experiments with redox couples involved 2.5 M sulfuric acid in order to avoid the precipitation of redox ions by urea. Two methods for long term electrolysis of waste were investigated: (1) the oxidation on Pt and lead dioxide electrodes using the galvanostatic methods; and (2) potentiostatic method on other electrodes. The advantage of the first method is the faster rate of oxidation. The chlorine evolution in the second method is ten times less then in the first. The accomplished research has shown that urine/feces mixtures can be oxidized to carbon dioxide and water, but current densities are low and must be improved. The perovskite and Ti4O7 coated with RuO2 are the best electrode materials found. Recent experiment with the redox agent improves the current density, however, sulphuric acid is required to keep the redox agent in solution to enhance oxidation effectively. It is desirable to reduce the use of acid and/or find substitutes.

Bhardwaj, R. C.; Sharma, D. K.; Bockris, J. Om.



ATR-SEIRAS??an approach to probe the reactivity of Pd-modified quasi-single crystal gold film electrodes  

NASA Astrophysics Data System (ADS)

Quasi-single crystalline gold films of 20 nm thickness and preferential (1 1 1) orientation on Si hemispheres were modified by controlled potentiostatic deposition of Pd (sub-ML, ML, multi-L) from sulphate and/or chloride-containing electrolyte. The electrochemical properties of these model electrodes were characterised for hydrogen and (hydrogen-) sulphate adsorption as well as for surface oxide formation by cyclic voltammetry. Conditions were developed to fabricate defined and stable Pd monolayers. In situ ATR-SEIRAS (Attenuated Total Reflection Surface Enhanced Infrared Reflection Absorption Spectroscopy) experiments were carried out to describe the electrochemical double layer of Pd modified gold film electrodes in contact with aqueous 0.1 M H 2SO 4 with focus on interfacial water and anion adsorption. Based on an analysis of the non-resonant IR background signal the potential of zero charge is estimated to 0.10-0.20 V (vs. RHE). CO was found to be weakly physisorbed in atop sites on Au(1 1 1-20 nm)/0.1 M H 2SO 4 only in CO saturated electrolyte. CO, deposited on a quasi-single crystal gold film modified with 1 ML Pd, is chemisorbed with preferential occupation of bridge sites and atop positions at step edges. Saturated CO adlayers, as obtained by deposition at 0.10 V, contain isolated water species and are covered by a second layer of hydrogen bonded water. Potentiodynamic SEIRAS experiments of CO electro-oxidation on Pd-modified gold film electrodes demonstrate clearly the existence of a "pre-oxidation" region. They also provide spectroscopic evidence that isolated water and weakly hydrogen bonded water are consumed during the reaction and that atop CO on defect sites is a preferential reactant. The simultaneous in situ monitoring of the potential- and time-dependent evolution of characteristic vibrational modes in the OH- and CO-stretching regions are in agreement with the Gilman ("reactant pair") mechanism of CO oxidation.

Pronkin, S.; Wandlowski, Th.



High-performance Supercapacitor cells with Activated Carbon/MWNT nanocomposite electrodes  

NASA Astrophysics Data System (ADS)

The purpose of this work was to investigate and improve the performance of supercapacitor cells with carbon-based nanocomposite electrodes. The electrode structure comprised activated carbon (AC), four types of multi-wall nanotubes (MWNTs) and two alternative polymer binders, Polyvinyl alcohol (PVA) or Polyvinylidene fluoride (PVDF). Electrode fabrication involved various stages of mixing and dispersion of the AC powder and carbon nanotubes, rolling and coating of the AC/MWNT/binder paste on an aluminium substrate which also served as current collector. The organic electrolyte utilised was 1M tetraethylammonium tetrafluoroborate (TEABF4) fully dissolved in propylene carbonate (PC). All devices were of the electrochemical double layer capacitor (EDLC) type, incorporating four layers of tissue paper as separator material. The surface topography of the so fabricated electrodes was investigated with scanning electrode microscopy (SEM). Overall cell performance was evaluated with a multi-channel potentiostat/galvanostat/impedance analyser. Each supercapacitor cell was subjected to Cyclic Voltammetry (CV) at various scan rates from 0.01 V/s to 1 V/s, Charge-Discharge at a fixed current steps (2 mA) and Electrochemical Impedance Spectroscopy (EIS) with frequency range from 10 mHz to 1 MHz. It was established that an AC-based supercapacitor with 0.15%w/w MWNT content and 30 ?m roll-coated, nanocomposite electrodes provided superior energy and power and energy densities while the cells was immersed in the electrolyte; well above those generated by the AC-based EDLC cells.

Markoulidis, F.; Lei, C.; Lekakou, C.; Figgemeier, E.; Duff, D.; Khalil, S.; Martorana, B.; Cannavaro, I.



Rapid tissue dissolution efficiency of electrically-activated sodium hypochlorite on bovine muscle  

PubMed Central

Objective: Sodium hypochlorite (NaOCl) is a common antimicrobial and tissue-dissolving irrigant. The aim of this in vitro study is to evaluate and compare dissolution capacities of sodium hypochlorite solutions after electrically activation (E-NaOCl) on bovine muscle specimens at various time periods and concentrations. Materials and Methods: Three sodium hypochlorite solutions of 1.25%, 2.5%, and 5% were tested at 3-min. and 5-min. with and without activation by electrically. Distilled water and NaOCl solutions without electrically activation were used as controls. Pieces of bovine muscle tissue (34 2 mg) were placed in 10 mL of each solution at room temperature. In the group of E-NaOCl, electrically activation was performed through the potentiostat. The tissue specimens were weighed before and after treatment, and the percentage of weight loss was calculated. Results: Weight loss of the tissue increased with the concentration of E-NaOCl and NaOCl. Higher concentration and electrically activation considerably enhanced the efficacy of sodium hypochlorite. The effect of electrically activation on tissue dissolution was much greater than that of same concentrations in the groups of NaOCl (P < 0.001). Tissue weight loss was significantly higher in 2.5% and 5% E-NaOCl at 3 min. than in 2.5% and 5% NaOCl at 5 min. (P < 0.05). There were not any significant differences between the 2.5% E-NaOCl and 5% NaOCl at 5 min. (P > 0.05). Conclusion: Electrically activation can improve the tissue-dissolving effectiveness of sodium hypochlorite. PMID:25512725

Ertugrul, Ihsan Furkan; Maden, Murat; Orhan, Ekim Onur; Ozkorucuklu, Sabriye Percin; Aglarca, Ali Vasfi



Integration of solid-state nanopores in a 0.5 ?m CMOS foundry process  

NASA Astrophysics Data System (ADS)

High-bandwidth and low-noise nanopore sensor and detection electronics are crucial in achieving single-DNA-base resolution. A potential way to accomplish this goal is to integrate solid-state nanopores within a CMOS platform, in close proximity to the biasing electrodes and custom-designed amplifier electronics. Here we report the integration of solid-state nanopore devices in a commercial complementary metal-oxide-semiconductor (CMOS) potentiostat chip implemented in On-Semiconductors 0.5 ?m technology. Nanopore membranes incorporating electrodes are fabricated by post-CMOS micromachining utilizing the n+ polysilicon/SiO2/n+ polysilicon capacitor structure available in the aforementioned process. Nanopores are created in the CMOS process by drilling in a transmission electron microscope and shrinking by atomic layer deposition. We also describe a batch fabrication method to process a large of number of electrode-embedded nanopores with sub-10 nm diameter across CMOS-compatible wafers by electron beam lithography and atomic layer deposition. The CMOS-compatibility of our fabrication process is verified by testing the electrical functionality of on-chip circuitry. We observe high current leakage with the CMOS nanopore devices due to the ionic diffusion through the SiO2 membrane. To prevent this leakage, we coat the membrane with Al2O3, which acts as an efficient diffusion barrier against alkali ions. The resulting nanopore devices also exhibit higher robustness and lower 1/f noise as compared to SiO2 and SiNx. Furthermore, we propose a theoretical model for our low-capacitance CMOS nanopore devices, showing good agreement with the experimental value. In addition, experiments and theoretical models of translocation studies are presented using 48.5 kbp ?-DNA in order to prove the functionality of on-chip pores coated with Al2O3.

Uddin, A.; Yemenicioglu, S.; Chen, C.-H.; Corigliano, E.; Milaninia, K.; Theogarajan, L.



Tribocorrosive behaviour of commonly used temporomandibular implants in a synovial fluid-like environment: Ti-6Al-4V and CoCrMo  

NASA Astrophysics Data System (ADS)

The temporomandibular joint implant metal alloys, Ti6Al4V and CoCrMo, (n = 3/group) were tested under free-potential and potentiostatic conditions using a custom-made tribocorrosion apparatus. Sliding duration (1800 cycles), frequency (1.0 Hz) and load (16 N) mimicked the daily mastication process. Synovial-like fluid (bovine calf serum, pH = 7.6 at 37 C) was used to simulate the in vivo environment. Changes in friction coefficient were monitored throughout the sliding process. Changes in surface topography, total weight loss and roughness values were calculated using scanning electron microscopy and white-light interferometry. Finally, statistical analyses were performed using paired t-tests to determine significance between regions within each metal type and also independent sample t-tests to determine statistical significance between metal alloy types. Ti6Al4V demonstrated a greater decrease of potential than CoCrMo, a higher weight loss from wear (Kw = 257.8 versus 2.62 g p < 0.0001), a higher weight loss from corrosion (Kc = 17.44 versus 0.14 g p < 0.0001) and a higher weight loss from the combined effects of wear and corrosion (Kwc = 275.28 versus 2.76 g p < 0.0001). White-light interferometry measurements demonstrated a greater difference in surface roughness inside the wear region in Ti6Al4V than CoCrMo after the sliding (Ra = 323.80 versus 70.74 nm p < 0.0001). In conclusion, CoCrMo alloy shows superior anti-corrosive and biomechanical properties.

Royhman, D.; Yuan, J. C.; Shokuhfar, T.; Takoudis, C.; Sukotjo, C.; Mathew, M. T.



Ultrasensitive indicator-free and enhanced self-signal nanohybrid DNA sensing platform based on electrochemically grown poly-xanthurenic acid/Fe2O3 membranes.  


This paper describes a novel electrochemical DNA biosensor for simple, rapid, and specific detection of PML/RARA fusion gene in acute promyelocytic leukemia by using 18-mer single-stranded deoxyribonucleic acid as the capture probe. Nanosized Fe(2)O(3) was first immobilized on the surface of a carbon paste electrode (CPE). Then poly-xanthurenic acid (PXa), a new electroactive material, was electrogenerated by using the pulse potentiostatic method on the Fe(2)O(3) substrate to form a unique and uniform nanorhombus structure. Due to the unique binding ability of xanthurenic acid (Xa) with Fe(2)O(3), Xa monomers tended to be adsorbed around nanosized Fe(2)O(3), and the electropolymerization efficiency was greatly improved. Owing to the presence of abundant carboxyl groups, the capture probe was covalently attached on the carboxyl-terminated PXa/Fe(2)O(3) nanorhombus membranes through the free amines of DNA sequences based on the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydrosulfosuccinimide cross-linking reaction. The covalently immobilized capture probe could selectively hybridize with its target DNA to form double-stranded DNA on the PXa/Fe(2)O(3)/CPE surface. Electrochemical impedance spectroscopy was adopted for indicator-free monitoring of the hybridization reaction on the probe-captured electrode. As a result, the efficient probe immobilization platform, coupled with the ultrasensitive indicator-free impedance measurement, gave rise to a detection limit of 2.8 fmol/L and a dynamic range spanning 8 orders of magnitude. The excellent analytical properties of the proposed biosensor developed here holds great promise for ultrasensitive detection of other biorecognition events and diagnosis of diseases in practice. PMID:22047973

Zhang, Wei; Yang, Tao; Jiao, Kui



Automated two-dimensional separation flow system with electrochemical preconcentration, stripping, capillary electrophoresis and contactless conductivity detection for trace metal ion analysis.  


