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1

Electrochemical Array Microsystem with Integrated Potentiostat  

E-print Network

. INTRODUCTION Electronic measurement of biochemical analyte concentrations is essential for disease diagnose elements (BRE) to electronics utilizes a three-electrode electrochemical measurement technique. The key electronic component for electrochemical measurement is a potentiostat, which can be configured

Mason, Andrew

2

Variable gain CMOS potentiostat for dissolved oxygen sensor  

Microsoft Academic Search

This paper presents a variable gain potetiostat designed for the electrochemical control of Dissolved Oxygen (DO) sensors. The design is targeted for implementation using MIMOS 0.35 um CMOS process technology at 3.3V. The potentiostat amplifier for dissolved oxygen utilizes three electrodes (working, reference and counter) which work together to form the electrochemical reaction. There are several types of DO sensor

Mei Yee Ng; Yuzman Yusoff

2010-01-01

3

A Low Cost-Computer-Controlled and Powered Multichannel Potentiostat for General Use in Development of Inexpensive Electrochemical Sensors  

Microsoft Academic Search

Described herein, is an inexpensive 16?channel potentiostat that is both controlled and powered by a PC multifunction data acquisition card. As an enabling example, the potentiostat was used to measure the extent for which insoluble manganese oxide powder will pre?oxidize ascorbic acid in a phosphate buffered saline solution. This technique to reduce electroactive interferent species has recently been reported to

Mark A. Tapsak; Jamie G. Houseknecht; Paul V. Goode

2007-01-01

4

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

E-print Network

: In corrosion metal is able to dissolve because the anodic current required to oxidise the metal comes fromPractical 2P7 Corrosion Aims To introduce students to using a computer controlled potentiostat for electrochemical measurements and familiarise them with fundamental concepts of corrosion. You will study corrosion

Paxton, Anthony T.

5

Anodically potentiostatic deposition of flaky nickel oxide nanostructures and their electrochemical performances  

Microsoft Academic Search

Porous nickel oxide films composed of intercrossing nanoflakes are potentiostatically deposited onto the stainless steel substrate by a plating bath of sodium acetate, nickel sulfate and sodium sulfate. Deposition potential influences pore size of the deposited films. Pore size decreases as the deposition potential increases. Electrochemical performance of the deposited films is characterized by cyclic voltammogram. Specific capacity of the

Mao-Sung Wu; Yu-An Huang; Jiin-Jiang Jow; Wein-Duo Yang; Ching-Yuan Hsieh; Huei-Mei Tsai

2008-01-01

6

A high output power (70 V, 1.5 A) potentiostat-galvanostat  

Microsoft Academic Search

The design of a high-power potentiostat-galvanostat is presented. This instrument is capable of driving a cell within the rectangular region 0 to ± 72 V and 0 to ± 1.5 A. The anodic oxidation of titanium in acidic medium is given as an example of its application.

M. Froelicher; C. Gabrielli; J. P. Toque

1980-01-01

7

Corrosion resistance study of Fe Mn Al C alloys using immersion and potentiostatic tests  

NASA Astrophysics Data System (ADS)

The interaction of the Fe-32.7Mn-6.59Al-1.26Si-0.25C (wt.%) and Fe-32.3Mn-8.54Al-1.31Si-0.54C (wt.%) alloys with the environment was evaluated. Potentiostatic and total immersion tests, planned and analyzed by the statistic model of fixed effects were used for the evaluation of corrosion in gasoline, alcohol fuel, lactic acid solution (40 wt.%), sodium chloride solution (3 wt.%), and boiler water. Potentiostatic tests in 1N H 2SO 4 medium presented that the alloys showed a tendency towards passivation. The role that aluminum and silicon play in alloy corrosion mechanism was discussed.

Lins, Vanessa F. C.; Freitas, Marta Afonso; Silva, Evando M. Paula e.

2005-08-01

8

A novel multi-working electrode potentiostat for electrochemical detection of metabolites  

Microsoft Academic Search

A novel single-chip and multiplexed read-out circuit for multi-electrode electrochemical sensors, in standard 0.18 ?m UMC CMOS technology, is presented. The circuit is a part of a fully-integrated biochip (in design) for the detection of multiple metabolites. The proposed topology is based on the potentiostat approach, and it is devoted to detect currents within the range of 250 pA 650

Daniela De Venuto; Michele Daniel Torre; Cristina Boero; Sandro Carrara; Giovanni De Micheli

2010-01-01

9

A cost-effective and field-ready potentiostat that poises subsurface electrodes to monitor bacterial respiration.  

PubMed

Here, we present the proof-of-concept for a subsurface bioelectrochemical system (BES)-based biosensor capable of monitoring microbial respiration that occurs through exocellular electron transfer. This system includes our open-source design of a three-channel microcontroller-unit (MCU)-based potentiostat that is capable of chronoamperometry, which laboratory tests showed to be accurate within 0.95 ± 0.58% (95% Confidence Limit) of a commercial potentiostat. The potentiostat design is freely available online: http://angenent.bee.cornell.edu/potentiostat.html. This robust and field-ready potentiostat, which can withstand temperatures of -30°C, can be manufactured at relatively low cost ($600), thus, allowing for en-masse deployment at field sites. The MCU-based potentiostat was integrated with electrodes and a solar panel-based power system, and deployed as a biosensor to monitor microbial respiration in drained thaw lake basins outside Barrow, AK. At three different depths, the working electrode of a microbial three-electrode system (M3C) was maintained at potentials corresponding to the microbial reduction of iron(III) compounds and humic acids. Thereby, the working electrode mimics these compounds and is used by certain microbes as an electron acceptor. The sensors revealed daily cycles in microbial respiration. In the medium- and deep-depth electrodes the onset of these cycles followed a considerable increase in overall activity that corresponded to those soils reaching temperatures conducive to microbial activity as the summer thaw progressed. The BES biosensor is a valuable tool for studying microbial activity in situ in remote environments, and the cost-efficient design of the potentiostat allows for wide-scale use in remote areas. PMID:22209069

Friedman, Elliot S; Rosenbaum, Miriam A; Lee, Alexander W; Lipson, David A; Land, Bruce R; Angenent, Largus T

2012-02-15

10

Wide-range, picoampere-sensitivity multichannel VLSI potentiostat for neurotransmitter sensing.  

PubMed

Neurotransmitter sensing is critical in studying nervous pathways and neurological disorders. A 16-channel current-measuring VLSI potentiostat with multiple ranges from picoamperes to microamperes is presented for electrochemical detection of electroactive neurotransmitters like dopamine, nitric oxide etc. The analog-to-digital converter design employs a current-mode, first-order single-bit delta-sigma modulator architecture with a two-stage, digitally reconfigurable oversampling ratio for ranging the conversion scale. An integrated prototype is fabricated in CMOS technology, and experimentally characterized. Real-time multi-channel acquisition of dopamine concentration in vitro is performed with a microfabricated sensor array. PMID:17271192

Murari, Kartikeya; Thakor, Nitish; Stanacevic, Milutin; Cauwenberghs, Gert

2004-01-01

11

Potentiostatic and ac impedance studies of the hydrogen electrodes used in Ni/H2 batteries  

NASA Technical Reports Server (NTRS)

In a study of electrode activity for hydrogen evolution and hydrogen ionization, knowledge of the detailed kinetics and of the surface coverage by adsorbed hydrogen is essential. In the Ni/H2 battery, the hydrogen electrode is subjected to high hydrogen pressure; elucidation of the variation of kinetic parameters with hydrogen pressure is therefore of interest. Potentiostatic and ac impedance spectroscopic techniques were used in the present study. The equivalent circuit of the reaction, the kinetic parameters, and their pressure dependence have been determined.

Le Helloco, Jean-Guy; Bojkov, Hristo; Parthasarathy, Arvind; Srinivasan, Supramaniam; Appleby, A. J.

1992-01-01

12

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

13

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

PubMed

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

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

2013-09-15

14

Recovery of heavy metals from spent Ni-Cd batteries by a potentiostatic electrodeposition technique  

NASA Astrophysics Data System (ADS)

Two heavy metals, Cd and Ni, have been separately recovered from spent AA-size Ni-Cd batteries by the potentiostatic electrodeposition and chemical precipitation methods, respectively. Various types and concentrations of HCl, H 2SO 4, and HNO 3 acids had been used as leach extractants. Experimental results indicate that the acid with the best leach capability is 4 M HCl. Three complexing reagents of NH 3, sodium acetate, sodium citrate have been chosen and tested. The most effective buffer is sodium citrate. The optimum mole ratio of metallic ion to citrate ion is 1:1. The recovery process for Cd metal is conducted by the potentiostatic electrodeposition in a leach electrolyte with a sodium citrate complex. The optimum applied potential for Cd recovery is in the range -1100 to -1120 mV (versus saturated calomel electrode (SCE)). The current efficiency for the recovery process is between 70 and 90% and depends strongly on the process parameters, e.g. liquor, concentration, applied potential, temperature, type of complex reagents, mole ratio, mass-transfer rate.

Yang, Chun-Chen

15

POTENTIOSTATIC DEPOSITION OF COPPER INDIUM DISULFIDE THIN FILMS: EFFECT OF CATHODIC POTENTIALS ON THE OPTICAL AND PHOTOELECTROCHEMICAL PROPERTIES  

Microsoft Academic Search

CuInS 2 thin films were one-step potentiostatically deposited onto indium tin oxide (ITO) coated glass from aqueous solution containing CuCl 2, InCl 3 and Na 2S2O3. The effect of cathodic potentials on the structural, photoelectrochemical and optical properties of the deposited film were studied. X-ray diffraction (XRD) patterns showed that the deposited CuInS 2 material was polycrystalline with tetragonal structure.

Teo Sook Liang; Zulkarnain Zainal; Tan Wee Tee; Imad Hamadneh

16

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

PubMed

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

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

2010-05-01

17

Interfacing the AD5933 for bio-impedance measurements with front ends providing galvanostatic or potentiostatic excitation  

NASA Astrophysics Data System (ADS)

The AD5933 [1], a specialized single chip impedance analyzer, made by Analog Devices, is basically not intended for use with four electrode interface. Due to electrochemical phenomena at the electrodes connecting the material under test (MUT), especially in the low frequency region below 100 kHz, a two electrode interface generates considerable errors during the measurement. Thus, for most application in bio-impedance measurement only a four electrode interface can guarantee reliable results. Here we show how a four electrode interface with galvanostatic excitation but also for potentiostatic excitation can be realized by just a few external components.

Pliquett, Uwe; Barthel, Andreas

2012-12-01

18

Towards a miniature implantable in vivo telemetry monitoring system dynamically configurable as a potentiostat or galvanostat for two- and three-electrode biosensors  

Microsoft Academic Search

A miniature implantable and dynamically configurable potentiostat and galvanostat for two- and three-electrode biosensors with a telemetry electronics package was developed to provide remote monitoring of implantable amperometric and voltametric biosensors such as for glucose. Included are circuitry for sensor biasing, a transimpedance amplifier to produce the sensor proportional output signal, and a transceiver (transmitter and receiver) which can both

Richard D. Beach; Robert W. Conlan; Markham C. Godwin; Francis Moussy

2005-01-01

19

Parallel recording of neurotransmitters release from chromaffin cells using a 10×10 CMOS IC potentiostat array with on-chip working electrodes.  

PubMed

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 N; Herbst, Adam D; Kim, Sung J; Minch, Bradley A; Lindau, Manfred

2013-03-15

20

Parallel Recording of Neurotransmitters Release from Chromaffin Cells Using a 10 x 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

21

Highly sensitive indicator-free impedance sensing of DNA hybridization based on poly(m-aminobenzenesulfonic acid)/TiO2 nanosheet membranes with pulse potentiostatic method preparation.  

PubMed

A direct electrochemical detection procedure for DNA hybridization by using the electrochemical signal changes of conductive poly(m-aminobenzenesulfonic) acid (PABSA)/TiO(2) nanosheet membranes, which were electropolymerized by using the pulse potentiostatic method, is reported. Due to the unique properties of TiO(2) nanoparticles, m-aminobenzenesulfonic acid monomers tend to be adsorbed around the particles, and the electropolymerization efficiency is greatly improved. The combination of TiO(2) nanoparticles and PABSA resulted in a nanocomposite membrane with unique and novel nanosheet morphology that provides more activation sites and enhances the surface electron-transfer rate. These characteristics were propitious for the magnification of PABSA electrochemical signals and the direct detection of DNA hybridization. Owing to the presence of abundant sulfonic acid groups, PABSA could overcome the drawbacks of polyaniline and be used to detect bioanalytes at physiological pH. DNA probes could be covalently attached to the sulfonic groups through the amines of DNA sequences by using an acyl chloride cross-linking reaction. After immobilization of probe DNA, the electrochemical impedance value increased significantly compared to that of PABSA/TiO(2) nanosheet membranes, and then decreased dramatically after the hybridization reaction of the probe DNA with the complementary DNA sequence compared to that of the probe-immobilized electrode. Electrochemical impedance spectroscopy was adopted for indicator-free DNA biosensing, which had an eminent ability for the recognition between double-base mismatched sequences or non-complementary DNA sequences and complementary DNA sequences. A gene fragment, which is related to one of the screening genes for the transgenically modified plants, the cauliflower mosaic virus 35S gene was satisfactorily detected. This is the first report for the indicator-free impedance DNA hybridization detection by using PABSA/TiO(2) membranes under neutral conditions. PMID:20020515

Hu, Yu-Wei; Yang, Tao; Wang, Xin-Xing; Jiao, Kui

2010-02-01

22

Wireless Multichannel Integrated Potentiostat for Distributed Neurotransmitter Sensing  

E-print Network

of energy (e.g. temperature gradients, wind). For example, devices such as the Smart Dust distributed. This microchip is compact and has many advantages over traditional devices. However, this device is still to harvest power allow these wires to be removed. Energy harvesting uses the external environment as a source

Cauwenberghs, Gert

23

VLSI POTENTIOSTAT ARRAY FOR DISTRIBUTED ELECTROCHEMICAL NEURAL Abhishek Bandyopadhyay1  

E-print Network

, and digitized by a bank of current-mode delta-sigma analog-to-digital (A/D) converters. First-order noise-to-voltage conversion. #12;NOarray CurrentConveyers ProgrammableGain WRGain 4 I V 8 Vref DEMUX Addr 3 Delta-SigmaModulat NO transients. A shift register scans the buffered decimated delta-sigma outputs in bit-serial format providing

Cauwenberghs, Gert

24

A Fully Differential CMOS Potentiostat Meisam Honarvar Nazari  

E-print Network

of poor selectivity [1]. In FSCV a cyclic potential is applied between recording electrodes. It offers beneficial when supply voltage shrinks due to CMOS technology scaling. + - VOUT WE1WE2RE I1I2 I/V ION-SELECTIVE down to pico-ampere range. The fully differential architecture with differential recording electrodes

Genov, Roman

25

Wide-Range, Picoampere-Sensitivity Multichannel VLSI Potentiostat for Neurotransmitter Sensing  

E-print Network

-mode, first-order single-bit delta-sigma modulator architecture with a two-stage, digitally reconfigurable neurotransmitters like dopamine, nitric oxide etc. The analog-to-digital converter design employs a current of the probe). #12;1-bit + - Iin Counter + - D/A Analog Digital fs N fs fs NM {-1,0,+1} {-1,+1} {0,1} Shift reg

Stanacevic, Milutin

26

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

E-print Network

for electrochemical Oswald ripening. Experimental Methods Square arrays of gold nanoparticles (typical radius ) 37 on conductive substrates, such as ITO, undergo an electrochemical Oswalt ripening process20,21 in which larger, in this study, we use Au rather than Ag. We do not observe ripening of Au particles lithographically patterned

27

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

28

A potentiostatic study of oxygen transport through poly(2-ethoxyethyl methacrylate-co-2,3-dihydroxypropylmethacrylate) hydrogel membranes.  

PubMed

The oxygen permeability and diffusion coefficients of hydrogel membranes prepared with copolymers of 2-ethoxyethyl methacrylate (EEMA)/2,3-dihydroxypropylmethacrylate (MAG) with mole fraction of the second monomer in the range between 0 and 0.75 are described. Values of the permeability and diffusion coefficients of oxygen are determined by using electrochemical procedures involving the measurement of the steady-state current in membranes prepared by radical polymerization of the monomers. The results obtained for the transport properties were analyzed taking into account the fractional free volumes, the cohesive energy densities and the glass transition temperatures of the hydrogels. PMID:15626426

Compañ, Vicente; Tiemblo, Pilar; García, F; García, J M; Guzmán, Julio; Riande, Evaristo

2005-06-01

29

The Affect of Wellbutrin on Dopamine Reuptake Transporters in Rodent Striatal Tissue  

E-print Network

(Potentiostat set to 450 mV, and sample chamber heated to 37ºC with air flow set to 95% O2, 5% CO2 ) Inject in chamber. Constant Temperature Circulating Water Bath Rotator and Controller Potentiostat Oscilloscope

Collins, Gary S.

30

LAMINAR FLOW BASED MICROREACTOR FOR EFFICIENT REGENERATION OF NICOTINAMIDE COFACTORS FOR BIOCATALYIS  

E-print Network

LAMINAR FLOW BASED MICROREACTOR FOR EFFICIENT REGENERATION OF NICOTINAMIDE COFACTORS were run in potentiostatic mode using a PGSTAT 30 potentiostat (Autolab). In order to control as a reference electrode. Fluid flow in all experiments is pressure driven and regulated using a syringe pump

Kenis, Paul J. A.

31

Triboelectrochemical Characterization of Microelectronic Materials  

E-print Network

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...

Joo, Suk Bae

2013-03-21

32

A Low Noise Readout Circuit for Integrated Electrochemical Biosensor Arrays  

E-print Network

fully electronic measurement of biochemical analyte concentrations that are essential for disease recognition elements (BRE) to electronics utilizes a three- electrode electrochemical measurement technique. The key electronic component for electrochemical measurement is a potentiostat which can be configured

Mason, Andrew

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.

2011-03-25

34

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...

35

Open Archive TOULOUSE Archive Ouverte (OATAO) OATAO is an open access repository that collects the work of Toulouse researchers and  

E-print Network

on solid aluminium plate electrodes by electrorefining of U­Pu­Zr alloy in the molten salt. All the most. Preparation of U­Pu­Al alloys The initial material was prepared by potentiostatic electrorefin- ing of U

Boyer, Edmond

36

Mechanism of formation and growth of sunflower-shaped imperfections in anodic oxide films on niobium  

Microsoft Academic Search

Anodizing of niobium has been investigated to develop niobium solid electrolytic capacitors. Chemically polished niobium specimens were anodized in a diluted phosphoric acid solution, initially galvanostatically at ia=4Am?2 up to Ea=100V, and then potentiostatically at Ea=100V for tpa=43.2ks. During the galvanostatic anodizing, the anode potential increased almost linearly with time, while, during potentiostatic anodizing, the anodic current decreased up to

K. Nagahara; M. Sakairi; H. Takahashi; K. Matsumoto; K. Takayama; Y. Oda

2007-01-01

37

Growth of highly oriented ZnO films by the two-step electrodeposition technique  

Microsoft Academic Search

Compact and transparent ZnO films were deposited on the ITO\\/glass substrates from zinc nitrate aqueous solution by the two-step\\u000a electrodeposition technique. While the first potentiostatic step was used to produce ZnO seed layer, the ZnO film growth has\\u000a been done galvanostatically. Effects of the potentiostatic parameters on the crystal structure, morphology and optical properties\\u000a of ZnO films were investigated. Results

Xiang-Dong Gao; Fang Peng; Xiao-Min Li; Wei-Dong Yu; Ji-Jun Qiu

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

Characterization of electrochemically deposited polypyrrole using magnetoelastic material transduction elements.  

PubMed

Magnetoelastic alloy films have been used as a working electrode in an electrochemical cell. This material allows magnetic interrogation of electrochemical deposition. This technique was used to monitor the electrochemical deposition of polypyrrole by multisweep (CV) and potentiostatic methods. Since the determination of the mass-sensitive magnetoelastic film's resonance frequency is based on magnetic transduction, an inherent advantage of this method is that it requires no electrical connections other than the working lead of the potentiostat. Increases in pyrrole deposition correlated with a decrease in the peak resonance frequency of the magnetoelastic alloy. This technique provides a novel approach by which one can monitor electrochemical processes. PMID:12199573

Ersöz, Arzu; Ball, J Christopher; Grimes, Craig A; Bachas, Leonidas G

2002-08-15

40

Characterization of electrochemically deposited polypyrrole using magnetoelastic material transduction elements  

NASA Technical Reports Server (NTRS)

Magnetoelastic alloy films have been used as a working electrode in an electrochemical cell. This material allows magnetic interrogation of electrochemical deposition. This technique was used to monitor the electrochemical deposition of polypyrrole by multisweep (CV) and potentiostatic methods. Since the determination of the mass-sensitive magnetoelastic film's resonance frequency is based on magnetic transduction, an inherent advantage of this method is that it requires no electrical connections other than the working lead of the potentiostat. Increases in pyrrole deposition correlated with a decrease in the peak resonance frequency of the magnetoelastic alloy. This technique provides a novel approach by which one can monitor electrochemical processes.

Ersoz, Arzu; Ball, J. Christopher; Grimes, Craig A.; Bachas, Leonidas G.

2002-01-01

41

A Real Time Measuring Method for Complex Impedance in Biomedical Instrumentations  

NASA Astrophysics Data System (ADS)

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

Dendo, Isao

42

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

E-print Network

nanoparticles have attracted much attention because of their novel optical, catalytic, electrical and magnetic- cally in Fig. 1. The porous anodic aluminum oxide (AAO) templates were grown by potentiostatically to the SCE. The nobler element Cu was kept in so dilute a concentra- y Also at Graduate School of CAS

Gong, Jian Ru

43

A screen-printed amperometric dissolved oxygen sensor utilising an immobilised electrolyte gel and membrane  

Microsoft Academic Search

An amperometric dissolved oxygen sensor based on potentiostatic operation has been designed and fabricated using thick film technology. Calibration of the sensor has shown a strong linear relationship with dissolved oxygen concentration. The devices have been bulk tested for long-term stability and good device to device repeatability has been observed within the batch. Results indicate that a repeatable response to

Wendy Glasspool; John Atkinson

1998-01-01

44

Microelectrochemical corrosion study of super martensitic welds in chloride-containing media  

Microsoft Academic Search

Pitting corrosion was studied in welded joints of supermartensitic stainless steels. The electrochemical behavior of three different weldment zones (weld metal (WM), parent metal (PM) and heat affected zone (HAZ)) was characterized independently using an electrochemical minicell through potentiodynamic and potentiostatic techniques. The minicell design selected for this work has the additional advantage of showing promise for service application. Macro-electrochemical

M. D. Pereda; C. A. Gervasi; C. L. Llorente; P. D. Bilmes

2011-01-01

45

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

46

Features of cathode reduction of boiling solutions of nitric acid on a platinum electrode  

Microsoft Academic Search

Studies were conducted in boiling 2 M HNOâ (classified hp) by the potentiostatic method with simultaneous volumetric, chromatographic, and chemical analyses of the products of reduction (NOâ, NO, NâO, Nâ, NBâ\\/sup +\\/, Hâ). A sequence of electrode and secondary chemical reactions was proposed based on the results obtained which permits explaining the extreme character of the dependence of the rate

V. P. Razygraev; M. V. Lebedeva; S. A. Kabakchi; E. Yu. Ponomareva; R. S. Balovneva; L. P. Lobanova

1988-01-01

47

Quartz Crystal Analyzer Sensitive enough to measure weight changes in a monolayer  

E-print Network

QCA922 Quartz Crystal Analyzer · Sensitive enough to measure weight changes in a monolayer of 1 MHz to 10 MHz (calibrated for 9 MHz crystals) · Designed for EQCM with a potentiostat or stand is proud to offer the QCA922 Quartz Crystal Analyzer. The QCA922, an instrument developed for piezoelectric

Ulm, Universität

48

A telemetry-instrumentation system for chronically implanted glucose and oxygen sensors  

Microsoft Academic Search

An implantable potentiostat-telemetry system for in vivo operation of glucose and oxygen sensors is described. The device con- veys signals from implanted chemical-specific sensors to a remote re- ceiver via radio telemetry. Reference signals encoded in the analog FM transmission allow the receiver to automatically compensate for vari- ability between simultaneously operated transmitters. The implant has several programmable operating modes

BRIAN D. McKEAN; DAVID A. GOUGH

1988-01-01

49

IEEE ENGINEERING IN MEDICINE AND BIOLOGY MAGAZINE NOVEMBER/DECEMBER 2005 23 STUDENTPAPERAWARD  

E-print Network

-order single-bit delta-sigma modulator architecture with a digitally configurable oversampling ratio (OSR. The analog input current is digitized using an A/D converter design that employs a current-mode, first) for controlling the conversion scale. The potentiostat achieves superior sensitivity (in picoampere range) along

Stanacevic, Milutin

50

Temporal resolution of ion and solvent transfers at nickel hydroxide films exposed to LiOH  

Microsoft Academic Search

A combined electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) instrument was used to monitor mobile species transfers on short time scales following the application of a potential step to potentiostatically deposited ?-nickel hydroxide films exposed to aqueous LiOH solution. Upon film oxidation, hydroxide ions enter the film and protons are deintercalated. However, the protons are not detected

Heidi M French; Mark J Henderson; A. Robert Hillman; Eric Vieil

2002-01-01

51

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

52

Intergranular Corrosion in a Martensitic Stainless Steel Detected by Electrochemical Tests  

Microsoft Academic Search

Quenched and tempered martensitic stainless steel UNS S41000 was tested electrochemically for susceptibility to sensitization in specimens quenched from 975 C (1,248 K) and tempered for 2 h at different temperatures between 300 C (573 K) and 700 C (973 K). Besides an oxalic acid etch test, the following tests were performed using a potentiostat and 1 N sulfuric acid

N. Alonso-Falleiros; M. Magri; I. G. S. Falleiros

1999-01-01

53

Electrodeposition and characterization of polypyrrole films on aluminium alloy 6061-T6  

Microsoft Academic Search

Polypyrrole films on aluminium alloy 6061-T6 were prepared by electropolymerization of pyrrole in sulphuric acid using two different processes – cyclic voltammetry and potentiostatic polarization – and assessed through SEM observation and voltammetry. The anticorrosive properties of these films were studied by polarization curves and electrochemical impedance spectroscopy.The polypyrrole films formed by both methods are homogeneous and present a globular

N. C. T. Martins; T. Moura e Silva; M. F. Montemor; J. C. S. Fernandes; M. G. S. Ferreira

2008-01-01

54

High Levels of Electrochemical Doping of Carbon Nanotubes: Evidence for a Transition from Double-Layer Charging to Intercalation and Functionalization  

E-print Network

High Levels of Electrochemical Doping of Carbon Nanotubes: Evidence for a Transition from Double-Layer the transition from the electrochemical double-layer charging regime to intercalative doping of bundled single the initial stages of electrochemical doping in potentiostatic mode, they form a charged double layer only

Nabben, Reinhard

55

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

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

JOURNAL DE PHYSIQUE IV Colloque C5, supplement au Journal de Physique I, Vol. 1, decembre 1991 C 5 -2 3 7  

E-print Network

chimiques en phase homogène. Ahstract : We present here the electrochemical characteristics obtained protonated sulfurspeciesin liquid ammonia. From a formal point of view, the oxidation number of a polysulfide with a potentiostat EGG 273 and a three electrodes cell. The auxilary electrode was in gold or tungsten. The working

Paris-Sud XI, Université de

58

Biomass-modified carbon paste electrodes for monitoring dissolved metal ions  

Microsoft Academic Search

Electrodes were prepared by incorporating dried, nonliving biomass of a common lichen, Ramalina stenospora, and Sphagnum (peat) moss in carbon paste. The electrodes were tested on solutions containing Pb(II) and Cu(II) ions by immersing the electrode in the solution for selected periods of time to accumulate ions. Following this the electrode was connected to a potentiostat and the applied voltage

Hua Yao; Gerald J Ramelow

1998-01-01

59

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

60

Anodic electrochemistry of chalcopyrite  

Microsoft Academic Search

The anodic behaviour of chalcopyrite in 1 M H2SO4 and 1 M HCl was studied by linear sweep voltammetry and potentiostatic electrolysis. Voltammograms with a fresh surface showed a small prewave, attributed to a surface oxidation process, followed by a region of active dissolution characterized by a steeply rising anodic current. At still higher potentials the behaviour differed in the

T. Biegler; D. A. Swift

1979-01-01

61

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.

