Papers by Author: B. Matović

Abstract: The objective of this manuscript was to investigate the synthesis of SiC by carbothermal– reduction reactions of sepiolite. Sepiolite of Serbian origin and carbon (from various precursors) as a reducing agent were used. The green bodies with various C/SiO2 ratios were carbonized at 1073 K and heattreated at 1673 K in a controlled Ar flow atmosphere. Phase evolution and phase content were followed as a function of C/SiO2 ratio and carbon origin. The starting materials and products were characterized by means of XRD and SEM. The results show that sepiolite can be very effective source for obtaining silicon carbide powders.

Abstract: Two nanopowders with nominal compositions (Ca0.7La0.3)MnO3 (CLM) and (Ca0.7La0.3)(Mn0.8Ce0.2)O3 (CLMC) were synthesized by a modified glycine/nitrate procedure. XRD analysis revealed binary phase mixture in both samples. The influence of La and Ce on unit cell parameters, atom positions, and average bond distances were analyzed. According to these results and refined occupation factors of La and Ca, as well as quantitative phase analysis it was found that the CLM sample consists of 85 mass.% of Ca0.62La0.38MnO3 and 15 mass.% of Ca0.99La0.01MnO3, while the CLMC sample consists of 70 mass.% of Ca0.58La0.42MnO3 and 30 mass.% of CeO2. Microstructure size-strain analysis was performed and the Rietveld refinement gave crystallites of about 100 Å. TEM images showed particle sizes of about 100-500 Å.

Abstract: One of the methods for powder synthesis that is both cost and time effective is the selfpropagating room temperature synthesis. We applied this method to synthesize rare earth doped ceria nanopowders. Since they exhibit very high ionic conductivity at intermediate temperatures these compositions are attractive for a new generation of nanostructured ceramics applicable in solid oxide fuel cells as electrolytes. In this paper we paid our attention to the reaction based on methathetical pathway, whereby solid solution nanopowders of rare earth elements with ceria were obtained at room temperature. Compositions of Ce1-xRexO2-δ (Re = Y , Nd) were synthesized with x ranging from 0 to 0.20. The reaction course is discussed and the properties of the obtained powders are presented.

Abstract: This paper deals with densification and a®b phase transformation of Si3N4, with a constant b-Si3N4 seeds concentration regarding sintering temperature and different additive types. The seeds of b-Si3N4 were obtained by sintering of silicon nitride in a-form and additive mixture consisting of Y2O3 and SiO2. Two different Si3N4/additive mixtures (Y2O3 + Al2O3 and CeO2) containing constant amount of seeds were prepared and tested. Characterization of sintered samples involved phase analysis by X−ray diffraction and density measurements. The results indicated that in the presence of yttria-alumina mixture both the phase transformation and the densification were enhanced as compared to samples containing only CeO2 as a sintering additive. The reasons for observed behavior are discussed in detail.

Abstract: This paper deals with Gd-doped ceria solid solutions: Ce1−XGdXO2−d with "x" ranging from 0 to 0.2. Four different powders were synthesized by modified glycine nitrate procedure with very precise stoichiometry according to tailored composition. The method was modified by decreasing glycine/nitrate ratio to 0.5. All obtained solid solutions exhibit a fluorite-type crystal structure with composition dependent lattice parameters. The variation of the lattice parameter was studied and correlated with the equation describing the ion-packing model. It has been found that the change of lattice parameter versus Gd concentration obeys Vegard's rule very well. Results also show that all powders are nanometric in size. The average size of Ce1−XGdXO2−d particles is about 20 nm.