Zur Chemie des Chlorisocyanates, 1. Mitt.: Polymerisation,thermisches Verhalten und Photolyse

Zusammenfassung Es wird auf Grund der Untersuchung der Polymerisation, des thermischen Verhaltens und der Photolyse der Stabilitätsbereich von Chlorisocyanat, Cl-N=C=O, umgrenzt und dadurch die Möglichkeiten der Aufbewahrung und Werwendung für Reaktionen mit anderen Substanzen aufgezeigt.

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Chemistry of chloro-isocyanate, I: Polymerisation, thermic behaviour, and photolysis

The stability of chloro-isocyanate, Cl-N=C=O, is determined by investigating its polymerisation and thermic and photolytic behaviour. The possibilities of storing and using for reactions with other substances are discussed.

     

Determination of the chemical diffusion coefficient of lithium in multiwall carbon nanotubes

Electrochemical intercalation of lithium into multiwall carbon nanotubes produced by the arc-electric technique has been carried out in button cells to estimate the solid state diffusion coefficients of lithium. An extension of the Galvanostatic Intermittent Titration Technique (G.I.T.T.) of Weppner and Huggins and further developed by Honders is employed. The results are interpreted providing that the lithium species enter the nanotubes perpendicularly to their walls and thus give rise to a necklace structure as observed by Transmission Electron Microscopy (TEM). Finally, the results are compared with the data obtained for different kinds of carbon: carbon fiber, petroleum coke and graphite. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

Effect of surface chemistry on the thermodynamics and conductivity of water in silica nanopores

The thermodynamics and conductivity of water confined in nanoporous silicas SBA-15 are studied using differential scanning calorimetry and impedance spectroscopy. The effect of the water/surface interaction is addressed by investigating samples with different surface chemistries.     

Pure-tone increment detection in harmonic and inharmonic backgrounds

The present study investigated the effect of increasing the number and frequency range of background components upon the detection of an increment to the intensity of the center component. Previous studies [e.g., Green et al., J. Acoust. Soc. Am. 75, 1163-1167 (1984)] have demonstrated that, for background stimuli consisting of logarithmically spaced pure-tone components, as the number of background components is increased, the threshold for detection of an increment to the center component is decreased. The present study investigated this effect using harmonically spaced, as well as logarithmically spaced, backgrounds, because many natural sounds, including voiced speech sounds, consist of harmonically spaced components. Two conditions were employed for both types of backgrounds, fixed-level and roving-level within a trial. Group results revealed a small decrease in threshold with increasing number of components only for the fixed-level, logarithmically spaced backgrounds. No decrease in threshold was observed for the other three conditions, including the roving-level, logarithmically spaced backgrounds which were the same as those used by Green et al. (1984). The present results suggest that the decrease in signal threshold with increasing number of background components exists only under limited conditions and that it is a highly individual phenomenon. The present results also suggest that the effect does not occur for harmonically spaced complexes such as most natural sounds including voiced speech.     

Nickel hydroxide obtained by high-temperature two-step synthesis as an effective material for supercapacitor applications

Hybrid supercapacitors with nickel hydroxide electrode are widely used as modern power sources for electrovehicles, ignition of different electric engines, etc. Nickel hydroxide for supercapacitor use must satisfy special features which are quite different from those requested for battery application. The aim of this work is to improve the promising two-stage high-temperature method by altering hydrolysis condition (hot and cold) in order to obtain Ni(OH)₂ with improved electrochemical activity. Ni(OH)₂ samples have been investigated by PXRD, TG, DSC, SEM, TEM, cyclic voltammogramm, and galvanostatic charge-discharge cycling. It has been established from PXRD, TG, and DSC analyses that material obtained by hydrolysis at high temperature is a highly crystalline β-Ni(OH)₂ characterized by high thermal stability. Materials prepared by cold hydrolysis are a highly defective β_bc-Ni(OH)₂, with 6.3 % water content and a lower thermal stability. It has been shown that samples prepared by hot hydrolysis have a high redox reversibility and electrochemical cycling stability, but a lower electrochemical capacity. This suggests that the electrochemical processes are localized in the thin layer at the particle surface. Cyclic voltammograms of samples prepared by cold hydrolysis exhibit gradual activation of the active material, anyhow resulting in higher capacity. By means of the galvanostatic charge-discharge curves at different current densities, the specific capacities of the samples have been calculated. The sample prepared by cold hydrolysis has higher specific capacities than the sample prepared by hot hydrolysis.