Electrochemical oxidation of carbon in a 62/38 mol % Li/K carbonate melt

The electrochemical gasification of coal to CO in a direct carbon fuel cell (DCFC) has thermodynamical advantages, including the conversion of heat into power at a reversible efficiency of 100%. Molten carbonate fuel cell (MCFC) technology may form the basis for constructing DCFC's. Here the electrochemical oxidation of carbon in a 62/38 mol % Li/K carbonate melt is studied using impedance spectroscopy (IS) and cyclic voltammetry (CV). A set of equilibria is introduced which fully describes the electrochemical equilibrium of the system. From IS it is shown that for temperatures lower than 700 °C, charge transfer is the slowest step, while at higher temperatures a second unidentified step also contributes significantly to the d.c. resistance of the electrode. The d.c. resistance is 100 to 220 cm² at 650 °C and 12 to 60 cm² at 750 °C, depending on the carbon surface roughness.     

Preparation and Properties of Woodceramic Thin Films

Woodceramic thin films were prepared onto alumina sheet and glass slide substrates by conventional radio frequency sputtering in an argon plasma. A woodceramic disk, 100 mm in diameter, sintered at 850°C was used as a target. The deposition rate was about 90 nm/h for 200 W input power. Remarkable differences were observed in the characteristics of films depending on the substrate temperature. Films prepared below 100°C had insulating properties, > 106 cm, and had transmission in the visible region ( > 600 nm), and had smooth surfaces. Increasing the substrate temperature causes sharp a decrease in the film resistivity and the growth of grain was 3–5 m. The film prepared at 300°C had semiconductor characteristics with an energy gap of about 0.05 eV.     

Effect of pulse reversal on the properties of pulse plated CdSe x Te1−x thin films

CdSe _x Te_1–x thin films with 0 < x < 1 were deposited on titanium and conducting glass substrates by pulse electrodeposition using microprocessor control. Formation of the solid solution takes place for values of x(0 < x < 1). The films were characterized by X-ray diffraction. While the as-deposited films are cubic in nature, those annealed at 475 °C in air indicate hexagonal structure and the lattice parameters increase with increasing value of x. From the optical absorption measurements the band gap of the material was calculated. The value of the band gap varies from 1.42 to 1.70 eV as x varies from 0 to 1. The photoelectrochemical (PEC) characteristics were obtained for all compositions of CdSe _x Te_1–x (x = 0–1). The output parameters for CdSe_0.66Te_0.34 with 9% duty cycle at an intensity of 80 mW cm^–2 using 1 M polysulphide as the redox electrolyte, are V _OC of 398 mV, J _SC of 5.59 mA cm^–2, ff of 0.45, of 4.73%, R _s of 13 , R _sh of 1.50 k. The output parameters were found to increase with 60 ms pulse reversal. After photoetching for 40 s, a V _OC of 481 mV, J _SC of 16.00 mA cm^–2, ff of 0.57, of 5.46%, R _s of 6 , R _sh of 2.16 k were obtained.     

Electrical resistance of polybenzimidazole membranes

Measurements of electrical resistance were made on several polybenzimidazole membranes prepared for use in reverse osmosis. In contact with 1 M KCl, different samples had resistances which ranged from 0.087 to 22 cm². Smaller ranges of resistance were seen with membranes in contact with 36% H₂SO₄ (0.022 to 0.030 cm²) and 40% KOH (0.0063 to 0.096 cm²). With all three electrolytes, however, increasing resistance followed increasing salt rejection measured under reverse osmosis conditions. This offers a rapid and convenient diagnostic test for reverse osmosis performance of the membranes.     

