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Richard G. Compton - One of the best experts on this subject based on the ideXlab platform.

  • Evaluation of a simple disposable microband electrode device for amperometric gas sensing
    Sensors and Actuators B-chemical, 2013
    Co-Authors: Linhongjia Xiong, Peter Goodrich, Christopher Hardacre, Richard G. Compton
    Abstract:

    Abstract We report a simple and facile methodology for constructing Pt (6.3 mm × 50 μm) and Cu (6.3 mm × 30 μm) annular microband electrodes for use in room temperature ionic liquids (RTILs) and propose their use for amperometric gas sensing. The suitability of microband electrodes for use in electrochemical analysis was examined in experiments on two systems. The first system studied to validate the electrochemical responses of the annular microband electrode was decamethylferrocene (DmFc), as a stable internal reference probe commonly used in ionic liquids, in [Pmim][NTf2], where the diffusion coefficients of DmFc and DmFc+ and the standard electron rate constant for the DmFc/DmFc+ couple were determined through fitting chronoamperometric and cyclic voltammetric responses with relevant simulations. These values are independently compared with those collected from a commercially available Pt microdisc electrode with excellent agreement. The second system focuses on O2 reduction in [Pmim][NTf2], which is used as a model for gas sensing. The diffusion coefficients of O2 and O 2 − ˙ and the electron transfer rate constant were again obtained using chronoamperometry and cyclic voltammetry, along with simulations. Results determined from the Microbands are again consistent to those evaluated from the Pt microdisc electrode when compared these results from home-made microband and commercially available microdisc electrodes. These observations indicate that the fabricated annular microband electrodes are suitable for quantitative measurements. Further the successful use of the Cu electrodes in the O2 system suggests a cheap disposable sensor for gas detection.

  • Fabrication of disposable gold macrodisc and platinum microband electrodes for use in room-temperature ionic liquids
    Analyst, 2013
    Co-Authors: Linhongjia Xiong, Denise Lowinsohn, Kristopher R. Ward, Richard G. Compton
    Abstract:

    We report a simple and facile methodology for constructing gold macrodisc and platinum microband electrodes for use in room temperature ionic liquids (RTILs). To validate the use of gold macrodisc electrodes, the voltammetry of Ru(NH3)63+ was studied in 0.1 M aqueous KCl. The Randles–Sevcik equation was used to calculate the diffusion coefficient, giving excellent agreement with literature values, suggesting that the gold macrodisc electrode is capable of performing quantitative electroanalysis in aqueous media. Gold macrodisc electrodes were used to study oxidation of ferrocene in N-butyl-N-methylpyrrolidinium bis(fluoromethylsulfonyl)imide ([C4mpyrr][NTf2]) using cyclic voltammetry. The diffusion coefficient of ferrocene, (2.43 ± 0.07) × 10−11 m2 s−1, was obtained. This value is very close to the literature value, indicating good performance of gold electrodes in RTILs. Platinum microband electrodes were tested in 1-propyl-3-methylimidazolium bis-trifluoromethylsulfonylimide ([Pmim][NTf2]) containing decamethylferrocene. Diffusion coefficients and electron transfer rates were obtained by fitting relevant simulations to the experimental data. For comparison, analogous experiments and analyses were performed on a commercial platinum microdisc, where the results obtained from both microdisc and microband agree well, further suggesting that the platinum microband electrode is suitable to be used in RTILs. Finally, gold macrodisc and platinum microband electrodes were used for oxygen detection. Gold macrodisc electrodes were used to find the peak currents of oxygen at each volume percentage analysed. Platinum microband electrodes showed steady-state currents of different volumes of oxygen. These two results are compared which resulted in excellent agreement. This is further confirmed by studying Henry's law constants obtained from both electrodes. The excellent behaviour of these two fabricated electrodes suggests that they are suitable for quantitative measurements and practicable for real world applications.