2011-03-30

62

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

63

The influence of dichromate ions on aluminum dissolution kinetics in artificial crevice electrode cells  

Microsoft Academic Search

Dissolution kinetics for pits and crevices in aluminum and the effect of dichromate ions on the dissolution kinetics were investigated by using artificial crevice electrodes. The aluminum artificial crevice electrodes were potentiostatically polarized over a range of potential in 0.1 M NaCl solution with and without dichromate ions. The anodic dissolution charge, and cathodic charges for the hydrogen and dichromate

E. Akiyama; G. S. Frankel

1999-01-01

64

Formic acid oxidation at spontaneously deposited palladium on polyaniline modified carbon fibre paper  

Microsoft Academic Search

Extended reaction zone anodes for formic acid oxidation have been prepared by the spontaneous deposition of Pd on polyaniline coated carbon fibre paper. The PANI supports, deposited on carbon fibre paper either galvanostatically, potentiostatically, or potentiodynamically, were characterized by electron microscopy, cyclic voltammetry and impedance spectroscopy. Pd was deposited on them by spontaneous reduction of Pd(II) by the reduced form

Reza B. Moghaddam; Peter G. Pickup

2011-01-01

65

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

E-print Network

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

66

Development of a wireless environmental sensor system and MEMS-based RF circuit components  

Microsoft Academic Search

This paper reports a miniaturized environmental sensor system integrated with RF communication module. This system has been developed for on-site monitoring of water pollution by heavy metal ions. The system is composed of an electrochemical sensor, a custom potentiostat module, and an RF module for wireless communication. Also, the authors presented monolithic MEMS VCOs integrated with high-Q MEMS inductors and

Euisik Yoon; Kwang-Seok Yun

2005-01-01

67

Electrochemical dealloying of Al2(Au,X) (X = Pt, Pd, PtPd, Ni, Co and NiCo) alloys in NaCl aqueous solution.  

PubMed

The electrochemical dealloying of rapidly solidified Al2(Au,X) (X = Pt, Pd, PtPd, Ni, Co and NiCo) precursors in a 1.0 M NaCl aqueous solution has been systematically investigated using electrochemical measurements including open-circuit measurement, potentiodynamic polarization and potentiostatic polarization, and microstructural analysis. The results show that the kind of alloying element(s) has a significant influence on the open-circuit and corrosion potentials of the rapidly solidified Al2(Au,X) precursors. The bulk dealloying of the Al2(Au,X) precursors is affected by the kind of alloying element(s) and also sensitive to the applied potential (or overpotential). The addition of Ni or/and Co easily leads to passivation on the surface of precursors during potentiostatic dealloying. The potentiostatic dealloying of Al2(Au,Pt), Al2(Au,Pd) and Al2(Au,Pt,Pd) results in the formation of ultrafine nanoporous AuPt, AuPd and AuPtPd alloys, owing to the pinning effect of Pt or/and Pd on surface diffusion of Au adatoms. In comparison, the potentiostatic dealloying of Al2(Au,Ni), Al2(Au,Co) and Al2(Au,Ni,Co) leads to the formation of nanoporous Au with a ligament/channel size of ~40 nm due to the simultaneous dissolution of Al and Ni/Co. Moreover, the addition of Pt, Pd or PtPd not only inhibits surface diffusion of Au adatoms (lower diffusivities), but also improves the activation energy for the diffusion process during potentiostatic dealloying. Based upon the present results, nanoporous metals or alloys can be greenly fabricated through electrochemical dealloying in NaCl solutions. PMID:23455475

Wang, Yan; Xu, Junling; Wu, Bo

2013-04-21

68

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

69

A hybrid electrochemical\\/chemical synthesis of semiconductor nanocrystals on graphite: a new role for electrodeposition in materials synthesis  

Microsoft Academic Search

Metal (copper and cadmium) nanocrystallites —electrochemically deposited on the graphite basal plane— have been converted on a particle-by-particle basis to nanocrystals of a semiconducting metal salt (CuI and CdS). Deposition of the metal nanocrystals from a dilute ([Mn+]?1.0mM) plating solution is accomplished using a potentiostatic pulse with an overpotential of ?500mV and a duration in the range 50–200ms. Non-contact atomic

S. Gorer; G. S. Hsiao; M. G. Anderson; R. M. Stiger; J. Lee; R. M. Penner

1998-01-01

70

Investigation of Ti(Zr–Ni) Hydrogen-Sorbing Alloys as Electrode Materials for Nickel–Metal-Hydride Storage Batteries  

Microsoft Academic Search

We studied cyclic charge–discharge characteristics of partially substituted and oxygen-containing derivatives of a Ti2Ni alloy by using specially designed equipment based on PI-50-1 potentiostats and a computer. For Ti3.8Zr0.2Ni2Ox alloys, a twofold increase in the discharge capacity was detected as the oxygen content increased from x = 0 to x = 0.3. It was established that the effect of the

I. Yu. Zavalii; I. V. Saldan

2002-01-01

71

Caustic Stress Corrosion Cracking of Mild Steel  

Microsoft Academic Search

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

Douglas Singbeil; Desmond Tromans

1982-01-01

72

MnO 2-coated Ni nanorods: Enhanced high rate behavior in pseudo-capacitive supercapacitor  

Microsoft Academic Search

Ni nanorods prepared by electrochemical growth through an anodized aluminium oxide membrane were used as substrate for the electrodeposition of MnO2 either in potentiostatic mode or by a pulsed method. Electrochemical deposition parameters were chosen for an homogeneous deposit onto Ni nanorods. Resulting Ni supported MnO2 electrodes were tested for electrochemical performances as nanostructured negative electrodes for supercapacitors. They exhibited

Y. Lei; B. Daffos; P. L. Taberna; P. Simon; F. Favier

2010-01-01

73

Single step electrosynthesis of Cu 2ZnSnS 4 (CZTS) thin films for solar cell application  

Microsoft Academic Search

The Cu2ZnSnS4 (CZTS) thin films have been electrodeposited onto the Mo coated and ITO glass substrates, in potentiostatic mode at room temperature. The deposition mechanism of the CZTS thin film has been studied using electrochemical techniques like cyclic voltammetery. For the synthesis of these CZTS films, tri-sodium citrate and tartaric acid were used as complexing agents in precursor solution. The

S. M. Pawar; B. S. Pawar; A. V. Moholkar; D. S. Choi; J. H. Yun; J. H. Moon; S. S. Kolekar; J. H. Kim

2010-01-01

74

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

75

Structural, magnetic, and electrochemical properties of poly( o-anisidine)\\/maghemite thin films  

Microsoft Academic Search

Electrodeposition of semiconducting poly(o-anisidine)\\/?-Fe2O3 (maghemite) thin films was carried out using an aqueous alkaline medium containing ferrous sulphate and o-anisidine. Potentiostatic composite deposition was made at 55°C. X-ray diffraction and FTIR analysis indicated the presence of iron oxide (maghemite), o-anisidine, and chemical interaction between the components. The magnetic characterization of the resulting composite indicated a magnetically ordered state for the

L. H. M. Fonseca; A. W. Rinaldi; A. F. Rubira; L. F. Cótica; S. N. de Medeiros; A PAESANOJR; I. A. Santos; E. M. Girotto

2006-01-01

76

Ellipsometric study of anodic oxide films formed on niobium surfaces  

Microsoft Academic Search

.   Anodic oxide films formed potentiostatically on niobium surfaces, from open circuit potential (OCP) to 10 V, were studied\\u000a by performing in situ and ex situ ellipsometric measurements. The kinetics of the film thickness growth in 1 M H2SO4 and complex indices of refraction of these films were determined. A strong influence of the surface preparation conditions\\u000a on the complex refractive indices

Irena Lj. Arsova; Abdurauf R. Prusi; Ljubomir D. Arsov

2003-01-01

77

The effects of inclusion of iodine in CdTe thin films on material properties and solar cell performance  

Microsoft Academic Search

CdTe thin films were potentiostatically electrodeposited from a non-aqueous electrolytic bath containing ethylene glycol. In order to dope the CdTe using an n-type dopant according to a proposed new model, varying concentrations of iodine were added into the electrolytic bath. The resulting materials were studied for structural, morphological, optical and electrical properties. Structural analysis indicated the formation of CdTe layers

N. B Chaure; A. P Samantilleke; I. M Dharmadasa

2003-01-01

78

Cathodic copper deposition at 65 °C in the absence and presence of Bi 3+ and Sb 3+ additives in acidified CuSO 4 aqueous solutions  

Microsoft Academic Search

An electrochemical study by cyclic voltammetry and potentiostatic pulse method of the cathodic deposition of copper on polycrystalline\\u000a copper electrode was carried out in acidic aqueous copper sulfate solution. Comparative electrochemical investigations were\\u000a performed in electrolytes in the absence and presence of Bi3+ and Sb3+ ions. All experiments were performed at 65 ?C. For bulk copper deposition, the results indicate

R. G. Barradas; M. Girgis

1991-01-01

79

An amperometric non-enzymatic glucose sensor by electrodepositing copper nanocubes onto vertically well-aligned multi-walled carbon nanotube arrays  

Microsoft Academic Search

A non-enzymatic glucose (Glc) sensor was developed by potentiostatically electrodepositing metallic Cu nanocubes from a precursor solution onto vertically well-aligned multi-walled carbon nanotube arrays (MWCNTs). The electrochemical characteristics of the sensor were studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The sensor shows significantly higher electrocatalytic activity to the oxidation of Glc in 0.1M NaOH alkaline solution after

Jiang Yang; Wei-De Zhang; Sundaram Gunasekaran

2010-01-01

80

Effects of boric acid on the electrodeposition of iron, nickel and iron-nickel  

Microsoft Academic Search

Iron (Fe), nickel (Ni), and iron-nickel (Fe?Ni) platings were carried out potentiostatically on rotating disk electrodes. The effects of boric acid on the iron and nickel reduction rates were evaluated. Experimental results support the surface competition of adsorption of ferrous and nickel ions on the electrode surface in Fe?Ni alloy deposition. Boric acid prevents the electrode surface passivation on nickel

K.-M. Yin; B.-T. Lin

1996-01-01

81

Study of neodymium extraction in molten fluorides by electrochemical co-reduction with aluminium  

Microsoft Academic Search

This work describes the co-deposition process of Al–Nd alloys in LiF–CaF2 medium (79–21%mol) on tungsten electrode at 860°C using electrochemical techniques: cyclic and square wave voltammetries and potentiostatic electrolyses. Specific peaks of Al–Nd alloys formation were observed in cyclic voltammograms between the reduction waves of Nd(III) and Al(III), in a fluoride melt containing neodymium and aluminium ions. The potential difference

M. Gibilaro; L. Massot; P. Chamelot; P. Taxil

2008-01-01

82

In vitro mechanical integrity of hydroxyapatite coated magnesium alloy  

Microsoft Academic Search

The mechanical integrity of resorbable implants during service, especially in load bearing orthopaedic applications, is critical. The high degradation rate of resorbable magnesium and magnesium-based implants in body fluid may potentially cause premature in-service failure. In this study, a magnesium alloy (AZ91) was potentiostatically coated with hydroxyapatite at different cathodic voltages in an attempt to enhance the mechanical integrity. The

M. Bobby Kannan; Lynnley Orr

2011-01-01

83

Effect of the number of ECAP pass time on the electrochemical properties of 1050 Al alloys  

Microsoft Academic Search

The effect of equal channel angular pressing (ECAP) pass number on the electrochemical properties of AA 1050 (UNS A91050) were investigated by electrochemical techniques (potentiodynamic polarization test, potentiostatic test, electrochemical impedance spectroscopy (EIS) measurement) and surface analyses (OM, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS)) in 0.1M Na2SO4 solution containing 100ppm chloride ions. The ECAPed specimens that

Min-Kyong Chung; Yoon-Seok Choi; Jung-Gu Kim; Young-Man Kim; Jae-Chul Lee

2004-01-01

84

Development of compositionally modulated multilayer Zn–Ni deposits as replacement for cadmium  

Microsoft Academic Search

Compositionally modulated multilayer (CMM) Zn–Ni deposits were electrodeposited from single acidic bath (pH=4.7) by using a potentiostatic sequence. The Zn and Ni composition in the alloy was tailored as a function of distance from the steel substrate. X-ray diffraction studies of the deposit showed the presence of ?-phase with a composition of Ni5Zn21. The corrosion properties of modulated multilayer coatings

Prabhu Ganesan; Swaminatha P. Kumaraguru; Branko N. Popov

2007-01-01

85

Electrochemical behavior of the glycine-iodide-perchlorate ternary system at the gold electrode  

Microsoft Academic Search

Potentiostatic electrolysis and potentiodynamic triangular sweeps were used to study the electrochemical effects observed at the gold electrode in solutions containing glycine, NaI, and NaClOâ. It was found that in this system gold dissolves rather rapidly when anodically polarized, so that with 30 min of electrolysis one can obtain solutions with a metal concentration of over 70 mg\\/liter. The iodide

A. Yu. Safronov; G. V. Tsykunova; G. G. Mineev; O. V. Kokho; A. S. Chernyak

1987-01-01

86

Electrochemical treatments for selective growth of different calcium carbonate allotropic forms on carbon steel  

Microsoft Academic Search

Different allotropic forms of calcium carbonate scales (calcite and aragonite) were electrochemically deposited on carbon steel surfaces, using different electrochemical techniques: cyclic voltammetry or potentiostatic pulses. To simulate conditions of Mexican refinery cooling systems, this study was performed in the presence of known concentrations of other salts at pH 7.8 and 40°C with low and high calcium carbonate concentrations. Reduction

J. Mar??n-Cruz; E. Garc??a-Figueroa; M. Miranda-Hernández; I. González

2004-01-01

87

Voltammetric sensors with chiral recognition capability: The use of a chiral inducing agent in polyaniline electrochemical synthesis for the specific recognition of the enantiomers of the pesticide dinoseb  

Microsoft Academic Search

An electrochemical method for chiral polyaniline synthesis has been optimised to develop voltammetric sensors capable of target enantiomer recognition. The methodologies for both R- and S-specific sensor development have been carefully optimised in order to obtain the highest chiral discrimination capacity. R and S specific sensors were synthesised potentiostatically at 0.5V and 0.6V, respectively in 0.28M R- or S-camphorsulphonic acid,

Itsaso Basozabal; Alberto Gómez-Caballero; Nora Unceta; M. Aranzazu Goicolea; Ramón J. Barrio

88

A novel automated electrochemical ascorbic acid assay in the 24-well microtiter plate format  

Microsoft Academic Search

Automatic ascorbic acid (AA) voltammetry was established in 24-well microtiter plates. The assay used a movable assembly of a pencil rod working, an Ag\\/AgCl reference and a Pt counter electrode with differential pulse voltammetry (DPV) for concentration-dependent current generation. A computer was in command of electrode (z) and microtiter plate (x, y) positioning and timed potentiostat operation. Synchronization of these

Sireerat Intarakamhang; Christian Leson; Wolfgang Schuhmann; Albert Schulte

2011-01-01

89

THE INHIBITION ACTION OF ETHYL2PHENYL HYDROZONO-3-OXOBUTYRATE ON THE CORROSION OF 6061 Al ALLOY\\/SiCp COMPOSITE IN HYDROCHLORIC ACID MEDIUM  

Microsoft Academic Search

The inhibition behavior of ethyl-2-phenyl hydrozono-3-oxobutyrate on the corrosion of 6061 Al alloy\\/SiCp composite in 0.1, 0.5 and 1 N hydrochloric acid solution at four different temperatures (30-60 °C) has been investigated using potentiostatic polarization techniques and weight loss method. The results indicated that the corrosion inhibition efficiency and the extent of surface coverage were increased with the increase in

U ACHUTHA KINI; PRAKASH SHETTY; S DIVAKAR SHETTY; ARUN ISLOOR; RAMADEV HERLE

2010-01-01

90

Growth kinetics of passivating oxide film of Inconel alloy 600 in 0.1 M Na 2SO 4 solution at 25–300 °C using the abrading electrode technique and ac impedance spectroscopy  

Microsoft Academic Search

The growth kinetics of passivating oxide film of Inconel alloy 600 has been investigated in aqueous 0.1M Na2SO4 solution at temperatures 25–300°C and at pressures 0.1–8MPa by analyses of potentiostatic current transients and ac impedance spectra. From the analysis of current transients, it was realized that the oxide film grown on the specimen has only one-layer structure below 60°C, but

Jin-Ju Park; Su-Il Pyun; Seung-Bok Lee

2004-01-01

91

Phenomenological kinetics of irreversible electrochemical dissolution of metal-oxide microparticles  

Microsoft Academic Search

The electrochemical dissolution of metal oxides and other stable solid phases composed of nano- to micro-crystalline particles\\u000a is generally a complex process. It can be simplified by distinguishing two main contributions to the reactivity of the solid:\\u000a the potential-dependent rate coefficient k(E), and the conversion-dependent function f(y). These contributions can be evaluated by a combination of potentiostatic and potentiodynamic experiments.

Tomáš Grygar

1998-01-01

92

Synergistic inhibition of carbon steel by tertiary butyl phosphonate, zinc ions and citrate  

Microsoft Academic Search

Purpose – To develop a new corrosion inhibitor formulation for carbon steel in low chloride environments. Design\\/methodology\\/approach – Corrosion inhibition efficiencies were evaluated by the weight loss method and by impedance measurement studies. The nature of the inhibition process was evaluated using potentiostatic polarization studies. The nature of the protective film was investigated using X-ray diffraction, X-ray photoelectron spectroscopy, and

P. Narmada; M. Venkateswara Rao; G. Venkatachari; B. V. Appa Rao

2006-01-01

93

Annealing induced microstructural evolution of electrodeposited electrochromic tungsten oxide films  

Microsoft Academic Search

A significant influence of microstructure on the electrochromic and electrochemical performance characteristics of tungsten oxide (WO3) films potentiostatically electrodeposited from a peroxopolytungstic acid (PPTA) sol has been evaluated as a function of annealing temperature. Powerful probes like X-ray diffractometry (XRD), transmission electron microscopy (TEM), UV–vis spectrophotometry, multiple step chronoamperometry and cyclic voltammetry have been employed for the thin film characterization.

M. Deepa; A. K. Srivastava; T. K. Saxena; S. A. Agnihotry

2005-01-01

94

Large-area network of polyaniline nanowires supported platinum nanocatalysts for methanol oxidation  

Microsoft Academic Search

Nanocomposites comprised of Pt nanoparticles and electrically conducting polymers were prepared and tested for the electrocatalytic performance towards oxidation of methanol. Films of polyaniline (PANI) synthesized independently by potentiostatic and galvanostatic method, PANI(V) and PANI(I), respectively, were used as the supporting matrix for loading Pt nanoparticles. PANI(V), PANI(I), PANI(V)\\/Pt, and PANI(I)\\/Pt films were characterized for structure and morphology using scanning

Feng-Jiin Liu; Li-Ming Huang; Ten-Chin Wen; A. Gopalan

2007-01-01

95

Nano-mechano-electrochemistry of passive metal surfaces  

Microsoft Academic Search

In situ nanoindentation tests were performed to evaluate the mechanical properties of the iron (100) and (110) surfaces passivated potentiostatically for 1 h in pH 8.4 borate solution after or without immersion in 5×10?2 M K2Cr2O7 solution for 24 h. It was found from the measured load–depth curves at a maximum load of 400 ?N that the hardness (3.2–3.3 GPa)

Masahiro Seo; Makoto Chiba

2001-01-01

96

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

Microsoft Academic Search

A potentiostatic electrodeposition technique was used to directly fabricate large-scale, well-aligned, and single-crystalline submicron ZnO rod arrays on tin doped indium oxide glass substrate without a pre-prepared seed layer of ZnO from an aqueous solution only containing zinc nitrate. The effects of electrochemical parameters, such as electrodeposition potential, electrodeposition duration, solution temperature, and precursor concentration, on the orientation, morphology, aspect

Feng Xu; Yinong Lu; Lili Xia; Yan Xie; Min Dai; Yunfei Liu

2009-01-01

97

Effects of seed layer on the structure and property of zinc oxide thin films electrochemically deposited on ITO-coated glass  

Microsoft Academic Search

ZnO films with different morphologies were deposited on the ITO-coated glass substrate from zinc nitrate aqueous solution at 65°C by a seed-layer assisted electrochemical deposition route. The seed layers were pre-deposited galvanostatically at different current densities (isl) ranging from ?1.30 to ?3.0mA\\/cm2, and the subsequent ZnO films had been done using the potentiostatic technique at the cathode potential of ?1.0V.

Sufeng Wei; Jianshe Lian; Xuejiao Chen; Qing Jiang

2008-01-01

98

Corrosion behavior of high-density tungsten alloys. Final report  

Microsoft Academic Search

The corrosion behavior of high-density tungsten alloys was examined by electrochemical potentiostatic polarization methods and weight-loss measurements in full-immersion tests. Electrochemical tests were carried out in aqueous solutions, buffered to pH 4, 9, 12 with and without 0.1M sodium chloride and immersion tests in 5% NaCl solution. Pure tungsten and all the alloys studied undergo active-passive transitions and corrosion rates

M. Levy; F. C. Chang

1987-01-01

99

Proton transfer in oxidized adenosine self-aggregates  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

100

The corrosion behavior and microstructure of high-velocity oxy-fuel sprayed nickel-base amorphous\\/nanocrystalline coatings  

Microsoft Academic Search

The corrosion characteristics of two Ni-Cr-Mo-B alloy powders sprayed by the high-velocity oxy-fuel (HVOF) process have been studied using potentiodynamic and potentiostatic corrosion analysis in 0.5 M H2SO4. The deposits were also microstructurally characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM) (utilizing both secondary electron and backscattered electron modes), and transmission electron microscopy (TEM). Results from the microstructural examination

A. H. Dent; A. J. Horlock; D. G. McCartney; S. J. Harris

1999-01-01

101

A low-power area efficient voltage reference and data generation unit for inductively powered implant system  

Microsoft Academic Search

This paper reports a low-power sensor signal processing and load shift keying (LSK) telemetry scheme for an inductively powered implant system. The entire system manifests a voltage reference (VR), a potentiostat, and a current controlled oscillator (CCO). All of the functional blocks are designed using subthreshold MOSFETs to achieve ultra-low-power consumption. Relatively simpler architecture of the VGR saves area and

M. Roknsharifi; M. R. Haider; S. K. Islam

2011-01-01

102

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

103

Corrosion resistance tests on NiTi shape memory alloy  

Microsoft Academic Search

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

Gianni Rondelli

1996-01-01

104

Electrochemical characteristics and applications of boron-doped polycrystalline diamond film electrodes  

Microsoft Academic Search

The electrochemical characteristics of boron-doped polycrystalline diamond thin film (BDF) electrode 4 ? 4 mm2 in size were studied using cyclic voltammetry and potentiostatic method. The diamond clectrode exhibits adequate electrochemical\\u000a activity and its response current changes linearly with K3Fe(CN)6 concentrations. The response current is proportional to the square root of the scan rate, reflecting mass transport controlled\\u000a by planar

Zhu Jianzhong; Lu Deren; Zhang Guoxiong

1998-01-01

105

Kinetics of the electrodeposition of Pb?Sn alloys  

Microsoft Academic Search

The electrodeposition of lead, tin and lead–tin alloys on glassy carbon has been studied by electrochemical techniques. Potentiostatic I–t transients were recorded to obtain the nucleation mechanism, while cyclic voltammetry was used to characterize the system. The alloy composition was determined by differential pulse anodic stripping voltammetry. Since the redox potentials for lead and tin are similar in the non-complexing

I Petersson; E Ahlberg

2000-01-01

106

Localized passivity breakdown of iron in chlorate- and perchlorate-containing sulphuric acid solutions: A study based on current oscillations and a point defect model  

Microsoft Academic Search

Current oscillations are used to study the effect of chlorate and perchlorate ions on the iron passivity in sulphuric acid solutions. Quasi steady-state current–potential and potentiostatic current–time curves show the emergence of complex current oscillations, besides the simple periodic ones attributed to general corrosion occurring across the passive–active transition of the Fe|0.75M H2SO4 electrochemical system. The complex current oscillations arising

M. Pagitsas; M. Pavlidou; D. Sazou

2008-01-01

107

The determination of kinetics parameters of the hydrogen evolution on Ti?Ni alloys by ac impedance  

Microsoft Academic Search

The kinetics and mechanism of hydrogen evolution at Ti?Ni alloys electrode has been studied by means of steady-state potentiostatic polarization and ac impedance spectrum measurements. Complex-plane spectrum plots are derived for the h.e.r. at one of the most inactive, typical hydridic, Ti?Ni, and one of the most active, typical electrocatalytic, Ti?Ni3, intermetallic alloy compounds at various potentials. The rate constants

N. V. Krstaji?; B. N. Grgur; N. S. Mladenovi?; M. V. Vojnovi?

1997-01-01

108

Short-term canine implantation of a glucose monitoring-telemetry device  

Microsoft Academic Search

In this study we report the development and short-term in vivo evaluation of an integrated implantable device consisting of an amperometric glucose biosensor, a miniature potentiostat, a FM signal transmitter, and power supply. The device (dimensions: 5.0 × 7.0 × 1.5 cm) was implanted under the skin of medium-size anaesthetized dog. The experimental set-up included several methods for data collection:

P. Atanasov; S. Yang; C. Salehi; A. L. Ghindilis; E. Wilkins

1996-01-01

109

Diffusion layer interpretation of the interaction of electrorefining addition agents  

Microsoft Academic Search

The roles of various addition agents in commercial electrorefining electrolytes were studied by means of 190 potentiostatic\\u000a scans. The role of each addition agent and their interactions with one another were clarified. The protein material caused\\u000a increased polarization at low current densities, presumably by adsorbing on the cathode growth sites. The effect of protein\\u000a additions was strongly affected by the

Herbert S. Jennings; Frank E. Rizzo

1973-01-01

110

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

Microsoft Academic Search

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

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

2000-01-01

111

A novel protocol for covalent immobilization of thionine on glassy carbon electrode and its application in hydrogen peroxide biosensor.  

PubMed

A novel protocol for effectively covalent immobilization of thionine (Th) was proposed, which was based on Schiff-base reaction between -NH(2) of Th and -COH which was in situ generated on glassy carbon electrode (GCE) via simple potentiostatic activation in diluted nitric acid. GCE pretreated by potentiostatic activation possessed CHO-riched surface and microporous structure with high distribution density of electron transfer sites, and thus it became a good candidate for effective immobilization of Th through imine bond with high stability. The application of the resulting Th modified electrode in hydrogen peroxide biosensor was also investigated and it exhibited rapid response to H(2)O(2) within 3s. The linear calibration ranged from 5.0x10(-7) to 5.8x10(-3)M with a detection limit of 1.0x10(-7)M. The effective immobilization of Th on potentiostatically activated GCE surface has deep significance in mediator immobilization, on which further researches based are under way. PMID:20400288

Xu, Xingyong; Feng, Yan; Li, Jingjing; Li, Feng; Yu, Hongjun

2010-06-15

112

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

PubMed

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

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

2003-07-15

113

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

114

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

115

History effects in lithium-oxygen batteries: how initial seeding influences the discharge capacity.  

