Faraday Constant Research Articles

A Novel Method for Analyzing Silver Sediment With High Precision.

A technique has been devised which is sufficiently accurate to aid in an electrochemical determination of the Faraday constant using the silver coulometer. The technique is used to recover the silver residue which falls from the anode during operation of the silver coulometer. In contrast to previous efforts at recovery, which involved weighing of the silver residue, the method here described is to convert the silver atoms to ions and then to plate the silver onto a cathode held at constant potential with respect to a reference electrode. The current involved in the electrolysis is integrated electronically. An overall standard deviation of 5 μg is achieved for samples ranging in size from 400 μg to 1.8 mg.

Growth rate limitations in electrochemical crystallization

During growth by the Electrochemical Czochralski Technique (ECT), the relationship between the linear growth rate (d y/d t) and the total current can be expressed by the equation dy/ dt = K∈ I/ A = K∈ i, where ∈ is the deposition efficiency and A the interfacial area. The growth rate constant K is defined by K = M/ nFϱ, where M is the molecular weight of the depositing material, ϱ its density, n the number of electrons transferred and F Faraday's constant. ECT was quite successful in its application to the growth of sodium tungsten bronze single crystals. Metals, unlike sodium tungsten bronze, have isotropic growth kinetics and it was expected that crystal morphology and diameter control would differ significantly. The present studies show that metals are difficult to grow by ECT and clearly point out the significance of the growth rate constant K.

Energetics of sodium transport in toad urinary bladder.

The ratio of the rate of transepithelial sodium transport, JNa, across the isolated toad urinary bladder to the simultaneously measured rate of transport-dependent metabolism, JsbCO2, has been measured as a function of the transepithelial electrical voltage, deltapsi. The ratio remains constant with a mean value of 18 to 20 over the range of imposed voltages of 0 to +70 mV. With increasing hyperpolarization of the bladder, JNa decreases and the calculated electromotive force or apparent "ENa" of the sodium pump increases. From thermodynamic and kinetic arguments it is shown that the apparent "ENa" approaches the maximal electrochemical potential gradient, ENa, against which sodium can be transported by this tissue only when JNa approximately 0. At this unique condition F ENa (in which F is the Faraday constant) is the maximal free energy of the chemical reaction driving sodium transport and thus equal to the maximal extramitochondrial phosphorylation potential and the maximal free energy of the mitochondrial respiratory chain within the transporting cells.

PHYSICO CHEMICAL PROPERTIES OF NICKEL OXIDE AT HIGH TEMPERATURE

PHYSICO CHEMICAL PROPERTIES OF NICKEL OXIDE AT HIGH TEMPERATURE

Determination of m, e/m, and M p/m by the study of the isotope structure in hydrogen

Using a commercially available hydrogen–deuterium light source and a 3.4-m Ebert plane grating spectrograph, the wavelengths of the first six pairs of the Balmer series are obtained. From the results, first, the series limit, Rydberg constant, and ionization potential of hydrogen are found from the graph. Then, by means of formulas involving wave numbers of hydrogen and deuterium and by knowing the Faraday constant, the values of m, e/m, and Mp/m are determined. All the values are found to be in good agreement with accepted values. From the results, this experiment is recommended for an upper division optics and spectroscopy or quantum physics laboratory.

Reduction of Crotonic Acid with Hydrogen on a Slurry Electrode

A slurry electrode system consisting of a suspension of metal or a supported metal powder in an electrolyte in contact with a gold foil electrode was studied as a hydrogen electrode for the reduction of crotonic acid in a supporting electrolyte of sodium p‐toluene sulfonate. Current‐voltage curves and current efficiency were studied. Effects of suspension concentration, crotonic acid concentration, butyric acid concentration, pH, and temperature were studied for platinum black and palladium‐on carbon slurries. The results are consistent with the view that the potential‐determining reaction is the discharge of hydrogen atoms adsorbed on the catalyst. Olefin competes for adsorbed hydrogen and this modifies the observed potential. Very low anodic limiting currents were observed in the presence of olefin, suggesting that it is strongly adsorbed on the anodic hydrogen electrode. The following electrokinetic expressions were established for cathodic currents: (i) for 5% Pd on and (ii) for Pt black where is the current, is a constant, is hydrogen ion concentration, is crotonic acid concentration, is butyric acid concentration, is catalyst concentration, is the electrode potential, is Faraday's constant, is universal gas constant, and is the absolute temperature.