  • Voltammetry at regular microband electrode arrays : Theory and experiment
    Journal of Physical Chemistry C, 2007
    Co-Authors: Ian Streeter, Nicole Fietkau, Javier Campo, Roser Mas, And Francesc Xavier Mũnoz, Richard G. Compton
    Abstract:

    Microband electrode arrays are useful tools for the electrochemist, offering the enhanced sensitivity associated with microelectrodes but with a higher total current output. For optimum performance, the array may be designed such that space is used efficiently but the individual Microbands behave as isolated electrodes on the time scale of the experiment. For a linear sweep experiment, the optimum specifications of a microband array depend on the scan rate used and the diffusion coefficient of the electroactive species. A two-dimensional simulation method is used to examine the nature of the diffusion to a regular array of Microbands. Cyclic voltammetry of hexaammineruthenium(III)chloride is performed at a regularly spaced microband array to test the theory.

  • Microband electrodes of ideal and nonideal geometries: AC impedance spectroscopy
    Electroanalysis, 2005
    Co-Authors: John A. Alden, Richard G. Compton
    Abstract:

    The AC impedance behavior of microband electrode geometries which deviate from the ideal is derived via numerical modelling of the chronoamperometric response under diffusion-only conditions. Specifically attention is given to four electrode shapes in addition to the ideal microband geometry: elevated microband electrodes (with conducting supporting sides), recessed microband electrodes (with insulating pit walls), platform electrodes (with insulating supporting sides) and, for the purposes of comparison, a hypothetical line electrode without any support which permits diffusional mass transport to both sides of the infinitesimally thin electrode. Simple analytical expressions are established for the frequency dependence of the AC impedance in each case.

  • A comparison of finite difference algorithms for the simulation of microband electrode problems with and without convective flow
    Journal of Electroanalytical Chemistry, 1996
    Co-Authors: John A. Alden, Richard G. Compton
    Abstract:

    Various microband electrode problems are simulated using finite difference methods. These are (i) the chronoamperometric transient obtained under diffusion-only conditions, and (ii) the steady-state and (iii) the transient responses observed when the microband electrode is located in a convective flow. Three separate algorithms are employed to solve the problems, namely the strongly implicit procedure (SIP), the alternating direction implicit (ADI) method and the backwards implicit (BI) method. The different approaches are compared and contrasted in terms of their relative efficiencies. Optimal simulation approaches to the solution of microband electrode problems are identified.

Dierk Raabe - One of the best experts on this subject based on the ideXlab platform.

  • Microbanding mechanism in an Fe–Mn–C high-Mn twinning-induced plasticity steel
    Scripta Materialia, 2013
    Co-Authors: Ivan Gutiérrez-urrutia, Dierk Raabe
    Abstract:

    We study the microbanding mechanism in an Fe–22Mn–0.6C (wt.%) twinning-induced plasticity steel. Dislocation substructures were examined by electron channeling contrast imaging and electron backscatter diffraction. We observe a pronounced effect of the strain path on microbanding, which is explained in terms of Schmid’s law. Microbands created under shear loading have a non-crystallographic character. This is attributed to the microbanding mechanism and its relation with the dislocation substructure. Further insights into the dislocation configuration of Microbands are provided.

  • investigation of the internal substructure of Microbands in a deformed copper single crystal experiments and dislocation dynamics simulation
    Modelling and Simulation in Materials Science and Engineering, 2010
    Co-Authors: O Dmitrieva, J V Svirina, Eralp Demir, Dierk Raabe
    Abstract:

    We investigate the internal structure of Microbands in a shear-deformed copper single crystal. The microstructure is characterized using high-resolution electron backscatter diffraction. The occurrence of Microbands is due to the alternation of local orientation, which is characteristic of a deformation laminate. These Microbands contain a substructure consisting of further local 1°-orientation alternations. A two-dimensional discrete dislocation dynamics model is used to describe the orientation substructure within the Microbands. The boundary conditions for the simulation were estimated from the distribution of the geometrically necessary dislocation density obtained from the orientation map. The dislocation arrangement in the dynamic simulation explains the formation of the experimentally observed substructure.

Cl. Maurice - One of the best experts on this subject based on the ideXlab platform.

