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1

An Inexpensive Field-Programmable Potentiostat  

NSDL National Science Digital Library

This article describes the practical design and construction of a small, inexpensive programmable potentiostat including a list of the components and circuitry for building a complete self-contained potentiostat - all for approximately $50 in component cost. Explanation is given about the basics and the operational characteristics of this potentiostat, illustrated by running cyclic voltammetric scans of potassium ferricyanide in a 3-electrode cell. The noise, as seen by the small oscillations on the voltammograms, may be lessened by the use of a shielded/grounded case with use of BNC connectors for attaching the electrodes to the potentiostat. Some of the components may no longer be manufactured and may have to substituted with equivalent available parts. Students interested in analytical instrumentation or electrochemistry, including projects involving field-portable electrochemical instrumentation, might also find this potentiostat useful. This is a good example of a practical instrument/ circuit design.

Gopinath, Ashwini Vittal

2

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.

1969-01-01

3

Limitations of potentiostatic control in stress corrosion crack growth measurements  

Microsoft Academic Search

The electrode potential distribution along a crack in a potentiostatically polarized specimen has been derived analytically\\u000a by including polarization behavior and solution conductance considerations. The analysis has been applied to the stress corrosion\\u000a cracks within low alloy steels in an 8M sodium hydroxide solution at 373 K and shows that the electrode potential at the tip\\u000a falls to the normal

P. Doig; P. E. J. Flewitt

1978-01-01

4

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)

1996-05-01

5

A Current-Mode Potentiostat for Multi-Target Detection Tested with Different Lactate Biosensors  

E-print Network

A Current-Mode Potentiostat for Multi-Target Detection Tested with Different Lactate Biosensors S Hz. The circuit was fabricated in 0.18 µm technology and tested for two lactate biosensors fabricated with a commercial lactate oxidase and an engineered one. Chronoamperometry experiments performed with the circuit

De Micheli, Giovanni

6

A low-cost miniaturized potentiostat for point-of-care diagnosis.  

PubMed

This paper presents a novel approach of using a miniaturized potentiostat (M-P) chip (LMP91000) to perform full range cyclic voltammetry (CV) measurements for the detection of biomarkers. The LMP91000 evaluation board was reconfigured to perform three-electrode CV measurements in order to achieve electrochemical cortisol immunosensing. The microelectrodes for cortisol estimation were fabricated by immobilizing monoclonal anti-cortisol antibody (Anti-M-Cab) onto self-assembled monolayer (SAM) modified Au microelectrodes. The results obtained using the M-P were compared to those obtained using a conventional potentiostat. The M-P was successful in measuring cortisol levels in the range of pM. The outcomes of the studies suggest that M-P can effectively perform biochemical measurements on three electrode systems, enabling the development of miniature systems for point-of-care (POC) diagnosis. PMID:25016332

Cruz, Andres Felipe Diaz; Norena, Nicolas; Kaushik, Ajeet; Bhansali, Shekhar

2014-12-15

7

Structural and annealing studies of potentiostatically deposited Cu 2O thin films  

Microsoft Academic Search

Cuprous oxide (Cu2O) thin films were deposited on Cu and tin oxide coated glass substrates through potentiostatic electrodeposition. The optimum range of deposition parameters was experimentally investigated. X-ray diffraction studies revealed the formation of single-phase cubic Cu2O films in the deposition potential range from ?0.355 to ?0.555V versus SCE. Studies revealed that an optimum pH of 9.0 yielded single-phase cubic

T. Mahalingam; J. S. P. Chitra; J. P. Chu; S. Velumani; P. J. Sebastian

2005-01-01

8

Comparison Between Potentiodynamic and Potentiostatic Tests for Pitting Potential Measurement of Duplex Stainless Steels  

Microsoft Academic Search

Potentiodynamic and potentiostatic polarization techniques were used to investigate pitting corrosion of the solution-annealed duplex stainless steels (DSS) UNS S31500 and UNS S32404. Tests were performed in naturally aerated 3.5% sodium chloride (NaCl) aqueous solution at 23 C [+-] 2 C. With the potentiodynamic test, it was only possible to measure the pitting potential (E[sub pit]) of UNS S32404, which

N. Alonso-Falleiros; S. Wolynec; A. Hakim

1999-01-01

9

In-channel amperometric detection for microchip electrophoresis using a wireless isolated potentiostat  

PubMed Central

The combination of microchip electrophoresis (ME) with amperometric detection leads to a number of analytical challenges that are associated with isolating the detector from the high voltages used for the separation. While methods such as end-channel alignment and the use of decouplers have been employed, they have limitations. A less common method has been to utilize an electrically isolated potentiostat. This approach allows placement of the working electrode directly in the separation channel without using a decoupler. This paper explores the use of microchip electrophoresis and electrochemical detection (ME-EC) with an electrically isolated potentiostat for the separation and in-channel detection of several biologically important anions. The separation employed negative polarity voltages and tetradecyltrimethylammonium bromide (TTAB, as a buffer modifier) for the separation of nitrite (NO2-), glutathione (GSH), ascorbic acid (AA), and tyrosine (Tyr). A half-wave potential (E½) shift of approximately negative 500 mV was observed for NO2- and H2O2 standards in the in-channel configuration compared to end channel. Higher separation efficiencies were observed for both NO2- and H2O2 with the in-channel detection configuration. The limits of detection were approximately two-fold lower and the sensitivity was approximately two-fold higher for in-channel detection of nitrite when compared to end-channel. The application of this microfluidic device for the separation and detection of biomarkers related to oxidative stress is described. PMID:21437918

Gunasekara, Dulan B.; Hulvey, Matthew K.; Lunte, Susan M.

2012-01-01

10

CheapStat: An Open-Source, “Do-It-Yourself” Potentiostat for Analytical and Educational Applications  

PubMed Central

Although potentiostats are the foundation of modern electrochemical research, they have seen relatively little application in resource poor settings, such as undergraduate laboratory courses and the developing world. One reason for the low penetration of potentiostats is their cost, as even the least expensive commercially available laboratory potentiostats sell for more than one thousand dollars. An inexpensive electrochemical workstation could thus prove useful in educational labs, and increase access to electrochemistry-based analytical techniques for food, drug and environmental monitoring. With these motivations in mind, we describe here the CheapStat, an inexpensive (<$80), open-source (software and hardware), hand-held potentiostat that can be constructed by anyone who is proficient at assembling circuits. This device supports a number of potential waveforms necessary to perform cyclic, square wave, linear sweep and anodic stripping voltammetry. As we demonstrate, it is suitable for a wide range of applications ranging from food- and drug-quality testing to environmental monitoring, rapid DNA detection, and educational exercises. The device's schematics, parts lists, circuit board layout files, sample experiments, and detailed assembly instructions are available in the supporting information and are released under an open hardware license. PMID:21931613

Rowe, Aaron A.; Bonham, Andrew J.; White, Ryan J.; Zimmer, Michael P.; Yadgar, Ramsin J.; Hobza, Tony M.; Honea, Jim W.; Ben-Yaacov, Ilan; Plaxco, Kevin W.

2011-01-01

11

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

E-print Network

Potentiostatic Start-Up of PEMFCs from Subzero Temperatures Fangming Jiang* and Chao-Yang Wang fuel cell PEMFC from subfreezing temperatures is explored in this work. Taking advantage of hydration. Quick start-up of a proton exchange membrane fuel cell PEMFC engine from subzero temperatures remains

12

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)

2007-07-01

13

The use of a new potentiostat/coulometer in the controlled-potential coulometric determination of plutonium  

SciTech Connect

We evaluated a PAR 273 potentiostat and PAR 279 coulometer using iron as a stand-in for plutonium. Over 400 tuns consisting of electrical checks, blanks, and iron solutions were made. Manual operation of the instrumentation produced precisions better than 0.1%. Computer control of the instrumentation produced precisions better than 0.1%. Computer control of the instrumentation using a PC and a program written in QuickBASIC produced precisions of about 0.12%. The computer program automatically set up and controlled the instrumentation and recorded the data. The potentionstat`s current autoranging function caused erractic coulometer results. Use of the PAR 273`s low-pass filter (LPF) removed the amperometric end-point current noise, but it also biased the current. The PAR 273A`s LPF filtered the noise without introducing a bias. The coulometer functions, such as current integration and communication interface, occasionally locked up after a current overrange condition. The occasional procedural error revealed that the potentionstat`s ability to produce >1 A current can ruin the coulometer`s impact circuitry, which is protected up to 0.2 A for current ranges <1 A.

Mendoza, P.G. Jr.; Temer, D.J.; Jackson, D.D.

1993-10-01

14

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

PubMed

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 (5 nA to 1.2 mA) and short conversion time (10 ms) 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 3.06 pg/mL. The measurements obtained in real undiluted urine samples fell within the reference concentration range of 50-550 ng/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

2015-05-15

15

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

2015-02-01

16

Parallel Recording of Neurotransmitters Release from Chromaffin Cells Using a 10 × 10 CMOS IC Potentiostat Array with On-Chip Working Electrodes  

PubMed Central

Neurotransmitter release is modulated by many drugs and molecular manipulations. We present an active CMOS-based electrochemical biosensor array with high throughput capability (100 electrodes) for on-chip amperometric measurement of neurotransmitter release. The high-throughput of the biosensor array will accelerate the data collection needed to determine statistical significance of changes produced under varying conditions, from several weeks to a few hours. The biosensor is designed and fabricated using a combination of CMOS integrated circuit (IC) technology and a photolithography process to incorporate platinum working electrodes on-chip. We demonstrate the operation of an electrode array with integrated high-gain potentiostats and output time-division multiplexing with minimum dead time for readout. The on-chip working electrodes are patterned by conformal deposition of Pt and lift-off photolithography. The conformal deposition method protects the underlying electronic circuits from contact with the electrolyte that covers the electrode array during measurement. The biosensor was validated by simultaneous measurement of amperometric currents from 100 electrodes in response to dopamine injection, which revealed the time course of dopamine diffusion along the surface of the biosensor array. The biosensor simultaneously recorded neurotransmitter release successfully from multiple individual living chromaffin cells. The biosensor was capable of resolving small and fast amperometric spikes reporting release from individual vesicle secretions. We anticipate that this device will accelerate the characterization of the modulation of neurotransmitter secretion from neuronal and endocrine cells by pharmacological and molecular manipulations of the cells. PMID:23084756

Kim, Brian Namghi; Herbst, Adam D.; Kim, Sung June; Minch, Bradley A.; Lindau, Manfred

2012-01-01

17

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

PubMed

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, José A F; de Abreu, Fabiane C; Lunte, Susan M

2015-02-01

18

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

2014-03-01

19

A CMOS Potentiostat for Control of Integrated MEMS Actuators  

E-print Network

Abshire Department of Electrical and Computer Engineering University of Maryland College Park, Maryland Smela Department of Mechanical Engineering University of Maryland College Park, Maryland 20742 Abstract

Maryland at College Park, University of

20

Practical 2P7 To introduce students to using a computer controlled potentiostat for  

E-print Network

and to compare the corrosion current obtained by linear extrapolation of Tafel lines and using the Stern and the corrosion current estimated, by extrapolating the linear Tafel regions to the corrosion potential. B polarisation curves for stainless steel to see different behaviours. 1: Determination of the Tafel constants

Paxton, Anthony T.

21

images/UMDlog Measuring photoactivity with a potentiostat Our experimental setup Preliminary results Time Scales  

E-print Network

results Time Scales Cu2O for water splitting RAA Laboratory Department of Chemical & Biomolecular Engineering Department Insitute for Systems Research University of Maryland March 28, 2012 Support: NSF CBET wire Platinum coiled wire Cu2 O on Cu 1''x1'' Cu 1''x1'' RAA Lab Electrolysis Experimental setup 150 W

Ehrman, Sheryl H.

22

A new type of oxygen analyzer utilizing a potentiostatic coulometric titration technique  

NASA Astrophysics Data System (ADS)

A new type of oxygen analyzer was constructed utilizing the electrochemical oxygen pump: Pt, air/ZrO2 (+ CaO)/Ar + H2 + H20 gas mixture, Pt. Copper, indium, or tin samples were melted in a circulating Ar + H2 gas mixture; the oxygen content was then determined within 3 minutes from the change in the electrical current passing through the oxygen pump. The analytical values were highly consistent and reliable despite the fairly low oxygen concentrations in the samples. Neither standard samples nor the establishment of blank conditions was necessary. This type of oxygen analyzer appears to be useful for determining oxygen concentrations less than 1 wt ppm.

Otsuka, Shinya; Kozuka, Zensaku

1985-12-01

23

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

2007-01-01

24

Achieving high electrode specific capacitance with materials of low mass specific capacitance: Potentiostatically grown thick micro-nanoporous PEDOT films  

Microsoft Academic Search

Electrode materials for supercapacitors are at present commonly evaluated and selected by their mass specific capacitance (CM, Fg?1). However, using only this parameter may be a misleading practice because the electrode capacitance also depends on kinetics, and may not increase simply by increasing material mass. It is therefore important to complement CM by the practically accessible electrode specific capacitance (CE,

Graeme A. Snook; Chuang Peng; Derek J. Fray; George Z. Chen

2007-01-01

25

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

PubMed

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; Gómez, Roberto

2014-07-01

26

Electrochemical modeling of intercalation processes with phase field models  

E-print Network

Intermittent Titration Technique (GITT) and Potentiostatic Intermittent Titration Technique (PITT). We show Intermittent Titration Technique (GITT) and Potentiostatic Intermittent Titration Technique (PITT) methods [15

Ceder, Gerbrand

27

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...

28

Elaboration and characterization of polyaniline films electrodeposited on tin oxides  

Microsoft Academic Search

This paper presents the electrochemical synthesis of polyaniline films on fluorine tin oxide (FTO) and indium tin oxide (ITO) in acidic medium by both potentiodynamic and potentiostatic methods. The use of potentiodynamic deposition showed that conductive polyaniline films were synthesized by the same process than on noble metals and allowed the determination of the electrodeposition potential used for further potentiostatic

C. C. Buron; B. Lakard; A. F. Monnin; V. Moutarlier; S. Lakard

2011-01-01

29

Simultaneous Wireless Electrophysiological and Neurochemical Monitoring  

E-print Network

features a picoampere sensitivity potentiostat with a dynamic range spanning 6 decades from picoamperes into the synapse1 upon arrival of a nerve impulse. These chemical messenger molecules like dopamine, glutamate etc

Cauwenberghs, Gert

30

A photoelectrochemical cell for detecting pollutant-induced effects on the activity of immobilized cyanobacterium Synechococcus sp.  

E-print Network

in a single-compartment photoelectrochemical cell using platinum electrodes in potentiostatic mode were and are generally inhibitors of photosystem II (PSII)-dependent electron flow. However, while the use

Carpentier, Robert

31

SWEPT-POTENTIAL ELECTROCHEMICAL DETECTOR FOR FLOW STREAMS  

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...

32

Effect of electrode configuration and electronic conductivity on current density distribution measurements in PEM fuel cells  

E-print Network

of commercially available gas diffusion layers. Both galvanostatic and potentiostatic discharge modes were employed. Irrespective of the type of gas diffusion layer, when a common electrode was employed, significant performance variations were encountered between...

Natarajan, Dilip; Van Nguyen, Trung

2004-09-03

33

Educator's Reference Guide for Electrochemistry  

NSDL National Science Digital Library

This is a 70 page primer on analytical electrochemistry of interest to faculty, students and practitioners wanting to learn basic concepts and applications of the topic. The material discusses voltammetry, major techniques and minor variations, the potentiostat and electrochemical cells.

34

Analytica Chimica Acta 485 (2003) 263269 Dual amperometric biosensor device for analysis of  

E-print Network

of laccase and tyrosinase for different phenolic compounds. A multichannel potentiostat was used to monitor simultaneously laccase- and tyrosinase-based biosensors, and the data were treated using the partial least

Ferreira, Márcia M. C.

35

The application of small amplitude square root of time potential pulses in electrochemical trace analysis  

E-print Network

PULSE DAC SQRT GENERATOR X-AXIS FUNCTION GE NERATOR SORT Y4XI S EXCITE SIGNAL POTENTIOSTAT 8, SIGNAL PROCESSOR 32 The timing controller performs the basic timing operations, which originate from a 4. 000 MHz crystal oscillator Type 850... Polarography 3. Pulse Polarography 4. Differential Pulse Polarography 5. Derivative Pulse Polarography 6. Dii'ferential Square Root Pulse Polarography 7. Flow Diagram of the Instrument 8. General Timing Diagram 9. Function Generator 10. Potentiostat...

Cranston, Stacy Eugene

1975-01-01

36

Influence of pH on the electrochemical behaviour of a duplex stainless steel in highly concentrated LiBr solutions  

Microsoft Academic Search

The objective is to study the influence of pH on the corrosion and passive behaviour of duplex stainless steels (DSS) using potentiodynamic measurements, potentiostatic tests and electrochemical impedance spectroscopy (EIS).DSS are spontaneously passive in heavy brine LiBr solutions. Under potentiostatic conditions at applied anodic potentials within the passive domain an equivalent circuit with two time constants is the most suitable

V. Guiñón-Pina; A. Igual-Muñoz; J. García-Antón

2011-01-01

37

Electrochemically deposited polypyrrole films and their characterization  

Microsoft Academic Search

Ionically conductive polypyrrole films have been deposited at 295 K from anhydrous acetonitrile, acetonitrile\\/H2O and NaBF4 aqueous solutions onto platinum, mild steel and stainless steel discs, using cyclic voltammetry, potentiostatic and galvanostatic techniques. Cyclic voltammetry of the polymer films has been studied as a function of water content of the acetonitrile solvent, polypyrrole concentration and potential sweep rate. Potentiostatic growth of

J. Tietje-Girault; C. Ponce de León; F. C. Walsh

2007-01-01

38

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.

2013-05-01

39

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

DOEpatents

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)

1981-01-01

40

Corrosion behavior and electrical conductivity of niobium implanted 316L stainless steel used as bipolar plates in polymer electrolyte membrane fuel cells  

Microsoft Academic Search

The corrosion behavior and interfacial contact resistance (ICR) of niobium implanted SS316L used as the bipolar plate in a polymer electrolyte membrane fuel cell (PEMFC) are investigated. The ICR values of the bare and niobium implanted SS316L are measured to evaluate the electrical conductivity. The effects of ion implantation on the corrosion behavior are investigated by potentiodynamic and potentiostatic tests

Kai Feng; Zhuguo Li; Xun Cai; Paul K. Chu

2010-01-01

41

Electrochemical behaviour of titanium in fluoride-containing saliva  

Microsoft Academic Search

The effect of fluoride on the electrochemical behaviour of titanium was studied. Open circuit potentials, breakdown potentials (Eb) and potentiostatic transient currents were measured in synthetic salivas of different compositions. Optical and scanning electron microscopic observations were also made. Results show that the growth rate of Ti oxide layer is affected by fluoride anions and tensile stresses are developed. The

M. Fernández Lorenzo de Mele; M. C. Cortizo

2000-01-01

42

Role of Preparation Method on the Microstructure and Mechanical Properties of PPy/Ni Organic-Inorganic Hybrid Bilayer Coatings on Carbon Steel  

NASA Astrophysics Data System (ADS)

The efficacy of the conducting polymers as coating on a metallic substrate is strongly dependent on the manner how they are applied. Polypyrrole (PPy)/Ni organic-inorganic hybrid coatings were electropolymerized on commercial carbon steel (AISI 1018) by combining potentiostatic and potentiodynamic techniques. In first instance, it was analyzed the electrodeposition of PPy using a constant potential regime and cyclic voltammetry techniques evaluating different synthesis parameters such as deposition time, applied potential, and potential cycles, respectively. Thereafter, it was used a potentiostatic method to obtain PPy/Ni bilayer films. The morphological, mechanical, and adhesion properties of these films depend on the synthesis parameters. The results revealed that polypyrrole films formed by both methods provide a globular-type structure, although coatings produced by cyclic voltammetry are denser and slightly thicker than those produced potentiostatically. Ni (oxide/hydroxide) particles are capable of sealing the pores of globular PPy coatings, thus increasing the hardness of the carbon steel (CS)/PPy/Ni system. As a result of the study, we have seen that PPy/Ni bilayer films are more uniform, compact and enhanced the hardness when the PPy is obtained by cyclic voltammetry than that observed for potentiostatic approach. Specifically, when four potential cycles are used to electropolymerized pyrrole, the more convenience properties in the CS/PPy/Ni arrangement are obtained.

Torres-Huerta, A. M.; Dominguez-Crespo, M. A.; Alanis-Valdelamar, A.; Onofre-Bustamante, E.; Escudero, M. L.; García-Alonso, M. C.; Lois-Correa, J. A.

2015-02-01

43

An assessment of the crack tip potential of ?-titanium alloys during hydrogen environmentally assisted crack propagation based on crack tip and passive surface electrochemical measurements  

Microsoft Academic Search

We have previously proposed a scenario for intergranular hydrogen-assisted crack initiation of metastable ?-titanium alloys exposed to aqueous chloride solution. This scenario requires the loss of potentiostatic control due to ohmic drop in solution such that the crack tip potential falls to a potential where hydrogen production is viable regardless of the applied potential. It is of interest to examine

D. G Kolman; J. R Scully

2000-01-01

44

Evaluation of a diffusion\\/trapping model for hydrogen ingress in high-strength alloys. Annual technical report Sep-Nov 91  

Microsoft Academic Search

A potentiostatic pulse technique was used to study the ingress of hydrogen in titanium (pure and grade 2) in an acetate buffer. Hydrogen ingress did not occur with pure titanium, indicating that the surface oxide is an effective barrier to hydrogen entry. In contrast, the data for Ti grade 2 were shown to fit a model for hydrogen diffusion and

Pound

1991-01-01

45

Critical crevice temperature for high-alloyed stainless steels in chlorinated seawater applications  

SciTech Connect

Eleven high-alloyed stainless steels (SS) were tested for application in chlorinated seawater. Critical crevice temperatures (CCT) were determined using a potentiostatic test method. Results were evaluated in terms of the critical crevice index (CCI) value of the alloys and compared to results of duplicate specimens in other tests.

Steinsmo, U.; Rogne, T.; Drugli, J.M.; Gartland, P.O. [SINTEF Corrosion Center, Trondheim (Norway)

1997-01-01

46

Khillah extract as inhibitor for acid corrosion of SX 316 steel  

Microsoft Academic Search

The inhibitive effect of the extract of khillah (Ammi visnaga) seeds, on the corrosion of SX 316 steel in HCl solution was determined using weight loss measurements as well as potentiostatic technique. It was found that the presence of the extract reduces markedly the corrosion rate of steel in the acid solution. The inhibition efficiency increases as the extract concentration

A. Y. El-Etre

2006-01-01

47

Effects of rare earth metals addition on the resistance to pitting corrosion of super duplex stainless steel – Part 1  

Microsoft Academic Search

To elucidate the effects of rare earth metals addition on the resistance to pitting corrosion of super duplex stainless steel, a metallographic examination, potentiodynamic and potentiostatic polarization tests, a SEM-EDS and a SAM analysis of inclusion, austenite phase and ferrite phase were conducted. The addition of rare earth metals to the base alloy led to the formation of (Mn, Cr,

Soon-Tae Kim; Soon-Hyeok Jeon; In-Sung Lee; Yong-Soo Park

2010-01-01

48

Hydrous Manganese Dioxide Nanowall Arrays Growth and Their Ions Intercalation Electrochemical Properties  

E-print Network

Hydrous Manganese Dioxide Nanowall Arrays Growth and Their Li+ Ions Intercalation Electrochemical, 2007 Nanowall arrays of hydrous manganese dioxide MnO2 ·0.5H2O were deposited on cathodic substrates by the potentiostatic method from a mixed aqueous solution of manganese acetate and sodium sulfate, and the Li+ ions

Cao, Guozhong

49

Methodology to Determine Dominant Noise Source in a System-On-Chip Based Implantable Device  

E-print Network

Methodology to Determine Dominant Noise Source in a System-On-Chip Based Implantable Device Zhihua- referred switching noise in a system-on-chip based implantable device, where input sensitivity noise in the frequency domain. An implantable potentiostat that monitors neurochemical activity

Stanacevic, Milutin

50

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.

1972-01-01

51

Electrochemistry Resources  

NSDL National Science Digital Library

This is a general interest website in electrochemistry, offering answers to many common questions. Sections include impedance spectroscopy, quartz crystal microbalance, reference electrodes, simulation voltammetry, potentiostats and handling of mercury. A list of web and book references is available, as is a "contact us" tab for questions to the author.

52

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

1989-01-01

53

MICROFABRICATED ELECTROCHEMICAL ANALYSIS SYSTEM FOR HEAVY METAL DETECTION. (R825511C047)  

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 ...

54

Electric field strength effects on time-dependent passivation of metal Balaji Krishnamurthy, Ralph E. White 1  

E-print Network

Electric field strength effects on time-dependent passivation of metal surfaces Balaji Krishnamurthy, Ralph E. White 1 , Harry J. Ploehn * Department of Chemical Engineering, Swearingen Engineering- sumed that under potentiostatic conditions, the electric field strength within the film varied inversely

55

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

1982-01-01

56

Cationic surfactant as corrosion inhibitor for aluminum in acidic and basic solutions  

Microsoft Academic Search

Purpose – To investigate the inhibiting effect of the cationic surfactant cetyl trimethylammonium chloride (CTAC) on aluminum (Al). Design\\/methodology\\/approach – Pure aluminum rods were immersed in hydrochloric acid (HCl) and sodium hydroxide (NaOH) solutions for weight-loss tests and potentiostatic polarization measurements. Findings – The inhibition action depends on the concentration of the inhibitor, the concentration of the corrosive media, and

N. A. F. Al-Rawashdeh; A. K. Maayta

2005-01-01

57

Inhibition of acidic corrosion of pure aluminum by some organic compounds  

Microsoft Academic Search

Inhibition of the corrosion of aluminum (Al) in hydrochloric acid (HCl) by sulfonic acid (SA), sodium cumene sulfonate (SCS), and sodium alkyl sulfate (SAS) has been studied using weight-loss and potentiostatic polarization methods. The results drawn from the two techniques are comparable and exhibit small discrepancy. The inhibition action depends on the chemical structure and the concentration of the inhibitors,

A. K. Maayta; N. A. F. Al-Rawashdeh

2004-01-01

58

Electrochemical Investigations of Pitting Corrosion in Nitrogen-Bearing Type 316LN Stainless Steel  

Microsoft Academic Search

Nitrogen (N) alloying was found to inhibit active dissolution and to introduce a secondary loop with fluctuating currents in the anodic polarization curve of type 316LN stainless steel (SS) (UNS S31653) in 1 N hydrochloric acid (HCl) solution. Potentiostatic tests in this potential range confirmed the occurrence of current transients as a result of metastable pits, resulting in secondary loop

G. C. Palit; H. S. Gadiyar; V. C. Kain

1993-01-01

59

Electrochemical evaluation of crevice corrosion of 430 ferritic stainless steel using the microcapillary tube technique  

Microsoft Academic Search

The aim of this study was to investigate the initiation of crevice corrosion for ferritic 430 stainless steel in artificial crevice electrode cells using the IR drop mechanism. The 430 stainless steel artificial crevice electrodes were potentiodynamically polarized in solutions of sodium chloride with different concentrations. The potentiostatic polarization was measured for various artificial crevice sizes by measuring the potentials

Eun-Young Na; Jae-Yong Ko; Shin-Young Baik

2005-01-01

60

Amperometric Readout and Electrode Array Chip for Bioelectrochemical Sensors  

Microsoft Academic Search

As nanostructured bioelectronic interfaces continue to evolve for sensor applications, new readout circuits are needed to harness their capabilities. This paper presents a single-chip amperometric readout circuit and electrode array system suitable for bioelectrochemical measurements. The chip features a CMOS potentiostat with high resolution, range- programmable current readout and electrochemical cell potential drive circuitry, which can perform on-chip chronoamperometry and

Andrew Mason; Yue Huang; Chao Yang; Jichun Zhang

2007-01-01

61

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

E-print Network

* Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, Missouri 63130, USA *e-mail: angenent@seas.wustl.edu Received: June 27, 2006 Accepted: July 27, 2006 breakthroughs are made. Keywords: Microbial fuel cell, Biofuel cell, Biocathode, Potentiostat-poised half cell

62

TiO(2) nanotube arrays: intrinsic peroxidase mimetics.  

PubMed

TiO2 nanotube arrays (NTA), prepared by potentiostatic anodization, were discovered to possess an intrinsic peroxidase-like activity. The colorimetric and electrochemical assays both demonstrated their excellent catalytic activity towards H2O2 reduction. On this basis, a simple and inexpensive electrochemical biosensor for glucose detection was developed. PMID:24084751

Zhang, Lingling; Han, Lei; Hu, Peng; Wang, Li; Dong, Shaojun

2013-11-18

63

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.

2005-01-01

64

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.

2009-01-01

65

Journal of Power Sources 159 (2006) 14221427 Li diffusion in LiCoO2 thin films prepared by pulsed laser deposition  

E-print Network

spectroscopy (EIS) and potentiostatic intermittent titration technique (PITT). ~DLi was found to be in the range of 10-11 to 10-13 cm2 s-1 depending on Li concentration and on the characterization method used) using PLD. In this study, crack free LiCoO2 thin films have been prepared by PLD. EIS and PITT were used

Ceder, Gerbrand

66

EIS characterization of tantalum and niobium oxide films based on a modification of the point defect model  

Microsoft Academic Search

Electrochemical impedance spectroscopy (EIS) studies were performed to analyze the passive properties of tantalum and niobium oxides films potentiostatically formed in a 0.1M KOH solution. The quantitative characterization of these passive materials was carried out through a transfer function previously developed by our research group, which is based on the point defect model (PDM) framework considering the formation of molecular

Román Cabrera-Sierra; José Manuel Hallen; Jorge Vazquez-Arenas; Gerardo Vázquez; Ignacio González

2010-01-01

67

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.

2003-01-01

68

Correlation between critical pitting temperature and degree of sensitisation on alloy 2205 duplex stainless steel  

Microsoft Academic Search

In this study effect of different ageing conditions on intergranular corrosion, pitting corrosion and relation between critical pitting temperature (CPT) and degree of sensitisation (DOS) was investigated by potentiostatic polarisation and double loop-EPR methods. The results showed by increasing sensitisation time, DOS increased and measured CPT value decreased. In addition the values of DOS and CPT of specimens aged at

N. Ebrahimi; M. Momeni; M. H. Moayed; A. Davoodi

2011-01-01

69

Cyclic charge-discharge behaviour of sintered plate and planar cadmium electrodes  

Microsoft Academic Search

The cyclic charge-discharge behaviour of sintered plate and planar cadmium electrodes has been studied using galvanostatic and potentiostatic sweep techniques. The cycling inefficiency of sintered electrodes reflected more the discharge process as shown by analytical monitoring of cadmium levels before and after charge. The effect of discharge rate on cycling efficiency was also investigated. Open-circuit recovery experiments indicated that a

R. Barnard; K. Edmondson; J. A. Lee; F. L. Tye

1976-01-01

70

Efficiencies of Bio-electrocatalytic Production of Hydrogen from Lactate Using Shewanella oneidensis MR-1  

Technology Transfer Automated Retrieval System (TEKTRAN)

Shewanella oneidensis MR-1 was grown in a chemostatic, continuously-fed bioelectrochemical cell under slightly aerated conditions. The start-up phase was controlled potentiostatically (0.4 V vs. SHE). When a stable performance was achieved, the reactor was switched to bio-electrocatalytic producti...

71

AN ADVANCED FLUE GAS MONITOR FOR SO2 - PHASE I  

EPA Science Inventory

The development of an instrument for continuously monitoring SO2 levels in flue gas is proposed. The SO2 will be detected by means of an electrochemical sensor cell, which operates in a three-electrode potentiostatic mode. The proposed innovation is develop-ment of an advan...

72

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

PubMed

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

2014-03-11

73

Recent advances in electrochemical impedance measurement  

Microsoft Academic Search

Summary form only given as follows: Accurate measurements of electrochemical impedance requires highly sophisticated instrumentation, especially in applications where small stimulating signals are employed. The combination of a frequency response analyser (FRA) and a potentiostat are the most widely utilised for these applications, but have limitations when measuring high impedances, or high frequency (>1 MHz). Some of these may be

N. J. Evans; B. Sayers

1994-01-01

74

Single-molecule Fluorescence Spectroelectrochemistry of Cresyl Violet  

SciTech Connect

We coupled scanning fluorescence microscopy with a potentiostat via a three-electrode electrochemical cell to enable single-molecule fluorescence spectroelectrochemistry of cresyl violet in aqueous solution, where the single-molecule fluorescence intensity of cresyl violet is modulated synchronously with the cyclic voltammetric potential scanning.

Lei, Chenghong; Hu, Dehong; Ackerman, Eric J.

2008-11-21

75

The effect of water content on the electropolishing behavior of Inconel 718 alloy in perchloric–acetic acid mixtures  

Microsoft Academic Search

The electropolishing behavior of Inconel 718 alloy was studied in perchloric–acetic acid mixtures using a rotating disc electrode. The electropolishing behavior of an Inconel 718 weld, which was prepared with electron beam welding, was also investigated. A leveled but not brightened surface can be achieved when Inconel 718 alloy is potentiostatically polished in the acid mixture with 20vol.% perchloric acid.

