Gibbs Energy of Formation of MnO: Measurement and Assessment

Based on the measurements of Alcock and Zador, Grundy et al. estimated an uncertainty of the order of +/- 5 kJ mol(-1) for the standard Gibbs energy of formation of MnO in a recent assessment. Since the evaluation of thermodynamic data for the higher oxides Mn3O4, Mn2O3, and MnO2 depends on values for MnO, a redetermination of its Gibbs energy of formation was undertaken in the temperature range from 875 to 1300 K using a solid-state electrochemical cell incorporating yttria-doped thoria (YDT) as the solid electrolyte and Fe + Fe1-delta O as the reference electrode. The cell can be presented as Pt, Mn + MnO/YDT/Fe + Fe1+delta O, Pt Since the metals Fe and Mn undergo phase transitions in the temperature range of measurement, the reversible emf of the cell is represented by the three linear segments. Combining the emf with the oxygen potential for the reference electrode, the standard Gibbs energy of formation of MnO from alpha-Mn and gaseous diatomic oxygen in the temperature range from 875 to 980 K is obtained as: Delta G(f)(o)/Jmol(-1)(+/- 250) = -385624 + 73.071T From 980 to 1300 K the Gibbs energy of formation of MnO from beta-Mn and oxygen gas is given by: Delta G(f)(o)/Jmol(-1)(+/- 250) = -387850 + 75.36T The new data are in excellent agreement with the earlier measurements of Alcock and Zador. Grundy et al. incorrectly analyzed the data of Alcock and Zador showing relatively large difference (+/- 5 kJ mol(-1)) in Gibbs energies of MnO from their two cells with Fe + Fe1-delta O and Ni + NiO as reference electrodes. Thermodynamic data for MnO is reassessed in the light of the new measurements. A table of refined thermodynamic data for MnO from 298.15 to 2000 K is presented.

A FEM-Based Forward Solver for Studying the Forward Problem of Electrical Impedance Tomography (EIT) with A Practical Biological Phantom

A Finite Element Method based forward solver is developed for solving the forward problem of a 2D-Electrical Impedance Tomography. The Method of Weighted Residual technique with a Galerkin approach is used for the FEM formulation of EIT forward problem. The algorithm is written in MatLAB7.0 and the forward problem is studied with a practical biological phantom developed. EIT governing equation is numerically solved to calculate the surface potentials at the phantom boundary for a uniform conductivity. An EIT-phantom is developed with an array of 16 electrodes placed on the inner surface of the phantom tank filled with KCl solution. A sinusoidal current is injected through the current electrodes and the differential potentials across the voltage electrodes are measured. Measured data is compared with the differential potential calculated for known current and solution conductivity. Comparing measured voltage with the calculated data it is attempted to find the sources of errors to improve data quality for better image reconstruction.

Fabrication of Fe-doped WO3 films for NO2 sensing at lower operating temperature

Fe-doped tungsten oxide thin films with different concentrations (0 to 2.6 at%) were synthesized on glass and alumina substrates at room temperature using DC reactive sputtering and subsequently annealed at 300oC for 1 hour in air. The alumina substrate has pre-printed interdigitated Pt-electrodes for gas sensing measurements. The effects of Fe-doping on the film structure and morphology, electronic and optical properties for gas sensing were investigated. The grain size of the different films on the alumina and Pt regions of the substrate vary only slightly between 43-57 nm with median size of about 50 nm. Raman spectra showed that the integrated intensity of W=O to O–W–O bands increases with increasing Fe concentrations and this indicated an increase in the number of defects. From XPS the different concentrations of the Fe-doped films were 0.03 at%, 1.33 at% and 2.6 at%. All the films deposited on glass substrate have shown similar visible transmittance (about 70%) but the optical band gap of the pure film decreased form 3.30 eV to 3.15 eV after doping with 2.6 at% Fe. The Fe-doped WO3 film with the highest Fe concentration (2.6 at% Fe) has shown an enhanced gas sensing properties to NO2 at relatively lower operating temperature (150oC) and this can be attributed to the decrease in the optical band gap and an increase in the number of defects compared to the pure WO3 film.

