【作者】 谭亮；

【导师】 徐南平； 时钧；

【作者基本信息】 南京工业大学 ， 化学工程， 2003， 博士

【摘要】 钙钛矿型透氧膜在氧气分离、固体燃料电池和甲烷部分氧化制合成气等方面有着良好的应用前景，受到了人们的广泛关注，但其大规模的工业化应用受到了两个因素的限制：一是透氧率不能满足要求，二是膜材料在高温还原性气氛下的稳定性较差。 本文针对目前研究工作中存在的两个偏向：重材料组成而忽视微观结构对膜性能的影响以及重表面修饰而忽视掺杂对膜表面交换的影响，从制备工艺-微观结构-性能的关系出发，研究了膜微观结构的调控方法及其对膜透氧性能的影响规律，并从掺杂-结构-性能的关系出发，对掺杂了不同离子的透氧膜的性能进行了研究。 1．粉料制备方法对Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ透氧膜性能的影响 采用固相反应法、改进柠檬酸法和柠檬酸-EDTA络合法制备了Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ粉料，并在相同的烧结条件下制备了透氧膜。 首先对粉料的晶型结构进行了表征，结果表明用柠檬酸-EDTA络合法制备的粉料完全转变为钙钛矿晶型所需要的灼烧温度最低，其原因是有机物的存在促进了钙钛矿相的形成。尽管改进柠檬酸法也使用了有机物，但其中的有机物在粉料的干燥过程中已经完全燃烧掉。 从扫描电镜照片可以看出固相反应法制得的粉料存在明显的孤立颗粒，而改进柠檬酸法制备的粉料表现为珊瑚状结构，用柠檬酸-EDTA法制得的粉料也存在颗粒边界，但其晶粒发生了一定的融合，不同的粉料制备方法造成了晶粒形貌上的差异。 膜片的收缩率、微观结构的致密程度和透氧速率的大小顺序相同，即固相反应法＞改进柠檬酸法＞柠檬酸-EDTA络合法。晶界阻碍了氧离子在膜内部的传导，因而膜越致密，晶界越少，从而膜的透氧率越高。不同的粉料制备方法是导致不同透氧速率的原因。实验结果进一步表明了膜的透氧活化能是材料的本征特性，与膜的微观结构没有必然的联系。 2．烧结条件对Ba_0.8Sr_0.2Co_0.8Fe_0.2O_3-δ透氧膜性能的影响 采用固相反应法制备了Ba（0.8）Sr_0.2Co_0.8Fe_0.2O_3-δ粉料，在不同烧结温度（1273、1323、1373和1423 K，保温时间保持为300 min）和不同保温时间（5、150、300 南京工业大学博士学位论文 和 450 min，烧结温度为 1373 K）下制备了透氧膜，表征了粉料的晶型结构、膜 的微观结构及膜的透氧率。 制得的粉料以BaFeOu和BO．仔。Coo．sFeo、。O林的固溶体形式存在，烧结温 度的提高促进了两相之间的共溶，而保温时间对两相的共溶没有明显的影响。 晶型结构的分析结果还表明，提高烧结温度和延长保温时间均有利于钙钛矿相 的形成。 在相同保温时间下烧结得到的膜，烧结温度越高其微观结构越致密，在同 一烧结温度下制备的膜，致密程度随保温时间没有明显的变化。二次再结晶导 致了在 1423 K烧结、保温300 min的膜片呈现出致密的烧结体。由于晶粒的大 小在烧结过程中发生了变化，在 1373 K烧结、保温 150 min的膜片呈现出最大 的收缩率。膜的透氧率没有随相对密度的增加而增大，其原因是膜的微观结构 和晶型结构对氧渗透性能共同施加影响。 3．掺杂Ag的SrCo。。Fe。。O。a透氧膜的研究 用固相反应法制备了不同Ag掺杂量的SrCoosFeo．ZOs6粉料，并制备了相应 的透氧膜，与未掺杂的SrCoo。Feo。O。。粉料及膜从晶型结构、稳定性及氧渗透性 能方面进行了比较。 晶型结构的表征结果表明Ag。O相存在于掺杂Ag的SrCoo．沪．ZO)。中，其 对钙钛矿结构的影响很小。SfCOO．8F80刃34晶胞参数随着Ag掺杂量的增加而减 小，表明了Ag对SrCo。沪emO。。中A位S／”的部分取代程度很小。从粉料的热 重表征结果可以看出，Ag的掺杂促进了SrCoo。Feo。O的钙钛矿相的形成，并且 温度的升高促进了Ag。O相固溶到SrCoosFeo。Os．8的晶格内部。 对在He中活化后的粉料的晶型结构进行了表征，结果表明掺杂Ag对 SfCOO．SFC。。O3．8的稳定性没有明显的影响，热重结果也表明了SfCOO二SFCO，2O3＿8从 有序到无序的相转变温度没有因为掺杂Ag而发生明显的变化。 通过对膜的透氧率的分析，得出掺杂Ag增大了SrCoo．sFeo。O。8膜的表面交 换速率，其效果随着Ag掺杂量的不同和膜操作温度的不同而变化。当Ag掺杂 量为2．5％和5％时，表面交换速率的增大占了主导地位，透氧率变大，当用过 多的ag掺杂时，氧缺陷浓度的减小则起了决定性作用，膜的透氧率减小。实验 中理想的 Ag掺杂量为 5％。通过比较膜在不同温度下的透氧率，可以得出在较 低的温度时，掺杂Ag对SrCOO沪CMO3．8膜表面交换速率的改善更加显著。 4．掺杂离子大小对SrCoo．sEe。ics．a透氧膜性能的影响 工互—－M—一．二——一M－－－’－－－－－－－－－－－－－－－－ai－－u－－－－ffe＊＊＊＊＊一 南京工?更多还原

