Electrochemical investigations on the stationary and non-stationary behaviour of the PbO2 electrode

The kinetic behaviour of the PbO₂ electrode is determined by three reactions: (i) deposition/dissolution of lead dioxide, (ii) changes in the stoichiometry of the oxide, especially by incorporation/dissolution of hydrogen; (iii) anodic evolution of oxygen.Immediately following commencement of current flow the stoichiometry-changing reaction predominates, because, we postulate, the proton transfer across the PbO₂/electrolyte phase boundary is almost uninhibited. Investigations of the kinetics of this reaction have therefore been carried out by means of current pulse measurements. Under appropriate conditions the current in the stationary state is used for PbO₂ deposition/dissolution only. Current-overvoltage curves for these reactions have been obtained from measurements with thin PbO₂ layers, where the stationary state was reached quickly.     

Bubble flow in pressurized gas/solid fluidized beds

This contribution presents the measurements of bubble behaviour in presence of A, B and D powders in a semi-industrial scale pressurized fluidized bed. Local measurements were taken at static pressures of 0.2, 1.0 and 2.5 MPa, using capacitance probes. Quartz sand with mean particle diameter of 157 μm was fluidized in small “two-dimensional” transparent equipment with Frigen R 115. In addition, pressure fluctuations in the bulk of the fluidized bed with inner diameter of 0.4 m were studied experimentally.     

Inner surface and void system of regenerated cellulose fibers

Both the inner surface and the void system of different cellulose regenerate fibers are investigated with X-ray small angle scattering. Thereby it turns out that all fibers have a void system of 0.01 to 0.1% (volume fraction 10^?4–10^?3). However, the amount of the void system has little influence on the mechanical properties. Rather, it is the shape of the voids and their orientation which proves essential. It is found that elongated voids, probably well oriented, are responsible for superior mechanical properties. This explains also improved textile properties of lyocell fibers of the NMMO type.     

Kinetic studies of steam gasification of char in the presence of H2, CO2 and CO

Kinetic studies have been carried out to elucidate the mechanisms of steam and CO₂ gasification of char and the interactions of these gasifying agents. The positive and negative influences of all product gases, excluding methane, were considered. An empirical approach was derived to describe the effects of the degree of carbon conversion on the reaction rate as a function of relevant test parameters (pressure range 1–70 bar, temperature 800–1000 °C). To assess the validity of the derived kinetic equation a model of a fluidized-bed gasifier is presented.     

Einfluß von Restaustenit auf die Korngröße des Austenits nach der Reaustenitisierung von Stählen für schwere Schmiedestücke

Die Korngröße des Austenits nach der Reaustenitisierung von Stählen für schwere Schmiedestücke wurde in Abhängigkeit von der Art des Ausgangsgefüges, den Wiedererwärmungsbedingungen und den chemischen Zusammensetzungen untersucht. Besonders wurde der Einfluß von Restaustenit im Ausgangsgefüge auf die Korngröße des Austenits nach erneuter Austenitisierung betrachtet. Nach den Ergebnissen bleibt das Austenitkorn bei der Reaustenitisierung von Gefügen der Martensitstufe und der unteren Bainitstufe grob, wenn bei der Wiedererwärmung werkstoffabhängige Grenzerwärmungsgeschwindigkeiten unterschritten werden. Maßgeblich für eine mit zunehmender Erwärmungsgeschwindigkeit – in Abhängigkeit auch von den örtlichen chemischen Zusammensetzungen – mögliche Austenitkornverfeinerung ist das zeitabhängige Wachsen von Restaustenitfilmen zwischen den Kristalliten des Ausgangsgefüges in Konkurrenz zu den Anlaufzeiten für Keimbildung und -wachstum an den Grenzflächen Carbid/Ferrit. Ist wenig oder kein Restaustenit vorhanden, wie in einigen Gefügen der Bainit- bzw. der Perlitstufe, so entsteht der Austenit unabhängig von den Wiedererwärmungsbedingungen durch Neubildung und Wachsen von Austenitkeimen an den Grenzflächen Ferrit/Carbid. Unter den gegebenen Versuchsbedingungen entstand dabei immer ein feines Austenitkorn.     

Untersuchungen zur Korrosion von metallischen Werkstoffen in hochkonzentrierten,siedenden Salzlösungen

Investigations into corrosion of metallic materials in highly concentrated boiling salt solutions Container for the disposal of radioactive waste in carnallite formations can be exposed to corrosion by highly concentrated hot salt solutions. Previous investigations of the corrosion resistance of candidate materials have been supplemented by measurements of the current density-potential curves of iron-silicon, cobalt-silicon, titanium-nickel and nickel-molybdenum alloys and of tantal. The electrolyte was a concentrated MgCl₂-NaCl-KCl-MgSO₄ solution at its boiling point of 170°C. The measurements give useful information on the stability of the corrosion resistance of these materials.