A Simple Instrumentation Calibration Technique for Electrical Impedance Tomography (EIT) Using A 16-Electrode Phantom

A simple analog instrumentation for Electrical Impedance Tomography is developed and calibrated using the practical phantoms. A constant current injector consisting of a modified Howland voltage controlled current source fed by a voltage controlled oscillator is developed to inject a constant current to the phantom boundary. An instrumentation amplifier, 50 Hz notch filter and a narrow band pass filter are developed and used for signal conditioning. Practical biological phantoms are developed and the forward problem is studied to calibrate the EIT-instrumentation. An array of sixteen stainless steel electrodes is developed and placed inside the phantom tank filled with KCl solution. 1 mA, 50 kHz sinusoidal current is injected at the phantom boundary using adjacent current injection protocol. The differential potentials developed at the voltage electrodes are measured for sixteen current injections. Differential voltage signal is passed through an instrumentation amplifier and a filtering block and measured by a digital multimeter. A forward solver is developed using Finite Element Method in MATLAB7.0 for solving the EIT governing equation. Differential potentials are numerically calculated using the forward solver with a simulated current and bathing solution conductivity. Measured potential data is compared with the differential potentials calculated for calibrating the instrumentation to acquire the voltage data suitable for better image reconstruction.

Supercapacitor studies of electrochemically deposited PEDOT on stainless steel substrate

There has been increasing interest on various properties and applications of electronically conducting polymers. Polyethylenedioxythiophene (PEDOT) is an interesting polymer of this type as it exhibits very high ionic conductivity. In the present study, PEDOT has been electrochemically deposited on stainless steel (SS) substrate for supercapacitor studies. PEDOT/SS electrodes prepared in 0.1M H2SO4 in presence of a surfactant, sodium dodecylsulphate (SDS), have been found to yield higher specific capacitance (SC) than the electrodes prepared from neutral aqueous electrolyte. The effects of concentration of H(2)SO4(,) concentration of SDS, potential of deposition, and nature of supporting electrolytes used for capacitor studies on SC of the PEDOT/SS electrodes have been studied. SC values as high as 250 F/g in 1M oxalic acid have been obtained during the initial stages of cycling. However, there is a rapid decrease in SC on repeated charge-discharge cycling. Spectroscopic data reflect structural changes in PEDOT on extended cycling. (C) 2007 Wiley Periodicals, Inc.

A Study of Practical Biological Phantoms with Simple Instrumentation for Electrical Impedance Tomography (EIT)

16-electrode phantoms are developed and studied with a simple instrumentation developed for Electrical Impedance Tomography. An analog instrumentation is developed with a sinusoidal current generator and signal conditioner circuit. Current generator is developed withmodified Howland constant current source fed by a voltage controlled oscillator and the signal conditioner circuit consisting of an instrumentation amplifier and a narrow band pass filter. Electronic hardware is connected to the electrodes through a DIP switch based multiplexer module. Phantoms with different electrode size and position are developed and the EIT forward problem is studied using the forward solver. A low frequency low magnitude sinusoidal current is injected to the surface electrodes surrounding the phantom boundary and the differential potential is measured by a digital multimeter. Comparing measured potential with the simulated data it is intended to reduce the measurement error and an optimum phantom geometry is suggested. Result shows that the common mode electrode reduces the common mode error of the EIT electronics and reduces the error potential in the measured data. Differential potential is reduced up to 67 mV at the voltage electrode pair opposite to the current electrodes. Offset potential is measured and subtracted from the measured data for further correction. It is noticed that the potential data pattern depends on the electrode width and the optimum electrode width is suggested. It is also observed that measured potential becomes acceptable with a 20 mm solution column above and below the electrode array level.

Growth of ionization currents in dry air at high values of E/N

Uniform field steady-state ionization currents were measured in dry air as a function of N at constant E/N (E is the electric field strength and N the gas number density) and constant electrode separation d for 14·13 × 10-16 less-than-or-eq, slant E/N less-than-or-eq, slant 282·5 × 10-16 V cm2. Uniform field sparking potentials were also measured for Nd range 1·24 × 1016 less-than-or-eq, slant Nd less-than-or-eq, slant 245 × 1016 cm-2. The ratio of the Townsend primary ionization coefficient α to N, α/N, was found to depend on E/N only. The secondary coefficients were also evaluated for aluminium and gold-plated electrodes for the above range of E/N. Measurements of the sparking potentials showed that Paschen's law is not obeyed in air at values of Nd near and below the Paschen minimum.

