Dielectric barrier discharge | EPFL Graph Search

Dielectric-barrier discharge (DBD) is the electrical discharge between two electrodes separated by an insulating dielectric barrier. Originally called silent (inaudible) discharge and also known as ozone production discharge or partial discharge, it was first reported by Ernst Werner von Siemens in 1857. Process The process normally uses high voltage alternating current, ranging from lower RF to microwave frequencies. However, other methods were developed to extend the frequency range all the way down to the DC. One method was to use a high resistivity layer to cover one of the electrodes. This is known as the resistive barrier discharge. Another technique using a semiconductor layer of gallium arsenide (GaAs) to replace the dielectric layer, enables these devices to be driven by a DC voltage between 580 V and 740 V. Construction DBD devices can be made in many configurations, typically planar, using parallel plates separated by a dielectric or cyl

An In Situ FTIR Study of DBD Plasma Parameters for Accelerated Germination of Arabidopsis thaliana Seeds

Ivo Furno, Alan Howling, Lorenzo Ibba, Alexandra Waskow

Current agricultural practices are not sustainable; however, the non-thermal plasma treatment of seeds may be an eco-friendly alternative to alter macroscopic plant growth parameters. Despite numerous successful results of plasma-seed treatments reported in the literature, the plasma-treatment parameters required to improve plant growth remain elusive due to the plethora of physical, chemical, and biological variables. In this study, we investigate the optimal conditions in our surface dielectric barrier discharge (SDBD) setup, using a parametric study, and attempt to understand relevant species in the plasma treatment using in situ Fourier transform infrared (FTIR) absorption spectroscopy. Our results suggest that treatment time and voltage are key parameters for accelerated germination; however, no clear conclusion on causative agents can be drawn.

MDPI2021

Carbon dioxide hydrogenation to methanol at low pressure and temperature

The measurements obtained were used to investigates the methanol synthesis reaction from pure carbon dioxide and hydrogen over binary (CuO/ZrO2) and ternary supported catalysts (CuO/ZnO/Al2O3). A comparison of different catalysts is presented. The influence of the most important reaction parameters, i.e. temperature, pressure, space velocity and feed gas composition is examined at moderate temperatures (≤ 300 °C) and pressures (≤ 20 bar). The influence of the partial pressures of hydrogen, carbon dioxide, carbon monoxide, water and methanol are studied in detail with the most efficient catalyst. According to the results, water has a decisive effect on the catalyst activity and performance. The measured results were used to derive a possible Langmuir-Hinshelwood kinetic model of the methanol synthesis reaction. The catalyst surface is analyzed by in situ diffuse reflectance Fourier transform infrared spectroscopy. The identification and evolution of intermediates on CuO/ZnO/Al2O3 catalysts confirm that the reaction proceeds by prior formation of the carbonate on the copper, followed by hydrogenation of the carbonate to the formate and thereafter to methoxy and methanol. For CuO/ZrO2 catalysts results demonstrate that the methanol formation occurs via π – bound formaldehyde and methoxy. Responses of sine shape variation applied to the reactants are also examined. The conversion of CO2 with hydrogen to methanol is investigated in dielectric-barrier discharges with and without catalysts at low temperatures (≤ 100 °C) and pressures (≤ 10 bar). The combination of discharges and catalysts lower the activation energy of the reaction resulting in a decrease in the catalyst optimum temperature. The presence of the catalyst in the discharge increases the methanol yield and selectivity by more than a factor of 10. Electrochemical reduction of carbon dioxide is briefly investigated by using TiO2/Ni complex and TiO2/Ru complex thin film electrodes. A considerable decrease in overvoltage is achieved together with respectable current densities.

EPFL1998

Cold Atmospheric Plasma Inactivation of Microbial Spores Compared on Reference Surfaces and Powder Particles

Alan Howling, David Martinet

Heat-resistant spores on a dry, heat- and water-sensitive food matrix are difficult to inactivate. Radioactive or X-ray exposure is allowed and accepted only for some selected commodities. Non-thermal atmospheric pressure plasma treatments could offer an efficient, fast, and chemical-free solution. The effectiveness of direct contact cold atmospheric plasma (CAP) generated by a dielectric barrier discharge (DBD) device and air as process gas was evaluated against spores of Bacillus spp., Geobacillus spp., and Penicillium spp. A maximum of 3 log(10) cycles of inactivation was achieved for B. coagulans spores exposed for only 10 s at low surface energy of 0.18 W/cm(2) determined directly at the electrodes. This corresponds to an initial decimal reduction time of D-1 = 0.1 min. Spores of B. subtilis are the most resistant amongst the studied strains (D-1 = 1.4 min). The determining parameter in the modeling of the inactivation curve is surface energy. Non-porous, native starch granules or shells from diatoms, a highly porous material, were also contaminated with spores and treated by DBD CAP. The inactivation level was significantly reduced by the presence of powders. Considering plasma diagnostics, it can be concluded that the spore shell is the primary and main target for a plasma-induced inactivation. The inactivation affect scales with surface energy and can be controlled directly via process time and/or discharge power.

SPRINGER2020

Carbon dioxide hydrogenation to methanol at low pressure and temperature

EPFL1998