This paper describes the automation of a fully electrochemical system for preconcentration, cleanup, separation and detection, comprising the hyphenation of a thin layer electrochemical flow cell with CE coupled with contactless conductivity detection (CE-C?D). Traces of heavy metal ions were extracted from the pulsed-flowing sample and accumulated on a glassy carbon working electrode by electroreduction for some minutes. Anodic stripping of the accumulated metals was synchronized with hydrodynamic injection into the capillary. The effect of the angle of the slant polished tip of the CE capillary and its orientation against the working electrode in the electrochemical preconcentration (EPC) flow cell and of the accumulation time were studied, aiming at maximum CE-C?D signal enhancement. After 6 min of EPC, enhancement factors close to 50 times were obtained for thallium, lead, cadmium and copper ions, and about 16 for zinc ions. Limits of detection below 25 nmol/L were estimated for all target analytes but zinc. A second separation dimension was added to the CE separation capabilities by staircase scanning of the potentiostatic deposition and/or stripping potentials of metal ions, as implemented with the EPC-CE-C?D flow system. A matrix exchange between the deposition and stripping steps, highly valuable for sample cleanup, can be straightforwardly programmed with the multi-pumping flow management system. The automated simultaneous determination of the traces of five accumulable heavy metals together with four non-accumulated alkaline and alkaline earth metals in a single run was demonstrated, to highlight the potentiality of the system. PMID:21394730

Lopes, Fernando Silva; Coelho, Lcia Helena Gomes; Gutz, Ivano Gebhardt Rolf



Low temperature operation and influence parameters on the cold start ability of portable PEMFCs  

NASA Astrophysics Data System (ADS)

The start up behaviour of PEM fuel cells below 0 C is one of the most challenging tasks to be solved before commercialisation. The automotive industry started to develop solutions to reduce the start up time of fuel cell systems in the middle of the nineties. The strategies varied from catalytic combustion of hydrogen on the electrode catalyst to fuel starvation or external stack heating via cooling loops to increase the stack temperature. Beside the automotive sector the cold start ability is as well important for portable PEMFC applications for outdoor use. But here the cold start issue is even more complicated, as the fuel cell system should be operated as passive as possible. Below 0 C freezing of water inside the PEMFC could form ice layers in the electrode and in the gas diffusion layer. Therefore the cell reaction is limited or even inhibited. Product water during the start up builds additional barriers and leads to a strong decay of the output power at isothermal operating conditions. In order to find out which operational and hardware parameters affect this decay, potentiostatic experiments on single cells were performed at isothermal conditions. These experiments comprise investigations of the influence of membrane thickness and different GDL types as well as the effect of gas flow rates and humidification levels of the membrane. As pre stage to physical based models, empirical based prediction models are used to gain a better understanding of the main influence parameters during cold start. The results are analysed using the statistical software Cornerstone 4.0. The experience of single cell investigations are compared to start up behaviour of portable fuel cell stacks which are operated in a climate chamber at different ambient temperatures below 0 C. Additional flow sharing problems in the fuel cell stack could be seen during cold start up experiments.

Oszcipok, M.; Zedda, M.; Riemann, D.; Geckeler, D.


Integration of solid-state nanopores in a 0.5?m CMOS foundry process.  


High-bandwidth and low-noise nanopore sensor and detection electronics are crucial in achieving single-DNA-base resolution. A potential way to accomplish this goal is to integrate solid-state nanopores within a CMOS platform, in close proximity to the biasing electrodes and custom-designed amplifier electronics. Here we report the integration of solid-state nanopore devices in a commercial complementary metal-oxide-semiconductor (CMOS) potentiostat chip implemented in On-Semiconductor's 0.5?m technology. Nanopore membranes incorporating electrodes are fabricated by post-CMOS micromachining utilizing the n+polysilicon/SiO2/n+polysilicon capacitor structure available in the aforementioned process. Nanopores are created in the CMOS process by drilling in a transmission electron microscope and shrinking by atomic layer deposition. We also describe a batch fabrication method to process a large of number of electrode-embedded nanopores with sub-10nm diameter across CMOS-compatible wafers by electron beam lithography and atomic layer deposition. The CMOS-compatibility of our fabrication process is verified by testing the electrical functionality of on-chip circuitry. We observe high current leakage with the CMOS nanopore devices due to the ionic diffusion through the SiO2 membrane. To prevent this leakage, we coat the membrane with Al2O3, which acts as an efficient diffusion barrier against alkali ions. The resulting nanopore devices also exhibit higher robustness and lower 1/f noise as compared to SiO2 and SiNx. Furthermore, we propose a theoretical model for our low-capacitance CMOS nanopore devices, showing good agreement with the experimental value. In addition, experiments and theoretical models of translocation studies are presented using 48.5kbp ?-DNA in order to prove the functionality of on-chip pores coated with Al2O3. PMID:23519330

Uddin, A; Yemenicioglu, S; Chen, C-H; Corigliano, E; Milaninia, K; Theogarajan, L



Increased carbon uptake in marine sediment enabled by naturally occurring electrical conductors  

NASA Astrophysics Data System (ADS)

Reduction-oxidation (redox) gradients are common across marine sediment-water interfaces and result from microbially-mediated reactions such as the oxidation of organic matter coupled to reduction of electron acceptors. Most microbes living in sediments do not have direct access to oxygen in their immediate environment, however it has recently been shown that sulfide-oxidizing microbes may employ extracellular electron transfer (EET) to couple the oxidation of sulfide in the anoxic zone to reduction of oxygen at the sediment-water interface located several centimeters away. However, no mechanisms for this observed phenomenon have been validated. Accordingly, we tested the hypothesis that conductive minerals in marine sediment (specifically pyrite) can couple spatially separated redox reactions such as anaerobic respiration and oxygen reduction. Marine sediment was amended with naturally occurring pyrite in varying concentrations (0, 2, 10 and 50 weight-percent) and then incubated with 10 ?M 13C-labeled acetate. After six hours, the treatments with the greatest amount of added pyrite showed the greatest incorporation of acetate from the labeled pool. The fraction of labeled acetate incorporation more than doubled in the 10 and 50 weight-percent treatments compared to the control sediment. We also designed a circuit to investigate the electrical conductivity of the sediment treatments as a function of added pyrite. A potentiostat was used to establish a known voltage across a sediment column and current was measured. Resistance (the inverse of conductance) was calculated from a linear fit of current data over a range of voltages ranging from 0.5 to 1.0 V. The treatments with added pyrite had lower resistance than background sediment, with the lowest resistance corresponding to the 50% pyrite treatment. We also examined the effect of varying pyrite content on microbial community composition using massively parallel 16S rRNA sequencing. Microbial community analyses reveal that the majority of microbes in the sediment belong to the deltaproteobacteria or gammaproteobacteria classes, which have been previously implicated in EET in laboratory and field-based bioelectrochemical studies. These data force us to reconsider the role of EET and conductive minerals in organic carbon cycling -particularly in metaliferous sediments- and suggest that EET-enabled anaerobic metabolism may represent a significant contribution to marine carbon cycling.

Nielsen, M. E.; Cahoon, D. P.; Girguis, P. R.



Electrochemical insertion of lithium into polymer derived silicon oxycarbide and oxycarbonitride ceramics  

NASA Astrophysics Data System (ADS)

There has recently been great interest in lithium storage at the anode of Li-ion rechargeable battery in order to replace the carbon-based anode. Over the last two decades, carbon-based anode, especially graphite, was utilized as anode in lithium ion batteries because of its cyclic stability and coulombic efficiency. However, low capacity and the thermal runaway resulted from the solid electrolyte interface (SEI) formation on the graphite anode during charging and discharging cycles. This inhibited the further development of lithium ion batteries for Plug-in Hybrid Electrical Vehicle (PHEV) or Electrical Vehicle (EV) which demand both high energy and high power density. The goal of this research was to develop the anode material, Silicon Oxycarbide (SixOyCz) and Silicon Carbonitride (SixCyNz), from Polymer Derived Ceramics (PDCs) for lithium-ion batteries application and to understand the thermodynamics and kinetics of intercalation mechanism in the host material. This includes as three main categories: (1) Characterization of PDCs, (2) measurement of electrochemical phenomena of PDCs anode in half-cell which used lithium foil as anode, (3) analysis of the lithium intercalation mechanism and diffusion coefficient in PDCs. In this thesis, the first objective was to synthesize possible anode materials and construct the proper battery structure to experiment its intercalation and deintercalation behaviors. Also, various experiments such as cyclic stability, capacity retention and C-rate capability were performed in order to estimate the feasibility of PDCs as new anode materials for the next generation. The second objective was to determine the reversible and irreversible capacity from different fraction of Si, C, O and N composition. Based on this analysis, the mixed bond sites in SixOyCz had higher reversible and irreversible capacity than the free carbon sites. The third objective was to examine the hysteretic response of lithium intercalation to SiCO. According to the coulometric titration results on both traverses of the cycle, an intrinsic polarization was measured and this polarization-potential, which is measured to be 250--500mV, is attributed to a differential between the potential of Li-ions across the anode-electrolyte interface. Finally, the kinetic property, diffusion coefficient, of lithium was studied when the lithium was intercalated and deintercalated into SiCO. Galvanostatic Intermittent Titration Technique (GITT) and Potentiostatic Intermittent Titration Technique (PITT) have been adapted to measure the diffusivity of lithium as a function of the lithium concentration in PDCs.

Ahn, Dongjoon


Electrochemical Detection of Multiple Bioprocess Analytes  

NASA Technical Reports Server (NTRS)

An apparatus that includes highly miniaturized thin-film electrochemical sensor array has been demonstrated as a prototype of instruments for simultaneous detection of multiple substances of interest (analytes) and measurement of acidity or alkalinity in bioprocess streams. Measurements of pH and of concentrations of nutrients and wastes in cell-culture media, made by use of these instruments, are to be used as feedback for optimizing the growth of cells or the production of desired substances by the cultured cells. The apparatus is designed to utilize samples of minimal volume so as to minimize any perturbation of monitored processes. The apparatus can function in a potentiometric mode (for measuring pH), an amperometric mode (detecting analytes via oxidation/reduction reactions), or both. The sensor array is planar and includes multiple thin-film microelectrodes covered with hydrous iridium oxide. The oxide layer on each electrode serves as both a protective and electrochemical transducing layer. In its transducing role, the oxide provides electrical conductivity for amperometric measurement or pH response for potentiometric measurement. The oxide on an electrode can also serve as a matrix for one or more enzymes that render the electrode sensitive to a specific analyte. In addition to transducing electrodes, the array includes electrodes for potential control. The array can be fabricated by techniques familiar to the microelectronics industry. The sensor array is housed in a thin-film liquid-flow cell that has a total volume of about 100 mL. The flow cell is connected to a computer-controlled subsystem that periodically draws samples from the bioprocess stream to be monitored. Before entering the cell, each 100-mL sample is subjected to tangential-flow filtration to remove particles. In the present version of the apparatus, the electrodes are operated under control by a potentiostat and are used to simultaneously measure the pH and the concentration of glucose. It is anticipated that development of procedures for trapping more enzymes into hydrous iridium oxide (and possibly into other electroactive metal oxides) and of means for imparting long-term stability to the transducer layers should make it possible to monitor concentrations of products of many enzyme reactions for example, such key bioprocess analytes as amino acids, vitamins, lactose, and acetate.

Rauh, R. David



Localized surface plasmon mediated photochemistry and charge transfer in noble metal nanoparticles  

NASA Astrophysics Data System (ADS)

This thesis addresses the fundamental physical and chemical processes of localized surface plasmon mediated photochemistry and charge transfer in noble metal nanoparticles. The first chapter introduces the theory and application of surface plasmons. It includes a discussion of propagating and localized surface plasmons, plasmon decay dynamics, factors governing plasmon excitation of metal nanoparticles, near-field enhanced photochemistry and plasmon mediated charge transfer. The second chapter presents a photovoltage mechanism for room light conversion of citrate stabilized silver nanocrystal seeds to large nanoprisms. The process relies on the excitation of silver surface plasmons and requires citrate and oxygen. The transformation rate is first-order in seed concentration. The mechanism involves oxidative etching of seeds and subsequent photoreduction of aqueous silver ions preferentially onto silver prisms that have a cathodic photovoltage resulting from plasmon hot hole citrate photo- oxidation. This idea also explains several previously reported experiments including single and dual wavelength irradiation and the core/shell synthesis of silver layers on gold seeds. The third chapter explores the photo-driven growth of citrate stabilized silver nanoparticles. Under plasmon excitation, particles that absorb/scatter light weakly reduce dioxygen and lose silver ions, whereas particles with resonant plasmons build up a high photovoltage due to citrate photo-oxidation and reduce silver ions. Overall, growth is favored for on-resonant particles. Compared to the borohydride reduction method, more monodisperse, round 10-20 nm diameter silver nanoparticles are obtained by plasmon mediated approaches. Adding a trace amount of potassium chloride can speed up the growth and inhibit the formation of Ag aggregates. The fourth chapter investigates the plasmon induced photochemical charge separation in gold nanoparticles on a transparent indium tin oxide (ITO) substrate. Photocurrent and photovoltage are directly measured under potentiostatic control in air. It is proposed that gold plasmon excitation causes hot electrons to inject into the ITO conduction band, while hot holes are scavenged by citrate and other solution redox species. A resonant increase in the photocurrent generated at more oxidizing potentials is observed.

Wu, Xiaomu


Heat transfer and thermal management studies of lithium polymer batteries for electric vehicle applications  

NASA Astrophysics Data System (ADS)

The thermal conductivities of the polymer electrolyte and composite cathode are important parameters characterizing heat transport in lithium polymer batteries. The thermal conductivities of lithium polymer electrolytes, including poly-ethylene oxide (PEO), PEO-LiClO4, PEO-LiCF3SO 3, PEO-LiN(CF3SO2)2, PEO-LiC(CF 3SO2)3, and the thermal conductivities of TiS 2 and V6O13 composite cathodes, were measured over the temperature range from 25C to 150C by a guarded heat flow meter. The thermal conductivities of the electrolytes were found to be relatively constant for the temperature and for electrolytes with various concentrations of the lithium salt. The thermal conductivities of the composite cathodes were found to increase with the temperature below the melting temperature of the polymer electrolyte and only slightly increase above the melting temperature. Three different lithium polymer cells, including Li/PEO-LiCF3 S O3/TiS2, Li/PEO-LiC(CF3 S O2)3/V6 O13, and Li/PEO-LiN(CF3 S O2)2/ Li1+x Mn2 O4 were prepared and their discharge curves, along with heat generation rates, were measured at various galvanostatic discharge current densities, and at different temperature (70C, 80C and 90C), by a potentiostat/galvanostat and an isothermal microcalorimeter. The thermal stability of a lithium polymer battery was examined by a linear perturbation analysis. In contrast to the thermal conductivity, the ionic conductivity of polymer electrolytes for lithium-polymer cell increases greatly with increasing temperature, an instability could arise from this temperature dependence. The numerical calculations, using a two dimensional thermal model, were carried out for constant potential drop across the electrolyte, for constant mean current density and for constant mean cell output power. The numerical calculations were approximately in agreement with the linear perturbation analysis. A coupled mathematical model, including electrochemical and thermal components, was developed to study the heat transfer and thermal management of lithium polymer batteries. The results calculated from the model, including temperature distributions, and temperatures at different stages of discharge are significantly different from those calculated from the thermal model. The discharge curves and heat generation rates calculated by the electrochemical-thermal model were in agreement with the experimental results. Different thermal management approaches, including a variable conductance insulation enclosure were studied.