PubMed

In laboratory experiments, Li-O2 systems show "sudden death" at capacities far below the theoretical value. Identifying how discharge products limit the total capacity is crucial in Li-O2 system. We investigated the effect of Li2O2 seed layer deposited on carbon cathode under potentiostatic conditions at increasing overpotentials to the subsequent slow discharge at galvanostatic condition. The discharge capacity attainable in the second step is found to vary by more than a factor of 3 depending on the history, i.e., the seed layer. These results provide evidence that the battery history is decisive for the total discharge capacities. PMID:24591297

Rinaldi, Ali; Wijaya, Olivia; Hoster, Harry E; Yu, Denis Y W

2014-05-01

116

Characterization and corrosion protection properties of polypyrrole \\/ montmorillonite electropolymerized onto aluminium alloy 1100  

Microsoft Academic Search

Films of Polypyrrole\\/Montmorillonite (PPy\\/MT) clays were electropolymerized potentiostatically on aluminium alloy 1100, using\\u000a sodium dodecylbenzenesulfonate (SDBS) as a dopant. Two clay species were used: Na+-Montmorillonite (MT-Na) and modified-Montmorillonite (MT-M). The characterization of the PPy\\/MT films performed by XRD and\\u000a TEM shows that the exfoliation method employed, as well the electrochemical polymerization method used in this work, allow\\u000a nanocomposite materials to

Kátia R. L. Castagno; Viviane Dalmoro; Raquel S. Mauler; Denise S. Azambuja

2010-01-01

117

Al-Cd Alloy Formation by Aluminum Underpotential Deposition from AlCl3+NaCl Melts on Cadmium Substrate  

NASA Astrophysics Data System (ADS)

Aluminum was incorporated into a polycrystalline cadmium electrode surface by underpotential deposition from equimolar AlCl3+ NaCl melt at 473 K, 523 K, and 573 K (200 °C, 250 °C, and 300 °C). The process was studied by linear sweep voltammetry and potentiostatic deposition/galvanostatic striping. The deposits were characterized X-ray diffraction (XRD), Auger electron spectroscopy (AES), and electron probe microanalyzer (EPMA). The electrochemical measurements showed evidence of Cd-Al alloys being formed but they could not be identified. The growth kinetics of the Cd-Al layers of various proportion and depths that depended on temperature and deposition time were described.

Jovi?evi?, Niko; Cvetkovi?, Vesna S.; Kamberovi?, Željko J.; Jovi?evi?, Jovan N.

2013-02-01

118

Separation of metal ions from aqueous solutions  

DOEpatents

A process and apparatus for quantitatively and selectively separating metal ions from mixtures thereof in aqueous solution. The apparatus includes, in combination, a horizontal electrochemical flow cell containing flow bulk electrolyte solution and an aqueous, metal ion-containing solution, the cell containing a metal mesh working electrode, a counter electrode positioned downstream from the working electrode, an independent variable power supply/potentiostat positioned outside of the flow cell and connected to the electrodes, and optionally a detector such as a chromatographic detector, positioned outside the flow cell. This apparatus and its operation has significant application where trace amounts of metal ions are to be separated.

Almon, Amy C. (Augusta, GA)

1994-01-01

119

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

120

Electrical/thermoelectric characterization of electrodeposited Bi x Sb2- x Te3 thin films  

NASA Astrophysics Data System (ADS)

Bi x Sb2- x Te3 films were electrodeposited potentiostatically from acidic nitric baths at room temperature by controlling the electrodeposition parameters (i.e., the applied potential). Nearly stoichiometric Bi x Sb2- x Te3 thin films were obtained at applied potentials between -0.10 and -0.15 V versus the saturated calomel electrode (SCE). The electrical and thermoelectric properties of the as-deposited films were degraded at more negative deposition potentials; this might be attributed to the greater defect density formed. The post-annealing process in the reducing environment improved the electrical and thermoelectric properties, possibly because of a decrease in antistructure defects.

Yoo, In-Joon; Lim, Dong Chan; Myung, Nosang V.; Jeong, Young-Keun; Kim, Yang Do; Lee, Kyu Hwan; Lim, Jae-Hong

2013-09-01

121

Electrochemical reduction of the iodinated contrast medium iomeprol: iodine mass balance and identification of transformation products  

Microsoft Academic Search

Potentiostatic-controlled electrochemical reduction of iomeprol was used to deiodinate iomeprol (IMP), a representative of\\u000a the iodinated X-ray contrast media. The reduction process was followed by product analysis with liquid chromatography-electrospray\\u000a ionization-tandem mass spectrometry and ion chromatography-inductively coupled plasma-mass spectrometry. The identification\\u000a is mainly based on the interpretation of the mass fragmentation. The product analysis showed a rather selective deiodination\\u000a process

Christian Zwiener; Thomas Glauner; Jochen Sturm; Michael Wörner; Fritz H. Frimmel

2009-01-01

122

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

123

Effect of Applied Potential on the Electrochemical Deposition of Styrene-Butadiene Co-Polymer Based Conducting Polymer Composite  

NASA Astrophysics Data System (ADS)

Homogeneous conducting polymer composite films with improved electrical properties are synthesized via electrochemical polymerization of polyaniline on Styrene butadiene rubber coated steel electrode. The electrochemical polymerization is carried out by potentiostatic method using an aqueous solution of 0.2 M aniline and 1.5 M sulphuric acid as electrolyte in a single compartment electrochemical cell. The optical studies show successful incorporation of polyaniline into the matrix polymer film. The effect of applied potential on the electrodeposition of composite is studied by cyclic voltammetry and by impedance spectroscopic measurements.

Mathew, Anisha Mary; Neena, P.

2011-10-01

124

Influence of recharge potential and acid concentration on the discharge behavior of PbO2 electrodes  

NASA Astrophysics Data System (ADS)

During the recharge of PbO2 electrodes, the electrode single potential and the acid concentration within its porous system usually changes over a wide range. A potentiostat and the Eloflux technique of forced flow-through of the electrolyte has been applied to keep these parameters homogeneous over all of the electrode for the whole period of recharge. A distinct dependence of the discharge capacity at a given rate on potential and acid-concentration conditions of the proceeding recharge has been found.

Meissner, Eberhard

1993-10-01

125

The corrosion behavior and microstructure of high-velocity oxy-fuel sprayed nickel-base amorphous\\/nanocrystalline coatings  

Microsoft Academic Search

The corrosion characteristics of two Ni-Cr-Mo-B alloy powders sprayed by the high-velocity oxy-fuel (HVOF) process have been\\u000a studied using potentiodynamic and potentiostatic corrosion analysis in 0.5 M H2SO4. The deposits were also microstructurally characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM)\\u000a (utilizing both secondary electron and backscattered electron modes), and transmission electron microscopy (TEM). Results\\u000a from the microstructural examination

A. H. Dent; A. J. Horlock; D. G. McCartney; S. J. Harris

1999-01-01

126

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

127

Dynamics and Topography of QUASI-2D Needle-Like Silver Electrochemical Deposits Under a Quasi-Steady Regime  

NASA Astrophysics Data System (ADS)

The electrochemical formation of single silver needles from aqueous silver sulfate was studied under both potentiostatic and galvanostatic conditions utilizing different quasi-2D cells. Under potentiostatic conditions, four (I-IV) stages of growth were distinguished. Stage III involved single needle growth under a quasi-steady-state (q-ss) regime in which, at the millimeter scale, the tip profile remained almost unchanged. Fast growing needles exhibited a truncated quasi-conical tip, and slow growing ones approached prolate hemispheroids. At stage III, the almost constant q-ss silver deposition rate was evaluated from the tip front displacement (dLz/dt) perpendicularly to the tangential plane of the tip. For the cathode to anode potential difference in the range -1.00 ? Ec-a ? -0.22 V, values of (dLz/dt) in the range 0.08-2.0 ?m s-1 were obtained. At the needle stem, the q-ss radial silver deposition rate (dLx/dt) was about two orders of magnitude lower than (dLz/dt). The transition from stage III to IV was characterized by tip thickening, i.e. a change in the tip q-conical profile to that of a prolate hemispheroid, and eventual tip splitting. Scanning electron micrographs at the micrometer scale of single silver needle tips from potentiostatic runs showed either a defined crystallography or an irregular topography covered by a large number of tiny crystals. In contrast, stems were always faceted. This difference indicated that surface relaxation processes following silver ion mass transport and discharge played a relevant role in the needle growth mode. At stage III, the growth regime is described utilizing a dual diffusion (D) and migration (M) model consisting of a DM direct contribution that becomes dominant at the needle stem, and a space charge (SC)-assisted DM contribution that operates at the tip apex. This explanation is consistent with the local cathodic current density values, the concentration ratio of silver clusters at the stem and tip apex surface, and the distinct kinetic behavior of needles produced from potentiostatic and galvanostatic runs. The complex link between mass transport phenomena of silver ions from the binary solution side, the silver ion discharge at the interface and the surface relaxation of silver adatoms and clusters at the metal lattice shed new light on the aspects of single silver needle formation.

Pasquale, M. A.; Vicente, J. L.; Arvia, A. J.

128

Electrodeposited heterojunctions based on cadmium chalcogenide, CdX (X = S, Se, Te) and polyaniline  

Microsoft Academic Search

We have fabricated heterojunctions based on all-electrodeposited cadmium chalcogenides CdX (X = S, Se, Te) and polyaniline\\u000a thin film. Cadmium chalcogenide films were deposited onto low cost stainless steel substrate using potentiostatic mode. Over\\u000a Cd chalcogenide film, polyaniline was deposited potentiodynamically. The junctions were heated at 353 K for 20 min and junction\\u000a current–voltge (I–V) and capacitance–voltage (C–V) plots were studied. From I–V plots,

S. S. Joshi; C. D. Lokhande

2007-01-01

129

Further XRD characterization of electrochromic nickel oxide thin films prepared by anodic deposition  

Microsoft Academic Search

Electrochromic (EC) behaviour of nickel oxide (NiOx) thin films, formed by potentiostatic electrodeposition in a nickel ammine complex solution (Ni(NH3)x2+; pH 9), were investigated using alkaline electrolyte solutions, KOH and (CH3)4NOH (pH 12.9). In both electrolytes, the fully oxidized composite films (F0.7\\/1.1), prepared by electrolysis at 1.1V (vs. Ag\\/AgCl) followed by electrolysis at 0.7V, commonly showed broadened UV–VIS spectra in

Masaya Chigane; Masami Ishikawa; Hiroshi Inoue

2000-01-01

130

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

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

131

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

PubMed Central

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

2011-01-01

132

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

133

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

134

Electrochemical behaviour of silver in borate buffer solutions  

NASA Astrophysics Data System (ADS)

The electrochemical behaviour of Ag in aqueous 0.15 M borax and 0.15 M boric acid buffer solution was studied under various conditions using cyclic voltammetry and potentiostatic techniques. It was found that the anodic polarization curve of Ag in borate buffer solution was characterized by the appearance of two potential regions, active and passive, prior to the oxygen evolution reaction. The active potential region was characterized by the appearance of three anodic peaks, the first two peaks A 1 and A 2 correspond to the oxidation of Ag and formation of [Ag(OH) 2] - soluble compound and a passive film of Ag 2O on the electrode surface. The third anodic peak corresponds to the conversion of both [Ag(OH) 2] - and Ag 2O to Ag 2O 2. X-ray diffraction patterns confirmed the existence of Ag 2O and Ag 2O 2 passive layers on the electrode surface potentiodynamically polarized up to 800 mV. Potentiostatic current transient measurements showed that the formation of Ag 2O and Ag 2O 2 involves a nucleation and growth mechanism under diffusion control.

Zaky, Ayman M.; Assaf, Fawzi H.; Abd El Rehim, Sayed S.; Mohamed, Basheer M.

2004-01-01

135

A simple approach for producing colloidal noble metal nanocrystals: Alternating voltage induced electrochemical synthesis  

NASA Astrophysics Data System (ADS)

Intense research has been focused on developing bottom-up nanocrystal synthesis techniques to obtain nanocrystals with sophisticated compositions and enhanced perfomances. Three popular methods are: 1) the reduction of metal complex ions or molecules with selected reducing agents, 2) the decomposition of metal compounds at elevated temperatures, and 3) the electrochemical reduction of metal ions using specialized potentiostats. The first two require expensive metal salt precursors while the last requires specialized potentiostats and either employ a single sacrificial electrode or metal salt precursors. To resolve these issues, we have focused on a facile and generic approach to generate nanocrystals by an alternating voltage induced electrochemical synthesis (AVIES) method. Nanocrystals are produced when an alternating voltage is applied by a common laboratory transformer to two sacrificial electrodes that are inserted in an electrolyte solution containing capping ligands. This work focuses on the ability of the AVIES approach to synthesize Au, Pd, and Pt noble metal nanocrystals. The nanocrystals synthesized were found to be dependent on the electrolyte identity, capping ligand, applied voltage, reaction temperature. The ability of AVIES to produce alloyed nanocrystals starting with alloyed electrodes will be discussed. The AVIES approach requires neither expensive metal compounds nor specialized instruments, is environmentally benign, and can be easily adoptable to any research lab.

McCann, Kevin

136

Crevice Corrosion on Ni-Cr-Mo Alloys  

SciTech Connect

Ni-Cr-Mo alloys were developed for their exceptional corrosion resistance in a variety of extreme corrosive environments. An alloy from this series, Alloy-22, has been selected as the reference material for the fabrication of nuclear waste containers in the proposed Yucca Mountain repository located in Nevada (US). A possible localized corrosion process under the anticipated conditions at this location is crevice corrosion. therefore, it is necessary to assess how this process may, or may not, propagate if the use of this alloy is to be justified. Consequently, the primary objective is the development of a crevice corrosion damage function that can be used to assess the evolution of material penetration rates. They have been using various electrochemical methods such as potentiostatic, galvanostatic and galvanic coupling techniques. Corrosion damage patterns have been investigated using surface analysis techniques such as scanning electron microscopy (SEM) and optical microscopy. All crevice corrosion experiments were performed at 120 C in 5M NaCl solution. Initiating crevice corrosion on these alloys has proven to be difficult; therefore, they have forced it to occur under either potentiostatic or galvanostatic conditions.

P. Jakupi; D. Zagidulin; J.J. Noel; D.W. Shoesmith

2006-05-12

137

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

138

Intergranular corrosion in a martensitic stainless steel detected by electrochemical tests  

SciTech Connect

Quenched and tempered martensitic stainless steel UNS S41000 was tested electrochemically for susceptibility to sensitization in specimens quenched from 975 C (1,248 K) and tempered for 2 h at different temperatures between 300 C (573 K) and 700 C (973 K). Besides an oxalic acid etch test, the following tests were performed using a potentiostat and 1 N sulfuric acid (H{sub 2}SO{sub 4}) solution: potentiokinetic polarization, potentiostatic etch, and electrochemical potentiokinetic reactivation in the double-loop version (DL-EPR). Tested surfaces were observed metallographically. The maximum susceptibility to intergranular corrosion was observed in the condition tempered at 550 C (823 K), and a sensitized structure was detected. For lower tempering temperatures, steel was less sensitized, or not at all, and for higher tempering temperatures, steel was less sensitized. All tests except for the oxalic acid etch were able to evaluate quantitatively different degrees of sensitization as a function of tempering temperature. The DL-EPR method was the best to discriminate degrees of sensitization.

Alonso-Falleiros, N.; Magri, M.; Falleiros, I.G.S. [Univ. of Sao Paulo (Brazil)

1999-08-01

139

Comparative studies of self-discharge by potential decay and float-current measurements at C double-layer capacitor and battery electrodes  

NASA Astrophysics Data System (ADS)

Charged electrochemical capacitors and battery electrodes are in a state of high Gibbs energy in relation to that of their discharged states; hence there is a thermodynamic "driving force" for their self-discharge on open-circuit. Several mechanisms for self-discharge can be envisaged and diagnostically distinguished. They must take place by mixed cathodic/anodic electrochemical processes (as in corrosion) or, in some cases, by a surface-chemical process. Self-discharge can be characterized by two procedures: (a) measurement of open-circuit decline of electrode potential or state-of-charge with time or (b) by establishing the polarizing currents, so-called float-currents, at various potentials in the self-discharge process that are required just to maintain those respective potentials constant. The importance, for either case, of characterizing the self-discharge behavior individually for each electrode of a cell pair (using a third electrode as a reference) is stressed. Experimental data are presented for potentiostatic float-current measurements at porous C-cloth and glassy-C electrodes, and related to digital potential-decay measurements under the same conditions in aqueous H 2SO 4 below the decomposition potential of the solution. Treatment of an equivalent circuit model enables the time dependence of components of double-layer charging and self-discharge under potentiostatic float conditions to be understood and evaluated.

Niu, Jianjun; Conway, Brian E.; Pell, Wendy G.

140

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

141

Growth and etch rate study of low temperature anodic silicon dioxide thin films.  

PubMed

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

142

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

143

Flow-Injection Amperometric Determination of Tacrine based on Ion Transfer across a Water-Plasticized Polymeric Membrane Interface  

PubMed Central

A flow-injection pulse amperometric method for determining tacrine, based on ion transfer across a plasticized poly(vinyl chloride) (PVC) membrane, was developed. A four-electrode potentiostat with ohmic drop compensation was used, while a flow-through cell incorporated the four electrodes and the membrane, which contained tetrabutylammonium tetraphenylborate. The influence of the applied potential and of the flow-injection variables on the determination of tacrine was studied. In the selected conditions, a linear relationship between peak height and tacrine concentration was found up to 4×10-5M tacrine. The detection limit was 1×10-7M. Good repeatability was obtained. Some common ions and pharmaceutical excipients did not interfere.

Ortuno, Joaquin A.; Rueda, Carlos

2007-01-01

144

Copper-selective electrochemical filling of macropore arrays for through-silicon via applications  

PubMed Central

In this article, the physico-chemical and electrochemical conditions of through-silicon via formation were studied. First, macropore arrays were etched through a low doped n-type silicon wafer by anodization under illumination into a hydrofluoric acid-based electrolyte. After electrochemical etching, ‘almost’ through-silicon macropores were locally opened by a backside photolithographic process followed by anisotropic etching. The 450?×?450-?m² opened areas were then selectively filled with copper by a potentiostatic electrochemical deposition. Using this process, high density conductive via (4.5?×?105?cm?²) was carried out. The conductive paths were then electrically characterized, and a resistance equal to 32 m?/copper-filled macropore was determined. PMID:22776559

2012-01-01

145

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

146

Influence of Step Annealing Temperature on the Microstructure and Pitting Corrosion Resistance of SDSS UNS S32760 Welds  

NASA Astrophysics Data System (ADS)

In the present work, the influence of step annealing heat treatment on the microstructure and pitting corrosion resistance of super duplex stainless steel UNS S32760 welds have been investigated. The pitting corrosion resistance in chloride solution was evaluated by potentiostatic measurements. The results showed that step annealing treatments in the temperature ranging from 550 to 1000 °C resulted in a precipitation of sigma phase and Cr2N along the ferrite/austenite and ferrite/ferrite boundaries. At this temperature range, the metastable pits mainly nucleated around the precipitates formed in the grain boundary and ferrite phase. Above 1050 °C, the microstructure contains only austenite and ferrite phases. At this condition, the critical pitting temperature of samples successfully arrived to the highest value obtained in this study.

Yousefieh, M.; Shamanian, M.; Saatchi, A.

2011-12-01

147

X-Ray Photoelectron Spectroscopy Depth Profiling of Electrochemically Prepared Thin Oxide Layers on Duplex Stainless Steel  

NASA Astrophysics Data System (ADS)

The surface oxidation of duplex stainless steel (DSS 2205) was studied by X-ray photoelectron spectroscopy (XPS). The experiments were performed on the alloy after controlled oxidation in a chloride-enriched solution at controlled potentials. The evolution of the passive film formed on the DSS in a chloride solution was studied using cyclic voltammetry with XPS surface characterization at selected potentials. The evolution of the oxide films and its specific compositions formed on the DSS was studied as a function of depth. Fe/Cr oxidized layers and oxide thicknesses were observed and correlated with the various potentiostatic potentials. The importance of Mo and Cr inside the oxide films in this article is studied and described, whereas their role in the protective layer, as oxides, is significant.

Donik, ?rtomir; Kocijan, Aleksandra; Mandrino, Djordje; Jenko, Monika

2011-10-01

148

Corrosion behavior of sensitized duplex stainless steel.  

PubMed

The present work investigates the corrosion behavior of 2205 duplex stainless steel in 0.9% NaCl solution after various heat-treatments, and compares it to that of 316L austenitic stainless steel. Both stainless steels were heat-treated at 500, 650, and 800 degrees C in air for 1 h, followed by furnace cooling. Each heat-treated sample was examined for their microstructures and Vickers micro-hardness, and subjected to the X-ray diffraction for the phase identification. Using potentiostatic polarization method, each heat-treated sample was corrosion-tested in 37 degrees C 0.9% NaCl solution to estimate its corrosion rate. It was found that simulated sensitization showed an adverse influence on both steels, indicating that corrosion rates increased by increasing the sensitization temperatures. PMID:9713683

Torres, F J; Panyayong, W; Rogers, W; Velasquez-Plata, D; Oshida, Y; Moore, B K

1998-01-01

149

Influence of acidity of solutions of lithium perchlorate in acetone on protective effect of azole in anodic dissolution of nickel  

SciTech Connect

This paper studies the anodic behavior of nickel cathodically deposited from a chloride-free electrolyte in solutions of xM HC10/sub 4/ + (0.05-x)M LiC10/sub 4/ in acetone in the presence of 2-methylbenzimidazole at 25 degrees C. The water content in all cases was 0.01 M. The potentiostatic measurements were made in steps of 50 mV with 3 min holding time in solutions saturated with hydrogen or argon. The pH was measured with a glass electrode. Possible anodic processes can be the ionization of nickel or adsorbed hydrogen and the oxidation of azole. The 100% current yield of the process of ionization of nickel enables one to regard this process as practically the only one.

Ekilik, V.V.; Balakshina, E.N.; Grigor'ev, V.P.

1986-03-01

150

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

151

Comparison between several methods for determining the depassivation threshold value for corrosion onset  

NASA Astrophysics Data System (ADS)

Numerous studies have been already carried out to study the chloride threshold value for depassivation of the steel embedded in concrete. Most of them were based on natural penetration of chlorides, whose main disadvantage is that it is very time consuming and makes necessary a long time to obtain reliable data. Other methods used are the potentiostatic tests that, depending on the potential applied, may also take very long. Recently, an accelerated method to determine the threshold value of corrosion of steel by application of electrical fields has been developed. In this paper, results obtained, for the same concrete, using every method are given as well as a comparison of the advantages and drawbacks of each of them.

de Viedma, P. G.; Castellote, M.; Andrade, C.

2006-11-01

152

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

153

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

154

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

NASA Astrophysics Data System (ADS)

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

Vequizo, Junie Jhon M.; Ichimura, Masaya

2014-04-01

155

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

SciTech Connect

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

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

1994-12-31

156

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

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

157

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

158

Pitting corrosion resistance of nickel-titanium rotary instruments with different surface treatments in seventeen percent ethylenediaminetetraacetic Acid and sodium chloride solutions.  

PubMed

This study evaluated the pitting corrosion resistance of nickel-titanium (NiTi) rotary instruments with different surface treatments in 17% ethylenediaminetetraacetic acid (EDTA) and NaCl solutions. Electropolished RaCe instruments were allocated to group A, non-electropolished RaCe instruments to group B, and physical vapor deposition (PVD)-coated Alpha files to group C (10 instruments per group). Electrochemical measurements were carried out by using a potentiostat for galvanic current measurements. On the basis of electrochemical tests, no localized corrosion problems are to be expected in EDTA. In NaCl, pitting potential occurred at higher values for the electropolished and PVD instruments, indicating an increased corrosion resistance. There appears to be a risk of corrosion for NiTi instruments without surface treatments in contact with NaCl. NiTi files with PVD and electropolishing surface treatments showed an increase corrosion resistance. PMID:18215684

Bonaccorso, Antonio; Tripi, Teresa Roberta; Rondelli, Gianni; Condorelli, Guglielmo Guido; Cantatore, Giuseppe; Schäfer, Edgar

2008-02-01

159

Electrochemical behavior of the glycine-iodide-perchlorate ternary system at the gold electrode  

SciTech Connect

Potentiostatic electrolysis and potentiodynamic triangular sweeps were used to study the electrochemical effects observed at the gold electrode in solutions containing glycine, NaI, and NaClO/sub 4/. It was found that in this system gold dissolves rather rapidly when anodically polarized, so that with 30 min of electrolysis one can obtain solutions with a metal concentration of over 70 mg/liter. The iodide ions present in the solution are responsible for this process, as they can be oxidized at potentials above 0.5 V (nhe) and enter redox reactions with the gold. The anodic gold dissolution is slower when glycine is present, which can be attributed to glycine adsorption on the gold electrode occurring under the conditions studied.

Safronov, A.Yu.; Tsykunova, G.V.; Mineev, G.G.; Kokho, O.V.; Chernyak, A.S.

1987-09-01

160

Anticorrosion characteristics of a Zn-primer coating in a ballast tank under various chloride concentrations  

NASA Astrophysics Data System (ADS)

At an open-circuit potential, the anodic polarization curves had very similar values, and no significant differences were observed among the conditions. In the cathodic polarization curves, total residual chloride (TRC) reacted with the Zn-primer coating and created a film that had anticorrosion properties. Therefore, the anticorrosion property improved. With an increase in applied potential in the potentiostatic experiment, the observed surface corrosion occurred due to the dissolution reaction. From Tafel analysis, the corrosion current density had the highest value in natural seawater and the lowest value in the 2 ppm solution. Generally, metals corrode faster with increasing TRC concentration, but with the formation of Zn(OH)2, which has anticorrosion properties, the corrosion resistance of a Zn-primer-coated specimen in seawater can be improved.

Kim, Seong-Jong; Lee, Seung-Jun

2010-05-01

161

Modeling and analysis of a molten salt electrowinning system with liquid cadmium cathode  

SciTech Connect

In the present work, an electrowinning process in the LiCl-KCl/Cd system is considered to model and analyze the equilibrium behavior and electro-transport of the actinide and rare-earth elements. Equilibrium distributions of the actinide and rare-earth elements in a molten salt and liquid cadmium system have been estimated for an infinite potentiostatic electrolysis from the thermodynamic data and material balance. A simple dynamic modeling of this process was performed by taking into account the material balances and diffusion-controlled electrochemical reactions in a diffusion layer at an electrode interface between the molten salt and liquid cadmium cathode. This model demonstrated a prediction of the concentration behaviors, a faradic current of each element and an electrochemical potential as function of the time up to the corresponding electro-transport satisfying a given applied current based on a galvano-static electrolysis. (authors)

Kim, K.R.; Ahn, D.H.; Paek, S.; Kwon, S.W.; Kim, S.H.; Shim, J.B.; Chung, H.; Kim, E.H. [Korea Atomic Energy Research Institute, P.O. Box 105, Yuseong, Daejeon, 305-353 (Korea, Republic of)

2007-07-01

162

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

163

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

PubMed

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

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

2013-06-01

164

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

165

Electrochemical study of silver thiosulphate reduction in the absence and presence of ultrasound.  