Ching An Huang; Yu Chen Chen

2009-01-01

76

Rhodanine azosulpha drugs as corrosion inhibitors for corrosion of 304 stainless steel in hydrochloric acid solution  

Microsoft Academic Search

The effect of rhodanine azosulpha drugs on the corrosion behaviour of 304 stainless steel in 1.0 M hydrochloric acid solution as corrosive medium has been investigated using weight loss and potentiostatic polarization techniques. Some corrosion parameters such as anodic and cathodic Tafel slope, corrosion potential, corrosion current, exchange current densities, surface coverage and inhibition efficiency were calculated. The polarization measurements

M Abdallah

2002-01-01

77

Influence of the reaction temperature on the electrochemical promoted catalytic behaviour of platinum impregnated catalysts for the reduction of nitrogen oxides under lean burn conditions  

Microsoft Academic Search

The aim of this work was to study the influence of the reaction temperature on the efficiency of the electrochemical promotion to improve the catalytic performance of a Pt impregnated catalyst for the reduction of nitrogen oxides under lean burn conditions. Open circuit catalytic and potential measurements were carried out in order to explain the potentiostatic behaviour of the electrochemical

Fernando Dorado; Antonio de Lucas-Consuegra; Carmen Jiménez; José Luis Valverde

2007-01-01

78

Role of Preparation Method on the Microstructure and Mechanical Properties of PPy/Ni Organic-Inorganic Hybrid Bilayer Coatings on Carbon Steel  

NASA Astrophysics Data System (ADS)

The efficacy of the conducting polymers as coating on a metallic substrate is strongly dependent on the manner how they are applied. Polypyrrole (PPy)/Ni organic-inorganic hybrid coatings were electropolymerized on commercial carbon steel (AISI 1018) by combining potentiostatic and potentiodynamic techniques. In first instance, it was analyzed the electrodeposition of PPy using a constant potential regime and cyclic voltammetry techniques evaluating different synthesis parameters such as deposition time, applied potential, and potential cycles, respectively. Thereafter, it was used a potentiostatic method to obtain PPy/Ni bilayer films. The morphological, mechanical, and adhesion properties of these films depend on the synthesis parameters. The results revealed that polypyrrole films formed by both methods provide a globular-type structure, although coatings produced by cyclic voltammetry are denser and slightly thicker than those produced potentiostatically. Ni (oxide/hydroxide) particles are capable of sealing the pores of globular PPy coatings, thus increasing the hardness of the carbon steel (CS)/PPy/Ni system. As a result of the study, we have seen that PPy/Ni bilayer films are more uniform, compact and enhanced the hardness when the PPy is obtained by cyclic voltammetry than that observed for potentiostatic approach. Specifically, when four potential cycles are used to electropolymerized pyrrole, the more convenience properties in the CS/PPy/Ni arrangement are obtained.

Torres-Huerta, A. M.; Dominguez-Crespo, M. A.; Alanis-Valdelamar, A.; Onofre-Bustamante, E.; Escudero, M. L.; García-Alonso, M. C.; Lois-Correa, J. A.

2015-04-01

79

Electrochemical destruction of dilute cyanide by copper-catalyzed oxidation in a flow-through porous electrode  

SciTech Connect

Aqueous cyanide-ion concentrations can be reduced from 100 ppm to below 1 ppm by oxidation in a porous flow-through reticulated vitreous carbon anode catalyzed by copper. Proper control of solution pH combined with potentiostatic operation maintains high current efficiency. A theoretical model that accounts for interactions between mass transfer and chemical reactions is capable of describing process performance.

Hofseth, C.S.; Chapman, T.W. [Univ. of Wisconsin, Madison, WI (United States). Dept. of Chemical Engineering] [Univ. of Wisconsin, Madison, WI (United States). Dept. of Chemical Engineering

1999-01-01

80

Synthesis of High Coercivity Core–Shell Nanorods Based on Nickel and Cobalt and Their Magnetic Properties  

PubMed Central

Hybrid magnetic nanostructures with high coercivity have immense application potential in various fields. Nickel (Ni) electrodeposited inside Cobalt (Co) nanotubes (a new system named Ni @ Co nanorods) were fabricated using a two-step potentiostatic electrodeposition method. Ni @ Co nanorods were crystalline, and they have an average diameter of 150 nm and length of ~15 ?m. The X-ray diffraction studies revealed the existence of two separate phases corresponding to Ni and Co. Ni @ Co nanorods exhibited a very high longitudinal coercivity. The general mobility-assisted growth mechanism proposed for the growth of one-dimensional nanostructures inside nano porous alumina during potentiostatic electrodeposition is found to be valid in this case too. PMID:20651915

2010-01-01

81

Corrosion resistance tests on NiTi shape memory alloy.  

PubMed

The corrosion performances of NiTi shape memory alloys (SMA) in human body simulating fluids were evaluated in comparison with other implant materials. As for the passivity current in potentiostatic conditions, taken as an index of ion release, the values are about three times higher for NiTi than for Ti6Al4V and austenitic stainless steels. Regarding the localized corrosion, while plain potentiodynamic scans indicated for NiTi alloy good resistance to pitting attack similar to Ti6Al4V, tests in which the passive film is abruptly damaged (i.e. potentiostatic scratch test and modified ASTM F746) pointed out that the characteristics of the passive film formed on NiTi alloy (whose strength can be related to the alloy's biocompatibility) are not as good as those on Ti6Al4V but are comparable or inferior to those on austenitic stainless steels. PMID:8894095

Rondelli, G

1996-10-01

82

Nano electrode arrays for in-situ identification and quantification of chemicals in water.  

SciTech Connect

The nano electrode arrays for in-situ identification and quantification of chemicals in water progress in four major directions. (1) We developed and engineering three nanoelectrode array designs which operate in a portable field mode or as distributed sensor network for water systems. (2) To replace the fragile glass electrochemical cells using in the lab, we design and engineered field-ready sampling heads that combine the nanoelectrode arrays with a high-speed potentiostat. (3) To utilize these arrays in a portable system we design and engineered a light weight high-speed potentiostat with pulse widths from 2 psec. to 100 msec. or greater. (4) Finally, we developed the parameters for an analytical method in low-conductivity solutions for Pb(II) detection, with initial studies for the analysis of As(III) and As(V) analysis in natural water sources.

Gurule, Natalia J.; Kelly, Michael James; Brevnov, Dmitri A. (University of New Mexico, Albuquerque, NM); Ashby, Carol Iris Hill; Pfeifer, Kent Bryant; Yelton, William Graham

2004-12-01

83

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

1996-07-01

84

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.

2013-12-01

85

Effect of formation of surface hydroxide on hydrogen permeability of iron membranes and hydrogen embrittlement of high-strength steels  

Microsoft Academic Search

UDC 541.138:669.788 permeability of iron membranes. The working cell consisted of two parts separated by a bipolar electrode, i.e., an iron membrane. In the polarization part of the cell, contained in the examined solution, the membrane was hydrogen-charged in the potentiostatic condition. A potential of +0.3 V (here and in the rest of the article the potential is given with

V. A. Marichev; V. V. Molokanov

1992-01-01

86

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

Pound

1990-01-01

87

Corrosion behavior of hypereutectic Al23%Si alloy (AC9A) processed by severe plastic deformation  

Microsoft Academic Search

Ultrafine-grained(UFG) hypereutectic Al-23%Si (mass fraction) alloy was achieved through equal-channel angular pressing(EACP) procedure. And the electrochemical properties after various ECAP passes were investigated in neutral NaCl solution. Potentiostatic polarization curves show that the corrosion potential of the ECAPed sample after 4 passes decreases markedly, while the corrosion current density reaches 1.37 times that of the as-cast alloy. However, the ?corr

Jing-hua JIANG; Ai-bin MA; Dan SONG; N. SAITO; Yu-chun YUAN; Y. NISHIDA

2010-01-01

88

Ordered arrays of copper nanowires enveloped in polyaniline nanotubes  

Microsoft Academic Search

Copper nanowires enveloped in polyaniline (PANI) nanotubes were obtained by ‘second order’ electrodeposition into the pores\\u000a of anodic porous alumina. The templated synthesis of copper nanowires was performed by both potentiostatic and galvanostatic\\u000a methods. The morphology of the polyaniline nanotubes, copper nanowires as well as the copper-filled polyaniline nanotubes\\u000a was investigated by means of scanning electron microscopy. The copper nanowires

A. Prun?; V. Brânzoi; F. Brânzoi

2011-01-01

89

Effect of the protogenic nature of the medium on the rate of corrosion transformations in PT3V titanium alloy  

Microsoft Academic Search

Polarization was carried out using a P-5 827M potentiostat, and of volt-ampere graphs were recorded using a PDP-4 automatic recording device. Measurements were taken using the three-electrode method. The working electrode, whose radius was determined with an error to 1 ~m rotated at a frequency ~ = 2.4-27 sec -I. An auxiliary platinum electrode was placed in a side container

V. I. Pokhmurskii; O. S. Kalakhan

1992-01-01

90

An electrochemical evaluation on the crevice corrosion of 430 stainless steel by micro capillary tubing method  

Microsoft Academic Search

The aim of this study was to investigate the initiation of crevice corrosion for ferritic 430 stainless steel in artificial\\u000a crevice electrode cells using the IR drop mechanism. The 430 stainless steel artificial crevice electrodes were potentiodynamically\\u000a polarized in solutions of sodium chloride with different concentrations. The potentiostatic polarization was measured for\\u000a various artificial crevice sizes by measuring the potentials

Eun-Young Na

2006-01-01

91

Effects of alloy and solution chemistry on the fracture of passive films on austenitic stainless steel  

Microsoft Academic Search

The Taguchi analysis method was used to simultaneously study the effects of alloy chemistry, pH, and halide ion concentrations on the fracture of electrochemically grown passive films using a nanoindentation technique. Three austenitic stainless steels, 304L, 316L, and 904L were potentiostatically polarized in hydrochloric acid solutions. The fracture load was dominated primarily by alloy chemistry. Passive films mechanically weaken as

A. Alamr; D. F. Bahr; Michael Jacroux

2006-01-01

92

Electronic conductivities of commercial ZrO 2 + 3 to 4 wt pct CaO electrolytes  

Microsoft Academic Search

Potentiostatic electrochemical experiments with liquid metal electrodes have been analyzed to provide values for the mixed\\u000a electrical conduction parameters (PMion, o?o, Oo , Po,P\\u000a o, and E O,C.) associated with commercial-grade ZrO2 + 3 to 4 wt pct CaO electrolytes. Good agreement between experimental and calculated values for the open-circuit cell voltage,E o. c., for relatively high oxygen concentrations in

Lawrence M. Friedman; Karl E. Oberg; William M. Boorstein; Robert A. Rapp

1973-01-01

93

Electrodeposition and optical characterisation of CdS thin films on ITO-coated glass  

Microsoft Academic Search

Cadmium sulfide thin films have been deposited by electrodeposition using the potentiostatic method on indium tin oxide (ITO)-coated glass substrates from aqueous solution containing CdCl2 · 2H2O and Na2S2O3 at 90 °C. The depositions were carried out for various cathodic potentials. Good quality films were obtained at a cathodic potential of ?0.6 V. Voltammograms have been recorded to optimize the

G. Sasikala; R. Dhanasekaran; C. Subramanian

1997-01-01

94

An amperometric biosensor based on acetylcholinesterase immobilized onto iron oxide nanoparticles\\/multi-walled carbon nanotubes modified gold electrode for measurement of organophosphorus insecticides  

Microsoft Academic Search

An acetylcholinesterase (AChE) purified from maize seedlings was immobilized covalently onto iron oxide nanoparticles (Fe3O4NP) and carboxylated multi walled carbon nanotubes (c-MWCNT) modified Au electrode. An organophosphorus (OP) biosensor was fabricated using this AChE\\/Fe3O4\\/c-MWCNT\\/Au electrode as a working electrode, Ag\\/AgCl as standard and Pt wire as an auxiliary electrode connected through a potentiostat. The biosensor was based on inhibition of

Nidhi Chauhan; Chandra Shekhar Pundir

2011-01-01

95

Effect of minor nickel alloying with zinc on the electrochemical and corrosion behavior of zinc in alkaline solution  

Microsoft Academic Search

The electrochemical and corrosion behavior of pure zinc and Zn–0.5Ni alloy in strong alkaline solution (7M KOH) was investigated by Tafel plot, potentiodynamic, potentiostatic and electrochemical impedance spectroscopy (EIS) methods, and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Measurements were conducted under different experimental conditions. The results of both Tafel plot extrapolation and the electrochemical impedance spectroscopy

Abdel-Rahman El-Sayed; Hossnia S. Mohran; Hany M. Abd El-Lateef

2010-01-01

96

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.

1995-03-01

97

Mechanism of film formation on nickel anodes in a molten NH 4F·2HF  

Microsoft Academic Search

The mechanism of film formation on the Ni anode in a well dehydrated melt of NH4F·2HF was studied at 100°C. The potentiodynamic and potentiostatic polarization behaviors of the Ni anode were investigated to elucidate the anodic processes. The oxidized layer was composed of NiF2 with a small amount of nickel oxides such as NiO and Ni2O3 or oxyfluorides having plural

A. Tasaka; Y. Tsukuda; S. Yamada; K. Matsushita; A. Kohmura; N. Muramatsu; H. Takebayashi; T. Mimaki

1999-01-01

98

A wound-type lithium\\/polyaniline secondary cell  

Microsoft Academic Search

A wound-type cell with a polyaniline (PAn) positive electrode, a LiClON4-propylene carbonate (PC) electrolyte, and a lithium-foil negative electrode is constructed. The two electrodes are separated by a polypropylene separator. The PAn is deposited on carbon felt from a HClON4 solution containing aniline by galvanostatic or potentiostatic electrolysis. Using cyclic voltammetry charge\\/discharge cycles and charge\\/retention tests, the following results are

Changzhi Li; Borong Zhang; Baochen Wang

1992-01-01

99

Crack developmentrate and electromechanical characteristics of titanium alloy AT3 in certain media  

Microsoft Academic Search

TO determine the effect of the temperature factor and the composition of the working medium of the hydrolysis plant (0.5-0.7% sulfuric acid; 0.3-0.7% organic acids; 3.1-3.3% reducing sugar; 0.03-0.06% furfural; remainder -- water) on the tendency of AT-3 alloy to overall corrosion, we recorded the potentiostatic curves in 0.6% sulfuric acid at 20, 50, and 96~ and in a sulfuric

V. S. Fedchenko; A. M. Krutsan; R. K. Melekhov; V. E. Blashchuk

1978-01-01

100

New observations on the anodic oxidation of copper in hot acidified copper sulfate solutions  

Microsoft Academic Search

The anodic oxidation of copper in acidified copper sulfate solution has been investigated by potentiostatic and voltammetric\\u000a techniques. The morphology and composition of the films were determined by X-ray photoelectron spectroscopy (XPS) and scanning\\u000a electron microscopy (SEM). The passive layer is mainly composed of CuSO4. The presence of a Cu2O phase becomes detectable after multiple sweeps and thorough rinsing of

Stéphane Garneau; Edward Ghali; Magdy Girgis; R. G. Barradas

1991-01-01

101

Poly(malachite green) at nafion doped multi-walled carbon nanotube composite film for simple aliphatic alcohols sensor  

Microsoft Academic Search

Conductive composite film which contains nafion (NF) doped multi-walled carbon nanotubes (MWCNTs) along with the incorporation of poly(malachite green) (PMG) has been synthesized on glassy carbon electrode (GCE), gold and indium tin oxide (ITO) electrodes by potentiostatic methods. The presence of MWCNTs in the composite film (MWCNTs–NF–PMG) enhances surface coverage concentration (?) of PMG to ?396%, and increases the electron

Yogeswaran Umasankar; Arun Prakash Periasamy; Shen-Ming Chen

2010-01-01

102

Development of pitting corrosion of stainless steel 403 in sodium chloride solutions  

Microsoft Academic Search

Pitting corrosion of stainless steel 403 in the NaCl solutions is studied. It is shown that the experimental results obtained\\u000a under the potentiostatic conditions do not provide sufficient information on the behavior of steel under the conditions of\\u000a free corrosion. The corrosion experiments take long time, their results exhibit poor reproducibility; however, they are necessary\\u000a for obtaining reliable data on

K. V. Rybalka; V. S. Shaldaev; L. A. Beketaeva; A. N. Malofeeva; A. D. Davydov

2010-01-01

103

Linking electrochemical corrosion behaviour and corrosion mechanisms of thermal spray cermet coatings (WC–CrNi and WC\\/CrC–CoCr)  

Microsoft Academic Search

In this experimental study the corrosion characteristics (rates and mechanisms) of two thermally-sprayed cermet (ceramic\\/metal composite) coatings have been examined in a static saline environment. The coatings have complex microstructures where the ceramic hard-phase constituents are embedded in a metallic matrix. Their electrochemical response during accelerated corrosion DC polarisation tests reflects this complexity. A test protocol involving potentiostatic and potentiodynamic

V. A. D Souza; A Neville

2003-01-01

104

Monitoring pitting corrosion of AISI 316L austenitic stainless steel by acoustic emission technique: Choice of representative acoustic parameters  

Microsoft Academic Search

This experimental work was aimed at investigating the monitoring of pitting corrosion by the acoustic emission (AE) technique, for pits developed by potentiostatic or galvanostatic polarization on two types of 316L austenitic stainless steels, in a 3% NaCl solution acidified to pH 2. The study of the evolution of AE global activity during the test showed the existence of a

M. Fregonese; H. Idrissi; H. Mazille; L. Renaud; Y. Cetre

2001-01-01

105

The effects of some anions on metastable pitting of 316L stainless steel  

Microsoft Academic Search

The effects of PO43?, CrO42?, SO42? and NO3? anions on metastable pitting of 316L stainless steel in NaCl solutions were investigated using potentiostatic and potentiodynamic polarization tests. The four anions all retard nucleation of metastable pitting. The inhibition effect decreases in the order: PO43?>CrO42?>SO42?>NO3?. The propagation rates of metastable pits are also decreased by the anions tested. Both metastable pitting

Yu Zuo; Haitao Wang; Jingmao Zhao; Jinping Xiong

2002-01-01

106

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

Microsoft Academic Search

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 µm long (110 nm pore diameter, 20 nm wall thickness)

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

2006-01-01

107

A study of the heat-affected zone (HAZ) of an Inconel 718 sheet welded with electron-beam welding (EBW)  

Microsoft Academic Search

In this paper the heat-affected zones (HAZs) of the Inconel 718 sheets welded with electron-beam welding (EBW) were studied by using hardness measurement, metallographic etch and electrochemically potentiostatic etch methods. Before EBW, the Inconel 718 sheets were pretreated in three different conditions: as-received, solution- and precipitation-treatments. The results show that there is an obvious difference in the dimension of the

C. A. Huang; T. H. Wang; C. H. Lee; W. C. Han

2005-01-01

108

Anticorrosive properties of electrosynthesized poly(o-anisidine) coatings on copper from aqueous salicylate medium  

Microsoft Academic Search

Poly(o-anisidine) (POA) coatings were electrosynthesized on copper (Cu) from an aqueous solution containing o-anisidine and sodium salicylate by using cyclic voltammetry, galvanostatic and potentiostatic modes. The extent of corrosion protection offered by these coatings to Cu in aqueous 3% NaCl solution was evaluated by the open circuit potential measurements, potentiodynamic polarization technique and electrochemical impedance spectroscopy. Potentiodynamic polarization and electrochemical

Sudeshna Chaudhari; S. R. Sainkar; P. P. Patil

2007-01-01

109

Studies on corrosion protection of Al2024 T6 alloy by electropolymerized polyaniline coating  

Microsoft Academic Search

Aqueous electropolymerized polymer coatings on aluminum alloys can replace the carcinogenic chromate coating. In this work, the corrosion protection ability of electropolymerized polyaniline coating on Al2024 T6 alloy has been found out. The polyaniline coatings on aluminum were formed by galvanostatic and potentiostatic methods from a bath of 0.5M oxalic acid containing 0.1M aniline. The corrosion protection ability of the

V. Karpagam; S. Sathiyanarayanan; G. Venkatachari

2008-01-01

110

Modeling of the Current Distribution in Aluminum Anodization  

Microsoft Academic Search

The growth of porous anodic Al2O3 films, formed potentiostatically in continuously stirred 15 wt.% H2SO4 electrolyte was studied as a function of the anodization voltage (14–18 V), bath temperature (15–25 °C) and anodization time (15–35 min). The variation of the anodic surface overpotential with the current density was measured experimentally. The film thickness at the more accessible portions of the

Rohan Akolkar; Uziel Landau; Harry Kuo; Yar-Ming Wang

2004-01-01

111

Nickel and cobalt recycling from lithium-ion batteries by electrochemical processes.  

PubMed

The presence of LiCoO(2) and LiCo(x)Ni((1-x))O(2) in the cathodic material of Li-ion and Li-polymer batteries has stimulated the recovery of Co and Ni by hydrometallurgical processes. In particular, the two metals were separated by SX method and then recovered by electrochemical (galvanostatic and potentiostatic) processes. The metallic Ni has been electrowon at 250 A/m(2), pH 3-3.2 and 50 degrees C, with 87% current efficiency and 2.96 kWh/kg specific energy consumption. Potentiostatic electrolysis produces a very poor Ni powder in about 1 h with current efficiency changing from 70% to 45% depending on Ni concentration in the electrolyte. Current efficiency of 96% and specific energy consumption of 2.8 kWh/kg were obtained for Co at 250 A/m(2), pH 4-4.2 and 50 degrees C, by using a solution containing manganese and (NH(4))(2)SO(4). The Co powder, produced in potentiostatic conditions (-0.9 V vs. SCE, pH 4, room temperature) appears particularly suitable for Co recycling as cobaltite in new batteries. PMID:15737721

Lupi, C; Pasquali, M; Dell'era, A

2005-01-01

112

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

Microsoft Academic Search

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

M. ?ahin; S. Bilgiç; H. Y?lmaz

2002-01-01

113

Influence of ultrasound on the kinetic parameters of electrochemical redox reactions.  

PubMed

The aim of this work is to determine the Tafel parameters with and without ultrasound. The total overvoltage has been corrected for diffusion by using rotating disk technique and potentiostatic extrapolation to infinite rotating speed. Three well known redox systems have been selected regardless to their different electrochemical behaviour: the quinone-hydroquinone, the Fe(II)Fe(III) chlorides and Fe(II)-Fe(III) cyanide systems. This work shows that the reversibility is higher with ultrasound only in the case of the quinone-hydroquinone system. PMID:11237025

Jung, C G; Chapelle, F; Fontana, A

1997-04-01

114

Synthesis, characterization and optoelectrochemical properties of poly(1,6-bis(2,5-di(thiophen-2-yl)-1 H-pyrrol-1-yl)hexane) and its copolymer with EDOT  

Microsoft Academic Search

A new polythiophene derivative was synthesized by electrochemical oxidative polymerization of 1,6-bis(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)hexane (TPH). The structure of the monomer was elucidated by 1H, 13C, FTIR and mass analyses. The polymer P(TPH) and its copolymer with 3,4-ethylenedioxythiophene (P(TPH-co-EDOT)) were synthesized via potentiostatic electrochemical polymerization. Characterizations of the resulting polymers were performed by cyclic voltammetry (CV), FTIR, UV–vis spectroscopies and conductivity measurements. Moreover,

Metin Ak; Ertu?rul ?ahmetlio?lu; Levent Toppare

2008-01-01

115

Effects of magnetic fields from underwater electrical cutting on in vitro corrosion of dental amalgam  

SciTech Connect

Metallic taste has been reported from divers working with underwater electric welding and cutting. An in vitro model was designed to simulate the intraoral situation of the divers with respect to the magnetic field. Potentiostatic analyses were performed on amalgam samples exposed to AC and DC magnetic fields. Morphologic changes were analyzed using differential interference light microscopy and scanning electron microscopy. Chemical changes on the surface of the amalgam samples were analyzed with secondary ion mass spectrometry. Results demonstrated that dental amalgams exposed to a specific AC magnetic field underwent morphologic and chemical changes in the superficial amalgam layers.

Ortendahl, T.W.; Hoegstedt, P.O.; Odelius, H.; Noren, J.G.

1988-11-01

116

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

Microsoft Academic Search

Two hydrophobic ionic liquids (room temperature molten salts) based on 1-butyl-3-methylimidazolium cation (BMI+), BMI+PF6? and BMI+Tf2N?, 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+PF6?and BMI+Tf2N? maintained high apparent anodic efficiency (up to 100%) under potentiostatic polarization (at +0.5V versus open-circuit potential (OCP))

Yancheng Zhang; Mirna Urquidi-Macdonald

2005-01-01

117

Potential dependence of rate of solution of chromium  

SciTech Connect

The authors study the solution kinetics of chromium and measure the potential dependence of the stationary rate of solution of chromium in 1 N H/sub 2/SO/sub 4/ at 20 degrees C. By means of the potentiostatic method, the experiments are performed in conjunction with high-sensitivity gamma-spectrometric and atomic absorption methods of analysis of a solution for dissolved products. There is satisfactory quantitative agreement between this dependence and an analogous one previously obtained by a less sensitive method.

Knyazheva, V.M.; Babich, S.G.; Dembrovskii, M.A.

1986-03-01

118

The electrochemical and morphological behavior of lead and its alloys in 5M H/sub 2/SO/sub 4/  

SciTech Connect

An electrochemical and morphological study of pure lead and its alloys has been carried out using linear sweep voltammetry, potentiostatic step experiments and scanning electron microiscopy. The results are discussed from a nucleation and growth mechanism as they are major factors in the current control processes. The results showed that: 1) the nucleation and growth mechanisms for the discharge reaction of the various alloys followed similar mechanisms, namely 2D-growth with progressive nucleation, 2) Pb-Sb alloys have a prolonged cycle life, 3) Pb-Sb alloys engender a surface film of highest porosity.

Webster, S.; Dyson, J.I.; Hampson, N.A.; Mitchell, P.J.

1984-10-01

119

Siloxane-based thin films for corrosion protection of stainless steel in chloride media  

Microsoft Academic Search

The corrosion protection of stainless steel (SS 316L) provided by layers of SiO2 and by siloxane-anchored self-assembled monolayer (SAMs) was assessed by cyclic voltammetry (CV) and by potentiostatic current\\u000a transient in sodium chloride media. The SAMs were composed of octadecyltrimethoxysilane anchored onto a thin (1–2 nm) layer\\u000a of SiO2. The initial SiO2 layer was obtained by treatment with tetraethoxyorthosilicate. Successive layers

Sérgio Meth; Natali Savchenko; Federico A. Viva; David Starosvetsky; Alec Groysman; Chaim N. Sukenik

2011-01-01

120

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

PubMed

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

2013-05-01

121

Supercapacitor application of nickel oxide–titania nanocomposites  

Microsoft Academic Search

Highly-ordered and well-separated titania nanotube array was prepared by a potentiostatic anodization process. The desired nickel oxide–titania (NiO–TiO2) nanocomposites were constructed through incorporating nickel hydroxide into titania nanotubes by a one-cycle or multi-cycle alternate electrodeposition–oxidation and then a thermal dehydration process. By means of the microstructure promotion from particulate to flower-like NiO–TiO2 nanocomposite, specific capacitances were accordingly increased from 26.9

Yibing Xie; Chuanjun Huang; Limin Zhou; Yang Liu; Haitao Huang

2009-01-01

122

Thin flexible intercalation anodes  

SciTech Connect

Poly(acrylonitrile) fibers have been pyrolyzed under various conditions to form flexible carbon yarns capable of intercalating lithium ions. These fibers have also been formed into both woven and non woven cloths. Potentiostatic, potentiodynamic and galvanostatic tests have been conducted with these materials in several electrolytes. In some tests, a potential hold was used after each constant current charge and discharge. These tests have shown some of these flexible materials to reversibly intercalate lithium ions to levels that are suitable for use as a practical battery anode.

Levy, S.C.; Cieslak, W.R.; Klassen, S.E.; Lagasse, R.R.

1994-10-01

123

Electrochemical properties of Cr doped V 2O 5 between 3.8 V and 2.0 V  

Microsoft Academic Search

Cr0.1V2O5.15 was prepared by an oxalic acid assisted sol–gel method. X-ray diffraction showed that Cr doping induced a slight expansion (?V\\/V?2.3%) in the crystal lattice of V2O5. The electrochemical properties of Cr0.1V2O5.15 in the potential range of 3.8–2.0 V were studied by cyclic voltammetry, galvanostatic charge–discharge cycling and potentiostatic intermittent titration technique. Cyclic voltammetry showed that the irreversible phase transition of

S. Y. Zhan; C. Z. Wang; K. Nikolowski; H. Ehrenberg; G. Chen; Y. J. Wei

2009-01-01

124

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: fmross@us.ibm.com [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)

2014-02-01

125

Structural properties of single step electrochemically deposited ZnS nanofibers  

NASA Astrophysics Data System (ADS)

ZnS thin films are prepared by electro deposition technique over stainless steel substrates in potentiostatic mode from an aqueous acidic bath containing ZnSo4 and Na2S2O3. The growth kinetics of the film was studied and the deposition parameters such as electrolyte bath concentration, deposition time, deposition potential and pH of electrolyte bath are optimized. The X-ray diffraction (XRD) analysis of the deposited film showed presence of polycrystalline nature. The surface morphology studied by scanning electron microscope (SEM) shows fibrous morphology with well adherence and uniform distribution of nanosized fibers over the surface of substrate.

Bhalerao, Anuradha B.; Wagh, B. G.; Lokhande, C. D.

2013-06-01

126

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.

2014-09-01

127

Kinetics and mechanism of electroless copper deposition at moderate-to-high copper ion and low-to-moderate formaldehyde concentrations  

Microsoft Academic Search

Studies were carried out to establish the effect of moderate-to-high copper ion and low-to-moderate formaldehyde concentrations\\u000a on electroless deposition of copper. The individual half-cell polarization curves were generated from a steady-state two-compartment\\u000a cell as well as from potentiostatic measurements. The anodic and cathodic plots were superimposed on one another to get the\\u000a mixed potential (E\\u000a m) and mixed current(i\\u000a m).

K. G. Mishra; R. K. Paramguru

1999-01-01

128

Stress corrosion cracking of carbon steel in caustic aluminate solutions—crack propagation studies  

Microsoft Academic Search

Stress corrosion cracking of a commercial 0.19 pct C steel (SA-516 Grade 70) was studied in hot (92 ‡C) caustic solutions\\u000a of NaOH and NaOH plus aluminate (AlO?\\u000a 2) species. Potentiostatically controlled tests were conducted near the active-passive transition, using fracture mechanics\\u000a testing techniques and fatigue precracked double cantilever beam specimens. Crack propagation rates (?) were determined for\\u000a a range

Rajagopal Sriram; Desmond Tromans

1985-01-01

129

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.

1992-01-01

130

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)

1998-09-01

131

Heterosupramolecular chemistry: Long-lived light-induced charge separation by vectorial electron flow in a heterotriad  

SciTech Connect

A redox molecule (acceptor) is attached, using a surface chelate (spacer), to a semiconductor electrode (donor). Such donor-spacer-acceptor complexes, referred to as heterodyads, offer the prospect of testing important aspects of the theory of heterogeneous electron transfer (ET) at the semiconductor electrode liquid electrolyte interface (SLI). Specifically, potentiostatically controlled ET from the conduction band of the semiconductor electrode to a redox species held at a fixed distance and orientation with respect to the SLI is possible. Extending the above approach, a modified SLI has been prepared at which potentiostatically controlled vectorial electron flow leading to long-lived charge trapping is possible. Specifically, a spacer-acceptor I-acceptor II complex is adsorbed at a semiconductor electrode to form a heterotriad. Application of a potential more negative than the potential of the conduction band at the SLI results in acceptor I mediated reduction of acceptor II. The reduced form of acceptor II is stabilized and long-lived charge trapping results. Efficient light induced charge separation by vectorial electron flow at the above modified SLI is also possible.

Marguerettaz, X.; Nagaraja Rao, S.; Redmond, G.; Fitzmaurice, D. [University College, Dublin (Ireland). Dept. of Chemistry

1994-12-31

132

Electrochemical extraction of neodymium by co-reduction with aluminum in LiCl-KCl molten salt  

NASA Astrophysics Data System (ADS)

The electrochemical behavior of Nd(III) ions in LiCl-KCl and LiCl-KCl-AlCl3 melts on a Mo electrode at 723 K was studied by various electrochemical techniques. The results showed that Nd(III) ions are reduced to Nd(0) through two consecutive steps, and the underpotential deposition of neodymium on pre-deposited Al electrode formed two kinds of Al-Nd intermetallic compounds in LiCl-KCl-AlCl3 solutions. The electrochemical extraction of neodymium was carried out in LiCl-KCl-AlCl3 melts on a Mo electrode at 873 K by potentiostatic and galvanostatic electrolysis. The extraction efficiency was 99.25% after potentiostatic electrolysis for 30 h. Al-Li-Nd bulk alloy was obtained by galvanostatic electrolysis. X-ray diffraction (XRD) suggested that Al2Nd and Al3Nd phases were formed in Al-Li-Nd alloy. The microstructure and micro-zone chemical analysis of Al-Li-Nd alloy were characterized by scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS), respectively.

Yan, Yong-De; Xu, Yan-Lu; Zhang, Mi-Lin; Xue, Yun; Han, Wei; Huang, Ying; Chen, Qiong; Zhang, Zhi-Jian

2013-02-01

133

Aerated Shewanella oneidensis in continuously fed bioelectrochemical systems for power and hydrogen production.  

