Abstract
In the present work, preceramic nanocrystallite barium cerate (BaCeO3) was successfully synthesized using the hydrazine-nitrate combustion method. Using carbon-free hydrazine (N2H4) as fuel significantly reduced the formation of carbonate by-products. Subsequent annealing of combustion products in the air atmosphere at temperatures in the range of 500–1000 °С yielded preceramic powders based on chemically and phase-pure BaCeO3. Characterization of the as-received powders was performed by X-ray diffraction, energy-dispersive X-ray spectroscopy (EDXS), scanning electron microscopy (SEM), simultaneous thermal analysis (DTA-TGA) and adsorption-structural analysis (N2, 77 K). Thermophysical properties of the sample annealed at 1000 °С were investigated using laser flash analysis (LFA) in the temperature interval of 1000 °С. As a result of a comprehensive study, the sequence of chemical and phase transformations that lead to the formation of barium cerate with a rhombic structure (Pnma, a = 6.2145 Å, b = 8.7776 Å, c = 6.2337 Å) during the thermal processing of combustion products was investigated. It was established that the average size of the obtained nanocrystals is 38 ± 3 nm and that they form micron-sized agglomerates with a specific surface area of the powder of 4.8 m2/g. It was shown that the sintered sample of barium cerate is characterized by thermal diffusivity values of 0.28 to 0.20 mm2/s and thermal conductivity values of 0.41–0.35 W/mK, depending on temperature. These results, given the impact of porosity on the sample (~40%), show very good agreement with the thermophysical characteristics of densely sintered ceramics based on BaCeO3—a solid oxide electrolyte SOFC. Consequently, the proposed method of hydrazine-nitrate synthesis of barium cerate presents itself as a promising approach to obtaining preceramic powders and ceramics in the area of solid oxide fuel cells.
Highlights
A solid oxide fuel cell (SOFC) is a device that allows converting the energy of chemical bonds into electric energy both effectively and ecologically
The nanocrystallite BaCeO3 obtained in this work has density and porosity characteristics that correspond to known preceramic powders based on barium cerate, which lends to the conclusion that it can be used in this capacity
It was demonstrated that using hydrazine as fuel has the advantage of the lack of carbon residue in the combustion products, which significantly lowers the formation of carbonate impurities
Summary
A solid oxide fuel cell (SOFC) is a device that allows converting the energy of chemical bonds into electric energy both effectively and ecologically. The method of solution combustion allows obtaining nanopowders of simple and complex oxides with the desired crystalline structure and size parameters via both direct synthesis and synthesis involving thermal processing of amorphous combustion products [23,24,25] Advantages of this method include simplicity, short duration, and the possibility to inject large amounts of dopants while preserving the single-phaseness of the products of synthesis. Hydrazine (N2H4), known as a constituent in rocket fuels that helps preserve solution combustion, presents itself as a promising carbon-free fuel On this basis, it is essential to develop new original methods for obtaining barium cerate particles characterized by nano-size and low specific surface area with a high degree of aggregation. Based on the conclusions of these analyses, we discuss possible implementations of this method in obtaining advanced ceramic SOFC materials
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