Structural evolution of a Ta-filament during hot-wire chemical vapour deposition of Silicon investigated by electron backscatter diffraction

We report on the application of electron backscatter diffraction to investigate the structural changes of a tantalum filament operated at typical hot-wire chemical vapour deposition conditions for the synthesis of hydrogenated nanocrystalline silicon. Various tantalum-silicides, identified by electron backscatter diffraction, form preferentially along the length of the filament. The filament has a recrystallized Ta inner core and a TaSi₂ layer encapsulated with a Si layer at the cooler ends. The αTa₅Si₃, metastable Ta₅Si₃ and Ta₂Si phases formed in addition to recrystallized Ta and TaSi₂ at the centre regions. Cracks and porosity were prevalent throughout the length of the filament. The microstructural evolution of the aged tantalum filament can be ascribed to the thermal gradient along the filament length, recrystallization of Ta and the variation of silicon content within the filament.     

Rural electrification: The institutional dimension

The institutional aspects of rural electrification programmes are often given much less attention than their importance warrants. In a number of important ways, rural electrification is in conflia with the primary concerns of the utilities mandated to implement it. Resolving this dilemma requires a separation of functions, with the agency responsible for rural electrification being given substantial autonomy. The range of institutional options for achieving this is wide and the choice should be tailored to the local context ana programme objectives.     

Vermeidung von str?mungsinduzierte CO2-Korrosion in der Erdgasproduktion mit Hilfe von Korrosionsinhibitoren

CO₂ corrosion of carbon steel is a serious problem in oil and gas production, since the most used materials are low alloyed carbon steels. There are many approaches to handle the problem of CO₂ corrosion. One flexible and economic way to control corrosion in oil and gas facilities is inhibition but the efficiency of an inhibitor is often limited by flow velocities. To investigate inhibitor efficiency in a superficial flow with high gas velocities neither standardized test had been available nor publications about that topic. Therefore the goal was to do the first investigations in that important field. To reach this aim a special, not standardized flow loop test system has been constructed. Results of these investigations have shown that differences in inhibitor efficiencies are related to chemical composition and flow velocities.     

Coal liquids distillation tower corrosion: Chloride pathways in the Wilsonville,Alabama SRC-I pilot plant when processing a high chloride coal

The pilot plant was operated during a three-week period with a coal containing about 0.25 wt.% chloride. During this period, samples were collected at about 20 sample points throughout the process. The mass balance and chloride content of these samples provided data to define the chloride pathway to the atmospheric distillation tower where it subsequently caused severe corrosion problems. A fortuitous processing change, made about half-way through the period, provided a marker that helped define the chloride pathway through the process. About 10% of the chloride entering the dissolver flashed overhead in the high pressure separator; this fraction remained constant even thought the total chloride entering this separator area changed by a factor of 5 to 10. In the Wilsonville plant about 50% of the total chloride entering the reactor was carried to the atmospheric tower in the highest boiling distillate process stream. Essentially all of the chloride entering the atmospheric tower was converted to iron chloride by corrosion of a lower portion of the tower.     

Ethik im Medizinstudium –

Ohne Zusammenfassung     

Transient volume holograms in polymethylmethacrylate

New transient volume holographic recording materials are described in this report. These consist of either coronene or 1,2;5,6-dibenzanthracene incorporated into polymethylmethacrylate. The largely amplitude, volume holograms formed as a result of triplet-state absorption have lifetimes of 6.4 and 0.9 s respectively and diffraction efficiencies close to the predicted values of 10⁻⁴. Production of permanent holograms has been prevented by careful control of the polymerization conditions to produce a matrix of sufficient rigidity to prevent reactions between the triplet states and the polymer. By using spectrally well separated write and read wavelengths, erasure of the holograms by the read beam is avoided.