PubMed

We studied the effects of aeration of Shewanella oneidensis on potentiostatic current production, hydrogen production in a microbial electrolysis cell, and electric power generation in a microbial fuel cell (MFC). The potentiostatic performance of aerated S. oneidensis was considerably enhanced to a maximum current density of 0.45 A/m(2) or 80.3 A/m(3) (mean: 0.34 A/m(2), 57.2 A/m(3)) compared to anaerobically grown cultures. Biocatalyzed hydrogen production rates with aerated S. oneidensis were studied within the applied potential range of 0.3-0.9 V and were highest at 0.9 V with 0.3 m(3) H(2)/m(3) day, which has been reported for mixed cultures, but is approximately 10 times higher than reported for an anaerobic culture of S. oneidensis. Aerated MFC experiments produced a maximum power density of 3.56 W/m(3) at a 200-Omega external resistor. The main reasons for enhanced electrochemical performance are higher levels of active biomass and more efficient substrate utilization under aerobic conditions. Coulombic efficiencies, however, were greatly reduced due to losses of reducing equivalents to aerobic respiration in the anode chamber. The next challenge will be to optimize the aeration rate of the bacterial culture to balance between maximization of bacterial activation and minimization of aerobic respiration in the culture. PMID:19998276

Rosenbaum, Miriam; Cotta, Michael A; Angenent, Largus T

2010-04-01

134

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?Å/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

2014-01-01

135

Aqueous corrosion characteristics and corrosion-related cracking susceptibilities of Fe sub 3 Al-type iron aluminides  

SciTech Connect

In certain fossil-energy applications, iron aluminides may be subjected to ambient-temperature aqueous corrosion conditions. In the present project, the aqueous corrosion characteristics and the cracking tendencies under aqueous-corrosion conditions were studied. In these studies, electrochemical, immersion and electrochemical-mechanical evaluation techniques were employed. For a range of iron-aluminide compositions, cyclic anodic polarization tests were conducted in a number of electrolytes to provide information on anodic dissolution characteristics including tendencies for either active uniform corrosion, localized corrosion, or passivation. Average corrosion penetration rates were determined by application of Tafel methods or the polarization-resistance method in combination with Faraday's law. Immersion test methods were employed to verify corrosion behavior as determined by electrochemical methods and to evaluate localized-corrosion initiation times. U-bend corrosion tests were conducted at open-circuit corrosion potentials and at potentiostatically-controlled anodic and cathodic potentials to investigate the cracking tendencies of selected iron aluminides and to provide information on the cracking mechanism. And finally, slow-strain-rate corrosion tests were conducted at open-circuit and potentiostatically-controlled cathodic potentials to study the ductility response as related to cracking tendencies and the mechanism responsible. 32 refs., 19 figs., 11 tabs.

Buchanan, R.A.; Kim, J.G. (Tennessee Univ., Knoxville, TN (USA). Dept. of Materials Science and Engineering)

1991-04-01

136

Localized corrosion of a high nitrogen stainless steel: N-Mo synergism  

SciTech Connect

A series of twelve austenitic stainless steels with a composition range of Fe-22Cr-5Ni-5Mn-(1-5)Mo-(0-0.7)N were studied for resistance to localized corrosion in a deaerated 3.5 wt.% NaCl solution. Test temperatures ranged from 30 to 97 C. Results are compared to those of 304 and 316L stainless steel. The potentiodynamic polarization technique was used to determine the critical pit nucleation and protection potentials, and the potentiostatic cyclic thermometry technique was used to determine the critical pitting temperature. Results using the potentiodynamic polarization technique have shown that all of the stainless steels containing both nitrogen and molybdenum have pit nucleation potentials significantly higher than either 304 and 316 stainless steels. The nitrogen-molybdenum synergism is demonstrated by the fact that as little as 0.47 wt% N has a large effect on increasing the pit nucleation potential when molybdenum is present. Results using the potentiostatic cyclic thermometry technique have shown that the critical pitting potential is a linear function of the pitting resistance equivalent (PRE) and strongly dependent on both Mo and N concentration in the alloy.

Covino, Bernard S. Jr.; Russell, James H.; Holcomb, Gordon R.; Bullard, Sophie J. [Dept. of Energy, Albany, OR (United States). Albany Research Center

1997-01-01

137

Applications of electrochemical methods for investigations of localized corrosion of nitrogen-molybdenium stainless steels  

SciTech Connect

Electrochemical methods were used to determine the localized corrosion resistance of 12 austenitic stainless steels (SS) with a composition range of 22%Cr-5%Ni-5%Mn-(1% to 5%)Mo-(0.0% to 0.7%)N-balance Fe in a deaerated 3.5 wt% sodium chloride (NaCl) solution from 10°C to 97°C. Potentiodynamic polarization was used to determine the critical pitting potential (CPP), protection potentials, and polarization resistance (Rp), and potentiostatic cyclic thermometry was used to determine the critical pitting temperature (CPT) and critical crevice temperature (CCT). The results of potentiodynamic polarization showed that all of the SS containing both N and Mo have CPP significantly higher than either Type 304 (UNS S30400) or Type 316L (UNS S31603) SS. Rp correlated with the pitting resistance equivalent (PRE) for PRE from 20 to 45; however, for PRE > 45 there was no correlation. Results obtained by potentiostatic cyclic thermometry showed that CPT and the CCT are both linear functions of PRE, and strongly dependent on both Mo and N concentration in the alloy.

Russell, James H.; Covino, Bernard S., Jr.; Bullard, Sophie J.

2001-04-01

138

Underpotential-overpotential phase transformation phenomena in copper deposition processes on glassy carbon  

SciTech Connect

The initial stages of copper electrodeposition on glassy carbon were studied from a solution of 1 M CuSo{sub 4} in 0.5 M H{sub 2}SO{sub 4} by the methods of potentiostatic current transients and pulse experiments. The experimental data were analyzed according to the theory of potentiostatic current transients for three-dimensional multiple nucleation with diffusion controlled growth. The theory was found to be in good agreement with experimental data for instantaneous copper nucleation in the cathodic overpotential range {eta} = {minus}0.18--{minus}0.40 V. It is shown that in case of progressive nucleation at {eta} = {le} {minus}0.16 V, this theory can be used only for trend analysis of copper nucleation process parameters. An important influence of the initial state of glassy carbon surface on the nucleation rate was found determined by the underpotential. It is shown that the dependence of nucleation rate on the underpotential is inadequate and is determined by cathodic overpotential.

Arzhanova, T.A. [Russian Academy of Sciences, Vladivostok (Russian Federation)

1998-12-31

139

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

2014-12-01

140

Electrochemical reaction of lithium with nanosized vanadium antimonate  

SciTech Connect

Nanometric vanadium antimonate, VSbO{sub 4}, was prepared by mechanical milling from Sb{sub 2}O{sub 3} and V{sub 2}O{sub 5} and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Mossbaueer spectroscopy (MS) and X-ray photoelectron spectroscopy (XPS) techniques. Its reactivity towards lithium was examined by testing Li/VSbO{sub 4} cells under galvanostatic and potentiostatic regimes. The amount of Li inserted was found to be consistent with a two-step process involving the reactions (i) VSbO{sub 4}+8 Li{sup {yields}}Sb+V+4 Li{sub 2}O and (ii) Sb+3 Li{sup {yields}}Li{sub 3}Sb, the former being virtually irreversible and the latter reversible as suggested by the shape of the anodic and cathodic curves. Ex situ XPS measurements of the discharged and charged electrode provided direct evidence of the formation of alloyed Sb and confirmed the results of the potentiostatic curves regarding the irreversible or reversible character of the previous reactions. The Li/VSbO{sub 4} cell exhibited acceptable electrochemical performance, which surpassed that of other Sb-based compounds as the likely result of the formation of V and its associated enhanced electrode conductivity. - Graphical abstract: TEM image of nanosized VSbO{sub 4} sample.

Morales, Julian [Departamento de Quimica Inorganica e Ingenieria Quimica, Facultad de Ciencias, Campus de Rabanales, Edificio Marie Curie, Universidad de Cordoba, 14071 Cordoba (Spain); Sanchez, Luis [Departamento de Quimica Inorganica e Ingenieria Quimica, Facultad de Ciencias, Campus de Rabanales, Edificio Marie Curie, Universidad de Cordoba, 14071 Cordoba (Spain)]. E-mail: luis-sanchez@uco.es; Martin, Francisco [Laboratorio de Materiales y Superficie (Unidad Asociada al CSIC), Universidad de Malaga (Spain); Berry, Frank [Department of Chemistry, Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom)

2006-08-15

141

Effects of 2-amino-5-(ethylthio)-1,3,4-thiadiazole on copper corrosion as a corrosion inhibitor in 3% NaCl solutions  

NASA Astrophysics Data System (ADS)

Effects of 2-amino-5-(ethylthio)-1,3,4-thiadiazole (ATD) on copper corrosion as a corrosion inhibitor in de-aerated, aerated and oxygenated 3% NaCl solutions have been studied using potentiodynamic polarization, potentiostatic current-time, electrochemical impedance spectroscopic (EIS), weight loss and pH measurements along with scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) investigations. Potentiodynamic polarization measurements indicated that the presence of ATD in these solutions greatly decreases cathodic, anodic and corrosion currents. Potentiostatic current-time measurements and SEM/EDX investigations also showed that the ATD molecules are strongly adsorbed on the copper surface preventing it from being corroded easily. EIS measurements revealed that the charge transfer resistance increases due to the presence of ATD, and this effect increases with oxygen content in the solution. Weight loss measurements gave an inhibition efficiency of about 83% with 1.0 mM ATD present, increasing to about 94% at the ATD concentration of 5.0 mM. Results together are internally consistent with each other, showing that ATD is a good mixed-type inhibitor for copper corrosion with its inhibition efficiency increasing in the order of oxygenated > aerated > de-aerated 3% NaCl solutions.

Sherif, El-Sayed M.

2006-10-01

142

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

PubMed

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

2013-10-01

143

Design of a miniaturized electrochemical instrument for in-situ O2 monitoring  

NASA Astrophysics Data System (ADS)

The authors are working toward the design of a device for the detection of oxygen, following a discrete and an integrated instrumentation implementation. The discrete electronics are also used for preliminary analysis, to confirm the validity of the conception of system, and its set-up would be used in the characterization of the integrated device, waiting for the chip fabrication. This paper presents the design of a small and portable potentiostat integrated with electrodes, which is cheap and miniaturized, which can be applied for on-site measurements for the simultaneous detection of O2 and temperature in water systems. As a first approach a discrete PCB has been designed based on commercial discrete electronics and specific oxygen sensors. Dissolved oxygen concentration (DO) is an important index of water quality and the ability to measure the oxygen concentration and temperature at different positions and depths would be an important attribute to environmental analysis. Especially, the objective is that the sensor and the electronics can be integrated in a single encapsulated device able to be submerged in environmental water systems and be able to make multiple measurements. For our proposed application a small and portable device is developed, where electronics and sensors are miniaturized and placed in close proximity to each other. This system would be based on the sensors and electronics, forming one module, and connected to a portable notebook to save and analyze the measurements on-line. The key electronics is defined by the potentiostat amplifier, used to fix the voltage between the Working (WE) and Reference (RE) electrodes following an input voltage (Vin). Vin is a triangular signal, programmed by a LabViewinterface, which is also used to represent the CV transfers. To obtain a smaller and compact solution the potentiostat amplifier has also been integrated defining a full custom ASIC amplifier, which is in progress, looking for a point-of-care device. These circuits have been designed with a 0.13 ?m technology from ST Microelectronics through the CMP-TIMA service.

Colomer-Farrarons, Jordi; Miribel-Català, Pedro L.; Samitier, Josep; Arundell, Martin; Rodríguez, Ivón

2009-05-01

144

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

PubMed

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 CoCl2 aqueous solution by X-ray absorption and emission spectroscopy is presented. PMID:25362384

Schwanke, C; Golnak, R; Xiao, J; Lange, K M

2014-10-01

145

Crevice corrosion products of dental amalgam.  

PubMed

The objective of this study was to determine the in vitro corrosion products that resulted from crevice corrosion of low- and high-copper dental amalgams. Specimens were potentiostatically polarized in a chloride-containing electrolyte while set against a PTFE surface to form a crevice. After 16 h, corrosion products were examined by light microscopy, SEM, EDS, and XRD. Analysis showed the presence of three previously reported products [Sn4(OH)6Cl2, SnO, and Cu2O] and a new product, CuCl, which formed on high-copper, gamma 2-free amalgams. Thermodynamic considerations show that CuCl is stable for the reported in vivo potentials of amalgam restorations and the high acidity and high chloride ion concentration associated with crevice corrosion. PMID:2066490

Sutow, E J; Jones, D W; Hall, G C; Owen, C G

1991-07-01

146

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.; Bilgiç, S.; Y?lmaz, H.

2002-07-01

147

Electrochemical oxidation of tantalum and titanium in nitrate melts  

SciTech Connect

The authors present the results of a study of the anode oxidation of tantalum and titanium in nitrate melts. The studies were conducted in NaNO/sub 3/-KNO/sub 3/ (50 mole %) at 515-660 K. They used various electrochemical methods: the volt-ampere curves with linear sweep of the potential and the chronopotentiometric and chronoamperometric dependences were recorded. Oxidation of the metals was realized under galvano- or potentiostatic conditions. X-ray diffraction studies of the oxides were made. The thickness of the oxide film was determined by gravimetric, volumetric, or spectrophotometric methods. In individual experiments the thickness of the oxide was estimated by means of electron microscopy.

Yurkinskii, V.P.; Firsova, E.G.; Makhalova, M.Yu.; Morachevskii, A.G.

1988-06-20

148

Synthesis of nano-structured polypyrrole/copper electrodes for nitrate and nitrite electroreduction  

NASA Astrophysics Data System (ADS)

Nanostructured polypyrrole film was synthesized onto a copper electrode in solutions of oxalic and salicylic acids and their buffers. The electrooxidation of pyrrole to form polypyrrole film and the electroreduction of nitrate and nitrite ions at synthesized Ppy modified copper electrodes (Ppy/Cu) in potassium chloride aqueous solutions were studied using chronoamperometry. The nanoporous structure of the synthesized Ppy films was characterized by scanning electron microscopy (SEM). Nitrate and nitrite reduction were performed by an electrochemical method under potentiostatic conditions. The Ppy/Cu electrodes prepared in the oxalate buffer and salicylic acid solutions perform more stable catalytic activity for nitrate reduction; their service life is about ten times longer than that for the electrodes prepared in oxalic acid solution. After 20?h of electrolysis, the nitrite was reduced completely with 100% efficiency and the nitrate was reduced with 35% efficiency. Report submitted to the 5th International Workshop on Advanced Materials Science and Nanotechnology IWAMSN, Hanoi, 9–12 November 2010.

Phuong Thoa Nguyen, Thi; Thinh Nguyen, Viet; Nguyen Bui, Nhat; Do, Duong Kim Bao; Pham, Anh Minh

2010-09-01

149

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.

1992-01-01

150

Corrosion resistance of polyurethane-coated nitinol cardiovascular stents.  

PubMed

Corrosion of metal stents implanted inside an artery can have two adverse effects: (1) tissue reaction and possible toxic effects from the metal ions leaching out of the stent, and (2) loss of mechanical strength of the stent caused by corrosion. The corrosion resistance of Nitinol (Nickel-Titanium) stents and its modulation with different film thickness of polymer coating was studied against an artificial physiological solution using a Potentiostat/Galvanostat and an electrochemical corrosion cell. The corrosion rate decreased rapidly from 275 microm/year for an uncoated surface down to less than 13 microm/year for a 30 microm thick polyurethane coating. Stainless steel (316L) and Nitinol both contain potentially toxic elements, and both are subject to stress corrosion. Minimization of corrosion can significantly reduce both tissue reaction and structural degradation. PMID:14870939

Mazumder, M M; De, S; Trigwell, S; Ali, N; Mazumder, M K; Mehta, J L

2003-01-01

151

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.; Gündel, A.; Maroun, F.; Allongue, P.; Schuster, R.

2008-08-01

152

Investigation into the susceptibility of corrosion resistant alloys to biocorrosion. Final report, September 1991-October 1995  

SciTech Connect

The influence of sulfate-reducing bacteria (SRB) on the passivity of Mo-bearing (type 317L) and low Mo content (type 304) austenitic stainless steels (SS) was investigated by x-ray photoelectron spectroscopy (XPS), microbiological and electrochemical techniques. Samples were exposed to SRB, and then the resulting surfaces were analyzed by XPS, and the corrosion resistance by potentiodynamic polarization in deaerated 0.1 M HCI. In order to further understand their passivity, the SRB-exposed samples were also analyzed by XPS after potentiostatic polarization at a passive potential in the hydrochloric solution. The characterization was performed under two surface conditions: unrinsed and rinsed by deaerated alcohol and deionized water.

Clayton, C.R.

1996-02-02

153

Structure and dye-sensitized solar cell application of TiO2 nanotube arrays fabricated by the anodic oxidation method  

NASA Astrophysics Data System (ADS)

Well-ordered TiO2 nanotube arrays were fabricated by the potentiostatic anodic oxidation method using pure Ti foil as a working electrode and ethylene glycol solution as an electrolyte with the small addition of NH4F and H2O. The influence of anodization temperature and time on the morphology and formation of TiO2 nanotube arrays was examined. The TiO2 nanotube arrays were applied as a photoelectrode to dye-sensitized solar cells. Regardless of anodizing temperature and time, the average diameter and wall thickness of TiO2 nanotube arrays show a similar value, whereas the length increases with decreasing reaction temperature. The conversion efficiency is very low, which is due to a morphology breaking of the TiO2 nanotube arrays in the manufacturing process of a photoelectrode.

Ok, Seon-Yeong; Cho, Kwon-Koo; Kim, Ki-Won; Ryu, Kwang-Sun

2010-05-01

154

Ferroelectric lithography: bottom-up assembly and electrical performance of a single metallic nanowire.  

PubMed

We report on both the assembly of noble-metal nanowires by means of the nanotechnological and large-scale integrable approach of ferroelectric lithography and their performance testing upon electrical transport. Our results on LiNbO(3) single crystal templates show that the deposition of different elemental metals from ionic solutions by photochemical reduction is confined to the ferroelectric 180 degrees domain walls. Current-voltage-characteristics recorded from such nanowires of typically 30-300 microm in length revealed an Ohmic behavior that even improved with time. Additionally, we also examined the local topographic and potentiostatic properties of such wires using dynamic scanning force microscopy in combination with Kelvin probe force microscopy. PMID:19159245

Haussmann, Alexander; Milde, Peter; Erler, Christiane; Eng, Lukas M

2009-02-01

155

High-throughput screening of thin-film semiconductor material libraries I: system development and case study for ti?w?o.  

PubMed

An automated optical scanning droplet cell (OSDC) enables high-throughput quantitative characterization of thin-film semiconductor material libraries. Photoelectrochemical data on small selected measurement areas are recorded including intensity-dependent photopotentials and -currents, potentiodynamic and potentiostatic photocurrents, as well as photocurrent (action) spectra. The OSDC contains integrated counter and double-junction reference electrodes and is fixed on a precise positioning system. A Xe lamp with a monochromator is coupled to the cell through a thin poly(methyl methacrylate) (PMMA) optical fiber. A specifically designed polytetrafluoroethylene (PTFE) capillary tip is pressed on the sample surface and defines through its diameter the homogeneously illuminated measurement area. The overall and wavelength-resolved irradiation intensities and the cell surface area are precisely determined and calibrated. System development and its performance are demonstrated by means of screening of a Ti?W?O thin film. PMID:25727402

Sliozberg, Kirill; Schäfer, Dominik; Erichsen, Thomas; Meyer, Robert; Khare, Chinmay; Ludwig, Alfred; Schuhmann, Wolfgang

2015-04-13

156

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

2012-01-01

157

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

NASA Astrophysics Data System (ADS)

Large-sized titanium dioxide (TiO2) nanotube arrays with an outer diameter of approximately 500 nm have been successfully synthesized by potentiostatic anodization at 180 V in a used electrolyte with the addition of 1.5 M 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).

Liu, Xiaolin; Guo, Min; Cao, Jianjun; Lin, Jia; Tsang, Yuen Hong; Chen, Xianfeng; Huang, Haitao

2014-07-01

158

Engineering PQS Biosynthesis Pathway for Enhancement of Bioelectricity Production in Pseudomonas aeruginosa Microbial Fuel Cells  

PubMed Central

The biosynthesis of the redox shuttle, phenazines, in Pseudomonas aeruginosa, an ubiquitous microorganism in wastewater microflora, is regulated by the 2-heptyl-3,4-dihydroxyquinoline (PQS) quorum-sensing system. However, PQS inhibits anaerobic growth of P. aeruginosa. We constructed a P. aeruginosa strain that produces higher concentrations of phenazines under anaerobic conditions by over-expressing the PqsE effector in a PQS negative ?pqsC mutant. The engineered strain exhibited an improved electrical performance in microbial fuel cells (MFCs) and potentiostat-controlled electrochemical cells with an approximate five-fold increase of maximum current density relative to the parent strain. Electrochemical analysis showed that the current increase correlates with an over-synthesis of phenazines. These results therefore demonstrate that targeting microbial cell-to-cell communication by genetic engineering is a suitable technique to improve power output of bioelectrochemical systems. PMID:23700414

Cao, Bin; Seviour, Thomas; Nesatyy, Victor J.; Marsili, Enrico; Kjelleberg, Staffan; Givskov, Michael; Tolker-Nielsen, Tim; Song, Hao; Loo, Joachim Say Chye; Yang, Liang

2013-01-01

159

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)

2013-06-01

160

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: byyoo@hanyang.ac.kr [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: lgh1636@kims.re.kr [Materials Processing Division, Korea Institute of Materials Science, 66, Sangnam-dong, Changwon 641-010 (Korea, Republic of)

2012-10-15

161

Effects of anodization growth of TiO2-nanotube array membrane on photo-conversion efficiency of dye-sensitized solar cell  

NASA Astrophysics Data System (ADS)

Membranes of TiO2 nanotube(NT) arrays were grown by potentiostatic anodic oxidation in an ethylene glycol electrolyte with small addition of H2O and NH4F. Ti metal plate with a thickness of 0.1 mm was completely converted into ?0.2 mm-thick TiO2 NT membrane for 24 to 96 h of anodization. Stacked NTs in membrane were separated into individual NT from the neighboring NTs as anodization continues up to 96 h. As-fabricated membrane of NTs were mechanically grinded to yield fine NT particles for the photoanode application to dye-sensitized solar cells (DSCs), in replacement of conventional TiO2 particles. Photo-conversion efficiency of the DSC using TiO2 crystalline NT particles is varying from 2.22% to 5.03%. Fine TiO2 NT particles can increase dye attachment due to high surface to volume ratio.

Park, Min-Woo; Chun, Ki-Young

2009-03-01

162

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

163

Electrochemical formation of Al-Tm intermetallics in eutectic LiCl-KCl melt containing Tm and Al ions  

NASA Astrophysics Data System (ADS)

This work focuses on investigating the electrochemical formation of Al-Tm and Al-Li-Tm alloys in LiCl-KCl-AlCl3-Tm2O3 melt on both W and Al electrodes. Thermodynamic calculation and electrochemical behavior of LiCl-KCl melt containing both AlCl3 and Tm2O3 showed that AlCl3 can chlorinate Tm2O3 to release Tm(III) ions. Three kinds of Al-Tm intermetallics at about -1.26, -1.32 and -1.43 V were detected by means of various electrochemical measurement techniques, i.e. cyclic voltammetry, square wave voltammetry and open circuit chronopotentiometry. Potentiostatic and galvanostatic electrolysis were carried out on Al and W electrodes to prepare Al-Tm and Al-Li-Tm alloys, respectively. The composition of Al-Li-Tm alloys was analyzed by inductive coupled plasma atomic emission spectrometer (ICP-AES).

Li, Xing; Yan, Yong-De; Zhang, Mi-Lin; Tang, Hao; Ji, De-Bin; Han, Wei; Xue, Yun; Zhang, Zhi-Jian

2014-09-01

164

Electrochemical behavior of CrN coating for polymer electrolyte membrane fuel cell  

NASA Astrophysics Data System (ADS)

CrN films on a bipolar plate in polymer electrolyte membrane fuel cells have several advantages owing to their excellent corrosion resistance and mechanical properties. Three CrN samples deposited at various radio frequency (RF) powers by RF magnetron sputtering were evaluated under potentiodynamic, potentiostatic and electrochemical impedance spectroscopy conditions. The electrochemical impedance spectroscopy data were monitored for 168 h in a corrosive environment at 70 °C to determine the coating performance at +600 mVSCE under simulated cathodic conditions in a polymer electrolyte membrane fuel cell. The electrochemical behavior of the coatings increased with decreasing RF power. CrN films on the AISI 316 stainless steel substrate showed high protective efficiency and charge transfer resistance, i.e. increasing corrosion resistance with decreasing RF power. X-ray diffraction confirmed the formation of a CrN(200) preferred orientation at low RF power.

Nam, N. D.; Park, I. J.; Kim, J. G.; Tai, P. H.; Yoon, D. H.

2010-05-01

165

Integrated circuit-based electrochemical sensor for spatially resolved detection of redox-active metabolites in biofilms  

PubMed Central

Despite advances in monitoring spatiotemporal expression patterns of genes and proteins with fluorescent probes, direct detection of metabolites and small molecules remains challenging. A technique for spatially resolved detection of small molecules would benefit the study of redox-active metabolites produced by microbial biofilms, which can drastically affect colony development. Here we present an integrated circuit-based electrochemical sensing platform featuring an array of working electrodes and parallel potentiostat channels. “Images” over a 3.25 × 0.9 mm area can be captured with a diffusion-limited spatial resolution of 750 ?m. We demonstrate that square wave voltammetry can be used to detect, identify, and quantify (for concentrations as low as 2.6 ?M) four distinct redox-active metabolites called phenazines. We characterize phenazine production in both wild-type and mutant Pseudomonas aeruginosa PA14 colony biofilms, and find correlations with fluorescent reporter imaging of phenazine biosynthetic gene expression. PMID:24510163

Bellin, Daniel L.; Sakhtah, Hassan; Rosenstein, Jacob K.; Levine, Peter M.; Thimot, Jordan; Emmett, Kevin; Dietrich, Lars E. P.; Shepard, Kenneth L.

2014-01-01

166

The relationship between induction time for pitting and pitting potential for high purity aluminum.  

SciTech Connect

The objective of this study was to determine if a distribution of pit induction times (from potentiostatic experiments) could be used to predict a distribution of pitting potentials (from potentiodynamic experiments) for high-purity aluminum. Pit induction times were measured for 99.99 Al in 50 mM NaCl at potentials of -0.35, -0.3, -0.25, and -0.2 V vs. saturated calomel electrode. Analysis of the data showed that the pit germination rate generally was an exponential function of the applied potential; however, a subset of the germination rate data appeared to be mostly potential insensitive. The germination rate behavior was used as an input into a mathematical relationship that provided a prediction of pitting potential distribution. Good general agreement was found between the predicted distribution and an experimentally determined pitting potential distribution, suggesting that the relationships presented here provide a suitable means for quantitatively describing pit germination rate.

Wall, Frederick Douglas; Vandenavyle, Justin J.; Martinez, Michael A.

2003-08-01

167

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

PubMed

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

2014-09-28

168

Microdialysis sampling coupled to microchip electrophoresis with integrated amperometric detection on an all-glass substrate.  

PubMed

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 J; Lunte, Susan M

2013-07-22

169

Electro-active sensor, method for constructing the same; apparatus and circuitry for detection of electro-active species  

NASA Technical Reports Server (NTRS)

An electro-active sensor includes a nonconductive platform with a first electrode set attached with a first side of a nonconductive platform. The first electrode set serves as an electrochemical cell that may be utilized to detect electro-active species in solution. A plurality of electrode sets and a variety of additional electrochemical cells and sensors may be attached with the nonconductive platform. The present invention also includes a method for constructing the aforementioned electro-active sensor. Additionally, an apparatus for detection and observation is disclosed, where the apparatus includes a sealable chamber for insertion of a portion of an electro-active sensor. The apparatus allows for monitoring and detection activities. Allowing for control of attached cells and sensors, a dual-mode circuitry is also disclosed. The dual-mode circuitry includes a switch, allowing the circuitry to be switched from a potentiostat to a galvanostat mode.

Buehler, Martin (Inventor)

2009-01-01

170

Surface phenomena of hydroxyapatite film on the nanopore formed Ti-29Nb-xZr alloy by anodization for bioimplants.  

PubMed

In this study, surface phenomena of hydroxyapatite (HA) film on the nanopore formed Ti-29Nb-xZr alloy by anodization for bioimplants have been investigated by electron beam physical vapor deposition (EB-PVD), field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), potentiostat and contact angle. The microstructure of Ti-29Nb-xZr alloys exhibited equiaxed structure and alpha" phase decreased, whereas beta phase increased as Zr content increased. The increment of Zr contents in HA coated nanotubular Ti-29Nb-xZr alloys showed good corrosion potential in 0.9% NaCI solution. The wettability of HA coated nanotubular surface was higher than that of non-coated samples. PMID:23755573

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

2013-03-01

171

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.

1977-01-01

172

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

2014-09-01

173

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

PubMed

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

2014-03-21

174

Recovery of the actinides by electrochemical methods in molten chlorides using solid aluminium cathode  

SciTech Connect

An electrorefining process in molten chloride salts is being developed at ITU to reprocess the spent nuclear fuel. According to the thermochemical properties of the system, aluminium is the most promising electrode material for the separation of actinides (An) from lanthanides (Ln). The actinides are selectively reduced from the fission products and stabilized by the formation of solid and compact actinide-aluminium alloys with the reactive cathode material. In this work, the maximum loading of aluminium with actinides was investigated by potentiostatic and galvano-static electrorefining of U-Pu- Zr alloys. A very high aluminium capacity was achieved, as the average loading was 1.6 g of U and Pu into 1 g of aluminium and the maximum achieved loading was 2.3 g. For recovery of the actinides from aluminium, a process based on chlorination and a subsequent sublimation of AlCl{sub 3} is proposed. (authors)

Malmbeck, R.; Mendes, E.; Serp, J.; Soucek, P.; Glatz, J.P. [European Commission, JRC, Institute for Transuranium Elements, Postfach 2340, 76125 Karlsruhe (Germany); Cassayre, L. [Laboratoire de Genie Chimique - LGC, Universite Paul Sabatier, UMR 5503, 118 route de Narbonne, 31062 Toulouse Cedex 04 (France)

2007-07-01

175

Chemical versus Electrochemical Synthesis of Carbon Nano-onion/Polypyrrole Composites for Supercapacitor Electrodes.  

PubMed

The development of high-surface-area carbon electrodes with a defined pore size distribution and the incorporation of pseudo-active materials to optimize the overall capacitance and conductivity without destroying the stability are at present important research areas. Composite electrodes of carbon nano-onions (CNOs) and polypyrrole (Ppy) were fabricated to improve the specific capacitance of a supercapacitor. The carbon nanostructures were uniformly coated with Ppy by chemical polymerization or by electrochemical potentiostatic deposition to form homogenous composites or bilayers. The materials were characterized by transmission- and scanning electron microscopy, differential thermogravimetric analyses, FTIR spectroscopy, piezoelectric microgravimetry, and cyclic voltammetry. The composites show higher mechanical and electrochemical stabilities, with high specific capacitances of up to about 800?F?g(-1) for the CNOs/SDS/Ppy composites (chemical synthesis) and about 1300?F?g(-1) for the CNOs/Ppy bilayer (electrochemical deposition). PMID:25736714

Mykhailiv, Olena; Imierska, Monika; Petelczyc, Martyna; Echegoyen, Luis; Plonska-Brzezinska, Marta E

2015-04-01

176

Sulfurized activated carbon for high energy density supercapacitors  

NASA Astrophysics Data System (ADS)

Sulfurized activated carbon (SAC), made by coating the pore surface with thiophenic sulfur functional groups from the pyrolysis of sulfur flakes, were characterized and tested for supercapacitor applications. From X-ray photoelectron spectroscopy (XPS), the sulfur content in the SAC was found to be 2.7 at%. Electrochemical properties from potentiostatic and galvanostatic measurements, and electrochemical impedance spectroscopy (EIS) were used to evaluate the effect of sulfur on porous carbon electrodes. The SAC electrode exhibits better conductivity, and an obvious increase in specific capacitance that is almost 40% higher than plain activated carbons (ACs) electrode at a high current density of 1.4 A g-1. The proposed mechanism for improved conductivity and capacitive performance due to the sulfur functional groups on ACs will be discussed.

Huang, Yunxia; Candelaria, Stephanie L.; Li, Yanwei; Li, Zhimin; Tian, Jianjun; Zhang, Lili; Cao, Guozhong

2014-04-01

177

Silver nanowires electrodeposited into nanoporous templates: Study of the influence of sizes on crystallinity and structural properties  

NASA Astrophysics Data System (ADS)

In this work, results on the study of the influence of silver nanowire dimensions on the crystallinity and structural properties are presented. Silver nanowire arrays with high aspect ratios were prepared in the hollow structures of nanoporous templates using potentiostatic electrodeposition. Two types of material were employed as a template: commercial porous anodic aluminum oxide (with a mean pore diameter of 180 nm) and track-etched polycarbonate membranes (with a mean pore diameter of 15, 30 and 80 nm). Characterization of the silver nanowires has been done by EDS, XRD, TEM and electron diffraction. The degree of preferred crystallographic orientation (along the (1 1 1), (2 0 0) or (2 2 0) crystallographic planes) and the crystallite size of the silver nanowires as a function of template pore diameter are given and discussed.

Dalchiele, E. A.; Marotti, R. E.; Cortes, A.; Riveros, G.; Gómez, H.; Martínez, L.; Romero, R.; Leinen, D.; Martin, F.; Ramos-Barrado, J. R.

2007-03-01

178

Silver nanowire arrays electrochemically grown into nanoporous anodic alumina templates  

NASA Astrophysics Data System (ADS)

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 µm, respectively, which coincide with the dimensions of the template used. Structural characterization using x-ray diffraction shows that the Ag nanowires are highly crystalline, and those obtained at higher overpotentials present a very strong [220] preferred crystallographic orientation. The optical properties of the silver nanowires embedded in the alumina template show a clear edge close to 320 nm, that is an expected value for a silver-alumina composite material.

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

2006-01-01

179

Preparation and Characterization of the Porous (TiO2) Oxide Films of Nanostructure for Biological and Medical Applications  

SciTech Connect

In this paper, galvanostatically and potentiostatically formed surface oxide film on titanium in H2O2 free and H2O2 containing H2SO4 solutions were investigated. Conventional electrochemical techniques and electrochemical impedance spectroscopy (EIS) measurements beside the scanning electron microscope (SEM) were used. In absence of H2O2, the impedance response indicated a stable thin oxide film which depends on the mode of anodization of the metal. However, the introduction of H2O2 into the solution resulted in significant changes in the film characteristics, which were reflected in the EIS results. The film characteristics were found to be affected by the mode of oxide film growth and polarization time. The H2O2 addition to the solution has led to a significant decrease in the corrosion resistance of the passive film. The electrochemical and the use of equivalent circuit models have led to the understanding of the film characteristics under different conditions.