Song, Li


Enhancement of electrochemical hydrogen storage in NiCl2-FeCl3-PdCl2-graphite intercalation compound effected by chemical exfoliation  

NASA Astrophysics Data System (ADS)

In the present work, a quaternary NiCl2-FeCl3-PdCl2-graphite intercalation compound (NiCl2-FeCl3-PdCl2-GIC) was successfully synthesized by molten salts method. A part of this compound was subsequently subjected to chemical exfoliation to obtain expanded compound (NiCl2-FeCl3-PdCl2-EGIC). The changes created in crystalline structure, morphology and chemical composition of GIC due to exfoliation were examined by XRD, SEM and EDS techniques and then related to electrochemical behaviour of electrodes made of the original and exfoliated compound. The results of electrochemical studies carried out by the cyclic voltammetry (CV) method in 6 M KOH solution showed that current charges of all the cathodic and anodic peaks recorded for NiCl2-FeCl3-PdCl2-EGIC are considerably higher already in the first two cycles as compared to those observed for the original NiCl2-FeCl3-PdCl2-GIC. This improvement is ascribed to chemical exfoliation leading to a tremendous development of surface area of the compound due to the splitting and wrinkling of graphite flakes followed by easier access of hydroxyl ions of the electrolyte to active species of intercalates preserved between the graphene interspaces as well as expelled from the graphite interspacing. A large anodic peak was recorded on CV curves after the potentiostatic polarization of electrodes at the potential of -1.2 V where the reaction of hydrogen sorption/evolution occurs and intercalates highly dispersed in the graphite matrix are reduced to a metal form. This peak mainly corresponding to the recovery of hydrogen stored in the electrode appeared to be over five times higher for electrode made of exfoliated compound. This significant enhancement of the hydrogen storage capacity is attributed to electrochemically active Pd nanoparticles highly dispersed in porous structure of exfoliated compound and likely functioning in synergy with Ni/Fe clusters.

Skowro?ski, J. M.; Rozmanowski, T.; Krawczyk, P.



Tribocorrosion behavior of CoCrMo alloy for hip prosthesis as a function of loads: a comparison between two testing systems  

PubMed Central

Metal-on-metal (MOM) hip prosthesis bearings have enjoyed renewed popularity, but concerns remain with wear debris and metal ion release causing a negative response in the surrounding tissues. Further understanding into the wear and corrosion mechanisms occurring in MOM hips is therefore essential. The purpose of this study was to evaluate the tribocorrosion behaviour, or interplay between corrosion and wear, of a low-carbon CoCrMo alloy as a function of loading. The tribocorrosion tests were performed using two tribometer configurations. In the first configuration, System A, a linearly reciprocating alumina ball slid against the flat metal immersed in a phosphate buffer solution (PBS). In the second configuration, System B, the flat end of a cylindrical metal pin was pressed against an alumina ball that oscillated rotationally, using bovine calf serum (BCS) as the lubricant and electrolyte. System B was custom-built to emulate in vivo conditions. The tribocorrosion tests were performed under potentiostatic conditions at -0.345V, with a sliding duration of 1800 seconds and a frequency of 1Hz. In System A the applied loads were 0.05, 0.5, and 1N (138, 296 and 373MPa, respectively) and in System B were 16, 32, and 64N (474, 597, and 752MPa, respectively). Electrochemical impedance spectroscopy (EIS) and polarization resistance were estimated. The total mass loss (Kwc) in the CoCrMo was determined. The mass loss due to wear (Kw) and that due to corrosion (Kc) were determined. The dominant wear regime for the CoCrMo alloy subjected to sliding changes from wear-corrosion to mechanical wear as the contact stress increases. An attempt was made to compare both system, in their tribochemical responses and formulate some insights in the total degradation processes. Our results also suggest that the proteins in the serum lubricant assist in the generation of a protective layer against corrosion during sliding. The study highlights the need of adequate methodology/guidelines to compare the results from different test systems and translating in solving the practical problems. PMID:21921971

Mathew, M.T.; Runa, M.J.; Laurent, M.; Jacobs, J.J.; Rocha, L.A.; Wimmer, M.A.




SciTech Connect

Crevice corrosion is currently studied using either one of two techniques depending on the data needed. The first method is a multi-crevice former over a metallic sample; this provides information on the severity of crevice corrosion (depth, position, frequency) but delivers little to no electrochemical information [1]. The second method involves the potentiodynamic or potentiostatic study of an uncreviced sample in model crevice solution or under a crevice former in aggressive solution [2]. Crevice corrosion is highly dependent on the position in the crevice. The distance from the crevice mouth will affect the depth of attack, the solution composition and pH, and the ohmic drop and the true potential in the crevice [3-6]. These in turn affect the current density as a function of potential and position. A Multi-Channel Micro-Electrode Analyzer (MMA) has been recently used to demonstrate the interaction between localized corrosion sites (pitting corrosion and intergranular corrosion) [7]. MMA can provide spatial resolution of electrochemical properties in the crevice. By coupling such a tool with scaling laws derived from experimental data (a simple equation linking the depth of crevice corrosion initiation to the crevice gap), it is possible to produce highly instrumented crevices, rescaled to enable spatial resolution of local corrosion processes. In this study, the use of multi-wires arrays (up to 100 closed packed wires simulating a planar electrode, divided in 10 distinctively controllable groups) electrically coupled through zero resistance ammeters enables the observation of the current evolution as a function of position inside and outside the crevice. For instance, the location of crevice initiation sites and propagation behavior can be studied under various conditions. Experiments can be conducted with various realistic variables. These can either be electrochemical (such as proximate cathode) or physical (crevice former material or position). Using new impedance-capable MMA, it is also possible to monitor the film breakdown and the early stages of crevice corrosion as a function of the wires position. In this talk, the use of multi-electrode array to study crevice corrosion of 316 stainless steel and a Ni-Cr-Mo alloy is reviewed.

F. Bocher and J. R. Scully




SciTech Connect

Crevice corrosion is currently studied using either one of two techniques depending on the data needed. The first method is a multi-crevice former over a metallic sample; this provides information on the severity of crevice corrosion (depth, position, frequency) but delivers little to no electrochemical information [1]. The second method involves the potentiodynamic or potentiostatic study of an uncreviced sample in model crevice solution or under a crevice former in aggressive solution [2]. Crevice corrosion is highly dependent on the position in the crevice. The distance from the crevice mouth will affect the depth of attack, the solution composition and pH, and the ohmic drop and the true potential in the crevice [3-6]. These in turn affect the current density as a function of potential and position. An Multi-Channel Micro-Electrode Analyzer' (MMA) has been recently used to demonstrate the interaction between localized corrosion sites (pitting corrosion and intergranular corrosion) [7]. MMA can provide spatial resolution of electrochemical properties in the crevice. By coupling such a tool with scaling laws derived from experimental data (a simple equation linking the depth of crevice corrosion initiation to the crevice gap), it is possible to produce highly instrumented crevices, rescaled to enable spatial resolution of local corrosion processes. In this study, the use of multi-wires arrays (up to 100 closed packed wires simulating a planar electrode, divided in 10 distinctively controllable groups) electrically coupled through zero resistance ammeters enables the observation of the current evolution as a function of position inside and outside the crevice. For instance, the location of crevice initiation sites and propagation behavior can be studied under various conditions. Experiments can be conducted with various realistic variables. These can either be electrochemical (such as proximate cathode) or physical (crevice former material or position). Using new impedance-capable MMA, it is also possible to monitor the film breakdown and the early stages of crevice corrosion as a function of the wires position. In this talk, the use of multi-electrode array to study crevice corrosion of 316 stainless steel and a Ni-Cr-Mo alloy is reviewed.

F. Bocher, J. R. Scully



Sodium molybdate - an additive of choice for enhancing the performance of AC/AC electrochemical capacitors in a salt aqueous electrolyte.  


Sodium molybdate (Na2MoO4) has been used as an additive to 1 mol L(-1) lithium sulfate electrolyte for electrochemical capacitors based on activated carbon (AC) electrodes, in order to reduce the corrosion of stainless steel current collectors. We demonstrate that the MoO4(2-) anions improve the overall capacitance owing to pseudofaradaic processes. In a two-electrode cell, capacitance values of 121 F g(-1) have been achieved up to 1.6 V using 1 mol L(-1) Li2SO4 + 0.1 mol L(-1) Na2MoO4, as compared to 103 F g(-1) when 1 mol L(-1) Li2SO4 is used. Further, by using a two-electrode setup equipped with a reference electrode, we could demonstrate that, at 1.6 V, the positive electrode potential reaches a value of 0.96 V vs. NHE in 1 mol L(-1) Li2SO4, crossing the thermodynamic potential limit of oxygen evolution (Eox = 0.846 V vs. NHE), and the pitting potential, Epit = 0.95 V vs. NHE. By contrast, in 1 mol L(-1) Li2SO4 + 0.1 mol L(-1) Na2MoO4, the pseudofaradaic contribution occurring at -0.05 V vs. NHE due to MoO4(2-) anions drives the positive electrode to reach only 0.798 V vs. NHE. Hence, the oxidation of the AC and corrosion of the stainless steel current collector at the positive electrode are unlikely in Li2SO4 + Na2MoO4 when the capacitor operates at 1.6 V. During potentiostatic floating of the capacitor at 1.6 V for 120 hours in Li2SO4 + Na2MoO4, the capacitance and resistance remain constant at 125 F g(-1) and ?1.0 ?, respectively, while the resistance increases from 1.4 ? to 3.1 ? in Li2SO4. Overall, the addition of MoO4(2-) anions to Li2SO4 aqueous electrolyte allows the capacitance to be enhanced, corrosion of the positive stainless steel current collector to be inhibited and the AC/AC electrochemical capacitor to demonstrate stable performance up to 1.6 V. PMID:25427248

Abbas, Q; Ratajczak, P; Bguin, F



Application of highly-ordered TiO2 nanotube-arrays in heterojunction dye-sensitized solar cells  

NASA Astrophysics Data System (ADS)

Highly-ordered TiO2 nanotube arrays are made by potentiostatic anodization of a titanium film in a fluoride containing electrolyte. Here we describe the application of this unique material architecture in both front-side and back-side illuminated dye-sensitized solar cells (DSSCs). The back-side illuminated solar cells are based on the use of 6.2 m long (110 nm pore diameter, 20 nm wall thickness) highly-ordered nanotube-array films made by anodization of a 250 m thick Ti foil in a KF electrolyte. Front-side illuminated solar cells use a negative electrode composed of optically transparent nanotube arrays, approximately 3600 nm in length (46 nm pore diameter, 17 nm wall thickness), grown on a fluorine doped tin oxide coated glass substrate by anodic oxidation of a previously deposited RF-sputtered titanium thin film in a HF electrolyte. After crystallization by oxygen annealling the nanotube-arrays are treated with TiCl4 to enhance photocurrent amplitudes. The arrays are then sensitized by a self-assembled monolayer of bis(tetrabutylammonium)-cis-(dithiocyanato)-N, N'- bis(4-carboxylato-4'-carboxylic acid-2, 2'-bipyridine)ruthenium(II) (commonly called 'N719'). Superior photoresponse is obtained using acetonitrile as the dye solvent. Voltage decay measurements indicate that the highly-ordered TiO2 nanotube-arrays, in comparison with nanoparticulate systems, provide excellent pathways for electron percolation with superior electron lifetimes. The front-side illuminated DSSCs, show a typical AM 1.5 photocurrent of 10.3 mA cm-2, open circuit voltage of 0.84 V, 0.54 fill factor, and 4.7% efficiency although the transparent nanotube-array negative electrode is only 360 nm thick. The back-side illuminated DSSCs show an AM 1.5 short-circuit current density of 10.6 mA cm-2, 0.82 V open circuit potential and a 0.51 fill factor yielding a solar conversion efficiency of 4.4%.

Paulose, Maggie; Shankar, Karthik; Varghese, Oomman K.; Mor, Gopal K.; Grimes, Craig A.