  • Microband evolution during large plastic strains of stable {110} < 1 1 2 > Al and Al-Mn crystals
    Acta Materialia, 2010
    Co-Authors: Adeline Albou, J. Driver, Cl. Maurice
    Abstract:

    The deformation microstructures or Al and Al-Mn {1 1 0}< 1 1 2 > single crystals have been characterized after room temperature channel-die compression up to true strains of 2 1 The evolution of local misorientations and microband structures were quantified by high-resolution electron backscatter diffraction in a field emission gun scanning electron microscope and their alignments compared with the traces of active slip planes and macroscopic shear stress planes During plane-strain compression these "Brass" oriented crystals remain stable in terms of the final, average, orientation, with a small orientation spread However, the microband alignment varies with strain and also with solute content There is a general tendency for the Microbands to be both crystallographic and non-crystallographic at low strains, then crystallographic, and finally mixed again at high strains (with some lamellar banding) (C) 2010 Acta Materialia Inc Published by Elsevier Ltd All rights reserved

  • Microband evolution during large plastic strains of stable {1 1 0}〈1 1 2〉 Al and Al–Mn crystals
    Acta Materialia, 2010
    Co-Authors: A. Albou, Julian H. Driver, Cl. Maurice
    Abstract:

    Abstract The deformation microstructures of Al and Al–Mn {1 1 0}〈1 1 2〉 single crystals have been characterized after room temperature channel-die compression up to true strains of 2.1. The evolution of local misorientations and microband structures were quantified by high-resolution electron backscatter diffraction in a field emission gun scanning electron microscope and their alignments compared with the traces of active slip planes and macroscopic shear stress planes. During plane-strain compression these “Brass” oriented crystals remain stable in terms of the final, average, orientation, with a small orientation spread. However, the microband alignment varies with strain and also with solute content. There is a general tendency for the Microbands to be both crystallographic and non-crystallographic at low strains, then crystallographic, and finally mixed again at high strains (with some lamellar banding).

Michael Ferry - One of the best experts on this subject based on the ideXlab platform.

  • 3D microband boundary alignments and transitions in a cold rolled commercial purity aluminum alloy
    Materials Characterization, 2013
    Co-Authors: Cassandra George, M.z. Quadir, Michael Ferry, Brian Soe, K. King, Lori Bassman
    Abstract:

    Abstract In the study of microband formation during plastic deformation of face centered cubic metals and alloys, two theories have been proposed regarding the orientations of their boundaries: (i) they are aligned parallel to crystallographic planes associated with dislocation glide (i.e. {111} planes in FCC metals), or (ii) they are aligned in accordance with the macroscopic stress state generated during deformation. In this study, high resolution 3D electron backscatter diffraction (3D EBSD) was used to investigate the morphology and crystallographic nature of microband boundaries within a 19 × 9 × 8.6 μm volume of a deformed grain in commercial purity aluminum cold rolled to 22% reduction. It was found that microband boundaries correspond to both theories of orientation. Additionally, a single surface may contain both crystallographic and non-crystallographic alignments. Misorientations across boundaries in the regions of microband triple junctions have been identified for both boundary alignments.

  • Spatial orientations and structural irregularities associated with the formation of Microbands in a cold deformed Goss oriented Ni single crystal
    Acta Materialia, 2012
    Co-Authors: N. Afrin, M.z. Quadir, Michael Ferry
    Abstract:

    Abstract The crystallographic nature of microband boundaries was investigated in a Goss oriented nickel single crystal following cold deformation in channel die plane strain compression. Standard electron backscatter diffraction (EBSD), three-dimensional (3-D)-EBSD and transmission electron microscopy (TEM) were used in the investigation. When viewed in the three orthogonal sections microband boundary traces were classically aligned in the transverse direction section at an acute angle from the rolling direction (RD), but appeared wavy in the normal direction (ND) section. The latter observation may lead to the conclusion that microband boundaries are non-crystallographic. 3-D EBSD was used to reconstruct actual Microbands in a deformed volume that revealed significant new information about their structure. Here microband surfaces are largely planar over large distances, but frequently interrupted by local distortions and undulations due to interactions between intersecting non-coplanar Microbands. The combined EBSD/TEM investigation has revealed that microband boundaries are aligned close to an active {1 1 1} slip plane (i.e. they are crystallographic), but the undulations and distortions they contain are non-crystallographic in the sense that they deviate from an active slip plane. The non-crystallographic features of Microbands (as revealed by their wavy structure in the ND section) may be explained by the crystallographic oscillations of up to ±7.5° towards RD that occur during plastic deformation. Such oscillations result in varying fractions of slip on a given {1 1 1} plane, resulting in varying degrees of interaction between the two sets of non-coplanar Microbands. These local and intense microband interactions result in their deviation from their active slip planes.