Impedance parameters and the state-of-charge. II. Lead-acid battery

The determination of the state-of-charge of the lead-acid battery has been examined from the viewpoint of internal impedance. It is shown that the impedance is controlled by charge transfer and to a smaller extent by diffusion processes in the frequency range 15–100 Hz. The equivalent series/parallel capacitance as well as the a.c. phase-shift show a parabolic dependence upon the state-of-charge, with a maximum or minimum at 50% charge. These results are explained on the basis of a uniform transmission-line analog equivalent circuit for the battery electrodes.Nomenclature Battery This word is used synonymous with the word cell - R _p equivalent parallel resistance () - R _s equivalent series resistance () - ¦Z¦ modulus of impedance () - C _p equivalent parallel capacitance (F) - C _s equivalent series capacitance (F) - a.c. phase-shift (radians or degrees) - 2f - f a.c. frequency (Hz) - R resistance of electrolyte solution and separator () - ¯C double layer capacity (F) - W diffusional (Warburg) impedance () - R _t resistance due to polarization () - energy transfer coefficient - T absolute temperature (K) - R gas constant - F Faraday constant - C _O ⁰ bulk concentration of the oxidant - C _R ⁰ bulk concentration of the reductant - D _O diffusion coefficient of the oxidant - D _R diffusion coefficient of the reductant - Warburg coefficient - N number of pores/area - A active area of the electrode (cm²) - S state-of-charge - a anode - c cathode - L inductance - I _o exchange current     

A model for bipolar current leakage in cell stacks with separate electrolyte loops

A model predicting leakage current in a bipolar battery stack is presented. This model applies current balance and potential balance equations to a stack and treats the electrolyte, manifold and membrane separator as resistance elements in an electric circuit analog. This results in a set of linear difference equations with constant coefficients. Leakage currents in stacks made up of different numbers of cells are predicted and the effect of each resistance component on stack performance is investigated.Nomenclature C _j j=1 ... 5, constants in Equations 24–29, defined in the Appendix - D _j j=1 ... 5, constants in Equations 25–29, defined in the Appendix - E difference operator, Ef _n=f _n+1 - I _L load current (A) - K manifold current, anodie (A) - L manifold current, cathodic (A) - N number of cells in the bipolar stack - R _A lateral electrolyte resistance, anodic () - R _C lateral electrolyte resistance, cathodic () - R _e1 electrolyte resistance, anodic () - R _e2 electrolyte resistance, cathodic () - R _MA manifold resistance, anodic () - R _MC manifold resistance, cathodic () - R _s membrane resistance () - V ₀ cell potential (V) - i ₁ battery current, anodic (A) - i ₂ battery current, cathodic (A) - k leakage current, anodic (A) - l leakage current, cathodic (A) - r _j j=1 ... 5, roots of the characteristic equation, solved in the Appendix     

Moisture sensor device of plasma-films doped with methylbromide

Summary Films plasma-polymerized from the tetramethylsilane/ammonia gas mixture were sensitive in electrical resistance to moisture. A linear relationship between the logarithm of the electrical resistance and the relative humidity was observed. This susceptibility in the electrical resistance to moisture was improved by doping of methylbromide. This improvements by the doping treatment may be as results of quaternization of amino groups and of hydrolysis of methylbromide. The improved device could detect relative humidity from 20 to 90 % where the electrical resistance varied from 10⁷ to 10⁴ . The response time was less than twenty-five seconds, and the hysteresis in cyclic changing of the relative humidity was negligible.     