Applications of Radioisotopes in Polarography

Abstract In radiopolarography the classical polarographic curves are substituted by radioactivity-potential diagrams. The method allows to follow radio-metrically typical polarographic phenomena as the occurrence of maxima. As for the diffusion current constant, I, also a relationship between Ad, Atot and the product m⅔t⅙ can be derived giving the diffusion activity constant A. Determining experimentally the values of I and A allows to verify the activity recovered by calculating the corresponding value of the faraday constant. The influence of a large excess (≥ 10−2 M) of a more readily reducible ion on the electrolytic discharge of an ion reduced at more negative potentials was investigated, showing experimentally an increase of deposition above concentrations of 10−2 M. The increase depends on the medium as well as on the nature of the ions involved.

Energetics of Sodium Transport in Frog Skin

Sodium transport and oxygen consumption were studied simultaneously in the short-circuited frog skin. Sodium transport was evaluated from I(o)/F, where I(o) is the short-circuit current measured with standard Ringer's solution bathing each surface and F is the Faraday constant. Oxygen tension was measured polarographically. Under a variety of circumstances the rate of oxygen consumption from the outer solution exceeded that from the inner solution, the ratio being constant (0.57 +/- 0.09 SD). Both I(o) and the associated rate of oxygen consumption J(ro) declined nonlinearly with time, but the relationship between them was linear, suggesting that the basal oxygen consumption was constant. For each skin numerous experimental points were fitted by the best straight line. The intercept (J(ro))(Io=0) then gave the basal oxygen consumption, and the slope dNa/dO(2) gave an apparent stoichiometric ratio for a given skin. The basal oxygen consumption was about one-half the total oxygen consumption in a representative untreated short-circuited skin. Values of dNa/dO(2) in 10 skins varied significantly, ranging from 7.1 to 30.9 (as compared with Zerahn's and Leaf and Renshaw's values of about 18). KCN abolished both I(o) and J(ro). 2,4-dinitrophenol (DNP) depressed I(o) while increasing J(ro) four- to fivefold. Anti-diuretic hormone stimulated and ouabain depressed both I(o) and J(ro); in both cases apparent stoichiometric ratios were preserved.

Variation of Stripe-Domain Spacing in a Faraday Effect Light Deflector

Stripe-domain ferromagnetic films with high Faraday rotation and low optical absorption will rotate the angle of polarization of light transmitted through even-numbered domains an angle φ = FT and through odd-numbered domains an amount −φ, where F is the Faraday constant and T is the film thickness. The result of the differential rotation is that the film will act like a transmission diffraction grating. Since the orientation and spacing of the stripes may be altered by appropriate applied fields, the film may be used as a laser light deflector. A two dimensional model is proposed for stripe domains in some ferromagnetic films. This model differs from previous models (see Ref. 4–8) in that it includes the dependence of wall width on wall angle and thereby shows that variations in stripe-domain spacing of more than an order-of-magnitude are possible. Variations of this amount were observed experimentally in a YIG platelet which was used as a stripe-domain light deflector.

PREFERENTIAL ION TRANSPORT THROUGH ION EXCHANGE MEMBRANES BY ELECTRODIALYSIS

The preferential transport of a certain ionic species to others through an ion exchange membrane has been investigated. It was found from some experimental data that the preferential ion transport, SBA, should be closely related to an operating parameter ξ, where SK+NA+ for example, is defined as the ratio of the Sherwood number concerning the transfer rate of K+ to that of Na+, and E is defined as (∧Δφ/2FDV). The Stanton number St=(l/F)/C10V defined as the ratio of the total ionic flux in the direction to the membrane to that in the direction of the bulk flow, was also a function of ξ. These factors, ∧, Δφ, F, D, V, I, and C10 are the equivalent conductivity, the effective applied voltage to a single desalting compartment, the Faraday constant, the channel thickness, the linear flow velocity, the current density and the total equivalent concentration, respectively. Under the operating condition of ξ> IO-3, no ion exchange membrane will serve to transport a certain ion preferentially. If ξ∧1O-4, however, the membrane will fully reveal its own ability for selecting a certain ionic species, because the concentration ratio of two ionic species at the membrane surface will approach that in the equilibrium state.

