孔内自生莫来石棒晶强化钛酸铝多孔支撑体的机理研究

Because aluminium titanate has excellent physicochemical properties, such as high temperature resistance, low thermal expansion coefficient, thermal shock resistance and good corrosion resistance, it will be a promising candidate for use as the high temperature flue gas filtration supporter and substrates in catalytic converters for motor vehicles. However，industrial applications of this material are hindered due to two major limitations. The first one concerns with its low sintering strength. The second is due to its tendency to decompose to α-Al2O3 and TiO2. Research results show that mullite has good compatibility with aluminium titanate, and it can be used to reinforce and stabilize aluminium titanate. Moreover, mullite whisker is a good candidate for strengthening materials. The stablization and compressive strength of aluminium titanate porous materials will be improved by in-situ synthesis large size of rodlike mullite crystals among the hole. Therefore, aluminium titanate porous support reinforced by in-situ synthesis large size of rodlike mullite crystals among the hole is prepared by reaction sintering method in this topic, and the thermal stability of aluminium titanate will be controlled by modifying agent Fe2O3 and mullite. The growth mechanism and strengthening mechanism of rodlike mullite crystal synthesized in the aluminium titanate matrix will be revealed through investigating the relationship between micro-structure and the influence factors of thermodynamic and dynamics, as well as relationship between compressive strength and the influence factors of thermodynamic and dynamics. On the basis of investigations mentioned above, aluminium titanate porous support with pore structure reinforced by in-situ synthesis rodlike mullite crystals will be obtained. The pore forming mechanism of porous material will be revealed by investigating micro-structure and composition changing of the green bodies and sintered products. Through optimizing the technological parameters of materials, molding and sintering processhe, porous support with high apparent porosity and reasonable pore size distribution can be obtained. All the works mentioned above will provide technical support and theoretical guidance for the practical applications of aluminium titanate porous support reinforced by rodlike mullite crystals.

钛酸铝具有优良的耐高温、低膨胀、抗热震性和耐蚀性，是作为高温烟气过滤、机动车尾气净化用多孔支撑体的理想材料。但其存在烧结强度低、易分解两大缺陷，严重影响实际应用。研究表明莫来石与其具有良好的相容性，能起到一定的增强和稳定作用，加之莫来石晶须在材料强韧化方面的优异表现，通过孔内原位生成莫来石棒晶有望提高其多孔材料稳定性及抗压强度。因此，本项目提出采用反应烧结法孔内原位合成大尺寸莫来石棒晶增强钛酸铝多孔支撑体，利用莫来石与Fe2O3协同作用提高其热稳性。通过对合成过程中材料微观结构及抗压强度与其热力学、动力学影响因素之间关系研究，揭示棒晶在钛酸铝基体中的生长机制和强化机理，得到具有贯穿棒晶强化孔结构的莫来石棒晶增强稳定钛酸铝多孔材料；选择合适原料组成、成型工艺，研究素坯及烧结过程中材料微观结构和组成变化，揭示成孔机理，得到孔隙率高、孔径分布合理的多孔支撑体，为其实际应用提供技术支持和理论指导。

随着经济社会的发展、工业化进程的加快，以资源、能源消耗性为主的重工业（电力、建材、冶金、化工、汽车等）得到迅速发展，由此导致的环境污染问题凸显。大量工业三废排放，尤其是工业高温烟气以及机动车尾气、粉尘颗粒的排放已成为城市污染的罪魁祸首。因此，开展高温烟气过滤、机动车尾气净化处理的研究，减少固体颗粒的排放成为节能减排、环境保护工程中的重要工作。.钛酸铝具有优良的耐高温、低膨胀、抗热震性和耐蚀性，是作为高温烟气过滤、机动车尾气净化用多孔支撑体的理想材料。但其存在烧结强度低、易分解两大缺陷，严重影响实际应用。因此，本研究从钛酸铝两大主要缺陷入手，首先研究钛酸铝的热稳定性，通过氧化铁和莫来石的添加以期改善其热稳定性，结果发现，氧化铁的添加，通过形成Fe2TiO5与Al2TiO5固溶体，可以明显改善其热稳性，当氧化铁添加量达到20%的时候，生成钛酸铝相在1100℃保温120h未见分解，而单纯莫来石相的添加对稳定性影响非常小。在此基础上，研究了氧化铁稳定的莫来石棒晶增强的钛酸铝的制备，首先从莫来石晶须的生长发现，原料粉体中铝源AlOOH与Al(OH)3比惰性的氧化铝更有利于晶须的形成，并且晶须尺寸随着成型压力的升高，晶须径向增大，长径比明显减小，由晶须向棒晶变化，在成型压力为78MPa时，晶须直径为0.5-1μm，长10-20μm，由晶须微观形貌分析，主要为固气生长机制。因此，莫来石中铝源由AlOOH引入，随着莫来石成分含量的增加，气孔率先降低，在20%时达到最低，之后随着莫来石含量增加气孔率增加，在莫来石含量达到50%时，气孔率约为40%，抗压强度与抗折强度分别为50MPa和15MPa，由微观结构分析可知，通过孔洞中棒晶的支撑作用，以及孔壁的桥联作用，可以显著提高多孔支撑体的强度。多孔支撑体孔径分布为双峰分布，分别在0.5-1μm和20μm，基本满足高温烟气过滤的需求。此外，为了进一步改善多孔支撑体的强度，实验还研究了氧化铝片晶对钛酸铝-莫来石多孔支撑体的增强作用，结果发现，当氧化铝片晶添加量为10wt.%时，得到多孔支撑体的气孔率为47.2%，抗压强度为138.1MPa，抗折强度为40.3MPa。从上述研究，较好的改善了钛酸铝多孔支撑体的热稳性及强度性能，远远优于现有文献报道结果，可以很好地满足实际应用的需要，为其进一步实际应用提供技术支持和理论指导。