Analysis of the inductance influence on the measured electrochemical impedance

The high-frequency region of the impedance diagram of an electrochemical cell can be deformed by the inductance of the wiring and/or by the intrinsic inductance of the measuring cell. This effect can be noticeable even in the middle frequency range in the case of low impedance systems such as electrochemical power sources. A theoretical analysis of the errors due to inductance effects is presented here, on the basis of which the admissible limiting measuring frequency can be evaluated. Topology deformations due to the effect of inductance in the case of a single-step electrochemical reaction are studied by the simulation approach. It is shown that an inductance can not only change the actual values of the parameters (electrolytic resistance, double layer capacitance, reaction resistance), but can also substantially alter the shape of the impedance diagram, this leading to erroneous structure interpretations. The effect of the size and surface area of the electrode on its intrinsic inductance is also evaluated.Nomenclature A linear dimension of the surface area confined by the circuit (cm) - C _D double layer capacitance (F) - C _M measured capacitance - d diameter of the mean effective current line (mm) - f _max limiting (maximum) frequency of measurement (Hz) - K ₁,K ₂ shape coefficients with values of 2×10^–9 and 0.7 for a circle, and 8×10^–9 and 2 for a square (dimensionless) - L intrinsic inductance of the electrochemical cell assumed as an additive element (H) - R _E electrolyte resistance () - R _M measured resistance () - R _P reaction resistance () - r ₀ specific resistance ( cm) - S electrode surface area (cm²) - T _c time constant (s) - Z impedance () - Z _lm imaginary component of the impedance without accounting for the influence of inductance () - Z _lm imaginary component of the impedance accounting for the influence of the additive inductance () - shape coefficient; =1 for a square and =^1/2/2 for circle (dimensionless) - _L relative complex error due to the influence of inductance (dimensionless) - _L ^A relative amplitude error due to inductance (%) - ^L relative phase error due to inductance (%) - ratio between the effective inductance time constant and the capacitive time constant (dimensionless) - angular frequency (s^–1) - _R characteristic frequency at which the inductive and capactive parts of the imaginary component of impedance are equal (s^–1)     

Stress Measurement Technique to Monitor Porous Silicon Processing

Macroscopic stress measurements are used to monitor Porous Silicon processing. Silicon wafer of 1 cm resistivity, n-type and 1 0 0 orientation were used as starting material. Porous Silicon layers with a porosity of 57% and a thickness of 85 m, fabricated by electrochemical anodisation, were differently dried, then the evolution of the wafer deflection has been followed with storage time in air. Thermal treatments both in inert and oxidant atmosphere have been performed up to 1000°C. The stress behaviour vs. temperature allows to estimate the hydrogen desorption activation energy.     

Electrical conductivity of hot-pressed zirconium dioxide

Conclusions Hot-pressing was used to obtain samples of products of zirconium dioxide with a density of 97–99% of the theoretical value. Their electrical conductivity was considerably greater than in the case of sintered samples with the corresponding stabilizing additive. In the temperature interval 1300–2000°C, it was lower than 1 ^–1.cm^–1 in all cases.Translated from Ogneupory, No. 3, pp. 44–46, March, 1969.     

Chromatographic determination of polymer solubility parameters

Summary Weight fraction activity coefficients (₁) and interaction parameters x have been determined for seven different solvents in Polyarylate at three temperatures by the gas chromatographic method (inverse gas chromatography). Data have been used to calculate infinite dilution solubility parameters according to the method proposed by DiPaola-Baranyi and Guillet. The validity of the plots involved in the above mentioned method is also discussed.     

