Constant Current Technique Research Articles

Determination of transport and electrochemical kinetic parameters of M-H electrodes

Electrochemical and transport properties of La0.65Ce0.35Ni3.55Co0.75Mn0.4Al0.3 electrode were investigated in alkaline solution. The exchange current density, polarization resistance and the symmetry factor were determined from polarization curves obtained at low overpotentials. The symmetry factor was estimated to be 0.55 ± 0.01 and is independent of the state of charge. The equilibrium potential of the electrode was found to depend upon the hydrogen content in the alloy. The constant current discharge technique was used to determine the hydrogen diffusion coefficient in the alloy. The estimated value of \(\bar D\)/a2 at 0.1 C discharge rate was 1.39 × 10−4s−1.

Determination of Transport and Electrochemical Kinetic Parameters of Bare and Copper‐Coated LaNi4.27Sn0.24 Electrodes in Alkaline Solution

Electrochemical properties of bare and copper‐coated electrodes were investigated in alkaline solution. The exchange current density, polarization resistance, and equilibrium potential were determined as functions of the state of charge in the electrodes. The symmetry factors for bare and copper‐coated electrodes were estimated to be 0.53 and 0.52, respectively. By using a constant current discharge technique, the hydrogen diffusion coefficient in bare and coated was estimated to be .

Predicting future behavior of transient events rapidly enough to evaluate remedial control options in real-time

Electric utilities are becoming increasingly interested in using synchronized phasor measurements from around power systems to enhance their protection and remedial action control strategies. Accordingly, the task of predicting future behavior of the power system before it actually occurs has become an important area of research. This paper presents and analyses several approaches for solving the real-time prediction problem. In order to solve power systems with detailed load models fast enough for real-time prediction, the authors present a new piecewise constant current load model approximation technique that can solve a model as complex as the New England 39 bus system with composite voltage dependent loads much faster than in real-time. If the reduced order model is too large for real-time solution, then a pattern recognition tool such as decision trees can be trained off line to associate the post-fault phasor measurements with the outcome of future behavior. In this case also, the piecewise constant current technique would be needed to perform the offline training set generation with sufficient speed and accuracy. >

Measurement of anode potentials at high current densities in NaNO3 and NaClO3 media by the current interruption method for metals used in aviation technology

TheIR-free anode potential of mild steel, nickel and four Ni-Cr-Fe alloys were studied at high current densities (1–100 A cm−2) in NaNO3 and NaClO3 solutions. A constant current interruption technique was employed and the flow rate of the electrolytes was 14 ms−1 (Re = 7370). A plot of the anode potential against logarithm of current density yielded a Tafel line over a broad range of current densities. The plateau visible on the anode potential against current density curve was attributed to salt film formation. This explanation was confirmed by visual observation of the anode surface.

Statistical Characteristics of Void Fraction Fluctuations and Flow Regime Identification in Vertical Gas-Liquid Two-Phase Flow

In this investigation, an objective and quantitative method is developed for the identification and classification of flow regimes in vertical gas-liquid two-phase flow. It is clarified that the features of probability density function (PDF) and the parameters of the PDF expected according to the maximum entropy principle (MEP) can be used as objective flow regime indicators and quantitative flow regime discriminators, respectively. In this experiment, the void fraction fluctuations are measured by the constant current technique. The PDFs are classified into three major types and correspond to three dominant flow patterns: bubbly, intermittent and annular. That is, a uni-modal PDF with a low void fraction corresponds to a bubbly flow pattern; a bimodal PDF corresponds to an intermittent flow pattern; and a uni-modal PDF with a high void fraction corresponds to an annular flow pattern. Furthermore, the relationship between the statistical parameters of the void fraction fluctuations (the mean value, the standard deviation, and the coefficients of skewness and kurtosis) and the flow patterns is discussed. It is shown that classification of uni-modal and bimodal PDFs can be made according to the coefficients of skewness and kurtosis.