Investigations on the corrosion resistance of metallic bipolar plates (BPP) in proton exchange membrane fuel cells (PEMFC) - understanding the effects of material, coating and manufacturing  

NASA Astrophysics Data System (ADS)

Polymer Electrolyte Membrane Fuel Cell (PEMFC) systems are promising technology for contributing to meet the deficiency of world`s clean and sustainable energy requirements in the near future. Metallic bipolar plate (BPP) as one of the most significant components of PEMFC device accounts for the largest part of the fuel cell`s stack. Corrosion for metallic bipolar plates is a critical issue, which influences the performance and durability of PEMFC. Corrosion causes adverse impacts on the PEMFC`s performance jeopardizing commercialization. This research is aimed at determining the corrosion resistance of metallic BPPs, particularly stainless steels, used in PEMFC from different aspects. Material selection, coating selection, manufacturing process development and cost considerations need to be addressed in terms of the corrosion behavior to justify the use of stainless steels as a BPP material in PEMFC and to make them commercially feasible in industrial applications. In this study, Ti, Ni, SS304, SS316L, and SS 430 blanks, and BPPs comprised of SS304 and SS316L were examined in terms of the corrosion behavior. SS316L plates were coated to investigate the effect of coatings on the corrosion resistance performance. Stamping and hydroforming as manufacturing processes, and three different coatings (TiN, CrN, ZrN) applied via the Physical Vapor Deposition (PVD) method in three different thicknesses were selected to observe the effects of manufacturing processes, coating types and coating thicknesses on the corrosion resistance of BPP, respectively. Uncoated-coated blank and formed BPP were subjected to two different corrosion tests: potentiostatic and potentiodynamic. Some of the substantial results: 1- Manufacturing processes have an adverse impact on the corrosion resistance. 2- Hydroformed plates have slightly higher corrosion resistance than stamped samples. 3- BPPs with higher channel size showed better corrosion resistance. 4- Since none of the uncoated samples meet the 2015 target of the U.S. Department of Energy, surface coating is required. 5- ZrN and CrN coated BPPs exhibited higher corrosion resistance meeting DOE target while TiN coated samples had the lowest corrosion resistance. Higher coating thicknesses improved the corrosion resistance of the BPPs. 6- Process sequence between coating and manufacturing is not significant for hydroforming case (ZrN and CrN) and stamping case (CrN) in terms of the corrosion resistance. In other words, coating the BPP`s substrate material before manufacturing process does not always decrease the corrosion resistance of the BPPs.

Dur, Ender


Mechanisms of interfacial electron-transfer within high-surface-area metal-oxide thin films  

NASA Astrophysics Data System (ADS)

The direct conversion of solar photon energy into electrical power is achieved with photovoltaic technology, yet existing technology is too inefficient or expensive to implement on a global scale. Dye sensitized solar cells (DSSCs) based on earth abundant low cost materials could overcome the barriers for world-wide implantation of photovoltaic technology. Historically the most efficient regenerative DSSCs utilize iodide based redox mediators in nitrile solvents. Despite the dominance of iodide redox mediator in DSSCs, the chemical attribute(s) that make iodide based electrolytes superior to other electrolyte is yet unproven. Discovering the chemical cause of iodide's superiority as a redox mediator was and important aspect of this thesis research. In Chapter 2 the photoinitated formation and cleavage of I-I bonds is demonstrated at an un-sensitized potentiostatically controlled mesoporous nanocrystalline (anatase) TiO2 thin film. After pulsed laser excitation of a TiO2 thin film, I2- was observed that disproportionated to yield I3- and I-, but did not react with TiO2. In contrast evidence for a quasi-Fermi level dependent reaction between TiO2(e -) and I3- was observed. In agreement with the findings at un-sensitized TiO2 in Chapter 2, the results presented in Chapter 3 demonstrate that after pulsed laser excitation of an operational DSSC: I2- is observed, I2-does not react with TiO 2, and that charge recombination between I3- and TiO2(e-) is operative. In addition to absorption changes attributed to iodide redox chemistry, evidence for a transient electric field induced Stark effect was observed in the operational DSSC. Absorption changes reporting on the electric field at the TiO2 surface were simultaneously quantified at specific power conditions fo the operational DSSC. Chapter 4 explores alternative redox mediators to the iodide/triiodide couple. The photophysical studies presented herein provide key mechanistic details on kinetic processes pertinent to operational DSSCs. Specifically, electron transfer to and from iodide species found in an operational DSSC were quantified. Taken together this research advances the body of knowledge quantifying the chemical properties that make iodide based electrolytes a superior redox mediator in dye sensitized solar cells.

Rowley, John G.


Fabrication of nanocrystalline aluminum-magnesium alloy powders by electrodeposition and their characterization  

NASA Astrophysics Data System (ADS)

Aluminum-magnesium alloy powders can potentially be used as hydrogen storage materials. In order to enhance the kinetics of hydrogenation it is desirable to have agglomerates of fine powders with very small grain size. In this study, nanocrystalline Al-Mg alloys in the form of powders were successfully fabricated by the electrodeposition technique using an organometallic based electrolyte. Mg was introduced into the electrolyte by a process called "pre-electrodeposition". The mechanism for Mg accumulation can be explained considering the electrode reactions as well as the chemical changes in the electrolyte. Using a copper cathode, the effects of the electrolyte composition and current density on composition of the deposit, its constituent phases and morphology were investigated. The magnesium content of the deposits improved with increasing Mg concentration in the electrolyte, temperature and current density. Depending on the composition, the deposits consisted of FCC-Al(Mg) and HCP-Mg(Al) phases and no intermetallic phase was found except for long deposition times. Generally, the deposits formed initially on the copper substrate with three dendritic morphologies namely, rod-like, feather-like and small globular, which eventually evolved into the large globular morphology. This observation is attributed to the establishment of spherical diffusion conditions at the sharp dendrite tips. Potentiostatic studies suggested that the appearance of different morphologies is associated with differing rates of deposition. While the initial dendrites consisted of the FCC Al-rich phase, the large globular morphology manifested as both FCC Al-rich and HCP Mg-rich phases, with the latter always forming over the former. The observation of formation of only the FCC phase implies that the nucleation barrier for the HCP phase on the copper substrate is quite high. The investigation of the effect of substrate, namely, Cu, graphite and Mg, revealed that the HCP phase can directly nucleate on an oxide-free Mg surface. This finding can be explained in terms of surface/interfacial energies. Detailed TEM analysis revealed that the observed morphologies consist of randomly distributed nanocrystalline grains except for the feather-like dendrites, which exhibited a strong crystallographic texture.

Tatiparti, Sankara Sarma V.


Reduction of Metal Oxide to Metal using Ionic Liquids  

SciTech Connect

A novel pathway for the high efficiency production of metal from metal oxide means of electrolysis in ionic liquids at low temperature was investigated. The main emphasis was to eliminate the use of carbon and high temperature application in the reduction of metal oxides to metals. The emphasis of this research was to produce metals such as Zn, and Pb that are normally produced by the application of very high temperatures. The reduction of zinc oxide to zinc and lead oxide to lead were investigated. This study involved three steps in accomplishing the final goal of reduction of metal oxide to metal using ionic liquids: 1) Dissolution of metal oxide in an ionic liquid, 2) Determination of reduction potential using cyclic voltammetry (CV) and 3) Reduction of the dissolved metal oxide. Ionic liquids provide additional advantage by offering a wide potential range for the deposition. In each and every step of the process, more than one process variable has been examined. Experimental results for electrochemical extraction of Zn from ZnO and Pb from PbO using eutectic mixtures of Urea ((NH2)2CO) and Choline chloride (HOC2H4N(CH3)3+Cl-) or (ChCl) in a molar ratio 2:1, varying voltage and temperatures were carried out. Fourier Transform Infra-Red (FTIR) spectroscopy studies of ionic liquids with and without metal oxide additions were conducted. FTIR and induction coupled plasma spectroscopy (ICPS) was used in the characterization of the metal oxide dissolved ionic liquid. Electrochemical experiments were conducted using EG&G potentiostat/galvanostat with three electrode cell systems. Cyclic voltammetry was used in the determination of reduction potentials for the deposition of metals. Chronoamperometric experiments were carried out in the potential range of -0.6V to -1.9V for lead and -1.4V to -1.9V for zinc. The deposits were characterized using XRD and SEM-EDS for phase, morphological and elemental analysis. The results showed that pure metal was deposited on the cathode. Successful extraction of metal from metal oxide dissolved in Urea/ChCl (2:1) was accomplished. The current efficiencies were relatively high in both the metal deposition processes with current efficiency greater than 86% for lead and 95% for zinc. This technology will advance the metal oxide reduction process by increasing the process efficiency and also eliminate the production of CO2 which makes this an environmentally benign technology for metal extraction.

Dr. Ramana Reddy



Mechanistic, kinetic, and processing aspects of tungsten chemical mechanical polishing  

NASA Astrophysics Data System (ADS)

This dissertation presents an investigation into tungsten chemical mechanical polishing (CMP). CMP is the industrially predominant unit operation that removes excess tungsten after non-selective chemical vapor deposition (CVD) during sub-micron integrated circuit (IC) manufacture. This work explores the CMP process from process engineering and fundamental mechanistic perspectives. The process engineering study optimized an existing CMP process to address issues of polish pad and wafer carrier life. Polish rates, post-CMP metrology of patterned wafers, electrical test data, and synergy with a thermal endpoint technique were used to determine the optimal process. The oxidation rate of tungsten during CMP is significantly lower than the removal rate under identical conditions. Tungsten polished without inhibition during cathodic potentiostatic control. Hertzian indenter model calculations preclude colloids of the size used in tungsten CMP slurries from indenting the tungsten surface. AFM surface topography maps and TEM images of post-CMP tungsten do not show evidence of plow marks or intergranular fracture. Polish rate is dependent on potassium iodate concentration; process temperature is not. The colloid species significantly affects the polish rate and process temperature. Process temperature is not a predictor of polish rate. A process energy balance indicates that the process temperature is predominantly due to shaft work, and that any heat of reaction evolved during the CMP process is negligible. Friction and adhesion between alumina and tungsten were studied using modified AFM techniques. Friction was constant with potassium iodate concentration, but varied with applied pressure. This corroborates the results from the energy balance. Adhesion between the alumina and the tungsten was proportional to the potassium iodate concentration. A heuristic mechanism, which captures the relationship between polish rate, pressure, velocity, and slurry chemistry, is presented. In this mechanism, the colloid reacts with the chemistry of the slurry to produce active sites. These active sites become inactive by removing tungsten from the film. The process repeats when then inactive sites are reconverted to active sites. It is shown that the empirical form of the heuristic mechanism fits all of the data obtained. The mechanism also agrees with the limiting cases that were investigated.

Stein, David


Fretting corrosion of CoCrMo and Ti6Al4V interfaces.  


Mechanically assisted corrosion (fretting corrosion, tribocorrosion etc.,) of metallic biomaterials is a primary concern for numerous implant applications, particularly in the performance of highly-loaded medical devices. While the basic underlying concepts of fretting corrosion or tribocorrosion and fretting crevice corrosion are well known, there remains a need to develop an integrated systematic method for the analysis of fretting corrosion involving metal-on-metal contacts. Such a method can provide detailed and quantitative information on the processes present and explore variations in surfaces, alloys, voltages, loadings, motion and solution conditions. This study reports on development of a fretting corrosion test system and presents elements of an in-depth theoretical fretting corrosion model that incorporates both the mechanical and the electrochemical aspects of fretting corrosion. To demonstrate the capabilities of the new system and validate the proposed model, experiments were performed to understand the effect of applied normal load on fretting corrosion performance of Ti6Al4V/Ti6Al4V, CoCrMo/Ti6Al4V, and CoCrMo/CoCrMo material couples under potentiostatic conditions with a fixed starting surface roughness. The results of this study show that fretting corrosion is affected by material couples, normal load and the motion conditions at the interface. In particular, fretting currents and coefficient of friction (COF)vary with load and are higher for Ti6Al4V/Ti6Al4V couple reaching 3mA/cm(2) and 0.63 at about 73MPanominal contact stress, respectively. Ti6Al4V coupled with CoCrMo displayed lower currents (0.6mA/cm(2)) and COF (0.3), and the fretting corrosion behavior was comparable to CoCrMo/CoCrMo couple (1.2mA/cm(2) and 0.3, respectively). Information on the mechanical energy dissipated at the interface, the sticking behavior, and the load dependence of the inter-asperity distance calculated using the model elucidated the influence of mechanical factors on the experimental results. It was observed that the lowest amount of work was required to generate some of the highest fretting corrosion currents in Ti6Al4V/Ti6Al4V couples compared to the other combinations. The elements of the model presented here provide an excellent basis to explain many of the observed behaviors of these interfaces. PMID:22575833

Swaminathan, Viswanathan; Gilbert, Jeremy L



Direct electrochemical oxidation of ammonia on graphite as a treatment option for stored source-separated urine.  