Electrical conductivities of aqueous ZnSO4−H2SO4 solutions

Conductivities of aqueous ZnSO₄–H₂SO₄ solutions are reported for a wide range of ZnSO₄ and H₂SO₄ concentrations (ZnSO₄ concentrations of 01.2 M and H₂SO₄ concentrations of 02 M) at 25°C, 40°C and 60°C. The results indicate that the solution conductivity at a given ZnSO₄ concentration is controlled by the H₂SO₄ (H⁺) concentration. The variation of the specific conductivity with ZnSO₄ concentration is complex, and depends on the H₂SO₄ concentration. At H₂SO₄ concentrations lower than about 0.25 M, the addition of ZnSO₄ increases the solution conductivity, likely because the added Zn²⁺ and SO ₄ ^2– ions increase the total number of conducting ions. However, at H₂SO₄ concentrations higher than about 0.25 M, the solution conductivity decreases upon the addition of ZnSO₄. This behaviour is attributed to decreases in the amount of free water (through solvation effects) upon the addition of ZnSO₄, which in turn lowers the Grotthus-type conduction of the H⁺ ions. At H₂SO₄ concentrations of about 0.25 M, the addition of ZnSO₄ does not appreciably affect the solution conductivity, possibly because the effects of increasing concentrations of Zn²⁺ and SO ₄ ^2– ions are balanced by decreases in Grotthus conduction.Nomenclature a ion size parameter (m) - a ^* Bjerrum distance of closest approach (m) - C stoichiometric concentration (mol m^–3 or mol L^–1) - I ionic strength (mol L^–1) - k constant in Kohlrausch's law - M molar concentration (mol L^–1) - T absolute temperature (K) - z _i electrochemical valence of speciesi (equiv. mol^–1) - z (z _–|z _–|)^1/2=2 for ZnSO₄ - z ₊ valence of cation in salt (=+2 for Zn²⁺) - z _– valence of anion in salt (=–2 for SO ₄ ^2– ) Greek letters fraction of ZnSO₄ dissociated - specific conductivity (^–1 m^–1) - ^expt measured specific conductivity (^–1 m^–1) - equivalent conductivity (^–1 m² equiv.^–1) - equivalent conductivity at infinite dilution (^–1 m² equiv.^–1) - ⁰ equivalent conductivity calculated using Equation 2 (^–1 m² equiv.^–1) - _cale measured equivalent conductivity (^–1 m² equiv.^–1) - _expt equivalent conductivity of ioni at infinite dilution (^–1 m² equiv.^–1) - reciprocal of radius of ionic cloud (m^–1) - viscosity of solvent (Pa s) - dielectric constant - ± mean molar activity coefficient - density (g cm^–3)     

Conditions for Formation of Conducting Aluminum-Bearing Coatings

The conditions for the formation of conducting coatings based on a composite containing aluminum powder and barium-aluminum borate glass are investigated. It is demonstrated that additional introduction of chromium oxide makes it possible after heat treatment at 660 – 750°C to obtain coatings with a surface resistivity of 0.05 – 0.50 · cm on various enameled substrates.     

Improving the thermal-shock resistance of siliceous refractories

Conclusion The thermal-shock resistance of siliceous specimens with additions, measured by the water-heat cycling method, as a rule, is increased with increase in the content of the additives from 5 to 30%, and is maximal for a content of 30% chromite-periclase. The crack resistance, determined by the air-heat cycling method is characterized by a maximum ¯R_T factor for each type of additive with a content of 15–20%. The maximum ¯R_T value is shown by specimens containing 20% chromite periclase.The maximum thermal-shock resistance of the specimens, without additives and with additions of silciding filling scrap, chrome-ore fractions <0.5 and 0.09 mm, clay, and chromitepericlase relate to each other respectively as follows: 11.82.52.83.55, and the crack resistance as 10.44.63.82.98.1. The number 2.9 obtained with specimens containing clay apparently is not maximal, since the clay content was limited to 15% for the reasons stated.Clay additives increase the thermal-shock resistance of the dinas [3], but markedly redice the temperature of initial softening under load and the mechanical strength. Therefore, thermal-shock resistant dinas with clay additions can be used only in special working conditions.The most promising of the compositions studied is one with an addition of chromite-periclase scrap. This helps to create a porous, microcracked structure which increases the thermal-shock resistance by five times (water-heat cycle tests) and the crack resistance by more than eight times (air-heat cycle method) compared with the ordinary dinas.The optimum content of chromite-periclase scrap, to obtain siliceous refractories with the maximum thermal shock resistance, is 15–20%. However, considering the reduced refractoriness under load noted with this (respectively to 1480 and 1370 deg C) we recommend that the additive be limited to 10%.Translated from Ogneupory, No. 4, pp. 9–11, April, 1991.     