PubMed

The electrochemical reduction of silver thiosulphate was studied potentiostatically on platinum electrodes in the absence and presence of ultrasound (20 kHz). This system is irreversible and the reaction is both diffusion and kinetically controlled. The slowest step is the kinetic reaction especially the chemisorption of ions at the electrode surface. Ultrasound greatly improves the mass transport, which can be explained by changing from diffusion to mainly convection. This paper reports the effect of ultrasound upon electrode kinetic and mass-transport parameters at various RDE rotation speeds and ultrasonic intensities. It was found that the heterogeneous rate constant (kf) is improved in the presence of ultrasound due to the increase in the formal or standard heterogeneous rate constant (k0) (approximately by 10-fold under sonication). PMID:15474946

Pollet, Bruno; Lorimer, J P; Hihn, J-Y; Touyeras, F; Mason, T J; Walton, D J

2005-01-01

166

High-efficiency synergistic conversion of CO2 to methanol using Fe2O3 nanotubes modified with double-layer Cu2O spheres.  

PubMed

Cuprous oxide/hematite nanotubes (Cu2O/Fe2O3NTs) were prepared by a potentiostatic electrodeposited method, in which different structured Cu2O materials were modified onto Fe2O3 NTs surface. Among them, the material with double-layer Cu2O spheres (Cu2O/Fe2O3 NTs-30) showed excellent photoelectrocatalytic (PEC) properties with a suitable energy band gap (1.96 eV) and a smaller overpotential (0.18 V). Furthermore, Cu2O/Fe2O3 NTs-30 showed two types of synergisms in the PEC reduction of CO2: (i) between electrocatalysis and photocatalysis and (ii) between Cu2O and Fe2O3NTs. The faradaic efficiency and methanol yield reached 93% and 4.94 mmol L(-1) cm(-2) after 6 h, respectively. PMID:25144767

Li, Peiqiang; Jing, Hua; Xu, Jinfeng; Wu, Chenxiao; Peng, Hui; Lu, Jing; Lu, Fusui

2014-09-12

167

Synthesis of TiO2 nanotube arrays and its application in mini-3D dye-sensitized solar cells  

NASA Astrophysics Data System (ADS)

Here we report a mini-three-dimensional dye-sensitized solar cell (3D DSSC) based on TiO2 nanotube arrays (TNAs). TNAs were directly grown on spiral-shaped titanium wire via a facile potentiostatic anodization. Furthermore, the TNAs film was characterized by scanning electron microscopy, x-ray diffraction and transmission electron microscopy, indicating that the annealed TNAs were composed of single-crystalline anatase particles. Unlike conventional flat DSSC, this mini-3D DSSC could easily hold liquid electrolyte due to the capillary force which facilitated sealing the cell. This mini-3D DSSC showed an energy conversion efficiency of 4.1% under the AM 1.5 condition, which was much higher compared with that (3.2%) of the backside illuminated TNAs based DSSC of the same projected area.

Liu, Yong; Li, Ming; Wang, Hai; Zheng, Jiemin; Xu, Hongmei; Ye, Qihong; Shen, Hui

2010-05-01

168

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

169

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

170

On-site fuel electroanalysis: determination of lead, copper and mercury in fuel bioethanol by anodic stripping voltammetry using screen-printed gold electrodes.  

PubMed

The potential application of commercial screen-printed gold electrodes (SPGEs) for the trace determination of lead, copper, and mercury in fuel bioethanol is demonstrated. Samples were simply diluted in 0.067 mol L(-1) HCl solution prior to square-wave anodic stripping voltammetry (SWASV) measurements recorded with a portable potentiostat. The proposed method presented a low detection limit (<2 ?g L(-1)) for a 240 s deposition time, linear range between 5 and 300 ?g L(-1), and adequate recovery values (96-104%) for spiked samples. This analytical method shows great promise for on-site trace metal determination in fuel bioethanol once there is no requirement for sample treatment or electrode modification. PMID:25000856

Almeida, Eduardo S; Richter, Eduardo M; Munoz, Rodrigo A A

2014-07-21

171

Electrochemical corrosion and metal ion release from Co-Cr-Mo prosthesis with titanium plasma spray coating.  

PubMed

The corrosion behavior of CoCrMo implants with rough titanium coatings, applied by different suppliers by either sintering or vacuum plasma spraying, has been evaluated and compared with uncoated material. The open-circuit potential, corrosion current and polarization resistance were determined by electrochemical techniques. The Co, Cr and Ti ions released from the samples into the electrolyte during a potentiostatic extraction technique were analyzed using ICP-MS. The Ti coatings from the different suppliers showed a different porous morphology, and the implants exhibited a distinct corrosion activity, underlining the importance of the coating process parameters. Among the titanium coated samples, the one with the sintered overcoat turned out to be the most resistant. Yet, on an absolute scale, they all showed a corrosion resistance inferior to that of uncoated CoCrMo or wrought titanium. PMID:15763254

Reclaru, Lucien; Eschler, Pierre-Yves; Lerf, Reto; Blatter, Andreas

2005-08-01

172

Copper-selective electrochemical filling of macropore arrays for through-silicon via applications.  

PubMed

In this article, the physico-chemical and electrochemical conditions of through-silicon via formation were studied. First, macropore arrays were etched through a low doped n-type silicon wafer by anodization under illumination into a hydrofluoric acid-based electrolyte. After electrochemical etching, 'almost' through-silicon macropores were locally opened by a backside photolithographic process followed by anisotropic etching. The 450?×?450-?m² opened areas were then selectively filled with copper by a potentiostatic electrochemical deposition. Using this process, high density conductive via (4.5?×?105?cm-²) was carried out. The conductive paths were then electrically characterized, and a resistance equal to 32 m?/copper-filled macropore was determined. PMID:22776559

Defforge, Thomas; Billoué, Jérôme; Diatta, Marianne; Tran-Van, François; Gautier, Gaël

2012-01-01

173

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

174

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

175

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

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

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

178

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

179

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

180

Simultaneous telemetric monitoring of brain glucose and lactate and motion in freely moving rats.  

PubMed

A new telemetry system for simultaneous detection of extracellular brain glucose and lactate and motion is presented. The device consists of dual-channel, single-supply miniature potentiostat-I/V converter, a microcontroller unit, a signal transmitter, and a miniaturized microvibration sensor. Although based on simple and inexpensive components, the biotelemetry device has been used for accurate transduction of the anodic oxidation currents generated on the surface of implanted glucose and lactate biosensors and animal microvibrations. The device was characterized and validated in vitro before in vivo experiments. The biosensors were implanted in the striatum of freely moving animals and the biotelemetric device was fixed to the animal's head. Physiological and pharmacological stimulations were given in order to induce striatal neural activation and to modify the motor behavior in awake, untethered animals. PMID:24102201

Rocchitta, Gaia; Secchi, Ottavio; Alvau, Maria Domenica; Farina, Donatella; Bazzu, Gianfranco; Calia, Giammario; Migheli, Rossana; Desole, Maria Speranza; O'Neill, Robert D; Serra, Pier A

2013-11-01

181

Kinetics of the transpassive oxidation of pyrite. Technical progress report, July 1, 1992--October 20, 1992  

SciTech Connect

In the transpassive region, about 0.4 to 0.8 V (SCE), aggressive oxidation of pyrite occurred. The reaction products in this region were Fe(III) oxide, sulfate ion and partially oxidized sulfur intermediates. The growth kinetics of the reaction of pyrite were studied using chronoamperometry measurement with both stationary and rotating disk electrodes. The effect of electrode rotation speed, solution pH and temperature were examined. Potentiostatic measurements were well correlated by a paralinear rate equation, suggesting the formation of an intermediate passive film, associated with the simultaneous dissolution of the outer layer of the film. Activation energies of 66.17 kJ/mole (15.83 kcal/mole) and 38.67 kJ/mole (9.25 kcal/mole) were obtained for associated parabolic and linear rate constants respectively, at an applied potential of 0.6 V.

Hu, Weibai; Huang, Qinping; Zhu, Ximeng; Li, Jun; Bodily, D.M.; Wadsworth, M.E.

1992-12-31

182

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

183

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

SciTech Connect

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

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

2009-06-03

184

The effect of deposition electrolyte on polypyrrole surface interaction with biological environment  

NASA Astrophysics Data System (ADS)

The effects of electrolyte type used in electrodeposition of polypyrrole (PPy) films on Ti6Al7Nb alloy was studied in order to design a titanium modified surface with enhanced antibacterial activity and better biocompatibility. Therefore, the polypyrrole coatings were synthesized by potentiostatic electrochemically technique from pyrrole and lithium perchlorate (LiClO4) using aqueous and non-aqueous solutions. The both PPy films were characterized by electrochemical methods in Hank's Balanced Salt Solution (HBSS), and surface characterization by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) analysis, adhesion test and contact angle measurements. A correlation between the film stability and surface properties, synthesis parameters and the interaction with biological environment was established. The physical-chemical properties of the studied PPy films are in direct related with the doping level and have an important influence of the biocompatibility and antibacterial activity.

Mîndroiu, Mihaela; Ungureanu, Camelia; Ion, Raluca; Pîrvu, Cristian

2013-07-01

185

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

186

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

187

A microfluidic paper-based electrochemical biosensor array for multiplexed detection of metabolic biomarkers  

NASA Astrophysics Data System (ADS)

Paper-based microfluidic devices have emerged as simple yet powerful platforms for performing low-cost analytical tests. This paper reports a microfluidic paper-based electrochemical biosensor array for multiplexed detection of physiologically relevant metabolic biomarkers. Different from existing paper-based electrochemical devices, our device includes an array of eight electrochemical sensors and utilizes a handheld custom-made electrochemical reader (potentiostat) for signal readout. The biosensor array can detect several analytes in a sample solution and produce multiple measurements for each analyte from a single run. Using the device, we demonstrate simultaneous detection of glucose, lactate and uric acid in urine, with analytical performance comparable to that of the existing commercial and paper-based platforms. The paper-based biosensor array and its electrochemical reader will enable the acquisition of high-density, statistically meaningful diagnostic information at the point of care in a rapid and cost-efficient way.

Zhao, Chen; Thuo, Martin M.; Liu, Xinyu

2013-10-01

188

Template-assisted electrochemical growth of polypyrrole nanotubes for development of high sensitivity glucose biosensor.  

PubMed

In this paper, we report the growth of polypyrrole (PPy) nanotube arrays using template-assisted electrochemical polymerization to fabricate enzymatic glucose biosensors. The PPy nanotubes were grown on platinum-coated alumina membranes (Anodisc™s). By varying the polymerization time during the potentiostatic electropolymerization, the size/diameter of the PPy nanotubes were controlled, leading to changes in the subsequent enzyme immobilization (via physical adsorption). Enzyme electrode thus fabricated resulted in to the optimum sensitivity of 18.6 mA cm(-2) M(-1), a wide range of linear operation (0.25-20 mM) and the lowest detection limit of 0.25 mM glucose concentration for the biosensor with the polymerization time of 40 s. The effect of polymerization duration on the sensitivity has been explained on the basis of porosity and enzyme-loading capacity of polymerized electrodes. PMID:24912977

Palod, Pragya Agar; Pandey, Shyam S; Hayase, Shuji; Singh, Vipul

2014-10-01

189

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

190

Recovering Silver from Photographic Process Wastes  

NASA Astrophysics Data System (ADS)

Spent color bleach-fix solution (CBFS), a product of photographic processing operations, is a potential source of silver. Of the extraction reactors used in recovering this silver, the rotating cylindrical electrode (RCE) has an advantage in that it provides improved mass transfer with an extended effective surface area. In addition, the application of a potentiostatic technique allows the silver deposition reaction to take place preferentially, without the formation of silver sulfide. The process consists of prior physical treatment, subsequent chemical reduction of the ferric-EDTA (ethylene diamine tetra-acetic acid) complex present in the CBFS with sodium dithionite (monitored by measuring the redox potential of Fe3+/Fe2+ couple), followed by electrodeposition of silver in a divided cell using a cation exchange membrane. The combined procedure results in increased current efficiency and reduced electrolysis time.

Sathaiyan, N.; Adaikkalam, P.; Abdul Kader, J. A. M.; Visvanathan, S.

1990-10-01

191

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

192

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

NASA Astrophysics Data System (ADS)

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

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

2009-11-01

193

High-efficiency synergistic conversion of CO2 to methanol using Fe2O3 nanotubes modified with double-layer Cu2O spheres  

NASA Astrophysics Data System (ADS)

Cuprous oxide/hematite nanotubes (Cu2O/Fe2O3NTs) were prepared by a potentiostatic electrodeposited method, in which different structured Cu2O materials were modified onto Fe2O3 NTs surface. Among them, the material with double-layer Cu2O spheres (Cu2O/Fe2O3 NTs-30) showed excellent photoelectrocatalytic (PEC) properties with a suitable energy band gap (1.96 eV) and a smaller overpotential (0.18 V). Furthermore, Cu2O/Fe2O3 NTs-30 showed two types of synergisms in the PEC reduction of CO2: (i) between electrocatalysis and photocatalysis and (ii) between Cu2O and Fe2O3NTs. The faradaic efficiency and methanol yield reached 93% and 4.94 mmol L-1 cm-2 after 6 h, respectively.Cuprous oxide/hematite nanotubes (Cu2O/Fe2O3NTs) were prepared by a potentiostatic electrodeposited method, in which different structured Cu2O materials were modified onto Fe2O3 NTs surface. Among them, the material with double-layer Cu2O spheres (Cu2O/Fe2O3 NTs-30) showed excellent photoelectrocatalytic (PEC) properties with a suitable energy band gap (1.96 eV) and a smaller overpotential (0.18 V). Furthermore, Cu2O/Fe2O3 NTs-30 showed two types of synergisms in the PEC reduction of CO2: (i) between electrocatalysis and photocatalysis and (ii) between Cu2O and Fe2O3NTs. The faradaic efficiency and methanol yield reached 93% and 4.94 mmol L-1 cm-2 after 6 h, respectively. Electronic supplementary information (ESI) available: High-efficiency synergistic conversion of CO2 to methanol using Fe2O3 nanotubes modified with double-layer Cu2O spheres. See DOI: 10.1039/c4nr02902j

Li, Peiqiang; Jing, Hua; Xu, Jinfeng; Wu, Chenxiao; Peng, Hui; Lu, Jing; Lu, Fusui

2014-09-01

194

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

PubMed

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

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

2008-08-01

195

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.

196

Silver(I) ions ultrasensitive detection at carbon electrodes-analysis of waters, tobacco cells and fish tissues.  

PubMed

We used carbon paste electrodes and a standard potentiostat to detect silver ions. The detection limit (3 Signal/Noise ratio) was estimated as 0.5 ?M. A standard electrochemical instrument microanalysis of silver(I) ions was suggested. As a working electrode a carbon tip (1 mL) or carbon pencil was used. Limits of detection estimated by dilution of a standard were 1 (carbon tip) or 10 nM (carbon pencil). Further we employed flow injection analysis coupled with carbon tip to detect silver(I) ions released in various beverages and mineral waters. During first, second and third week the amount of silver(I) ions releasing into water samples was under the detection limit of the technique used for their quantification. At the end of a thirteen weeks long experiment the content of silver(I) ions was several times higher compared to the beginning of release detected in the third week and was on the order of tens of nanomoles. In subsequent experiments the influence of silver(I) ions (0, 5 and 10 ?M) on a plant model system (tobacco BY-2 cells) during a four-day exposition was investigated. Silver(I) ions were highly toxic to the cells, which was revealed by a double staining viability assay. Moreover we investigated the effect of silver(I) ions (0, 0.3, 0.6, 1.2 and 2.5 ?M) on guppies (Poecilia reticulata). Content of Ag(I) increased with increasing time of the treatment and applied concentrations in fish tissues. It can be concluded that a carbon tip or carbon pencil coupled with a miniaturized potentiostat can be used for detection of silver(I) ions in environmental samples and thus represents a small, portable, low cost and easy-to-use instrument for such purposes. PMID:22399980

Krizkova, Sona; Krystofova, Olga; Trnkova, Libuse; Hubalek, Jaromir; Adam, Vojtech; Beklova, Miroslava; Horna, Ales; Havel, Ladislav; Kizek, Rene

2009-01-01

197

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

SciTech Connect

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

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

1996-12-31

198

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

199

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

200

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

NASA Astrophysics Data System (ADS)

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

Donovan, Conrad Koble

201

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

202

a Study of Cobalt Electrodes in Alkaline Media.  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. This thesis is a study of the anodic oxidation of cobalt in alkaline solution. The main interest is on the electrochemical behaviour of the Co/Co(OH) _2 couple as a potentially high energy density anode in rechargeable batteries. Fundamental studies on solid cobalt electrodes were carried out to determine its kinetics of oxidation. The anodic formation of cobalt hydroxide films at different current densities showed that the film thickness varied with changing current and that the films were most likely to be formed by a nucleation and growth mechanism. Steady state measurements provided kinetic parameters such as Tafel slopes and reaction order. Two Tafel slopes were observed and it was deduced from theoretically predicted Tafel slopes that the oxidation of the cobalt metal electrode was initially dominated by an electrodissolution of the metal followed by the formation of the hydroxide film. Potentiostatic experiments performed in conjunction with a.c. impedance measurements confirmed that the formation of the hydroxide film was a solid phase reaction involving the nucleation and growth of cobalt hydroxide crystallites on the metal surface. The effect of adding lithium hydroxide to the electrolyte was also examined. Better discharge performance was observed from both galvanostatic and potentiostatic studies for the oxidation of cobalt in lithiated electrolyte. Investigations on the dissolution accompanying the passivation of Co showed the presence of a higher concentration of Co(II) ions in the lithiated electrolyte. It is concluded that the slower rate of nucleation in the presence of LiOH results in the more severe corrosion of the metal. The evaluation of the reversibility of the Co/Co ^{2+} couple gave promising results. It was found that the cobalt electrode recharged efficiently even under non gassing conditions. The fact that it is possible to charge the electrode without gassing is of significant importance in that no reserve negative material needs to be included as is normally the case in existing secondary batteries. Finally some preliminary studies were carried out to examine methods of preparing porous cobalt electrodes. Electrodes prepared from high surface area cobalt, obtained by reducing Co_3O_4 in H_2, performed well and initial results indicate that it is the best manufacture method. (Abstract shortened by UMI.).

Yon Hin, Foo Yueh Yin

203

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

204

Degradation and failure susceptibility of carbon steels in simulated Yucca Mountain nuclear repository environments  

NASA Astrophysics Data System (ADS)

Environmental degradation and cracking of medium carbon steel (MCS) rock bolts and low carbon steel (LCS) I-beam have been investigated by experimental methods such as linear polarization, impedance spectroscopy, weight loss measurements, and electro-mechanical dynamic slow strain rate tensile (SSRT) tests, along with potentiostatic in-situ potential-current monitoring techniques. The experiments were conducted in concentrated aqueous environments of various temperatures, which simulated the conditions at the Yucca Mountain (YM) nuclear waste repository site, where the candidate structural materials introduced above, will be used for supporting the waste repository tunnels. MCS corroded at medium general rates approximately around 40 mum/year to 200 mum/year in de-aerated simulated YM waters of various temperatures and concentrations. Increased temperatures increased the corrosion rates in the all de-aerated waters. Increased concentrations of overall species in the simulated waters also increased the corrosion rates, but only slightly. Impedance spectroscopy revealed similar trends for temperature and concentration effects on the rates in both aerated and deaerated environments. Aeration increased corrosion rates significantly in dilute (1X) and ten times concentrated (10X) waters at all temperatures. However, inhibitive precipitates on the specimens formed by oxygen-environment reactions at higher temperatures (up to 85°C) in hundred times concentrated (100X) waters decreased corrosion rates drastically, resulting some localized corrosion and pitting. The average rates were determined to be between approximately 100 mu/year and 1000 mu/year in the entire concentration and temperature range tested. Electrochemical results showed slightly higher rates compared to the other tests because of their much shorter testing period, therefore in general they should be taken as conservative upper bounds. SSRT on LCS under various imposed metal-electrolyte interface potentials revealed strain aging embrittlement (SAE) and hydrogen induced cracking (HIC) at 85°C in simulated de-aerated 100X YM waters. The failures were brittle and of sharp cracks which always inclined in ˜45° to the load axis. Ductile failures along secondary trans-granular cracks around the main cracks occurred at room temperature (25°C) with some anodic and cathodic over-potentials around Ecorr, revealing susceptibility of LCS to stress corrosion cracking (SCC) in the simulated repository environments. SSRT combined with in-situ current and potential monitoring by potentiostatic methods revealed that Portevin LeChatelier (PLC) effect in LCS starts at ˜55°C, and showed precise correlations with open circuit potential Ecorr and the corresponding current. Therefore, SSRT along the in-situ potential-current monitoring in aqueous environments becomes a powerful diagnostic research tool especially for investigating dynamic strain aging (Portevin-LeChatelier Effect) phenomena of metals in aqueous environments.

Yilmaz, Ahmet

205

Structural and optical properties of electrochemically deposited ZnO films in electrolyte containing Al2(SO4)3  

NASA Astrophysics Data System (ADS)

The present work concerns the electrochemical deposition of aluminium doped ZnO nanostructured thin films on SnO2:F covered glass substrates. Doped with Al nanostructured ZnO (ZnO:Al) films are obtained by an electrochemical process using a three-electrode potentiostatic system with a saturated calomel electrode as reference electrode, in aqueous solution containing ZnCl2, KCl and Al2(SO4)3. The influence of the deposition parameters on the structural properties of the obtained ZnO:Al layers is investigated by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Atomic Force Microscopy (AFM). Energy Dispersive X-ray Analysis (EDAX) is applied for measurement of the Al content in the films. The SEM micrographs and AFM pictures show that the ZnO:Al films consist of nanograins with a shape of walls. The XRD spectra demonstrate (100), (002), (101), (110) and (103) the characteristic reflexes of the ZnO. Influence of the Al concentration on the IR reflectance spectra and haze ratio of ZnO:Al thin films are presented and discussed.

Lovchinov, K.; Ganchev, M.; Rachkova, A.; Nichev, H.; Angelov, O.; Mikli, V.; Dimova-Malinovska, D.

2012-12-01

206

Reduction of CO2 to low carbon alcohols on CuO FCs/Fe2O3 NTs catalyst with photoelectric dual catalytic interfaces.  

PubMed

In this paper, the CuO FCs/Fe2O3 NTs catalyst was obtained after Fe2O3 nanotubes (Fe2O3 NTs) were decorated with CuO flower clusters (CuO FCs) by the pulse electrochemical deposition method. The in situ vertically aligned Fe2O3 NTs were prepared on the ferrous substrate by a potentiostatic anodization method. The SEM result showed the volcano-like Fe2O3 NTs were arranged in order and the CuO FCs constituted of flaky CuO distributed on the Fe2O3 NTs surface uniformly. After CuO FCs were loaded on Fe2O3 NTs, the absorption of visible light was enhanced noticeably, and its band gap narrowed to 1.78 eV from 2.03 eV. The conduction band and valence band locating at -0.73 eV and 1.05 eV, respectively were further obtained. In the PEC reduction of CO2 process, methanol and ethanol were two major products identified by chromatography. Their contents reached 1.00 mmol L(-1) cm(-2) and 107.38 ?mol L(-1) cm(-2) after 6 h, respectively. This high-efficiency catalyst with photoelectric dual catalytic interfaces has a great guidance and reference significance for CO2 reduction to liquid carbon fuels. PMID:24121703

Li, Peiqiang; Wang, Huying; Xu, Jinfeng; Jing, Hua; Zhang, Jun; Han, Haixiang; Lu, Fusui

2013-12-01

207

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

208

New Ni-free superelastic alloy for orthodontic applications.  

PubMed

A potential new Ni-free Ti alloy for biomedical applications was assessed in order to investigate the superelastic behavior, corrosion resistance and the biocompatibility. The alloy studied was Ti19.1Nb8.8Zr. The chemical composition was determined by X-ray microanalysis, the thermoelastic martensitic transformation was characterized by high sensitivity calorimeter. The critical stresses were determined by electromechanical testing machine and the corrosion behavior was analyzed by potentiostatic equipment in artificial saliva immersion at 37°C. The results were compared with six different NiTi orthodontic archwire brands. The biocompatibility was studied by means of cultures of MG63 cells. Ni-free Ti alloy exhibits thermoelastic martensitic transformation with Ms=45°C. The phase present at 37°C was austenite which under stress can induce martensite. The stress-strain curves show a superelastic effect with physiological critical stress (low and continuous) and a minimal lost of the recovery around 150 mechanical cycles. The corrosion resistance improves the values obtained by different NiTi alloys avoiding the problem of the Ni adverse reactions caused by Ni ion release. Cell culture results showed that adhered cell number in new substrate was comparable to that obtained in a commercially pure Ti grade II or beta-titanium alloy evaluated in the same conditions. Consequently, the new alloy presents an excellent in-vitro response. PMID:23706217

Arciniegas, M; Manero, J M; Espinar, E; Llamas, J M; Barrera, J M; Gil, F J

2013-08-01

209

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

210

The influence of complexing agent and proteins on the corrosion of stainless steels and their metal components.  

PubMed

The present work is devoted to the problem of biodegradation of orthopaedic implants manufactured from stainless steel. In vitro simulations of the biocompatibility of two types of stainless steel, AISI 304 and AISI 316L, and their individual metal components, i.e. iron, chromium, nickel and molybdenum, were carried out in simulated physiological solution (Hank's) containing complexing agents. Knowledge of the effects of the chemical and biological complexing agents, EDTA and proteins, respectively, on the corrosion resistance of a metal should provide a better understanding of the processes occurring in vivo on its surface. The behavior of stainless steels and metal components was studied under open circuit and under potentiostatic conditions. The concentration of dissolved corrosion products in the form of released ions was determined by differential pulse polarography (DPP) and atomic emission spectrometry using inductively coupled plasma (ICP-AES). The composition of solid corrosion products formed on the surface was analyzed by energy dispersive X-ray spectroscopy (EDS) and their morphology was viewed by scanning electron microscopy (SEM). The addition of EDTA and proteins to physiological solution increased the dissolution of pure metals and stainless steels. The effect of particular protein differs on different metals and alloys. PMID:15348541

Kocijan, Aleksandra; Milosev, Ingrid; Pihlar, Boris

2003-01-01

211

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

212

An electrochemical noise study of tribocorrosion processes of AISI 304 L in Cl- and SO_{4}^{2-} media  

NASA Astrophysics Data System (ADS)

Electrochemical noise measurements were performed to investigate the intrinsically stochastic character of the tribocorrosion process. Unidirectional sliding tests (pin-on-disc) were performed using AISI 304L stainless steel sliding against corundum. Experiments were carried out in Cl- and SO_{4}^{2-} containing media under open-circuit and potentiostatic polarization conditions. The power spectral density (PSD) of the current and potential signals showed a strong dependence on the sliding frequency but did not depend significantly on the normal load between 5 and 20 N. The fluctuations of the tangential and normal loads were also recorded, and a critical comparison between the PSD of the electrochemical response and the PSD of the mechanical solicitation (load) is proposed. At high frequencies (f > 0.1 Hz), the PSD of current or potential fluctuations have significantly different shapes than the PSD of load signals: the electrochemical signal PSD is governed by the dynamic balance between local depassivation and repassivation which only depends on the kinetics of the electrochemical phenomena. For lower frequencies, a plateau is observed for both the electrochemical PSD and the load PSD. The electrochemical signal is then governed by the continuous depassivation induced by sliding which appears as a low frequency component. These results suggest that the electrochemical noise technique investigated in the frequency domain might be a promising electrochemical tool for successfully unfolding tribocorrosion signatures for material parings in sliding-corrosion tests.