Electrolysis can be a viable technology for ammonia removal from source-separated urine. Compared to biological nitrogen removal, electrolysis is more robust and is highly amenable to automation, which makes it especially attractive for on-site reactors. In electrolytic wastewater treatment, ammonia is usually removed by indirect oxidation through active chlorine which is produced in-situ at elevated anode potentials. However, the evolution of chlorine can lead to the formation of chlorate, perchlorate, chlorinated organic by-products and chloramines that are toxic. This study focuses on using direct ammonia oxidation on graphite at low anode potentials in order to overcome the formation of toxic by-products. With the aid of cyclic voltammetry, we demonstrated that graphite is active for direct ammonia oxidation without concomitant chlorine formation if the anode potential is between 1.1 and 1.6V vs. SHE (standard hydrogen electrode). A comparison of potentiostatic bulk electrolysis experiments in synthetic stored urine with and without chloride confirmed that ammonia was removed exclusively by continuous direct oxidation. Direct oxidation required high pH values (pH>9) because free ammonia was the actual reactant. In real stored urine (pH=9.0), an ammonia removal rate of 2.90.3gNm(-2)d(-1) was achieved and the specific energy demand was 42WhgN(-1) at an anode potential of 1.31V vs. SHE. The measurements of chlorate and perchlorate as well as selected chlorinated organic by-products confirmed that no chlorinated by-products were formed in real urine. Electrode corrosion through graphite exfoliation was prevented and the surface was not poisoned by intermediate oxidation products. We conclude that direct ammonia oxidation on graphite electrodes is a treatment option for source-separated urine with three major advantages: The formation of chlorinated by-products is prevented, less energy is consumed than in indirect ammonia oxidation and readily available and cheap graphite can be used as the electrode material. PMID:25497427

Zllig, Hanspeter; Fritzsche, Cristina; Morgenroth, Eberhard; Udert, Kai M



Effect of doping (C or N) and co-doping (C+N) on the photoactive properties of magnetron sputtered titania coatings for the application of solar water-splitting.  


The photocatalytic splitting of water into hydrogen and oxygen using a photoelectrochemical (PEC) cell containing titanium dioxide (TiO2) photoanode is a potentially renewable source of chemical fuels. However, the size of the band gap (-3.2 eV) of the TiO2 photocatalyst leads to its relatively low photoactivity toward visible light in a PEC cell. The development of materials with smaller band gaps of approximately 2.4 eV is therefore necessary to operate PEC cells efficiently. This study investigates the effect of dopant (C or N) and co-dopant (C+N) on the physical, structural and photoactivity of TiO2 nano thick coating. TiO2 nano-thick coatings were deposited using a closed field DC reactive magnetron sputtering technique, from titanium target in argon plasma with trace addition of oxygen. In order to study the influence of doping such as C, N and C+N inclusions in the TiO2 coatings, trace levels of CO2 or N2 or CO2+N2 gas were introduced into the deposition chamber respectively. The properties of the deposited nano-coatings were determined using Spectroscopic Ellipsometry, SEM, AFM, Optical profilometry, XPS, Raman, X-ray diffraction UV-Vis spectroscopy and tri-electrode potentiostat measurements. Coating growth rate, structure, surface morphology and roughness were found to be significantly influenced by the types and amount of doping. Substitutional type of doping in all doped sample were confirmed by XPS. UV-vis measurement confirmed that doping (especially for C doped sample) facilitate photoactivity of sputtered deposited titania coating toward visible light by reducing bandgap. The photocurrent density (indirect indication of water splitting performance) of the C-doped photoanode was approximately 26% higher in comparison with un-doped photoanode. However, coating doped with nitrogen (N or N+C) does not exhibit good performance in the photoelectrochemical cell due to their higher charge recombination properties. PMID:22905523

Rahman, M; Dang, B H Q; McDonnell, K; MacElroy, J M D; Dowling, D P



Compact autonomous voltammetric sensor for sulfide monitoring in deep sea vent habitats  

NASA Astrophysics Data System (ADS)

In situ chemical monitoring at deep-sea hydrothermal vents remains a challenge. Particularly, tools are still scarce for assessing the ranges and temporal variability of sulfide in these harsh environmental conditions. There is a particular need for compact and relatively simple devices to enlarge the capacity of in situ measurements of this major energy source in chemosynthetic ecosystems. With this objective, a voltammetric sensor based on a bare-silver working electrode was developed and tested in real conditions. In the laboratory, the sensor presented a linear response from 10 to 1000 ?M sulfide, together with a low pH sensitivity and moderate temperature dependence. The device was operated at 850 and 2500 m depth during 3 cruises over two different vent fields. The autonomous potentiostat (290 mm length, ? 35 mm) equipped with laboratory-made electrodes was mounted on a wand, for manipulation from a submersible, or on a holder for unattended deployments. The system was applied in mussel, tubeworm and annelid worm habitats, characterized by different ranges of sulfide concentration, pH and temperature. Calibrations performed before and after each deployment confirmed the stability of the sensor response over a few hours to 11 days, with a maximum drift of 11.4% during this period. Short-term measurements in the vicinity of Riftia pachyptila and Alvinella pompejana were consistent with previous results on these habitats, with concentrations ranging from 20 to 140 ?M and 100 to 450 ?M and sulfide versus temperature ratio of 14 ?M C-1 and 20 ?M C-1, respectively. A continuous 4-day record on a bed of Bathymodiolus Thermophilus mussels furthermore illustrated the capacity of the sensor to capture fluctuating sulfide concentration between 0 and 70 ?M, in combination to temperature, and to investigate the changes in the sulfide versus temperature ratio over time. The method has a higher detection limit (<10 ?M) than previous in situ sulfide measurement methods, but has the advantage of selectivity to free sulfide (compared to colorimetry), low pH sensitivity (compared to amperometry) and lower reconditioning requirement for electrode surface (with respect to gold-amalgam voltammetry). This sensor is therefore a valuable complementary tool for discrete and continuous measurements within the moderate temperature environment of fauna at deep-sea vents.

Contreira-Pereira, Leonardo; Ycel, Mustafa; Omanovic, Dario; Brulport, Jean-Pierre; Le Bris, Nadine



Utilization of natural and supplemental biofuels for harvesting energy from marine sediments  

NASA Astrophysics Data System (ADS)

A benthic microbial fuel cell (BMFC) is an electrochemical device that generates current from the redox gradient at the sediment-water interface. Early prototypes had anodes buried in anoxic sediments and cathodes in overlying water. The BMFCs described in this dissertation are based on a chamber design that enables the use of high surface-area fiber electrodes and facilitates enhanced mass transport to the anode. Results from Yaquina Bay, OR, show that mass transport resistance accounted for at least 93% of the total internal resistance for a particular BMFC configuration. Power output was increased 18-fold by mechanically induced fluid transport through the anode chamber. At a cold seep in Monterey Canyon, CA, naturally driven advection resulted in a five-fold increase in power from a BMFC with low-pressure check valves relative to an identical BMFC with high-pressure check valves. Enhanced transport coincided with a change in the microbial community on the anode from one dominated by epsilonproteobacteria to one with relatively even representation from deltaproteobacteria, epsilonproteobacteria, firmicutes and flavobacterium/cytophaga/bacterioides. Laboratory experiments investigated the effect of adding supplemental carbon sources to anode chambers. Repeated lactate injections appeared to stimulate sulfate reduction resulting in short term power gains but did not apparently shift the process responsible for baseline current. When a specific inhibitor of sulfate reduction was added, lactate-supplemented and unsupplemented BMFCs performed similarly. BMFCs have been proposed as power sources for monitoring systems in remote locations. Practical implementation of this technology is governed by three conditions: (1) low-voltage current must be stepped up to meet the requirements of off-the-shelf electronic devices, (2) modest power production and variable power demands require integrated energy storage, and (3) BMFCs should be operated at the most efficient potential for energy production. A combination power converter/potentiostat/rechargeable battery system was described based on these considerations and tested with a chambered BMFC in Yaquina Bay, OR. The BMFC provided intermittent power to an acoustic receiver, and results highlight the need to increase power, make design improvements to better seal the chamber to the sediment and increase the capacity for energy storage.

Nielsen, Mark E.


Ultrasensitive electrochemical biomolecular detection using nanostructured microelectrodes.  


Electrochemical sensors have the potential to achieve sensitive, specific, and low-cost detection of biomolecules--a capability that is ever more relevant to the diagnosis and monitored treatment of disease. The development of devices for clinical diagnostics based on electrochemical detection could provide a powerful solution for the routine use of biomarkers in patient treatment and monitoring and may overcome the many issues created by current methods, including the long sample-to-answer times, high cost, and limited prospects for lab-free use of traditional polymerase chain reaction, microarrays, and gene-sequencing technologies. In this Account, we summarize the advances in electrochemical biomolecular detection, focusing on a new and integrated platform that exploits the bottom-up fabrication of multiplexed electrochemical sensors composed of electrodeposited noble metals. We trace the evolution of these sensors from gold nanoelectrode ensembles to nanostructured microelectrodes (NMEs) and discuss the effects of surface morphology and size on assay performance. The development of a novel electrocatalytic assay based on Ru(3+) adsorption and Fe(3+) amplification at the electrode surface as a means to enable ultrasensitive analyte detection is discussed. Electrochemical measurements of changes in hybridization events at the electrode surface are performed using a simple potentiostat, which enables integration into a portable, cost-effective device. We summarize the strategies for proximal sample processing and detection in addition to those that enable high degrees of sensor multiplexing capable of measuring 100 different analytes on a single chip. By evaluating the cost and performance of various sensor substrates, we explore the development of practical lab-on-a-chip prototype devices. By functionalizing the NMEs with capture probes specific to nucleic acid, small molecule, and protein targets, we can successfully detect a wide variety of analytes at clinically relevant concentrations and speeds. Using this platform, we have achieved attomolar detection levels of nucleic acids with overall assay times as short as 2 min. We also describe the adaptation of the sensing platform to allow for the measurement of uncharged analytes--a challenge for reporter systems that rely on the charge of an analyte. Furthermore, the capabilities of this system have been applied to address the many current and important clinical challenges involving the detection of pathogenic species, including both bacterial and viral infections and cancer biomarkers. This novel electrochemical platform, which achieves large molecular-to-electrical amplification by means of its unique redox-cycling readout strategy combined with rapid and efficient analyte capture that is aided by nanostructured microelectrodes, achieves excellent specificity and sensitivity in clinical samples in which analytes are present at low concentrations in complex matrices. PMID:24961296

Sage, Andrew T; Besant, Justin D; Lam, Brian; Sargent, Edward H; Kelley, Shana O



Microfluidic cells with interdigitated array gold electrodes: Fabrication and electrochemical characterization.  


Microfluidic flow cells combined with an interdigitated array (IDA) electrode and/or individually driven interdigitated electrodes were fabricated and characterized for application as detectors for flow injection analysis. The gold electrodes were produced by a process involving heat transfer of a toner mask onto the gold surface of a CD-R and etching of the toner-free gold region by short exposure to iodine-iodide solution. The arrays of electrodes with individual area of 0.01cm(2) (0.10cm of lengthx0.10cm of width and separated by gaps of 0.05 or 0.03cm) were assembled in microfluidic flow cells with 13 or 19mum channel depth. The electrochemical characterization of the cells was made by voltammetry under stationary conditions and the influence of experimental parameters related to geometry of the channels and electrodes were studied by using K(4)Fe(CN)(6) as model system. The obtained results for peaks currents (I(p)) are in excellent agreement with the expected ones for a reversible redox system under stationary thin-layer conditions. Two different configurations of the working electrodes, E(i), auxiliary electrode, A, and reference electrode, R, on the chip were examined: E(i)/R/A and R/E(i)/A, with the first presenting certain uncompensated resistance. This is because the potentiostat actively compensates the iR drop occurring in the electrolyte thin layer between A and R, but not from R to each E(i). This is confirmed by the smaller difference between the cathodic and anodic peak potentials for the second configuration. Evaluation of the microfluidic flow cells combined with (individually driven) interdigitated array electrodes as biamperometric or amperometric detectors for FIA reveals stable and reproducible operation, with peak heights presenting relative standard deviations of less than 2.2%. For electrochemically reversible species, FIA peaks with enhanced current signal were obtained due to redox cycling under flow operation. The versatility of microfluidic flow cells, produced by simple and low-cost technique, associated with the rich information content of electrochemical techniques with arrays of electrodes, opens many future research and application opportunities. PMID:18970340

Daniel, Daniela; Gutz, Ivano G R



Predictive Framework and Experimental Tests of the Kinetic Isotope Effect at Redox-Active Interfaces  

NASA Astrophysics Data System (ADS)

Electrochemical reactions provide a compelling framework to study kinetic isotope effects because redox-related processes are important for a wide variety of geological and environmental processes. In the laboratory, electrochemical reaction rates can be electronically controlled and measured in the laboratory using a potentiostat. This enables variation of redox reactions rates independent of changes in chemistry and, and the resulting isotope compositions of reactants and products can be separated and analyzed. In the past years, a series of experimental studies have demonstrated a large, light, and tunable kinetic isotope effect during electrodeposition of metal Fe, Zn, Li, Cu, and Mo from a variety of solutions (e.g. Black et al., 2009, 2010, 2011). A theoretical framework based on Marcus kinetic theory predicts a voltage-dependent kinetic isotope effect (Kavner et al., 2005, 2008), however while this framework was able to predict the tunable nature of the effect, it was not able to simultaneously predict absolute reaction rates and relative isotope rates. Here we present a more complete development of a statistical mechanical framework for simple interfacial redox reactions, which includes isotopic behavior. The framework is able to predict a kinetic isotope effect as a function of temperature and reaction rate, starting with three input parameters: a single reorganization energy which describes the overall kinetics of the electron transfer reaction, and the equilibrium reduced partition function ratios for heavy and light isotopes in the product and reactant phases. We show the framework, elucidate some of the predictions, and show direct comparisons against isotope fractionation data obtained during laboratory and natural environment redox processes. A. Kavner, A. Shahar, F. Bonet, J. Simon and E. Young (2005) Geochim. Cosmochim. Acta, 69(12), 2971-2979. A. Kavner, S. G. John, S. Sass, and E. A. Boyle (2008), Geochim. Cosmochim. Acta, vol 72, pp. 1731-1741. J. R. Black, Umeda, G., Dunn, B., McDonough, W. F. and A. Kavner. (2009), J. Amer. Chem. Soc., vol. 131, No.29 2009 pp. 9904-9905 DOI: 10.1021/ja903926x. J. R. Black, S. John, E.D. Young, and A. Kavner, (2010), Geochim. Cosmochim. Acta, vol 74 (18) pp. 5187-5201. J. R. Black, J. Crawford, S. John, and A. Kavner, (2011) Redox-driven stable isotope fractionation, in Aquatic Redox Chemistry ACS Symposium Series, Vol. 1071. Tratnyek, P.G., T. J. Grundl, and S. B. Haderlein, eds. Chapter 16, pp 345-359

Kavner, A.; John, S.; Black, J. R.