Behaviour of a tall vertical gas-evolving cell. Part I: Distribution of void fraction and of ohmic resistance

Electrolysis of a 22 wt % NaOH solution has been carried out in a vertical tall rectangular cell with two segmented electrodes. The ohmic resistance of the solution between a segment pair has been determined as a function of a number of parameters, such as, current density and volumetric rate of liquid flow. It has been found that the ohmic resistance of the solution during the electrolysis increases almost linearly with increasing height in the cell. Moreover, a relation has been presented describing the voidage in the solution as a function of the distance from the electrodes and the height in the cell.Notation A _e electrode surface area (m²) - a _s parameter in Equation 12 (A^–1) - b _s parameter in Equation 12 - d distance (m) - d _ac distance between the anode and the cathode (m) - d _wm distance between the working electrode and an imaginary separator (m) - F Faraday constant (C mol^–1) - h height from the leading edge of the working electrode corresponding to height in the cell (m) - h _e distance from the bottom to the top of the working electrode (m) - h _s height of a segment of working electrode (m) - I current (A) - I ₂₀ current for segment pair 20 (A) - I _1–19 total current for the segment pairs from 1 to 19 inclusive (A) - I _x-19 total current for the segment pairs fromx to 19 inclusive (A) - i current density A m^–2 - N _s total number of gas-evolving pairs - n ₁ constant parameter in Equation 8 - n _a number of electrons involved in the anodic reaction - n _c number of electrons involved in the cathodic reaction - n _s number of a pair of segments of the segmented electrodes from their leading edges - Q _g volumetric rate of gas saturated with water vapour (m³ s^–1) - Q ₁ volumetric rate of liquid (m³ s^–1) - R resistance of solution () - R ₂₀ resistance of solution between the top segments of the working and the counter electrode () - R _p resistance of bubble-free solution () - R _p,20 R _p for segment pair 20 () - r _s reduced specific surface resistivity - r _s,0 r _s ath=0 - r _s,20 r _s for segment pair 20 - r _s, r _s for uniform distribution of bubbles between both the segments of a pair - r _s,,20 r _s, for segment pair 20 - S _b bubble-slip ratio - S _b,20 S _b at segment pair 20 - S _b,h S _b at heighh in the cell - T temperature (K) - V _m volume of 1 mol gas saturated with water vapor (m³ mol^–1) - v ₁ linear velocity of liquid (m s^–1) - v _1,0 v ₁ through interelectrode gap at the leading edges of both electrodes (m s^–1) - W _e width of electrode (m) - X distance from the electrode surface (m) - Z impedance () - Z real part of impedance () - Z imaginary part of impedance () - resistivity of solution ( m) - _p resistivity of bubble-free solution ( m) - gas volumetric flow ratio - ₂₀ at segment pair 20 - _s specific surface resistivity ( m²) - _{s, p s} for bubble-free solution ( m²) - thickness of Nernst bubble layer (m) - ₀ ath=0 (m) - voidage - _x,0 atx andh=0 - _0,0 voidage at the leading edge of electrode wherex=0 andh=0 - _,h voidage in bulk of solution at heighth - ₂₀ voidage in bubble of solution at the leading edge of segment pair 20     

The estimation of the residual capacity of sealed lead-acid cells using the impedance technique

The problem of estimating the residual usable energy of a lead-acid cell has been intensified by the introduction of fully sealed units. These rely on the recombination of gaseous oxygen produced during overcharge at the positive electrode with the active material at the negative electrode. This introduction has removed the possibility of electrolyte density measurements, third electrode measurements and restricted residual capacity assessments to the two cell terminals. A method for this process is described using a parameter based on a characteristic frequency. The parameter is also a useful measure of cell ageing.Nomenclature R _SOL Ohmic resistance of cell () - Charge-transfer resistance of positive and negative electrodes () - CL Double-layer capacitance of both positive and negative electrodes (F) - Warburg diffusion (S^–1/2) - C _EXT External series capacitor in analogue Fig. 5 (F) - R _EXT External resistor in parallel withC _EXT in the anologue circuit Fig. 5 () - IND Inductor in Fig. 5 representing the geometrical effects of the cell at high frequencies (Henries) - R _IND External resistor in parallel with IND in the analogue circuit Fig. 5 () - Roughness factor allowing for the porosity of both electrodes     