Berradja, A.; Déforge, D.; Nogueira, R. P.; Ponthiaux, P.; Wenger, F.; Celis, J.-P.

2006-08-01

213

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

NASA Astrophysics Data System (ADS)

Au was electrodeposited potentiostatically at 0.3 V for 5 min on nanoporous Pt nanoparticle-coated F-doped SnO2 (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 Sn2- + 2e- (CE) ? Sn-12- + S2- at the CE/electrolyte interface, resulting in a significantly hindered recombination reaction, Sn2- + 2e- (TiO2 in the photoanode) ? Sn-12- + S2-, and significantly improved overall energy conversion efficiency.

Yoon, Yeung-Pil; Kim, Jae-Hong; Kang, Soon-Hyung; Kim, Hyunsoo; Choi, Chel-Jong; Kim, Kyong-Kook; Ahn, Kwang-Soon

2014-08-01

214

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

215

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

NASA Technical Reports Server (NTRS)

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

Abdelmassir, A. A.

1982-01-01

216

Packaged Au-PPy valves for drug delivery systems  

NASA Astrophysics Data System (ADS)

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

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

2006-03-01

217

Coupling EELS/EFTEM Imaging with Environmental Fluid Cell Microscopy  

SciTech Connect

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

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

2012-01-01

218

Two-step electrodeposition construction of flower-on-sheet hierarchical cobalt hydroxide nano-forest for high-capacitance supercapacitors.  

PubMed

A novel flower-on-sheet hierarchical morphology of ?-Co(OH)2 nanostructures was achieved via an easy two-step synthesis strategy. The method is based on first a galvanostatic electrodeposition (GE) of vertically aligned interconnected Co(OH)2 nanosheets to form a branch layer and second a potentiostatic electrodeposition (PE) of Co(OH)2 microflowers on the obtained branch layer from the secondary growth of their sheet-like precursors. The formation mechanism of this special PE time-dependent nanostructure was proposed and their morphology-dependent supercapacitor properties were also investigated. For a given areas mass loading, high specific capacitances of 1822 F g(-1) have been achieved for the electrode obtained after 200 s GE followed by a 300 s PE in a three-electrode configuration, and it maintained 91% of its initial capacity after 1000 constant-current charge/discharge cycles. Even when the discharge current density was increased from 1 to 50 mA cm(-2), the capacitance was still as high as 1499 F g(-1), indicating an excellent rate performance of the fabricated electrodes. The high performances of the electrodes are attributed to the special porous structure, 3D hierarchical morphology, vertical aligned orientation, and low contact resistance between active material and charge collector. PMID:24048435

Yang, Wanlu; Gao, Zan; Ma, Jing; Wang, Jun; Zhang, Xingming; Liu, Lianhe

2013-11-28

219

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

220

Template assisted electrodeposition of germanium and silicon nanowires in an ionic liquid.  

PubMed

In this paper we report for the first time on the room temperature template synthesis of germanium and silicon nanowires by potentiostatic electrochemical deposition from the air- and water stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py(1,4)]Tf(2)N) containing GeCl(4) and SiCl(4) as a Ge and Si source, respectively. Commercially-available track-etched polycarbonate membranes (PC) with an average nominal pore diameter of 90-400 nm were used as templates. Ge and Si nanowires with an average diameter corresponding to the nanopores' diameter and lengths of a few micrometres were reproducibly obtained. Structural characterization of the nanowires was performed by EDX, TEM, HR-SEM and Raman spectroscopy. Despite the rough surface of the nanowires, governed mostly by the original shape of the nanopore's wall of the commercially-available PC membrane, preliminary structural characterizations demonstrate the promising prospective of this innovative elaboration process compared to constraining high vacuum and high temperature methods. PMID:18936846

Al-Salman, R; Mallet, J; Molinari, M; Fricoteaux, P; Martineau, F; Troyon, M; Zein El Abedin, S; Endres, F

2008-11-01

221

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

NASA Astrophysics Data System (ADS)

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

Mohamed, Nedal; Boulfiza, Mohamed; Evitts, Richard

2013-03-01

222

Polymer film selection for corrosion protection of data storage magnetic materials.  

PubMed

Due to the current requirement of high recording density of hard disk drive, the thickness of DLC layer which is the protective layer is needed to be reduced. Therefore, the corrosion of read-write elements that are fabricated from soft magnetic materials is more critical. During the photolithography process, polymer photoresist is playing the major role on controlling the corrosion of soft magnetic materials. Two different types of polymer photoresists are selected to investigate, noted as wet photoresist and dry photoresist, respectively. Contact angle measurement, AFM and SEM are techniques using to determine the quality of polymer photoresists. Furthermore, the direct corrosion is also studied by using potentiostat/galvanostat-based measurements. The result suggested that the wet photoresist, AZ4999 Clariant, is better as compared to that of dry photoresist. No surface degradation as well as surface defects of the wet photoresist was found after lithography process. The corrosion rate of the specimen coated by this corresponding wet film is found to be only 1.44 x 10(-6) mm/y. In addition, the wet photoresist surface is hydrophobic posed of more than 75 degree of contact angle. PMID:22408952

Chatruprachewin, Santi; Supadee, Laddawan; Titiroongruang, Wisut

2011-12-01

223

Immobilization of lysine oxidase on a gold-platinum nanoparticles modified Au electrode for detection of lysine.  

PubMed

A commercial lysine oxidase (LyOx) from Trichoderma viride was immobilized covalently onto gold nanoparticles (AuNPs) and platinum nanoparticles (PtNPs) electrodeposited onto Au electrode using 3-aminopropyltriethoxy silane (3-APTES) and glutaraldehyde cross linking chemistry. A lysine biosensor was fabricated using LyOx/3-APTES/AuNPs-PtNPs/Au electrode as a working electrode, Ag/AgCl (3M KCl) as standard electrode and Pt wire as auxiliary electrode connected through a potentiostat. The enzyme electrode was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The cumulative effect of AuNPs and PtNPs showed excellent electrocatalytic activity at low applied potential for detection of H2O2, a product of LyOx reaction. The sensor showed its optimum response within 4s, when polarized at 0.2V vs. Ag/AgCl in 0.1M phosphate buffer, pH 7.5 at 30°C. The linear range and detection limit of the sensor were 1.0-600?M and 1.0?M (S/N=3), respectively. Biosensor measured lysine level in sera, milk and amino acid tablet, which correlated well with those by standard HPLC method. The enzyme electrode lost 50% of its initial activity after 200 uses over a period of 4 months. PMID:23540929

Chauhan, N; Narang, J; Sunny; Pundir, C S

2013-04-10

224

Photovoltaic output limitation of n-FeS2 (pyrite) Schottky barriers: A temperature-dependent characterization  

NASA Astrophysics Data System (ADS)

Metal/n-pyrite (metal=Pt, Au, Nb) Schottky barrier type diodes were fabricated on electrochemically reduced either synthetic or natural (100) and (111) surfaces of single crystalline n-FeS2. The temperature dependence of I-V curves in darkness were analyzed in the range of 200-350 K on the basis of thermionic emission and recombination models. The calculated effective barrier height was ˜0.60 eV and the activation energy for recombination ˜0.50 eV for all investigated n-FeS2/Pt samples. The doping density and the extrapolated potential (pseudo flatband situation) from the Mott-Schottky plot, obtained from capacities deduced from potentiostatic complex impedance measurements, were 2.0×1016 cm-3 and 0.25 eV vs Pt for the synthetic n-pyrite crystal, respectively. From the donor density and barrier height a band bending of 0.5 eV was deduced. Photovoltaic parameters like open-circuit photovoltage and short-circuit photocurrent were studied down to temperatures of 200 K. The main phenomenon preventing the generation of a photopotential approaching the band bending (0.50 eV) appears to be the pinning of the Fermi-level by recombination centers located in the middle of the band gap (Eg=0.95 eV) of pyrite.

Büker, K.; Alonso-Vante, N.; Tributsch, H.

1992-12-01

225

Transport, phase reactions, and hysteresis of iron fluoride and oxyfluoride conversion electrode materials for lithium batteries.  

PubMed

Potentiostatic intermittent titration technique (PITT) was applied to FeF2, FeF3, and FeO0.67F1.33 to gain insight into the transport-related aspects of the conversion reaction by quantitative analysis of Li(+) diffusion and hysteresis. PITT derived diffusion coefficient measurements were benchmarked relative to values extracted by electrochemical impedance spectroscopy (EIS). A reverse-step PITT methodology was used to evaluate true hysteresis by eliminating nucleation induced overpotentials. This method evaluates the minimum potential hysteresis and allowed an accurate representation of the potential required to move conversion reactions forward at C/1000 rates in both lithiation and delithiation. The high resolution PITT data were also used to gain further insight into reaction mechanisms involved in the reversible conversion reactions. Physical evidence, based on pair distribution function (PDF) structural analysis, and electrochemical evidence are presented regarding a new step in the reaction during the rutile FeF2 reconversion reaction. PMID:24708435

Ko, Jonathan K; Wiaderek, Kamila M; Pereira, Nathalie; Kinnibrugh, Tiffany L; Kim, Joshua R; Chupas, Peter J; Chapman, Karena W; Amatucci, Glenn G

2014-07-23

226

The electrochemical behaviors of Mg, Mg-Li-Al-Ce and Mg-Li-Al-Ce-Y in sodium chloride solution  

NASA Astrophysics Data System (ADS)

The electrochemical performances of magnesium, magnesium-lithium-aluminum-cerium and magnesium-lithium-aluminum-cerium-yttrium as the anode of magnesium-hydrogen peroxide semi-fuel cells have been studied by methods of potentiodynamic, potentiostatic and electrochemical impedence measurements. The surface morphologies of magnesium and its alloys have been examined by scanning electron microscopy (SEM). It has been found that magnesium-lithium-aluminum-cerium and magnesium-lithium-aluminum-cerium-yttrium electrodes are less corrosion resistant than that of magnesium electrode in 0.7 mol L-1 NaCl solution and the corrosion current density decreases with the following order: magnesium < magnesium-lithium-aluminum-cerium-yttrium < magnesium-lithium-aluminum-cerium. The magnesium-lithium-aluminum-cerium-yttrium anode is more active than magnesium-lithium-aluminum-cerium and magnesium. The magnesium-hydrogen peroxide semi-fuel cell with magnesium-lithium-aluminum-cerium-yttrium anode shows better performance than that with Mg-Li-Al-Ce and Mg.

Lv, Yanzhuo; Xu, Yan; Cao, Dianxue

2011-10-01

227

A 1000-cell SOFC reactor for domestic cogeneration  

NASA Astrophysics Data System (ADS)

A cogeneration system was built using 1000 cells with the intention of supplying 30 kW of hot water and 500 W of power. The basis of the cogenerator was the small tubular SOFC design. 8Y zirconia was mixed into a plastic paste and extruded to form thin-walled tubes. The process produced a zirconia material with high strength and good electrical properties. After drying and firing to full density, electrodes were coated onto the inner and outer surfaces of the electrolyte, then sintered. Current collecting wires were wound around the tubular cells and the tubes were assembled into a reactor. Either hydrogen or a premix of natural gas and air was fed through the tubes and ignited by a hot wire. The ignition shock did not damage the cells in any way. Cycling was achieved within minutes. A steel heat exchanger/recuperator was used to feed hot air to the cell stack. The electrical output was measured via a potentiostat.

Alston, T.; Kendall, K.; Palin, M.; Prica, M.; Windibank, P.

228

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

229

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

230

Effects of passive films on corrosion resistance of uncoated SS316L bipolar plates for proton exchange membrane fuel cell application  

NASA Astrophysics Data System (ADS)

The effects of passive films on the corrosion behaviors of uncoated SS316L in anode and cathode environments of proton exchange membrane fuel cells (PEMFCs) are studied. Potentiodynamic and potentiostatic polarizations are employed to study the corrosion behavior; Mott-Schottky measurements are used to characterize the semiconductor properties of passive films; X-ray photoelectron spectroscopy (XPS) analyses are used to identify the compositions and the depth profiles of passive films. The passive films formed in the PEMFC anode and cathode environments under corresponding conditions both behave as n-type semiconductor. The passive film formed in the anode environment has a single-layer structure, Cr is the major element (Cr/Fe atomic ratio > 1), and the Cr/Fe atomic ratio decreases from the surface to the bulk; while the passive film formed in the PEMFC cathode environment has a bi-layer structure, Fe is the major element (Cr/Fe atomic ratio < 0.5), and in the external layer of the bi-layer structure Fe content increases rapidly and gradually in the internal layer. SS316L shows better corrosion resistance owing to both the high content of Cr oxide in the passive film and low band bending in normal PEMFC anode environments.

Yang, Ying; Ning, Xiaohui; Tang, Hongsheng; Guo, Liejin; Liu, Hongtan

2014-11-01

231

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

232

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

233

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

234

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

235

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. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 185-193, 2015. PMID:24616416

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

2015-01-01

236

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

237

Immobilization of rat brain acetylcholinesterase on porous gold-nanoparticle-CaCO? hybrid material modified Au electrode for detection of organophosphorous insecticides.  

PubMed

An acetylcholinesterase (AChE) purified from rat brain was immobilized onto gold nanoparticles (AuNPs) assembled on the surface of porous calcium carbonate (CaCO(3)) microsphere. The resulting AChE-AuNPs-CaCO(3) bioconjugate was mounted on the surface of Au electrode with the help of silica sol-gel matrix to prepare the working electrode. This electrode was connected to Ag/AgCl (3M/saturated KCl) as standard and Pt wire as an auxiliary electrode through a potentiostat to construct an organophosphorus (OP) biosensor. The biosensor was based on inhibition of AChE by OP compounds/insecticides. The biosensor showed optimum response at pH 7.0, 30°C, when polarized at +0.2V. Two OP compounds, malathion and chlorpyrifos could be detected in the range of 0.1-100 nM and 0.1-70 nM, respectively at 2.0-3.0% inhibition level of AChE. The sensor was reactivated by immersing it in 0.1 mM 2-pyridine aldoxime for 10 min. The detection limit of the sensor was 0.1 nM for both malathion and chlorpyrifos. The biosensor exhibited good reusability (50 times without considerable loss) and storage stability (50% within 60 days, when stored at 4°C). PMID:21856330

Chauhan, Nidhi; Narang, Jagriti; Pundir, C S

2011-12-01

238

The electrocatalytic hydrogenation of glucose; 1: Kinetics of hydrogen evolution and glucose hydrogenation on Raney nickel powder  

SciTech Connect

The kinetics of H[sub 2] evolution and glucose reduction to sorbitol was investigated using a batch slurry reactor containing Raney nickel powder catalyst. In the presence and absence of glucose, hydrogen evolution proceeds via a Volmer-Heyrovsky mechanism, with both steps simultaneously rate controlling at low overpotentials and the Volmer reaction rate limiting at high cathodic overvoltages. A kinetic model for the electrocatalytic hydrogenation of glucose with simultaneous H[sub 2] generation was developed and tested. The model contains rate equations for the individual Volmer, Heyrovsky, and glucose hydrogenation steps, a Langmuir adsorption isotherm for glucose, an equation describing the shift in open-circuit potential due to glucose adsorption on the nickel catalyst, and steady-state atomic hydrogen and charge balance relationships. The theory accurately predicted potentiostatic polarization data and glucose hydrogenation rates. The results indicate that the mechanism for sorbitol formation with electrogenerated atomic hydrogen on Raney nickel is the same as that for the high temperature and pressure chemical catalytic hydrogenation process.

Anantharaman, V.; Pintauro, P.N. (Tulane Univ., New Orleans, LA (United States). Dept. of Chemical Engineering)

1994-10-01

239

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

NASA Astrophysics Data System (ADS)

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

Wagner, N.; Gülzow, E.

240

Simultaneous analysis of dopamine and homovanillic acid by high-performance liquid chromatography with wall-jet/thin-layer electrochemical detection.  

PubMed

Wall-jet/thin-layer amperometric electrochemical detection (ECD) coupled with high-performance liquid chromatography (HPLC) was used here for the simultaneous analysis of dopamine (DA) and homovanillic acid (HVA) at a glassy carbon electrode. Compared with the conventional thin-layer mode and wall-jet mode, the presented wall-jet/thin-layer ECD has the advantages of enhanced capture of electroactive DA and HVA on the working electrode to give enhanced responses and more convenient washing/refreshment of the working electrode surface. Under optimized conditions, the HPLC-ECD calibration curves show good linearity from 0.01 to 100 ?M for DA and HVA, and the limits of detection (LODs) obtained were 1.1 nM for DA and 0.7 nM for HVA which are lower than those obtained with an UV-vis detector and a commercial electrochemical detector. The method was tested on human urine with satisfactory results. The balance of response-signal, signal-background and noise level for our HPLC-ECD system is also discussed. In addition, a demethylation electrooxidation mechanism for HVA is suggested through potentiostatic bulk electrolysis, electrospray ionization-mass spectrometry, fluorescent spectrophotometry and cyclic voltammetry studies. PMID:24116372

Zhou, Yaping; Yan, Hongling; Xie, Qingji; Huang, Siyu; Liu, Jiali; Li, Zou; Ma, Ming; Yao, Shouzhuo

2013-12-01

241

Determination of ?-Potential and Tortuosity in Rat Organotypic Hippocampal Cultures from Electroosmotic Velocity Measurements under Feedback Control  

PubMed Central

Extracellular translational motion in the brain is generally considered to be governed by diffusion and tortuosity. However, the brain as a whole has a significant ?-potential, thus translational motion is also governed by electrokinetic effects under a naturally occurring or applied electric field. We have previously measured ?-potential and tortuosity in intact brain tissue, however the method was tedious. In this work, we use a four-electrode potentiostat to control the potential difference between two microreference electrodes in the tissue, creating a constant electric field. Additionally, some alterations have been made simplify our previous procedure. The method entails simultaneously injecting two 70 kDa dextran conjugated fluorophores into rat organotypic hippocampal cultures and observing their mobility using fluorescence microscopy. We further present two methods of data analysis: regression and two-probe analysis. Statistical comparisons are made between the previous and current methods as well as between the two data analysis methods. In comparison to the previous method, the current, simpler method with data analysis by regression gives statistically indistinguishable mean values of ?-potential and tortuosity, with a similar variability for ?-potential, ?21.3 ± 2.8 mV, and a larger variability for the tortuosity, 1.98 ± 0.12. On the other hand, we find that the current method combined with the two-probe analysis produces accurate and more precise results, with a ?-potential of ?22.8 ± 0.8 mV and a tortuosity of 2.24 ± 0.10. PMID:19298057

Guy, Yifat; Muha, Robert J.; Sandberg, Mats; Weber, Stephen G.

2009-01-01

242

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

243

Effects of concentration-dependent elastic modulus on the diffusion of lithium ions and diffusion induced stress in layered battery electrodes  

NASA Astrophysics Data System (ADS)

A stress assisted diffusion model considering concentration-dependent elastic modulus of active material has been established for the multi-layered electrodes of lithium batteries. The physical mechanism for the effect of modulus variation on the Li-ion diffusion and corresponding biaxial stress is well elucidated. Moreover, the analytic solutions of maximum stress in both active layer and collector are respectively derived. It has been found that the modulus stiffening gives rise to the additional stress gradient and enhances Li-ion diffusion, therefore to increase the biaxial stress in the plate electrode. In contrast, modulus softening makes the stress assisted diffusion less significant and the corresponding stresses are reduced. These coupled effects are more significant during potentiostatic charging and galvanostatic charging with high charging rates. Moreover, the maximum stress in the active layer is independent of charging process, but depends upon the elastic modulus variation due to Li-ion insertion. Finally, with increasing thickness ratio between collector and active material, the impacts of concentration dependent modulus on the Li-ion diffusion in active layer decreases, whereas this effect on maximum stress in the current collector increases.

He, Y.-L.; Hu, H. J.; Song, Y.-C.; Guo, Z.-S.; Liu, C.; Zhang, J.-Q.

2014-02-01

244

New Ni xMg 6- xMnO 8 Mixed Oxides as Active Materials for the Negative Electrode of Lithium-Ion Cells  

NASA Astrophysics Data System (ADS)

New mixed oxides with an Ni xMg 6- xMnO 8 ( x=0, 2, 4, 5 and 6) stoichiometry and NaCl-related structure have been prepared by heating mixed oxalate precursors at 600°C. The existence of a solid solution was confirmed by the decrease of the cubic unit-cell parameter when magnesium was substituted by nickel. The solids were used as electrode materials in lithium cells, which were potentiostatically cycled. The structural transformations during reaction with lithium have been studied by ex-situ X-ray diffraction. A maximum value of ca. 20 F mol -1 is found during the first discharge of Ni 6MnO 8 electrodes. Annealing the non-crystalline discharged electrodes at 600°C allows to detect metallic nickel. While Ni 5MgMnO 8 improves capacity retention as compared with pure nickel, the extended substitution of nickel by magnesium leads to a progressive decrease in cell capacity. The reversible capacity values of ?640 mA h g -1 are explained in terms of the formation of Ni oxide that reacts with lithium reversibly. The potential in which the cell current peaks occur decreases on increasing the Mg content.

Alcántara, R.; Jaraba, M.; Lavela, P.; Tirado, J. L.

2002-07-01

245

Biomass-modified carbon paste electrodes for monitoring dissolved metal ions.  

PubMed

Electrodes were prepared by incorporating dried, nonliving biomass of a common lichen, Ramalina stenospora, and Sphagnum (peat) moss in carbon paste. The electrodes were tested on solutions containing Pb(II) and Cu(II) ions by immersing the electrode in the solution for selected periods of time to accumulate ions. Following this the electrode was connected to a potentiostat and the applied voltage scanned from -1.0 to +0.5 V vs. SCE. Any adsorbed metal ions were stripped back into solution at the appropriate oxidizing voltage. The ratio of biomass to mineral oil to graphite has been found to be crucial to electrode performance. Different ratios of the three components using the lichen Ramalina stenospora were evaluated for maximum electrode performance. Only two electrode compositions gave a good electrode response for lead. Electrodes containing peat moss were superior in performance to lichen-containing electrodes for lead. Electrodes based on the lichens Cladina evansii and Letharia vulpina, the marine algae Ulva lactuca and Sargassum fluitans, the blue-green alga Spirulina platensis, and the aquatic plant Eichhornia crassipes did not respond to lead at all. All functioning electrodes studies showed a poor response toward copper(II) ions. PMID:18967106

Yao, H; Ramelow, G J

1998-04-01

246

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

247

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

248

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

249

Amperometric determination of xanthine in fish meat by zinc oxide nanoparticle/chitosan/multiwalled carbon nanotube/polyaniline composite film bound xanthine oxidase.  

PubMed

Xanthine oxidase (XOD) was immobilized on a composite film of zinc oxide nanoparticle/chitosan/carboxylated multiwalled carbon nanotube/polyaniline (ZnO-NP/CHIT/c-MWCNT/PANI) electrodeposited over the surface of a platinum (Pt) electrode. A xanthine biosensor was fabricated using XOD/ZnO-NP/CHIT/c-MWCNT/PANI/Pt as working electrode, Ag/AgCl as reference electrode and Pt wire as auxiliary electrode connected through a potentiostat. The ZnO-NPs were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the enzyme electrode was characterized by cyclic voltammetry, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS). The biosensor showed optimum response within 4 s at 0.5 V potential, pH 7.0, 35 °C and linear range 0.1-100 ?M with a detection limit of 0.1 ?M. The enzyme electrode was employed for determination of xanthine in fish meat during storage. The electrode lost 30% of its initial activity after 80 uses over one month, when stored at 4 °C. PMID:22135777

Devi, Rooma; Yadav, Sandeep; Pundir, C S

2012-02-01

250

Controllable fabrication and modulations on oxide nanotube arrays toward high performance solar cells  

NASA Astrophysics Data System (ADS)

TiO2 nanotubes have been now an attractive nanostructured material due to their unique opto-electronic catalytic ability, compatibility to particle materials and feasibility to fabricate. However, these advantages were usually limited by morphological and structural defects from the electrochemical anodization method. More detailed understandings of the tube formation process are also needed. We have systematically investigated the tube formation with varying conditions. Beside discovery of new nanosphere structure, we have systematically investigated the spontaneous oscillating phenomena in potentiostatic anodization of TiO2 tubes. Consequently, we have established a novel comprehensive physical and chemical method that effectively influences the morphology and structural properties of TiO2 nanotubes. With assistance of periodical anodic voltage and moderate mechanical stirring, the efficiency of dye sensitized solar cells (DSSCs) can be significantly enhanced. For instance, the efficiency of DSSC with small TiO2 islands in the anode can be 114% higher than the control sample. This method has also turned the efficiency of DSSC with TiO2 nanotubes by low temperature current annealing into announceable value (from 2.05% to 3.51%).

Liu, Hong; Tao, Liang; Xiong, Yan; Shen, Wenzhong

2013-12-01

251

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

252

Direct electrochemical sensor for label-free DNA detection based on zero current potentiometry.  

PubMed

A direct electrochemical DNA biosensor based on zero current potentiometry was fabricated by immobilization of ssDNA onto gold nanoparticles (AuNPs) coated pencil graphite electrode (PGE). One ssDNA/AuNPs/PGE was connected in series between clips of working and counter electrodes of a potentiostat, and then immersed into the solution together with a reference electrode, establishing a novel DNA biosensor for specific DNA detection. The variation of zero current potential difference (?E(zcp)) before and after hybridization of the self-assembled probe DNA with the target DNA was used as a signal to characterize and quantify the target DNA sequence. The whole DNA biosensor fabrication process was characterized by cyclic voltammetry and electrochemical impedance spectroscopy with the use of ferricyanide as an electrochemical redox indicator. Under the optimized conditions, ?E(zcp) was linear with the concentrations of the complementary target DNA in the range from 10nM to 1?M, with a detection limit of 6.9nM. The DNA biosensor showed a good reproducibility and selectivity. Prepared DNA biosensor is facile and sensitive, and it eliminates the need of using exogenous reagents to monitor the oligonucleotides hybridization. PMID:22884003

Wu, Nai-ying; Gao, Wei; He, Xu-lun; Chang, Zhu; Xu, Mao-tian

2013-01-15

253

A novel automated electrochemical ascorbic acid assay in the 24-well microtiter plate format.  

