钙长石基多孔陶瓷中莫来石晶须的原位合成机理与调控

Due to its good properties, porous ceramics is one of the best substitute materials which can be used as thermal insulator materials in near space hypersonic vehicle. But the contradiction among high strength, high porosity and low thermal conductivity restricts its application. A recent study indicates that it is an effective way to solve that problem by adding mullite whiskers into anothite porous ceramics. This project focuses on in-situ synthesis mechanism and control mechanism of mullite whisker. The main content includes: conforming key processing parameters to prepare in situ synthesized mullite whiskers reinforced anothite porous ceramics with tunable microstructure; investigating the effects of pososity, pore size, pore distribution and the microstructure of anorthite matrix on synthesis of mullite whisker and revealing its synthesis mechanism; researching the effects of mullite whisker content, aspect ratio and interface structure on thermal and mechanic properties; finding the law between thermal conductivity and strength; revealing control mechanism of mullite whisker. The purpose of this project is to reveal the in-situ synthesis and control mechanism of mullite whisker and to solve the contradiction among high strength, high porosity and low thermal conductivity. It is reasonable to believe that creative results can be achieved by performing this project. The present study is beneficial to promote the applications of anorthite based porous ceramics in near space hypersonic vehicle.

低热导率-高气孔率-高强度之间的矛盾制约了多孔陶瓷在近空间高超声速飞行器用防/隔热关键部件的应用,申请者前期研究结果表明晶须增强是解决此矛盾的有效方法。在此结果启发下，本项目以原位合成莫来石晶须增强钙长石多孔陶瓷为研究对象，集中研究莫来石晶须的原位合成机理及调控机制。主要研究内容包括：确定关键工艺参数，制备结构可调的莫来石晶须增强钙长石多孔陶瓷；研究气孔率、气孔尺寸、孔径分布及钙长石基体结构对晶须合成过程的影响,揭示莫来石晶须的合成机理；研究晶须含量、长径比及与界面结合对热学、力学性能的影响规律；探究晶须增强多孔陶瓷的热力匹配规律，确定晶须调控机制。本项目旨在揭示多孔条件下晶须合成机理、晶须增强材料的热力匹配规律及晶须调控机制，从而解决低热导率-高气孔率-高强度之间的矛盾。本项目的开展，能取得创新性的成果，其成功实施对促进多孔陶瓷在近空间高超声速飞行器用防/隔热关键部件的应用具有指导意义。

具有优良特性的钙长石基多孔陶瓷是近空间高超声速飞行器用超轻、高强防/隔热用关键部件的优秀备选材料，但高防/隔热-高气孔率-高强度之间的矛盾制约了其应用进程，晶须增强复合材料的出现为解决此矛盾提供了可能。主要研究分为以下三部分：采用泡沫注凝法制备了多孔陶瓷，研究了烧结温度、发泡剂浓度及固含量等重要工艺参数对制备材料结构与性能的影响规律，研究发现烧结温度对物相组成、晶粒大小有显著影响，高发泡剂浓度及低固含量条件下均可制备出高气孔率的材料，低固含量下制备的材料具有更高的强度；结合热分析、XRD分析、SEM观察及TEM观察分析获得的实验结果，详细研究了在泡沫注凝法制备过程中的物相演变过程及钙长石、莫来石晶须的形成机理，研究发现钙长石形成于固相反应且其形成受坯体排胶过程中残碳及硫的影响很大，而莫来石晶须的形成主要为气固机理且不受坯体中残余碳的影响，而且坩埚密封程度对于莫来石晶须的生长及钙长石的合成均有巨大的影响；采用泡沫注凝法制备的多孔陶瓷的热导率与气孔率遵循特定条件下的通用模型而与经典模型差别很大，而抗压强度与气孔率满足指数为2.46~2.65的Gibson-Ashby模型，复杂的气孔结构是影响其热导率及强度的主要原因。本项目的完成后，研究者掌握了兼具高强低热导且结构可调的制备技术，为其产业化推广奠定了基础；获得的莫来石晶须及钙长石的形成机理、热/力匹配规律具有重要的科学意义，并为材料设计提供了依据；研究结果对促进钙长石基多孔陶瓷在近空间高超声速飞行器特殊防/隔热部位的应用具有指导意义。