Fadl-Allah, Sahar A.; El Sherief, Rabab M.; Badawy, Waheed A. [Chemistry Department, Faculty of Science, University of Cairo (Egypt)

2007-02-14

180

The electrochemical behaviour of 316L austenitic stainless steel in Cl- containing environment under different H2S partial pressures  

NASA Astrophysics Data System (ADS)

In oil-gas production environments, presence of H2S-Cl- can induce deterioration of the passive film, leading to pitting corrosion of stainless steels. In this paper, by using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and capacitance measurements (Mott-Schottky analysis), the electrochemical behaviour of AISI 316L austenitic stainless steel was investigated in Cl- solutions under different H2S partial pressures (from 0 to 1.0 bar). The results indicated that presence of H2S in Cl- solution can accelerate both the cathodic and anodic current density, leading to a metastable passive state in higher passive potential range, changing the semiconductor behaviour from p-type to n-type, increasing its susceptibility to corrosion. XPS analysis was employed to characterize the surface film after potentiostatic polarization, whose results provide good evidences for the electrochemical measurements.

Ding, Jinhui; Zhang, Lei; Lu, Minxu; Wang, Jing; Wen, Zhibin; Hao, Wenhui

2014-01-01

181

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

PubMed

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

2015-02-16

182

Self-organized highly ordered TiO{sub 2} nanotubes in organic aqueous system  

SciTech Connect

A simple method to achieve self-organized, freestanding TiO{sub 2} nanotube array was constructed, free of corrosive etching process which was traditionally employed to separate TiO{sub 2} nanotubes from the metallic Ti substrate. The TiO{sub 2} nanotube arrays were constructed through potentiostatic anodization of Ti foil in aqueous electrolyte containing NH{sub 4}F and ethylene glycol. The nanotubes in the array were of 45 {mu}m lengths and 100 nm average pore diameters. The effect of NH{sub 4}F concentration on the length of the self-organized nanotube arrays was investigated. Electrochemical and spectroscopic measurements showed that the as-prepared nanotubes possessed large surface areas, good uniformity, and were ready for enzyme immobilization. The as-prepared nanotube arrays were amorphous, but crystallized with annealing at elevated temperatures, as demonstrated by X-ray diffraction (XRD).

Wan Jun [College of Life Science and Pharmaceutical Engineering, Nanjing University of Technology, 210093 Nanjing, Jiangsu (China); Key Laboratory of Eco-chemical Engineering, Ministry of Education, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042 (China); Yan Xia; Ding Junjie; Wang Meng [Key Laboratory of Eco-chemical Engineering, Ministry of Education, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042 (China); Hu Kongcheng, E-mail: wanjundz@sohu.com [College of Life Science and Pharmaceutical Engineering, Nanjing University of Technology, 210093 Nanjing, Jiangsu (China)

2009-12-15

183

Development of the high-temperature redox electrode and improved corrosion rate meter. Interim report for period ending September 1980  

SciTech Connect

The oxidation-reduction (redox) electrode studies at Pacific Northwest Laboratory (PNL) were completed with the examination of the sulfide-sulfate system. This system is extremely reducing, and it was concluded that the redox electrode would still respond to the entry of oxygen even though sulfide is an oxygen getter. The corrosion rate of platinum in oxygenated brine was determined at 250/sup 0/C. It was concluded that the mechanism of response to oxygen fits a mixed potential model. Work began on the improved corrosion rate meter (ICR). A potentiostat and programmer were constructed and successfully tested. Corrosion tests were carried out in 25/sup 0/C brine with and without oxygen, and the ICR response was very good when compared to corrosion rates determined by weight loss. Future work will involve autoclave tests and development of microprocessor control of the electronics to simplify the measurements.

Danielson, M.J.; Koski, O.H.

1981-09-01

184

Electrochemical deposition and characterization of Ni-P alloy thin films  

SciTech Connect

Nickel phosphorus (Ni-P) alloy thin films were prepared by electrodeposition on pre-cleaned copper substrates using a potentiostatic cathodic electrodeposition method from sulfate electrolyte baths at various sodium hypophosphite (NaH{sub 2}PO{sub 2}) concentrations. X-ray diffraction studies reveal polycrystalline cubic alloys at low concentrations of phosphorus (< 13.5 at.%) and these transformed into amorphous alloys at higher concentrations. X-ray photoelectron spectra show the presence of Ni{sub 2}p and P{sub 2}p lines corresponding to their binding energies. Scanning electron microscopic studies reveal spherical shaped grains at low phosphorus contents and modules of cauliflower type morphology at higher phosphorus concentrations. The effects of phosphorus concentration on the crystal structure, composition and morphology are studied and discussed.

Mahalingam, T. [Department of Physics, Alagappa University, Karaikudi, 630 003 (India) and Department of Electrical and Computer Engineering, College of Information Technology, Ajou University, Suwon 443-749 (Korea, Republic of)]. E-mail: maha51@rediffmail.com; Raja, M. [Department of Physics, Alagappa University, Karaikudi, 630 003 (India); Thanikaikarasan, S. [Department of Physics, Alagappa University, Karaikudi, 630 003 (India); Sanjeeviraja, C. [Department of Physics, Alagappa University, Karaikudi, 630 003 (India); Velumani, S. [Departamento de Fisica, ITESM-Campus Monterrey, Nuevo Leon, C.P. 64849 (Mexico); Moon, Hosun [Department of Electrical and Computer Engineering, College of Information Technology, Ajou University, Suwon 443-749 (Korea, Republic of); Kim, Yong Deak [Department of Electrical and Computer Engineering, College of Information Technology, Ajou University, Suwon 443-749 (Korea, Republic of)

2007-08-15

185

Oscillating electrochemical reaction in copper-containing imidazolium ionic liquids.  

PubMed

An example of an electrochemical oscillator in ionic liquids is presented. Solutions of the ionic liquid 1-ethyl-3-methylimidazolium chloride, [C(2)mim]Cl, which contain both Cu(+) and Cu(2+) ions, show current oscillations during potentiostatic polarization. The oscillations were analyzed by the Quartz Crystal Microbalance (QCM) technique and by Electrochemical Impedance Spectroscopy (EIS). The electrochemical oscillations are of the N-NDR-type, because the low frequency end of the impedance spectrum has negative real impedances. The oscillating current leads to an oscillating growth speed of a metallic copper layer. Besides the presence of both Cu(+) and Cu(2+), the presence of chloride is a necessary, yet not a sufficient, condition for the occurrence of current oscillations. Oscillating currents were also observed for the ionic liquids 1-butyl-3-methylimidazolium chloride and 1-butyl-2,3-dimethylimidazolium chloride, but not for tributyltetradecylphosphonium chloride and N-butylpyridinium chloride. PMID:21808767

Schaltin, Stijn; Binnemans, Koen; Fransaer, Jan

2011-09-14

186

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 500 nm have been successfully synthesized by potentiostatic anodization at 180 V in a used electrolyte with the addition of 1.5 M 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

2014-01-01

187

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.

1987-07-01

188

Graphitic mesoporous carbon as a durable fuel cell catalyst support  

SciTech Connect

Highly stable graphitic mesoporous carbons (GMPCs) are synthesized by heat-treating polymer-templated mesoporous carbon (MPC) at 2600 C. The electrochemical durability of GMPC as Pt catalyst support (Pt/GMPC) is compared with that of carbon black (Pt/XC-72). Comparisons are made using potentiostatic and cyclic voltammetric techniques on the respective specimens under conditions simulating the cathode environment of PEMFC (proton exchange membrane fuel cell). The results indicate that the Pt/GMPC is much more stable than Pt/XC-72, with 96% lower corrosion current. The Pt/GMPC also exhibits a greatly reduced loss of catalytic surface area: 14% for Pt/GMPC vs. 39% for Pt/XC-72.

Dai, Sheng [ORNL; Liang, Chengdu [ORNL; Shanahan, Paul [University of California; Xu, Lianbin [University of California; Waje, Mahesh [University of California; Yan, Y.S. [University of California

2008-01-01

189

In Situ Characterization of Triboelectrochemical Effects on Topography of Patterned Copper Surfaces  

NASA Astrophysics Data System (ADS)

The topographic response of patterned copper surfaces to chemical-mechanical polishing (CMP) was investigated using a triboelectrochemical approach. Experimental methods include using a combined system containing a tribometer and a potentiostat. Results showed that more step height reduction and lower average surface roughness were obtained via CMP in acidic than in alkaline slurry. The increased contact area between wafer, pad, and abrasives was associated with the increase in friction. It was found that pH-dependent oxide formation and removal dominate the step height reduction for both acidic and alkaline slurries. The in situ approach pinpointed interactions between mechanical stimulation, chemical reaction, and electrochemical passivation. This research is beneficial to understanding triboelectrochemistry in Cu chemical-mechanical polishing of patterned wafers, an important application in semiconductor manufacturing.

Joo, Sukbae; Liang, Hong

2013-06-01

190

Characterization of blister formation and pitting of tungsten ion implanted aluminum  

SciTech Connect

the application of W implantation to Al1100 has resulted in improved resistance to pitting corrosion in a neutral pH, 1 wt% NaCl solution. Doses ranging from 3 {times} 10{sup 16} to 9 {times} 10{sup 16} ions/cm{sup 2} greatly enhanced the range of passivity during anodic polarization, and potentiostatic and immersion testing results indicated the implanted W acts to resist the growth of a nucleated pit. Although moderate increases in the pitting potential of Al 1100 (and also 99.9999% pure Al) have been realized, the extremely high pitting potentials achieved by co-sputtering thin films of Al and W were not reproducibly translated to bulk aluminum alloys. This discrepancy can possibly be traced to the morphology of the localized corrosion and breakdown of the passive film on ion-implanted Al, which takes the form of oxide blistering as a forerunner of pit growth.

Smith, P.P.; Buchanan, R.A. [Univ. of Tennessee, Knoxville, TN (United States)] [Univ. of Tennessee, Knoxville, TN (United States); Williams, J.M. [Oak Ridge National Lab., TN (United States)] [Oak Ridge National Lab., TN (United States)

1995-06-15

191

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.

2014-09-01

192

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: Kathrin.lange@helmholtz-berlin.de [Helmholtz-Zentrum Berlin für Materialien und Energie, Institute of Solar Fuels, Albert-Einstein-Straße 15, 12489 Berlin (Germany); Golnak, R.; Xiao, J. [Helmholtz-Zentrum Berlin für Materialien und Energie, Institute of Methods for Material Development, Albert-Einstein-Straße 15, 12489 Berlin (Germany)

2014-10-15

193

Integrated circuit-based electrochemical sensor for spatially resolved detection of redox-active metabolites in biofilms  

NASA Astrophysics Data System (ADS)

Despite advances in monitoring spatiotemporal expression patterns of genes and proteins with fluorescent probes, direct detection of metabolites and small molecules remains challenging. A technique for spatially resolved detection of small molecules would benefit the study of redox-active metabolites that are produced by microbial biofilms and can affect their development. Here we present an integrated circuit-based electrochemical sensing platform featuring an array of working electrodes and parallel potentiostat channels. ‘Images’ over a 3.25 × 0.9?mm2 area can be captured with a diffusion-limited spatial resolution of 750??m. We demonstrate that square wave voltammetry can be used to detect, identify and quantify (for concentrations as low as 2.6??M) four distinct redox-active metabolites called phenazines. We characterize phenazine production in both wild-type and mutant Pseudomonas aeruginosa PA14 colony biofilms, and find correlations with fluorescent reporter imaging of phenazine biosynthetic gene expression.

Bellin, Daniel L.; Sakhtah, Hassan; Rosenstein, Jacob K.; Levine, Peter M.; Thimot, Jordan; Emmett, Kevin; Dietrich, Lars E. P.; Shepard, Kenneth L.

2014-02-01

194

Sodium insertion into vanadium pentoxide in methanesulfonyl chloride-aluminum chloride ionic liquid  

NASA Astrophysics Data System (ADS)

Methanesulfonyl chloride (MSC) forms a room temperature ionic liquid with AlCl 3. The electrochemical properties of vanadium pentoxide (V 2O 5) films prepared by the sol-gel route were studied in this electrolyte. As a potential cathode, sodium is reversibly intercalated into the V 2O 5 film up to a stoichiometry of 1.6 mole Na/mole V 2O 5 (-1 V versus Al(III)/Al<1.5 V) after the first discharge. The diffusion coefficient ( DNa +) in the V 2O 5 film was determined to be between 5E-14 and 9E-12 cm 2/s using the potentiostatic intermittent-titration technique.

Su, Lianyoung; Winnick, Jack; Kohl, Paul

195

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

PubMed

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

García-Torres, J; Gispert, C; Gómez, E; Vallés, E

2015-01-21

196

High frequency reference electrode  

DOEpatents

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)

1994-01-01

197

Corrosion behavior of boride layers evaluated by the EIS technique  

NASA Astrophysics Data System (ADS)

The corrosion behavior of boride layers at the AISI 304 steel surface is evaluated in the present study. Electrochemical impedance spectroscopy (EIS) technique was used for the evaluation of the polarization resistance at the steel surface, with the aid of AUTOLAB potentiostat. Samples were treated with boron paste thickness of 4 and 5 mm, in the range of temperatures 1123 ? T ? 1273 K and exposed time of 4 and 6 h. The electrochemical technique employed 10 mV AC with a frequency scan range from 8 kHz to 3 mHz in deaerated 0.1 M NaCl solution. Nyquist diagrams show that the highest values of corrosion resistance are present in the samples borided at the temperature of 1273 K, with treatment time of 4 h and 4 mm of boron paste thickness. The values of corrosion resistance on borided steels are compared with the porosity exhibited in the layers.

Campos, I.; Palomar-Pardavé, M.; Amador, A.; VillaVelázquez, C.; Hadad, J.

2007-09-01

198

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

2014-01-01

199

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

PubMed

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

2014-07-31

200

Effect of electrochemical deposition parameters on the synthesis, structure and properties of polyaniline-polypyrrole composite coatings on steel  

NASA Astrophysics Data System (ADS)

Polyaniline-polypyrrole composite coatings were formed on low carbon steel using oxalic acid as electrolyte by aqueous potentiostatic electrodeposition. Potentiostatic method is a powerful technique that can force simultaneous polymerization of both pyrrole and aniline. A passive layer of iron (II) oxalate is deposited on the steel surface prior to the formation of composite coatings. The electrochemical deposition process shows three distinct regimes---dissolution of steel, formation of passive layer and formation of polymeric composite coatings. These three regimes have been studied in depth using spectroscopic techniques and electron microscopy. Quantitative analysis of the Current-time transient (I-t) curves show that the nucleation and growth of the passive layer occur by diffusion controlled 3-D instantaneous nucleation. It has also been shown that the morphology and the chemical structure of the composite coatings depend upon the electrochemical deposition (ECD) parameters. The ECD parameters that affect the formation of the coatings are the applied potential; molar feed ratio of monomers and the reaction time. The development of the composite coatings on steel was studied in depth using Infrared Spectroscopy, Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy. For equimolar feed ratio of monomers (aniline and pyrrole), it was shown that polypyrrole starts to form on the steel surface prior to the incorporation of polyaniline. Corrosion resistance and adhesion strength of the coatings were evaluated using DC polarization tests and Lap Joint tests respectively. It was shown that the electrochemical deposition parameters (molar feed ratio of monomers, applied potential and reaction time) influence the corrosion and adhesion performance of the coatings. In general, polyaniline-polypyrrole composite coatings show much better performance than the homopolymers. Especially, the coatings formed using equimolar feed ratio of monomers showed better results than those formed at all other feed ratios.

Rajagopalan, Ramakrishnan

201

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

2012-01-01

202

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.

203

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

2003-04-15

204

Real-Time Telemetry System for Amperometric and Potentiometric Electrochemical Sensors  

PubMed Central

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

2011-01-01

205

Investigations of the O sub 2 reduction reaction at the Platinum/Nafion interface using a solid-state electrochemical cell  

SciTech Connect

This paper reports on research in solid polymer electrolyte fuel cells gaining momentum because of the prospects of attaining high energy efficiencies and power densities essential for transportation and space applications. The most advanced solid polymer electrolytes for these fuel cells are the perfluorosulfonate ionomers (PFSIs), such as Du Pont's Nafion and the Dow PFSIs. The high oxygen solubility, chemical stability, proton conductivity and permselectivity exhibited by Nafion and the Dow PFSIs make them ideal candidates as electrolytes for fuel cells. Furthermore, the minimal anion adsorption on the Dow PFSIs make them ideal candidates as electrolytes for fuel cells. Furthermore, the minimal anion adsorption on electrodes from fluorinated acids enhances oxygen reduction kinetics. The objectives of this work were to determine the concentration and diffusion coefficient of oxygen in Nafion, and the electrode kinetic parameters for the reduction of oxygen at the Pt/Nafion interface under totally solid-state conditions (i.e., no contacting liquid electrolyte phase). Cyclic voltammetric and potentiostatic transient measurements were made at the Pt/Nafion interface. From cyclic voltammetric measurements, the purity of Nafion was ascertained and the roughness factor of the electrode was calculated. The slow sweep experiments yielded the Tafel parameters for oxygen reduction. From the two-section Tafel plot, the calculated exchange current densities were found to be higher than those obtained at any other Pt/acid interface. From an analysis of the potentiostatic transients, the calculated values of oxygen solubility and diffusion coefficient in Nafion were higher than previously reported. These differences in mass-transfer data were attributed to differences in water content of the Nafion membrane.

Srinivasan, S.; Parthasarathy, A.; Martin, C.R. (Texas A and M Univ., College Station, TX (US))

1991-04-01

206

Corrosion Behavior of Titanium Grade 7 in Fluoride-Containing NaCl Brines  

SciTech Connect

Titanium Grade 7 (UNS R52400) is a titanium-based alloy with 0.12-0.25% Pd. The addition of the small amount of palladium is to ennoble the corrosion potential of Ti, thus improving the corrosion resistance of titanium in reducing environments. In most aqueous environments, Ti and Ti alloys demonstrate excellent corrosion resistance due to the protective oxide film that forms spontaneously and remains stable on the surface. However, Ti and Ti alloys are susceptible to corrosion in fluoride-containing environments due to the formation of complexes such as TiF{sub 6}{sup 2-} and TiF{sub 6}{sup 3-}, which are stable and soluble in electrolyte solutions. Without the presence of fluoride, only slight effects from [Cl{sup -}], pH and temperature have been reported [1]. It has been reported that the kinetics of passive corrosion of titanium in neutral solutions and controlled by the migration of the defects in the oxide across the surface film [2]. Thus, the increase in thickness and improvement in film properties, by thermal oxidation, would lead to a significant decrease in the susceptibility to film breakdown and in the passive corrosion rate. This report summarizes recent experiment results in studies of the environmental influence on the corrosion behavior of Titanium Grade 7 (Ti-7) in NaCl brines containing fluoride. The environmental factors to be studied include temperature, pH, chloride and fluoride concentration. This report also includes the effects of oxide film, formed during an anneal treatment, on the corrosion behavior of Ti-7. Polarization measurement techniques including potentiodynamic and potentiostatic scans were use3d to characterize corrosion kinetics and susceptibility. Due to the unique alloying in Titanium Grade 7, the long-term corrosion behavior is heavily influenced by the surface enrichment of Pd. Use of electrochemical impedance spectroscopy in conjunction with a potentiostatic scan will reveal the transformation in the corrosion behavior as a function of Pd enrichment on the metal surface. Surface characterization was done using various analytical techniques including X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM). The effect of fluoride ion on the corrosion behavior of Ti-7 is strongly dependent on the solution pH. In neutral (pH 8) and alkaline (pH 11) solutions, fluoride did not affect the corrosion rate significantly even though it altered the anodic polarization curve drastically. With pH decreased to 4, the corrosion rate of Ti-7 was increased significantly by the presence of fluoride.

NA

2004-05-18

207

A metal-decorated nickel foam-inducing regulatable manganese dioxide nanosheet array architecture for high-performance supercapacitor applications  

NASA Astrophysics Data System (ADS)

Three dimensional manganese dioxide/Pt/nickel foam (shortened to MnPtNF) hybrid electrodes were prepared by double-pulse polarization and potentiostatic deposition technologies for supercapacitor applications. The decoration of Pt nanoparticles onto nickel foam varies the nucleation mechanism of the manganese dioxide species, inducing the formation of manganese dioxide nanosheets. Additionally, controlling the size of the Pt nanoparticles leads to modulated nanosheet architecture and electrochemical properties of the manganese dioxide electrode, as revealed by XRD, Raman spectra, SEM, TEM, cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The nanosheet architecture of the MnPtNF electrode favors the transportation of electrons and ions, which results in the enhanced electrochemical properties. Importantly, the optimized MnPtNF electrode obtains a maximum specific capacitance of 1222 F g-1 at 5 A g-1 (89% of the theoretical specific capacitance of MnO2) and 600 F g-1 at 100 A g-1. Moreover, the presence of Pt nanoparticles in the MnO2 electrode effectively improves its cycling stability, which is confirmed by the increase of the specific capacitance retention from 14.7% to 90% after 600 cycles.Three dimensional manganese dioxide/Pt/nickel foam (shortened to MnPtNF) hybrid electrodes were prepared by double-pulse polarization and potentiostatic deposition technologies for supercapacitor applications. The decoration of Pt nanoparticles onto nickel foam varies the nucleation mechanism of the manganese dioxide species, inducing the formation of manganese dioxide nanosheets. Additionally, controlling the size of the Pt nanoparticles leads to modulated nanosheet architecture and electrochemical properties of the manganese dioxide electrode, as revealed by XRD, Raman spectra, SEM, TEM, cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The nanosheet architecture of the MnPtNF electrode favors the transportation of electrons and ions, which results in the enhanced electrochemical properties. Importantly, the optimized MnPtNF electrode obtains a maximum specific capacitance of 1222 F g-1 at 5 A g-1 (89% of the theoretical specific capacitance of MnO2) and 600 F g-1 at 100 A g-1. Moreover, the presence of Pt nanoparticles in the MnO2 electrode effectively improves its cycling stability, which is confirmed by the increase of the specific capacitance retention from 14.7% to 90% after 600 cycles. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr02119j

Tang, Peng-Yi; Zhao, Yong-Qing; Wang, Yin-Mei; Xu, Cai-Ling

2013-08-01

208

Triboelectrochemical characterization of microelectronic materials  

NASA Astrophysics Data System (ADS)

Non-uniformity in chemical-mechanical planarization (CMP) due to diverse pattern geometry in copper damascene structures has been a critical limit to process yield. Fundamental understanding in tribology and electrochemistry is crucial to solve this problem. This research develops novel triboelectrochemical techniques to characterize the polished wafer surface and to understand mechanisms of materials removal. There are two approaches in this research. Experimentally, a setup containing a tribometer and a potentiostat was built. It enabled simultaneous measurement in friction coefficient and electrochemical response of wafer materials. Theoretically, electrochemical reactions and Hertzian contact were analyzed on ECMPed wafers in terms of mechanisms of step height reduction in anodic and cathodic ECMP in corresponds to surface chemistry. Results revealed the nature of limitation of ECMP for global planarization. In order to further the fundamental investigation of ECMP, the potentiostatic electrochemical impedance spectroscopy (EIS) was utilized to study the interface kinetics. It was revealed that the formation of Cu oxide films was affected by the electrical potentials. Through in situ measurement, it was found that the tribological behavior depend on the surface chemistry and surface morphology under the influence of anodic potentials. The potentiodynamic polarization results explained the removal and formation mechanisms of interface. The results showed that the cycle of passivation/removal was a function of mechanical factor such as the load and speed. The new model was developed via material removal rate (MRR) in both electrochemical and mechanical aspects. The quantitative contribution of iii electrochemical potential to overall removal was established for the first time. It was further confirmed by Ru and the electrochemical constant j was developed for metal ECMP. This dissertation includes seven chapters. Chapter I Introduction and II Motivation and Objectives are followed by the materials setup and testing conditions discussed in Chapter III. The tribological and electrochemical characterization of the Cu patterned geometry is discussed in Chapter IV. Chapter V discusses the kinetics of the interface during polishing and its removal mechanisms. Chapter VI discusses the synergism of ECMP, followed by Conclusions and Future work.

Joo, Suk Bae

209

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.

1975-01-01

210

Influence of porosity on corrosion behaviour of Ti-39Nb alloy for dental applications.  

PubMed

Porous materials allow for easier osseointegration of implants and their firmer connection with the bone. The presence of pores in a material may become a source of both mechanical and corrosion problems. The presented study explored a Ti-39Nb alloy with a porosity of 0-33%. Specimens were exposed in the physiological solution of two pH values. In view of this material's possible use in dental applications, the effect of fluoride ions on its corrosion behaviour was studied. The open circuit potential and polarization resistance were measured. Data concerning susceptibility to crevice corrosion were obtained from potentiostatic measurements based on the ASTM F746 standard. In terms of corrosion behaviour, specimens with a lower porosity were not much different from the non-porous material. Porosity produced its effect at the level of 24 and 33%. It is obvious that porosity affects corrosion behaviour of this type of material. This conclusion was confirmed by measurements of susceptibility to crevice corrosion which grew with the specimens' increasing porosity. Corrosion resistance of the Ti-39Nb alloy was comparable with that of the compact material, but the presence of pores initiated a local attack of the material. PMID:23629532

Fojt, Jaroslav; Joska, Ludek

2013-01-01

211

Effect of Acidified Feronia elephantum Leaf Extract on the Corrosion Behavior of Mild Steel  

NASA Astrophysics Data System (ADS)

Mild steel is used as a structural material for pipes, tank, reaction vessels, etc. which are known to corrode invariably in contact with various solvents. From the view point of a nation's economy and financial implications of corrosion hazard, it is necessary to adopt appropriate means and ways to reduce the losses due to corrosion. The use of eco-friendly corrosion inhibitors are increasing day by day. Feronia elephantum leaf extract (FELE) has been tested as eco-friendly corrosion inhibitor for A262 mild steel in 1 M H2SO4 and 1 M HCl solutions using non-electrochemical (Gravimetric, X-ray diffraction analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy) and electrochemical techniques (open circuit potential, potentiostatic polarization, and electrochemical impedance measurements). The protection efficiency is found to increase with increase in FELE concentration but decrease with temperature, which is suggestive of physical adsorption mechanism. The adsorption of FELE on mild steel surface obeys the Langmuir adsorption isotherm. SEM results confirm the formation of a protective layer by FELE over mild steel surface.

Muthukrishnan, Pitchaipillai; Prakash, Periakaruppan; Ilayaraja, Murugan; Jeyaprabha, Balasubramanian; Shankar, Karikalan

2015-03-01

212

Electrochemical oxidation of tramadol in low-salinity reverse osmosis concentrates using boron-doped diamond anodes.  

PubMed

The electrochemical treatment of low-salinity reverse osmosis (RO) concentrates was investigated using tramadol (100 ?M) as a model substance for persistent organic contaminants. Galvanostatic degradation experiments using boron-doped diamond electrodes at different applied currents were conducted in RO concentrates as well as in ultra-pure water containing either sodium chloride or sodium sulfate. Kinetic investigations revealed a significant influence of in-situ generated active chlorine besides direct anodic oxidation. Therefore, tramadol concentrations decreased more rapidly at elevated chloride content. Nevertheless, reduction of total organic carbon (TOC) was found to be comparatively low, demonstrating that transformation rather than mineralization was taking place. Early stage product formation could be attributed to both direct and indirect processes, including demethylation, hydroxylation, dehydration, oxidative aromatic ring cleavage and halogenation reactions. The latter led to various halogenated derivatives and resulted in AOX (adsorbable organic halogens) formation in the lower mg/L-range depending on the treatment conditions. Characterisation of transformation products (TPs) was achieved via MS(n) experiments and additional NMR measurements. Based on identification and quantification of the main TPs in different matrices and on additional potentiostatic electrolysis, a transformation pathway was proposed. PMID:25660808

Lütke Eversloh, Christian; Schulz, Manoj; Wagner, Manfred; Ternes, Thomas A

2015-04-01

213

Optical properties of electrochemically synthesized polypyrrole thin films: the electrolyte effect  

NASA Astrophysics Data System (ADS)

Polypyrrole thin films are prepared by the potentiostatic mode of electrodeposition at +0:7 V versus a saturated calomel electrode (SCE). The polypyrrole films are prepared in the presence of different electrolytes such as: p-toluene sulphonic acid (PTS), oxalic acid and H2SO4. The prepared films are characterized by UV—vis absorption spectroscopy and normal reflectance measurements. The electrochemically synthesized films are semiconductor in nature. The band gap energy of polypyrrole thin films is found to be 1.95, 1.92 and 1.79 eV for H2SO4, oxalic acid and p-toluene sulphonic acid, respectively. The normal reflectance spectroscopy of polypyrrole films shows that the maximum reflectance is in the presence of p-toluene sulphonic acid; this is may be due to a more distinct microstructure than the others. The optical constants such as the extinction coefficient, refractive index, optical conductivity, etc. are calculated and studied with various electrolytes.

Thombare, J. V.; Shinde, S. K.; Lohar, G. M.; Chougale, U. M.; Dhasade, S. S.; Dhaygude, H. D.; Relekar, B. P.; Fulari, V. J.

2014-06-01

214

Zinc oxide nanostructures for electrochemical cortisol biosensing  

NASA Astrophysics Data System (ADS)

In this paper, we report on fabrication of a label free, highly sensitive and selective electrochemical cortisol immunosensors using one dimensional (1D) ZnO nanorods (ZnO-NRs) and two dimensional nanoflakes (ZnO-NFs) as immobilizing matrix. The synthesized ZnO nanostructures (NSs) were characterized using scanning electron microscopy (SEM), selective area diffraction (SAED) and photoluminescence spectra (PL) which showed that both ZnO-NRs and ZnO-NFs are single crystalline and oriented in [0001] direction. Anti-cortisol antibody (Anti-Cab) are used as primary capture antibodies to detect cortisol using electrochemical impedance spectroscopy (EIS). The charge transfer resistance increases linearly with increase in cortisol concentration and exhibits a sensitivity of 3.078 K?. M-1 for ZnO-NRs and 540 ?. M -1 for ZnO-NFs. The developed ZnO-NSs based immunosensor is capable of detecting cortisol at 1 pM. The observed sensing parameters are in physiological range. The developed sensors can be integrated with microfluidic system and miniaturized potentiostat to detect cortisol at point-of-care.

Vabbina, Phani Kiran; Kaushik, Ajeet; Tracy, Kathryn; Bhansali, Shekhar; Pala, Nezih

2014-05-01

215

Lab-on-a-Bird: Biophysical Monitoring of Flying Birds  

PubMed Central

The metabolism of birds is finely tuned to their activities and environments, and thus research on avian systems can play an important role in understanding organismal responses to environmental changes. At present, however, the physiological monitoring of bird metabolism is limited by the inability to take real-time measurements of key metabolites during flight. In this study, we present an implantable biosensor system that can be used for continuous monitoring of uric acid levels of birds during various activities including flight. The system consists of a needle-type enzymatic biosensor for the amperometric detection of uric acid in interstitial fluids. A lightweight two-electrode potentiostat system drives the biosensor, reads the corresponding output current and wirelessly transfers the data or records to flash memory. We show how the device can be used to monitor, in real time, the effects of short-term flight and rest cycles on the uric acid levels of pigeons. In addition, we demonstrate that our device has the ability to measure uric acid level increase in homing pigeons while they fly freely. Successful application of the sensor in migratory birds could open up a new way of studying birds in flight which would lead to a better understanding of the ecology and biology of avian movements. PMID:25880904

Gumus, Abdurrahman; Lee, Seoho; Ahsan, Syed S.; Karlsson, Kolbeinn; Gabrielson, Richard; Guglielmo, Christopher G.; Winkler, David W.; Erickson, David

2015-01-01

216

Porous NiTi surfaces for biomedical applications  

NASA Astrophysics Data System (ADS)

In this study, the NiTi shape memory alloy was surface modified by plasma electrolytic oxidation (PEO) in Na3PO4 with the aim to produce porous NiTi surfaces for biomedical applications. The oxidation was performed potentiostatically and the characteristics of the resultant surfaces were compared with those obtained in NaAlO2/NaPO2H2 under similar conditions. Surfaces with sub-micron sized pores could be produced in Na3PO4 electrolyte at 300 V. The process was accompanied by intense gas evolution and enhanced thermal effects relative to the NaAlO2/NaPO2H2 electrolyte. The EDS analyses revealed the presence of O, Ti, P, Ni, and a Ni/Ti atomic ratio of 0.4 suggesting preferential oxidation of titanium during the process and depletion of Ni from the surface. No crystalline oxide phases were detected by X-ray diffraction (XRD). By comparison, the layers formed in NaAlO2/NaPO2H2 consisted of crystalline Al2O3 and the Ni/Ti atomic ratio was 0.74. Following oxidation, the wettability and surface free energy of NiTi increased significantly. The findings of this study indicate that the PEO process shows potential for expanding the biofunctionality of NiTi.

Huan, Z.; Fratila-Apachitei, L. E.; Apachitei, I.; Duszczyk, J.

