【作者】 黄莹；

【导师】 沈美庆；

【作者基本信息】 天津大学 ， 化学工艺， 2006， 硕士

【摘要】 机动车尾气排放造成的大气环境污染问题日趋严重,采用三元净化催化剂的机外净化方法是目前治理机动车尾气排放最为有效的措施之一。但是,金属载体和活性涂层的结合强度一定程度上制约了金属蜂窝催化剂的推广应用,如何改善并提高二载涂层在基体合金表面的牢固度已成为研究者关注的问题。本文围绕Fe-Cr-Al金属载体的活性涂层工艺展开研究,利用SEM、XRD、EDX和BET等表征技术并结合超声波检测、热冲击性能实验等手段,考察了金属载体预处理工艺条件及浆料固含量、粒径分布、浆料pH值及铈锆添加等对涂层性能的影响。预处理工艺条件研究结果表明:最佳的预处理条件是950℃空气气氛氧化10h,采用该条件预处理后,金属载体的表面性能得到了显著改善。一方面,载体表面形成α氧化铝过渡层,大幅增加了载体表面粗糙度和比表面积,提高了二载涂层和载体结合的牢固度;另一方面,高温处理改善了Fe、Cr、Al三种元素在载体表面的分布状态,Al元素向载体表层扩散,而元素Fe、Cr向内层迁移。浆料制备工艺研究结果表明:浆料最优配方为固含量35wt.%、pH值4.0、CZ/Al2O3比例控制在30%左右、粒径分布d90在10.00μm以下。采用该配方可使涂层保持较高的负载量和较小的脱落率,显著提高了涂层的均匀性和热稳定性,对开发制备长寿命、高性能的尾气净化催化剂有较好的理论指导。通过研究得到的最佳预处理工艺条件对金属载体进行表面处理后,利用最优化浆料配方对金属载体进行二载涂层的涂覆,发现涂层的比表面和脱落率的综合指标较好,能较好满足催化剂的负载要求。更多还原

【Abstract】 After-treatment control technique, especially catalytic convert is an effective method to solve the increasing serious atmospheric pollution from the automotive exhaust particularly. The poor coating binding strength between the metallic substrate and the washcoat has attracted more attention by the most researchers.The coating technique of theγ-Al2O3 based ceramic washcoat on surface of FeCrAl metallic substrate was investigated in this paper, partly including the pretreatment condition of the metallic substrate and preparation of slurry. The washcoat quality was measured by SEM, XRD, EDX, BET, ultrasonic vibration and thermal shock test.The results of the pretreatment of the metallic substrate show that the optimal pretreatment condition is oxidized at 950℃for 10h and the metallic substrate surface performance is obviously improved after pretreatment. The transition layer grown on the surface of FeCrAl metallic substrate during such pretreatment increases the specific surface areas and coarseness of the surface of FeCrAl metallic substrate, which improves the combination ability between each other. Moreover, the metallic surface element distribution is improved and Al diffuses towards the interface and forms oxidation transition layer preferentially with oxygen while Fe and Cr in the opposite direction.Adhesion and loading percentages of washcoat primarily depend on the variables of slurries employed in the coating process. The results show that the achievement of satisfactory adhesion and loading percentage can be obtained by the adequate slurries: pH about 4.0, particle sizes of d90 below 10.00μm, CZ/Al2O3 ratio about 30% and solid content below 35 wt.%. The formulation ensures satisfied loading percentages and good adhesion of the washcoats, meanwhile enhances the washcoat uniformity and thermal stability of the coating.The washcoat prepared with above method has excellent properties of ultrasonic vibration, thermal shock test and high surface area.更多还原