Direct Electrolytic Deposition of Mats of Mn(x)O(y) Nanowires  

NASA Technical Reports Server (NTRS)

Mats of free-standing manganese oxide (MnxOy) nanowires have been fabricated as experimental electrode materials for rechargeable electrochemical power cells and capacitors. Because they are free-standing, the wires in these mats are electrochemically accessible. The advantage of the mat-of-nanowires configuration, relative to other configurations of electrode materials, arises from the combination of narrowness and high areal number density of the wires. This combination offers both high surface areas for contact with electrolytes and short paths for diffusion of ions into and out of the electrodes, thereby making it possible to charge and discharge at rates higher than would otherwise be possible and, consequently, to achieve greater power densities. The nanowires are fabricated in an electrolytic process in which there is no need for an electrode binder material. Moreover, there is no need to incorporate an electrically conductive additive into the electrode material; the only electrically conductive material that must be added is a thin substrate contact film at the anchored ends of the nanowires. Hence, the mass fraction of active electrode material is close to 100 percent, as compared with about 85 percent in conventional electrodes made from a slurry of active electrode material, binder, and conductive additive pressed onto a metal foil. The locations and sizes of the nanowires are defined by holes in templates in the form of commercially available porous alumina membranes. In experiments to demonstrate the present process, alumina membranes of various pore sizes and degrees of porosity were used. First, a film of Au was sputtered onto one side of each membrane. The membranes were then attached, variously, to carbon tape or a gold substrate by use of silver or carbon paste. Once thus attached, the membranes were immersed in a plating solution comprising 0.01 M MnSO4 + 0.03 M (NH4)2SO4. The pH of the solution was kept constant at 8 by addition of H2SO4 or NH4OH as needed. Mn(x)O(y) nanowires were potentiostatically electrodeposited in the pores in the alumina templates. Depending on the anodic deposition potentials, Mn(x)O(y) was deposited in various oxidation states [divalent (Mn3O4), trivalent (Mn2O3), or tetravalent (MnO2)]. The Mn(x)O(y) wires were made free-standing (see figure) by dissolving the alumina templates, variously, in KOH or NaOH at a concentration of 20 volume percent.

Myung, Nosang; West, William; Whitacre, Jay; Bugga, Ratnakumar



Role of synergy between wear and corrosion in degradation of materials  

NASA Astrophysics Data System (ADS)

Tribocorrosion is a term used to describe the material degradation due to the combination of electrochemical and tribological processes. Due to a synergetic effect, the material loss can be larger than the sum of the losses due to wear and corrosion acting separately. In this thesis, the synergy of wear and corrosion was investigated for different types of material, namely the Ti-6Al-4V alloy, the SS316L stainless steel coated with a thin film of Diamond Like Carbon (DLC), and the SS301 stainless steel coated with a thin film of chromium silicon nitride (CrSiN). A tribocorrosion apparatus was designed and constructed to conduct wear experiments in corrosive media. Sliding ball-on-plate configuration was used in this design, where the contact between the ball and the specimen is totally immersed in the test electrolyte. The specimen was connected to a potentiostat to control its electrochemical parameters, namely the potential and the current. Electrochemical techniques were used to control the kinetics of corrosion reactions, and therefore it was possible to assess separately the role of corrosion and wear in the total degradation of material, and to evaluate the synergy between them. For Ti-6Al-4V, it was found that the corrosion and tribocorrosion depend strongly on the structure of the material. The alpha-equiaxed microstructure with fine dispersed beta-phase exhibited the best corrosion resistance. The corrosion resistance was found to decrease when the basal plane was preferentially aligned parallel to the surface, which is attributed to a low resistance to charge transfer in the oxide films formed on this plane. On the other hand, when wear and corrosion were involved simultaneously, the oxide layer protecting the substrate against dissolution was mechanically destroyed leading to a high corrosion rate. It was found that the hardness was the most important factor determining the tribocorrosion behavior of the Ti-6Al-4V alloy; samples with high hardness exhibited less mechanical wear, less wear-enhanced corrosion, and less corrosion-enhanced wear. For DLC coatings, it was found that interface engineering plays a crucial role in the tribocorrosion behavior of DLC films. DLC films with nitrided interface layer (SSN3hDLC) were shown to have very poor tribocorrosion resistance; the DLC film delaminated from the substrate after 50 cycles of sliding wear at 9 N load in Ringer's solution. It should be mentioned that a previous study performed at Ecole Polytechnique de Montreal [4] has shown that the same coating resisted 1800 cycles of dry wear at 22 N without delamination. This demonstrates clearly the effect of corrosion on the wear resistance of DLC films. The use of a-SiN:H bond layer between the SS316L substrate and the DLC film improved significantly the tribocorrosion behavior of the coating. This layer acts as a barrier against corrosion reaction; the polarization resistance was 5.76 GO.cm2 compared to 27.5 MO.cm2 and 1.81 MO.cm2 for the DLC-coated SS316L with nitrided interface layer and the bare substrate, respectively. For CrSiN coatings, it was also shown that nitriding treatment of the substrate prior to deposition reduces significantly the tribocorosion resistance of the CrSiN-coated SS301 substrates. This is attributed to the peculiar morphology of the nitrided surface prior to deposition. The high relives at the grain boundaries of the substrate may be the reason for the generation, during sliding wear, of defects in the film, which makes the infiltration of the liquid easier, and consequently leads to the destruction of the CrSiN film.

Azzi, Marwan


Electrochemical response of a biofilm community to changes in electron-acceptor redox potential elucidated using microbial fuel cells  

NASA Astrophysics Data System (ADS)

Currently, we have limited insight into how mineral properties affect dissimilatory metal-reducing bacteria (DMRB) or the microbial communities that contain them. Advances in our understanding of DMRB metabolism have been achieved using microbial fuel cells (MFCs), which exploit the ability of these organisms to transfer electrons extracellularly. By replacing the mineral electron acceptor with a conductive electrode under potentiostat control, the activity of microorganisms capable of interfacial electron transfer can be quantified by the current flowing through the electrode and related to the thermodynamics of respiration. We seek to understand how communities and their individual members respond to changes in mineralogy, and expect mineral redox potential to be a primary control. The ability to precisely control the redox potential of the electron-accepting anodic electrode is our primary motivation for using MFCs. We inoculated duplicate MFCs containing 10 mM acetate in phosphate buffered media with a slurry of subsurface sediment and groundwater obtained from the Integrated Field-Scale Research Challenge Site at Rifle, CO. Electroactive biofilms were established on graphite anodes poised at a favorable potential (0.0 V vs. SHE) before poising at -0.2 Va potential representative of natural iron reduction. The current was stable across both anodes over more than 100 days of operation, and the percentage of the electrons in acetate recovered as current ("Coulombic efficiency") was typically 70 to >90%. Current density reached 0.4 A/m2 at -0.2 V, to a max of over 1.0 A/m2 at or above ~0.0 V (based on geometric electrode surface area). Media exchanges and biofilm cyclic voltammetry (CV) experiments indicate that electrode-attached microbial communities were responsible for primary electron transfer. Cryo-electron and confocal fluorescence microscopies of the biofilm reveal numerous morphologies of viable microorganisms that are currently being characterized using 16S rRNA gene clone library analysis. We studied how the microbial activity changed when the anode potential was varied. Altering the anode potential caused reversible changes in the mid-point potential(s), Em, measured using CV. Qualitatively, the average Em always shifted toward the set anode potential. A maximum shift in the peak of the derivative CV spectra of ~100 mV defines the approximate upper and lower Em values for the proteins contributing to this feature. The change in the electrochemical response was complete ~30 minutes after a 400 mV anode-potential step. We attribute these observations to either a switch in the principle electron-transport pathway (different enzymes) that individual species use to deliver electrons to the anode or changes in the relative contributions of different community members, or both. However, some impact of changes in pH within the biofilm could contribute to the change in Em. Ongoing investigations attempt to resolve these possibilities.

Arbour, T.; Wrighton, K. C.; Mullin, S. W.; Luef, B.; Gilbert, B.; Banfield, J. F.



Aligned Titania Nanotube Array Thin Films: Growth Kinetics, Branched Structures, and Photovoltaic Characterization  

NASA Astrophysics Data System (ADS)

Titanium dioxide or titania is an attractive raw materials in many applications such as energy generation, storage and delivery, gas sensing, and water purification. Titania due to its excellent photocatalytic activity, stability, and non-toxic nature helps in the efficient realization of number of applications. There is a great deal of interest to synthesize titania nanostructures by inexpensive methods to reap the photocatalytic activity over large surface areas for enhanced application. Recent developments have lead to huge effort that has been put into titania nanomaterials, which has resulted in a rich knowledge for their synthesis, properties and applications. We study and investigate in detail the physical, chemical, electronic, and thermodynamic properties of titania and understand the applications of titania from the point of view of its properties. We emphasize and explore the synthesis of titania nanotubes promising greater surface area and enhanced mass and charge transport. We report the kinetics of titania nanotube length evolution during anodizartion of titanium films. Our results show that the nanotube length increase is thermally activated, and governed by a voltage-dependent activation energy 0.6 eV ? Eef f ? 1.1 eV expressed by Eef f = E 0 -- alphaVanod where alpha is a constant and E0 = 1.6 eV is a voltage-independent term. The proximity of E0 to that of oxygen diffusion in titania suggests that oxygen transport across the titania walls at the pore bottoms is the rate-limiting step. These results provide insights into the mechanism of titania nanotube formation and a framework for their rational synthesis. We further demonstrate synthesis of branched titania nanotube formation during potentiostatic anodization of titanium films or foils in a single electrochemical bath by stepping down the anodization voltage Vanod below a threshold value. The linear dependence on the titanium nanotube diameter with V anod and the lack of nanotube formation for Vanod<20 V constrains homogeneous branching to occur only V2 ? V12 -- V0, where V1 and V 2 are the initial and final anodization voltages and V0 is a voltage offset dependent on the anodization bath chemistry. Our technique circumvents the constraints of multi-bath and multi-temperature methods for branching, and provides a versatile means for creating hierarchically sized and/or interconnected titania nanotubes for applications. Pore microstructure and photovoltaic characteristics of dye-sensitized solar cells fabricated from branched titania nanotube arrays are compared with those from unbranched ones. Branched titania nanotubes result in increased efficiency and short circuit density without any discernible increases in dark current, than in devices with unbranched tubes due to increased internal surface area measured by adsorption isotherms. Enhanced photovoltaic and photocatalytic activities in branched titania nanotubes could be attractive for use in photovoltaics, water purification and energy storage applications.