A model of the electrochemical behaviour within a stress corrosion crack

A mathematical model of the electrochemical behaviour within a stress corrosion crack is proposed. Polarization field, crack geometry, surface condition inside the crack, electrochemical kinetics, solution properties and applied stress can be represented by the polarization potential and current, the electrochemical reactive equivalent resistance of the electrode, the change in electrolyte specific resistance and surface film equivalent resistance, respectively. The theoretical calculated results show that (i) when anodic polarization potential is applied, the change in the crack tip potential is small; (ii) when cathodic polarization potential is applied, the crack tip potential changes greatly with the applied potential; (iii) the longer the crack, the smaller the effect of the applied potential on the crack tip potential in both anodic polarization and cathodic polarization conditions. The calculated results are in good agreement with previous experimental results.Notation coordinate, from crack mouth (on the metal surface) to crack tip (cm) - y y = s _L L/(s ₀ – s _L) + L – , function of (cm) - y ₀ y ₀ = s _L L/(s ₀ – s _L) + L (cm) - V polarization potential (V) - galvanic potential of electrode (V) - ₁ galvanic potential of electrolyte (V) - t sample thickness (cm) - w sample width (cm) - S _L crack tip width (cm) - S _o crack mouth width (cm) - L crack length (cm) - s() crack width at position (cm) - _lo specific resistance of electrolyte, as a constant ( cm) - _s specific resistance of metal ( cm) - (, y) specific resistance of electrolyte, varies with potential and crack depth ( cm) - R _b (, y) electrochemical reactive equivalent resistance of electrode, varies with potential and crack depth () - R ₁ electrolyte resistance () - R _s metal resistance () - r(, y) surface film equivalent resistance, varies with potential and crack depth () - r _o surface film equivalent resistance, as a constant () - I _o total polarization current (A) - I net polarization current from integrating 0 to in Fig. 2 (A) - polarization overpotential (V) - _a anodic polarization overpotential (V) - _c cathodic polarization overpotential (V) - Euler's constant     

Effect of state of charge on impedance spectrum of sealed cells Part I: Ni-Cd cells

Alternating current impedance spectroscopy (ACIS) was performed on commercial sealed Ni-Cd cells. A method previously developed in the literature was modified to determine the state of charge of sealed Ni-Cd cells by obtaining the impedance spectrum in a wide frequency range. The impedance parameters were sensitive to state of charge at low frequencies. A modified Randles' circuit was used to fit the impedance data. Appropriate modifications were made to account for an additional high frequency arc or a low frequency finite diffusion element. The effect of the state of charge on the equivalent circuit parameters was determined.List of symbols R ohmic resistance of battery (ohms) - C _dl double layer capacitance (F) - Q ₁ constant phase element representing double layer capacitance - Q ₂ constant phase element representing Warburg diffusion - O finite diffusion element - R _t charge transfer resistance () - R _s,R _p equivalent series and parallel resistance () - C _s,C _p equivalent series and parallel capacitance (F)     

Beta-silicon carbide whisker-polymer composites

Summary The beta silicon carbide whiskers, as prepared by the Los Alamos Process, have been found to have conductivities as high as 300 (cm)^–1. Random, uniform incorporation of these whiskers in two high temperature polymers (polybenzimidazole and polypyrrone) in 10 and 20 wt% concentrations generated films with conductivities as high as 1 × 10^–9 (cm) and 1 × 10^–5 (cm)^–1 respectively. The polymers without the whiskers had conductivities in the 10^–10 to 10^–17 (cm)^–1 range.     

Statistical regularities of the effect of slag activity on the slag corrosion of chamotte refractories in various media

Statistical regularities of the effect of slag basicity and the mass fraction of FeO in the slag in oxidizing and reducing media and in vacuum at 1500–1600°C on the slag corrosion of chamotte ladle refractories are investigated. It is shown that slag penetration and corrosion in the refractories depend mainly on the mass fraction of FeO in the slag, and the slag resistance decreases in the following order: oxidizing medium reducing medium vacuum.Translated from Ogneupory, No. 2, pp. 22 – 23, February, 1996.