Papers by Author: R. Dimitrijević

Abstract: Ceramic materials, barium and strontium diphyllosilicates doped with ytterbium ions, were obtained by thermal treatment from Ba–LTA and Sr–LTA zeolites. The samples were characterized with Differential Scanning Calorimetry, Infra–Red Spectroscopy and Scanning Electron Microscopy. The crystal structures of diphyllosilacetes have been refined.

Abstract: The mixtures NiO-WO3 were synthesized by the combustion of gels obtained by drying common solutions of nickel nitrate, polytungstic acid and citric acid. The X-ray diffractograms of oxide mixtures confirmed mutual interaction of oxides during synthesis leading to a new phase, NiWO4. The reduction of oxide mixtures in hydrogen atmosphere was investigated thermogravimetrically. The temperature of reduction of the oxide mixture lies between the temperatures of reduction of pure oxides and monotonously increases with the increase in WO3 mole fraction; however, the reduction itself is a multi-step process, preferably in the composition region rich in NiO. The X-ray diffractometry of metallic residues evidenced Ni-W alloys and tungsten excess to be the reduction products.

Abstract: A series of hexacelsians with different compositions were synthesized by thermally induced transformation of a LTA zeolite. Various forms of hexacelsians have been characterized by XRPD, IR, Raman and 29Si MAS NMR method. The phase transformation a
b hexacelsian was investigated by DSC method. This phase transformation is sensitive to synthesis conditions, doping and thermal treatment. The peak maximum temperature, Tm, varies from 302 up to 353 oC. Heat of transformation changes from 0.42 to 1.77 kJ/mol.