Butail, Gorun


Towards highly efficient water photoelectrolysis  

NASA Astrophysics Data System (ADS)

The motivation for this work was to develop an efficient and relatively inexpensive material architecture suitable for solar water splitting by photoelectrolysis. Iron (III) Oxide (hematite), has bandgap energy ( 2.2 eV) well suited for capturing solar spectrum, is abundant and non-toxic. However, it suffers from recombination losses due to low electron mobility and a minority carrier diffusion length of only 2--4 nm. The primary focus of this dissertation was to synthesize thin walled, self-aligned, vertically oriented nanotubular/nanoporous iron (III) oxide structures through electrochemical oxidation. The underlying hypothesis was that thin walled nanotubes would allow charge separation prior to recombination, resulting in a significant increase in the photoelectrochemical properties. Both aqueous and non-aqueous electrolytes were explored as an electrochemical oxidation solvent. Iron oxide film topologies achieved include nanopillar, nanoporous and nanoplatelet structures from aqueous electrolytes, and nanoporous and nanochannel architectures from non-aqueous electrolytes. This dissertation encompasses the first report on synthesis of nanoporous/nanochannel iron (III) oxide structures through potentiostatic anodization, as well as the use of ethylene glycol for the electrochemical oxidation of both iron and titanium. Through control of anodization parameters, including potential and anodization bath composition, excellent control over the morphology and dimensions of the synthesized iron (III) nanostructures have been achieved. As dependent upon the applied potential and electrolytic composition, diameters of the self-aligned nanopores range from 30 nm to 250 nm. The synthesized structures were crystallized in nitrogen ambient to form hematite photoanodes; a maximum photocurrent efficiency of 0.73% was obtained from nanoporous iron (III) oxide synthesized using a glycerol anodization bath. The electrochemical oxidation of titanium in fluoride ion containing ethylene glycol resulted in remarkable growth characteristics of titania nanotube arrays, hexagonal closed packed up to 1 mm in length, with tube aspect ratios of approximately 10,000. For the first time, complete anodization of the starting titanium foil has been demonstrated resulting in back to back nanotube array membranes ranging from 360 mum--1 mm in length. The nanotubes exhibited growth rates of up to 15 mum/hr. A detailed study on the factors affecting the growth rate and nanotube dimensions is presented. It is suggested that faster high field ionic conduction through a thinner barrier layer is responsible for the higher growth rates observed in electrolytes containing ethylene glycol. Methods to fabricate free standing, titania nanotube array membranes ranging in thickness from 50 microm--1000 mum has also been an outcome of this dissertation. In an effort to combine the charge transport properties of titania with the light absorption properties of iron (III) oxide, films comprised of vertically oriented Ti-Fe-O nanotube arrays on FTO coated glass substrates have been successfully synthesized in ethylene glycol electrolytes. Depending upon the Fe content the bandgap of the resulting films varied from about 3.26 to 2.17 eV. The Ti-Fe oxide nanotube array films demonstrated a photocurrent of 2 mA/cm2 under global AM 1.5 illumination with a 1.2% (two-electrode) photoconversion efficiency, demonstrating a sustained, time-energy normalized hydrogen evolution rate by water splitting of 7.1 mL/Whr in a 1 M KOH solution with a platinum counter electrode under an applied bias of 0.7 V. The Ti-Fe-O material architecture demonstrates properties useful for hydrogen generation by water photoelectrolysis and, more importantly, this dissertation demonstrates that the general nanotube-array synthesis technique can be extended to other ternary oxide compositions of interest for water photoelectrolysis.

Elavambedu Prakasam, Haripriya


Structure-composition-property relationships in 5xxx series aluminum alloys  

NASA Astrophysics Data System (ADS)

Al-Mg alloys are well suited for marine applications due to their low density, ease of fabrication, structural durability, and most notably resistance to corrosion. The purpose of this study is to investigate the effects of alloying additions, mechanical processing and heat treatments on the development of grain boundary phases that have an effect on intergranular corrosion (IGC). Cu, Zn, and Si modified compositions of AA5083 were produced that were subjected to a low and high degree of cold work and various heat treatments. ASTM G67 (NAMLT) intergranular corrosion testing and detailed microstructural characterization for various alloys was carried out. An optimal composition and processing condition that yielded the best intergranular corrosion resistant material was identified based on the ASTM G67 test screening. Further, the outstanding modified AA5083 was selected for further microstructural analysis. This particular alloy with has a magnesium level high enough to make it susceptible to intergranular corrosion is very resistant to IGC. It was found that development of the appropriate sub-structure with some Cu, Si and Zn resulted in a material very resistant to IGC. Formation of many sinks, provided by sub-boundaries, within microstructure is very beneficial since it produces a relatively uniform distribution of Mg in the grain interiors, and this can suppress sensitization of this alloy very successfully. This is a very promising rote for the production of high-strength, and corrosion resistant aluminum alloys. Additionally in this study, TEM sample preparation become very crucial step in grain boundary phase investigation. Focus Ion Beam (FIB) milling was used as a primary TEM sample preparation technique because it enables to extract the samples from desired and very specific locations without dissolving grain boundary phases as it was in conventional electropolishing method. However, other issues specifically relevant to FIB milling of aluminum alloys related to Ga accumulation were discovered, that produce significant microstructural artifacts. It is well known that liquid gallium can cause Liquid Metal Embitterment (LME) aluminum alloys, and gallium readily penetrates aluminum grain boundaries. Low energy Ar ion nanomilling is potentially quite effective at removing gallium from the external and internal surfaces of aluminum thin foils, but can still leave persistent artifacts. Al-Mg alloys can be also susceptible to localized corrosion such as pitting corrosion in the presence of chloride ions. In this study the phases responsible for this type of corrosion were identified. ASSET (ASTM G66) test was used to determine the influence of heat-treatment on pitting corrosion on various modified AA5083 alloys. Additionally, potentiodynamic polarization as well as potentiostatic measurements in conjunction with SEM analysis were carried out to obtain pitting potential (Epit) and to determine the location of metastable pit initiation, respectively.

Unocic, Kinga A.


Anode materials for sour natural gas solid oxide fuel cells  

NASA Astrophysics Data System (ADS)

Novel anode catalysts have been developed for sour natural gas solid oxide fuel cell (SOFC) applications. Sour natural gas comprises light hydrocarbons, and typically also contains H2S. An alternative fuel SOFC that operates directly on sour natural gas would reduce the overall cost of plant construction and operation for fuel cell power generation. The anode for such a fuel cell must have good catalytic and electrocatalytic activity for hydrocarbon conversion, sulfur-tolerance, resistance to coking, and good electronic and ionic conductivity. The catalytic activity and stability of ABO3 (A= La, Ce and/or Sr, B=Cr and one or more of Ti, V, Cr, Fe, Mn, or Co) perovskites as SOFC anode materials depends on both A and B, and are modified by substituents. The materials have been prepared by both solid state and wet-chemical methods. The physical and chemical characteristics of the materials have been fully characterized using electron microscopy, XRD, calorimetry, dilatometry, particle size and area, using XPS and TGA-DSC-MS. Electrochemical performance was determined using potentiodynamic and potentiostatic cell testing, electrochemical impedance analysis, and conductivity measurements. Neither Ce0.9Sr0.1VO3 nor Ce0.9 Sr0.1Cr0.5V0.5O3 was an active anode for oxidation of H2 and CH4 fuels. However, active catalysts comprising Ce0:9Sr0:1V(O,S)3 and Ce0.9Sr 0.1Cr0.5V0.5(O,S)3 were formed when small concentrations of H2S were present in the fuels. The oxysulfides formed in-situ were very active for conversion of H2S. The maximum performance improved from 50 mW cm-2 to 85 mW cm -2 in 0.5% H2S/CH4 at 850C with partial substitution of V by Cr in Ce0.9Sr0.1V(O,S)3. Selective conversion of H2S offers potential for sweetening of sour gas without affecting the hydrocarbons. Perovskites La0.75Sr0.25Cr0.5X 0.5O3--delta, (henceforth referred to as LSCX, X=Ti, Mn, Fe, Co) are active for conversion of H2, CH4 and 0.5% H2S/CH4. The order of activity in the different fuels depends on the substituent element: CH4, X = Fe>Mn>Ti; H 2, X = Fe>Mn>Ti; and 0.5% H2S/CH4, X = Fe>Ti>Mn. The electrocatalytic activity for methane oxidation in a fuel cell correlates with ex-situ temperature programmed catalytic activity. A process is proposed to explain the difference in catalyst order and enhanced activities in H 2S/CH4 as fuel compared to CH4 alone. The maximum power density of 250 mW cm-2 was attained using a fuel cell with a composite anode, LSCFe-GDC | YSZ(0.3 mm) | Pt, operated at 850C (GDC is Ce0.9Gd0.1O3, a good mixed conductor under reducing conditions).

Danilovic, Nemanja


Dissolution of PZT 52/48 in aqueous sulfuric acid environments  

NASA Astrophysics Data System (ADS)

With the recent interest for PZT use as a self-powered nanonsensor in extreme environments, such as an oil well, it is important to ensure the stability of the material under these conditions. Oil wells are known for being extremely caustic, with high temperature, low pH and high pressures. It has been shown that in the presence of sulfuric acid PZT is subject to chemical attack. This study attempts to identify the effects that pH and temperature have on the rate of the reaction. Sulfuric acid was used as a proxy for the H2S environment found in oil wells. Exposure of bulk PZT and thin film specimens to H2S was studied. PZT 52/48 thin films were fabricated via the sol gel process. PZT was exposed to both single drops of aqueous sulfuric acid and submerged in a bath of solution. During bath exposure potential on the substrate surface of thin film samples was recorded using a voltmeter vs. and Ag/AgCl reference electrode. Thin Film samples were exposed to a single drop of 0.1 N and 1 N aqueous sulfuric acid solutions at temperatures between 25 C and 92 C. It was optically observed that a white filmed appeared on the surface as a reaction product. At both concentrations, increases in temperature lead to an increase in reaction rate for droplet exposed samples. These reactions were found to follow Arrhenius behavior. The 1 N solution activation energy of film appearance was found to be 69100 J, and for 0.1 N solution was found to be 48300 J. It was expected that an increase in concentration would lead to an increase in reaction rate as well. However for single droplet exposure it was found that lower concentrations resulted in increased reaction rate. This may be due to the difference in interfacial energy between the solution and PZT surface as a result of the concentration of sulfuric acid. The potential on the substrate during bath exposure was between -0.22 V and 0.1 V. As a ferroelectric, PZT is expected to spontaneously polarize and variations in potential are expected. The value of -0.22 V corresponds to the potential of a normal hydrogen electrode, the conditions that would be found if the platinum layer were exposed, which could occur due to pinholes in the sample. The potential on the substrate and time of exposure were not found to correspond to dissolution depth using XPS depth profiling. A proposed reason is that attack was not found to be uniform across the surface, most likely as a result of high energy regions such as pinholes in the PZT film. Using XPS and XRD characterization techniques, PbSO4 was found to be one reaction product of both the PZT bulk sample exposed to a bath of solution, and thin film samples exposed to a single droplet of solution. Other reaction products were not able to be identified using the analysis techniques in this study, because the reaction products of zirconium and titanium are believed to take the form of ions in solution. While XPS confirmed their elemental presence in solution after evaporation, analysis of the solution itself was never conducted. Suggested future work and analytical techniques are also proposed to fully characterize the dissolution kinetics of PZT in aqueous sulfuric acid. These include the characterization of the interfacial energy between solution droplets and PZT surface, potentiostatic bath exposure of thin films in which the potential on the substrate is fixed, solution analysis via ICP-MS or other alternative, and the comparison of dissolution rate between bulk PZT and thin film PZT to determine the effect pinholes may have on the reaction. Various temperatures and acid concentrations are also proposed in order to fully characterize the Arrhenius behavior of reaction rate.

Calebrese, Steven


Modeling the environmental dependence of localized corrosion evolution in AA7075-T651  

NASA Astrophysics Data System (ADS)

In this work, the localized corrosion of AA7075-T651 as a function of environment is empirically modeled using neural network approaches. The modeling approach is divided into three stages: pit initiation, corrosion mode differentiation, and propagation. This study characterized the effect of temperature (0-60C), pH (2.5-12.5), [Cl-] (0.01-0.6M NaCl), electrochemical potential (-780 to -640mVSCE), orientation (LS, ST), time (1-720h), and alloy microstructure on each stage. Examination of metastable pits during potentiostatic testing was employed to study pit initiation, while differentiation and propagation were investigated by extensive observation of corrosion after immersion exposure using optical profilometry and scanning electron microscopy (SEM). Pit initiation rate, lambda, was shown to have an exponential dependence on electrochemical potential, E, a logarithmic dependence on [Cl-], an exponential dependence on temperature, and peaked at intermediate pH. Additionally, lambda scaled with the number density of intermetallic particles. Pitting event intensity (related to the peak current sustained) was also an important parameter in this study. Combining the effects of pit initiation rate and event intensity, [Cl-] and temperature had a profound impact on the total damage incurred (the total charge passed from pitting events). It was established that pit location was determined by the alloy microstructure, while the environment determined the severity of damage. Unlike previous studies that indicate lambda decreases exponentially with time, the pit initiation rate was shown to remain constant with time for most of the conditions studied. A trained neural network model was able to accurately predict lambda as a function of environmental variables. The neural network was able to reflect previously observed trends in this work and in the literature. Pitting was determined to be the main mode of localized attack in this study, since no intergranular corrosion (IGC) was detected. Grain boundary attack (distinguished from IGC by presenting on the exposed face rather than in the cross-section), uniform corrosion, and pits forming at both anodic and cathodic particles were observed. Circumferential pits were shown to occur when the reduction current on cathodic particles was 10 times larger than icorr in a given environment. Solution pH was shown to have a large effect on the corrosion morphology, while temperature and exposure time affected the severity of damage. [Cl-] and orientation had a limited effect on the damage accumulation in this alloy. The number of pit sites after 720h exposure was determined to be 100-200/mm 2 in all environments investigated. Tested neural network models were able to predict, not only the maximum pit depth and diameter as a function of environment, but also entire pit depth and diameter distributions. Pit growth kinetics varied depending on the exposure conditions, but most environments followed t1/3 kinetics, which is within the range reported in the literature.

