The magnitude and distribution of the electric field between two conducting electrodes of a capacitive deionization (CDI) device plays an important role in governing the desalting capacity. A dielectric coating on these electrodes can polarize under an applied potential to modulate the net electric field and hence the salt adsorption capacity of the device. Using finite element models, we show the extent and nature of electric field modulation, associated with changes in the size, thickness, and permittivity of commonly used nanostructured dielectric coatings such as zinc oxide (ZnO) and titanium dioxide (TiO). Experimental data pertaining to the simulation are obtained by coating activated carbon cloth (ACC) with nanoparticles of ZnO and TiO and using them as electrodes in a CDI device. The dielectric-coated electrodes displayed faster desalting kinetics of 1.7 and 1.55 mg g min and higher unsaturated specific salt adsorption capacities of 5.72 and 5.3 mg g for ZnO and TiO, respectively. In contrast, uncoated ACC had a salt adsorption rate and capacity of 1.05 mg g min and 3.95 mg g, respectively. The desalting data is analyzed with respect to the electrical parameters of the electrodes extracted from cyclic voltammetry and impedance measurements. Additionally, the obtained results are correlated with the simulation data to ascertain the governing principles for the changes observed and advances that can be achieved through dielectric-based electrode modifications for enhancing the CDI device performance.
Heterostructures consisting of two different silicon carbide (SiC) polytypes have been of interest for several years, promising application in the field of UV LEDs and sensors. Direct bonding (also called diffusion welding) is a technology that could possibly be used for manufacturing SiC heterostructures. The technology has been proven in experimental production of power devices for ohmic-and Schottkycontacts to SiC, as well as high-voltage stacks. The fabrication of heterostructures has not been successful yet, due to the hardness of SiC as well as the high temperature and pressure needed for accomplishing a reliable joint between two SiC polytype wafers. No thorough analysis is available in studying the quality of achieved contacts and the causes for their short breakdown in time. The intention is to try higher temperatures than used before for direct bonding of SiC different polytypes. To understand the contact failure causes there is a need for quick non-destructive measurements of the heterojunction properties in the depth of bonded layers. Eddy currents measurements seems to be the best solution for further investigation. Simulations with COMSOL Multiphysics general-purpose simulator are carried out with different electrode shapes and different electrode placements. The numerical simulation and test equipment building results at the Thomas Johann Seebeck Department of Electronics are analyzed and discussed.
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