Superposition of DC voltage and submicrosecond impulses for energization of electrostatic precipitators

This paper discusses the development of an impulsive microelectrostatic precipitation technology, which uses superposition of submicrosecond high-field pulses and dc electric field. Short impulses allow the application of higher voltages to the ionization electrodes of a precipitation system without the initiation of breakdown. These higher levels of electric field generate higher ionic concentrations, resulting in more efficient charging of the airborne particles, and can potentially improve precipitation efficiency. This work is focused on the analysis of the behavior of impulsive positive corona discharges in a coaxial reactor designed for precipitation studies. The efficiency of precipitation of coarse and fine particles has been investigated using different dc and impulse voltage levels in order to establish optimal energization modes

Micro electrostatic precipitation for air treatment

Micro-Electrostatic precipitation uses combining impulses and dc voltage in order to charge and remove fine, sub-micron particles efficiently. Short impulses are expected to increase the precipitation efficiency and to reduce power consumption

Thermal aging of nanocomposites

Předkládaná práce se zabývá studiem vlastností nanokompozitních materiálů a jejich tepelným stárnutím. V první části práce jsou teoreticky rozebrány některé ze základních pojmů souvisejících s nanokompozitními materiály. Rovněž jsou zde stručně nastíněny metody výroby těchto materiálů. Nejdůležitější je však přiblížení jednotlivých vlastností, přičemž větší pozornost je věnována vlastnostem elektrickým. Praktická část se zabývá tepelným stárnutím vzorků nanokompozitního materiálu plněného nanočásticemi Al2O3. Sledován byl vliv doby stárnutí na hodnoty vnitřní rezistivity, ztrátového činitele a relativní permitivity.This thesis deals with issues of properties of nanocomposites and it´s heat aging. In the first part there are theoretically analysed some of the basic therms connected with nanocomposites. Also there are outlined basic methods of production of these matherials. The most important is specification of individual properties when bigger attention is gived to electrical properties. Practic part deals with heat aging of samples of nanocomposites filled with nanoparticles Al2O3. There was monitored impact of time of aging on values of internal resistance, dissipation factor and relative permitivity.

Cu2ZnSnS4 Nanocrystal Ink Absorber Layers for Thin Film Solar Cells

A promising approach to low-cost photovoltaic devices is to fabricate thin film solar cells using solution-processable nanocrystal inks. This is applicable to the material class of kesterites having favourable opto-electronic properties and the potential for high efficiencies. This study looks at the chalcogenide compound Cu2ZnSnS4 (CZTS) in particular which consists of earth-abundant elements and therefore provides means for truly sustainable energy generation. Re-dispersed in an organic solvent, the nanoparticles can easily be deposited in thin films on top of glass substrates. Subsequent annealing is used to promote grain growth for a dense, polycrystalline absorber layer. The resulting films (or as-synthesised particles) are analysed with respect to their crystal structure, phase purity, morphology, chemical composition, and opto-electronic properties. Combining a variety of methods helps to disentangle the complex material characteristics of the quaternary compound. The reproducibility of CZTS nanocrystal synthesis by the hot-injection method is briefly discussed. The focus of this thesis is on the influence of the annealing temperature held at a constant value in a range between 400°C and 600°C for 1h on the film development. This is supplemented by an investigation of the influence of different annealing times between 0.5h and 3.0h at a moderate temperature of 500°C and by an exemplary analysis of cross-sections through samples of a CZTS absorber on a molybdenum rear contact layer. The experiments suggest that temperatures around 600°C are preferable in order to enhance the quality of the crystal structure and to obtain large-grained films which is seen as a major area of improvement in this field of research. Increasing the annealing time, in contrast, does induce hardly any changes in the material and is therefore less effective in achieving high-quality absorber layers. The final state of the films is reached after only about 1h of annealing

Reusing Waste Coffee Grounds as Electrode Materials: Recent Advances and Future Opportunities

Coffee industry produces more than eight million tons of waste coffee grounds (WCG) annually. These WCG contain caffeine, tannins, and polyphenols and can be of great environmental concern if not properly disposed of. On the other hand, components of WCG are mainly macromolecular cellulose and lignocellulose, which can be utilized as cheap carbon precursors. Accordingly, various forms of carbon materials have been reportedly synthesized from WCG, including activated carbon, mesoporous carbon, carbon nanosheets, carbon nanotubes, graphene sheet fibers (i.e., graphenated carbon nanotubes), and particle-like graphene. Upcycling of various biomass and/or waste into value-added functional materials is of growing significance to offer more sustainable solutions and enable circular economy. In this context, this review offers timely insight on the recent advances of WCG derived carbon as value-added electrode materials. As electrodes, they have shown to possess excellent electrochemical properties and found applications in capacitor/supercapacitor, batteries, electrochemical sensors, owing to their low cost, high electrical conductivity, polarization, and chemical stability. Collectively, these efforts could represent an environmentally friendly and circular economy approach, which could not only help solve the food waste issue, but also generate high performance carbon-based materials for many electrochemical applications