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ChemInform Abstract: THE INFLUENCE OF THE TUNNEL PROBABILITY ON THE ANODIC OXYGEN EVOLUTION AND OTHER REDOX REACTIONS AT OXIDE COVERED PLATINUM ELECTRODES

AbstractPotentiostatische und galvanostatische Impulsmessungen wurden vorgenommen, um die anodische Sauerstoffentwicklung an Pt‐Elektroden in In H2SO4 in Abhängigkeit von Oxidschichtdicke und Elektrodenpotential zu untersuchen.

The influence of the tunnel probability on the anodic oxygen evolution and other redox reactions at oxide covered platinum electrodes

Potentiostatic and galvanostatic pulse measurements were carried out to investigate the anodic oxygen evolution at platinum electrodes in 1N H 2SO 4 in dependence on the oxide layer thickness d and the electrode potential ε. The thickness d (1·5–10 Å) was obtained from cathodic charging curves. Further, the temperature dependence (0°–81°C) was evaluated from Bowden's measurements. Summarizing, the current i o2 follows the relation, log i = A - ( E 0 a - α Fη)/2·3 RT - d/d o. The experimental activation energy E o = E o a = α Fη decreases linearly with increasing overvoltage η. The linear decrease of log i with increasing d, which is given by the term d/d o, is correlated to the probability of the quantum mechanical tunnel transition of the electron from adsorbed ions, OH − ad or O 2− ad respectively, through the oxide layer to the metal. Similar effects of the oxide layer thickness on the current density were observed in the case of the oxygen evolution at iridium, the CO-oxidation on platinum, and the reduction of Cl − and Ce 4+ at platinum. In these cases a rate determining electron transfer through the oxide layer is also assumed.

U.V. induced thermoluminescence on natural calcium fluoride.

Abstract Samples of a green variety of fluorite found at Circuit, Brazil, annealed at 580°C for 10 min and then at 400°C for 2 hr were exposed to 365 nm u.v. light. The transferred TL from deep trap to lower temperature trap gives rise to a glow curve containing peaks I, II, III', III and IV in a readout up to 400°C. This TL response was measured as a function of u.v. exposure time t and the result is not a saturation curve, but, TL tends to zero for large t indicating a simultaneous bleaching effect. The curve of TL vs number n of cycles in an exposure-readout cycle was obtained for different durations of exposure in each cycle. For large n the rate of decrease of log (TL) is independent of the time interval of exposure to u.v. light in each cycle. The effect of duration and temperature of pre-annealing on TL transfer under u.v. exposure as well as the dependence of transferred TL on previous gamma radiation were investigated. Finally a mathematical model is proposed.

Viscoelastic properities of cross-linked solutions of poly (β-hydroxyethyl methacrylate) in diethylene glycol. V. Influence of secondary low-temperature transitions

Abstract The influence of secondary low-temperature dispersions on the storage and loss compliances of four poly(β-hydroxyethyl methacry-late) solutions in diethylene glycol was studied by comparing previously published double-transducer data with isochronal torsion pendulum data measured starting from the temperature of liquid nitrogen. It was found that the contribution of the main transition as observed in the storage compliance J'p decreased with increasing swelling degree of the samples. For a sample swollen to volume fraction of polymer v2 = 0.168, log Jp changes only about one decade, from −6 to −7; the further decrease of log J′p from −7 to −10.5 corresponds to the secondary low-temperature dispersion characteristic for polar side chains—polar diluent systems. For the latter dispersion the Arrhenius plot obtained using the double-transducer data gave δH = 24 kcal/mole. It was concluded that in some special cases the role of low-temperature secondary dispersions can be of primary importance in infl...