Showing papers on "Electrode potential published in 1974"

Relative and absolute electrochemical quantities. Components of the potential difference across the electrode/solution interface

Abstract: The absolute value of the standard potential of the hydrogen electrode is calculated on the basis of a value of –263.1 kcal mol–1 for [graphic ommitted], the standard chemical free energy of hydration of the proton. This quantity, in turn, is evaluated from the experimental value of [graphic ommitted], the standard real free energy of hydration, as measured by Randles, and the value of 0.13 V for χH2O, the surface potential of water at the air/solution interface. The reliability of the derivation of χH2O is much increased by using, as a basis, a value for g(Hg)H2O(dipole), the surface potential of water at the mercury/solution interface, derived from indirect experimental measurements. The values of g(M)H2O(dipole) on a number of other metals are correlated to the enthalpy of formation of oxides MO and the resulting linear relationship interpreted in terms of different interaction of water with different metal surfaces. The significance of Iµabs°(H+/H2), the absolute potential of the standard hydrogen electrode, and its relation to ΔMSϕ, the actual potential difference across the electrode/solution boundary (operative electrode potential) are discussed. An attempt to calculate ΔMSϕ for alkali metals is made on the basis of chemical potentials of electrons as calculated from the theory of metals. Incorrect conclusions in previous works on the significance of µMe, the chemical potential of electrons, are shown and discussed. Implications are extended to the field of potentials of zero charge.

The Selectivity Evaluation of an Ion-selective Electrode with a Liquid Membrane by Electrode Response to a Foreign Ion

Abstract: The potential responses of liquid-membrane electrodes to foreign ions were examined. The electrode response obeyed the Nikolsky equation when the selectivity for the foreign ion was nearly equal to or higher than that for the objective ion and when the concentration of the foreign ion in the sample solution was sufficiently higher than that of the ion-exchanger in the liquid membrane. The Nikolsky equation, however, did not hold for the response when the selectivity for the foreign ion over the objective ion was extremely low or when the concentration of the sample was not so high. Such a non-ideal response was ascribed to the variation in the ionic composition at the membrane-solution interface caused by the ion-exchange. From the measurement of the electrode potential under conditions when the response obeyed the Nikolsky equation, the selectivity coefficient for the foreign ion over the objective ion could be obtained successfully as an intrinsic value of the electrode membrane. The selectivity value t...

Effect of the Thickness of Anodic Oxide Films on the Rate of the Oxygen Evolution Reaction at Pt in H 2 SO 4 Solution: I . Growth at Constant Current

Abstract: Ellipsometry and standard electrochemical techniques are used to determine whether, and if so, how the thickness of an anodic oxide film affects the catalysis of the oxygen evolution reaction at platinum. A prereduced electrode is first polarized in sulfuric acid solution with a constant current density, for a given time and then the thickness, , of the anodic film and the electrode potential, , are determined for various current densities . It is found that the thickness of the oxide film affects the catalytic activity in an exponential way, i.e. where and δ are constants. For the same time of polarization both the oxide thickness and the electrode potential increase with the logarithm of the polarization current density, . The potential dependence is . This is in contrast with the value of about 115 mV usually reported for the oxygen evolution reaction. The latter value can be obtained only when the electrode is anodically treated at a current density, , and the relationship is subsequently determined at current densities . Ellipsometry shows that under these conditions the anodic film thickness remains essentially constant at the value achieved during the initial polarization at a higher current density.

Basic Aspects of Electrode Potential Change in Submerged Fermentation

Abstract: The platinum electrode potentials relative to the standard half cell depended on a pH value, dissolved oxygen concentration, equilibrium constant and oxidation reduction potentials of the liquid The overall potential change in submerged fermentation gave no independent information on these individual factors A thermostatic and pH-static apparatus excluded influences of temperatures and pH values on the electrode pontentials If the determination was completed for short time duration, potentials were governed by the dissolved oxygen tension. While the oxygen concentration was maintained at a same level, redox potential changes became a dominant. This measurement of redox potential, which gave the concentration of extremely low dissolved oxygen that could not be detected by the membrane-coated oxygen electrode, was practically useful for the control of aerobic fermentation

Studies on oxygen transfer in submerged fermentation. XII. Basic aspects of electrode potential change in submerged fermentation.