PubMed

Automatic ascorbic acid (AA) voltammetry was established in 24-well microtiter plates. The assay used a movable assembly of a pencil rod working, an Ag/AgCl reference and a Pt counter electrode with differential pulse voltammetry (DPV) for concentration-dependent current generation. A computer was in command of electrode (z) and microtiter plate (x, y) positioning and timed potentiostat operation. Synchronization of these actions supported sequential approach of all wells and subsequent execution of electrode treatment procedures or AA voltammetry at defined intervals in a measuring cycle. DPV in well solutions offered a linear current/concentration range between 0.1 and 8.0 mM, a sensitivity of about 1 ?A mM(-1) AA, and a detection limit of 50 ?M. When used with a calibration curve or standard addition, automated voltammetry of samples with added known amounts of AA demonstrated good recovery rates. Also, the assay achieved the accurate determination of the AA content of vitamin C tablets, a fruit juice and an herbal tea extract. Robotic AA voltammetry has the advantage of conveniently handling multiple samples in a single measuring run without the continuous attention of laboratory personnel. It is a good option when the goal is cost-effective AA screening of sample libraries and has potential for applications in health care and the food processing, cosmetic and pharmaceutical industries. PMID:21241840

Intarakamhang, Sireerat; Leson, Christian; Schuhmann, Wolfgang; Schulte, Albert

2011-02-14

254

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

255

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

256

Electrodeposition and Characterization of Yttrium Barium Copper Oxide Superconducting Thin Films  

NASA Astrophysics Data System (ADS)

Precursor thin films of Y-Ba-Cu-O superconductor were produced by potentiostatic and pulse electrodeposition from the dissolved nitrate salts of Y, Ba, Cu in dimethylformamide (DMF). The films were deposited on metal foils such as Ag-coated Cu, Ag, Ni, and Zr. Films were also synthesized on Ag-coated SrTiO_3, CaTiO _3, and Al_2O _3. The electrodeposited films were heat treated in flowing O_2 in order to produce the superconducting phase. The film composition as a function of the salt concentration in DMF was determined by energy dispersive x-ray analysis. Surface compositions were obtained by Auger electron spectroscopy. Crystal structure and phases were identified by means of x-ray diffraction. The superconducting dimagnetic behaviour has been observed in magnetic measurements. Films formed by pulse plating on the titanates and on Zr exhibited the best uniformity with highest T_{rm c}. Y-Ba-Cu-O films formed on Zr had highest T_{rm c} onset at 93 K (resistance measurement). The pulse plating process was extended to the synthesis of Er-Ba-Cu-O films. On Zr, the latter resulted in a T_{rm c} onset at 80 K.

Weston, Alan James

257

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

258

Short-term canine implantation of a glucose monitoring-telemetry device.  

PubMed

In this study we report the development and short-term in vivo evaluation of an integrated implantable device consisting of an amperometric glucose biosensor, a miniature potentiostat, a FM signal transmitter, and power supply. The device (dimensions: 5.0 x 7.0 x 1.5 cm) was implanted under the skin of medium-size anaesthetized dog. The experimental set-up included several methods for data collection: analog recording via wired X-T chart recorders; data collection by wearable microprocessor--data logger, and remote data collection via antenna and receiver linked to a computer-based data acquisition system. The device (sensor) performance was evaluated in vitro prior to implantation, using different model solutions simulating the physiological environment. A linear response to glucose concentration was obtained up to 25 mM glucose, with a sensitivity of 0.5 microA/mM. The results of short-term subcutaneous implantation of the integrated device reveal adequate monitoring of an artificially-induced glycaemia. The delay-time was 3-7 minutes. These tests demonstrate the feasibility of data transmission by the telemetry system through the skin of a medium-sized dog and allow the commencement of chronic in vivo experimentation. PMID:8953555

Atanasov, P; Yang, S; Salehi, C; Ghindilis, A L; Wilkins, E

1996-12-01

259

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

PubMed

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. PMID:23887746

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

2013-09-01

260

The influence of dichromate ions on aluminum dissolution kinetics in artificial crevice electrode cells  

SciTech Connect

Dissolution kinetics for pits and crevices in aluminum and the effect of dichromate ions on the dissolution kinetics were investigated by using artificial crevice electrodes. The aluminum artificial crevice electrodes were potentiostatically polarized over a range of potential in 0.1 M NaCl solution with and without dichromate ions. The anodic dissolution charge, and cathodic charges for the hydrogen and dichromate reduction reactions, were measured. The addition of dichromate ions did not suppress the active dissolution. This indicates that the mechanism of localized corrosion inhibition by dichromates is something other than anodic inhibition of Al dissolution in the pit or crevice environment. The relative amount of local cathodic reactions on Al was increased by the addition of dichromate because of the dichromate reduction. The initial dissolution of aluminum in a crevice was ohmic controlled. From the change in the dissolution current with time, the conductivity of the crevice and potential at the bottom of crevice were estimated. The conductivity and the bottom potential decreased with the ratio of cathodic charge of hydrogen evolution to anodic dissolution charge. The conductivity in the crevice and thus the dissolution current seem to be controlled by hydrogen evolution and only indirectly by dichromate concentration.

Akiyama, E.; Frankel, G.S.

1999-11-01

261

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

SciTech Connect

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

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

2009-08-05

262

Assessment of corrosion rate in prestressed concrete with acoustic emission  

NASA Astrophysics Data System (ADS)

Acoustic Emission (AE) sensing was employed to assess the rate of corrosion of steel strands in small scale concrete block specimens. The corrosion process was accelerated in a laboratory environment using a potentiostat to supply a constant potential difference with a 3% NaCl solution as the electrolyte. The embedded prestressing steel strand served as the anode, and a copper plate served as the cathode. Corrosion rate, half-cell potential measurements, and AE activity were recorded continuously throughout each test and examined to assess the development of corrosion and its rate. At the end of each test the steel strands were cleaned and re-weighed to determine the mass loss and evaluate it vis-á-vis the AE data. The initiation and propagation phases of corrosion were correlated with the percentage mass loss of steel and the acquired AE signals. Results indicate that AE monitoring may be a useful aid in the detection and differentiation of the steel deterioration phases, and estimation of the locations of corroded areas.

Mangual, Jesé; ElBatanouny, Mohamed K.; Vélez, William; Ziehl, Paul; Matta, Fabio; González, Miguel

2011-04-01

263

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

264

Photocatalytic degradation of gaseous toluene over Ag-doping TiO? nanotube powder prepared by anodization coupled with impregnation method.  

PubMed

In this work, Ag-doping TiO(2) nanotubes were prepared and employed as the photocatalyst for the degradation of toluene. The TiO(2) nanotube powder was produced by the rapid-breakdown potentiostatic anodization of Ti foil in chloride-containing electrolytes, and then doped with Ag through an incipient wetness impregnation method. The samples were characterized by scanning electron microscope, high-resolution transmission electron microscopy, X-ray diffraction, surface photovoltage measurements, X-ray photoelectron spectroscopy and N(2) adsorption. The nanotubular TiO(2) photocatalysts showed an outer diameter of approximately 40nm, fine mesoporous structure and high specific surface area. The photocatalytic activity of Ag-doping TiO(2) nanotube powder was evaluated through photooxidation of gaseous toluene. The results indicated that the degradation efficiency of toluene could get 98% after 4h reaction using the Ag-doping TiO(2) nanotubes as the photocatalyst under UV light illumination, which was higher than that of the pure TiO(2) nanotubes, Ag-doping P25 or P25. Benzaldehyde species could be observed during the photocatalytic oxidation monitored by in situ FTIR, and the formed benzaldehyde intermediate during reaction would be partially oxidized into CO(2) and H(2)O. PMID:21435692

Li, Xinyong; Zou, Xuejun; Qu, Zhenping; Zhao, Qidong; Wang, Lianzhou

2011-04-01

265

Hybrid pulse anodization for the fabrication of porous anodic alumina films from commercial purity (99%) aluminum at room temperature.  

PubMed

Most porous anodic alumina (PAA) or anodic aluminum oxide (AAO) films are fabricated using the potentiostatic method from high-purity (99.999%) aluminum films at a low temperature of approximately 0-10 degrees C to avoid dissolution effects at room temperature (RT). In this study, we have demonstrated the fabrication of PAA film from commercial purity (99%) aluminum at RT using a hybrid pulse technique which combines pulse reverse and pulse voltages for the two-step anodization. The reaction mechanism is investigated by the real-time monitoring of current. A possible mechanism of hybrid pulse anodization is proposed for the formation of pronounced nanoporous film at RT. The structure and morphology of the anodic films were greatly influenced by the duration of anodization and the type of voltage. The best result was obtained by first applying pulse reverse voltage and then pulse voltage. The first pulse reverse anodization step was used to form new small cells and pre-texture concave aluminum as a self-assembled mask while the second pulse anodization step was for the resulting PAA film. The diameter of the nanopores in the arrays could reach 30-60 nm. PMID:19417342

Chung, C K; Zhou, R X; Liu, T Y; Chang, W T

2009-02-01

266

Iron oxide nanotube layer fabricated with electrostatic anodization for heterogeneous Fenton like reaction.  

PubMed

Iron oxide nanotubes (INT) were fabricated with potentiostatic anodization of zero valent iron foil in 1M Na2SO4 containing 0.5wt% NH4F electrolyte, holding the potential at 20, 40, and 60V for 20min, respectively. Field emission scanning electron microscopy and X-ray diffractometry were used to evaluate the morphology and crystalline structure of the INT film. The potential of 40V for 20min was observed to be optimal to produce an optimal catalytic film. Cyanide dissolved in water was degraded through the Fenton-like reaction using the INT film with hydrogen peroxide (H2O2). In case of INT-40V in the presence of H2O2 3%, the first-order rate constant was found to be 1.7×10(-2)min(-1), and 1.2×10(-2)min(-1) with commercial hematite powder. Degradation of cyanide was much less with only H2O2. Therefore, this process proposed in this work can be an excellent alternative to traditional catalysts for Fenton-like reaction. PMID:24704548

Jang, Jun-Won; Park, Jae-Woo

2014-05-30

267

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

268

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

269

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

SciTech Connect

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

Orzalli, J.C.

1994-05-01

270

Effect of composition on corrosion resistance of high-alloy austenitic stainless steel weld metals  

SciTech Connect

The corrosion resistance of stainless steel weld metal in the ranges of 17 to 28% chromium (Cr), 6 to 60% nickel (Ni), 0 to 9% molybdenum (Mo), and 0.0 to 0.37% nitrogen (N) was examined. Critical pitting temperatures were determined in ferric chloride (FeCl[sub 3]). Passive film breakdown potentials were assessed from potentiodynamic scans in 3% sodium chloride (NaCl) at 50 C. Potentiodynamic and potentiostatic tests were carried out in 30% sulfuric acid (H[sub 2]SO[sub 4]) ar 25 C, which was representative of chloride-free acid media of low redox potential. Metallographic examination and microanalysis were conducted on the test welds. Because of segregation of alloying elements, weld metal pitting resistance always was lower than that of matching composition base steel. The difference increased with higher Cr, Mo, and N contents. Segregation also reduced resistance to general corrosion in H[sub 2]SO[sub 4], but the effect relative to the base steel was less marked than with chloride pitting. Segregation of Cr, Mo, and N in fully austenitic deposits decreased as the Ni[prime][sub eq-]Cr[prime][sub eq] ratio increased. Over the compositional range studied, weld metal pitting resistance was dependent mainly on Mo content and segregation. N had less effect than in wrought alloys. Both Mo and N enhanced weld metal corrosion resistance in H[sub 2]SO[sub 4].

Marshall, P.I. (British Aerospace, Bristol (United Kingdom)); Gooch, T.G. (Welding Inst., Cambridge (United Kingdom))

1993-06-01

271

Galvanic corrosion of dental cobalt-chromium alloys and dental amalgam in artificial saliva.  

PubMed

When two or more metals or alloys are placed in contact with one another inside the oral cavity, galvanic coupling may occur which may lead to galvanic corrosion. Galvanic corrosion may release elements from the alloy into the oral cavity with possible harm to the patient. This in vitro study was conducted to determine the extent of galvanic corrosion where different dental amalgams and Co-Cr alloy combinations were placed in contact with artificial saliva as an electrolyte. The tests were conducted with potential measurements as well as potentiodynamic and potentio-static polarisation techniques. Results showed that the galvanic corrosion current density is much lower than the corrosion current density, indicating that galvanic coupling of the samples does not have a substantial effect on the overall corrosion of the samples. The corrosion potential differences between three of the four couples were above the minimum 50 mV potential difference, which is considered a potential harmful level, with only the Wironium Plus and Dispersalloy combination being under 50 mV potential difference. It is concluded that: Galvanic corrosion does not pose a greater threat to the alloys than ordinary corrosion. A Wironium Plus and Dispersalloy combination may be the safest where a Co-Cr and amalgam combination is required in the mouth of a patient. PMID:18543740

van Vuuren, L Jansen; Odendaal, J S J; Pistorius, P C

2008-02-01

272

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

PubMed

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

González, M; Peña, J; Gil, F J; Manero, J M

2014-09-01

273

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

274

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

275

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

276

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

277

Effect of annealing on properties of ZrSe 2 thin films  

NASA Astrophysics Data System (ADS)

Thin films of ZrSe 2 have been prepared on stainless steel and fluorine-doped tin oxide-coated glass substrates using electrodeposition technique at potentiostatic mode. Double-distilled water containing precursors Zr and Se with ethylene diamine tetra-acetic acid disodium salt as a complexing agent was used to obtain good quality deposits by controlling the rate of reaction. The preparative parameters such as concentration of bath, deposition time, bath temperature, pH of the bath and annealing temperature have been optimized using photoelectrochemical (PEC) technique. The films deposited at optimum preparative parameters are annealed at different temperatures. The film annealed at 200 °C shows more photosensitivity. The as-deposited and annealed films at 200 °C have been characterized by X-ray diffraction (XRD), energy dispersive analysis by X-ray (EDAX), optical absorption and scanning electron microscopy (SEM). The XRD analysis of the as-deposited and annealed films showed the presence of polycrystalline nature with hexagonal crystal structure. EDAX study reveals that deposited films are almost stoichiometric. Optical absorption study shows the presence of direct transition and band gap energies are found to be 1.5 and 1.38 eV, respectively, for the as-deposited and annealed films. SEM study revels that the grains are uniformly distributed over the surface of substrate for the as-deposited as well as annealed film, which indicates formation of good and compact type of crystal structure.

Hankare, P. P.; Asabe, M. R.; Kokate, A. V.; Delekar, S. D.; Sathe, D. J.; Mulla, I. S.; Chougule, B. K.

2006-09-01

278

The effect of carbon nanotubes on the electrochemical hydrogen storage performance of LaNi 5 rare earth alloy  

NASA Astrophysics Data System (ADS)

We have investigated the electrochemical hydrogen storage performances of LaNi 5 electrodes doped with carbon nanotubes (CNTs); the CNTs were prepared by chemical vapor deposition using a rare earth alloy as catalyst in a C 2H 2/H 2 atmosphere. A three-electrode system was introduced; the above electrodes were used as the cathodes of the electronic cell, NiOOH/Ni(OH) 2 as the anodes, and Hg/HgO as the reference electrodes. A 6 M aqueous KOH solution was introduced as the electrolyte. When the LaNi 5 electrode was doped with 10% carbon nanotubes to its active material, it had a capacity of 407 mAh/g under the charge/discharge current density 200 and 100 mA/g, respectively. The discharge voltage limit was set as 0 V. The discharge trend is steadier while discharge plateau is improved to 0.875 V. Furthermore, we compared the electrochemical hydrogen storage capability of the LaNi 5 electrodes doped with different ratios of CNTs (15%, 10%, 7% and 5%) under the same charge/discharge condition and found that the optimum doped quantity of CNTs is 10% in our experiment confines. The polarization peculiarity of each electrode was tested by the Transistor Potentiostat, which exhibited that LaNi 5 electrodes doped with CNTs of different ratios have different electrochemical activation character.

Fu, Xiaojuan; Zhang, Haiyan; Chen, Yiming; Li, Shunhua; Yi, Shuangping; Zhou, Chun; Li, Minghua; Zhu, Yanjuan; Chen, Jin

2005-01-01

279

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

280

In situ electrochemical STM study of platinum nanodot arrays on highly oriented pyrolythic graphite prepared by electron beam lithography  

NASA Astrophysics Data System (ADS)

Model electrodes consisting of platinum dots with a mean diameter of (30 ± 5) nm and heights of 3-5 nm upon highly oriented pyrolytic graphite (HOPG) were prepared by electron beam lithography and subsequent sputtering. The Pt nanodot arrays were stable during scanning tunnelling microscopy (STM) measurements in air and in sulphuric acid electrolyte, indicating the presence of "anchors", immobilising the dots on the HOPG surface. Electrochemical STM was used to visualise potential induced Pt, carbon and Pt-influenced carbon corrosion in situ in 0.5 M sulphuric acid under ambient conditions. Potentiostatic hold experiments show that the Pt dots start to disappear at electrode potentials of E > 1.4 V vs. SHE. With increasing time and potential a hole pattern congruent to the original dot pattern appears on the HOPG basal planes. Corrosion and peeling of the HOPG substrate could also be followed in situ. Dissolution of Pt dots appears to be accelerated for potential cycling experiments compared to the potential hold statistics.

Foelske-Schmitz, A.; Peitz, A.; Guzenko, V. A.; Weingarth, D.; Scherer, G. G.; Wokaun, A.; Kötz, R.

2012-12-01

281

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

282

Electrically evoking and electrochemically resolving quantal release on a microchip.  

PubMed

A microchip was applied to electrically depolarize rat pheochromocytoma (PC12) cells and to simultaneously detect exocytotic catecholamine release amperometrically. Results demonstrate exocytosis elicited by flowing cells through an electric field generated by a potentiostat circuit in a microchannel, as well as exocytosis triggered by application of an extracellular voltage pulse across. Electrical finite element model (FEM) analysis illustrated that larger cells experienced greater depolarizing excitation from the extracellular electric fields due to the smaller shunt path and higher resistance to current flow in the channel around the cell. Consistent with these simulations, data recorded from cell clusters and large cells exhibited increased release rates relative to data from the smaller cells. Overall, the system was capable of resolving single vesicle quantal release, in the zeptomole range, as well as the kinetics associated with the vesicle fusion process. Analysis of spike population statistics suggested detection of catecholamines from multiple release sites around the cells. The potential for such a device to be used in flow cytometry to evoke and detect exocytosis was demonstrated. PMID:20024047

Dittami, Gregory M; Rabbitt, Richard D

2010-01-01

283

Electrical Conductivity Measurement and Anisotropy of Mylonite and Cataclasite  

NASA Astrophysics Data System (ADS)

Resent studies of electromagnetic survey reveal the electrical conductivity structure at the deeper part of faults. There seems to be high conductivity region around the focal areas. The high conductivity may be related to the existence of water in rocks, which affect the strength and activity of faults, i.e., earthquake. Investigations on the electrical conductivity structure suggest important clues on the mechanism and conditions of earthquake occurrence. Rocks at the focal zone of a fault are expected to suffer from hard deformation and/or fracturing with alteration. Rocks have characteristic fabrics. They are called fault-related rocks, such as mylonite and cataclasite. We collected mylonite and cataclasite samples from the Hatagawa fracture zone in northeast Japan. The Hatagawa fracture zone is regarded as a major exhumed fault. We can observe the mylonite and cataclasite at a surface now that were produced from granitic rocks at the focal depth region in the past. We conducted measurements of electrical conductivities of the fault-related rocks at ambient condition, as a first step. We connected a frequency response analyzer and a potentiostat to measure AC impedance spectra. The combination of the two instruments performs sine wave correlation between signals passing trough a sample and a reference resistance. In addition, the potentiostat can measure a micro current. As a result, the measurement system is basically resistant to an electrical noise around the sample under severe condition and is able to measure up to 109 ? . We observed clearly foliations and lineations in mylonite samples. We cut each mylonite sample into three cylindrical chips parallel to three directions: parallel to both the foliation and the lineation (x-axis), parallel to the foliation and perpendicular to the lineation (y-axis), perpendicular to the foliation (z-axis). We did not observe any planar or linear fabric on the cataclasite samples. Porosities of the samples were less than 1 %. The conductivities at 1 Hz of samples under dry condition (samples are heated at 120 degree C for 6 hours) are about 10-8 1/? m and have little difference among samples. Under wet condition at the same frequency (samples were forcibly saturated by distilled water in a vacuum chamber), conductivities of all samples increased by more than one order of magnitude, but conductivities along three direction of mylonite are significantly different. The conductivity along x-axis and y -axis was higher by about one order and several times, respectively, than that along z-axis. This result suggests the distribution and connectivity of cracks in mylonite are anisotropic and more conductive water than rock matrix connected along x-axis. At focal deep region along a fault, cracks must be compacted, but, if thin sheets of water are distributed anisotropically in mylonite zone, some anisotropic conductivity structure may be detected.

Omura, K.

2001-12-01

284

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

285

Electrochemical properties of suprastructures galvanically coupled to a titanium implant.  

PubMed

In recent years, dental implants have been widely used for the aesthetic and functional restoration of edentulous patients. Dental implants and restorative alloys are required with high corrosion resistance. Suprastructures and implants of different compositions in electrical contact may develop galvanic or coupled corrosion problems. In addition to galvanic corrosion, crevice and pitting corrosion may occur in the marginal gap between dental implant assemblies. In this study, gold, silver-palladium, cobalt-chromium, and nickel-chromium suprastructures were used to investigate their galvanic and crevice corrosion characteristics in combination with titanium (Ti) implants. Potentiodynamic and potentiostatic testing were performed in artificial saliva at 37 degrees C. Potentiodynamic testing was carried out at the potential scan rate of 1 mV/s in the range of -600-1600 mV (SCE). Potentiostatic testing was performed with an open-circuit potential and current densities at -250, 0, and 250 mV (SCE) in artificial saliva. After electrochemical testing, surface morphologies and cross-sections were examined using micrographs of the samples. Potentiodynamic test results indicated that suprastructure/Ti implant couples produced passive current densities in the range of 0.5-12 microA/cm(2); Ti abutment/Ti implant and gold/Ti implant couples exhibited relatively low passive current densities; Co-Cr/Ti implant couples the highest. Co-Cr and Ni-Cr/Ti implant couples showed breakdown potentials of 700 and 570 mV (SCE), respectively. The open-circuit potentials of silver, Ti abutment, gold, Ni-Cr, and Co-Cr/Ti implant couples were -93.2 +/- 93.9, -123.7 +/- 58.8, -140.0 +/- 80.6, -223.5 +/- 35.1, and -312.7 +/- 29.8 mV (SCE), respectively, and did not change with immersion time. The couples exhibited cathodic current densities at -250 mV (SCE); in particular, gold and silver alloys showed high cathodic current densities of -3.18 and -6.63 microA/cm(2), respectively. At 250 mV (SCE), Ti abutment/Ti implant couples exhibited a minimum current density of 9.48 x 10(-2) microA/cm(2), but gold, Ni-Cr, Co-Cr, and silver/Ti implant couples exhibited 0.313, 1.27, 5.60, and 8.06 microA/cm(2), respectively. All couples exhibited relatively low current densities at 0 mV (SCE). Photomicrographs after electrochemical testing showed crevice or pitting corrosion in the marginal gap and at the suprastructure surface. Although of the tested samples Co-Cr/Ti implant couples showed the possibility of galvanic corrosion, its degree was not significant. However, it should be borne in mind that galvanic corrosion can accelerate localized corrosion, such as crevice or pitting corrosion. PMID:15264315

Oh, Keun-Taek; Kim, Kyoung-Nam

2004-08-15

286

Reduction of CO2 to low carbon alcohols on CuO FCs/Fe2O3 NTs catalyst with photoelectric dual catalytic interfaces  

NASA Astrophysics Data System (ADS)

In this paper, the CuO FCs/Fe2O3 NTs catalyst was obtained after Fe2O3 nanotubes (Fe2O3 NTs) were decorated with CuO flower clusters (CuO FCs) by the pulse electrochemical deposition method. The in situ vertically aligned Fe2O3 NTs were prepared on the ferrous substrate by a potentiostatic anodization method. The SEM result showed the volcano-like Fe2O3 NTs were arranged in order and the CuO FCs constituted of flaky CuO distributed on the Fe2O3 NTs surface uniformly. After CuO FCs were loaded on Fe2O3 NTs, the absorption of visible light was enhanced noticeably, and its band gap narrowed to 1.78 eV from 2.03 eV. The conduction band and valence band locating at -0.73 eV and 1.05 eV, respectively were further obtained. In the PEC reduction of CO2 process, methanol and ethanol were two major products identified by chromatography. Their contents reached 1.00 mmol L-1 cm-2 and 107.38 ?mol L-1 cm-2 after 6 h, respectively. This high-efficiency catalyst with photoelectric dual catalytic interfaces has a great guidance and reference significance for CO2 reduction to liquid carbon fuels.In this paper, the CuO FCs/Fe2O3 NTs catalyst was obtained after Fe2O3 nanotubes (Fe2O3 NTs) were decorated with CuO flower clusters (CuO FCs) by the pulse electrochemical deposition method. The in situ vertically aligned Fe2O3 NTs were prepared on the ferrous substrate by a potentiostatic anodization method. The SEM result showed the volcano-like Fe2O3 NTs were arranged in order and the CuO FCs constituted of flaky CuO distributed on the Fe2O3 NTs surface uniformly. After CuO FCs were loaded on Fe2O3 NTs, the absorption of visible light was enhanced noticeably, and its band gap narrowed to 1.78 eV from 2.03 eV. The conduction band and valence band locating at -0.73 eV and 1.05 eV, respectively were further obtained. In the PEC reduction of CO2 process, methanol and ethanol were two major products identified by chromatography. Their contents reached 1.00 mmol L-1 cm-2 and 107.38 ?mol L-1 cm-2 after 6 h, respectively. This high-efficiency catalyst with photoelectric dual catalytic interfaces has a great guidance and reference significance for CO2 reduction to liquid carbon fuels. Electronic supplementary information (ESI) available: Reduction of CO2 to low carbon alcohols on CuO FCs/Fe2O3 NTs catalyst with photoelectric dual catalytic interfaces. See DOI: 10.1039/c3nr03352j

Li, Peiqiang; Wang, Huying; Xu, Jinfeng; Jing, Hua; Zhang, Jun; Han, Haixiang; Lu, Fusui

2013-11-01

287

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

288

Determination of the critical potentials for pitting, protection, and stress corrosion cracking of 67-33 brass in fluoride solutions  

SciTech Connect

Pitting potentials and protection potentials have been determined for {alpha}-brass (33% Zn) using a cyclic polarization method. Increasing the F{sup {minus}} concentration shifts the critical potential to more active values. The pitting potentials, E{sub p}, and protection potentials, E{sub pp}, depend on the logarithmic concentration of F{sup {minus}} ions according to the equations: E{sub p} = a + b log [F{sup {minus}}] and E{sub pp} = a + b log [F{sup {minus}}]. Slow strain rate tests (SSRT), at a strain rate of 5 {times} 10{sup {minus}5} s{sup {minus}1}, were performed under open-circuit and potentiostatic conditions to study the stress corrosion cracking (SCC) characteristics of the {alpha}-brass in NaF solutions of various concentrations (pH 6.8) at 25 C. The minimum concentration of NaF that caused intergranular stress corrosion cracking (IGSCC) was 1 {times} 10{sup {minus}4} M. This concentration, was also the critical level for repassivation, observed in cyclic polarization tests. These results demonstrate a good correlation between the electrical and the mechanical breakdown of the passive film. In the presence of 10{sup {minus}1}M NaF the potential range for IGSCC was {minus}150 to {minus}50 mV (SCE). These critical potentials were restricted to the stable passive potential range and also fell within the potential-pH region where Cu{sub 2}O was stable. The formation of a Cu{sub 2}O film on the brass after polarization in the passive region was confirmed by X-ray diffraction (XRD). At more noble potentials and at cathodic potentials below the Cu{sub 2}O domain, the failure mode was ductile fracture. These observations of IGSCC of the brass in fluoride solutions support a film rupture-dissolution mechanism.

Lee, C.K.; Shih, H.C. [National Tsing Hua Univ., Hsinchu (Taiwan, Province of China). Dept. of Materials Science and Engineering

1995-03-01

289

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

PubMed

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

Gemene, Kebede L; Meyerhoff, Mark E

2010-03-01

290

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

NASA Astrophysics Data System (ADS)

High-bandwidth and low-noise nanopore sensor and detection electronics are crucial in achieving single-DNA-base resolution. A potential way to accomplish this goal is to integrate solid-state nanopores within a CMOS platform, in close proximity to the biasing electrodes and custom-designed amplifier electronics. Here we report the integration of solid-state nanopore devices in a commercial complementary metal-oxide-semiconductor (CMOS) potentiostat chip implemented in On-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.