Determination ofeh, Using Macroscopic Quantum Phase Coherence in Superconductors: Implications for Quantum Electrodynamics and the Fundamental Physical Constants

The implications of the new determination of $\frac{e}{h}$ using the ac Josephson effect in superconductors for both quantum electrodynamics (QED) and our knowledge of the fundamental physical constants are analyzed in detail. The implications for QED are investigated by first deriving a value of the fine structure constant $\ensuremath{\alpha}$ from experimental input data which do not require the use of QED theory for their analysis. These include the Josephson-effect value of $\frac{e}{h}$, the Faraday constant, the gyromagnetic ratio of the proton, the magnetic moment of the proton in units of the nuclear magneton, the ratio of the ampere as maintained by the United States National Bureau of Standards to the absolute ampere, and certain accurately known auxiliary constants. This is done by critically reevaluating all of the experimental data presently available on these quantities and applying the standard techniques of a least squares adjustment, including tests for imcompatibility. The value of $\ensuremath{\alpha}$ so obtained is then used to evaluate the theoretical expressions for the Lamb shift and fine structure splitting in hydrogen, deuterium, and ionized helium, the hyperfine splitting in hydrogen, muonium, and positronium, and the anomalous magnetic moment of the electron and muon. These theoretical values are compared with critically reexamined experimental values, thus providing a test of QED in which a priori information from QED itself is not essential. The consequences of the new measurement of $\frac{e}{h}$ for our present knowledge of the fundamental physical constants are demonstrated by deriving new "best" values for the fundamental constants from a critically selected subset of all the available data. In addition to providing a consistent set of constants, this analysis focuses attention on areas in which there remain important questions which require clarification. The experimental and theoretical work necessary for the resolution of these questions is discussed, with emphasis on ways in which the study of quantum phase coherence effects in low temperature superfluid systems can make significant contributions.

アルミニウムはんだ付部の耐食性について(第1報)

The external cathodic polarization curves of each cast alloy such as Al-Sn, Al-Zn and Zn-Sn systems, which were dipped in 3% NaCl aqueous solution, were investigated by a potentiostatic method to determine the corrosion behavior of soft-soldered joint in aluminum. The profiles of the polarization curves were conventionally divided into two categories: straight line and curved line type. The former was seen in Al-Sn system only and this phenomenon was presumed as the cathode reaction of Eyring's protrotopic process, because the value of transfer coefficient calculated by using the measured value in this type was about 0.33 and was nearly equal to that of tin having a cathode control of activation process. The latter was seen in all of metals used as alloying elements and the remainder among the alloys tested here and this phenomenon was considered as the concentration polarization, where a cathode reaction is controlled by a diffusion process of dissolved oxygen. To do this consideration, iL, a limiting current density, was approximately calculated by the following equation introduced by using Fick's-Law.iL=2⋅F⋅D01/2[O2]⋅t-1/2/√πWhere F is Faraday constant, D0 is the diffusion constant of oxygen, [O2] is the concentration of disolved oxygen, t is the dipping time of sample. While the measured value for iL was decided by appling an overvoltage intercept method to the external cathodic polarization curve.From the electrochemical measurements mentioned above, it has been concluded that the natural electrode potentials of soldered joints in aluminum were not necessarily the important factor governing the corrosion rate between the aluminum, the various phases in the solder and the layer that forms at the aluminum and solder interface.

The Fundamental Atomic Constants

In the first edition of this valuable little book the author mentioned the uncertainties associated with the value of the Faraday constant. Further experimental work has now been completed.