Abstract: The platinum electrode potentials relative to the standard half cell depended on a pH value, dissolved oxygen concentration, equilibrium constant and oxidation reduction potentials of the liquid The overall potential change in submerged fermentation gave no independent information on these individual factors A thermostatic and pH-static apparatus excluded influences of temperatures and pH values on the electrode pontentials If the determination was completed for short time duration, potentials were governed by the dissolved oxygen tension. While the oxygen concentration was maintained at a same level, redox potential changes became a dominant. This measurement of redox potential, which gave the concentration of extremely low dissolved oxygen that could not be detected by the membrane-coated oxygen electrode, was practically useful for the control of aerobic fermentation

Automatic controller for electrostatic precipitator

Abstract: By using a hill climbing technique, the input energy to the electrostatic precipitator electrodes is automatically increased until the electrode potential decreases. In response to the electrode potential decrease, the input energy is decreased. The electrode potential is controlled by an automatic voltage controller including an electrode potential sense circuit. The controller includes a digital store for increasing the count of the store and means responsive to the count in the store provide an output signal related to the count and means responsive to the signal from the electrode potential sensing circuit which is indicative of a fall in the electrode potential is used to reduce the count in the store. The count in the store is converted into an analog voltage used to control the duty cycle of thyristers and thus the precipitator electrode potential.

Electrolytic etching method

Abstract: A precise pattern figure can be formed on a thin film of permalloy, iron, nickel, cobalt and copper through an electrolysis with a mixture of ammonium persulfate and nitric acid electrolyte under control of the electrode potential. Particularly, a desired part of an electrode whose surface is in coexistence with aluminum can be electrolytically etched without damaging the aluminum.

Semiconductor voltage transformer

Abstract: A semiconductor device for increasing voltage levels is disclosed. The device comprises an MIS structure formed over a pn junction. Suitable biasing of the metal electrode depletes the semiconductor surface of majority carriers and causes the accumulation of minority carriers from the bulk. At the same time a bending of the energy bands in the n and p regions is effected forming a potential barrier. When the electrode is switched to a reference potential, the minority carriers are raised to a higher potential and are prevented from returning to the bulk of the semiconductor by the potential barrier. An electrical path is provided for removing the minority carriers from the surface and combining the signal with the applied electrode potential.

Effects of adsorbed ions on simple electrode reactions. Part 1.—Reduction of periodate ion in the presence of toluene-p-sulphonate anions

Abstract: The influence of adsorbed toluene-p-sulphonate ions on the rate of electroreduction of periodate ions at mercury has been studied as a function of electrode potential and bulk concentration of the adsorbing ions in solutions of constant ionic strength. The ratio of the reduction rate in the presence of adsorbed anions to that in their absence at constant potential was found to be a function of the surface concentration of the adsorbed species independent of electrode potential, bulk concentration of the adsorbing species and their orientation on the electrode surface. An analysis of the decelerating effect of the adsorbed ions in terms of an electrostatic model of the interface which considers discreteness-of-charge effects is presented. The results of the analysis indicate that the reacting anion pairs with non-adsorbed cations in the vicinity of the reaction site before entering the activated state.

Standard Electrode Potentials of R--/R+ Redox Couples and Medium Effects in Non-aqueous Solvents

Abstract: The standard electrode potentials of R-/R+ redox couples may be estimated from polarographic reversible half-wave potentials of R/R+ and R-/R couples. When R+ and R- are large ions, similar in size and structure, the standard potential may be assumed as a solvent-independent reference point of electrode potential in various solvents. A few possible candidates for the "reference redox couple" have been discussed.

Pulse radiolytic polarography. Competitive oxidation and reduction of hydroxycyclohexadienyl radicals at the mercury drop electrode in aqueous solutions

Abstract: Hydroxycyclohexadienyl are produced in the puls e irradiation of aqueous N/sub 2/O-staurated solutions of aromatic compunds by a 20-nsec pulse of high- energy electrons in the vicinity of a handing mercury drop electrode. The polarographic current is recorded as a function of timee and at constant potential. Simultaneously, the changes in the opticsl absorption of the radicals with time in the bulk of solution are measured. Short-time polerograms of radicals are obtained by plotting the current at about 20 mu sec after the pulse vs. the electrode potential. Many hydroxycyclohexadienyl radicals show a steep polarographic wave with an anodic part immediately followed by a cathodic part. These waves are interpreted in terms of competitive oxidation and reduction of radicals. In addition, the problem of disproportionation of hydroxycyclohexadienyl radicals via electron transfer is discussed. Both electrode processes can occur with large rate constants in a certain potential range. Shifts of the waves to more negative potentials in the case of phenol and cresol are explained by the existence of mesomeric structures of alpha -alcohol radicals in the dihydroxycyclohexadienyl radicals formed. In strongly alkaline solutions, O/sup -/ reacts with toluene and benzylalcohol to form the benzyl radical and the benzyl alcohol radicalmore » anion, respectively. The polarograms of these radicals have well separated anodic and cathodic waves. The current vs. time curve of some radicals show a chasge in the sign of the current signal at potentials close to the foot of the polarographic wave. This effect is attributed to temporary changes in the relative concentrations of adsorbed and mobile radicals in the vicinity of the mercury drop electrode. (auth)« less

Structure of the mercury/ethylene carbonate interface. Part 3.—Adsorption of thiourea

Abstract: The adsorption of thiourea at mercury from ethylene carbonate solutions containing 0.5 mol dm–3 KPF6 and varying amounts of thiourea has been studied by measuring the differential capacity of the polarisable interface as a function of potential. The data were analysed to obtain the surface excess of thiourea as a function of electrode potential and bulk concentration. The parameters characterising the adsorption isotherm are discussed in terms of the electrostatic model for dipole adsorption by Kir'yanov, Krylov and Damaskin. These parameters are also compared with those obtained previously for the adsorption of thiourea from water, methanol, formamide, and dimethylformamide.