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

2013-04-01

291

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

PubMed

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

2013-04-19

292

PdNi- and Pd-coated electrodes prepared by electrodeposition from ionic liquid for nonenzymatic electrochemical determination of ethanol and glucose in alkaline media.  

PubMed

Nonenzymatic electrochemical determination of ethanol and glucose was respectively achieved using PdNi- and Pd-coated electrodes prepared by electrodeposition from the novel metal-free ionic liquid (IL); N-butyl-N-methylpyrrolidinium dicyanamide (BMP-DCA). BMP-DCA provided an excellent environment and wide cathodic limit for electrodeposition of metals and alloys because many metal chlorides could dissolve in this IL where the reduction potentials of Pd(II) and Ni(II) indeed overlapped, leading to the convenience of potentiostatic codeposition. In aqueous solutions, the reduction potentials of Pd(II) and Ni(II) are considerably separated. The bimetallic PdNi coatings with atomic ratios of ? 80/20 showed the highest current for ethanol oxidation reaction (EOR). Ethanol was detected by either cyclic voltammetry (CV) or hydrodynamic amperometry (HA). Using CV, the dependence of EOR peak current on concentration was linear from 4.92 to 962 ?M with a detection limit of 2.26 ?M (?=3), and a linearity was observed from 4.92 to 988 ?M using HA (detection limit 0.83 ?M (?=3)). The Pd-coated electrodes prepared by electrodeposition from BMP-DCA showed electrocatalytic activity to glucose oxidation and CV, HA, and square-wave voltammetry (SWV) were employed to determine glucose. SWV showed the best sensitivity and linearity was observed from 2.86 ?M to 107 ?M, and from 2.99 mM to 10.88 mM with detection limits of 0.78 ?M and 25.9 ?M (?=3), respectively. For glucose detection, the interference produced from ascorbic acid, uric acid, and acetaminophen was significantly suppressed, compared with a regular Pt disk electrode. PMID:21111149

Huang, Hsin-Yi; Chen, Po-Yu

2010-12-15

293

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

294

Trap-governed hydrogen diffusivity and uptake capacity in ultrahigh-strength AERMET 100 steel  

NASA Astrophysics Data System (ADS)

The hydrogen-uptake capacity and mobility in ultrahigh-strength AERMET 100 are characterized for various electrochemical charging and baking conditions. From thermal desorption spectroscopy, the apparent hydrogen diffusivity ( D H < 3 × 10-8 cm2/s at 23 °C) is over tenfold less than the values typical of tempered martensitic steels such as AISI 4130. The value of D H decreases with decreasing temperature below 200 °C, with a relatively high apparent activation energy for diffusion of 17.7 to 18.8 ± 0.2 kJ/mol at the 95 pct confidence level. The value of D H also decreases with decreasing diffusible H concentration from less-severe charging or increased baking. Potentiostatic charging in saturated Ca(OH)2 produced total and diffusible H concentrations in AERMET 100 which increase with (H+/H) overpotential and are significantly higher than results for AISI 4130 steel under the same conditions. A significant H concentration was produced by zero overpotential deposition. These characteristics are explained by extensive reversible and irreversible H trapping involving at least three unique trap states in the ultrafine AERMET 100 microstructure. The former likely include coherent M2C carbides, soluble Ni, or precipitated austenite, and the latter include larger incoherent M x C y or martensite lathed-packet interfaces. Baking at 23 °C and 200 °C removes H from the lowest binding-energy sites, but results in reduced D H levels to prolong outgassing time. Additionally, substantial H was retained in stronger trap states. These trapping effects are pertinent to hydrogen embrittlement of AERMET 100 steel.

Thomas, Richard L. S.; Li, Daoming; Gangloff, Richard P.; Scully, John R.

2002-07-01

295

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

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

296

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

297

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

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

298

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

299

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

PubMed

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

Zhang, Wei; Yang, Tao; Jiao, Kui

2012-01-15

300

Impedance study of tea with added taste compounds using conducting polymer and metal electrodes.  

PubMed

In this study the sensing capabilities of a combination of metals and conducting polymer sensing/working electrodes for tea liquor prepared by addition of different compounds using an impedance mode in frequency range 1 Hz-100 KHz at 0.1 V potential has been carried out. Classification of six different tea liquor samples made by dissolving various compounds (black tea liquor + raw milk from milkman), (black tea liquor + sweetened clove syrup), (black tea liquor + sweetened ginger syrup), (black tea liquor + sweetened cardamom syrup), (black tea liquor + sweet chocolate syrup) and (black tea liquor + vanilla flavoured milk without sugar) using six different working electrodes in a multi electrode setup has been studied using impedance and further its PCA has been carried out. Working electrodes of Platinum (Pt), Gold (Au), Silver (Ag), Glassy Carbon (GC) and conducting polymer electrodes of Polyaniline (PANI) and Polypyrrole (PPY) grown on an ITO surface potentiostatically have been deployed in a three electrode set up. The impedance response of these tea liquor samples using number of working electrodes shows a decrease in the real and imaginary impedance values presented on nyquist plots depending upon the nature of the electrode and amount of dissolved salts present in compounds added to tea liquor/solution. The different sensing surfaces allowed a high cross-selectivity in response to the same analyte. From Principal Component Analysis (PCA) plots it was possible to classify tea liquor in 3-4 classes using conducting polymer electrodes; however tea liquors were well separated from the PCA plots employing the impedance data of both conducting polymer and metal electrodes. PMID:23035436

Dhiman, Mopsy; Kapur, Pawan; Ganguli, Abhijit; Singla, Madan Lal

2012-09-01

301

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.

302

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

303

Characterization of Nonmetallic Inclusions in High-Manganese and Aluminum-Alloyed Austenitic Steels  

NASA Astrophysics Data System (ADS)

The effects of Al and Mn contents on the size, composition, and three-dimensional morphologies of inclusions formed in Fe- xMn- yAl ( x = 10 and 20 mass pct, y = 1, 3, and 6 mass pct) steels were investigated to enhance our understanding of the inclusion formation behavior in high Mn-Al-alloyed steels. By assuming that the alumina is a dominant oxide compound, the volume fraction of inclusions estimated from the chemical analysis, i.e., insoluble Al, in the Fe-Mn-3Al steels was larger than the inclusion volume fractions in the Fe-Mn-1Al and Fe-Mn-6Al steels. A similar tendency was found in the analysis of inclusions from a potentiostatic electrolytic extraction method. This finding could be explained from the terminal velocities of the compounds, which was affected by the thermophysical properties of Fe-Mn-Al steels. The inclusions formed in the Fe-Mn-Al-alloyed steels are classified into seven types according to chemistry and morphology: (1) single Al2O3 particle, (2) single AlN or AlON particle, (3) MnAl2O4 single galaxite spinel particle, (4) Al2O3(-Al(O)N) agglomerate, (5) single Mn(S,Se) particle, (6) oxide core with Mn(S,Se) skin (wrap), and (7) Mn(S,Se) core with Al2O3(-Al(O)N) aggregate (or bump). The Mn(S,Se) compounds were formed by the contamination of the steels by Se from the electrolytic Mn. Therefore, the raw materials (Mn) should be used carefully in the melting and casting processes of Fe-Mn-Al-alloyed steels.

Park, Joo Hyun; Kim, Dong-Jin; Min, Dong Joon

2012-07-01

304

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

305

Polyaniline and poly(flavin adenine dinucleotide) doped multi-walled carbon nanotubes for p-acetamidophenol sensor.  

PubMed

A conductive biocomposite film (MWCNTs-PANIFAD) which contains multi-walled carbon nanotubes (MWCNTs) along with the incorporation of poly(aniline) and poly(flavin adenine dinucleotide) co-polymer (PANIFAD) has been synthesized on gold and screen printed carbon electrodes by potentiostatic methods. The presence of MWCNTs in the MWCNTs-PANIFAD biocomposite film enhances the surface coverage concentration (Gamma) of PANIFAD and increases the electron transfer rate constant (k(s)) to 89%. Electrochemical quartz crystal microbalance studies reveal the enhancements in the functional properties of MWCNTs and PANIFAD present in MWCNTs-PANIFAD biocomposite film. Surface morphology of the biocomposite film has been studied using scanning electron microscopy and atomic force microscopy. The surface morphology results reveal that PANIFAD incorporated on MWCNTs. The MWCNTs-PANIFAD biocomposite film exhibits promising enhanced electrocatalytic activity towards the oxidation of p-acetamidophenol. The cyclic voltammetry has been used for the measurement of electroanalytical properties of p-acetamidophenol by means of PANIFAD, MWCNTs and MWCNTs-PANIFAD biocomposite film modified gold electrodes. The sensitivity value of MWCNTs-PANIFAD film (88.5 mA mM(-1)cm(-2)) is higher than the values which are obtained for PANIFAD (28.7 mA mM(-1)cm(-2)) and MWCNTs films (60.7 mA mM(-1)cm(-2)). Finally, the flow injection analysis (FIA) has been used for the amperometric detection of p-acetamidophenol at MWCNTs-PANIFAD film modified screen printed carbon electrode. The sensitivity value of MWCNTs-PANIFAD film (3.3 mA mM(-1)cm(-2)) in FIA is also higher than the value obtained for MWCNTs film (1.1 mA mM(-1)cm(-2)). PMID:19559909

Li, Ying; Umasankar, Yogeswaran; Chen, Shen-Ming

2009-07-15

306

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

307

Comparing atrazine and cyanuric acid electro-oxidation on mixed oxide and boron-doped diamond electrodes.  

PubMed

The breakdown of pesticides has been promoted by many methods for clean up of contaminated soil and wastewaters. The main goal is to decrease the toxicity of the parent compound to achieve non-toxic compounds or even, when complete mineralization occurs, carbon dioxide and water. Therefore, electrochemical degradation (potentiostatic and galvanostatic) of both the pesticide atrazine and cyanuric acid (CA) at boron-doped diamond (BDD) and Ti/Ru0.3Ti0.7O2 dimensionally stable anode (DSA) electrodes, in different supporting electrolytes (NaCl and Na2SO4), is presented with the aim of establishing the influence of the operational parameters on the process efficiency. The results demonstrate that both the electrode material and the supporting electrolyte have a strong influence on the rate of atrazine removal. In the chloride medium, the rate of atrazine removal is always greater than in sulfate under all conditions employed. Furthermore, in the sulfate medium, atrazine degradation was significant only at the BDD electrode. The total organic carbon (TOC) load decreased by 79% and 56% at the BDD and DSA electrodes, respectively, in the chloride medium. This trend was maintained in the sulfate medium but the TOC removal was lower (i.e. 33% and 13% at BDD and DSA electrodes, respectively). CA, a stable atrazine degradation intermediate, was also studied and it is efficiently removed using the BDD electrode in both media, mainly when high current densities are employed. The use of the BDD electrode in the chloride medium not only degrades atrazine but also mineralized cyanuric acid leading to the higher TOC removal. PMID:23837356

Malpass, Geoffroy R P; Salazar-Banda, Giancarlo R; Miwa, Douglas W; Machado, Sérgio A S; Motheo, Artur J

2013-01-01

308

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

309

Angstrom-resolved real-time dissection of electrochemically active noble metal interfaces.  

PubMed

Electrochemical solid|liquid interfaces are critically important for technological applications and materials for energy storage, harvesting, and conversion. Yet, a real-time Angstrom-resolved visualization of dynamic processes at electrified solid|liquid interfaces has not been feasible. Here we report a unique real-time atomistic view into dynamic processes at electrochemically active metal interfaces using white light interferometry in an electrochemical surface forces apparatus. This method allows simultaneous deciphering of both sides of an electrochemical interface-the solution and the metal side-with microsecond resolution under dynamically evolving reactive conditions that are inherent to technological systems in operando. Quantitative in situ analysis of the potentiodynamic electrochemical oxidation/reduction of noble metal surfaces shows that Angstrom thick oxides formed on Au and Pt are high-ik materials; that is, they are metallic or highly defect-rich semiconductors, while Pd forms a low-ik oxide. In contrast, under potentiostatic growth conditions, all noble metal oxides exhibit a low-ik behavior. On the solution side, we reveal hitherto unknown strong electrochemical reaction forces, which are due to temporary charge imbalance in the electric double layer caused by depletion/generation of charged species. The real-time capability of our approach reveals significant time lags between electron transfer, oxide reduction/oxidation, and solution side reaction during a progressing electrode process. Comparing the kinetics of solution and metal side responses provides evidence that noble metal oxide reduction proceeds via a hydrogen adsorption and subsequent dissolution/redeposition mechanism. The presented approach may have important implications for designing emerging materials utilizing electrified interfaces and may apply to bioelectrochemical processes and signal transmission. PMID:24826945

Shrestha, Buddha R; Baimpos, Theodoros; Raman, Sangeetha; Valtiner, Markus

2014-06-24

310

The electrochemical behaviors of Mg-8Li-3Al-0.5Zn and Mg-8Li-3Al-1.0Zn in sodium chloride solution  

NASA Astrophysics Data System (ADS)

The electrochemical oxidation behaviors of Mg-8Li-3Al-0.5Zn and Mg-8Li-3Al-1.0Zn electrodes in 0.7 mol L-1 NaCl solution are investigated by methods of potentiodynamic polarization, potentiostatic oxidation, electrochemical impedance spectroscopy and scanning electron microscopy. The phase composition of Mg-8Li-3Al-0.5Zn and Mg-8Li-3Al-1.0Zn alloys is analyzed conducted by X-ray diffraction. The performances of Mg-8Li-3Al-0.5Zn and Mg-8Li-3Al-1.0Zn as the anode of Mg-H2O2 semi fuel cells are determined. The effect of Zn content on the corrosion resistant of these Mg-Li-based alloys is studied. It is found that the Mg-8Li-3Al-0.5Zn electrode has higher discharge activity and less corrosion resistance than that of Mg-8Li-3Al-1.0Zn electrode in 0.7 mol L-1 NaCl solution. The Mg-H2O2 semi fuel cell with Mg-8Li-3Al-0.5Zn anode presents a maximum power density of 100 mW cm-2 at room temperature, which is higher than that of Mg-8Li-3Al-1.0Zn anode (80 mW cm-2). The performance of semi fuel cell with the Mg-8Li-3Al-0.5Zn electrode is better than that with Mg-8Li-3Al-1.0Zn electrode, especially at higher current density (>30 mA cm-2).

Lv, Yanzhuo; Liu, Min; Xu, Yan; Cao, Dianxue; Feng, Jing

2013-03-01

311

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

PubMed

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 (Gamma) of PMG to approximately 396%, and increases the electron transfer rate constant (k(s)) to approximately 305%. Similarly, electrochemical quartz crystal microbalance study reveals the enhancement in the deposition of PMG at MWCNTs-NF film. The surface morphology of the composite film deposited on ITO electrode has been studied using scanning electron microscopy (SEM) and scanning tunneling microscopy (STM). These two techniques reveal that the PMG incorporated on MWCNTs-NF film. The MWCNTs-NF-PMG composite film also exhibits promising enhanced electrocatalytic activity towards the simple aliphatic alcohols such as methanol, ethanol and propanol. The electroanalytical responses of analytes at NF-PMG and MWCNTs-NF-PMG films were measured using both cyclic voltammetry (CV) and differential pulse voltammetry (DPV). From electroanalytical studies, well defined voltammetric peaks have been obtained at MWCNTs-NF-PMG composite film for methanol, ethanol and propanol at Epa=609, 614 and 602mV respectively. The sensitivity of MWCNTs-NF-PMG composite film towards methanol, ethanol and propanol in CV technique are 0.59, 0.36 and 0.92microAmM(-1)cm(-2) respectively, which are higher than NF-PMG film. Further, the sensitivity values obtained using DPV are higher than the values obtained using CV technique. PMID:20006058

Umasankar, Yogeswaran; Periasamy, Arun Prakash; Chen, Shen-Ming

2010-01-15

312

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

PubMed

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

DeWitt, Stephen; Thornton, Katsuyo

2014-05-13

313

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

314

A Miniaturized Transcutaneous System for Continuous Glucose Monitoring  

PubMed Central

Implantable sensors for continuous glucose monitoring hold great potential for optimal diabetes management. This is often undermined by a variety of issues associated with: (1) negative tissue response; (2) poor sensor performance; and (3) lack of device miniaturization needed to reduce implantation trauma. Herein, we report our initial results towards constructing an implantable device that simultaneously address all three aforementioned issues. In terms of device miniaturization, a highly miniaturized CMOS (complementary metal-oxide-semiconductor) potentiostat and signal processing unit was employed (with a combined area of 0.665 mm2). The signal processing unit converts the current generated by a transcutaneous, Clark-type amperometric sensor to output frequency in a linear fashion. The Clark-type amperometric sensor employs stratification of five functional layers to attain a well-balanced mass transfer which in turn yields a linear sensor response from 0 to 25 mM of glucose concentration, well beyond the physiologically observed (2 to 22 mM) range. In addition, it is coated with a thick polyvinyl alcohol (PVA) hydrogel with embedded poly(lactic-co-glycolic acid) (PLGA) microspheres intended to provide continuous, localized delivery of dexamethasone to suppress inflammation and fibrosis. In vivo evaluation in rat model has shown that the transcutaneous sensor system reproducibly tracks repeated glycemic events. Clarke’s error grid analysis on the as –obtained glycemic data has indicated that all of the measured glucose readings fell in the desired Zones A & B and none fell in the erroneous Zones C, D and E. Such reproducible operation of the transcutaneous sensor system, together with low power (140 ?W) consumption and capability for current-to-frequency conversion renders this a versatile platform for continuous glucose monitoring and other biomedical sensing devices. PMID:22992979

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

2012-01-01

315

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

316

Electrochemical cortisol immunosensors based on sonochemically synthesized zinc oxide 1D nanorods and 2D nanoflakes.  

PubMed

We report on label free, highly sensitive and selective electrochemical immunosensors based on one-dimensional 1D ZnO nanorods (ZnO-NRs) and two-dimensional 2D ZnO nanoflakes (ZnO-NFs) which were synthesized on Au-coated substrates using simple one step sonochemical approach. Selective detection of cortisol using cyclic voltammetry (CV) is achieved by immobilizing anti-cortisol antibody (Anti-Cab) on the ZnO nanostructures (NSs). 1D ZnO-NRs and 2D ZnO-NFs provide unique sensing advantages over bulk materials. While 1D-NSs boast a high surface area to volume ratio, 2D-NSs with large area in polarized (0001) plane and high surface charge density could promote higher Anti-Cab loading and thus better sensing performance. Beside large surface area, ZnO-NSs also exhibit higher chemical stability, high catalytic activity, and biocompatibility. TEM studies showed that both ZnO-NSs are single crystalline oriented in (0001) plane. The measured sensing parameters are in the physiological range with a sensitivity of 11.86µA/M exhibited by ZnO-NRs and 7.74µA/M by ZnO-NFs with the lowest detection limit of 1pM which is 100 times better than conventional enzyme-linked immunosorbant immunoassay (ELISA). ZnO-NSs based cortisol immunosensors were tested on human saliva samples and the performance were validated with conventional (ELISA) method which exhibits a remarkable correlation. The developed sensors can be integrated with microfluidic system and miniaturized potentiostat for point-of-care cortisol detection and such developed protocol can be used in personalized health monitoring/diagnostic. PMID:25064820

Vabbina, Phani Kiran; Kaushik, Ajeet; Pokhrel, Nimesh; Bhansali, Shekhar; Pala, Nezih

2015-01-15

317

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.

2014-01-01

318

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

319

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. Biotechnol. Bioeng. 2014;111: 1931-1939. © 2014 Wiley Periodicals, Inc. PMID:24729040

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

2014-10-01

320

Apparatus for in situ monitoring of copper in coastal waters.  

PubMed

Apparatus is designed and tested to determine metals in situ in seawater. Voltammetry with a vibrating gold microwire electrode (VGME) is combined with a battery powered potentiostat and a processor board and is tested for in situ monitoring of copper (Cu) in coastal waters. The VGME was combined with solid state reference and counter electrodes to make a single vibrating probe which was rated up to a depth of 40 m. The measuring mode for Cu was square-wave anodic stripping voltammetry whilst dissolved oxygen (DO) was monitored by a linear sweep scan in a negative potential direction. The working electrode was reactivated between measurements using a suitable potential sequence. The novelties of this work are the field-testing of apparatus incorporating a VGME for copper monitoring, which eliminates the need for pumping and reagents, but has sufficient sensitivity for low ambient levels of copper, and the use of a novel potential sequence to stabilise the response over a long time period. The apparatus has a measuring time of about 6 weeks and a measuring frequency of 12 h(-1). Measurement is reagent-free and power use is low as no pump is required. Experiments are carried out to test the stability of response of the system at various temperatures and its robustness with respect to long-term copper monitoring. Preliminary data were obtained during autonomous deployment over several weeks on a buoy in the Irish Sea. Vertical movement of the buoy caused individual measurements to have a variability of about 15%. It was found that longer term variability of the electrode could be minimised by normalisation of the Cu response over that of DO as the response was related to diffusion through the electrode surface which was similarly affected. The detected fraction of Cu (labile Cu) amounted to 1.5-4 nM during different deployments at a total Cu concentration of ?10 nM. The same ratio was found by voltammetry in samples taken to the laboratory. The new apparatus has demonstrated that metals in coastal waters can be monitored at trace level, much facilitating the monitoring of outfalls and local water contamination. Because of its sensitivity the apparatus would be of use in estuarine as well as coastal waters, with the aim of monitoring intermittent variability in the copper concentration. PMID:22983404

Chapman, Conrad S; Cooke, Richard D; Salaün, Pascal; van den Berg, Constant M G

2012-10-26

321

Well-defined ultrathin palladium films on platinum(111): Electrochemical preparation and interfacial chemistry  

NASA Astrophysics Data System (ADS)

Well-defined ultrathin films of palladium, with coverages ranging from submonolayer, thetaPd = 0.5 monolayer (ML), to multilayer, theta Pd = 8 ML, were electrochemically deposited on Pt(111) using potentiostatic and potentiodynamic methods. In both methods, between the coverage regimes studied, the growth of the Pd films follows the Stranski-Krastanov mechanism. The interfacial electrochemical properties associated with the film-to-bulk transition were characterized by conventional voltammetric techniques in combination with low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). The voltammetric peaks associated with H-atom adsorption and desorption on terrace sites indicate that the Pd electrodeposit starts to exhibit bulk-like properties at a coverage of 3 ML. Voltammetric cycling, in sulfuric acid solution, between the hydrogen evolution and the double-layer regions, was found to exert minimal influence on the annealing (smoothening) of the electrodeposited Pd films. However, cycling within the same potential region in the presence of bromide anions (at which Br- adsorption/Br desorption takes place) smoothens the initially rough Pd films essentially as well as high-temperature annealing. The influence of chemisorbed bromine on the anodic dissolution of Pd was also studied; this was for comparison with previous work on the anodic dissolution of Pd, in inert electrolyte, catalyzed by chemisorbed iodine. The present studies indicated that a small but measurable amount of bromine was desorbed along with dissolution of the Pd step atoms; bromine at the Pd terrace behaved identically to iodine in that the coverage of iodine is maintained regardless of the amount or origin of the anodically stripped Pd. Atomically smooth, well-defined ultrathin Pd films were prepared by a constant potential deposition (CPD) method followed by multiple potential cycles, in dilute Br- solution, within the double-layer region and reductive removal of Brads, by simple emersion at a potential just before the hydrogen evolution reaction potential (EHER ). A previously adapted method for the same purpose involved the chemisorption of iodine onto ultrathin PdCPD films, from dilute I- solution, followed by reductive desorption of Iads in iodide-free solution at pH 10 and at a potential just before EHER.

Park, Yeon Su

322

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

NASA Astrophysics Data System (ADS)

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

Song, Li

323

Investigations on the corrosion resistance of metallic bipolar plates (BPP) in proton exchange membrane fuel cells (PEMFC) - understanding the effects of material, coating and manufacturing  

NASA Astrophysics Data System (ADS)

Polymer Electrolyte Membrane Fuel Cell (PEMFC) systems are promising technology for contributing to meet the deficiency of world`s clean and sustainable energy requirements in the near future. Metallic bipolar plate (BPP) as one of the most significant components of PEMFC device accounts for the largest part of the fuel cell`s stack. Corrosion for metallic bipolar plates is a critical issue, which influences the performance and durability of PEMFC. Corrosion causes adverse impacts on the PEMFC`s performance jeopardizing commercialization. This research is aimed at determining the corrosion resistance of metallic BPPs, particularly stainless steels, used in PEMFC from different aspects. Material selection, coating selection, manufacturing process development and cost considerations need to be addressed in terms of the corrosion behavior to justify the use of stainless steels as a BPP material in PEMFC and to make them commercially feasible in industrial applications. In this study, Ti, Ni, SS304, SS316L, and SS 430 blanks, and BPPs comprised of SS304 and SS316L were examined in terms of the corrosion behavior. SS316L plates were coated to investigate the effect of coatings on the corrosion resistance performance. Stamping and hydroforming as manufacturing processes, and three different coatings (TiN, CrN, ZrN) applied via the Physical Vapor Deposition (PVD) method in three different thicknesses were selected to observe the effects of manufacturing processes, coating types and coating thicknesses on the corrosion resistance of BPP, respectively. Uncoated-coated blank and formed BPP were subjected to two different corrosion tests: potentiostatic and potentiodynamic. Some of the substantial results: 1- Manufacturing processes have an adverse impact on the corrosion resistance. 2- Hydroformed plates have slightly higher corrosion resistance than stamped samples. 3- BPPs with higher channel size showed better corrosion resistance. 4- Since none of the uncoated samples meet the 2015 target of the U.S. Department of Energy, surface coating is required. 5- ZrN and CrN coated BPPs exhibited higher corrosion resistance meeting DOE target while TiN coated samples had the lowest corrosion resistance. Higher coating thicknesses improved the corrosion resistance of the BPPs. 6- Process sequence between coating and manufacturing is not significant for hydroforming case (ZrN and CrN) and stamping case (CrN) in terms of the corrosion resistance. In other words, coating the BPP`s substrate material before manufacturing process does not always decrease the corrosion resistance of the BPPs.

Dur, Ender

324

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

325

Fabrication of nanocrystalline aluminum-magnesium alloy powders by electrodeposition and their characterization  

NASA Astrophysics Data System (ADS)

Aluminum-magnesium alloy powders can potentially be used as hydrogen storage materials. In order to enhance the kinetics of hydrogenation it is desirable to have agglomerates of fine powders with very small grain size. In this study, nanocrystalline Al-Mg alloys in the form of powders were successfully fabricated by the electrodeposition technique using an organometallic based electrolyte. Mg was introduced into the electrolyte by a process called "pre-electrodeposition". The mechanism for Mg accumulation can be explained considering the electrode reactions as well as the chemical changes in the electrolyte. Using a copper cathode, the effects of the electrolyte composition and current density on composition of the deposit, its constituent phases and morphology were investigated. The magnesium content of the deposits improved with increasing Mg concentration in the electrolyte, temperature and current density. Depending on the composition, the deposits consisted of FCC-Al(Mg) and HCP-Mg(Al) phases and no intermetallic phase was found except for long deposition times. Generally, the deposits formed initially on the copper substrate with three dendritic morphologies namely, rod-like, feather-like and small globular, which eventually evolved into the large globular morphology. This observation is attributed to the establishment of spherical diffusion conditions at the sharp dendrite tips. Potentiostatic studies suggested that the appearance of different morphologies is associated with differing rates of deposition. While the initial dendrites consisted of the FCC Al-rich phase, the large globular morphology manifested as both FCC Al-rich and HCP Mg-rich phases, with the latter always forming over the former. The observation of formation of only the FCC phase implies that the nucleation barrier for the HCP phase on the copper substrate is quite high. The investigation of the effect of substrate, namely, Cu, graphite and Mg, revealed that the HCP phase can directly nucleate on an oxide-free Mg surface. This finding can be explained in terms of surface/interfacial energies. Detailed TEM analysis revealed that the observed morphologies consist of randomly distributed nanocrystalline grains except for the feather-like dendrites, which exhibited a strong crystallographic texture.

