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  • Author or Editor: Ewa Drożdż-Cieśla x
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Abstract  

Thermal decomposition of zirconyl oxalate hydrate was studied using DTA, TG, QMS and XRD techniques. It was shown that decomposition occurs in two stages: dehydration to anhydrous oxalate and next, decomposition to zircon oxide (zirconia). These steps are not well separated. We observed that significant amount of water are released during second stage of decomposition. Zircon dioxide is obtained in tetragonal form. Moreover, we consider some dependences between conditions of preparations zirconyl oxalate hydrate and some properties of solid product of its decomposition. Although the reaction of thermal decomposition of zirconyl salts is generally utilized in technology, many aspects of this process are still not sufficiently explained. In our work, we present some new interesting observations concerning thermal behaviour of zirconyl oxalate.

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Abstract

Ceramic–metal composites (cermets) containing 4 mol% yttria-zirconia (4YSZ) and Ni particles as anode materials in solid oxide fuel cells were prepared by two methods. The first method involves nickel oxalate dihydrate precipitation on the 4YSZ powder and decomposition at 360 °C in inert Ar atmosphere. The second method consists of impregnation of the 4YSZ pellets with an aqueous solution of nickel nitrate. The temperature of oxalate decomposition was determined on the basis of TG/DTA experiments. Gaseous products of decomposition were analyzed by mass spectrometry. The structure of the materials was characterized by X-ray diffraction, scanning electron microscopy, porosity studies, and particle size measurements. The thermal expansion coefficient (TEC) was determined by dilathometric method. Electrochemical impedance spectroscopy was used to determine the electrical conductivity. Thus, determined TECs, porosity, and electrical properties were found suitable for anode materials of fuel cells.

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Abstract  

The purpose of this work was to investigate the influence of titanium and yttrium dopants on chemical stability of selected Ba(Ce1−xTix)1−yYyO3 compounds. The presented results are the part of wider research concerning the crystallographic structure, microstructure, electrical and transport properties of these groups of materials. Samples of Ba(Ce1−xTix)1−yYyO3 with x=0.05, 0.07, 0.10, 0.15, 0.20, 0.30 and y=0.05, 0.10, 0.20 (for x=0.05) were prepared by solid-state reaction method. Initially, differential thermal analysis (DTA) and thermogravimetry (TG) were used for optimization of preparation conditions. Subsequently, DTA-TG-MS (mass spectrometry) techniques were applied for evaluation of the stability of prepared materials in the presence of CO2. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results were used to determine the phase composition, structure and microstructure of materials and to assist the interpretation of DTA-TG-MS results. The strong influence of Ti and Y dopants contents (x and y) on the properties was found. The introduction of Ti dopant led to the improvement of chemical stability against CO2. The lower Ti concentration the better resistance against CO2 corrosion was observed. Doping by Y had the opposite effect; the decrease of chemical stability was determined. In this case the higher Y dopant concentration the better resistance was observed. The attempt to correlate the influence of dopant on structure and chemical stability was also presented.

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