Selective determination of magnesium in water with divalent ion electrode using ethyleneglycol-bis(2-aminoethylether)tetraacetic acid as a complexing agent

Abstract: The calculated conditional constants at pH 2 to 10 for the ethyleneglycol-bis(2-aminoethylether)-tetraacetic acid (EGTA) complexes of magnesium and other metals indicate that no significant amount of magnesium is complexed by EGTA at pH below 7. The effect of pH on the electrode potential in the presence and absence of EGTA has been studied. The optimum pH found to be 7.0. At this pH magnesium can be selectively determined with a divalent electrode in the presence of most other polyvalent metal ions. Large amounts of salts affect the activity of magnesium ion and the electrode potential. Organic amines have been studied as a base to neutralize free acids in a solution, an amount of 5×10−2M nitrilodiethanol could be tolerated. The plot of potential vs. concentration of magnesium from 1×10−5 to 1×10−1M gives a rectilinear relationship.

Modern Methods for the Study of Electrode Processes

Abstract: The investigation of electrode processes calls for the use of methods that yield information on the reaction mechanism and the reaction rate, on the nature and stability of intermediates, and on adsorption processes at the electrode. It is no longer enough to record current-voltage curves or charging curves. In addition to the potentiostatic scan method, other methods that have proved useful for the investigation of electrode kinetics are the rotating disc electrode in particular, and to a smaller extent AC polarography. Intermediates can be identified with rotating double electrodes and by ESR spectroscopy or mass spectrometry. Adsorption processes on electrode surfaces can be studied by optical methods or by radioactive tracer methods.

True electrode potentials of minerals and their relation to adsorption of reagents and flotation properties

Abstract: 1. The authors examine methods for calculating and determining the true electrode potentials. 2. They make approximate calculations of the true potentials of a number of minerals. 3. They examine the relationship between the potential and the adsorption of flotation reagents. 4. The experimental data obtained show that the reaction-rate constant depends directly on the true electrode potential.

The Simultaneous Measurement of Electrode Potential, Current, Temperature, and Heat Flow

Abstract: A horizontal platinum resistance thermometer, which supported a meniscus above a pool of electrolyte, was used as an electrode. The unique design allowed the simultaneous measurement of electrode potential, current, temperature, and heat flow. Initial results are presented.

Corrosion of Iron in Crevices

Abstract: : The crevice corrosion of iron has been studied in quiescent sodium chloride solutions with and without chromate inhibitor. Polarization curves have been obtained using a special device which features an adjustable crevice width and provides for measurement of electrode potential within the crevice.

A role of the electrode potential in the stalagmometric titration using a dropping mercury electrode

Abstract: 水銀・溶液界面の界面張力を追跡して滴定終点を知る界面張力滴定について研究した.この方法は,被滴定液中でポーラログラフ用の毛細管から水銀を滴下させ,その滴下時間を測定し,水銀・溶液間の界面張力の尺度として用いる水銀滴下時間法によるものである.Tateの法則により,滴下時間は界面張力に比例する量であるので,滴下時間を追跡測定すれば界面張力滴定が可能である.すでに報告された滴定例である陰イオン性界面活性剤のテトラフェニルホウ酸ナトリウム(Na・ph4B)を陽イオン性界面活性剤ゼフィラミン(Zeph・Cl)で滴定する沈殿滴定の系について,界面張力滴定曲線の形の解析を試みた.また,界面活性指示薬を用いる方法をも含め,その後新しく開発された界面張力滴定例についても述べる.

Catalytic Reactions on Li-Doped NiO Using Modulation-Spectroscopy

Abstract: The oxidation degree of nickeloxide-electrodes in aqueous solutions depends on the electrode potential, as it is known from the surface of passive nickel-electrodes. In addition to current-potential characteristics and the impedance of the solid state/electrolyte interface this behavior was investigated using modulated reflectance measurements. By modulating the electrode potential this method results in changing the oxidation degree in connection with the optical properties of a surface layer. The investigation of Li-doped (0.5–5 mol%) nickeloxide crystals shows, that the change of the oxidation degree is catalytically influenced by the Li-doping. Measurements of the modulated reflectance result that the electrochemical activity of the doped crystals increases approximately parabolic with rising Li-amount.