A comparative evaluation is reported of the performance of different discharge regimes—AC powered dielectric barrier discharge (DBD) and DC powered corona discharge of positive (DC+) and negative (DC−) polarity—implemented within the same reactor, a benchtop prototype for an advanced oxidation stage in water treatment. For all three modes of operation, DBD, DC+ and DC−, the reactor performance was tested using phenol as model pollutant and determining the process energy efficiency (kE and G50), kinetics (t1/2), nitrated byproducts and extent of mineralization to CO2. Finally, comparison with a smaller DBD reactor of similar configuration previously used in our lab (Marotta et al 2011 Plasma Proc. Polym. 8 867) shows that scaling up was carried out successfully and holds promise for larger scale applications.
Since the late 1950s, an effect of electrical current in addition to joule heating on the deformation of metals called the Electroplastic Effect (EPE) has been known. It is used nowadays in the so-called Electrically Assisted Forming (EAF) processes, but the understanding of the phenomenon is not very clear yet. It has been found that EPE increases the formability of high stacking fault energy (SFE) materials, while low SFE materials reach fracture prematurely. Since Duplex Stainless Steels (DSSs) possess a microstructure consisting of two phases with very different SFE (low SFE austenite and high SFE ferrite) and they are widely used in industry, we investigated EPE on those alloys. Tensile tests at 5 A/mm2, 10 A/mm2 and 15 A/mm2 current densities along with thermal counterparts were conducted on UNS S32101, UNS S32205, UNS S32304 and UNS S32750. The DSS grades were characterized by means of optical microscopy, X-ray diffraction and their mechanical properties (ultimate tensile strength, total elongation, uniform elongation and yield stress). An increase in uniform elongation for the electrical tests compared to the thermal counterparts as well as an increase in total elongation was found. No differences were observed on the yield stress and on the ultimate tensile strength. Un uneven distribution of the current because of the different resistivity and work hardening of the two phases has been hypothesized as the explanation for the positive effect of EPE.
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