Tatiparti, Sankara Sarma V.

326

Chromate-free corrosion inhibition of aluminum alloys: Vanadates and anionic exchange clay pigments  

NASA Astrophysics Data System (ADS)

In this study, aqueous vanadates and vanadate pigments were studied for possible use as chromate replacements to inhibit corrosion of Al 2024-T3. Vanadate inhibition on Al 2024-T3 was characterized as a function of pH and concentration using anodic and cathodic polarization experiments and scanning electron microscopy (SEM). The results showed a strong correlation between inhibition and the availability of tetrahedrally coordinated vanadate species in test solutions. In particular, solutions containing predominately tetrahedrally coordinated vanadates were observed to act as modest anodic inhibitors and to reduce cathodic kinetics through the suppression of oxygen reduction kinetics. Further, the effect of these tetrahedral vanadates on individual intermetallic particles commonly found in Al 2024-T3 was characterized using a microcapillary electrode. Tetrahedral vanadates were generally found to increase breakdown potentials and decrease cathodic kinetics on all tested materials. Open circuit potential (OCP) was observed to shift in the active direction as a result of decreased cathodic kinetics, just below the observed breakdown potential of Al2CuMg; a phase that plays a critical role in corrosion susceptibility of Al 2024-T3. OCP measurements, SEM images, and potentiostatic hold experiments were used to show suppressed Al2CuMg dissolution and damage accumulation in vanadate solutions. Furthermore, synthetic hydrotalcite anion exchange clay pigments were synthesized with vanadates and other possible inhibitor anions. Hydrotalcites allow the use of inhibitors that are too soluble for direct use in organic coatings without leading to coating blistering. A number of hydrotalcite pigments were synthesized and compared to a SrCrO4 standard using electrochemical impedance spectroscopy and salt spray exposure of scribed organically coated panels. Typically, vanadate pigmented PVB coatings were observed to have total impedance within an order of magnitude of SrCrO4 (2 x 10 7 ohms cm2). Further, all vanadate coatings were observed to provide some scribe protection during 750 hours of salt spray exposure, however, these coatings also had a tendency to blister. Release from vanadate hydrotalcites was characterized using neutron activation analysis. Interestingly, vanadate hydrotalcite pigments that released relatively small total concentrations of vanadium resulted in the best performance. Low concentrations of vanadium may promote the formation of tetrahedrally coordinated species which were shown to act as inhibitors earlier in this study.

Ralston, Kevin Douglas

327

Electrochemical growth behavior, surface properties, and enhanced in vivo bone response of TiO2 nanotubes on microstructured surfaces of blasted, screw-shaped titanium implants  

PubMed Central

TiO2 nanotubes are fabricated on TiO2 grit-blasted, screw-shaped rough titanium (ASTM grade 4) implants (3.75 × 7 mm) using potentiostatic anodization at 20 V in 1 M H3PO4 + 0.4 wt.% HF. The growth behavior and surface properties of the nanotubes are investigated as a function of the reaction time. The results show that vertically aligned nanotubes of ?700 nm in length, with highly ordered structures of ?40 nm spacing and ?15 nm wall thickness may be grown independent of reaction time. The geometrical properties of nanotubes increase with reaction time (mean pore size, pore size distribution [PSD], and porosity ?90 nm, ?40–127 nm and 45%, respectively for 30 minutes; ?107 nm, ?63–140 nm and 56% for one hour; ?108 nm, ?58–150 nm and 60% for three hours). It is found that the fluorinated chemistry of the nanotubes of F-TiO2, TiOF2, and F-Ti-O with F ion incorporation of ?5 at.%, and their amorphous structure is the same regardless of the reaction time, while the average roughness (Sa) gradually decreases and the developed surface area (Sdr) slightly increases with reaction time. The results of studies on animals show that, despite their low roughness values, after six weeks the fluorinated TiO2 nanotube implants in rabbit femurs demonstrate significantly increased osseointegration strengths (41 vs 29 Ncm; P = 0.008) and new bone formation (57.5% vs 65.5%; P = 0.008) (n = 8), and reveal more frequently direct bone/cell contact at the bone–implant interface by high-resolution scanning electron microscope observations as compared with the blasted, moderately rough implants that have hitherto been widely used for clinically favorable performance. The results of the animal studies constitute significant evidence that the presence of the nanotubes and the resulting fluorinated surface chemistry determine the nature of the bone responses to the implants. The present in vivo results point to potential applications of the TiO2 nanotubes in the field of bone implants and bone tissue engineering. PMID:20463928

Sul, Young-Taeg

2010-01-01

328

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

329

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

330

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

NASA Astrophysics Data System (ADS)

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

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

2006-06-01

331

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.

332

The isotopic effects of electron transfer: an explanation for Fe isotope fractionation in nature  

NASA Astrophysics Data System (ADS)

Recent developments in mass spectrometry techniques have created opportunities to examine the partitioning behavior of stable isotopes of transition metals with a focus on application to iron isotopes. Iron oxidizing and reducing bacteria have been shown to cause isotope fractionations similar in magnitude to those observed in sedimentary environments and it is believed that biological activity is responsible for the most significant Fe isotope fractionation in natural settings. Debate over the use of Fe isotopes as a biological marker resulted from subsequent measurements of fractionations in a variety of abiotic systems. The accumulated evidence, in both biotic and abiotic systems, points to a connection between redox processes and Fe isotope fractionation, however the exact mechanism for isotope fractionation is not yet well understood. Here, we present both a newly-developed theory based on chemical kinetics and preliminary experimental results that quantitatively delineate the relationship between driving force in a charge transfer reaction and resulting Fe isotope fractionation. The theory, based on R. Marcus's chemical kinetics theory for electron transfer (Ann. Rev. Phys. Chem. 15 (1964), 155), predicts that fractionation increases linearly with driving force with a proportionality related to two factors: the difference between isotopic equilibrium exchange of products and reactants, and the reorganization energy along the reaction coordinate. The theoretical predictions were confirmed by measurements of isotopic fractionation associated with electroplating iron metal from a ferrous chloride solution. Isotope fractionation of Fe electroplated under potentiostatic conditions was measured as a function of applied electrochemical potential. As plating voltage was varied from -50 mV to -2.0 V, the isotopic signature of the electroplated iron became depleted in heavy Fe, with ? 56Fe values ranging from -0.106(±0.01) to -2.290(±±0.006)‰ , and corresponding ? 57Fe values of -0.145(±.011) and -3.354(±.019)‰ . The slope of the line created by plotting ? 56Fe vs ? 57Fe is equal to 0.6723(±.0032), consistent with fractionation due to a kinetic process involving unsolvated iron atoms. This study demonstrates that there is a voltage-dependent isotope fractionation associated with the reduction of iron. The magnitude of fractionation is similar to observations of Fe reduction by certain bacteria, suggesting that electrochemical processes may be responsible for observed biogeochemical signatures. Charge transfer is a fundamental physicochemical process involving Fe as well as other transition metals with multiple isotopes. Partitioning of isotopes among elements with varying redox states holds promise as a tool in a wide range of the Earth and environmental sciences, biology, and industry.

Kavner, A.; Shahar, A.; Bonet, F.; Simon, J. I.; Young, E.

2004-12-01

333

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

334

Microplasticity of surfaces and small volumes: Microstructural and environmental effects  

NASA Astrophysics Data System (ADS)

The present study utilizes contact mechanics techniques to address several critical aspects of micro/nanotribology. An emphasis is placed on scale, structure and environmental effects. Scale effects refer to the earliest stages of plastic deformation where continuum laws are no longer applicable. Structure effects involve complex relationships between microstructure and mechanical behavior. Environmental effects are manifested in changes of deformation and fracture under exposure to aggressive environments. Scale effect studies involved evaluation of the plasticity initiation in MgO and W single crystal materials utilizing AE monitored nanoindentation. Newly developed AE sensors incorporated into indenter tips (Hysitron, Inc.) provided greatly enhanced resolution and sensitivity to localized plasticity and fracture events at submicron indentation depths. Based on the analysis of indentation curves and AE waveforms associated with the yield initiation events, new insights into yield point phenomenon were gained. Microstructure effects were addressed with a newly developed mechanical property evaluation method. With this method, mechanical properties of brittle porous nanocrystalline SiC film on Mo substrate were derived from the complex indentation response involving densification and fracture. Evaluation of environmental effects involved deformation and fracture of bulk materials and interfaces. Indentation curve analysis combined with the AFM imaging of tested areas provided quantitative measures of hydrogen induced hardening and plastic strain localization in 316 stainless steel. A newly developed indentation based experimental procedure allowed quantitative evaluation of hydrogen effects for Cu/SiO2 interfaces with and without several nm thick Ti interlayers. Up to 50% reduction of the apparent practical work of adhesion was observed in Cu/Ti/SiO 2 films as revealed by indentation testing immediately after hydrogen charging. Finally, a novel approach for the in-situ evaluation of passive film stresses and growth kinetics was developed. It was demonstrated that the evolution of passive films and the stress acting in these films can be followed using a depth sensing continuous indentation into surfaces under potentiostatic control. Based on the recorded indenter tip displacement, time-dependent passive film thickness and stress can be determined with the proposed theoretical model.

Tymiak, Natalia Igorivna

335

Selective dissolution in copper-tin alloys: Formation of the surface finish on early Chinese bronze mirrors  

NASA Astrophysics Data System (ADS)

In the early part of the twentieth century, scientists began to look at ancient artifacts both for clues to the stability of metals and alloys, and for ways to preserve the objects themselves. Chinese bronze mirrors often have a smooth patina that preserves the fine detail in the original cast surface decoration. Mirrors appear early in Chinese history and were produced in large numbers starting during the final, Warring States, period of the Zhou dynasty (475--221 BC). The average composition of ancient mirrors is 70% copper, 25% tin and 5% lead, by weight. The microstructure is two-phase and consists of acicular alpha-phase (Cu-rich) regions encased in a delta-phase (Sn-rich) matrix. Although the mirrors have been labeled "corrosion-resistant," the smooth surface includes a corroded layer on the order of 100 mum thick. In this layer, known as the "altered layer," there is evidence of selective dissolution of the alpha-phase; the alpha-phase regions are replaced by a mineral product with the delta phase remaining metallic. The current project was undertaken to investigate and replicate the stable metal surface found on ancient bronzes. Electrochemical methods were used to study the corrosion behavior of the copper-tin system. The replication was performed on model, cast two-phase bronze by treating under constant applied potential in two solutions. The alpha phase corroded preferentially in both solutions duplicating the microstructure of the altered layer on ancient mirrors. Characterization of the patinas on ancient Chinese bronze mirrors and modern treated samples was performed with optical and electron microscopy, and synchrotron x-ray diffraction and fluorescence. The alpha-phase replacement product was found to be nanocrystalline tin oxide (SnO2) in both ancient and modern samples. The corrosion-resistance of the potentiostatically-treated bronze samples was tested by extended outdoor exposure. Comparison with exposed, untreated samples indicated that the treatment was protective. A better understanding of the processes that resulted in the smooth surfaces on ancient Chinese mirrors has been attained through the replication of the surface microstructure and composition under the controlled conditions of this work.

Taube, Michelle

336

Electrochemical growth of vertically-oriented high aspect ratio titania nanotubes by rabid anodization in fluoride-free media.  

PubMed

Vertically-oriented high aspect ratio titania nanotube bundles have been grown by a potentiostatic anodization of titanium sheet in fluoride-free electrolytes. The anodization conditions like the applied voltage were optimized for the synthesis of titania nanotubes in HClO4 and NaCl electrolyte. The resulting nanotubes have a length of about 30 microm, outer diameter about 40 nm, inner pore size of about 10 nm and the aspect ratio was 750:1 by anodization in 0.1 M perchloric acid of pH approximaately 1 at applied voltage of 20 V. While for nanotubes prepared in 0.3 M NaCl of pH 4.3, the length was above 50 microm with the aspect ratio of 1250:1. A method to increase the uniformity of nanotube was demonstrated by pretreatment the titanium sheet by (4 wt% HF + 5 M HNO3) solution prior to anodization. Titania nanotubes were prepared, for the first time, by anodization in aqueous H2SO4 electrolyte alone with tube length above 500 nm. Annealing studies were performed, on high aspect ratio Titania nanotube layers produced in HClO4 electrolyte, in the temperature interval of 300 to 550 degrees C. The XRD patterns and TEM data confirmed the formation of single anatase phase after annealing at 450 degrees C with perfect nanoubular structure. While the rutile titania phase starts to emerege after annealing at about 500 degrees C and the evidence for the appearance of rutile phase due to the oxidation of the underlying Ti metal at the interface between nanotube/Ti-metal was given. On the other hand, the nanotubular structure starts to destroy upon annealing temperature of approximate 550 degrees C by tube flattening and losing of roll-up characteristics as indicated in SEM images. The superior morphology of these high aspect ratio nanotubes and their rapid growth rate foreshadow a bright future in wide applications like dye-sensitized solar cells, water photolysis and nanobiomedical. PMID:19435043

Fahim, Narges Fathy; Sekino, Tohru; Morks, Magdi Farouk; Kusunose, Takafumi

2009-03-01

337

Predictive Framework and Experimental Tests of the Kinetic Isotope Effect at Redox-Active Interfaces  

NASA Astrophysics Data System (ADS)

Electrochemical reactions provide a compelling framework to study kinetic isotope effects because redox-related processes are important for a wide variety of geological and environmental processes. In the laboratory, electrochemical reaction rates can be electronically controlled and measured in the laboratory using a potentiostat. This enables variation of redox reactions rates independent of changes in chemistry and, and the resulting isotope compositions of reactants and products can be separated and analyzed. In the past years, a series of experimental studies have demonstrated a large, light, and tunable kinetic isotope effect during electrodeposition of metal Fe, Zn, Li, Cu, and Mo from a variety of solutions (e.g. Black et al., 2009, 2010, 2011). A theoretical framework based on Marcus kinetic theory predicts a voltage-dependent kinetic isotope effect (Kavner et al., 2005, 2008), however while this framework was able to predict the tunable nature of the effect, it was not able to simultaneously predict absolute reaction rates and relative isotope rates. Here we present a more complete development of a statistical mechanical framework for simple interfacial redox reactions, which includes isotopic behavior. The framework is able to predict a kinetic isotope effect as a function of temperature and reaction rate, starting with three input parameters: a single reorganization energy which describes the overall kinetics of the electron transfer reaction, and the equilibrium reduced partition function ratios for heavy and light isotopes in the product and reactant phases. We show the framework, elucidate some of the predictions, and show direct comparisons against isotope fractionation data obtained during laboratory and natural environment redox processes. A. Kavner, A. Shahar, F. Bonet, J. Simon and E. Young (2005) Geochim. Cosmochim. Acta, 69(12), 2971-2979. A. Kavner, S. G. John, S. Sass, and E. A. Boyle (2008), Geochim. Cosmochim. Acta, vol 72, pp. 1731-1741. J. R. Black, Umeda, G., Dunn, B., McDonough, W. F. and A. Kavner. (2009), J. Amer. Chem. Soc., vol. 131, No.29 2009 pp. 9904-9905 DOI: 10.1021/ja903926x. J. R. Black, S. John, E.D. Young, and A. Kavner, (2010), Geochim. Cosmochim. Acta, vol 74 (18) pp. 5187-5201. J. R. Black, J. Crawford, S. John, and A. Kavner, (2011) Redox-driven stable isotope fractionation, in Aquatic Redox Chemistry ACS Symposium Series, Vol. 1071. Tratnyek, P.G., T. J. Grundl, and S. B. Haderlein, eds. Chapter 16, pp 345-359

Kavner, A.; John, S.; Black, J. R.

2013-12-01

338

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

339

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

NASA Astrophysics Data System (ADS)

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

Ahn, Dongjoon

340

Investigations at the Solid-Liquid Interface by Scanning Tunneling Microscopy.  

NASA Astrophysics Data System (ADS)

Scanning tunneling microscopy (STM) has been used to investigate electrochemical processes at the solid-liquid interface. These investigations have been conducted in two specific areas, namely bioelectrochemistry and semiconductor electrochemistry. In the area of bioelectrochemistry, the STM was used to examine the morphology of the surface and determine the conditions necessary to electrochemically deposit a monolayer of nucleic acids. Parameters that were varied included: substrate material (graphite and gold), nucleic acid concentration (1.0-150 mug/ml), applied potential (between +2 and -2 V vs. Ag/AgCl) and potentiostatic pulse duration (10-180 s), and Tris buffer solution concentration (0.1-10 mM) and pH (7.3-8). Under most of the conditions studied, the deposited material was heterogeneously distributed over the surface as aggregates with small patches of isolated or loosely packed molecules. Conditions for repeatable homogeneous coverage were obtained by applying +1 V vs. Ag/AgCl to a gold substrate for one minute in a solution of 3 mM Tris buffer (pH 7.3) and a DNA concentration of 10 mug/ml. However, the homogeneous deposits consisted of a buffer salt complex with the nucleic acid. This salt complex prevented high resolution STM imaging of the nucleic acid. In the area of semiconductor electrochemistry, the STM was used to locally modify semiconducting surfaces on the nanometer scale. This was achieved by using the STM tip to either etch into the semiconductor surface or deposit gold onto the surface, while under solution. In the case of etching, the applied electric field existing between the tip and sample probably causes local oxidation of the surface. Subsequently, an etching solution removes the oxidized portion and leaves a depression in the sample. The oxide growth depended upon the length of time that the STM tip spent over a region. In the case of deposition, photoelectrochemical techniques were used to generate additional electrons in p-type GaAs(100). The STM tip bias was then used to bend the semiconductor bands to allow the photo -generated electrons to move toward the surface. This band bending occurred only beneath the STM tip and thus localized the gold deposition to this region. The size of the gold deposit depended upon the magnitude and duration of the potential applied to the STM tip.

Nagahara, Larry Akio

341

The effect of alloy composition on the localized corrosion behavior of nickel-chromium-molybdenum alloys  

NASA Astrophysics Data System (ADS)

Ni-Cr-Mo alloys are one of the most versatile Ni-based alloys because they resist corrosion in a variety of environments. This versatility is due to the combination of Cr and Mo additions to the alloy. These alloying elements complement each other in producing a highly corrosion resistant alloy. The concentration of the elements in the alloy establishes the corrosion behavior of these alloys. In this study, Ni-Cr-Mo alloys with varying composition were studied using electrochemical methods. The dependency of pitting corrosion on the alloy chemistry was captured in empirical models that roughly rank the pitting susceptibility of the Ni-Cr-Mo alloys studied. The same type of model was also constructed for capturing the effect of alloy composition on the repassivation potential. It was found that these models were specific in terms of alloying element effects on the type of environments exposed to the alloys particularly, pH and temperature. The addition of chromium was shown to contribute to the higher pitting potential on the Ni-Cr-Mo alloys in neural chloride environment while molybdenum was dominant in acidified chloride solutions. In regards to the repassivation potential, both chromium and molybdenum affect the repassivation potential more or less evenly in neutral pH solutions. Under low pH high temperature conditions, molybdenum content has a greater effect on the repassivation potential value than chromium. Stabilization of localized corrosion is increasingly difficult as alloying element content increases. However, metastable pitting occurs in most alloys and the metastable pitting behavior of several Ni-Cr-Mo alloys was studied through potentiostatic analysis. Higher chromium and molybdenum contents decreased the metastable pitting incidence; although, the effect of Mo content was observed to be more dominant. Molybdenum additions were found to suppress the growth of the metastable pits. The growth rate of the fastest growing pits was also reduced by increasing the Mo content. Chromium affects the metastable pits during the repassivation process where higher Cr content produces faster repassivation rates. The last part of the study addressed the role of alloying additions on the repassivation behavior of Ni-Cr-Mo alloys. Alloys with similar Mo content but higher Cr or higher Ni contents exhibited higher repassivation potentials. Higher Mo-containing alloys were shown to be very corrosion resistant since they did not experience any localized corrosion after rigorous polarization tests given that enough Cr was present. The repassivation potential was determined by the surface overpotential and thermodynamic contribution. XPS analysis found evidence of Cr(III) oxide as the main passivating agent. Molybdenum species primarily Mo(VI) and Cr(III) hydroxide were detected on the crevice attack area and on layer of films that formed from transpassive dissolution of higher Cr or higher Mo-containing alloys.

Wong, Fariaty

342

Technological aspects of corrosion control in metallic systems  

NASA Astrophysics Data System (ADS)

Three corrosion control technologies were investigated, including the effect of nitrogen on the passivity of chromium in sulfate solutions, possible issues associated with the use of amines in steam turbine environments and the microstructure of naval advanced amorphous coatings. Nitrogen (N) is a minor alloying element commonly used to increase the strength of steels by stabilizing the austenite phase. Physical vapor deposited chromium + nitrogen (0, 6.8 and 8.9 at.%N) coatings were investigated as a model system, to test the model. Because Cr passive films have been observed to be generally n-type semiconductors, an impedance function containing a n-type Faradaic impedance was constructed and optimized to electrochemical impedance spectra for the model system at pH 4,7 and 10 1M sulfate solution at 30°C. An apparent deviation from theory was observed, however. The n-type model predicted steady state currents which were independent of potential, while the observed current densities had a positive correlation with potential. Mott-Schottky analysis revealed that the test potentials were within the n-p transition and p-type potential range, which resolves the apparent deviation. Despite this difficulty, however, the impedance model produced reasonably accurate results, calculating current densities to within one order of magnitude of the measured steady state currents where anodic currents were available and passive film thicknesses on the order of 1-2 nm. Various amines are commonly used to inhibit corrosion in thermal power generation systems, including steam turbines, by increasing the pH. However, during the shutdown phase of the power plant, it is possible for these inhibitors to concentrate and cause corrosion of the turbine rotor. The effect of two ammine inhibitors (monoethanolamine and dimethylamine) on the passivity of ASTM A470/471 steel is investigated in a simulated turbine environment at pH 7, and temperatures of 95°C and at 175°C. Potentiodynamic scans and potentiostatic measurements revealed that the steel depassivated with high (0.1M) concentrations of monoethanolamine, in combination with acetate. Because the steel depassivated at low potentials and at neutral pH, it is unlikely to be acid or transpassive depassivation. The proposed mechanism for this depassivation is resistive depassivation, whereby the potential drop incurred by the precipitated outer-layer robs the barrier layer of the passive film of the potential required to maintain a finite film thickness. High velocity oxy-fuel (HFOV) coatings are employed in maritime environments to protect against corrosion and wear. The performance of such coatings is dominated by flaws in the microstructure, such as porosity, delamination and secondary phases. A nondestructive evaluation technique that is capable of determining the quality of a HVOF coating was developed, based on electrochemical impedance spectroscopy (EIS). The EIS measurement was correlated to the microstructure observed via scanning electron microscopy (SEM). Because a transmission line model was unable to provide discriminatory information, a convenient mathematical impedance function was constructed, with two separated time constants defined by constant phase elements, with time constants for a "fast" and a "slow" process. Enabling the impedance studies above is a new software package for fitting complicated impedance functions of up to 50 parameters to complex impedance data, developed specifically for this work. The curve-fitting software utilizes differential evolution, an evolutionary algorithm which is relatively new to the field of impedance modeling, enabling the operator to obtain high quality fits without the need for excellent starting guesses, taking trial and error out of the curve-fitting process and vastly improving the man-hour efficiency involved in optimizing complicated impedance functions such as the Faradaic impedance of the Point Defect Model. (Abstract shortened by UMI.)

Taylor, Matthew Logan

343

Towards highly efficient water photoelectrolysis  

NASA Astrophysics Data System (ADS)

The motivation for this work was to develop an efficient and relatively inexpensive material architecture suitable for solar water splitting by photoelectrolysis. Iron (III) Oxide (hematite), has bandgap energy (˜ 2.2 eV) well suited for capturing solar spectrum, is abundant and non-toxic. However, it suffers from recombination losses due to low electron mobility and a minority carrier diffusion length of only 2--4 nm. The primary focus of this dissertation was to synthesize thin walled, self-aligned, vertically oriented nanotubular/nanoporous iron (III) oxide structures through electrochemical oxidation. The underlying hypothesis was that thin walled nanotubes would allow charge separation prior to recombination, resulting in a significant increase in the photoelectrochemical properties. Both aqueous and non-aqueous electrolytes were explored as an electrochemical oxidation solvent. Iron oxide film topologies achieved include nanopillar, nanoporous and nanoplatelet structures from aqueous electrolytes, and nanoporous and nanochannel architectures from non-aqueous electrolytes. This dissertation encompasses the first report on synthesis of nanoporous/nanochannel iron (III) oxide structures through potentiostatic anodization, as well as the use of ethylene glycol for the electrochemical oxidation of both iron and titanium. Through control of anodization parameters, including potential and anodization bath composition, excellent control over the morphology and dimensions of the synthesized iron (III) nanostructures have been achieved. As dependent upon the applied potential and electrolytic composition, diameters of the self-aligned nanopores range from 30 nm to 250 nm. The synthesized structures were crystallized in nitrogen ambient to form hematite photoanodes; a maximum photocurrent efficiency of 0.73% was obtained from nanoporous iron (III) oxide synthesized using a glycerol anodization bath. The electrochemical oxidation of titanium in fluoride ion containing ethylene glycol resulted in remarkable growth characteristics of titania nanotube arrays, hexagonal closed packed up to 1 mm in length, with tube aspect ratios of approximately 10,000. For the first time, complete anodization of the starting titanium foil has been demonstrated resulting in back to back nanotube array membranes ranging from 360 mum--1 mm in length. The nanotubes exhibited growth rates of up to 15 mum/hr. A detailed study on the factors affecting the growth rate and nanotube dimensions is presented. It is suggested that faster high field ionic conduction through a thinner barrier layer is responsible for the higher growth rates observed in electrolytes containing ethylene glycol. Methods to fabricate free standing, titania nanotube array membranes ranging in thickness from 50 microm--1000 mum has also been an outcome of this dissertation. In an effort to combine the charge transport properties of titania with the light absorption properties of iron (III) oxide, films comprised of vertically oriented Ti-Fe-O nanotube arrays on FTO coated glass substrates have been successfully synthesized in ethylene glycol electrolytes. Depending upon the Fe content the bandgap of the resulting films varied from about 3.26 to 2.17 eV. The Ti-Fe oxide nanotube array films demonstrated a photocurrent of 2 mA/cm2 under global AM 1.5 illumination with a 1.2% (two-electrode) photoconversion efficiency, demonstrating a sustained, time-energy normalized hydrogen evolution rate by water splitting of 7.1 mL/W·hr in a 1 M KOH solution with a platinum counter electrode under an applied bias of 0.7 V. The Ti-Fe-O material architecture demonstrates properties useful for hydrogen generation by water photoelectrolysis and, more importantly, this dissertation demonstrates that the general nanotube-array synthesis technique can be extended to other ternary oxide compositions of interest for water photoelectrolysis.

Elavambedu Prakasam, Haripriya

344

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

345

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