Single-Shot Preparation of Crystalline Nanoplate LiFePO4 by a Simple Polyol Route

Nanoplate LiFePO4 is synthesized by a polyol route starting from only two reactants, namely, FePO4 and LiOH. The crystalline compound forms by refluxing a tetraethylene glycol solution consisting of FePO4 and LiOH at 335 degrees C without further heating of the reaction product.The nanoplates have average dimensions of 30 nm width and 160 nm length, as measured from transmission electron microscopy micrographs.The surface area of the LiFePO4 sample is 38 m(2) g(-1). Also, the sample is porous with a broadly distributed pore around 50 nm. The electrodes fabricated out of the nanoplate of LiFePO4 exhibit a high electrochemical activity. Discharge capacity values measured are 160 and 100 mAh g(-1) at 0.15C and 3.45C, respectively. A stable capacity of about 155 mAh g(-1) is measured at 0.2C over a 50 charge-discharge cycle. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3425730] All rights reserved.

Role of entropy in the stability of cobalt titanates

The standard molar Gibbs free energy of formation of Co2TiO4, CoTiO3,and CoTi2O5 as a function of temperature over an extended range (900 to 1675) K was measured using solid-state electrochemical cells incorporating yttria-stabilized zirconia as the electrolyte, with CoO as reference electrode and appropriate working electrodes. For the formation of the three compounds from their component oxides CoO with rock-salt and TiO2 with rutile structure, the Gibbs free energy changes are given by:Delta(f)G degrees((ox))(Co2TiO4) +/- 104/(J . mol(-1)) = -18865 - 4.108 (T/K)Delta(f)G degrees((ox))(CoTiO3) +/- 56/(J . mol(-1)) = -19627 + 2.542 (T/K) Delta(f)G degrees((ox))(CoTi2O5) +/- 52/(J . mol(-1)) = -6223 - 6.933 (T/K) Accurate values for enthalpy and entropy of formation were derived. The compounds Co2TiO4 with spinel structure and CoTi2O5 with pseudo-brookite structure were found to be entropy stabilized. The relatively high entropy of these compounds arises from the mixing of cations on specific crystallographic sites. The stoichiometry of CoTiO3 was confirmed by inert gas fusion analysis for oxygen. Because of partial oxidation of cobalt in air, the composition corresponding to the compound Co2TiO4 falls inside a two-phase field containing the spinet solid solution Co2TiO4-Co3O4 and CoTiO3. The spinel solid solution becomes progressively enriched in Co3O4 with decreasing temperature. (c) 2010 Elsevier Ltd. All rights reserved.

Triggered vacuum gap for initiating electric arcs in vacuum

Describes a simple triggered vacuum gap developed for initiating electric arcs in vacuum which uses the property that the voltage required to breakdown a gap in vacuum in the presence of a solid insulating material is considerably less than the voltage required in the absence of such material. In this triggered vacuum gap a solid insulating material is used in the angular space between the main cathode and the concentric trigger electrode forming the auxiliary gap. Different materials like epoxy resin, Teflon (PTFE) and mica have been used. The trigger voltage was found to vary in the range 560-1840 V. The results with epoxy and Teflon were unsatisfactory because the trigger voltages showed wide scatter and the auxiliary gap was soon bridged by metal particles eroded from the electrodes. Though the trigger voltages required with mica were relatively high, consistent triggering could be obtained for a large number of trials before the auxiliary gap was bridged. This was probably due to better thermal stability of mica as compared with either epoxy or Teflon.

A Durable PEFC with Carbon-Supported Pt-TiO2 Cathode: A Cause and Effect Study

Durability is central to the commercialization of polymer electrolyte fuel cells (PEFCs). The incorporation of TiO2 with platinum (Pt) ameliorates both the stability and catalytic activity of cathodes in relation to pristine Pt cathodes currently being used in PEFCs. PEFC cathodes comprising carbon-supported Pt-TiO2 (Pt-TiO2/C) exhibit higher durability in relation to Pt/C cathodes as evidenced by cell polarization, impedance, and cyclic voltammetry data. The degradation in performance of the Pt-TiO2/C cathodes is 10% after 5000 test cycles as against 28% for Pt/C cathodes. These data are in conformity with the electrochemical surface area and impedance values. Pt-TiO2/C cathodes can withstand even 10,000 test cycles with nominal effect on their performance. X-ray diffraction, transmission electron microscope, and cross-sectional field-emission-scanning electron microscope studies on the catalytic electrodes reflect that incorporating TiO2 with Pt helps in mitigating the aggregation of Pt particles and protects the Nafion membrane against peroxide radicals formed during the cathodic reduction of oxygen. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3421970] All rights reserved.