2012-04-01

217

Electrodeposition of Cu-Pd alloys onto electrophoretic deposited carbon nanotubes for nitrate electroreduction  

NASA Astrophysics Data System (ADS)

Copper-palladium (Cu-Pd) alloys have been electrodeposited onto carbon nanotubes, which were uniformly and stably deposited on Ti plates via electrophoretic deposition. Electrodes with a wide range of Cu/Pd atomic ratios were fabricated by potentiostatic coelectrodeposition of Cu and Pd onto Ti/CNTs. They were characterized by energy-dispersive X-ray analyzer, X-ray diffraction and tested for nitrate electroreduction. The electrode deposited in bath with 5 mM Cu2+ and 5 mM Pd2+ (Ti/CNTs/Cu5-Pd5) possessed outstanding stability as well as the highest electrocatalytic activity with the best nitrate conversion yield and proper N2 selectivity, indicating a synergistic effect of Cu and Pd. X-ray photoelectron spectroscopy and scanning electron microscopy analysis of Ti/CNTs/Cu5-Pd5 and Ti/Cu5-Pd5 revealed that CNTs played a remarkable role in the homogeneous formation of the bimetal, significantly improving the alloy's electrocatalytic activity and stability. The fabricated Ti/CNTs/Cu5-Pd5 was proved to be a promising electrode for nitrate electroreduction.

Zhang, Qiu; Ding, Liang; Cui, Hao; Zhai, Jianping; Wei, Zhongbo; Li, Qin

2014-07-01

218

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

PubMed

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

2014-07-01

219

Fabrication of vertically aligned Pd nanowire array in AAO template by electrodeposition using neutral electrolyte  

PubMed Central

A vertically aligned Pd nanowire array was successfully fabricated on an Au/Ti substrate using an anodic aluminum oxide (AAO) template by a direct voltage electrodeposition method at room temperature using diluted neutral electrolyte. The fabrication of Pd nanowires was controlled by analyzing the current–time transient during electrodeposition using potentiostat. The AAO template and the Pd nanowires were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) methods and X-Ray diffraction (XRD). It was observed that the Pd nanowire array was standing freely on an Au-coated Ti substrate after removing the AAO template in a relatively large area of about 5 cm2, approximately 50 nm in diameter and 2.5 ?m in length with a high aspect ratio. The nucleation rate and the number of atoms in the critical nucleus were determined from the analysis of current transients. Pd nuclei density was calculated as 3.55 × 108 cm?2. Usage of diluted neutral electrolyte enables slower growing of Pd nanowires owing to increase in the electrodeposition potential and thus obtained Pd nanowires have higher crystallinity with lower dislocations. In fact, this high crystallinity of Pd nanowires provides them positive effect for sensor performances especially. PMID:20596417

2010-01-01

220

Electrochemical Oscillations of Nickel Electrodissolution in an Epoxy-Based Microchip Flow Cell  

PubMed Central

We investigate the nonlinear dynamics of transpassive electrodissolution of nickel in sulfuric acid in an epoxy-based microchip flow cell. We observed bistability, smooth, relaxation, and period-2 waveform current oscillations with external resistance attached to the electrode in the microfabricated electrochemical cell with 0.05 mm diameter Ni wire under potentiostatic control. Experiments with 1mm × 0.1 mm Ni electrode show spontaneous oscillations without attached external resistance; similar surface area electrode in macrocell does not exhibit spontaneous oscillations. Combined experimental and numerical studies show that spontaneous oscillation with the on-chip fabricated electrochemical cell occurs because of the unusually large ohmic potential drop due to the constrained current in the narrow flow channel. This large IR potential drop is expected to have an important role in destabilizing negative differential resistance electrochemical (e.g., metal dissolution and electrocatalytic) systems in on-chip integrated microfludic flow cells. The proposed experimental setup can be extendend to multi-electrode configurations; the epoxy-based substrate procedure thus holds promise in electroanalytical applications that require collector-generator multi-electrodes wires with various electrode sizes, compositions, and spacings as well as controlled flow conditions. PMID:21822407

Cioffi, Alexander G.; Martin, R. Scott; Kiss, István Z.

2011-01-01

221

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)

2013-01-01

222

On-site analysis of arsenic in groundwater using a microfabricated gold ultramicroelectrode array  

PubMed

Rapid on-site analysis of arsenic in groundwater was achieved with a small battery-powered unit in conjunction with a microfabricated gold ultramicroelectrode array (Au-UMEA). The sensor, consisting of 564 UME disks with a unique gold surface created by electron beam evaporation, was demonstrated to be highly sensitive to low-ppb As3+ using square wave anodic stripping voltammetry. The influence of the square wave frequency, pulse amplitude, and deposition potential on the arsenic peak stripping current was investigated. Varying those theoretical parameters yielded results surprisingly similar to those for the thin Hg film case. The performance of the Au-UMEA was evaluated for reproducibility and reliability. Three stability tests showed an average relative standard deviation of 2.5% for 15 consecutive runs. Limits of detection were investigated, and 0.05 ppb As3+ could be measured while maintaining a S/N of 3:1. Interference studies were performed in the presence of 50-500 ppb of Cu2+, Hg2+, and Pb2+. On-site analysis of groundwater containing arsenic was performed with a small battery-powered potentiostat. Quantification was done through standard additions, and these results were compared to the standard EPA methodology. PMID:10845367

Feeney; Kounaves

2000-05-15

223

Haemoglobin immobilized on nafion modified multi-walled carbon nanotubes for O2, H2O2 and CCl3COOH sensors.  

PubMed

A conductive biocomposite film (MWCNTs-NF-Hb) containing multi-walled carbon nanotubes (MWCNTs) incorporated with entrapped haemoglobin (Hb) in nafion (NF) has been synthesized on glassy carbon electrode (GCE), gold (Au), indium tin oxide (ITO) and screen printed carbon electrode (SPCE) separately by potentiostatic methods. The presence of both MWCNTs and NF in the biocomposite film enhances the surface coverage concentration (Gamma), and increases the electron transfer rate constant (K(s)) to 132%. The biocomposite film exhibits a promising enhanced electrocatalytic activity towards the reduction of O(2), H(2)O(2) and CCl(3)COOH. The cyclic voltammetry has been used for the measurement of electrocatalysis results of analytes by means of biocomposite film-modified GCEs. The MWCNTs-NF-Hb-modified GCEs' sensitivity values are higher than the values obtained for other film modified GCEs. The surface morphology of the biocomposite films which have been deposited on ITO has been studied using scanning electron microscopy and atomic force microscopy. The studies have revealed that there was an incorporation of NF and immobilization of Hb on MWCNTs. Finally, the flow injection analysis has been used for the amperometric studies of analytes at MWCNTs-Hb and MWCNTs-NF-Hb film modified SPCEs. The amperometric study results have shown higher slope values for MWCNTs-NF-Hb biocomposite film. PMID:19269447

Shie, Jan-Wei; Yogeswaran, Umasankar; Chen, Shen-Ming

2009-05-15

224

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

PubMed

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

2013-07-23

225

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

PubMed

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; Vázquez, M; Denardin, J C; Escrig, J

2015-02-01

226

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

2015-01-01

227

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.

2014-08-01

228

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

2014-06-01

229

Nucleation and growth in electrodeposition of thin copper films on pyrolytic graphite  

SciTech Connect

Electrodeposition of Cu on graphite electrodes was studied, with emphasis on nucleation. Various ex-situ and in-situ methods were investigated for determining the number density of nuclei. Two direct methods were studied (scanning electron microscopy and scanning tunneling microscopy); indirect determinations included Raman spectroscopy and analysis of potentiostatic current transients. Though some of the techniques correctly predicted the nucleation densities under special conditions, SEM was the most reliable tool. The large scatter in the data necessitated steps to minimize this effect. To electrodeposit Cu on graphite, a nucleation overpotential of 250 mV was measured with cyclic voltammetry; such a large overpotential does not occur on a Pt or on a Cu-covered graphite electrode. The deposition potential is the dominant parameter governing nucleation density. There is a sharp increase in the nucleation density with applied potential. Cu can be deposited on highly oriented pyrolytic graphite only between the nucleation overpotential and the hydrogen evolution potential. To increase the Cu nucleation density, while avoiding excessive H evolution, a double pulse potential technique was used; nucleation densities on the order of 10{sup 10} nuclei/cm{sup 2} were achieved. The use of inhibitors (PVA, benzotriazole) was also investigated. Deposition on conducting polymer electrodes was also studied; initial results with polyaniline show promise. 57 figs, 6 tabs, refs. (DLC)

Kinaci, F.S.; Muller, R.H.

1992-05-01

230

Microbiologically induced corrosive properties of the titanium surface.  

PubMed

Corrosion of titanium is the major concern when it is used for dental treatment. This study aimed to investigate the mechanism of the microbiologically induced corrosive properties of titanium. An experimental well was made of polymethyl methacrylate with pure titanium at the bottom. Viable or killed cells of Streptococcus mutans were packed into the well, and pH at the bacteria-titanium interface was monitored with and without glucose. Before and after 90-minute incubation, the electrochemical behavior on the titanium surface was measured by means of a potentiostat. The oxygen concentration under bacterial cells was monitored with oxygen-sensitive fluorescent film. The amount of titanium eluted was measured by inductively coupled plasma-mass spectrometry. The corrosion current and passive current under killed cells were low and stable during 90 min, while those under viable cells increased, regardless of the glucose-induced pH fall. The polarization resistance and oxygen concentration under killed cells were high and stable, while those under viable cells decreased. No elution of titanium was detected. Viable bacterial cells may form 'oxygen concentration cells' through metabolism-coupled oxygen consumption and subsequently induce corrosive properties of the titanium surface. PMID:24554541

Fukushima, A; Mayanagi, G; Nakajo, K; Sasaki, K; Takahashi, N

2014-05-01

231

Electrochemical characteristics of a carbon fibre composite and the associated galvanic effects with aluminium alloys  

NASA Astrophysics Data System (ADS)

The electrochemical behaviour of a carbon fibre reinforced epoxy matrix composite in 3.5% NaCl and 3.5% NaCl + 0.5 M CuSO4 electrolytes was examined by potentiodynamic polarisation, potentiostatic polarisation and scanning electron microscopy. Exposed carbon fibres on two defined regions (“front” and “side”) are a focus of the investigation. The large size of the exposed carbon fibres on the side region is responsible for a higher cathodic current density than the front region in the NaCl electrolyte. The deposition of copper on the front surface of composite confirmed that the significantly higher cathodic current resulted from the exposure of the fibres to the NaCl electrolyte. Galvanic coupling between the composite and individual aluminium alloys (AA7075-T6 and AA1050) was used to measure galvanic potentials and galvanic current densities. The highly alloyed AA7075-T6 alloy and its high population density of cathodic sites compared to the AA1050 acted to reduce the galvanic effect when coupled to the composite front or side regions.

Liu, Z.; Curioni, M.; Jamshidi, P.; Walker, A.; Prengnell, P.; Thompson, G. E.; Skeldon, P.

2014-09-01

232

Quasi-in-situ single-grain photoelectron microspectroscopy of Co/PPy nanocomposites under oxygen reduction reaction.  

PubMed

This paper reports an investigation into the aging of pyrolyzed cobalt/polypyrrole (Co/PPy) oxygen reduction reaction (ORR) electrocatalysts, based on quasi-in-situ photoelectron microspectroscopy. The catalyst precursor was prepared by potentiostatic reverse-pulse coelectrodeposition from an acetonitrile solution on graphite. Accelerated aging was obtained by quasi-in-situ voltammetric cycling in an acidic electrolyte. Using photoelectron imaging and microspectroscopy of single Co/PPy grains at a resolution of 100 nm, we tracked the ORR-induced changes in the morphology and chemical state of the pristine material, consisting of uniformly distributed ?20 nm nanoparticles, initially consisting of a mixture of Co(II) and Co(III) oxidation states in almost equal amounts. The evolution of the Co 2p, O 1s, and N 1s spectra revealed that the main effects of aging are a gradual loss of the Co present at the surface and the reduction of Co(III) to Co(II), accompanied by the emergence and growth of a N 1s signal, corresponding to electrocatalytically active C-N sites. PMID:25369153

Bocchetta, Patrizia; Amati, Matteo; Bozzini, Benedetto; Catalano, Massimo; Gianoncelli, Alessandra; Gregoratti, Luca; Taurino, Antonietta; Kiskinova, Maya

2014-11-26

233

In vitro corrosion of Ti-6Al-4V and type 316L stainless steel when galvanically coupled with carbon.  

PubMed

In vitro corrosion experiments were conducted employing potentiostatic polarization techniques, a saline environment and candidate biomaterial alloy/carbon combinations. Corrosion currents and potentials of carbon/metal couples were predicted by mixed-potential theory utilizing the polarization curves generated. The alloys examined were annealed ELI grade Ti-6A1-4V and cold-worked 316L stainless steel while the types of carbon examined were LTI pyrolytic carbon and vapor-deposited carbon. It was determined that galvanic couples of carbon to cold-worked 316L stainless steel with carbon/metal area ratios of 10:1 to 100:1 produced coupled corrosion potentials in the range of the observed breakdown potential of the stainless steel. It was therefore predicted that localized corrosion in the form of pitting could occur on the cold-worked stainless steel when coupled to carbon with area ratios of 10:1 or greater. The titanium alloy did not exhibit a breakdown potential up to a potential of 1.2 V. Therefore, accelerated corrosion was not predicted for the titanium alloy to carbon galvanic couples under these experimental conditions. Direct carbon/alloy coupling experiments were conducted to verify the corrosion currents and potentials predicted from mixed-potential theory and polarization curve analysis. The experimental and theoretical values showed good agreement. PMID:429383

Thompson, N G; Buchanan, R A; Lemons, J E

1979-01-01

234

In vitro crevice corrosion behavior of implant materials.  

PubMed

The crevice corrosion susceptibility of cold-worked Type 316LVM stainless steel, cast Co-Cr-Mo, wrought Co-Cr-W-Ni, non-nitrided and nitrided Ti-6Al-4V ELI, and c.p. Ti, Grades 1 and 4, was studied in vitro by means of a crevice cell. Occlusion was created by interfacing a disc specimen and a Teflon bar. Specimens were mechanically prepared through 2-4 micron Al2O3 and passivated in 30% HNO3, followed by steam sterilization. Tests were performed in a deaerated Ringer's solution, maintained at pH = 7 and 37 degrees C. Anodic polarization was conducted potentiostatically at pre-selected levels, and resultant currents were monitored: stainless steel, 50 and 100 mV (S.C.E.), 450 min; non-stainless materials, 600 mV, 1000 min. Results for the stainless steel demonstrated that a HNO3 passivation treatment reduced its crevice corrosion susceptibility. For the non-stainless steel materials, no crevice corrosion susceptibility was observed, although a dulling and discoloration of c.p. Ti was evident. Recognizing that 600 mV is in excess of the O2 reduction potential in vivo, it was concluded that, in the absence of fretting, implants of these non-stainless steel materials would not experience significant corrosion loss under crevice conditions. PMID:3858307

Sutow, E J; Jones, D W; Milne, E L

1985-05-01

235

Corrosion and Fretting Corrosion Studies of Medical Grade CoCrMo Alloy in a Clinically Relevant Simulated Body Fluid Environment  

NASA Astrophysics Data System (ADS)

In modular hip implants, fretting corrosion at the head/neck and neck/stem interfaces has been identified as a major cause of early revision in hip implants, particularly those with heads larger than 32 mm. It has been found that the type of fluid used to simulate the fretting corrosion of biomedical materials is crucial for the reliability of laboratory tests. Therefore, to properly understand and effectively design against fretting corrosion damage in modular hips, there is the need to replicate the human body environment as closely as possible during in vitro testing. In this work, corrosion and fretting corrosion behavior of CoCrMo in 0.14 M NaCl, phosphate buffered saline, and in a clinically relevant novel simulated body fluid was studied using a variety of electrochemical characterization techniques and tribological experiments. Electrochemical, spectroscopy and tribo-electrochemical techniques employed include Potentiodynamic polarization, Potentiostatic polarization, Electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, augur electron spectroscopy, inductively coupled plasma mass spectroscopy, and pin-on-disk wear simulation. The presence of phosphate ions in PBS accounted for the higher corrosion rate when compared with 0.14 M NaCl and the clinically relevant novel simulated body fluid. The low corrosion rates and the nature of the protective passive film formed in the clinically relevant simulated body fluid make it suitable for future corrosion and fretting corrosion studies.

Ocran, Emmanuel K.; Guenther, Leah E.; Brandt, Jan-M.; Wyss, Urs; Ojo, Olanrewaju A.

2015-03-01

236

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

2015-01-01

237

Tuning the electrochemical swelling of polyelectrolyte multilayers toward nanoactuation.  

PubMed

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; Vörös, János; Zambelli, Tomaso

2014-10-14

238

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

2015-01-01

239

Properties of the nano-thick Pt/W bilayered catalytic layer employed dye sensitized solar cells  

NASA Astrophysics Data System (ADS)

A Pt/W bilayered catalytic layer on a flat glass substrate was used as a counter electrode to improve the energy conversion efficiency of a dye-sensitized solar cell device with the structure of 0.45 cm2 effective area of glass/FTO/blocking layer/TiO2/N719 (dye)/electrolyte/50 nm Pt/50 nm W/glass. For comparison, 100 nm-thick Pt and W counter electrodes on flat glass substrates were also prepared using the same procedure. The photovoltaic properties, such as the short circuit current density, open circuit voltage, fill factor, energy conversion efficiency and impedance were characterized using a solar simulator and potentiostat. The phases and microstructures of the catalytic layers were examined by x-ray diffraction and field emission electron microscopy. The measured energy conversion efficiencies of the dye-sensitized solar cell devices with Pt only and Pt/W bilayer counter electrodes were 4.60% and 6.54%, respectively. The interface resistance at the interface between the counter electrode and electrolyte decreased when a Pt/W bilayered thin film was applied. The increase in efficiency resulted from the effect of compressive strain field formed by the intermetallic layer of Pt2W at Pt and W layer interface. This suggests that the use of Pt/W bilayered catalytic layers improves the efficiency of the dye-sensitized solar cells compared to those using the conventional Pt layers.

Noh, Yunyoung; Song, Ohsung

2014-05-01

240

Effect of surface groups on the electrocatalytic behaviour of Pt-Fe-Co alloy-dispersed carbon electrodes in the phosphoric acid fuel cell  

NASA Astrophysics Data System (ADS)

Effect of surface group on the electrocatalytic behaviour of 10 wt.% Pt-Fe-Co alloy-dispersed carbon (Pt-Fe-Co/C) electrode has been investigated as functions of applied potential and duration in 85% H 3PO 4 solution of 145°C, using Fourier transform infrared (FTIR) spectroscopy, combined with ac-impedance spectroscopy, potentiostatic current transient technique, and potentiodynamic polarization experiment. It was shown from FTIR spectra that surface group formed in this work mainly comprises carboxyl group and that the formation potential of carboxyl group lies between 600 and 700 mV RHE. From increase of charge transfer resistance ( Rct), and decrease of electrocatalytic activity for oxygen reduction with immersion time, it is suggested that above the formation potential of carboxyl group, further formation of carboxyl group on the carbon support around the catalyst particle reduces active surface area of the catalyst particle with immersion time. On the other hand, below the formation potential, dissolution of carboxyl group previously formed on the carbon support raises active surface area of the catalyst particle. In the present study, relationship between electrocatalytic aspect of the electrode, and the amount of carboxyl group formed on the carbon support around the catalyst particle was well discussed with a schematic illustration. The illustrative representation is underlain by formation on and dissolution from the catalyst particle of carboxyl group which cause the rise and fall in circumferential coverage of carboxyl group, respectively and hence the reduction and elevation in active surface area of the catalyst particle.

Pyun, Su-Il; Lee, Seung-Bok

241

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

2005-10-01

242

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

2006-08-17

243

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 (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 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: 1490–1499, 2012

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

2012-06-12

244

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 (1.5 × 10-3 S cm-1) and good Mg deposition-dissolution reversibility. More importantly, the same electrochemical window (2.6 V 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 0.25 mol L-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

2014-02-01

245

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

2014-09-01

246

Analyses of the genotoxic and mutagenic potential of the products formed after the biotransformation of the azo dye Disperse Red 1.  

PubMed

Azo dyes constitute the largest class of synthetic dyes. Following oral exposure, these dyes can be reduced to aromatic amines by the intestinal microflora or liver enzymes. This work identified the products formed after oxidation and reduction of the dye Disperse Red 1, simulating hepatic biotransformation and evaluated the mutagenic potential of the resultant solution. Controlled potential electrolysis was carried out on dye solution using a Potentiostat/Galvanostat. HPLC-DAD and GC/MS were used to determine the products generated after the oxidation/reduction process. The Salmonella/microsome assay with the strains TA98 and YG1041 without S9, and the mouse lymphoma assay (MLA) using the thymidine kinase (Tk) gene, were used to evaluate the mutagenicity of the products formed. Sulfate 2-[(4-aminophenyl)ethylamino]-ethanol monohydrate, nitrobenzene, 4-nitro-benzamine and 2-(ethylphenylamino)-ethanol were detected. This dye has already being assigned as mutagenic in different cell system. In addition, after the oxidation/reduction process the dye still had mutagenic activity for the Salmonella/microsome assay. Nevertheless, both the original dye Disperse Red 1 and its treated solutions showed negative results in the MLA. The present results suggest that the ingestion of water and food contaminated with this dye may represent human and environmental health problem, due to the generation of harmful compounds after biotransformation. PMID:21907275

Chequer, Farah Maria Drumond; Lizier, Thiago Mescoloto; de Felício, Rafael; Zanoni, Maria Valnice Boldrin; Debonsi, Hosana Maria; Lopes, Norberto Peporine; Marcos, Ricard; de Oliveira, Danielle Palma

2011-12-01

247

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

2008-01-01

248

Electrochemical Deposition of Ni on an Al-Cu Alloy  

NASA Astrophysics Data System (ADS)

Metallic coatings can be used to improve the wear and corrosion resistance of Al alloys. In this study, Ni was used as a candidate material for such a coating which was applied on the surface of Al 2014 alloy using electrodeposition in a standard Watt's bath. A two-step heat treatment procedure was employed that served to increase the adhesion as well as hardness of Ni. Deposition was undertaken for different durations using both galvanostatic and potentiostatic techniques. The effect of deposition parameters such as surface finish, current, potential, temperature, pH level and duration on the microstructure, adhesion, and surface properties of the Ni deposit was studied. Materials characterization was performed using scanning electron microscopy, atomic force microscopy, and x-ray diffraction. Cross-sectional scanning transmission electron microscope images revealed the fine-grained (10 nm) structure of Ni initially deposited at the Ni-Al alloy substrate. Microhardness, adhesion, and corrosion behavior of the Ni deposit were evaluated. Experimental results indicate that deposition by galvanostatic technique on 1 ?m surface finish at 45 °C with a pH level maintained at 3.6 represented the optimum conditions to generate a uniform Ni deposit on Al 2014. It was concluded that Ni deposition can be used to improve the surface properties of Al alloys.

Ul-Hamid, A.; Quddus, A.; Dafalla, H.; Saricimen, H.; Al-Hadhrami, L.

2012-02-01

249

Determination of solid phase chemical diffusion coefficient and density of states by electrochemical methods: Application to iridium oxide-based thin films  

NASA Astrophysics Data System (ADS)

Potentiostatic intermittent titration technique (PITT) and electrochemical impedance spectroscopy (EIS) were investigated as methods to determine solid phase chemical diffusion coefficient (D) and electronic density of states (DOS). These techniques were then applied to iridium oxide (IrOx) and iridium-tantalum oxide (IrTaOx) thin films prepared by sputter deposition. The experiments, performed in 1M propionic acid between -0.2 and 0.8V vs Ag /AgCl, showed effects of interfacial side reactions, whose contribution to the electrochemical response could be identified and corrected for in the case of PITT as well as EIS. It was found that D is strongly underestimated when using PITT with the common Cottrell formalism, which follows from non-negligible interfacial charge transfer and Ohmic resistances. EIS indicated an anomalous diffusion mechanism, and D was determined to be in the 10-11-10-10cm2/s range for IrOx and IrTaOx. Both PITT and EIS showed that the intercalated charge as a function of potential exhibits a shape that resembles the theoretical DOS of crystalline iridium oxide, especially for IrTaOx.

Backholm, Jonas; Georén, Peter; Niklasson, Gunnar A.

2008-01-01

250

Fatigue crack growth rates in a pressure vessel steel under various conditions of loading and the environment  

NASA Astrophysics Data System (ADS)

Corrosion fatigue (CF) tests have been carried out on SA508 Cl 3 pressure vessel steel, in simulated P.W.R. environments. The test variables investigated included air and P.W.R. water environments, frequency variation over the range 1 Hz to 10 Hz, transverse and longitudinal crack growth directions, temperatures of 20 °C and 50 °C, and R-ratios of 0.2 and 0.7. It was found that decreasing the test frequency increased fatigue crack growth rates (FCGR) in P.W.R. environments, P.W.R. environment testing gave enhanced crack growth (vs air tests), FCGRs were greater for cracks growing in the longitudinal direction, slight increases in temperature gave noticeable accelerations in FCGR, and several air tests gave FCGR greater than those predicted by the existing ASME codes. Fractographic evidence indicates that FCGRs were accelerated by a hydrogen embrittlement mechanism. The presence of elongated MnS inclusions aided both mechanical fatigue and hydrogen embrittlement processes, thus producing synergistically fast FCGRs. Both anodic dissolution and hydrogen embrittlement mechanisms have been proposed for the environmental enhancement of crack growth rates. Electrochemical potential measurements and potentiostatic tests have shown that sample isolation of the test specimens from the clevises in the apparatus is not essential during low temperature corrosion fatigue testing.

Hicks, P. D.; Robinson, F. P. A.

1986-10-01

251

A new electrochemical sensor for OH radicals detection.  

PubMed

A new, cheap modified electrode for indirect detection of OH radical is described. A glassy carbon (GC) electrode was modified with a polyphenol film prepared by oxidative potentiostatic electropolymerization of 0.05 M phenol in 1M H2SO4. The film having a thickness of ~10nm perfectly covered the GC surface and inhibited the charge transfer of many redox species. The degradation of the polyphenol film, that was induced by OH radicals generated by Fenton reaction or by H2O2 photolysis, is the analytical signal and it was evaluated by cyclic voltammetry and chronoamperometry using the redox probe Ru(NH3)6(3+). Some simulations of the kinetics of the reactions occurring in the solution bulk and near the electrode surface were carried out to fully understand the processes that lead to the analytical signal. The modified electrode was used to evaluate the performances of different TiO2-based photocatalysts and the results were successfully compared with those obtained from a traditional HPLC method that is based on the determination of the hydroxylation products of salicylic acid. PMID:24054662

Gualandi, Isacco; Tonelli, Domenica

2013-10-15

252

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

PubMed

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

2014-03-01

253

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

PubMed

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

2014-03-21

254

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

PubMed

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 60°C, 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; Gaberš?ek, Miran

2014-05-01

255

Electrodeposition and characterization of HgSe thin films  

SciTech Connect

In this article we present the results on the electrochemical synthesis of mercury selenide (HgSe), an interesting II-VI material. HgSe thin films were deposited potentiostatically on conducting glass substrates from an aqueous bath containing HgCl{sub 2} and SeO{sub 2}. The prepared films were characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), scanning electron microscope (SEM) and optical absorption techniques. Stoichiometric polycrystalline HgSe films were obtained at a deposition potential around - 0.7 V vs SCE, at a temperature 60 deg. C and a pH value of 3.5. The as-grown films exhibited a direct optical band gap of 0.78 eV. This report deals with the growth mechanism and a study related to the influence of electrolyte bath composition, deposition potential, temperature and pH on the properties of HgSe thin films.

Mahalingam, T. [Department of Physics, Alagappa University, Karaikudi - 630 003 (India) and Department of Electrical and Computer Engineering, College of Information Technology, Ajou University, Suwon 443-749 (Korea, Republic of)]. E-mail: maha51@rediffmail.com; Kathalingam, A. [Department of Physics, Alagappa University, Karaikudi - 630 003 (India); Sanjeeviraja, C. [Department of Physics, Alagappa University, Karaikudi - 630 003 (India); Chandramohan, R. [Physics Department, National Chang-Hua University of Education, Chang-Hua 50058, Taiwan (China); Chu, J.P. [Institute of Materials Engineering, National Taiwan Ocean University, Keelung 202, Taiwan (China); Kim, Yong Deak [Department of Electrical and Computer Engineering, College of Information Technology, Ajou University, Suwon 443-749 (Korea, Republic of); Velumani, S. [Departamento de Fisica, ITESM - Campus Monterrey, Nuevo Leon, C.P.64849 (Mexico)

2007-08-15

256

Voltammetric studies on the electrochemical determination of methylmercury in chloride medium at carbon microelectrodes.  

PubMed

Electroanalytical techniques have been used to determine methylmercury at low levels in environmental matrices. The electrochemical behaviour of methylmercury at carbon microelectrodes in a hydrochloric acid medium using cyclic, square wave and fast-scan linear-sweep voltammetric techniques has been investigated. The analytical utility of the methylmercury reoxidation peak has been explored, but the recorded peak currents were found to be poorly reproducible. This is ascribed to two factors: the adsorption of insoluble chloromercury compounds on the electrode surface, which appears to be an important contribution to hinder the voltammetric signal of methylmercury; and the competition between the reoxidation of the methylmercury radical and its dimerization reaction, which limits the reproducibility of the methylmercury peak. These problems were successfully overcome by adopting the appropriate experimental conditions. Fast-scan rates were employed and an efficient electrochemical regeneration procedure of the electrode surface was achieved, under potentiostatic conditions in a mercury-free solution containing potassium thiocyanate--a strong complexing agent. The influence of chloride ion concentration was analysed. Interference by metals, such as lead and cadmium, was considered. Calibration plots were obtained in the micromolar and submicromolar concentration ranges, allowing the electrochemical determination of methylmercury in trace amounts. An estuarine water sample was analysed using the new method with a glassy carbon microelectrode. PMID:17723747

Ribeiro, F; Neto, M M M; Rocha, M M; Fonseca, I T E

2006-10-10

257

The electrodeposition of Al[sub 3]Ti from chloroaluminate electrolytes  

SciTech Connect

The electrochemistry of Ti(2) in 2:1 AlCl[sub 3]:NaCl and the electrodeposition of metastable aluminum-titanium alloys containing up to 28 atom percent Ti are reported. Ti(2)/Ti(3) was studied by chronoamperometry, chronopotentiometry, cyclic voltammetry, and convolution voltammetry during the electrochemical dissolution of titanium. It was concluded that Ti(2)/Ti(3) behaves reversibly in this electrolyte and that, at low current densities, titanium dissolves to form Ti(2). The dissolution follows Faraday's law for Ti(2) concentrations approaching 75 mmol/liter, through concentrations up to 325 mmol/liter can be obtained at dissolution current efficiencies less than 100%. Single-phase Al[sub 3]Ti with the ordered face-centered cubic L1[sub 2] structure is deposited under conditions where the Ti partial current is not diffusion limited. Current transients and microscopic analysis of the early stages of potentiostatic deposition suggest that Al[sub 3]Ti forms by instantaneous three-dimensional nucleation at potentials where the growth process is under mixed kinetic and diffusion control.

Stafford, G.R. (National Inst. of Standards and Technology, Gaithersburg, MD (United States). Materials Science and Engineering Lab.)

1994-04-01

258

Examination of the metastable and stable pitting corrosion of aluminum modified with carbon by ion beam techniques  

NASA Astrophysics Data System (ADS)

It is well known that aluminum and aluminum alloys are sensitive to pitting corrosion when exposed to aqueous solutions containing aggressive anions like halides. The destructive nature of pitting is due to its high local dissolution rates at electrode potentials above the so-called pitting potential Up. Recently, it has been realized that also at potentials below Up, in the passive and cathodic regions and around the free corrosion potential, anodic current transients appear which have been attributed to metastable pitting events. For the purpose of full characterization of the pitting behavior, a program routine has been developed where the occurrence frequency, lifetime and rate of metastable pitting events are extracted from potentiostatic current/time-measurements depending on the electrode potential. The routine has been applied to measurements of carbon modified pure aluminum. Carbon modifications were done with carbon evaporation and carbon sputtering under concurrent argon ion bombardment. The results are discussed in terms of the applied modification technique, their parameters and their effects on the corrosion protection ability of aluminum modified by carbon.

Lensch, O.; Enders, B.; Knecht, J.; Ensinger, W.

2001-04-01

259

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.

2013-12-01

260

Influence of the cathode architecture in the frequency response of self-breathing proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

Self-breathing proton exchange membrane fuel cells are apparently simple devices, but efficient water management is critical for their performance. The cathode configuration should guarantee balanced rates between O2 accessibility from the circumventing air and H2O removal, and a good electric contact between catalyst layers and current collectors at the same time. By applying progressive modifications to the initial concept of a conventional PEMFC, the effect of the cathode architecture on cell performance has been analyzed. Frequency response analyses of the cell during steady-state potentiostatic stepping have yielded relevant information regarding limitations originated by the cathode impedance under high current load conditions. The primitive cell design has been optimized for self-breathing operation by means of this diagnostic tool. The thickness of the perforated plate in the cathode has been found to be one of the main factors contributing to limit oxygen accessibility when a high current load is demanded. Adequate cathode architecture is critical for reducing mass transport limitations in the catalytic layer and enhancing performance under self-breathing conditions.

Ferreira-Aparicio, P.; Chaparro, A. M.

2014-12-01

261

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.

2013-04-01

262

Low-cost 3D nanocomposite solar cells obtained by electrodeposition of CuInSe 2  

NASA Astrophysics Data System (ADS)

Thin CuInSe 2 films have been prepared by electrodeposition from a single bath aqueous solution on both dense and nanoporous TiO 2. The films are deposited potentiostatically using a N 2-purged electrolyte at different potentials. Various deposition times and solution compositions have been employed. The effect of annealing in air and in argon at different temperatures and times is also investigated. Thin films and nanocomposites of TiO 2 and CuInSe 2 have been studied with electron microscopy, X-ray diffraction, Raman spectroscopy, and optical absorption spectroscopy. After a thermal anneal in argon at 350 °C for 30 min excellent CuInSe 2 is obtained. In particular the nominal crystal structure and the bandgap of 1.0 eV are found. Although pinholes are present occasionally, good samples with diode curves showing a rectification ratio of 24 at ±1 V are obtained. Upon irradiation with simulated solar light of 1000 W m -2 a clear photoconductivity response is observed. Furthermore, also some photovoltaic energy conversion is found in TiO 2|CuInSe 2 nanocomposites.