垂直管内気液固三相流の体積率変動特性と流動様式遷移線図

In gas-liquid two-phase flow and gas-liquid-solid three-phase flow, many flow configurations are observed and the particular pattern depends on the flow rates and the physical properties. The knowledge of flow regime is very important in the study of mechanics and modeling of the flows. In the previous investigations the flow pattern has been judged mostly on a basis of visual observation, therefore it was depended on observers subjectively.In this work volumetric fraction fluctuations of gas phase (in gas-liquid two phase flow) or gas and solid phases (in gas-liquid-solid three-phase flow) were measured by the constant current technique and those probability density functions (PDF) were mathematically expected by the maximum entropy principle. Then the flow regime detemlination was made objectively by using the parameters of the PDFs.The features of the PDF were classified into three dominant flow patterns; bubbly, intermittent and annular flows. It is demonstrated that the regime boundary of transition from the bubbly flow to the intermittent flow is predicted by a semi empirical formula based on the drift flux model and the regime boundary of intermittent-annular transition is described by an empirical correlation based on Froude number.

The physical, electrical and electrochromic properties of poly(1,4 dithienylbenzene)

Poly(2′,2″-bithiophene)-5′,5″-diyl-1,4-phenylene (PDTB) has been produced in thin film form via the electrochemical oxidation of 1,4(2′,2″-dithienyl)benzene using a constant current technique. Materials produced using long deposition times are found to become powdery and detach from the substrate, while those produced utilising different counter-ions are found to possess varied morphologies. Preliminary evaluation of the films for use in electrochromic display devices indicates that the changes in colour and optical density are satisfactory as is the display lifetime.

Li insertion in Cu yTiS 2 spinels

Li insertion in Cu y TiS 2 spinels at 120°C is investigated by constant current technique on samples of different stoichiometry. It is shown that each Cu present in the structure blocks two sites otherwise available for Li insertion. However, at potentials below 1.79 V vs Li the affinity for Li insertion expels Cu from the lattice and a separate metallic Cu phase is formed. The Cu phase is identified by X-ray analysis. Upon current reversal Li is reversibly extracalated and Cu slowly reinserted. In all cases the maximal Li insertioin corresponds to the formation of the compound LiTiS 2.

Muscle fiber capacity in low conductivity solution.

A method is described for computing the effective capacity of muscle fibers, C = Q/V where Q is the charge stored, and V is the membrane potential, using a standard two-microelectrode, constant current injection technique. The method is used to compare physical (or effective) capacity of frog muscle fibers bathed in a low conductivity, 2.5 mMK+ solution, with circuittheory derived quantities in the same cells and in control fibers. No differences can be discerned and it is concluded that low conductivity of physiological solutions, per se, does not significantly reduce the length constant of frog muscle transverse tubules.

Radio-Frequency Probes in a Nonlinear Isotropic Plasma

Nonlinear cold-plasma and scalar-pressure theories are derived and applied to a spherical RF probe in a plasma. With two specified RF potentials on the probe at different frequencies, calculations are presented for the second-order probe output responses. These include the second harmonic, the sum and difference frequencies, and the d.c. increment (resonance rectification). The nonlinear response as a function of frequency is shown to depend strongly on whether the input signals are maintained at a constant current or a constant voltage; for diagnostics, the constant-current technique permits identification of the plasma frequency, whereas the constant-voltage technique does not.

Chronopotentiometry

I. INTRODUCTIONBy the term chronopotentiometry we mean an electrochemical technique in which a controlled current, usually a constant current, is caused to flow between two electrodes; the potential of one electrode is monitored as a function of time with respect to a suitable reference electrode. The solution is usually, but not necessarily, unstirred and contains an excess of a supporting electrolyte so that diffusion is the principal mechanism of mass transport. This technique is distinguished from constant-current coulometric analysis and coulometric titrimetry 1 in that the current in chronopotentiometry is sufficiently large that the current efficiency for the reduction of the species of interest falls below 100%, usually within a few seconds. It is distinguished from galvanostatics, a constant-current technique useful for the determination of heterogeneous electron-transfer rates,2, 3 in that the chronopotentiometric potential-time trace spans several hundred millivolts whereas the galvanostatic potential-time trace extends less than ten millivolts from the equilibrium potential.