Tiの不動態について

Passivation and activation of titanium in deaerated non-oxidizing acid solutions were studied in order to investigate on the passivity of titanium. Critical potential for passivity and Flade potential shift towards noble direction with increasing chloride and hydrogen ion concentration, thus passivation becoming difficult. The critical potentials are expressed as E=E0+mlog[Cl-]-n(RT/0.4343F)pH, where R, the gas constant, T, absolute temperature, F, Faraday constant, E0 and m are constants. The constant n varies from 0.9 to 3.0 with environmental conditions such as temperature and kind of anion. Such different pH dependence of the critical potentials is attributed to the presence of different equilibrium surface reactions corresponding to passivation or activation for the respective corrosion conditions. The equilibrium reactions are considered to beTia++2H2O=TiO2+4H++(4-a)e, 2Tib++3H2O=Ti2O3+6H++(6-2b)e, Ti+2H2O=TiO2+4H++4e, 2Ti+3H2O=Ti2O3+6H++6e.When the critical potentials expressed as equilibrium potentials of two former reactions, passivation or stability of passivity is affected directly by titanium ion. In such cases, as demonstrated for titanium-palladium alloy, corrosion resistance of titanium depends on the concentration of titanium ion in corrosive media.

The Limiting Thickness of an Electrolyzed Gas Film Capable of Sustaining a Given Negative Pressure

The critical thickness of a gas film that is just capable of withstanding a given negative pressure PN in a liquid column has been studied. The film was generated electrolytically on the surface of a spherical platinum electrode of known area. The number of gas molecules corresponding to the measured charge required to release the negative column was then computed from the relation between the Faraday constant and Avogadro's number. The number of gas molecules required to form a monolayer on the electrode was next computed from the molecular diameter, based on van der Waals' equation. The ratio of these numbers gives the ``thickness'' t of the film in fractions of a monolayer. Both O2 and H2 gas films were measured under conditions such that the same number of gas molecules were deposited on the same electrode and the corresponding critical negative pressures observed. Assuming the effectiveness of the film to be proportional to the area covered, the ratio of the diameters of the O2 and H2 molecules is inversely proportional to the square root of the ratio of their critical negative pressures. This gave O2/H2=1.11 as compared with 1.06 from measurements based on van der Waals' equation. Measurements of oxygen films were made at various negative pressures, ranging from PN=90 cm of water, t=0.55 monolayer, to PN=4 cm, t=0.87 monolayer. The results lie on a smooth curve down to PN=10 cm, t increasing steadily as PN is reduced. Below PN=10 cm, the thickness of the film no longer increases, indicating that the zone of influence of the gas molecule extends beyond its projected area.

The "1947 Values" of the Atomic Constants and the Revision of the Faraday Constant

The "1947 Values" of the Atomic Constants and the Revision of the Faraday Constant

The Donnan Membrane Equilibrium

THE famous theorem of Gibbs concerning the equality of the chemical potential µ of an independent component throughout a system of co-existent phases in equilibrium at constant temperature and pressure is widely known. It is perhaps not so well known that, if external fields of force or electrically charged components (ions or electrons, for example) are present, an extension of the foregoing theorem is required, though Gibbs himself dealt with this matter in the case of a gravitational field. The subject was very well discussed in an important paper by Milne1 in 1925. If the system of phases be under the action of an external field of potential O per unit of mass, then, corresponding to each independent component, an equation of the type µ + O= constant holds throughout the system. This corresponds to Gibbs' result for a gravitational field. A similar state of affairs holds good for a centrifugal field. A very interesting type of this sort was dealt with on Gibbsian lines by Kai O. Pedersen2 in 1934. Let us now suppose that certain components have associated with them electric charges of amount et- per unit mass (where the subscript refers to such a component i). The presence of the charges will give rise to an electrostatic field, and there may be also present an external electrostatic field. Denote the total electrostatic potential by?. Then, instead of the condition µ = constant, throughout the system of phases, we have the condition µ; + = constant, and if a gravitational field of potential O per unit of mass is also present, the condition becomes µ+ O + e,*Y = constant. If we are dealing with the distribution of ions in ordinary laboratory apparatus (say in experiments on membrane equilibria of ions across a semi-permeable membrane) the term O practically cancels out. Not so, however, the electrical term, which may now be written in the form zi, where Zi F? is the electrovalency of the ionic component i (positive for a cation and negative for an anion) and F is the Faraday constant. Both µ; and the term ZiF refer now to a gram molecule of the ion,i. The expression µ; -l- Zi F has been called the 'electrochemical potential' by Guggenheim3, to whom we are indebted for its introduction and practical use in modern physical chemistry. The Donnan Membrane Equilibrium By Dr. S. G. Chaudhury. Pp. viii + 112 + xv. (Howrah: A. P. Bhattacharya, 1945.) 10 rupees.