Valdés, M.; Frontini, M. A.; Vázquez, M.; Goossens, A.

2007-10-01

263

Schottky junction study for electrodeposited ZnO thin films and nanowires  

NASA Astrophysics Data System (ADS)

ZnO thin films and well-aligned nanowire arrays have been synthesized via electrochemical deposition method, a low temperature and low cost synthesis method. For the ZnO nanowires growth, the electrodeposition consists of two steps: the ZnO buffer layer was firstly deposited on the substrate using galvanostatic method at room temperature following by the ZnO nanowires growth under potentiostatic method at 80 °C. This second step has also used for the ZnO thin films growth directly on substrate. The morphological and microstructural properties of the as-deposited ZnO have been characterized using scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), as well as photoluminescence spectroscopy (PL). The electrical transport of the ZnO thin films and nanowire arrays have been studied at room temperature both in the symmetrical Al/ZnO/Al electrode configuration guarantying a good Ohmic contact and in the asymmetrical Al/ZnO/Au electrode configuration demonstrating a typical Schottky contact at the interface ZnO/Au. The feature parameters such as the series resistance, the Schottky barrier height, and the ideality factor, have been systematically analyzed. Comparing the diode parameters between thin films and nanowire arrays, we deduced that about 1/3 of the ZnO nanowires come into effective contact with the top Al electrode.

Brouri, Tayeb; Leprince-Wang, Yamin

2014-10-01

264

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

1991-01-01

265

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

2013-01-01

266

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 UV–visible 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: kamachi@igcar.gov.in [Corrosion Science and Technology Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India)

2013-02-15

267

Hydrogen trapping in high-strength steels  

SciTech Connect

Hydrogen trapping in three high-strength steels -- AerMet 100 and AISI 4340 and H11 -- was studied using a potentiostatic pulse technique. Irreversible trapping constants (k) and hydrogen entry fluxes were determined for these alloys in 1 mol/1 acetic acid/1 mol/1 sodium acetate. The order of the k values for the three steels and two 18Ni maraging steels previously studies inversely parallels their threshold stress intensities for stress corrosion cracking (K{sub 1SCC}). Irreversible trapping in AerMet 100 varies with aging temperature and appears to depend on the type of carbide (Fe{sub 3}C or M{sub 2}C) present. For 4340 steel, k can be correlated with K{sub 1SCC} over a range of yield strengths. The change in k is consistent with a change in the principal type of irreversible trap from matrix boundaries to incoherent Fe{sub 3}C. The principal irreversible traps in H11 at high yield strengths are thought to be similar to those in 4340 steel.

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

1998-10-09

268

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.

1990-11-14

269

Submicron patterned metal hole etching  

DOEpatents

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)

2000-01-01

270

Electrochemically reduced graphene oxide-based electrochemical sensor for the sensitive determination of ferulic acid in A. sinensis and biological samples.  

PubMed

An electrochemically reduced graphene oxide (ERGO) modified glassy carbon electrode (GCE) was used as a new voltammetric sensor for the determination of ferulic acid (FA). The morphology and microstructure of the modified electrodes were characterized by scanning electron microscopy (SEM) and Raman spectroscopy analysis, and the electrochemical effective surface areas of the modified electrodes were also calculated by chronocoulometry method. Sensing properties of the electrochemical sensor were investigated by means of cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that ERGO was electrodeposited on the surface of GCE by using potentiostatic method. The proposed electrode exhibited electrocatalytic activity to the redox of FA because of excellent electrochemical properties of ERGO. The transfer electron number (n), electrode reaction rate constant (ks) and electron-transfer coefficient (?) were calculated as 1.12, 1.24s(-1), and 0.40, respectively. Under the optimized conditions, the oxidation peak current was proportional to FA concentration at 8.49 × 10(-8)mol L(-1) to 3.89 × 10(-5)mol L(-1) with detection limit of 2.06 × 10(-8)mol L(-1). This fabricated sensor also displayed acceptable reproducibility, long-term stability, and high selectivity with negligible interferences from common interfering species. The voltammetric sensor was successfully applied to detect FA in A. sinensis and biological samples with recovery values in the range of 99.91%-101.91%. PMID:25063114

Liu, Linjie; Gou, Yuqiang; Gao, Xia; Zhang, Pei; Chen, Wenxia; Feng, Shilan; Hu, Fangdi; Li, Yingdong

2014-09-01

271

A reusable capacitive immunosensor based on a CuS ultrathin film constructed by using a surface sol-gel technique.  

PubMed

A capacitive sensing method based on a CuS ultrathin film modified electrode prepared by a surface sol-gel technique has been developed for the direct detection of human IgA. The resulting CuS film was investigated with cyclic voltammetry (CV), impedance spectroscopy, and quartz crystal microbalance (QCM). CV and impedance examinations showed that the CuS film formed on the gold electrode surface was insulated, and was applicable to form an insulating layer of a capacitive immunosensor. With QCM measurements, the thickness of the CuS film was evaluated to be 5.8 nm. The capacitance change was greatly increased by a CuS nanofilm-based immunosensor, which was initiated by the recognition of an immobilized antibody and the target antigen. The capacitance of the immunosensor corresponding to the concentration of human IgA was investigated by potentiostatic-step measurements. A linear calibration curve was obtained in the range of 1.81 - 90.5 ng ml(-1) with a detection limit of 1.81 ng ml(-1). There were no obvious interferences from the nonspecific adsorption of other proteins. With nice reproducibility and regeneration capacity, the CuS ultrathin film modified immunosensor could be used for the detection of human IgA in serum samples with a recovery of 96.1 - 104.4%, showing its promising applicability and reliability. PMID:20834134

Wu, Zhan; Cao, Zhong; Zeng, Ju-Lan; Zhang, Ling; Chu, Xia; Shen, Guo-Li; Yu, Ru-Qin

2010-01-01

272

Oriented electrophoretic deposition of GdOCl nanoplatelets.  

PubMed

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

2013-02-14

273

Using anodic aluminum oxide templates and electrochemical method to deposit BiSbTe-based thermoelectric nanowires  

NASA Astrophysics Data System (ADS)

In this study, the cyclic voltammetry method was first used to find the reduced voltages and anodic peaks of Bi3+, Sb3+, and Te4+ ions as the judgments for the growth of the (Bi,Sb)2 - x Te3 + x -based materials. Ethylene glycol (C2H6O2) was used as a solvent, and 0.3 M potassium iodide (KI) was used to improve the conductivity of the solution. Two different electrolyte formulas were first used: (a) 0.01 M Bi(NO3)3-5H2O, 0.01 M SbCl3, and 0.01 M TeCl4 and (b) 0.015 M Bi(NO3)3-5H2O, 0.005 M SbCl3, and 0.0075 M TeCl4. The potentiostatic deposition process was first used to find the effect of reduced voltage on the variation of compositions of the (Bi,Sb)2 - x Te3 + x -based materials. After finding the better reduced voltage, 0.01 M Bi(NO3)3-5H2O, 0.01 M SbCl3, and 0.01 M TeCl4 were used as the electrolyte formula. The pulse deposition process was successfully used to control the composition of the (Bi,Sb)2 - x Te3 + x -based materials and grow the nanowires in anodic aluminum oxide (AAO) templates.

Kuo, Hsin-Hui; Kuo, Chin-Guo; Yen, Chia-Ying; Yang, Cheng-Fu

2014-02-01

274

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

PubMed

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; Muñoz, Anna Igual

2011-11-01

275

Tribocorrosion mechanisms of Ti6Al4V biomedical alloys in artificial saliva with different pHs  

NASA Astrophysics Data System (ADS)

Titanium and its alloys has been widely used for the design of dental implants because of its biocompatibility, mechanical properties and corrosion resistance. The powder-metallurgy process is a promising alternative to the casting fabrication process of titanium alloys for bone implants design as the porous structure mimics the natural bone structures, allowing the bone to grow into the pores which results in a better fixation of the artificial implant. However, under in vivo conditions the implants are subjected to tribocorrosion phenomenon, which consists in the degradation mechanisms due to the combined effect of wear and corrosion. The aim of this study is to evaluate the tribocorrosion behaviour of cast and sintered Ti6Al4V biomedical alloy for dental applications using the cast material as reference. Titanium samples were tested in artificial human saliva solution with three different pHs (3, 6, 9) and in an acidic saliva with 1000 ppm fluorides (AS-3-1000F-) by different electrochemical techniques (potentiodynamic curves, potentiostatic tests and tribo-electrochemical tests). Cast and sintered titanium alloys exhibit the same tribocorrosion mechanisms in AS independently of the pH which consists in plastic deformation with passive dissolution, but the addition of fluorides to the acidified solution changes the degradation mechanism towards active dissolution of the titanium alloys.

Licausi, M. P.; Igual Muñoz, A.; Amigó Borrás, V.

2013-10-01

276

A commercial electrochemical method evaluated for measurement of iron status.  

PubMed

I evaluated a commercial electrochemical method (Environmental Science Associates), based on potentiostatic coulometry, for determining iron and total iron-binding capacity (TIBC). The method requires 25 and 100 microL of serum, respectively, for these measurements. Serum iron concentrations so determined in 99 normal volunteers satisfactorily correlated with those determined by the Iron Panel Method (Br J Haematol 1978;38:291-4), although the former required correction for lower-than-expected values. The coulometric TIBC results, on the other hand, correlated poorly with those by the Iron Panel Method. However, when the samples for TIBC were prepared according to the Iron Panel Method, by using the magnesium carbonate technique, and then read in the coulometer, there was satisfactory correlation between TIBC values as determined by the two methods. Variability and analytical recovery of the electrochemical method are satisfactory, and the method should be useful for measurement of serum iron when only relatively small volumes of blood are available. PMID:3621565

Skikne, B S

1987-09-01

277

Design of a high-speed electrochemical scanning tunneling microscope  

NASA Astrophysics Data System (ADS)

In this paper, we present a bottom-up approach to designing and constructing a high-speed electrochemical scanning tunneling microscope (EC-STM). Using finite element analysis (FEA) calculations of the frequency response of the whole mechanical loop of the STM, we analyzed several geometries to find the most stable one that could facilitate fast scanning. To test the FEA results, we conducted measurements of the vibration amplitudes using a prototype STM setup. Based on the FEA analysis and the measurement results, we identified the potentially most disturbing vibration modes that could impair fast scanning. By modifying the design of some parts of the EC-STM, we reduced the amplitudes as well as increased the resonance frequencies of these modes. Additionally, we designed and constructed an electrochemical flow-cell that allows STM imaging in a flowing electrolyte, and built a bi-potentiostat to achieve electrochemical potential control during the measurements. Finally, we present STM images acquired during high-speed imaging in air as well as in an electrochemical environment using our newly-developed EC-STM.

Yanson, Y. I.; Schenkel, F.; Rost, M. J.

2013-02-01

278

Amount of metallic ions released from Ti-Ni alloy by abrasion in simulated bioliquids.  

PubMed

The current density of Ti-56mass%Ni (Ti-50at.%) alloy after abrasion in simulated bioliquids was measured using a potentiostat to estimate the amount of metallic ions released from the alloy during repassivation and maturation. The current density in saline, saline with and without N2 bubbling, and Hanks' solutions with and without proteins after abrasion was measured and the amount of released ion was calculated from the integrated current density with time, assuming that Ti4+ and Ni2+ are equivalently released. No difference in the amount of released ion was observed between saline with and without N2 bubbling. Also, no difference was observed between saline and pH 7.4 Hanks' solution. More Ti4+ and Ni2+ were released in bioliquids with proteins than in saline with and without N2 bubbling (p < 0.05). That is, dissolved oxygen and inorganic ions in Hanks' solution did not influence the amount of released ion, but proteins influenced it. The release of metallic ions from metals and alloys in biological systems can be estimated by the methodology employed in this study. PMID:10524290

Watarai, M; Hanawa, T; Moriyama, K; Asaoka, K

1999-01-01

279

Polyion Selective Polymeric Membrane-Based Pulstrode as a Detector in Flow-Injection Analysis  

PubMed Central

A method for the detection of polyions using fully reversible polyion selective polymeric membrane type pulstrodes as detectors in a flow-injection analysis (FIA) system is examined. The detection electrode consists of a plasticized polymeric membrane doped with 10 wt % of tridodecylmethylammonium-dinonylnaphthalene sulfonate (TDMA/DNNS) ion-exchanger salt. The pulse sequence used involves a short (1 s) galvanostatic pulse, an open-circuit pulse (0.5 s) during which the EMF of the cell is measured, and a longer (15 s) potentiostatic pulse to return the membrane to its original chemical composition. It is shown that total pulse sequence times can be optimized to yield reproducible real-time detection of injected samples of protamine and heparin at up to 20 samples/h. Further, it is shown that the same membrane detector can be employed for FIA detection of both polycations at levels ?10 ?g/mL and polyanions at levels of ?40 ?g/mL by changing the direction of the galvanostatic pulse. The methodology described may also be applicable in the detection of polyionic species at low levels in other flowing configurations, such as in liquid chromatography and capillary electrophoresis. PMID:24650129

2015-01-01

280

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

PubMed

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

2014-05-13

281

Light-controlled bioelectrochemical sensor based on CdSe/ZnS quantum dots.  

PubMed

This study reports on the oxygen sensitivity of quantum dot electrodes modified with CdSe/ZnS nanocrystals. The photocurrent behavior is analyzed for dependence on pH and applied potential by potentiostatic and potentiodynamic measurements. On the basis of the influence of the oxygen content in solution on the photocurrent generation, the enzymatic activity of glucose oxidase is evaluated in solution. In order to construct a photobioelectrochemical sensor which can be read out by illuminating the respective electrode area, two different immobilization methods for the fixation of the biocatalyst have been investigated. Both covalent cross-linking and layer-by-layer deposition of GOD by means of the polyelectrolyte polyallylamine hydrochloride show that a sensor construction is possible. The sensing properties of this type of electrode are drastically influenced by the amount and density of the enzyme on top of the quantum dot layer, which can be advantageously adjusted by the layer-by-layer technique. By depositing four bilayers [GOD/PAH](4) on the CdSe/ZnS electrode, a fast-responding sensor for the concentration range of 0.1-5 mM glucose can be prepared. This study opens the door to multianalyte detection with a nonstructured sensing electrode, localized enzymes, and spatial read-out by light. PMID:21870859

Tanne, J; Schäfer, D; Khalid, W; Parak, W J; Lisdat, F

2011-10-15

282

Control of the redox potential by oxygen limitation improves bacterial leaching of chalcopyrite.  

PubMed

Shake flask and stirred tank bioleaching experiments showed that the dissolution of chalcopyrite is inhibited by ferric ion concentrations as low as 200 mg L(-1) and redox potentials >420 mV (vs. Ag/AgCl). Chemical leaching of chalcopyrite (4% suspension, surface area 2.3 m2 g(-1)) was enhanced fourfold in the presence of 0.1 M ferrous sulphate compared with 0.1 M ferric sulphate. A computer-controlled reactor was designed to function as a "potentiostat"-bioreactor by arresting the air supply to the reactor when the redox potential in solution was greater than a designated setpoint. Leaching at a low, constant redox potential (380 mV vs. Ag/AgCl) achieved final copper recoveries of 52%-61%, which was twice that achieved with a continuous supply of oxygen (<30% extraction). The bacterial populations were observed to continue growing under oxygen limitation but in a controlled manner that was found to improve chalcopyrite dissolution. As the control mechanism is easily established and is likely to decrease production cost, the use of this technology may find application in industry. PMID:11948450

Third, K A; Cord-Ruwisch, R; Watling, H R

2002-05-20

283

Controlled electrodeposition of bismuth nanocatalysts for the solution-liquid-solid synthesis of CdSe nanowires on transparent conductive substrates.  

PubMed

Semiconductor nanowires (NWs) composed of cadmium selenide (CdSe) have been directly grown on transparent conductive substrates via the solution-liquid-solid (SLS) approach using electrodeposited bismuth nanoparticles (Bi NPs) as catalyst. Bi NPs were fabricated on indium tin oxide (ITO) surfaces from a bismuth trichloride solution using potentiostatic double-pulse techniques. The size and density of electrodeposited Bi NPs were controlled by the pulse parameters. Since the NW diameter is governed by the dimension of the Bi catalyst, the electrodeposition is a reliable method to synthesize nanowires directly on substrates with a desired size and density. We show that the density can be adjusted from individual NWs on several square micrometer to very dense NW networks. The diameter can be controlled between thick nanowires above 100 nm to very thin NW of 7 nm in diameter, which is well below the respective exciton dimension. Hence, especially the thinnest NWs exhibit diameter-dependent photoluminescence energies as a result of quantum confinement effects in the radial dimension. PMID:24245969

Reim, Natalia; Littig, Alexander; Behn, Dino; Mews, Alf

2013-12-11

284

The Prediction of Long-Term Coating Performance from Short-Term Electrochemical Data. Part 2; Comparison of Electrochemical Data to Field Exposure Results for Coatings on Steel  

NASA Technical Reports Server (NTRS)

The pace of coatings development is limited by the time required to assess their corrosion protection properties. This study takes a step f orward from Part I in that it correlates the corrosion performance of organic coatings assessed by a series of short-term electrochemical measurement with 18-month beachside exposure results of duplicate pan els. A series of 19 coating systems on A36 steel substrates were test ed in a completely blind study using the damage tolerance test (DTT). In the DTT, a through-film pinhole defect is created, and the electro chemical characteristics of the defect are then monitored over the ne xt 4 to 7 days while immersed in 0.SM NaCl. The open circuit potentia l, anodic potentiostatic polarization tests and electrochemical imped ance spectroscopy were used to study the corrosion behavior of the co ating systems. The beachside exposure tests were conducted at the Ken nedy Space Center according to ASTM D610-01. It was found that for 79 % of the coatings systems examined, the 18 month beachside exposure r esults could be predicted by two independent laboratory tests obtained within 7 days.

Contu, F.; Taylor, S. R.; Calle, L. M.; Hintze, P. E.; Curran, J. P.; Li, W.

2009-01-01

285

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 0.8 V 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

2014-01-01

286

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

PubMed

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 30°C. The enzyme electrode had a linear working range of 0.005-400 µM, with a detection limit of 0.005 µM 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 4°C. PMID:24836212

Chauhan, Nidhi; Pundir, C S

2014-11-15

287

Characterization of local electrochemical doping of high performance conjugated polymer for photovoltaics using scanning droplet cell microscopy?  

PubMed Central

The electrochemical oxidation of a next generation low bandgap high performance photovoltaic material namely poly[4,8-bis-substituted-benzo[1,2-b:4,5-b0]dithiophene-2,6-diyl-alt-4-substituted-thieno[3,4-b] thiophene-2,6-diyl] (PBDTTT-c) thin film was investigated using a scanning droplet cell microscope. Cyclic voltammetry was used for the basic characterization of the oxidation/doping of PBDTTT-c. Application of the different final potentials during the electrochemical study provides a close look to the oxidation kinetics. The electrical properties of both doped and undoped PBDTTT-c were analyzed in situ by electrochemical impedance spectroscopy giving the possibility to correlate the changes in the doping level with the subsequent changes in the resistance and capacitance. As a result one oxidation peak was found during the cyclic voltammetry and in potentiostatic measurements. From Mott–Schottky analysis a donor concentration of 2.3 × 1020 cm?3 and a flat band potential of 1.00 V vs. SHE were found. The oxidation process resulted in an increase of the conductivity by two orders of magnitude reaching a maximum for the oxidized form of 1.4 S cm?1.

Gasiorowski, Jacek; Mardare, Andrei Ionut; Sariciftci, Niyazi Serdar; Hassel, Achim Walter

2013-01-01

288

In situ measurement of active catalyst surface area in fuel cell stacks  

NASA Astrophysics Data System (ADS)

Measurement of electrochemical surface area (ECSA) of fuel cell electrodes is a key diagnostic of performance and gives a useful parameter for monitoring degradation and state of health in polymer electrolyte membrane fuel cells (PEMFCs). However, conventional methods for determining ECSA require potentiostatic control of the cell, which is impractical in a fuel cell stack. Here we demonstrate for the first time the practical application of a galvanostatic technique that enables in situ monitoring of ECSA in each cell throughout the lifetime of a stack. The concept is demonstrated at single cell level using both H adsorption and CO stripping, and the H adsorption (cathodic current) method is extended to stack testing. The undesirable effects of H2 crossover on the measurement may be minimised by appropriate selection of current density and by working with dilute H2 on the anode electrode. Good agreement is achieved with ECSA values determined using conventional single cell voltammetry across a range of MEA designs. The technique is straightforward to implement and provides an invaluable tool for state of health monitoring during PEMFC stack lifetime studies.

Brightman, E.; Hinds, G.; O'Malley, R.

2013-11-01

289

Study of the effect of temperature on Pt dissolution in polymer electrolyte membrane fuel cells via accelerated stress tests  

NASA Astrophysics Data System (ADS)

Operation of polymer electrolyte membrane fuel cells (PEMFC) at higher cell temperatures accelerates Pt dissolution in the catalyst layer. In this study, a Pt dissolution accelerated stress testing protocol involving the application of a potentiostatic square-wave with 3 s at 0.6 V followed by 3 s at 1.0 V was developed to test fuel cell membrane electrode assemblies (MEAs). The use of this Pt dissolution protocol at three different temperatures (40 °C, 60 °C and 80 °C) was investigated for the same membrane electrode assembly composition. Impedance analysis of the membrane electrode assemblies showed an increase in polarization resistance during the course of the accelerated stress testing. Polarization analysis and electrochemical active surface area (ECSA) loss measurements revealed evidence of increased cathode catalyst layer (CCL) degradation due to Pt dissolution and deposition in the membrane as the cell temperature was raised. Scanning electron microscope (SEM) images confirmed the formation of Pt bands in the membrane. A diagnostic expression was developed to estimate kinetic losses due to oxygen reduction using the effective platinum surface area (EPSA) estimated from cyclic voltammograms. The results indicated that performance degradation occurred mainly due to Pt loss.

Dhanushkodi, S. R.; Kundu, S.; Fowler, M. W.; Pritzker, M. D.

2014-01-01

290

SnO2:F Coated Ferritic Stainless Steels for PEM Fuel Cell Bipolar Plates  

SciTech Connect

Ferrite stainless steels (AISI441, AISI444, and AISI446) were successfully coated with 0.6 {micro}m thick SnO{sub 2}:F by low-pressure chemical vapor deposition and investigated in simulated PEMFC environments. The results showed that a SnO{sub 2}:F coating enhanced the corrosion resistance of the alloys in PEMFC environments, though the substrate steel has a significant influence on the behavior of the coating. ICP results from the testing solutions indicated that fresh AISI441 had the highest dissolution rates in both environments, and coating with SnO2:F significantly reduced the dissolution. Coating AISI444 also improved the corrosion resistance. Coating AISI446 steel further improved the already excellent corrosion resistance of this alloy. For coated steels, both potentiostatic polarizations and ICP results showed that the PEMFC cathode environment is much more corrosive than the anode one. More dissolved metallic ions were detected in solutions for PEMFC cathode environment than those in PEMFC anode environment. Sn{sup 2+} was detected for the coated AISI441 and AISI444 steels but not for coated AISI446, indicating that the corrosion resistance of the substrate has a significant influence on the dissolution of the coating. After coating, the ICR values of the coated steels increased compared to those of the fresh steels. The SnO{sub 2}:F coating seems add an additional resistance to the native air-formed film on these stainless steels.

Wang, H.; Turner, J. A.

2007-01-01

291

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

2015-01-01

292

Influences of the main anodic electroplating parameters on cerium oxide films  

NASA Astrophysics Data System (ADS)

Cerium oxide thin films were fabricated onto 316 L stainless steel via a potentiostatically anodic electrodeposition approach in the solutions containing cerium(III) nitrate (0.05 M), ammonia acetate (0.1 M) and ethanol (10% V/V). The electrochemical behaviors and deposition parameters (applied potential, bath temperature, dissolving O2 and bath pH) have been investigated. Results show that, the electrochemical oxidation of Ce3+ goes through one electrochemical step, which is under charge transfer control. The optimum applied potential for film deposition is 0.8 V. Bath temperature plays a significant effect on the deposition rate, composition (different colors of the film) and surface morphology of the deposits. Due to the hydrolysis of Ce3+, cerous hydroxide is facility to form when the bath temperature is higher than 60 °C. The electroplating bath pH is another key role for the anodic deposition of cerium oxide thin films, and the best bath pH is around 6.20. N2 or O2 purged into the bath will result in film porosities and O2 favors cerium oxide particles and film generation.

Yang, Yang; Yang, Yumeng; Du, Xiaoqing; Chen, Yu; Zhang, Zhao; Zhang, Jianqing

2014-06-01

293

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: encu@infim.ro [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)

2011-11-15

294

Oxygen evolution electrocatalysis in alkaline medium at thin Mn xCo 3- xO4 (0 ? x ? 1) spinel films on glass / SnO 2: F prepared by spray pyrolysis  

NASA Astrophysics Data System (ADS)

Films of a series of manganese-cobalt mixed valency spinel oxides of theoretical formula Mn xCo 3-xO 4, (x = 0; 0.25; 0.5; 0.75 and 1), have been prepared by spray pyrolysis at 150 °C on conductive glass in order to relate solid state and surface chemistry to electrocatalytical activity towards the oxygen evolution reaction (OER). X-ray diffraction (XRD) and IR spectroscopy characterized their bulk crystalline properties. Both techniques have confirmed that all oxides belong to the spinel family. Their surface properties were characterized by XPS yielding the Co 3+ / Co 2+ surface ratio. The kinetics of the OER was investigated in 1 M KOH by means of steady state current-potential curves, obtained in the potentiostatic mode and by reaction order determination. The order of reaction ranging from 1.0 to 1.2, and the Tafel slopes ranging from 67 to 69 mV dec -1 can be tentatively interpreted by a mechanism involving a Temkin type of electrosorption of OH intermediates associated with an electrochemical rate-determining step. Replacing progressively Co by Mn, the electrodes were increasingly electrocatalytically less active, surface Co 3+ ions being the active sites, and making Co 3O 4 the most active in the series.

Rios, E.; Chartier, P.; Gautier, J.-L.

1999-07-01

295

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

2004-08-23

296

Fabrication and magnetic properties of La-X (X = Co, Ni, and Fe) nanotube arrays prepared by electrodeposition methods  

NASA Astrophysics Data System (ADS)

Well-ordered La-X (X = Co, Ni and Fe) nanotubes, with the average diameter of ˜200 nm, wall thicknesses of ˜40 nm, have been fabricated into anodized aluminum oxide template by potentiostatic electrodeposition method. Various composition of La-X nanotubes were obtained by tuning the applied deposition potential. Magnetization measurements reveal that doped La could enhance the coercivity (Hc) of La-X nanotubes and their easy axis is perpendicular to the nanotube axis. There is a transition from the curling to transverse mode with increase of angle. Temperature dependent magnetization indicates the existence of superparamagnetic nanoparticles and that the surface effect results in the increase of saturation magnetization (Ms) at low temperature. Abnormal behavior of temperature dependent Hc may result from thermal excitation, magnetoelastic anisotropy, as well as oxide layer of nanotube inner surface induced coupling. These one-dimensional rare-earth transition metal nanostructures could have potential applications in novel spintronics device, ultra-small magnetic media, drug delivery, or other nanodevice.

Chen, J. Y.; Shi, D. W.; Ahmad, N.; Liu, D. P.; Zhou, W. P.; Han, X. F.

2013-08-01

297

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

2014-01-01

298

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.

1983-12-01

299

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

2015-01-01

300

Evolution of novel bioresorbable iron-manganese implant surfaces and their degradation behaviors in vitro.  

PubMed

The purpose of this study is to advance understanding of surface degradation kinetics for Fe-Mn bioresorbable alloys (specifically Fe-20%Mn) and target degradable fracture fixation implants for hard tissues. This study addresses how arc melted Fe-20%Mn discs degrade in a static, osteogenic medium for up to a 3 month time span. Degradation behavior of these bulk alloys was investigated using both mass loss tests for measuring long-term corrosion rates and potentiostatic tests for following the instantaneous rate of degradation. It was discovered that cold-rolling Fe-20%Mn to 77% cold work (CW) suppressed the instantaneous corrosion rate compared with the cast structure. It was also found that an unstable iron-rich oxide layer forms on the entire surface of these bulk samples and the act of machining the bulk metal into a defined shape may affect the morphology of the oxide layer on the outer edge of the samples during degradation. The mechanisms behind the surface evolution of these potential orthopedic implants are investigated in detail. PMID:24616416

Heiden, Michael; Walker, Emily; Nauman, Eric; Stanciu, Lia

2015-01-01

301

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

PubMed

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 µg 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

2014-03-01

302

Multifrequency impedance measurement technique for wireless characterization of microbiological cell cultures  

NASA Astrophysics Data System (ADS)

An impedance measurement system with probe signal frequencies up to 50 kHz with AC-probe voltages below 30 mV rms was integrated for wireless and battery-free monitoring of microbiological cell cultures. The here presented modular design and the use of state-of-the-art components greatly eases adoptions to a wide range of biotechnological applications without the need of bulky LCR-meters or potentiostats. The device had a power consumption of less than 2.5 mA at a 3.3 V single power supply and worked trouble-free within the humid environment of a cell culture incubator. Measurements on lumped RC-elements showed an error of less than 1% for absolute values and less than 1° regarding the phase of the complex impedance. The performance of sensor devices with interdigitated electrode structures for the measurement of adherent cell cultures was tested in the presence of phosphate-buffered saline solution in the humid atmosphere of an incubator for biological cell cultures.

Wissenwasser, J.; Vellekoop, M. J.; Kapferer, W.; Lepperdinger, G.; Heer, R.

2011-11-01

303

Combinatorial microelectrochemistry: Development and evaluation of an electrochemical robotic system  

NASA Astrophysics Data System (ADS)

An electrochemical robotic system using standard microtiter plates as reaction wells for potentiostatic and galvanostatic electrosynthesis and high-throughput electroanalysis was conceived and realized using stepmotor driven positioning stages in combination with a flexible software. Electrode bundles specifically adapted to the experimental needs are accurately positioned in the wells of a microtiter plate followed by the automatic performance of sequences of electrosynthetic or electroanalytical techniques. The system allows us to work under inert-gas atmosphere, in aqueous and organic solvents, and to add or remove solutions by means of integrated syringe pumps. A specifically developed script language permits the user to perform very complex experimental sequences in the different wells of the microtiter plate. The hardware and software features of the developed electrochemical robotic system, the design of suitable electrode arrangements for electrosynthesis and electroanalytical techniques, as well as the reproducibility in aqueous and organic electrolytes are described. The performance of the system is demonstrated by redox screening of a Ru-complex library and by electrosynthesis with in situ analysis of a compound library.

Erichsen, Thomas; Reiter, Sabine; Ryabova, Victoria; Bonsen, Eva Maria; Schuhmann, Wolfgang; Märkle, Wolfgang; Tittel, Carsten; Jung, Günther; Speiser, Bernd

2005-06-01

304

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.

2009-12-01

305

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 80°C. 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 25°C 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

2005-11-01

306

EQCM analysis of titanium corrosion in peroxide- or fluoride-containing solutions.  

PubMed

Although offering superior resistance to corrosion, titanium is unable to withstand discoloration with exposure to peroxide or fluoride. The mechanism of this discoloration, however, remains to be clarified. The purpose of this study was to investigate the mechanism underlying discoloration of titanium with immersion in peroxide- or fluoride-containing solutions based on electrochemical quartz crystal microbalance (EQCM) analysis. A 9-MHz titanium-deposited quartz crystal was used as for the electrodes. Four test solutions were prepared for immersion of the electrodes: 154 mM (0.9%) NaCl; 150 mM H2O2+154 mM NaCl (pH=4 by addition of lactic acid); 150 mM H2O2+154 mM NaCl (pH=8 by addition of sodium hydroxide solution); and 48 mM (0.2%) NaF+154 mM NaCl (pH=5.0 by addition of lactic acid). A WinEchem electrochemistry software-controlled quartz crystal analyzer (QCA922) and the Potentiostat/Galvanostat (Princeton Applied Research) on Windows XP were used to measure concurrently the resonance frequency and potential of the electrodes. The EQCM data differed among solutions. In the acidulated fluoride-containing solution, the electrode showed lower open circuit potential and a gradual increase in electrode frequency, indicating a loss of mass by titanium dissolution. In the peroxide-containing solution, although open circuit potential showed no marked difference, electrode frequency showed a gentle decrease in acidic solution, indicating a gain in mass by oxidation; but an increase in alkaline solution, indicating a loss of mass by dissolution. These results confirmed that exposure to acidulated fluoride- or alkaline peroxide-containing solutions causes dissolution-induced discoloration, while that to acidulated peroxide-containing solutions resulted in the formation of an oxide film together with discoloration. PMID:24334626

Hattori, Masayuki; Oda, Yutaka

2013-01-01

307

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

PubMed

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

2011-08-01

308

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.

