Abstract
Thermogravimetry (TG) and Differential Thermal Analysis (DTA) techniques coupled with mass spectrometry were applied to evaluate the chemical stability of BaCeO3−δ-based materials in the CO2- and H2O-rich atmosphere. The different groups of materials were investigated: solid solutions of BaCeO3–BaTiO3 and BaCeO3–BaSnO3 acceptor doped by Y or In and composite materials with nominal composition (1−x)BaCe0.9Y0.1O3−δ-xYPO4. To evaluate the chemical stability towards carbon dioxide and water vapour samples were exposed to atmosphere containing CO2/H2O (7 % of CO2 in air, 100 % RH) at temperature of 25 °C for 350 h. Thermal analysis (TG/DTA) was applied to analyse the materials before and after the test. To support the interpretation of TG/DTA results, the analysis of gaseous products evoluted during thermal treatment of the samples was provided using mass spectrometer. This combined analysis clearly shows that during the exposition test, the conversion of barium cerate to barium carbonate and barium hydroxide occurs. The amount of BaCO3 and the degree of BaCeO3−δ conversion depend on the type of barium cerate modification. The mass loss observed after the exposition test can be treated as a measure of chemical instability of BaCeO3−δ-based materials. The correlation of chemical stability, described by the mass loss, on Goldschmidt tolerance factor, describing the deviation from ideal perovskite structure, was found in most of the materials investigated. However, the influence of the microstructure and the modification the grain boundaries on the chemical stability of BaCeO3−δ-based materials cannot be neglected.
Highlights
One of the greatest disadvantages of proton conductors based on BaCeO3-d is poor chemical stability especially in atmospheres containing CO2 and H2O
Thermogravimetry (TG) and Differential Thermal Analysis (DTA) techniques coupled with mass spectrometry were applied to evaluate the chemical stability of BaCeO3-d-based materials in the CO2- and H2Orich atmosphere
The reason of poor chemical stability of BaCeO3-d-based materials is possibility of barium cerate reaction with CO2 and H2O resulting the formation of secondary BaCO3 (or Ba(OH)2) and cerium oxide according to the reactions [1, 2]
Summary
One of the greatest disadvantages of proton conductors based on BaCeO3-d is poor chemical stability especially in atmospheres containing CO2 and H2O. The reason of poor chemical stability of BaCeO3-d-based materials is possibility of barium cerate reaction with CO2 and H2O resulting the formation of secondary BaCO3 (or Ba(OH)2) and cerium oxide according to the reactions [1, 2]. The XRD analysis of materials after such tests clearly shows the presence of barium carbonate which indicates that during the exposition of BaCeO3-d -based materials to the CO2-rich atmospheres the reaction (1) occurs. The amount of BaCO3 or Ba(OH) in the samples after the tests can be treated as the measure of chemical instability of BaCeO3d-based materials towards CO2- or H2O-containing atmospheres
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