Ewa Drożdż

Thermal decomposition of d-metal nitrates supported on alumina

The thermal decomposition of cobalt, nickel, manganese, zinc, and copper nitrates supported on nanometric alumina was investigated and compared with decomposition of corresponding bulk nitrates. TG, DTA, and MS measurements in air were performed. The supported nitrates decompose in lower temperatures than the bulk ones and their decomposition proceeds in fewer stages which are better separated. Synthesized materials and bulk nitrates before degradation of nitrates groups undergo dehydration. For decomposition of manganese and copper nitrates, the last step of water vapour releasing is combined with degradation of nitrate groups thus formation of anhydrous metal nitrate during decomposition is not achievable. Thermal decomposition of bulk nitrates leads to oxides—Co3O4, NiO, MnO2, ZnO, and CuO—respectively, as the solid residue. The nickel, zinc, copper, and manganese nitrates while supported on alumina decompose to corresponding oxides (NiO, ZnO, CuO, MnO2) as well. For decomposition of cobalt nitrate while supported on Al2O3 as the solid residue CoAl2O4 were identified. The correlation between dehydration and degradation of nitrates groups temperatures for bulk and supported nitrates was analysed in terms of atomic properties of d-metals.

The influence of the method of addition of Al2O3 to 3YSZ material on its thermal and electrical properties

The properties of tetragonal yttria-stabilized zirconia composites with the small addition of alumina (Al2O3−Y2O3−ZrO2 composite) obtained on two ways of synthesis were studied in terms of usability for anode materials in solid oxide fuel cell. Both methods were based on citric synthesis: in the first one, Al2O3 was coprecipitated with the tetragonal ZrO2 in the form of citrate by citric acid, while in the second Al2O3 was impregnated in the form of aluminium nitrate precursor on tetragonal ZrO2 matrix. The obtained materials were analysed by X-ray diffraction, dilatometry and impedance spectroscopy. The results of measurements show that regardless of synthesis method, the addition of Al2O3 influences the conductivity of samples by increasing their grain boundaries conductivity as an effect of removing of SiO2 and decreasing of conductivity activation energy. The impregnation of Al2O3 on tetragonal ZrO2 and sintering of this material above shrinking temperature cause, however, radical decrease of porosity of materials, which disqualifies these samples as anode materials. In the case of samples obtained by coprecipitation the significant decrease of porosity is not observed.

The structure, electrical properties and chemical stability of porous Nb-doped SrTiO3 – experimental and theoretical studies

A series of porous SrTi1−xNbxO3 samples (with x = 0, 1, 2 and 3 mol%) were prepared by wet synthesis and sintered at 1573 K. Single phase samples were obtained for each composition, as confirmed by XRD measurements. For all samples, aging tests in CO2/H2O atmosphere and electrochemical impedance spectroscopy measurements in air and hydrogen (reduced) atmosphere were carried out. Simultaneously, for model superstructures corresponding to 2 and 3 mol% experimental compositions, FP-LAPW DFT calculations of electronic structure and bonding properties (using QTAiM approach) were performed. Both experimental and theoretical results show an increase of cell parameters with increasing niobium amount. The influence of the amount of niobium on the microstructure of the synthesized samples as well as on their chemical stability was also observed. Electrical properties measurements showed different conduction mechanism for synthetic air and reduced atmosphere, i.e. mixed ionic-electron conduction and dominating electron conduction, respectively.

Synthesis, structural characterization, electrical properties and chemical stability of a (ZrO2)0.97(Y2O3)0.03−x(MgO)2x solid solution

This paper is concerned with ternary solid state ZrO2–Y2O3–MgO where the zirconia tetragonal phase is stabilized by incorporation of yttrium and/or magnesium in the ZrO2 lattice. This subject is especially important due to the broad application of yttria stabilized zirconia (YSZ) in (among others) electroceramic systems in particular as potential component of the composite anode material for SOFC technology. A series of samples with a starting composition corresponding to 3 mol% yttria-stabilized zirconia (3YSZ) and increasing substitution of yttrium by magnesium were synthesized. The resulting samples were examined in terms of structural properties, phase composition, electrical properties and chemical stability. The obtained results show close correlation between the amount of incorporated magnesium and structural parameters of the tetragonal phase as well as electrical properties of all samples. The substitution of yttrium with magnesium in the 3YSZ system leads to a significant decrease of conductivity and the appearance of a monoclinic phase in the system for x > 0.015 (3 mol% of Mg2+). Moreover, it was confirmed that exposing the ZrO2–Y2O3–MgO ternary system to a CO2 and H2O atmosphere can significantly decrease its chemical stability. From the point of view of both, basic and application research, these studies make an important contribution to the current knowledge of the properties of the ZrO2–Y2O3–MgO ternary solid solution system.

Some observations on the synthesis and electrolytic properties of (Ba1-xCax) (M0.9Y0.1)O3, M = Ce, Zr-based samples modified with calcium

Abstract In this paper, the impact of partial substitution of calcium for barium in (Ba1-xCax) (M0.9Y0.1) O3, M = Ce, Zr on physicochemical properties of the powders and sintered samples was investigated. The powders, with various contents of calcium (x = 0, 0.02, 0.05, 0.1), were prepared by means of thermal decomposition of organometallic precursors containing EDTA. All of the BaCeO3-based powders synthesised at 1100 °C were monophasic with a rhombohedral structure, however, completely cubic BaZrO3-based solid solutions were obtained at 1200 °C. A study of the sinterability of BaZr0.9Y0.1O3 and BaCe0.9Y0.1O3-based pellets was performed under non-isothermal conditions within a temperature range of 25 to 1200 °C. The partial substitution of barium for calcium in the (Ba1-xCax) (M0.9Y0.1) O3, M = Ce, Zr solid solution improved the sinterability of the samples in comparison to the initial BaCe0.9Y0.1O3 or BaZr0.9Y0.1O3. The relative density of calcium-modified BaCe0.9Y0.1O3-based samples reached approximately 95 to 97 % after sintering at 1500 °C for 2 h in air. The same level of relative density was achieved after sintering calcium-modified BaZr0.9Y0.1O3 at 1600 °C for 2 h. Analysis of the electrical conductivity from both series of investigated materials showed that the highest ionic conductivity, in air and wet 5 % H2 in Ar, was attained for the compositions of x = 0.02 to 0.05 (Ba1-xCax)(M0.9Y0.1)O3, M = Zr, Ce. The oxygen reduction reaction on the interface Pt│BaM0.9Y0.1O3, M = Ce, Zr was investigated using Pt microelectrodes. Selected samples of (Ba1-xCax) (M0.9Y0.1)O3, M = Zr, Ce were tested as ceramic electrolytes in hydrogen-oxygen solid oxide fuel cells operating at temperatures of 700 to 850 °C.