Fenton chemistry promoted by sub-microsecond pulsed corona plasmas for organic micropollutant degradation in water

Differences in the liquid chemistry due to different ground electrode materials (titanium, stainless steel) were compared for corona discharges in water. The plasma was generated by applying positive high voltage pulses that are characterized by short rise times of about 20 ns, a peak voltage of 80 kV and pulse lengths of about 150–160 ns (FWHM). Phenol was admixed to the water for quantification of the bulk reaction chemistry, such as phenol decomposition and H2O2-formation. Optical emission spectroscopy was conducted to relate chemistry to plasma processes. Possible electrode corrosion was determined by atomic absorption spectroscopy (AAS). The post-discharge chemistry strongly depends on ground electrode material. With stainless steel electrodes, decomposition efficiency of phenol increased by about three quarters (74.9 %) when compared with titanium electrodes. This result can be explained by dissolved metal ions corroded from the ground electrode, which catalytically decomposed the H2O2 that had been formed into hydroxyl radicals again. Ground electrodes were corroded due to electrochemical processes. Corrosion rates and overall reaction chemistries cannot readily be described similar to conventional DC electrochemical processes at low voltages. The repetitive application of sub-microsecond high voltage pulses has to be taken into account explicitly. Altogether, electrode materials, ground electrode corrosion and associated catalytic processes are more important for plasma processes in aqueous solutions than was recognized so far. Therefore, the effects need to be taken into account in the analysis of laboratory results as well as the development of respective novel water treatment technologies

Systematische Erweiterung der mikrostrukturellen Charakterisierung ferritischer Schweißgüter

This paper deals with the analytic gap during the microstructural examination of ferritic weld metals and points out which methods can be used to perform a meaningful evaluation of the weld metal microstructure. The designers of filler materials and the respective metallographs are provided with a tool to specifically search for weaknesses in the microstructural composition and invalidate them by alloying on the basis of their metallurgical context

Variation of Heat Input and Its Influence on Residual Stresses and Coating Properties in Arc Spraying with Different Gas Mixtures

This work is about the influence of heat input on arc-sprayed coatings, caused by varying spraying patterns. The highly cavitation erosion-resistant alloys CuAl9Ni5Fe4Mn and CuMn13Al8Fe3Ni2 were arc-sprayed with a spiral-shaped pattern, using both pressurized air and a mixture of nitrogen and hydrogen. Process temperatures were recorded by thermographic imaging, and residual stresses were measured by modified hole-drilling method. Moreover, analyses of the cavitation erosion behavior and other properties were performed. Compared to previous own works, in which a meander-shaped spray pattern was used, most importantly the thermal loads, for example the maximum temperatures, during the coating buildup were lowered up to approx. 20 °C. Moreover, a more even heating of the specimens and reduced tensile stresses for both atomizing gases and materials were achieved. Furthermore, also the course of the residual stresses was changed. Hence, the dominance of the quenching stresses regarding residual stresses and coating properties, especially when spraying with pressurized air, was found to be reduced. In addition, the cavitation erosion resistance was improved severely, i.e., erosion depth was decreased up to 57%. In contrast to the aforementioned positive effects, the deposition efficiency, Young’s moduli and hardness were reduced, but still sufficient considering the application