【作者】 赵春；

【导师】 王芬；

【作者基本信息】 陕西科技大学 ， 材料学， 2012， 硕士

【摘要】 Ca₂Fe₂O₅材料具有独特的晶体结构、高的电子离子混合导性、催化活性和化学稳定性以及低的热膨胀系数等特点，使其在工业催化，磁性，氧传感，高温电导等领域中具有潜在的应用前景。特别是在SOFC材料方面，与其他电池材料相比有着无法比拟的优势。Ca₂Fe₂O₅粉体制备是其材料的制备及功能充分发挥的关键，但目前常用的传统固相反应法合成Ca₂Fe₂O₅粉体工艺，反应温度高，合成时间长，限制了它们的广泛应用且不利于性能的发现和研究。所以新的高效节能的制备工艺是目前研究的重点。高能球磨处理可使原料粒度细化、结构缺陷浓度增高、化学位能提高，粉体反应活化能降低，促使原料在较低的温度下合成产物。依据此特点，本文分别以CaO-Fe₂O₃和CaCO₃-Fe₂O₃为原料，采用高能球磨结合固相反应的方法来制备Ca₂Fe₂O₅粉体。结果显示，当Ca与Fe摩尔比例合适时,经过球磨处理的CaCO₃-Fe₂O₃混合在800℃经过适当的保温很容易合成纯的单相Ca₂Fe₂O₅粉体，而以在CaO-Fe₂O₃体系，则因容易产生杂质相而很难实现。原因是CaCO₃-Fe₂O₃体系中混合粉末经机械球磨首先破碎的是Fe₂O₃颗粒，这些Fe₂O₃不仅会降低反应合成温度而且利于Ca的扩散；且体系中存在利于空气中氧进入的气体通道（CaCO₃分解时留下的），这些进入的氧可抑制结构中[FeO4]四方体转化成[FeO₆]，而CaO体系缺少这样的氧通道。研究发现，在CaCO₃-Fe₂O₃体系中，随着球磨时间的延长，合成Ca₂Fe₂O₅粉体保温时间也相应的减短。混合粉末球磨活化3h后，在800℃保温24h才可得到纯的单相Ca₂Fe₂O₅粉体；球磨活化时间延长到30h时，在800℃只需保温6h即可实现。但是保温时间越短合成的粉体的结晶度降低，同时随着保温时间的减短，合成的粉体粒度越来越细，在30h时合成的粉体粒度低于100nm。除此而外，粉体的形貌也发生变化，由块状逐渐变为片状最后转为球状的颗粒。研究指出，采用分段烧结合成粉体，其结晶度可以大大提高。另外，研究了采用SCS-液相燃烧法制备Ca₂Fe₂O₅粉体。液相燃烧法的特点是有机燃料和金属盐溶液可以在较低温度下（≤500℃）迅速燃烧反应，燃烧放出的热能自发的维持反应继续进行；另外燃烧放出的热能可使原料反应温度很快加热到1600℃以上，加速反应的进行，在短时间内合成低温下难合成的复杂的氧化物产物。本文以Fe（NO₃）₃、Ca（NO3）2为原料，以CO（NH2）2为助燃剂合成Ca₂Fe₂O₅粉体。借助XRD、SEM等测试手段，分析了燃烧过程及反应合成产物温度，并重点讨论了燃烧温度因素对合成钙铁石型的Ca₂Fe₂O₅粉体物相及形貌的影响,同时探讨了燃烧法合成的Ca₂Fe₂O₅粉体的反应过程。研究结果表明，燃烧温度达700℃时，原料全部反应合成Ca₂Fe₂O₅粉体，产物形貌为颗粒分布均匀的球状颗粒。更多还原

【Abstract】 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.更多还原