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Loess from the Danubian Plain (Bulgaria) was used as the raw material for the solid-state synthesis of ceramics. The mineral phase composition of the loess fraction used was determined by powder X-ray phase analysis, and the chemical composition by X-ray fluorescence analysis. The semi-quantitatively determined mineral phases are quartz, plagioclase, K-feldspar, mica, carbonates (calcite and dolomite), chlorite and amphibole. The major oxides of the chemical composition of loess fraction are (in wt. %): SiO2 - 53,61; Al2O3 - 12.57; Fe2O3 - 7.05; P2O5 - 0,23; TiO2 - 1.37; CaO - 19.36; and MgO - 1.48. Experiments were performed with sintering of pure loess without additives, and with addition of MgO and Na2O in order to obtain a composition corresponding to that of the pyroxene augite - (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6. Ceramics were obtained at three temperatures: 1000, 1100 and 1200°C. The phase composition, spectral characteristics and colour coordinates of the obtained ceramics were determined. The results show that when magnesium and sodium are added to the loess raw material, the ceramics obtained after sintering at 1100 and 1200°C have a predominant content of augite and have a yellow-beige colour. [ABSTRACT FROM AUTHOR]

High-energy milling has been employed for the preparation of CuWO4 nanopowders using the planetary ball and the shaker mills. The phase formations after each milling stage have been characterized by X-ray diffraction analysis (XRD) and infrared spectroscopy (IR). The optical band gap and the morphology of the obtained CuWO4 have been also studied. Based on the performed investigation the differences between the materials obtained from the same starting reagents (WO3 and CuO) and different mechanical activation have been analyzed. The single phase CuWO4 with crystallite size of 18 and 13 nm was synthesized by direct mechono-chemical synthesis using both mills. The crystallite size slowly increased after long milling time and no further phase formation was observed. It was established that the long milling time has influence on the symmetry of the structural units of the prepared CuWO4. It has been found that the morphology of particles was not affected by the type of the mills and the milling time. [ABSTRACT FROM AUTHOR]

Ni-Co alloys with varying cobalt content are electrodeposited in stationary potentiostatic mode employing citrate electrolyte, either with or without addition of saccharin (SHR) at different Ni/Co ratios and variable content of sodium citrate (Na3citrate) in the electrolyte. The changes in the microstructure, chemical composition and cathodic current efficiency of deposition (CCE) of Ni-Co alloys are studied. Scanning electron microscope, energy dispersive X-Ray and atomic absorbtion analysis are used to characterize the alloy coating.The alloy deposition is proved to be of an anomalous type. It is found that with the increase of the value of ratio Ni/Co in the solution from 1 to 5, the percentage of Ni in the Ni-Co alloy grows to 48 mass %, and the CCE decreases to about 70 %, whereas more fine-crystalline Ni-Co coatings (size of crystallites less than 100 nm) are deposited. The addition of SHR results in a strong decrease of CCE (up to 50 %), but also in formation of smooth and shimmering coatings with average size of crystallites much less than 50 nm. The coatings obtained from electrolyte with higher content of sodium citrate contain more Ni but are more coarse-crystalline, as the effect of the complexing agent is generally less pronounced in comparison with the case with SHR addition. [ABSTRACT FROM AUTHOR]

The kinetics of independent and joined deposition of Ni and Co in citrate electrolyte in the presence of three types of additives: saccharine (SCH), urotropine (URT) and gelatine (GLT), is examined. Comparison is made between the chemical composition, the current cathodic efficiency (CCE) and the morphology of Ni-Co alloys depending on the type of the additive, both in constant potential mode (CPM) and in pulse potental mode (PPM). The study specifies the effect of GLT and SCH for formation of smooth, shiny, nanostructured Ni-Co coatings with average crystallite size less than 100 nm with a high CCE (about 80 % for SCH, and over 90 % for GLT), in both potential modes. The presence of SCH in the electrolyte with simultaneous application of PPM increases the content of Ni in the alloy to 25-30 mass % Ni. The optimum additive of SCH containing 0.5 - 1.0 g dm-3 is specified, wherein the electrolyte remains stable during continuous operation. [ABSTRACT FROM AUTHOR]

Partial and almost complete barium exchange on clinoptilolite is performed and structurally studied for different durations (2 h, 24 h, 72 h, 168 h, 12 d, 22 d) at room temperature and 90 °C of the ion exchange process. Continuing ion exchange up to the 22nd day is proved by EDS analyses data and powder XRD (intensity changes of 020 and 200 peaks). Rietveld structure refinement was first performed on the maximum Ba exchanged clinoptilolite at 90 °C for 22 days (3.04 atoms per unit cell). Four barium positions and 9 H2O sites were refined. The split positions Ba2 and BaK (around M3 site in channel C) were found mostly occupied by 2.23 atoms per unit cell. The rest of refined samples showed different occupations of the positions of incoming Ba2+ and outgoing cations (Na+, Ca2+, K+, Mg2+) during ion exchange, describing extra-framework cationic movements, which are released easily without preferable directions. The exchanges at 90 °C and room temperature were found proceeding similarly up to the 2nd hour, but then at room temperature the process is slowed and at 22nd day 1.64 barium atoms per unit cell are structurally refined. [ABSTRACT FROM AUTHOR]