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[en] Water purification from ammonium hydroxide was carried out by using two methods of processing: treatment with ozone generated by a dielectric barrier discharge (DBD) as well as processing in plasma-chemical reactor equipped with a water electrode and a diaphragm, where the main oxidation factors were OH hydroxyl radicals. The volume of the treated aqueous solution was 300 ml and the NH4OH concentration was 0.025 ml in both cases. The phenolphthalein test was used for visual analysis of the content of an aqueous solution of ammonia in water. The ozone concentration was about 5.8 mg/l in water with ozone injection from an ozone generator and 0.7 mg/l in a plasma-chemical reactor, respectively. The analysis of OH and NO radicals in the water-air gap of the plasma-chemical reactor was carried out using a spectrometer operated in the range of 200…800 nm. (author)
[en] This thesis focuses on a number of aspects governing the transformation of gibbsite, via intermediate phases, to α-alumina. These aspects include the size and morphology of the gibbsite grains, the influence of additions of foreign elements, the effect of a mechanical treatment of the gibbsite prior to calcination, and combinations of these factors. The materials were characterised by scanning electron microscopy, X-ray diffraction and surface area measurements. For some of the calcined materials an attempt was made to sinter the powders to a dense body to investigate if any of the treatments during calcination had an effect on this process. The literature review covers the current state of understanding of the production of bulk alumina powder by the Bayer process and the phase changes seen on calcination of precursors to the stable α-alumina phase. A detailed description of the phase changes is given and the various routes and conditions necessary for the transformations to occur are considered. The transformations are examined in relation to the morphology of the crystals and the variables controlling the phase transformation route are discussed. Calcination in air showed that the size of the gibbsite grain governs the calcination route taken to reach oc-alumina. The standard gibbsites used in this work show a mixed calcination sequence transforming both via the boehmite phase, followed by the γ, δ and θ phases, and via the χ and κ phases. The formation of boehmite is attributed to retention of water vapour within the grain. Differences in morphology of the starting materials showed that for the range of materials seen, the morphology of the grain is less important than its size. The super fine material confirmed that a small grain size transforms via the non-boehmite route only, with the other gibbsites taking intermediate routes as for the standard gibbsites. Of the additions made prior to calcination, aluminium fluoride was found to reduce the transformation temperature to α-alumina by approximately 300 deg. C. Other additions had little effect on the transformation temperature although a reduction in grain size was seen with aluminium chloride. It was found that good mixing of the alumina fluoride was essential to obtain reliable and reproducible results. This is due to the small amounts of additive that are needed and the sensitivity of the process to concentration variations. Mineralisation of a range of gibbsites showed that the presence of sodium in the starting material was crucial in reducing the calcination temperature. This led to the conclusion that the sodium and fluoride react to form a liquid phase. The presence of a liquid phase increases the mobility of the aluminium and oxygen atoms resulting in a reduction of the transformation temperature. Fluoride additions to the gibbsites with different morphologies showed that the presence of sodium was the governing factor in reduction of the transformation temperature. Milling of the starting materials showed that there was a small reduction in the transformation temperature between some of the phases. The energy involved in milling leads to activation of the gibbsite. This activation takes the form of a reduction in the grain size and in a reduction of the crystallinity seen in the XRD pattern. Fluoride additions during the calcination of sapphire with a standard gibbsite powder showed preferential grain growth. It was possible to initiate growth of small plate-like crystals on the polished surface of a piece of sapphire parallel to the basal plane. Crystal growth was also seen in scratches on a polished surface perpendicular to the basal plane. (author)
[en] Natural waters has been researched by application of electro sedimentation method. Results of physical, chemical and bacteriological analysis before and after electro sedimentation has been got
[en] Highlights: • Chemical bath deposition was employed for synthesis of aligned Cd(OH)2 nanosheets. • Low turn-on field 1.4 V/μm for Cd(OH)2 nanosheets has been found. • Low turn-on field attributed due to nanometric feature and aligned nature of Cd(OH)2 nanosheets. • High current density of 9.8 mA/cm2 has been found. High current density of 9.8 mA/cm2 was drawn at an applied field of 4.1 V/μm from aligned Cd(OH)2 nanosheets and low turn-on field of 1.4 V/μm was found for the emission current density of 10 μA/cm2. The aligned Cd(OH)2 nanosheets were synthesized by CBD technique on Cadmium foil. To the best of our knowledge this is the first report on the field emission studies of Cd(OH)2 nanosheets. Simple synthesis route coupled with superior field emission properties indicate the possible use of Cd(OH)2 nanosheets for micro/nanoelectronic devices.