Showing papers in "Transactions of The Faraday Society in 1962"

Kinetic theory of pseudo-capacitance and electrode reactions at appreciable surface coverage

Abstract: Electrochemical kinetic studies have been carried out at the nickel oxide electrode showing that the reversible potential for the N i u N i l n system is independent of the state of oxidation of the bulk oxide in the electrode over a wide range of degrees of oxidation The properties of the electrode are shown to be determined by the state of a surface phase, which is completely charged when the bulk oxide material in the electrode has been charged to 10% of its total charge capacity Experiments on sparingly charged electrodes have proved that charging of the bulk oxide does not commence significantly until the electrode is charged to about 1 5 % Consecutive electrochemical reactions possibly involved in the charging process are discussed INTRODUCTION The real reversible potential of the nickel oxide (N^-Ni 1 1 1 ) electrode has been the subject of controversy for some years and previously reported values are misleading since they have not been based on well-defined equilibrium conditions or a well-defined state of the system Determination of the reversible potential is complicated by the self-discharge processes which occur at the electrode in the oxidized form and also by the fact that the electrode may exist in a range of chemical states corresponding to the extent of conversion of Ni to Ni (and possibly Ni under certain conditions) in the hydrated oxide In an earlier paper (1), the true reversible potential of partially charged nickel oxide electrodes at a single controlled state of oxidation \"NiOi 25\" was examined as a function of potassium hydroxide and water activities in aqueous alkali solutions, and distinguished from the mixed potential assumed in previous work (2, also 12, 13) to be the reversible potential A polarization decay method was employed (1, 3, 4) in which the reversible potential was approached both from the anodic and the cathodic directions In the present phase of our work, the same method has now been applied to the study of the potential of partiall) charged nickel oxide electrodes as a function of the degree of charge, at constant electrolyte composition This method was found to be applicable only over a limited range of degree of oxidation of the electrode (\"N1O1 iu\"-\"NiOi 30\") owing to problems of extrapolation to the reversible potential to be discussed below. Stationary potentials, taken at very long times on open circuit, were therefore also measured as a function of the degree of charge over a much wider range of degree of oxidation (\"INiOi 02B\"-\"NIOI 50\") The role of the surface and bulk phases in determining the measured potential was deduced It will be shown that three well-defined regions in the charging process can be distinguished experimentally. In the first, the surface phase alone is being charged, in the intermediate region, the Faradaic current is used to charge both phases, until the surface phase is fully charged, after which oxidation of the bulk is the main Faradaic process (Most of the charging process occurs at a potential anodic to the reversible oxygen electrode, so that oxygen evolution must occur to a certain extent as a parallel process in all three regions described above It does not, however, become appreciable until most of the bulk material has been charged ) Canadian Journal of Chemistry Volume 40 (1902) 1933 1934 CANADIAN JOURNAL OF CHEMISTRY VOL 4

Mechanism of crystal structure transformations. Part 3. Factors affecting the anatase-rutile transformation

Abstract: The particle size and crystallite size of anatase increase markedly in the region of the crystal structure transformation. The unit cell of anatase seems to expand prior to the transformation to rutile. This expansion has been attributed to a displacive transformation of the type defined by Buerger. Smaller particle size and larger surface area seem to favour the transformation. The kinetics of the transformation of anatase prepared by the hydrolysis of titanium sulphate have been studied at different temperatures and are found to be considerably different from the kinetics of the transformation of pure anatase. The transformation becomes immeasurably slow below ~695±10°C compared to ~610°C for pure anatase. An induction period is observed in the transformation of anatase obtained from sulphate hydrolysis and the duration decreases with increase in temperature. The activation energy is ~120 kcal/mole, a value higher than that for the pure anatase-rutile transformation. The results have been interpreted in terms of the relative rates of nucleation and propagation processes. The activation energy for the nucleation process seems to be much larger than for the propagation process. The kinetics of the transformation of anatase samples doped with different amounts of sulphate ion impurity have also been studied and the transformation is found to be progressively decelerated with increase in the impurity concentration. The energy of activation for the transformation appears to increase progressively with increase in impurity concentration.

Electron spin resonance spectra of alkyl radicals in γ-irradiated alkyl halides

Abstract: A study of the electron spin resonance spectra of radicals trapped in gamma -irradiated polycrystalline alkyl halides at -196 deg C established that in almost all cases the main species observed in the 1st hours after irradiation is the parent alkyl radical, though isomerization reactions such as isobutyl yields tert-butyl occur at this temperature. Hyperfine splitting constants for the interaction of the alpha - and BETA -protons with the unpaired electron were determined for radicals with the formulas (CH/sub 3/),CH/sub 3-n/(n = 0 to 3)RCH/ sub 2/CH/sub 2/,RR'CHCH/sub 2/, RR'CH (including cycloalkyl) and RR'R''C. It was found that alpha -protons and those in freely rotating methyl groups interact to give isotopic hyperfine splitting of 80-75 Mc/sec, while the magnitude of the interaction of the BETA -protons may vary from 130 Mc/sec, depending on the configuration of the radical. In panticular, the 2 BETA -protons in RCH/sub 2/CH/sub 2/ are not equivalent, impiying an unsymmetrical equilibrium configuration. Interpretation of the spectra of organic radicals trapped in polycrystalline matrices involves the consideration not only of the number of interacting protons and their relative orientation, but also more » of the effect of more distant groups which may affect the electron distribution and also the configuration of those groups which give observable hyperfine interaction. Simple alkyl radicals, with the single exception of the isobutyl radical, give spectra consisting of an even number of lines. Since differences in line separation are small, the interpretation must rely heavily on relative intensities which are readily altered by the superposition of similar spectra, or by incipient saturation. (H.H.D.) « less

Transition probability in molecular encounters. Part 5.—Vibrational-rotational energy transfer

Abstract: Vibrational relaxation times in CH/sub 4/, CD/sub 4/, SiH/sub 4/, and SiD/sub at 298 and 348 deg K were measured by the ultrasonic method. The deuterated molecules showed longer relaxation times than the unsubstituted molecules, and an explanation of this in terms of vibrational-rotational energy transfer is suggested. A similar explanation is offered for the existence of a separate line for hydrogen-containing molecules in the Lambert-Salter correlation plot for relaxation times.

Correlation of dissociation energies of gaseous molecules and of heats of vaporization of solids. Part 1. - Homonuclear diatomic molecules

Abstract: In this paper two correlations are proposed. The first correlation classifies the forty odd known homonuclear diatomic molecules according to the ratio α = ΔH 0 o (vap. M)/D 0 o(M 2) (heat of vaporization of an atom/dissociation energy of the diatomic molecule). Values of α = 0.5 to 1, 1.2 to 2.5 and >5 correspond to three categories each consisting of several whole groups of elements. The significance of this classification is discussed qualitatively. The second correlation shows that ΔH 0 o(vap. M) can be closely represented by Λ-BΣ ie i(M). Σ ie i(M) is the energy necessary to excite the atoms to a promoted " configuration " composed of equal contributions of a well-defined set of low lying electronic states of the free atom. Λ and B are empirical parameters. One set of electronic states is taken for Ca to Ni, Sr to Pd, and Ba to Pt with B = 1/2 and Λ = 178, 206, 250 kcal/g atom respectively; another set of electronic levels and Λ = 131 kcal and B = 1/4 represent ΔH 0 o(vap. M) for Ni, Cu, Zn, Pd, Ag, Cd, Pt, Au, Hg. Using the first classification, the experimental conditions are estimated for observation of the yet unknown homonuclear diatomic molecules of the transition elements. For this purpose a self-consistent set of free energy functions has been calculated.