Anode Potentials in High‐Rate Dissolution of Copper

A constant current interrupter technique was employed in the experimental determination of anode potentials during high‐rate anodic dissolution of copper. The influence of ohmic voltage drops in the solution on measured over‐voltage has been compensated by electronic means. For short electrolysis times, dissolution proceeds in the active mode; in sulfuric acid, Tafel behavior was observed up to the highest current densities employed (100 A/cm2). Passivation effects may lead to significantly higher anodic potentials.

The Formation of Thin Anodic Films of Silver Oxide

Abstract : The formation of thin anodic films of silver oxide was studied by means of a constant current technique. The results indicate that this is a diffusion-controlled process involving the hydroxide ion. The study was carried out at room temperature and over a range of potassium hydroxide concentrations. (Author)

Anodic behaviour of mild steel in strong sulphuric acid—II. The sulphation and passivation processes

The sulphation and passivation processes on mild steel in 60, 70, 78, 85 and 96% H 2SO 4 have been studied by the classical constant current technique and by sweeping the potential at a controlled rate over the ranges of interest using a potentiostat. The potential sweep curves show two positive loops, each consisting partly of a polarization curve and partly of a current decay that is essentially time-dependent. The loops are associated with the sulphation process and with oxidation of the sulphate film and subsequent passivation. The relative sizes of the two loops depend on acid concentration, and in 70 and 96% acid the two stages can be separated in experiments at constant current. The sulphation process involves formation of a supersaturated solution leading to nucleation and growth of the sulphate film; the process closely resembles the sulphation of iron, lead or silver in dilute sulphate solutions. When the potential is raised to the lower end of the passive region of the steady-state polarization curves (Part I) oxidation of the sulphate film begins and it becomes less protective. Nucleation of the passive film then begins; this occurs sooner the higher the potential and in 60 and 70% acid there is a significant potential range in which nucleation is impossible although the passive film is stable once it is formed. Consequently considerable loss of metal (as ferrous ions occurs before the true passivation process begins, whereas in the more concentrated acids nucleation of the passive film occurs more easily and passivation involves little loss of metal. This difference appears to be due to differences in the phase present in the sulphate film.

A constant current microcoulometric technique for dropping mercury electrodes: The determination of the number of electrons involved in polarographic reductions

A constant current microcoulometric method for determining the number of electrons involved in a unit of reaction at a dropping mercury electrode is described in detail. A large capacitor is connected in parallel with the microcell, and a constant current applied to the combination. The results obtained from several tests with both reversible and irreversible reductions are discussed, and the optimum conditions for accurate results with the method are presented. The principle advantage of the amperostatic method over the usual potentiostatic method is the ease with which the number of coulombs passed during the electrolysis can be calculated.

Automatic coulometric titration of acids

An apparatus is described for the automatic titration of acids by the constant current coulometric technique. The generator electrodes comprise a platinum cathode and a silver/silver bromide anode. The increase in pH resulting from the reduction of hydrogen ion at the cathode is indicated by a glass electrode, in conjunction with a Beckman Automatic Titrator which automatically monitors the titration and interrupts the generating current when the equivalence point pH is reached. Quantities of hydrochloric acid in the neighborhood of 0.12 millimole in 50 ml were titrated with a mean error of -0.07% and an average deviation from the mean of ±0.15%. The technique is applicable to any strong or weak acid, and to acid mixtures, provided that no substance is present which is either reducible at the platinum cathode or reactive in any way at the silver anode.