  • On the Bumps and Curves in the Microband Boundaries in a Channel-Die Compressed Goss-Oriented Ni Single Crystal
    Materials Science Forum, 2011
    Co-Authors: Nasima Afrin Zinnia, Lori Bassman, M. Zakaria Quadir, Julian H. Driver, Adeline Albou, Michael Ferry
    Abstract:

    The crystallographic alignment of Microbands in a Goss oriented single crystal was investigated by two and three dimensional electron back scatter diffraction. The microband boundaries were found to be curved instead of being perfectly flat interfaces, and the overall alignment closely matched a potential slip plane. The bumps and curved were created during subsequent deformation and, thus, deviates the microband boundaries from crystallographic nature.

  • The three-dimensional nature of Microbands in a channel die compressed Goss-oriented Ni single crystal
    Scripta Materialia, 2011
    Co-Authors: N. Afrin, M.z. Quadir, Lori Bassman, Julian H. Driver, A. Albou, Michael Ferry
    Abstract:

    The three-dimensional structure of microband boundaries in a plane strain compressed Goss-oriented nickel single crystal was generated by the electron backscatter diffraction technique. Rather than being perfectly planar, microband boundaries generally contained bumps and curves. The planar segments of these boundaries have orientations that coincide closely with one of the expected {1 1 1} slip planes of this crystal.

  • Three-dimensional morphology of Microbands in a cold-rolled steel
    Scripta Materialia, 2007
    Co-Authors: M.z. Quadir, Nora Mateescu, Lori Bassman, Michael Ferry
    Abstract:

    A three-dimensional (3-D) reconstruction of a typical microband in cold-rolled interstitial-free steel was generated by 3-D electron backscatter diffraction. The microband contained irregular curved surfaces that reconcile findings that Microbands appear straight and aligned along slip planes when viewed in normal direction–rolling direction sections but are wavy in transverse direction–rolling direction sections. Three slip planes were found within the angular range of the curved surface of the microband, which indicates that multiple planes is operative during deformation.

Peter A. Leigh - One of the best experts on this subject based on the ideXlab platform.

  • Hydrodynamic voltammetry with channel microband electrodes : potential step transients
    The Journal of Physical Chemistry, 1994
    Co-Authors: Richard G. Compton, Robert A.w. Dryfe, John A. Alden, Neil V. Rees, Peter J. Dobson, Peter A. Leigh
    Abstract:

    The current transients induced by a potential step at a microband electrode located in a rectangular channel through which solution is pumped under laminar flow conditions are described by theory which accounts for convection axially through the flow cell and diffusion normal, and parallel, to the electrode surface. The hopscotch algorithm is used to predict numerically the form of the chronoamperometric transients as a function of the flow cell/electrode geometries and as a function of flow rate. Experiments are reported for the reduction of p-chloranil in acetonitrile solution using gold channel Microbands: the effect of electrode size and solution flow rate is found to be in excellent agreement with the theoretical predictions

  • hydrodynamic voltammetry with microelectrodes channel microband electrodes theory and experiment
    The Journal of Physical Chemistry, 1993
    Co-Authors: Richard G. Compton, Peter J. Dobson, Adrian C Fisher, Geoffrey R Wellington, Peter A. Leigh
    Abstract:

    Theory is reported that predicts the mass-transport limited current flowing at a microband electrode located in a rectangular channel through which solution is pumped under laminar flow conditions. The effect of electrode size and solution flow rate is quantified and the relative roles of axial diffusion and convective mass transport are identified. Theory is found to be in excellent agreement with experiments conducted on the reduction of p-chloranil and the oxidation of ferrocene by using gold channel microband electrodes