2010-08-01

309

Electrochemical Deposition and Characterization of Thermoelectric Ternary (Bi x Sb1- x )2Te3 and Bi2(Te1- y Se y )3 Thin Films  

NASA Astrophysics Data System (ADS)

Thermoelectric thin films of the ternary compounds (Bi x Sb1- x )2Te3 and Bi2(Te1- y Se y )3 were synthesized using potentiostatic electrochemical deposition on gold-coated silicon substrates from aqueous acidic solutions at room temperature. The surface morphology, elemental composition, and crystal structure of the deposited films were studied and correlated with preparation conditions. The thermoelectric properties of (Bi x Sb1- x )2Te3 and Bi2(Te1- y Se y )3 films, i.e., Seebeck coefficient and electrical resistivity, were measured after transferring the films to a nonconductive epoxy support. (Bi x Sb1- x )2Te3 thin films showed p-type semiconductivity, and the highest power factor was obtained for film deposited at a relatively large negative potential with composition close to Bi0.5Sb1.5Te3. In addition, Bi2(Te1- y Se y )3 thin films showed n-type semiconductivity, and the highest power factor was obtained for film deposited at a relatively small negative potential, having composition close to Bi2Te2.7Se0.3. In contrast to Bi2Te2.7Se0.3 thin films, an annealing treatment was required for Bi0.5Sb1.5Te3 thin films to achieve the same magnitude of power factor as Bi2Te2.7Se0.3. Therefore, Bi2Te2.7Se0.3 thin films appear to be good candidates for multilayer preparation using electrochemical deposition, but the morphology of the films must be further improved.

Ma, Yi; Wijesekara, Waruna; Palmqvist, Anders E. C.

2012-06-01

310

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.

1998-01-29

311

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.

2015-01-01

312

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.

313

Subnanomolar detection limit of stripping voltammetric Ca²?-selective electrode: effects of analyte charge and sample contamination.  

PubMed

Ultrasensitive ion-selective electrode measurements based on stripping voltammetry are an emerging sensor technology with low- and subnanomolar detection limits. Here, we report on stripping voltammetry of down to 0.1 nM Ca(2+) by using a thin-polymer-coated electrode and demonstrate the advantageous effects of the divalent charge on sensitivity. A simple theory predicts that the maximum concentration of an analyte ion preconcentrated in the thin membrane depends exponentially on the charge and that the current response based on exhaustive ion stripping from the thin membrane is proportional to the square of the charge. The theoretical predictions are quantitatively confirmed by using a thin ionophore-doped polymer membrane spin-coated on a conducting-polymer-modified electrode. The potentiostatic transfer of hydrophilic Ca(2+) from an aqueous sample into the hydrophobic double-polymer membrane is facilitated by an ionophore with high Ca(2+) affinity and selectivity. The resultant concentration of the Ca(2+)-ionophore complex in the ~1 ?m-thick membrane can be at least 5 × 10(6) times higher than the aqueous Ca(2+) concentration. The stripping voltammetric current response to the divalent ion is enhanced to achieve a subnanomolar detection limit under the condition where a low-nanomolar detection limit is expected for a monovalent ion. Significantly, charge-dependent sensitivity is attractive for the ultrasensitive detection of multivalent ions with environmental and biomedical importance such as heavy metal ions and polyionic drugs. Importantly, this stripping voltammetric approach enables the absolute determination of subnanomolar Ca(2+) contamination in ultrapure water containing 10 mM supporting electrolytes, i.e., an 8 orders of magnitude higher background concentration. PMID:24992261

Kabagambe, Benjamin; Garada, Mohammed B; Ishimatsu, Ryoichi; Amemiya, Shigeru

2014-08-01

314

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)

1999-04-01

315

Functionalization and Characterization of Nanomaterial Gated Field-Effect Transistor-Based Biosensors and the Design of a Multi-Analyte Implantable Biosensing Platform  

NASA Astrophysics Data System (ADS)

Advances in semiconductor research and complementary-metal-oxide semiconductor fabrication allow for the design and implementation of miniaturized metabolic monitoring systems, as well as advanced biosensor design. The first part of this dissertation will focus on the design and fabrication of nanomaterial (single-walled carbon nanotube and quantum dot) gated field-effect transistors configured as protein sensors. These novel device structures have been functionalized with single-stranded DNA aptamers, and have shown sensor operation towards the protein Thrombin. Such advanced transistor-based sensing schemes present considerable advantages over traditional sensing methodologies in view of its miniaturization, low cost, and facile fabrication, paving the way for the ultimate realization of a multi-analyte lab-on-chip. The second part of this dissertation focuses on the design and fabrication of a needle-implantable glucose sensing platform which is based solely on photovoltaic powering and optical communication. By employing these powering and communication schemes, this design negates the need for bulky on-chip RF-based transmitters and batteries in an effort to attain extreme miniaturization required for needle-implantable/extractable applications. A complete single-sensor system coupled with a miniaturized amperometric glucose sensor has been demonstrated to exhibit reality of this technology. Furthermore, an optical selection scheme of multiple potentiostats for four different analytes (glucose, lactate, O 2 and CO2) as well as the optical transmission of sensor data has been designed for multi-analyte applications. The last part of this dissertation will focus on the development of a computational model for the amperometric glucose sensors employed in the aforementioned implantable platform. This model has been applied to single-layer single-enzyme systems, as well as multi-layer (single enzyme) systems utilizing glucose flux limiting layer-by-layer assembled outer membranes. The concentration of glucose and hydrogen peroxide within the sensor geometry, the transient response and the device response time has been simulated for both systems.

Croce, Robert A., Jr.

316

Influence of compressible aerogel electrodes on the properties of an electrochemical cell  

NASA Astrophysics Data System (ADS)

In the biomedical field the need for intra organ pressure measurement can only be facilitated by adapting existing pressure sensing technology to the specific tissues under test. The customization of these sensors has only driven up cost and the need to explore new technologies has become increasingly more important. For this dissertation, we explore the use of a new technology, particularly electrochemical pressure sensing to provide a low-cost pressure sensor to fill this need. Preliminary testing showed that electrically conductive polymers exhibited a change in voltage when pressurized if bubbles were first electrolyzed in the gel creating an aerogel, and that this effect was virtually undetectable without the bubbles present. Using electrochemical impedance spectroscopy (EIS) and model fitting, it was shown that this effect occurs at the electrode interface. Theoretical derivation supported by potentiostatic voltage measurements indicated that a change in the electrode surface area in contact with the fluid was responsible for the effect. Optical micrographs were taken as a bubble along the electrode was pressurized. Using image analysis, the relationship of the change in surface area of the bubble correlated to the relationship of the change in impedance of the electrochemical cell (ECC). The results further demonstrated that the electrochemical response to pressure of a gelatin aerogel electrode was linear for the pressure range of 0 to1034 mmHg. This finding lends itself well for use in medical devices. A new device was invented along with a manufacturing process for an electrochemical pressure transducer (EPT). The EPT was subject to in vitro testing using simulated gastric fluid to create a baseline efficacy of the device for use in the gastrointestinal tract. Multiple design specific techniques were developed to improve sensor performance during physiological conditions.

Sponheimer, Christopher

317

Identifying the microbial communities and operational conditions for optimized wastewater treatment in microbial fuel cells.  

PubMed

Microbial fuel cells (MFCs) are devices that exploit microorganisms as "biocatalysts" to recover energy from organic matter in the form of electricity. MFCs have been explored as possible energy neutral wastewater treatment systems; however, fundamental knowledge is still required about how MFC-associated microbial communities are affected by different operational conditions and can be optimized for accelerated wastewater treatment rates. In this study, we explored how electricity-generating microbial biofilms were established at MFC anodes and responded to three different operational conditions during wastewater treatment: 1) MFC operation using a 750 ? external resistor (0.3 mA current production); 2) set-potential (SP) operation with the anode electrode potentiostatically controlled to +100 mV vs SHE (4.0 mA current production); and 3) open circuit (OC) operation (zero current generation). For all reactors, primary clarifier effluent collected from a municipal wastewater plant was used as the sole carbon and microbial source. Batch operation demonstrated nearly complete organic matter consumption after a residence time of 8-12 days for the MFC condition, 4-6 days for the SP condition, and 15-20 days for the OC condition. These results indicate that higher current generation accelerates organic matter degradation during MFC wastewater treatment. The microbial community analysis was conducted for the three reactors using 16S rRNA gene sequencing. Although the inoculated wastewater was dominated by members of Epsilonproteobacteria, Gammaproteobacteria, and Bacteroidetes species, the electricity-generating biofilms in MFC and SP reactors were dominated by Deltaproteobacteria and Bacteroidetes. Within Deltaproteobacteria, phylotypes classified to family Desulfobulbaceae and Geobacteraceae increased significantly under the SP condition with higher current generation; however those phylotypes were not found in the OC reactor. These analyses suggest that species related to family Desulfobulbaceae and Geobacteraceae are correlated with the electricity generation in the biofilm and may be key players for optimizing wastewater treatment rates and energy recovery in applied MFC systems. PMID:24183402

Ishii, Shun'ichi; Suzuki, Shino; Norden-Krichmar, Trina M; Wu, Angela; Yamanaka, Yuko; Nealson, Kenneth H; Bretschger, Orianna

2013-12-01

318

Liquid infused porous surfaces for mineral fouling mitigation.  

PubMed

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

2015-04-15

319

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.

2012-09-01

320

Potential-dependent single molecule blinking dynamics for flavin adenine dinucleotide covalently immobilized in zero-mode waveguide array of working electrodes.  

PubMed

Single molecules exhibit a set of behaviors that are characteristic and distinct from larger ensembles. Blinking is one such behavior that involves episodic transitions between luminescent and dark states. In addition to the common blinking mechanisms, flavin adenine dinucleotide (FAD), a cofactor in many common redox enzymes, exhibits blinking by cycling between a highly fluorescent oxidized state and a dark reduced state. In contrast to its behavior in flavoenzymes, where the transitions are coupled to chemical redox events, here we study single FAD molecules that are chemically immobilized to the Au region of a zero-mode waveguide (ZMW) array through a pyrroloquinoline quinone (PQQ) linker. In this structure, the Au functions both to confine the optical field in the ZMW and as the working electrode in a potentiostatically controlled 3-elecrode system, thus allowing potential-dependent blinking to be studied in single FAD molecules. The subset of ZMW nanopores housing a single molecule were identified statistically, and these were subjected to detailed study. Using equilibrium potential, E(eq), values determined from macroscopic planar Au electrodes, single molecule blinking behavior was characterized at potentials E < E(eq), E - E(eq), and E > E(eq). The probability of observing a reduced (oxidized) state is observed to increase (decrease) as the potential is scanned cathodic of E(eq). This is understood to reflect the potential-dependent probability of electron transfer for single FAD molecules. Furthermore, the observed transition rate reaches a maximum near E(eq) and decreases to either anodic or cathodic values, as expected, since the rate is dependent on having significant probabilities for both redox states, a condition that is obtained only near E(eq). PMID:24466658

Zhao, Jing; Zaino, Lawrence P; Bohna, Paul W

2013-01-01

321

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.

2015-01-01

322

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

2014-09-01

323

Reference and counter electrode positions affect electrochemical characterization of bioanodes in different bioelectrochemical systems.  

PubMed

The placement of the reference electrode (RE) in various bioelectrochemical systems is often varied to accommodate different reactor configurations. While the effect of the RE placement is well understood from a strictly electrochemistry perspective, there are impacts on exoelectrogenic biofilms in engineered systems that have not been adequately addressed. Varying distances between the working electrode (WE) and the RE, or the RE and the counter electrode (CE) in microbial fuel cells (MFCs) can alter bioanode characteristics. With well-spaced anode and cathode distances in an MFC, increasing the distance between the RE and anode (WE) altered bioanode cyclic voltammograms (CVs) due to the uncompensated ohmic drop. Electrochemical impedance spectra (EIS) also changed with RE distances, resulting in a calculated increase in anode resistance that varied between 17 and 31?? (-0.2?V). While WE potentials could be corrected with ohmic drop compensation during the CV tests, they could not be automatically corrected by the potentiostat in the EIS tests. The electrochemical characteristics of bioanodes were altered by their acclimation to different anode potentials that resulted from varying the distance between the RE and the CE (cathode). These differences were true changes in biofilm characteristics because the CVs were electrochemically independent of conditions resulting from changing CE to RE distances. Placing the RE outside of the current path enabled accurate bioanode characterization using CVs and EIS due to negligible ohmic resistances (0.4??). It is therefore concluded for bioelectrochemical systems that when possible, the RE should be placed outside the current path and near the WE, as this will result in more accurate representation of bioanode characteristics. PMID:24729040

Zhang, Fang; Liu, Jia; Ivanov, Ivan; Hatzell, Marta C; Yang, Wulin; Ahn, Yongtae; Logan, Bruce E

2014-10-01

324

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)

2009-09-15

325

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.

1990-01-01

326

Multiple redox states of multiheme cytochromes may enable bacterial response to changing redox environments  

NASA Astrophysics Data System (ADS)

Multiheme c-type cytochromes (MHCs) are key components in electron-transport pathways that enable some microorganisms to transfer electron byproducts of metabolism to a variety of minerals. As a response to changes in mineral redox potential, microbial communities may shift their membership, or individual organisms may adjust protein expression. Alternatively, the ability to respond may be conferred by the innate characteristics of certain electron-transport-chain components. Here, we used potentiostat-controlled microbial fuel cells (MFCs) to measure the timescale of response to imposed changes in redox conditions, thus placing constraints on the importance of these different mechanisms. In the experiments, a solid electrode acts as an electron-accepting mineral whose redox potential can be precisely controlled. We inoculated duplicate MFCs with a sediment/groundwater mixture from an aquifer at Rifle, Colorado, supplied acetate as an electron donor, and obtained stable, mixed-species biofilms dominated by Geobacter and a novel Geobacter-related family. We poised the anode at potentials spanning the range of natural Fe(III)-reduction, then performed cyclic voltammetry (CV) to characterize the overall biofilm redox signature. The apparent biofilm midpoint potential shifted directly with anode set potential when the latter was changed within the range from about -250 to -50 mV vs. SHE. Following a jump in set potential by 200 mV, the CV-midpoint shift by ~100 mV over a timescale of ~30 minutes to a few hours, depending on the direction of the potential change. The extracellular electron transfer molecules, whose overall CV signature is very similar to those of purified MHCs, appear to span a broad redox range (~200 mV), supporting the hypothesis that MHCs confer substantial redox flexibility. This flexibility may be a principle reason for the abundance of MHCs expressed by microorganisms capable of extracellular electron transfer to minerals.

Arbour, T.; Wrighton, K. C.; Mullin, S. W.; Castelle, C.; Luef, B.; Gilbert, B.; Banfield, J. F.

2013-12-01

327

Application of the 'gate effect' of a molecularly imprinted polymer grafted on an electrode for the real-time sensing of heparin in blood.  

PubMed

Heparin is the most important anticoagulant drug used during surgeries and extracorporeal therapies. Although the blood levels of heparin should be monitored continuously during the procedure to ensure the safety of the patient, there is currently no technique for measuring heparin in real time. This study describes the use of a molecularly imprinted polymer (MIP) as a recognition element in the development of a heparin sensor for real-time monitoring. An indium tin oxide (ITO) electrode grafted with a heparin-specific MIP was used as a working electrode to perform cyclic voltammetry of ferrocyanide. The anodic current was found to be dependent on heparin concentration, probably due to the "gate effect", which is a change in the accessibility of the MIP-modified electrode to ferrocyanide, triggered by specific interaction between MIP and heparin. The kinetics of heparin interaction with the MIP-grafted electrode was evaluated using potentiostatic chronoamperometry of ferrocyanide in an electrochemical flow cell. The response time to stepwise changes in heparin concentration between 0 and 0.04 units per mL was estimated at 20 s, which is remarkably shorter than that achieved using conventional methods for monitoring heparin. The MIP-grafted electrode demonstrated exceptional sensitivity and could detect heparin in whole blood samples (0-6 units per mL) diluted 100-fold with physiological saline containing ferrocyanide. Therefore, the MIP-grafted electrode is suitable for real-time monitoring of heparin in blood. Another advantage is that a very small volume of blood is needed, which is very important, especially when regular measurements are required. PMID:23851360

Yoshimi, Yasuo; Sato, Kuniaki; Ohshima, Masaki; Piletska, Elena

2013-09-01

328

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.

1991-01-01

329

Enhanced electrocatalytic activity of the Au-electrodeposited Pt nanoparticles-coated conducting oxide for the quantum dot-sensitized solar cells  

SciTech Connect

Au was electrodeposited potentiostatically at 0.3?V for 5?min on nanoporous Pt nanoparticle-coated F-doped SnO{sub 2} (FTO/Pt) substrates. For comparison, Au-electrodeposited FTO (FTO/Au) and Au-uncoated FTO/Pt were prepared. FTO/Au showed large-sized Au clusters dispersed sparsely over FTO, which resulted in lower electrocatalytic activity than FTO/Pt. In contrast, FTO/Pt exhibited poor stability unlike FTO/Au due to poisoning by the adsorption of sulfur species. The Au-electrodeposited FTO/Pt (FTO/Pt/Au) consisted of small Au clusters deposited over the entire area of Pt due to the effective Au nucleation provided by nanoporous metallic Pt. FTO/Pt/Au exhibited enhanced electrocatalytic activity and excellent stability because the small Au particles well-dispersed over the nanoporous metallic Pt network provided numerous electrochemical reaction sites, and the Pt surface was not exposed to the electrolyte. When FTO/Pt/Au was used as the counter electrode (CE) of a quantum dot-sensitized solar cell, the significantly enhanced electrocatalytic activity of the FTO/Pt/Au CE facilitated the reduction reaction of S{sub n}{sup 2??}+?2e{sup ?} (CE) ? S{sub n?1}{sup 2?} +?S{sup 2?} at the CE/electrolyte interface, resulting in a significantly hindered recombination reaction, S{sub n}{sup 2??}+?2e{sup ?} (TiO{sub 2} in the photoanode) ? S{sub n-1}{sup 2?} +?S{sup 2?}, and significantly improved overall energy conversion efficiency.

Yoon, Yeung-Pil; Kim, Jae-Hong; Ahn, Kwang-Soon, E-mail: kstheory@ynu.ac.kr [School of Chemical Engineering, Yeungnam University, Gyeongsan 712-749 (Korea, Republic of); Kang, Soon-Hyung [Department of Chemistry Education, Chonnam National University, Gwangju 500-757 (Korea, Republic of); Kim, Hyunsoo; Choi, Chel-Jong [School of Semiconductor and Chemical Engineering, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Kim, Kyong-Kook, E-mail: kim.kk@kpu.ac.kr [Department of Nano-Optical Engineering, Korea Polytechnic University, Siheung 429-793 (Korea, Republic of)

2014-08-25

330

Electrodeposition of layered manganese oxide nanocomposites intercalated with strong and weak polyelectrolytes.  

PubMed

Multilayered manganese oxide nanocomposites intercalated with strong (poly(diallyldimethylammonium) chloride, PDDA) and weak (poly(allylamine hydrochloride), PAH) polyelectrolytes can be produced on polycrystalline platinum electrode in a thin film form by a simple, one-step electrochemical route. The process involves a potentiostatic oxidation of aqueous Mn2+ ions at around +1.0 V (vs Ag/AgCl) in the presence of polyelectrolytes. Fully charged PDDA polycations are accommodated tightly in the interlayer space by electrostatic interaction with negative charges on the manganese oxide layers, leading to an interlayer distance of 0.97 nm. The layered film prepared with PAH has a larger polymer content (PAH/Mn molar ratio of 0.98) than that (PDDA/Mn molar ratio of 0.43) made with PDDA because of the smaller charging degree of PAH, exhibiting a larger interlayer distance (1.19 nm). The interlayer PAH contains neutral (-NH2) and positively charged (-NH3(+)) amine groups, and the -NH3(+) groups are associated with Cl- (to generate -NH3(+) Cl- ion pairs) as well as the negatively charged manganese oxide layers. Both polyelectrolytes once incorporated were not ion exchanged with small cations in solution. The layered structure of PDDA/MnO(x) was collapsed during the reduction process in a KCl electrolyte solution, accompanying an expansion of the interlayer as a result of incorporation of K+ ions for charge neutrality. On the contrary, the layered PAH/MnO(x) film showed a good electrochemical response due to the redox reaction of Mn3+/Mn4+ couple with no change in the structure. X-ray photoelectron spectroscopy revealed that, in this case, excess negative charges generated on the manganese oxide layers upon reduction can be balanced by the protons being released from the -NH3(+) Cl- sites in the interlayer PAH; the Cl- anions becoming unnecessary are inevitably excluded from the interlayer, and vice versa upon oxidation. PMID:16584268

Nakayama, Masaharu; Tagashira, Hiroki

2006-04-11

331

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

PubMed

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, Grégoire; Sibottier, Emilie; Etienne, Mathieu; Walcarius, Alain

2013-01-01

332

Influence of the physical, structural and chemical properties on the photoresponse property of magnetron sputtered TiO2 for the application of water splitting.  

PubMed

The production of hydrogen from water (called "water splitting"), utilises sunlight as an energy source (solar-hydrogen) in a photoelectrochemical (PEC) solar cell, is a promising source of green energy. In this work, a PEC was used, for evaluating the photoactivity of a thin film TiO2 based photoanode by measuring photocurrent (which is comparable to hydrogen production rate by water splitting process in PEC). The main focus of this work is to study the effect of the TiO2 nanosurface and bulk properties on the photoresponse properties of the photoanode. The TiO2 coatings (360-400 nm) were deposited using a closed field reactive magnetron sputtering system. The structure and morphology of the TiO2 coatings were systematically altered by varying the deposition pressure between 5 x 10(-4) to 1 x 10(-2) mbar. The properties of the deposited nano-coatings were determined using Ellipsometry, SEM, AFM, profilometry, XPS, Raman and X-ray diffraction (XRD). Coating properties were correlated with the light absorption and photocurrent performance which were evaluated using UV-Vis spectroscopy and tri-electrode potentiostat measurements respectively. It was concluded from this study that the coating deposition pressure has a pronounced effect on the TiO2 photoanode properties leading to a significant enhancement in the photoactivity in PEC cell. Over a six fold increase in photocurrent at applied potential 0 V was observed for TiO2 photoanode prepared at 4 x 10(-3) mbar as compared to 5 x 10(-4) mbar. A correlation has been established between the deposition pressure, nano surface morphology and bulk properties, UV-Vis light absorbance and bandgap value, and the consequently higher (i) photocurrent density, (ii) negative flat band, and (iii) open circuit potential measured in Photoelectrochemical (PEC) cell. PMID:22400237

Rahman, M; MacElroy, J M D; Dowling, D P

2011-10-01

333

Characterization of anodized titanium for hydrometallurgical applications—Evidence 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

2013-10-01

334

Using anodic aluminum oxide templates and electrochemical method to deposit BiSbTe-based thermoelectric nanowires  

PubMed Central

In this study, the cyclic voltammetry method was first used to find the reduced voltages and anodic peaks of Bi3+, Sb3+, and Te4+ ions as the judgments for the growth of the (Bi,Sb)2 - x Te3 + x-based materials. Ethylene glycol (C2H6O2) was used as a solvent, and 0.3 M potassium iodide (KI) was used to improve the conductivity of the solution. Two different electrolyte formulas were first used: (a) 0.01 M Bi(NO3)3-5H2O, 0.01 M SbCl3, and 0.01 M TeCl4 and (b) 0.015 M Bi(NO3)3-5H2O, 0.005 M SbCl3, and 0.0075 M TeCl4. The potentiostatic deposition process was first used to find the effect of reduced voltage on the variation of compositions of the (Bi,Sb)2 - xTe3 + x-based materials. After finding the better reduced voltage, 0.01 M Bi(NO3)3-5H2O, 0.01 M SbCl3, and 0.01 M TeCl4 were used as the electrolyte formula. The pulse deposition process was successfully used to control the composition of the (Bi,Sb)2 - xTe3 + x-based materials and grow the nanowires in anodic aluminum oxide (AAO) templates. PMID:24502697

2014-01-01

335

Kinetic insights over a PEMFC operating on stationary and oscillatory states.  

PubMed

Kinetic investigations in the oscillatory state have been carried out in order to shed light on the interplay between the complex kinetics exhibited by a proton exchange membrane fuel cell fed with poisoned H(2) (108 ppm of CO) and the other in serie process. The apparent activation energy (E(a)) in the stationary state was investigated in order to clarify the E(a) observed in the oscillatory state. The apparent activation energy in the stationary state, under potentiostatic control, rendered (a) E(a) ? 50-60 kJ mol(-1) over 0.8 V < E < 0.6 V and (b) E(a) ? 10 kJ mol(-1) at E = 0.3 V. The former is related to the H(2) adsorption in the vacancies of the surface poisoned by CO and the latter is correlated to the process of proton conductivity in the membrane. The dependence of the period-one oscillations on the temperature yielded a genuine Arrhenius dependence with two E(a) values: (a) E(a) around 70 kJ mol(-1), at high temperatures, and (b) E(a) around 10-15 kJ mol(-1), at lower temperatures. The latter E(a) indicates the presence of protonic mass transport coupled to the essential oscillatory mechanism. These insights point in the right direction to predict spatial couplings between anode and cathode as having the highest strength as well as to speculate the most likely candidates to promote spatial inhomogeneities. PMID:22017227

Mota, Andressa; Gonzalez, Ernesto R; Eiswirth, Markus

2011-12-01

336

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

PubMed Central

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-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. PMID:23519330

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

2013-01-01

337

Optical and physical properties of cobalt oxide films electrogenerated in bicarbonate aqueous media.  

PubMed

For the first time, cobalt oxide films that are highly protective against localized corrosion and depicting a wide variety of bright and uniform colors due to light interference, have been successfully electrogenerated on polycrystalline cobalt disk electrodes under potentiostatic polarization in a mild aqueous bicarbonate medium. Open circuit potential measurements have shown the formation of a film with a bilayered structure, organized as a thin Co3O4 outer layer and a thick CoO inner layer. The existence of Co3O4 as a thin outer layer, previously postulated from galvanostatic reduction experiments, has been confirmed from XPS analysis. Raman spectroscopy, performed using a very low laser intensity, has shown that the films are mainly composed of CoO. The broadness of the Raman bands observed is associated to the amorphous character of the film, a result that has been confirmed by spectroscopic ellipsometry and X-ray diffraction analysis. Overall film thicknesses, well controlled by the anodization duration, were determined and correlated using mechanical (atomic force microscopy and profilometry) and spectroscopic (specular UV-vis-NIR reflectance and ellipsometry) techniques. Spectroscopic ellipsometry, using a simple amorphous dispersion model, has proved efficient for measuring thicknesses of films ranging from 31 to 290 nm with very low standard deviations. The real part of the complex refractive indices of these films, ranging from 1.8 to 2.2 (at lambda = 632.8 nm) depending on the anodization duration, is in good agreement with values reported in the literature for CoO. The film with the highest refractive index, and consequently the more densely packed structure, was obtained following a 30-minute anodization period. PMID:16570997

Gallant, Danick; Pézolet, Michel; Simard, Stéphan

2006-04-01

338

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.

2005-01-01

339

Characterization of size-controlled ZnO nanorods produced by electrochemical deposition technique  

NASA Astrophysics Data System (ADS)

ZnO nanorods have been grown onto indium thin oxide (ITO) coated glass substrates by electrochemical deposition technique using oxygenated zinc chloride solutions at the bath temperature of 80 °C and pH value of 5.8. The effect of the galvonostatic pretreatment process according to the size of the ZnO nanorods has been examined. The pretreatment consists of the formation of ZnO seed layers at different currents of -1.0 mA and -2.0 mA by the galvonostatic process and then the subsequent ZnO nanorods had been produced using the potentiostatic mode at the potential of -1.0 V. ZnO nanorods produced on the seed layers exhibited different morphological, structural, and optical properties. X-ray diffraction results showed that ZnO nanorods are highly crystalline and wurtzite hexagonal phase with preferred orientation along (0 0 2) direction. The energy band gaps were found to be 3.50 eV, 3.52 eV and 3.60 eV without and with the seed layer of -1.0 mA and -2.0 mA respectively. Atomic Force Microscopy (AFM) images revealed that the ZnO nanorods deposited on the ITO-coated substrates without and with the seed layer are composed of rod-shaped grains with a cross hexagonal section perpendicular to the substrate. The average diameters of the ZnO nanorods were found to be 560 ± 16.78 nm, 450 ± 32.12 nm and 370 ± 18.46 nm without and with the seed layer of -1.0 mA and -2.0 mA respectively. The SEM images have shown that the lengths of the ZnO nanorods varied between 1.0 ?m and 2.0 ?m.

Orhan, N.; Baykul, M. C.

2012-12-01

340

Electronic, Structural, and Electrochemical Properties of LiNi[subscript x]Cu[subscript y]Mn[subscript 2?x?y]O[subscript 4] (0 ; x ; 0.5, 0 ; y ; 0.5) High-Voltage Spinel Materials  

SciTech Connect

First principles computation is carried out for investigating the electronic, structural, and electrochemical properties of LiM{sub 1/2}Mn{sub 3/2}O{sub 4} (M = Ti, V, Cr, Fe, Co, Ni, and Cu). The computation results suggest that doping with Co or Cu can potentially lower Li diffusion barrier as compared to Ni doping. Our experimental research has focused on LiNi{sub x}Cu{sub y}Mn{sub 2-x-y}O{sub 4} (0 < x < 0.5, 0 < y < 0.5), and we found that the amount of Cu will affect the lattice parameters, the cation disorder in the spinel lattice, the particle morphology, as well as the electrochemical properties. Crystal structures, electronic structures, and electrochemical properties of LiNi{sub x}Cu{sub y}Mn{sub 2-x-6}O{sub 4} (0 < x < 0.5, 0 < y < 0.5) are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray absorption spectroscopy (XAS), and electrochemical measurements including potentiostatic intermittent titration technique (PITT). With detailed electrochemical measurements and in situ XAS experiments of LiNi{sub 0.25}Cu{sub 0.25}Mn{sub 1.50}O{sub 4}, the proposed explanation of the voltage profile by the first principles computation was proven, a second plateau at 4.2 V originates from the oxidation of Cu{sup 2+} to Cu{sup 3+}, and the plateau at 4.95 V may originate from extra electrons provided by oxygen ions. Although the reversible discharge capacity decreases with increasing Cu amount, optimized composition such as LiCu{sub 0.25}Ni{sub 0.25}Mn{sub 1.5}O{sub 4} exhibits high capacities at high rates.

Yang, Ming-Che; Xu, Bo; Cheng, Ju-Hsiang; Pan, Chun-Jern; Hwang, Bing-Joe; Meng, Ying S. (Florida); (UCSD); (NTU)

2011-09-06

341

Synthesis Structure Property Relations in Layered, Li-excess Oxides Electrode Materials Li[Li1/3-2x/3NixMn2/3-x/3]O2 (x=1/3, 1/4 and 1/5)  

SciTech Connect

Relations between synthesis conditions, detailed crystal structures, and electrochemical properties of the Li-excess layered oxides Li[Ni{sub x}Li{sub 1/3-2x/3}Mn{sub 2/3-x/3}]O{sub 2}(0 < x < 1/2) are studied by X-ray diffraction, scanning electron microscopy (EELS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electron energy-loss spectrometry, combined with electrochemical property measurements including potentiostatic intermittent titration technique (PITT). Optimal synthesis conditions are obtained for stoichiometric samples sintered at 1000 C in air followed by furnace cooling. The materials exhibit capacities of {approx}250, 230, and 200 mAh/g within a voltage range of 2-4.8 V on discharge for x = 1/5, 1/4 and 1/3, respectively. Diffraction data of electrochemically cycled electrode materials show an expanded c/a lattice ratio and changing Li/Ni interlayer mixing indicating peculiar cation migration in the structures. High resolution TEM images and XPS spectra show obvious differences in the surface characteristics of the samples synthesized with stoichiometric and excess amount of LiOH, suggesting that surface characteristics is one of the contributing factors to the difference in electrochemical properties. Our results suggest that the first cycle irreversible capacity is affected by both the bulk and surface characteristics of pristine materials, which is strongly influenced by precursor chemistry. The PITT results suggest that cation rearrangement during the charge/discharge has a significant impact on the lithium chemical diffusivity.

Fell, Christopher [University of Florida, Gainesville; Carroll, Kyler [Virginia Commonwealth University, Richland; Chi, Miaofang [ORNL; Meng, Ying Shirley [University of Florida, Gainesville

2010-01-01

342

Characteristic corrosion resistance of nanocrystalline TiN films prepared by high density plasma reactive magnetron sputtering.  

PubMed

Nanocytalline TiN films were deposited on non-alkali glass and Al substrates by reactive DC magnetron sputtering (DCMS) with an electromagnetic field system (EMF). The microstructure and corrosion resistance of the TiN-coated Al substrates were estimated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical methods. All the TiN films shows that they have a (111) preferred orientation at room temperature. TiN films deposited on Al substrate using only DCMS 400 W showed a sheet resistance of 3.22 x 10-1 omega/symbol see texts (resistivity, 3.22 x 10-5 omegacm). On the other hand, a relatively low sheet resistance of 1.91 x 10-1 omega/symbol see text (1.91 x 10-5 omegacm) was obtained for the dense nanocrystalline TiN film deposited on Al substrate using DCMS 375 W+ EMF 25 W, indicating that the introduction of an EMF system enhanced the electrical properties of the TiN film. TiN films deposited on Al substrate at 400 degreesC had a (200) preferred orientation with the lowest sheet resistance of 1.28x10-1 omega/symbol see texts (1.28 x 10-5 omegacm) which was attributed to reduced nano size defects and an improvement of the crystallinity. Potentiostatic and Potentiodynamic tests with a TiN-coated Al showed good corrosion resistance (l/corr, = 2.03 microA/cm2, Ecorr = -348 mV) compared to the uncoated Al substrate (/corr = 4.45 microA/cm2, Ecorr = -650 mV). Furthermore, EMF system showed that corrosion resistance of the TiN film also was enhanced compared to DCMS only. For the TiN film deposited on Al substrate at 400 degreesC, corrosion current and potential was 0.63 micro/cm2 and -1.5 mV, respectively. This improved corrosion resistance of the TiN film could be attributed to the densification of the film caused by enhancement of nitrification with increasing high reactive nitrogen radicals. PMID:23901480

Kim, J H; Kang, C G; Kim, Y T; Cheong, W S; Song, P K

2013-07-01

343

Growth of binary Ni-Fe films: Characterisations at low and high potential levels  

NASA Astrophysics Data System (ADS)

Binary Ni-Fe films relating their magnetoresistance and magnetic properties with crystal structure and surface morphology, and the corresponding film composition were investigated at low and high deposition potentials. Based on the results obtained from a cyclic voltammetry curve, a potential region between -1.3 V and -1.8 V was selected, and the current-time transients were recorded to control the proper film growth. The Ni-Fe films were potentiostatically electrodeposited on polycrystalline titanium substrates at low (-1.3 V) and high (-1.8 V) deposition potential. The data from the energy dispersive X-ray spectrometry and the inductively coupled plasma atomic emission spectroscopy demonstrated that the Ni and Fe content in the films varied as the potential changed. The magnetotransport properties and magnetic characteristics studied by a vibrating sample magnetometer (VSM) were observed to be affected by the deposition potentials. All films were also noted to exhibit anisotropic magnetoresistance behaviour. At low potential, the magnitude of the longitudinal magnetoresistance (LMR) was high (3.93%) and that of the transverse magnetoresistance (TMR) was low (3.49%) while for the film at high potential the LMR (2.76%) and the TMR (3.66%) magnitudes were obtained. Magnetization measurements by VSM revealed that the saturation magnetization, Ms was 779 emu/cm3 and saturation field, Hs was 142 Oe at low potential while for the films deposited at high potential the Ms and Hs were 749 emu/cm3 and 262 Oe, respectively. However, the coercivities in the films were found to be around 4.5 Oe, regardless of the potential. Also, the magnetic easy axis was found to be in the film plane for all samples. The structural analysis of the films was carried out using the X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. To XRD analysis, all films have a strong (111) texture of face-centred cubic structure and the lattice parameters, d-spacings and average grain size slightly changed with deposition potential. The films studied by SEM revealed that they have smaller grains grown at low deposition potential compared to those deposited at high potential. The differences observed in the properties of the films might be attributed to the compositional changes caused by the deposition potential.

