耐高温纳米莫来石纤维气凝胶结构设计及其隔热机制与结构稳定性研究

To develop aerogels for long-term application in oxidizing atmosphere at above 1300oC has been a scientific bottleneck in high-temperature insulation field. In this project, a new nanofibrous aerogel with heat-resistant mullite nanofibers as 3D porous skeleton and silica sol as high-temperature binder is designed by imitating the idea of functional nanofibrous aerogels, which thoroughly breaks the traditional thinking in solid particulate aerogel systems. The suspension characteristics of ceramic nanofibers in polymer monomer solution and the relationship between the driving force (the driving force from the ice crystals’ growth) and the resistance (the binding effect of the organic network structure) of forming the porous structure during gel-casting and freeze-drying are analyzed, and the formation mechanisms of the porous structure in fibrous aerogel are further defined. The insulation performance and structural stability of the material at both room temperature and high temperature are studied. Combined with the research results of the applicant’s National Youth Fund on the preparation of heat-resistant mullite nanofibers, the effects of the characteristics of individual fiber and the join structure between fibers on the insulating performance and other physical properties of the fibrous aerogel are systematically studied. On this base, the performance of the component can be simultaneously optimized in terms of the performance of raw materials and the microstructure of the component. The implementation of this project will provide a new way for developing heat-resistant aerogels.

研发可在1300oC以上有氧环境中长时间使用的超轻隔热气凝胶材料已成为高温隔热领域一项亟待解决的科学难题。本项目跳出以往固体颗粒气凝胶体系的研发思维惯性，借鉴广泛应用于功能材料领域的纳米纤维气凝胶的设计思路，设计了一种以耐高温纳米莫来石纤维为三维多孔骨架，以硅溶胶为高温粘结剂的纳米纤维气凝胶材料。分析纳米陶瓷纤维在有机单体溶液中的悬浮特性以及凝胶注模-冷冻干燥过程中多孔结构形成的动力（冰晶生长的推动力）与阻力（有机网络结构的束缚作用）之间的作用关系，进而明确纤维气凝胶孔结构的生成机制；研究材料的室温及高温的隔热性能以及结构稳定性，并结合申请人青年基金关于制备耐高温纳米莫来石纤维的研究成果，系统研究单根莫来石纤维性质、纤维之间的搭接结构对纤维气凝胶隔热及其他物理性能的影响规律，进而从原料性能和组件显微结构两个层面上来优化气凝胶的性能。本项目的实施为研发耐高温气凝胶的研究提供了新的方向。

气凝胶具有极低的密度和热导率，在各类飞行器、工业窑炉的隔热系统中有着广泛的应用。但由于纳米粒子的超高活性，传统固体颗粒气凝胶在高温时（1200℃）会发生结构性坍塌。因此，研发可在1300℃以上有氧环境中长时间使用的耐高温气凝胶材料是一项亟待解决的科学难题。项目跳出以往固体颗粒气凝胶体系的研发思维惯性，成功设计了一种以耐高温纳米莫来石纤维为三维多孔骨架的莫来石纳米纤维气凝胶，并系统研究了成型工艺参数（纤维尺寸、烧结温度、固相含量、硅溶胶含量）、样品显微结构（纳米莫来石纤维搭接方式、孔结构）和样品性能（强度、密度、热导率）三者间的关系，从而通过工艺优化实现性能优化。. 项目首先采用凝胶注模-冷冻浇注工艺成功制备出耐高温莫来石纳米纤维气凝胶。莫来石纳米纤维气凝胶展现出典型的多级孔结构，其中宏孔主要由冰晶的升华产生，而微孔则为纳米纤维搭接而成。由于独特的多孔结构，材料经1400℃烧结后仍具有极低的密度（34.64~48.89mg/cm3）和极低的热导率（0.03274~0.04317Wm-1K-1)。随后，针对冷冻干燥工艺过于复杂的缺点，项目进一步提出采用叔丁醇基凝胶注模工艺来制备莫来石纳米纤维气凝胶，并探究了固相含量和纤维长度对纳米纤维气凝胶各项物理性能的影响。结果表明，随着纳米纤维的固相含量从1.5wt%增加到2.5wt%，样品强度从0.114MPa增加到0.158MPa。与以短纤维为原料制备出的样品相比，采用长纤维制备出的样品展现出更低的密度（0.062g/cm3）和更低的热导率（0.0597Wm-1K-1）。最后，项目将上述研究成果拓展到其它体系，成功制备出轻质隔热的硼酸铝纳米纤维气凝胶和钛酸铝纳米纤维气凝胶，从而为设计各类型的陶瓷纤维气凝胶提供了理论支持.