Sythesis And Characteristics Of Ca₂Fe₂O₅Powdors

Ca₂Fe₂O₅have opened a new vista in view of their technologicalapplications such as magnetocaloric refrigeration, heterogeneous catalysis,catalytic material and ceramic membranes and high-temperature electrochemicaldevice and so on. Especially, compared with nomoral SOFCs cathode materials,Ca₂Fe₂O₅employed as cathode in solid oxide fuel cells has incomparableadvantage. Systhesis fine powders enhanced performance full playing. But fewpapers reported systhesis methods of Ca₂Fe₂O₅materials. So far, it was only usedthat solid-state synthesis of Ca₂Fe₂O₅proceeds. However, this demonstrates thatthe conventional solid-state synthesis of Ca₂Fe₂O₅proceeds very slowly andrequires higher temperatures, which lmitted Ca₂Fe₂O₅materials to be employedwidly. Thus, creating efficient and simple synthesis of Ca₂Fe₂O₅methods isimportant in further study.The activation properties of mechanical partical would be improved, such assize of particals refined, concentrations of lattice defects increased, chemicalpotentials improved, powder reaction activation reduced. This would enhance thereaction going under lower temperature. The present paper reported a novelsynthetic method--high energy milling, for preparation of the brownmilleritestructural Ca₂Fe₂O₅powder. It was revealed the high-purity powders ofbrownmillerite structural Ca₂Fe₂O₅were completely prepared under800℃frommechanical carbonate/oxide mixtures. While high-purity Ca₂Fe₂O₅powders werehardly synthesis in CaO/Fe2O3system via uniform treatment. The reason of thedifferent behaviour of the carbonate/oxide and oxide/oxide precursor systemsduring the processing may lie in both the different chemical affinity andmechanical properties of CaCO₃and CaO. Fe2O3nonapowders which can reducethe reaction temperature and be benifical for Ca diffusion at low temperaturereation had appeared after the CaCO₃/Fe2O3mixtures milled3h，but CaO/Fe₂O₃mixtures didn’t. Large pore passageway would leave in the position of CaCO₃decomposing, then air passing into pore passageway easily formed oxygen enrichment, which is favour in preparing Ca₂Fe₂O₅powders.What’ more, the powders has been mechanically activated （by high energymilling） for different time and then annealed at800°C. With the help of XRDand SEM analysis, the changes of phase and structure under different millingtime and annealed at800°C for different soaking time were analyzed, and thereaction mechanism was also discussed. It was revealed that the soaking time ofsysthesis Ca₂Fe₂O₅powder annealed at800°C decreased with milling timeenlongth. The mixtures milled3h completely systhsized pure Ca₂Fe₂O₅powderwith a85%degree of crystallization at800°C for24h, but the mixtures milled30h needed6h soaking time and the degree of crystallization of powders wasabout73%in detail. Meanwhile, the microstructures of Ca₂Fe₂O₅powder wasvital different with each other. With the milling time enlongth, themicrostructures had change from cube powders going by plane to globlularparticals, the size of which was lower100nm. Then, pure and high degree ofcrystallization（above on90%）Ca₂Fe₂O₅powders were needed16h prepared bymultistep soaking at800°C. Compared with powders prepared by onestepsoaking, the microstructure composed with more short and more uniformgrading cube particles.In addition, the pure Ca₂Fe₂O₅powders were also prepared by the lowtemperature liqude phase combustion method （SCS）. SCS is a method in whichthe saturated solution of metal nitrate （antioxidant） and organic matter （fuel）usually heated at a definite temperature, then metal nitrate fastly react using thereleased energy of the organicfuel, and the energy enhance the reactiontemperature to1600℃. In this paper, the as-synthesized powders werecharacterized by XRD, SEM. The results indicated that the single Ca₂Fe₂O₅powders prepared from Fe nitrate/Ca nitrate with the fuel of urea at700℃wereuniform grading porticals structure.