Solution-Combustion Synthesized Nanocrystalline Li4Ti5O12 As High-Rate Performance Li-Ion Battery Anode

Nanocrystalline Li4Ti5O12 (LTO) crystallizing in cubic spinel-phase has been synthesized by single-step-solution-combustion method in less than one minute. LTO particles thus synthesized are flaky and highly porous in nature with a surface area of 12 m(2)/g. Transmission electron micrographs indicate the primary particles to be agglomerated crystallites of varying size between 20 and 50 nm with a 3-dimensional interconnected porous network. During their galvanostatic charge-discharge at varying rates, LTO electrodes yield a capacity value close to the theoretical value of 175 mA h/g at C/2 rate. The electrodes also exhibit promising capacity retention with little capacity loss over 100 cycles at varying discharge rates together with attractive discharge-rate capabilities yielding capacity values of 140 mA h/g and 70 mA h/g at 10 and 100 C discharge rates, respectively. The ameliorated electrode-performance is ascribed to nano and highly porous morphology of the electrodes that provide short diffusion-paths for Li in conjunction with electrolyte percolation through the electrode pores ensuring a high flux of Li.

A new method of producing local enhancement of buoyancy in liquid flows

We describe here a novel method of generating large volumetric heating in a liquid. The method uses the principle of ohmic heating of the liquid, rendered electrically conducting by suitable additives if necessary. Electrolysis is prevented by the use of high frequency alternating voltage and chemically treated electrodes. The technique is demonstrated by producing substantial heating in an initially neutral jet of water. Simple flow visualisation studies, made by adding dye to the jet, show marked changes in the growth and development of the jet with heat addition.

Chemical potentials of oxygen for fayalite-quartz-lron and fayalite-quartz-magnetite equilibria

The oxygen potentials corresponding to fayalite-quartz-iron (FQI) and fayalite-quartz-magnetite (FQM) equilibria have been determined using solid-state galvanic cells: Pt,Fe + Fe2SiO4 + SiO2/(Y2O3)ZrO2/Fe + \r"FeO,\l"Pt and Pt, Fe3O4 + Fe2SiO4 + SiO2/(Y2O3)ZrO2/Ni + NiO, Pt in the temperature ranges 900 to 1400 K and 1080 to 1340 K, respectively. The cells are written such that the right-hand electrodes are positive. Silica used in this study had the quartz structure. The emf of both cells was found to be reversible and to vary linearly with temperature. From the emf, Gibbs energy changes were deduced for the reactions: 0.106Fe (s) + 2Fe0.947O (r.s.) + SiO2 (qz) → Fe2SiO4 (ol) δG‡= -39,140+ 15.59T(± 150) J mol-1 and 3Fe2SiO4 (ol) + O2 (g) → 2Fe3O4 (sp) + 3SiO2 (qz) δG‡ = -471,750 + 160.06 T±} 1100) J mol-1 The “third-law≓ analysis of fayalite-quartz-wustite and fayalite-quartz-magnetite equilibria gives value for δH‡298 as -35.22 (±0.1) and -528.10 (±0.1) kJ mol-1, respectively, independent of temperature. The Gibbs energy of formation of the spinel form of Fe2SiO4 is derived by com-bining the present results on FQI equilibrium with the high-pressure data on olivine to spinel transformation of Fe2SiO4.

Probing top-gated field effect transistor of reduced graphene oxide monolayer made by dielectrophoresis

We demonstrate a top-gated field effect transistor made of a reduced graphene oxide (RGO) monolayer (graphene) by dielectrophoresis. The Raman spectrum of RGO flakes of typical size of 5 mu m x 5 mu m shows a single 2D band at 2687 cm(-1), characteristic of single-layer graphene.The two-probe current-voltage measurements of RGO flakes, deposited in between the patterned electrodes with a gap of 2.5 mu m using ac dielectrophoresis, show ohmic behavior with a resistance of similar to 37 k Omega. The temperature dependence of the resistance (R) of RGO measured between 305 K and 393 K yields a temperature coefficient of resistance [dR/dT]/R similar to -9.5 x 10(-4)/K, the same as that of mechanically exfoliated single-layer graphene. The field-effect transistor action was obtained by electrochemical top-gating using a solid polymer electrolyte (PEO + LiClO4) and Pt wire. The ambipolar nature of graphene flakes is observed up to a doping level of similar to 6 x 10(12)/cm(2) and carrier mobility of similar to 50 cm(2)/V s. The source-drain current characteristics show a tendency of current saturation at high source-drain voltage which is analyzed quantitatively by a diffusive transport model. (C) 2010 Elsevier Ltd. All rights reserved.