【Abstract】 Perovskite-type membranes have been widely studied due to their potential applications in oxygen separation, solid oxide fuel cells, and partial oxidation of methane to syngas, etc. However, the commercialization of this kind of membranes is limited by two factors: one is the lower oxygen permeation flux than that is practically needed, and the other is the poor stability of the membrane materials at high temperature and reducing atmosphere.In current researches, the influence of the composition on the properties of the membrane is highlighted while the influence of the microstructure is neglected, and the influence of the surface modification on the surface exchange of the membranes is highlighted while the influence of doping is neglected. Aiming at these two aspects, the controlling means of the microstructure and its influence on the oxygen permeation performance of the membranes is studied in light of the relationship of preparation technology-microstructure-properties, and the oxygen permeation performance of the membranes doped with different ions is studied in terms of the relationship of doping-structure-properties.1. Influence of powders synthesis method on the properties of Ba0.5Sr0.5Co0.8Fe0.2O3-δ membraneBa0.5Sr0.5Co0.8Fe0.2O3-δ powders are synthesized by solid-state reaction method, modified citrate method and citrate-EDTA complexing method, and the corresponding membranes are sintered under the same conditions.The crystal structure of the powders synthesized by citrate-EDTA method completely transforms to perovskite structure at the lowest temperature, for which the reason is that the existence of the organic components promotes the formation of the perovskite phase.From the scanning electron micrographs, it could be seen that the powders synthesized by solid-state reaction method have distinct grains, while those synthesized by modified citrate method show coralline structure. Grain boundaries also exist for the powders synthesized by the citrate-EDTA method, although the grains merge for certain degree.The shrinkage rates, the relative densities of the microstructures and the oxygen permeation fluxes are in the same orders as solid-state reaction method > modified citrate method > citrate-EDTA method. The grain boundary hinders the transfer of the oxygen ion in the membrane bulk. Therefore, the denser the membrane, the few the grain boundaries, and the higher the oxygen permeation flux. The different powders synthesis method is the reason that leads to the different oxygen permeation flux. A further conclusion is that the activation energy of the membrane for oxygen permeation is the essential character of the material, while is independent of the microstructure of the membrane.2. Influence of sintering conditions on the properties of Bao.5Sro.sCoo.8Feo.2O3-8 membranesBa0.5Sr0.5Co0.8Fe0.2O3-δ powders are synthesized by solid-state reaction methods. The membranes are sintered at different temperatures (1273, 1323, 1373 and 1423 K, the dwell time is 300 min) and are dwelled for different times (5,150,300 and 450 min, the sintering temperature is 1373 K). The crystal structure, the microstructure and the oxygen permeation flux are characterized.The calcined powders consist of BaFeO2.9 phase and Ba0.8Sr0.2Co0.8Fe0.2O3-δ phase. Increasing sintering temperature could promote the solid dissolution of the above two phases, while there is no obvious relationship between the degree of the solid dissolution and the prolongation of the dwell time. It also can be found that the increase of the sintering temperature and the prolongation of the dwell time are beneficial to the formation of the perovskite phase.The relative density increases directly with the sintering temperature for the membrane dwelled for different times, while does not change obviously with the dwell time for the membrane sintered at different temperatures. The membrane sintered at 1423 K for 300 min shows a dense sintering body, which is thought to be caused by the secondary recrystallization. The grain更多还原