Cavanaugh, Mary Katherine


Long-term pressure and thermal cycling studies on lithium imide-lithium amide complex hydrides and vanadium-carbon hydrides, and electrochemical hydrogen permeation studies  

NASA Astrophysics Data System (ADS)

Solid-state hydrogen storage is becoming increasingly important for future development of non-polluting vehicular fuels and nuclear technology. Understanding the nature of classical and complex hydrides is of great importance in developing new high gravimetric or volumetric capacity hydrides. Towards the nuclear technology, we have studied vanadium hydrides with lattice impurities for high volumetric capacities and very low pressures. For the vehicular technology, we have studied complex hydrides with emphasis on gaseous impurity effects upon pressure cycling. Another aspect of this work is to understand fundamental hydrogen permeation in materials, for example permeations in steel. In nuclear applications, vanadium hydride has been generally studied at high pressures, but very little work has been done on low pressure hydriding and the effect of impurities. Thermodynamic pressure composition-isotherms and structural studies were performed on V-0.5 at.%C. The addition of carbon did not change the thermodynamics significantly but it had an impact on the decrepitation effects usually observed in metal hydrides. In vehicular applications, high gravimetric capacities are desirable. This study was focused on modern complex hydrides especially Li based imide-amide and binary amide-alanate systems. In this case, the emphasis was on effect of gaseous impurities upon pressure cycling, and other related. These contamination studies are important as candidate materials must have long-term stability under repeated loading of the hydride beds with fresh hydrogen charges. The starting material was Li3N and during hydriding Li2NH (imide) and subsequently, LiNH 2 (amide) phases were formed with a full capacity of 10 wt.% hydrogen. The pressure cycling occurred between the imide and amide phases, yielding 5.6 wt.% reversible hydrogen. The gaseous contamination effects on the amide-imide system were studied using 100 ppm levels of impurity gases such as O 2, H2O, CH4, CO and NH3 mixed with UHP hydrogen. In addition, commercial-grade industrial hydrogen was also used to simulate the hydrogen purchased from a commercial "Hydrogen gas" station. In the case of industrial hydrogen we found a 50% loss (2.6 wt% out of 5.6 wt% H2) after 1100 pressure cycles. Using the more oxygenated 100ppm O2-UHP H2 mixtures we found a capacity loss of 75% (1.4 wt% out of 5.6 wt%) after 560 pressure cycles. Ex-situ x-ray diffraction studies after cycling revealed formation of predominant new Li2O phase along with Li2NH-LiH phases. The addition of H2O, CH4, NH3, and CO showed varying degrees capacity loss. The alanate-imide binary mixed hydridese were also tested for resistance to impurity gases in hydrogen. These samples were obtained from DoE's Metal Hydride Center of Excellence (MHCoE) partner from University of Utah. Thermodynamic measurements were performed by pressure cycling with O2, and thermal aging with CO on the alanate-imide binary mixtures The initial desorption of the material showed 7 wt% hydrogen storage, and subsequent hydriding/dehydriding showed 3 wt.% capacity when using a maximum rehydriding pressure of 10 bar. The final portion of this work focuses on electrochemical hydrogen permeation experiments performed on steels for nuclear repository service at Yucca Mountain, Nevada. Hydrogen embrittlement and hydrogen induced cracking are common modes of failure when steel is exposed to hydrogen. In this, we studied the diffusion properties of hydrogen in both low and medium carbon steel using the electrochemical Devanathan-Stachurski method. The diffusivities and total hydrogen flux created by galvanostatic charging were measured in both standard 0.1 N NaOH electrolyte and in electrolyte simulating well water taken near Yucca Mountain. Potentiodynamic, potentiostatic permeation electrochemical tests, along with structural and elemental characterization was performed.

Lamb, Joshua H.


In situ solid-state NMR spectroscopy of electrochemical cells: batteries, supercapacitors, and fuel cells.  


Electrochemical cells, in the form of batteries (or supercapacitors) and fuel cells, are efficient devices for energy storage and conversion. These devices show considerable promise for use in portable and static devices to power electronics and various modes of transport and to produce and store electricity both locally and on the grid. For example, high power and energy density lithium-ion batteries are being developed for use in hybrid electric vehicles where they improve the efficiency of fuel use and help to reduce greenhouse gas emissions. To gain insight into the chemical reactions involving the multiple components (electrodes, electrolytes, interfaces) in the electrochemical cells and to determine how cells operate and how they fail, researchers ideally should employ techniques that allow real-time characterization of the behavior of the cells under operating conditions. This Account reviews the recent use of in situ solid-state NMR spectroscopy, a technique that probes local structure and dynamics, to study these devices. In situ NMR studies of lithium-ion batteries are performed on the entire battery, by using a coin cell design, a flat sealed plastic bag, or a cylindrical cell. The battery is placed inside the NMR coil, leads are connected to a potentiostat, and the NMR spectra are recorded as a function of state of charge. (7)Li is used for many of these experiments because of its high sensitivity, straightforward spectral interpretation, and relevance to these devices. For example, (7)Li spectroscopy was used to detect intermediates formed during electrochemical cycling such as LixC and LiySiz species in batteries with carbon and silicon anodes, respectively. It was also used to observe and quantify the formation and growth of metallic lithium microstructures, which can cause short circuits and battery failure. This approach can be utilized to identify conditions that promote dendrite formation and whether different electrolytes and additives can help prevent dendrite formation. The in situ method was also applied to monitor (by (11)B NMR) electrochemical double-layer formation in supercapacitors in real time. Though this method is useful, it comes with challenges. The separation of the contributions from the different cell components in the NMR spectra is not trivial because of overlapping resonances. In addition, orientation-dependent NMR interactions, including the spatial- and orientation-dependent bulk magnetic susceptibility (BMS) effects, can lead to resonance broadening. Efforts to understand and mitigate these BMS effects are discussed in this Account. The in situ NMR investigation of fuel cells initially focused on the surface electrochemistry at the electrodes and the electrochemical oxidation of methanol and CO to CO2 on the Pt cathode. On the basis of the (13)C and (195)Pt NMR spectra of the adsorbates and electrodes, CO adsorbed on Pt and other reaction intermediates and complete oxidation products were detected and their mode of binding to the electrodes investigated. Appropriate design and engineering of the NMR hardware has allowed researchers to integrate intact direct methanol fuel cells into NMR probes. Chemical transformations of the circulating methanol could be followed and reaction intermediates could be detected in real time by either (2)H or (13)C NMR spectroscopy. By use of the in situ NMR approach, factors that control fuel cell performance, such as methanol cross over and catalyst performance, were identified. PMID:24041242

Blanc, Frdric; Leskes, Michal; Grey, Clare P



Voltage effects on cells cultured on metallic biomedical implants  

NASA Astrophysics Data System (ADS)

Electrochemical voltage shifts in metallic biomedical implants occur in-vivo due to a number of processes including mechanically assisted corrosion. Surface potential of biomedical implants and excursions from resting open circuit potential (OCP), which is the voltage they attain while in contact with an electrolyte, can significantly change the interfacial properties of the metallic surfaces and alter the behavior of the surrounding cells, compromising the biocompatibility of metallic implants. Voltages can also be controlled to modulate cell function and fate. To date, the details of the physico-chemical phenomena and the role of different biomaterial parameters involved in the interaction between cells and metallic surfaces under cathodic bias have not been fully elucidated. In this work, changes in the interfacial properties of a CoCrMo biomedical alloy (ASTM F-1537) in phosphate-buffered saline (PBS) (pH 7.4) at different voltages was studied. Step polarization impedance spectroscopy technique was used to apply 50 mV voltage steps to samples, and the time-based current transients were recorded. A new equation was derived based on capacitive discharge through a Tafel element and generalized to deal with non-ideal impedance behavior. The new function compared to the KWW-Randles function, better matched the time-transient response. The results also showed a voltage dependent oxide resistance and capacitance behavior. Additionally, the in-vitro effect of static voltages on the behavior of MC3T3-E1 pre-osteoblasts cultured on CoCrMo alloy (ASTM-1537) was studied to determine the range of cell viability and mode of cell death beyond the viable range. Cell viability and morphology, changes in actin cytoskeleton, adhesion complexes and nucleus, and mode of cell death (necrosis, or intrinsic or extrinsic apoptosis) were characterized at different voltages ranging from -1000 to +500 mV (Ag/AgCl). Moreover, electrochemical currents and metal ion concentrations at each voltage were measured and related to the observed responses. Results show that cathodic and anodic voltages outside the voltage viability range (-400 < V < +500) lead to primarily intrinsic apoptotic and necrotic cell death, respectively. Cell death is associated with cathodic current densities of 0.1 uAcm-2 and anodic current densities of 10 uAcm-2. Significant increase in metallic ions (Co, Cr, Ni, Mo) was seen at +500 mV, and -1000 mV (Cr only) compared to open circuit potential. The number and total projected area of adhesion complexes was also lower on the polarized alloy (p < 0.05). These results show that reduction reactions on CoCrMo alloys leads to apoptosis of cells on the surface and may be a relevant mode of cell death for metallic implants in-vivo. . On the other hand, we studied how surface oxide thickness of Ti affects its voltage viability range and cellular response and whether anodic oxidation can serve as a means to extend this range. Cellular behavior (cell viability, cytoskeletal organization, and cellular adhesion) on bare and anodized Ti samples, potentiostatically held at voltages at the cathodic edge of the viability range, were assessed. Surfaces were characterized using contact angle (CA) measurement technique and atomic force microscopy (AFM), and the observed cellular response was related to the changes in the electrochemical properties (electrochemical currents, open circuit potential, and impedance spectra) of the samples. Results show that anodization at a low voltage (9 V) in phosphate buffer saline (PBS) generates a compact surface oxide with comparable surface roughness and energy to the starting native oxide on the bare surface. The anodized surface extends the viability range at 24 hours by about a 100 mV in the cathodic region, and preserved the cytoskeletal integrity and cell adhesion. Broadening of the viability range corresponds to an increase in impedance of the anodized surface at -400 mV(Ag/AgCl) and the resulting low average currents (below 0.1 uAcm-2) at the interface, which diminish the harmful cathodic r

Haerihosseini, Seyed Morteza


An investigation into the doping and crystallinity of anodically fabricated titania nanotube arrays: Towards an efficient material for solar energy applications  

NASA Astrophysics Data System (ADS)

The primary focus of this dissertation was to improve the properties of the anodically fabricated TiO2 nanotube arrays; notably its band gap and crystallinity while retaining its tubular structure unaffected. The underlying hypothesis was that controlling the crystallinity and band gap while retaining the tubular structure will result in an enormous enhancement of the photoconversion capability of the material. To this end, a direct one-step facile approach for the in-situ doping of TiO2 nanotube arrays during their electrochemical fabrication in both aqueous and non-aqueous electrolytes has been investigated. The effect of doping on the morphology, optical and photoelectrochemical properties of the fabricated nanotube arrays is discussed. In an effort to improve the crystallinity of the anodically fabricated TiO2 nanotube arrays while retaining the tubular morphology, novel processing routes have been investigated to fabricate crystalline TiO 2 nanotube array electrodes. For the sake of comparison, the nanotubes were annealed at high temperature using the conventionally used procedure. The samples were found to be stable up to temperatures around 580C, however, higher temperatures resulted in crystallization of the titanium support which disturbed the nanotube architecture, causing it to partially and gradually collapse and densify. The maximum photoconversion efficiency for water splitting using 7 mum-TiO2 nanotube arrays electrodes annealed at 580C was measured to be about 10% under UV illumination. We investigated the effect of subsequent low temperature crystallization step. Rapid infrared (IR) annealing was found to be an efficient technique for crystallizing the nanotube array films within a few minutes. The IR-annealed 7mum-nanotube array films showed significant photoconversion efficiencies (eta=13.13%) upon their use as photoanodes to photoelectrochemically split water under UV illumination. This was related, in part, to the reduction in the barrier layer thickness from 1100 nm for the thermally annealed sample down to 200 nm for the IR-annealed sample under same conditions. These results support the hypothesis that reducing the barrier layer thickness would result in better performance of the material. Regarding the possibility of low temperature crystallization, this dissertation encompasses the first report on low-temperature synthesis of crystalline TiO 2 nanotube arrays. Nanotube arrays of up to 1.4 mum length using a two-step process have been demonstrated. The two-step process consists of initial treatment of the Ti foil in an oxidizing agent (H2O 2 or (NH4)2S2O8)-containing electrolytes, followed by potentiostatic anodization of the resulting foil in NH4F-containing electrolytes. The as-synthesized crystalline nanotube arrays were successfully tested as anode electrodes for water photoelectrolysis, with performances comparable to samples annealed at high temperatures, and for liquid junction dye (N 719 dye)-sensitized solar cells. With the motivation of finding an electrolyte composition that might yield better crystalline nanotubes than that obtained in the HCl-containing electrolytes, the effect of using some polyol electrolytes (diethylene, triethylene, tetraethylene and polyethylene glycols) on the crystallinity and morphology of the fabricated TiO2 nanotube arrays was investigated. The study showed that the use of these electrolytes helped to induce partial crystallinity in the formed nanotube arrays with the intensity of anatase (101) peak was found to increase with increasing the molecular weight of the polyol electrolyte. This thesis reports, for the first time, synthesis of high-aspect-ratio tantalum oxide nanotube arrays via one-step anodization of Ta foil. The use of aqueous electrolytes containing HF:H2SO4 in the volumetric ratios 1:9 and 2:8 results in formation of ordered nanodimpled surfaces with 40-55 nm pore diameters over the potential range 10-20 V. The addition of 5-10% of either ethylene glycol (EG) or dimethyl sulfoxide (DMSO) to the HF and H2SO4 aqueous electrolytes resulted i

Allam Abdel-Motalib, Nageh Khalaf