Kuru, Hilal; Kockar, Hakan; Alper, Mursel; Karaagac, Oznur

2015-03-01

344

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; Yücel, Mustafa; Omanovic, Dario; Brulport, Jean-Pierre; Le Bris, Nadine

2013-10-01

345

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

346

Direct electrochemical oxidation of ammonia on graphite as a treatment option for stored source-separated urine.  

PubMed

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 1.6 V 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 2.9 ± 0.3 gN·m(-2)·d(-1) was achieved and the specific energy demand was 42 Wh·gN(-1) at an anode potential of 1.31 V 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

Zöllig, Hanspeter; Fritzsche, Cristina; Morgenroth, Eberhard; Udert, Kai M

2015-02-01

347

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

2010-01-01

348

COUPLED MULTI-ELECTRODE INVESTIGATION OF CREVICE CORROSION OF 316 STAINLESS STEEL  

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

2006-01-30

349

COUPLED MULTI-ELECTRODE INVESTIGATION OF CREVICE CORROSION OF 316 STAINLESS STEEL  

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

2006-01-30

350

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

PubMed

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 (K(wc)) in the CoCrMo was determined. The mass loss due to wear (K(w)) and that due to corrosion (K(c)) 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

2011-07-29

351

Institute for Advanced Materials at University of Louisville  

SciTech Connect

In this project, a university-wide, academic center has been established entitled ?Institute for Advanced Materials and Renewable Energy?. In this institute, a comprehensive materials characterization facility has been established by co-locating several existing characterization equipment and acquiring several state of the art instrumentation such as field emission transmission electron microscope, scanning electron microscope, high resolution X-ray diffractometer, Particle Size Distribution/Zeta Potential measurement system, and Ultra-microtome for TEM specimen. In addition, a renewable energy conversion and storage research facility was also established by acquiring instrumentation such as UV-Vis absorption spectroscopy, Atomic Layer Deposition reactor, Solar light simulator, oxygen-free glove box, potentiostat/galvanostats and other miscellaneous items. The institute is staffed with three full-time staff members (one senior research technologist, a senior PhD level research scientist and a junior research scientist) to enable proper use of the techniques. About thirty faculty, fifty graduate students and several researchers access the facilities on a routine basis. Several industry R&D organizations (SudChemie, Optical Dynamics and Hexion) utilize the facility. The established ?Institute for Advanced Materials? at UofL has three main objectives: (a) enable a focused research effort leading to the rapid discovery of new materials and processes for advancing alternate energy conversion and storage technologies; (b) enable offering of several laboratory courses on advanced materials science and engineering; and (c) develop university-industry partnerships based on the advanced materials research. The Institute?s efforts were guided by an advisory board comprising eminent researchers from outside KY. Initial research efforts were focused on the discovery of new materials and processes for solar cells and Li ion battery electrodes. Initial sets of results helped PIs to secure a successful EPSCoR cluster implementation grant by teaming with additional researchers from UK. In addition to research efforts, the project enabled several other outcomes: (a) helped recruit a junior faculty member (Dr. Moises Carreon) and establish a lab focused on meso-porous materials toward separation and catalysis; (b) enabled offering of three new, graduate level courses (Materials characterization using spectroscopy and microscopy; Electron and x-ray diffraction; and renewable energy systems); and (c) mentoring of a junior faculty members (Dr. Gerold Willing).

Sunkara, Mahendra; Sumaneskara, Gamini; Starr, Thomas L; Willing, G A; Robert W, Cohn

2009-10-29

352

HYBRID SULFUR ELECTROLYZER DEVELOPMENT, NHI WORK PACKAGE N-SR07TC0301, FY07 FIRST QUARTER REPORT  

SciTech Connect

The proof of concept of SO2 electrolysis for the hybrid sulfur (HyS) process is the second priority research target of the DOE Nuclear Hydrogen Initiative's thermochemical program for FY07. The proof of concept of the liquid-phase option must be demonstrated at the single cell level for an extended run times (>100 hours). The rate of development of HyS will depend on the identification of a promising membrane or an alternative means for controlling sulfur formation. Once successful long-duration operation has been demonstrated, SRNL will develop a multi-cell stack that can be connected to the H2SO4 decomposer being developed by SNL for the S-I ILS for a Hybrid Sulfur Integrated Laboratory-Scale Experiment during FY 2008. During the first quarter of FY07, SRNL continued the component development and membrane development activities with the goal of identifying and characterizing improved electrodes, electrocatalysts, membranes and MEA configurations which could then be tested at larger scale in the SDE test facility. A modified glass cell was fabricated to allow measurements of sulfur dioxide (SO2) transport across membrane samples at elevated temperatures (up to 70 C). This testing also includes evaluating SO2 transport in different sulfuric acid concentrations (30-70 wt%). A new potentiostat/frequency analyzer was installed for determining ionic conductivity of membranes. This instrument enhances our capabilities to characterize membrane, electrocatalyst and MEA properties and performance. Continuing work from FY06, evaluations were preformed on various commercial and experimental membranes and electrocatalyst materials for the SDE. Several different types of commercially-available membranes were analyzed for sulfur dioxide transport as a function of acid strength including perfluorinated sulfonic acid (PFSA), sulfonated polyetherketone-ketone, and poly-benzimidazole (PBI) membranes. Experimental membranes from the sulfonated diels-alder polyphenylenes (SDAPP) and modified Nafion{reg_sign} 117 were evaluated for SO{sub 2} transport as well. These membranes exhibited reduced transport coefficient for SO{sub 2} transport without the loss in ionic conductivity.

Summers, W

2006-12-20

353

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

2012-04-12

354

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.

355

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.

2011-01-01

356

Electrodeposition and device incorporation of bismuth antimony nanowire arrays  

NASA Astrophysics Data System (ADS)

Thermoelectric materials have the unique property where the application of a potential difference across the material results in the formation of a temperature gradient, and vice versa. There is continued interest in bulk thermoelectric materials for power generation and refrigeration applications, however these materials are not currently in widespread use due to their low conversion efficiency. It has been predicted that nanostructured thermoelectric materials will show enhanced performance over their bulk counterparts. In this study, bismuth antimony (Bi1-xSbx) nanowire arrays have been synthesized and assembled into devices in order to demonstrate an enhanced performance in nanostructured thermoelectric materials. Bi1-xSbx nanowire arrays were fabricated by potentiostatic electrodeposition into porous alumina templates from a dimethyl sulfoxide (DMSO) solution. The nanowire composition and texture were studied as a function of the electrodeposition conditions in order to maximize their thermoelectric performance. Energy dispersive spectrometry and electron microprobe analysis were used to study the nanowire composition as a function of the electroactive and non-electroactive species in solution. Texturing in the nanowire arrays was observed by X-ray diffraction and controlled by the applied voltage and presence of supporting electrolyte. The nanowire arrays were also optimized for device incorporation by maximizing the number of nanowires and minimizing their length distribution. The areal density of nanowire arrays was on the order of 1010 wires/cm2 due to the high density of pores in the alumina and the high degree to which those pores were filled with electrodeposited material. A narrow distribution of nanowire lengths was observed by scanning electron microscopy across millimeter-length portions of the arrays. A hybrid nanowire-bulk thermoelectric device was assembled after electrical contacts were electrodeposited over Bi1-xSbx nanowire arrays. Nickel was used as the contact material and its electrodeposition was studied with respect to the applied potential (direct and pulsed) and the deposition bath contents. The thermoelectric performance of hybrid devices assembled from these nanowire composites was determined by the Harman method. An unoptimized Bi1-xSbx nanowire array produced a temperature difference of 7°C and the hybrid device had a ZT of 0.12, which is on par with an equivalent bulk couple. The results of this work illustrate the proof of concept where a thermoelectric nanowire array was taken from fabrication to device to measurement.

Keyani, Jennifer

357

Seedless electrochemical deposition of copper on air-exposed tantalum nitride barriers with ultra-thin adhesion layers  

NASA Astrophysics Data System (ADS)

Copper has replaced aluminum for microelectronic applications, bringing the challenges of adapting to a new material with new processing systems. One impetus of changing from aluminum to copper for electronic applications is the lower resistivity which results in higher device speed. It is of the utmost importance to produce electrochemical deposition (ECD) copper with a resistivity as near to the bulk value of 1.7 muOcm as possible to assure maximum device performance [1]. Current technology requires ever decreasing feature geometries and increasing aspect ratios to improve device speed. The challenge in designing smaller devices is in achieving a uniformly continuous, adherent seed layer. As geometry size is reduced and aspect ratios increase, the ability to achieve coverage with physical vapor deposition (PVD) for a copper seed layer becomes impossible. It is projected that PVD seed layers will no longer be viable below the 90 nm node [2]. The development of plating baths for direct electrodeposition of copper onto metal and metal nitride barrier layers for interconnect technology is a primary concern. Basic electrochemical principles as well as specific reasons for the choice of copper bath base and additives are discussed. This work presented here includes electrochemical data consisting of potentiodynamic experiments, cyclic polarization data, and current density analysis for potentiostatic experiments as well as galvanostatic deposition. Samples were analyzed with electrochemical techniques, field emission scanning electron microscopy (FESEM), Scotch tape adhesion tests, and mass transport experiments utilizing a rotating disk electrode. Atomic Force Microscopy (AFM) has been employed to determine surface roughness changes indicative of the grain structure and surface condition of samples. An initial examination of copper plate has been conducted using transmission electron microscopy. Other experimental work includes a four point probe resistivity study with annealing to optimize copper conditions, XPS to quantify the impurity concentration of copper plate as well as possibility of impurity concentration in Cu deposits. The parameters of bath additive concentration and deposition potentials, that promote good adhesion of copper on barrier layers are one of the most important aspects of this study. This is quantified using four point bend testing to determine adhesion values. Superfilling using ultra thin adhesion promoting layers both an electrochemically deposited, ECD, copper seed and atomic layer deposition (ALD) deposited palladium and ruthenium will be quantified. (Abstract shortened by UMI.)

Lay, Nicole Elizabeth

358

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.  

PubMed

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

2012-06-01

359

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.

2011-12-01

360

Tribochemical investigation of microelectronic materials  

NASA Astrophysics Data System (ADS)

To achieve efficient planarization with reduced device dimensions in integrated circuits, a better understanding of the physics, chemistry, and the complex interplay involved in chemical mechanical planarization (CMP) is needed. The CMP process takes place at the interface of the pad and wafer in the presence of the fluid slurry medium. The hardness of Cu is significantly less than the slurry abrasive particles which are usually alumina or silica. It has been accepted that a surface layer can protect the Cu surface from scratching during CMP. Four competing mechanisms in materials removal have been reported: the chemical dissolution of Cu, the mechanical removal through slurry abrasives, the formation of thin layer of Cu oxide and the sweeping surface material by slurry flow. Despite the previous investigation of Cu removal, the electrochemical properties of Cu surface layer is yet to be understood. The motivation of this research was to understand the fundamental aspects of removal mechanisms in terms of electrochemical interactions, chemical dissolution, mechanical wear, and factors affecting planarization. Since one of the major requirements in CMP is to have a high surface finish, i.e., low surface roughness, optimization of the surface finish in reference to various parameters was emphasized. Three approaches were used in this research: in situ measurement of material removal, exploration of the electropotential activation and passivation at the copper surface and modeling of the synergistic electrochemical-mechanical interactions on the copper surface. In this research, copper polishing experiments were conducted using a table top tribometer. A potentiostat was coupled with this tribometer. This combination enabled the evaluation of important variables such as applied pressure, polishing speed, slurry chemistry, pH, materials, and applied DC potential. Experiments were designed to understand the combined and individual effect of electrochemical interactions as well as mechanical impact during polishing. Extensive surface characterization was performed with AFM, SEM, TEM and XPS. An innovative method for direct material removal measurement on the nanometer scale was developed and used. Experimental observations were compared with the theoretically calculated material removal rate values. The synergistic effect of all of the components of the process, which result in a better quality surface finish was quantitatively evaluated for the first time. Impressed potential during CMP proved to be a controlling parameter in the material removal mechanism. Using the experimental results, a model was developed, which provided a practical insight into the CMP process. The research is expected to help with electrochemical material removal in copper planarization with low-k dielectrics.

Kulkarni, Milind Sudhakar

361

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

2004-01-01

362

Electrochemical microfluidic biosensor for the detection of nucleic acid sequences.  

PubMed

A microfluidic biosensor with electrochemical detection for the quantification of nucleic acid sequences was developed. In contrast to most microbiosensors that are based on fluorescence for signal generation, it takes advantage of the simplicity and high sensitivity provided by an amperometric and coulorimetric detection system. An interdigitated ultramicroelectrode array (IDUA) was fabricated in a glass chip and integrated directly with microchannels made of poly(dimethylsiloxane) (PDMS). The assembly was packaged into a Plexiglas housing providing fluid and electrical connections. IDUAs were characterized amperometrically and using cyclic voltammetry with respect to static and dynamic responses for the presence of a reversible redox couple-potassium hexacyanoferrate (ii)/hexacyanoferrate (iii) (ferri/ferrocyanide). A combined concentration of 0.5 microM of ferro/ferricyanide was determined as lower limit of detection with a dynamic range of 5 orders of magnitude. Background signals were negligible and the IDUA responded in a highly reversible manner to the injection of various volumes and various concentrations of the electrochemical marker. For the detection of nucleic acid sequences, liposomes entrapping the electrochemical marker were tagged with a DNA probe, and superparamagnetic beads were coated with a second DNA probe. A single stranded DNA target sequence hybridized with both probes. The sandwich was captured in the microfluidic channel just upstream of the IDUA via a magnet located in the outside housing. Liposomes were lysed using a detergent and the amount of released ferro/ferricyanide was quantified while passing by the IDUA. Optimal location of the magnet with respect to the IDUA was investigated, the effect of dextran sulfate on the hybridization reaction was studied and the amount of magnetic beads used in the assay was optimized. A dose response curve using varying concentrations of target DNA molecules was carried out demonstrating a limit of detection at 1 fmol assay(-1) and a dynamic range between 1 and 50 fmol. The overall assay took 6 min to complete, plus 15-20 min of pre-incubation and required only a simple potentiostat for signal recording and interpretation. PMID:16511625

Goral, Vasiliy N; Zaytseva, Natalya V; Baeumner, Antje J

2006-03-01

363

Revisiting the crevice corrosion of stainless steel and aluminum in chloride solutions---The role of electrode potential  

NASA Astrophysics Data System (ADS)

Although the crevice corrosion of stainless steel and aluminum in chloride solutions has been studied extensively, there is little agreement on the mechanism of crevice corrosion for these materials. The present study attempted to resolve the ambiguity of the crevice corrosion mechanism by first reviewing previous relevant studies and then, by conducting an in-depth study of crevice corrosion with a focus on electrode potential and the IR mechanism. The crevice corrosion of aluminum (99.999 wt. %, AA2024) and stainless steel (304 and 444) in neutral and mildly acidic chloride solutions was investigated. For each alloy system, polarization curves were generated in simulated crevice solutions and potentiostatic crevice corrosion experiments with varying crevice gap opening dimensions were performed. Current and electrode potential along the crevice wall were measured. In-situ photographs of the developing crevice corrosion were obtained and in-situ and ex-situ pH measurements were performed. For the stainless steels, potentiodynamic and potentiostatic methods, including a novel applied potential shift method, were used in an attempt of detect the development of an anodic peak in a passive system, prior to the onset of crevice corrosion. Crevice corrosion of aluminum in a pH 6, 0.6M NaCl solution was not found to occur under open circuit or polarized conditions. Polarization curves in simulated crevice solutions did not show an anodic peak. Based on the polarization behavior, the IR mechanism correctly predicts the absence of crevice corrosion for this system. Crevice corrosion was observed for aluminum in a mildly acidic (pH 3), chloride free solution and found to be consistent with the IR mechanism. In this solution, crevice corrosion resulting in severe material loss was observed and a high current (10 mA) was measured. This is the first time crevice corrosion of aluminum, as indicated by significant material loss and high measured current, has been reported. Also of importance, is the fact that the corrosion occurred in the absence of pitting corrosion. The cause of corrosion in this case can be explained by alkalization of the crevice due to a high rate of hydrogen evolution reaction, driven by a potential drop within the crevice. For stainless steels, crevice corrosion was clearly demonstrated in a neutral 0.6M NaCl solution and in two mildly acidic simulated crevice solutions: pH 2, 0.6M NaCl and pH 1, 3M NaCl. The conclusive evidence of the occurrence of crevice corrosion was a high measured current and photographic evidence of showing severe material loss within the crevice and no attack on the uncreviced surfaces. All observations of the propagation of crevice corrosion for 304 and 444 were consistent with the IR mechanism. Additional efforts to understand the mechanism of stainless steel crevice corrosion focused on studying the initiation. No evidence was found to suggest initiation occurs due to a reduction of the pitting potential from chloride accumulation. Initiation of crevice corrosion was found to occur after the development of an anodic peak. This is the first time an anodic peak has been detected prior to the onset of crevice corrosion. This novel observation provides proof that an anodic peak can develop in a passive system. Since the IR mechanism requires an anodic peak, this observation provides convincing evidence for the applicability of IR mechanism in a passive system. Equally important, the observation shows that while compositional change is required to develop the anodic peak, another step is necessary to initiate crevice corrosion. Crevice corrosion mechanisms that rely solely on compositional change are inadequate in that they do not provide an explanation for the additional step. However, the IR mechanism clearly defines this additional step as the initiation event, IR>Deltaphi*, at which point the crevice wall in contact with the acidified crevice solution is activated and crevice corrosion begins. In summary, crevice corrosion of aluminum and stainless steels was clearly demonstrated

Deforce, Brian S.

364

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.

365

Coupled Multi-Electrode Investigation of Crevice Corrosion of 316 Stainless Steel and NiCrMo Alloy 625  

SciTech Connect

Crevice corrosion is currently mostly studied using either one of two techniques depending on the information desired. The first method involves two multicrevice formers or washers fastened on both sides of a sample plate. This technique provides exposure information regarding the severity of crevice corrosion (depth, position, frequency of attack) but delivers little or no electrochemical information. The second method involves the potentiodynamic or potentiostatic study of an uncreviced sample in a model crevice solution or under a crevice former in aggressive solution where crevice corrosion may initiate and propagate and global current is recorded. However, crevice corrosion initiation and propagation behavior is highly dependent on exact position in the crevice over time. The distance from the crevice mouth will affect the solution composition, the pH, the ohmic potential drop and the true potential in the crevice. Coupled multi-electrode arrays (MEA) were used to study crevice corrosion in order to take in account spatial and temporal evolution of electrochemistry simultaneously. Scaling laws were used to rescale the crevice geometry while keeping the corrosion electrochemical properties equivalent to that of a natural crevice at a smaller length scale. one of the advantages was to be able to use commercial alloys available as wires electrode and, in the case of MEA, to spread the crevice corrosion over many individual electrodes so each one of them will have a near homogeneous electrochemical behavior. The initial step was to obtain anodic polarization curves for the relevant material in acid chloride solution which simulated the crevice electrolyte. using the software Crevicer{trademark}, the potential distribution inside the crevice as a function of the distance from the crevice mouth was determined for various crevice gaps and applied potentials, assuming constant chemistry throughout the crevice. The crevice corrosion initiation location x{sub crit} is the position where the potential drops to E{sub Flade}. Figure 1 illustrates the resulting x{sub crit} vs. G scaling laws for 316 Stainless Steel in 1 M HCl at 50 C. The coupled multi-wire array is composed of one hundred identical 316 Stainless Steel wires in a five by twenty formation inserted in a groove of a 316 Stainless Steel rod such that the ends of the wires are flush mounted with the rod. The 100 wires are coupled electrically through in-line zero resistance ammeters. The diameter of the wires (250 {micro}m) was chosen so that x{sub crit} (critical initiation distance from the crevice mouth) and the expected zone of crevice corrosion (predicted from the scaling law) would be larger than the radius of a single wire. The array created a flush mounted planar electrode with the surface/volume ratio obtained in planar crevices. The observation of the current evolution as a function of position inside and outside the crevice as function of time was made possible as illustrated in Figure 2 in 0.6 M NaCl at 50 C.

F. Bocher; F.J. Presuel-Moreno; J.R. Scully

2006-06-08

366

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 850°C 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 850°C (GDC is Ce0.9Gd0.1O3, a good mixed conductor under reducing conditions).

Danilovic, Nemanja

367

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 (0-60°C), 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

368

In situ solid-state NMR spectroscopy of electrochemical cells: batteries, supercapacitors, and fuel cells.  

PubMed

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, Frédéric; Leskes, Michal; Grey, Clare P

2013-09-17

369

Characterising Redox-Related Isotope Effects  

NASA Astrophysics Data System (ADS)

Redox processes have played a pivotal role in shaping Earth's interior and surface and making life possible. A record of this evolution is found within stable isotope signatures arising from chemical redox changes occurring in our continents, oceans and atmosphere over time. Experimental and theoretical studies of redox- related transition metal isotope fractionation provide a physical basis to understand how isotopes are fractionated under natural conditions, relating geochemical signatures to earth processes from which they arise. Here we present experimental evidence that charge transfer processes drive the fractionation of stable isotopes of Fe and Zn, and the magnitude of fractionation can be tuned as a function of redox potential and other physical variables. To quantitatively evaluate isotopic signatures of redox processes, we have conducted electrochemical experiments measuring the fractionation of Fe and Zn isotopes during their electrodeposition from aqueous solution: M2+ + 2e- = M(s). The electrochemical cell consisted of anodic and cathodic half- cells separated by a salt bridge, and connected to a potentiostat which applied an adjustable constant voltage (vs. Ag/AgCl). Metallic Fe and Zn plated on glassy carbon electrodes was recovered in acid for analysis of the stable isotope composition on a Thermo-Finnigan Neptune MC-ICP-MS. Results are reported as a large delta difference between the isotopic composition (56Fe/54Fe and 66Zn/64Zn) of plated metal relative to the stock solution. The results show some clear trends; fractionation is a function of applied voltage (overpotential: ? = E- E0 Volts), ranging from ?56Fe ~ -4 to -0.9 ‰, and ?66Zn ~ - 5.5 to -4 ‰ at ? = -0.5 to -1.25 V and -0.1 to -0.5 V, respectively. Temperature affects fractionation in a counter-intuitive manner, with fractionation increasing with increasing temperature (at ? = -1.0 V: ?56Fe ~ -1.25 ‰ at 0°C and -1.62 ‰ at 35°C). The results can be explained in terms of two end-member processes: an electrochemically controlled regime which creates larger fractionations and a mass-transport/diffusion limited regime where smaller fractionations are expected [Rodushkin et al., 2004, Anal. Chem. 76: 2148]. To test whether charge transfer processes are responsible for the larger fractionations observed a series of experiments were run using a rotating disc electrode. In these experiments mass-transport properties near the electrode surface are controlled by the electrode's rotation rate (?). Results show that at low ? = -0.5 V a constant fractionation factor (?56Fe ~ -3.75 ‰) is obtained at ? > 2000 rpm. Our research has shown that electrochemical experiments can be used to separately study charge transfer and mass-transport processes that affect stable isotope fractionation. Charge transfer reactions produce a large fractionation of Fe and Zn isotopes in comparison to mass-transport/diffusion controlled processes. It is intriguing to note that the range in ?56Fe observed in these experimental systems nearly encompasses those seen in the geologic record [Anbar and Rouxel, 2007, Annu. Rev. Earth Planet. Sci. 35: 717]. Further studies may help link these isotopic signatures to past redox conditions and processes.

Black, J. R.; John, S.; Young, E. D.; Kavner, A.

2008-12-01

370

Portable Hand-Held Electrochemical Sensor for the Transuranics  

SciTech Connect

During the four-year period of the grant all of the goals of the originally proposed work were achieved, and some additional accomplishments are here reported. Two types of sensors were designed and built in the lab, capable of detecting uranium, plutonium and thorium at the 10 part-per-trillion level. The basis of both sensor types is a specially designed polymer having selective binding sites for actinyl ions of the form MO{sub 2}{sup 2+}(aq), where M is any actinide in the +6 oxidation state. This binding site also traps ions of the form MO{sub 2}{sup +}(aq), where M is any actinide in the +4 oxidation state. In this way, the polymer is responsive to the two most common water-soluble ions of the actinide series. The chelating ring responsible for binding the actinyl ions was identified from the literature, calix[n]arene where n = 6. Several versions of this sensing polymer were coated on conductive substrates and demonstrated for actinide sensing. An optimized sensor was developed and is fully described in this report. It has a polymer bilayer, fabricated under the particular conditions given below. Two different operating modes were demonstrated having different capabilities. One is the chemFET mode (a FET is a field effect transistor) and the other is the voltammetric mode. These two sensors give complementary information regarding the actinide species in a sample. Therefore our recommendation is that both be used together in a probe. A detailed design for such a probe has been filed as a patent application with the United States Patent Office, and is patent pending. The sensing polymer incorporating this actinyl-chelating ring was tested under a variety of conditions and the operating limits were determined. A full factorial experiment testing the polymerization method was conducted to optimize performance and characteristics of this polymer. The actinyl-sensing polymer was also deposited on the gate of a field effect transistor (FET) and demonstrated as a sensitive detector for uranium. Millimeter scale electrodes, operated by a hand-held instrument assembled in this lab and operated in the voltammetric mode, were transported to the DOE-Nevada test site (Las Vegas, NV) where field detection and quantitation of plutonium, uranium, and a mixture of these two elements was also demonstrated. Several probe designs were prepared, built and tested including probes with movable protective windows. A miniature, battery powered potentiostat was designed, built and demonstrated for use in a hand-held field portable instrument. This work was performed largely by undergraduates who gained valuable research experience, and many of them have continued on to graduate schools. In addition, they all gained exposure to and appreciation for national security research, in particular non-proliferation research. Four graduate students participated and one earned the MS degree on this project.

Dale D. Russell, William B. Knowlton, Ph.D.; Russel Hertzog, Ph.D

2005-11-25

371

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 V—a 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.

2012-12-01

372

Effect of slurry chemicals on chemical-mechanical planarization of copper  

NASA Astrophysics Data System (ADS)

An important component of the slurries used in chemical mechanical planarization (CMP) is an appropriately chosen corrosion/dissolution inhibitor, which facilitates selective material removal from protrusions while protecting recessed regions of the surface. The present work demonstrates the utility of two environmentally benign anionic surfactants, sodium dodecyl sulfate (SDS) and ammonium dodecyl sulfate (ADS) as dissolution inhibitors. Using these surfactants in a standard slurry (1 wt% glycine with 5 wt% H2O 2 at pH = 4.0) typically used for Cu CMP, and combining measurements of open circuit potentials and contact angles with those of Cu removal rates, we show that both SDS and ADS suppress chemical dissolution and polish rates of Cu. The dissolution inhibition efficiencies of ADS and SDS measured in these experiments are found to be superior to those of benzotriazole (BTA), a traditional inhibiting agent used for copper CMP. It has been demonstrated that ADS can also be utilized as an inhibiting agent for the application in electrochemical-mechanical planarization (ECMP) of copper. Using an acidic electrolyte of glycine and H2O 2, and small Cu discs, we show that the corrosion inhibition efficiency of ADS is superior to that of benzotriazole even in ECMP application. The relation between PE of Cu patterns and complexing agents has been investigated by measuring removal rates and surface topographies from patterns created on blanket Cu films. It has been observed that PE is dependent on the step height and drops significantly beyond a threshold step height that is in the range of 1000 A. Since the same type of polishing pad (IC 1400) was used in all the experiments, it might be the complexing agent that determines this characteristic PE threshold. Also, the huge increase in Cu dissolution rate for the citric acid system with increasing temperature appears to be responsible for the low PE values measured for this system. The synergetic effect of mixtures of ADS and BTA on Cu planarization has also been demonstrated. A model slurry containing a mixture of 3 mM ADS and 0.5 mM BTA shows much lower dissolution rate of Cu than that containing 10 mM BTA while sustaining similar polish rates of Cu at 2 psi. The planarization efficiency evaluated using the topographies created on Cu film surface (width: ˜ 15mum, depth: ˜ 5000 A) also shows better results while using the mixture of 3mM ADS and 0.5 mM BTA compared to 10 mM BTA. The relation between the copper dissolution rate and planarization efficiency is shown to be inversely logarithmically proportional to each other. The information from potentiostatic polarization, contact angle, UV/VIS spectroscopy and FTIR spectroscopy suggests that the synergetic effect of the mixture of BTA and ADS is due to electrostatic attraction between Cu/Cu-BTA complex and dodecyl sulfate as well as the complexation of Cu-BTA-dodecyl sulfate.

Hong, Youngki

373

Novel carbon nanostructures as catalyst support for polymer electrolyte membrane fuel cells  

NASA Astrophysics Data System (ADS)

Polymer electrolyte membrane fuel cell (PEMFC) technology has advanced rapidly in recent years, with one of active area focused on improving the long-term performance of carbon supported catalysts, which has been recognized as one of the most important issues to be addressed for the commercialization of PEMFCs. The central part of a PEMFC is the membrane electrode assembly (MEA) which consists of two electrodes (anode and cathode) and a cation exchange membrane. These electrodes are commonly made of carbon black (most often, Vulcan XC-72) supported on carbon paper or carbon cloth backings. It is the primary objective of this thesis to prepare and investigate carbon nanostructures (CNS, licensed to Hydrogen Research Institute -- IRH, Quebec, Canada), the carbon material with more graphite component like carbon nanotubes (CNTs) for use as catalyst support in PEMFCs. High energy ball-milling of activated carbon along with transition metal catalysts under hydrogen atmosphere, followed by heat-treatment leads to nanocrystalline structures of carbon called CNS. However, CNS formed in the quartz tube after heat-treatment is inevitably accompanied by many impurities such as metal particles, amorphous carbon and other carbon nanoparticules. Such impurities are a serious impediment to detailed characterization of the properties of nanostructures. In addition, since the surface of CNS is itself rather inert, it is difficult to control the homogeneity and size distribution of Pt nanoparticules. In this thesis work, we demonstrated a novel mean to purify and functionalize CNS via acid-oxidation under reflux conditions. To investigate and quantify these nanostructures X-ray diffraction, electrical conductivity measurements, specific surface area measurements, thermogravimetric analysis, X-ray photoelectron spectroscopy and transmission electron microscopy studies were used. Cyclic voltammetry studies were performed on different samples to derive estimates for the relationship between the composition of the acid mixture and their influence in producing high density of surface functional groups. Such surface functionalization on CNS enhances the reactivity, improves the specificity and provides an avenue for Pt deposition. It was also shown that a 1:1 mixture of 7.5 M sulphuric acid and 15 M nitric acid have generated higher composition of non-acidic functional groups over other acid compositions discussed in this thesis. In this thesis, we also demonstrated a novel method to deposit and disperse platinum clusters on carbon nanotubes via a chemically specific nucleation mechanism. To investigate and quantify these platinized CNS X-ray diffraction, thermogravimetric analysis, atomic adsorption spectroscopy and high resolution transmission electron microscopy were used. An average Pt cluster size of 4 nm was dispersed homogeneously on CNS that was functionalized with the method described above. The corrosive nature of carbon support material is a crucial issue for the commercialization of PEMFC systems. Therefore, electrochemical oxidations of Pt/CNS compared with Pt/C were studied in this thesis with the aim to understand their durability as catalyst support in PEMFCs. The surface oxidation of the catalyst materials has been compared following potentiostatic treatments up to 200 h under condition simulating the PEMFC cathode environment (80°C, nitrogen purged 0.5 M sulphuric acid, and a constant potential of 1.2 V). The degradation of Pt catalysts and the carbon support was also evaluated by measuring the cell voltage at constant load after different oxidation intervals at 1.2 V. The agglomeration of Pt catalyst particles and the changes in surface functional groups of the carbon material at different intervals of electrochemical oxidation was evaluated using X-ray diffraction and thermogravimetric studies. The subsequent electrochemical characterization at different treatment time intervals by both the above methods suggests that CNS is electrochemically more stable than Vulcan XC-72 with less surface oxide formation and Pt surface are

Natarajan, Sadesh Kumar

374

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

375

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