无机晶须低温原位生长自增韧耐高温胶黏剂的制备与增韧机制研究

To deal with the urgent need of heat-resistant adhesives with high toughness and good thermal-shock-resistance from aerospace field, in-situ growth technology of inorganic whiskers is proposed in this project to realize the self-toughness of heat-resistant adhesives in their service stage. In order to solve the exorbitant temperature demand of common in-situ growth methods based on gas-phase reaction and avoid the as-obtained low density of matrix, the project is using low melting transition metal oxides or halides as flux, and prefabricating the “reaction source-flux-reaction source” whisker precursors by using high energy ball milling or sol-gel processes. After establishing uniformly-distributed small eutectic systems in adhesive, Cr3C2 whiskers (anaerobic) or mullite whiskers (aerobic) can grow in-situ at relatively low temperatures (800~1000℃) and show the uniform distribution in adhesive matrix, based on the dissolution precipitation reactions in lots of small areas. Finally, the project will widen the temperature range for self-toughness of heat-resistant adhesives. The specific research content includes the crystallization process of precursor and the mechanism of whisker growth, the influence of whisker growth on adhesive’s phases evolution and microstructures, as well as the toughening effect and mechanism of whisker growth. The point is to elaborate the relation among whisker growth rhythm, physical and chemical property changes of adhesive and the toughness effect of whisker, thus, providing more information for the application of in-situ growth technology in heat-resistant adhesive fields.

为满足航天领域对高韧抗震耐高温胶黏剂的高需求，本项目选用无机晶须原位生长技术来实现耐高温胶在服役过程中的自增韧。为解决常规气相反应无机晶须生长工艺所需的温度过高和导致的低致密性问题，以低熔点的过渡金属氧化物或卤化物为引发（助熔）剂，利用高能球磨或溶胶凝胶法预制高反应活性的反应源-助熔剂-反应源三元晶须前驱体，在改性硅树脂基耐高温胶中建立分布均匀的三元低共熔体系，通过众多小区域液相内的溶解沉淀反应，实现耐高温胶内碳化铬晶须（无氧）和莫来石晶须（有氧）的低温（800~1000℃）快速生长和均匀化分布，从而拓宽耐高温胶实现自增韧的温度域。研究前驱体结晶过程和晶须生长机制，探究晶须生长对耐高温胶物相组成及微观结构的影响，考察晶须生长对耐高温胶的增韧效果并明确晶须增韧机制，阐明晶须生长规律、耐高温胶物理化学性质变化及晶须增韧效果三者之间的关系，为晶须生长自增韧技术在耐高温胶领域的应用提供更多的依据。

本工作在不同生长机制作用下实现了莫来石晶须、碳化铬（Cr3C2）晶须及碳化硅纳米线在耐高温胶内的原位生长，系统地比较了不同晶须原位生长技术对耐高温胶理化性质与机械性能的影响，阐明了不同晶须的生长规律及其强韧化机制，对比了不同粘结接头下晶须原位生长的强韧化效果。研究表明：（1）为突出S-L-S机制下晶须原位生长的优势，补充了以AlF3为催化剂基于V-S机制的莫来石晶须原位生长的研究，证实了AlF3的不均分布或含量过高极易侵蚀胶基体而降低粘结性能，且晶须生长需求温度始终高于1000℃。添加3~4wt.%AlF3可在1300℃获得高达90.6%的强度提高率与156%的断裂位移伸长率。（2）以高能球磨法预制的(3Al2O3·2SiO2)x(MoO3)y三元晶须前驱体可将耐高温胶内的莫来石晶须生成温度降至700℃，这极大地拓宽了晶须原位生长增韧技术的应用范围。x:y=8:2或x:y=7:3这两种前驱体的催化效果最佳，掺加5wt.%x:y=8:2前驱体的耐高温胶的粘结强度提高率从700℃的23%增至1200℃的69%，且断裂位移最大延长了161%。溶胶凝胶法制备的晶须前驱体生成莫来石晶须的温度为900℃，更适用于单独制备高分散的莫来石晶须；（3）水热-溶胶凝胶法虽然能实现Cr3C2晶须在800℃下的生长，但晶须生成量较少且长成形貌差异较大，加之胶内环境不易于碳热还原反应等原因，该晶须原位生长的强韧化效果较差，仅有10~11%。高能球磨法更适用于制备高分散的棒状Cr3C2晶须，其原位生长效果同样很差，且温度需求为1300℃；（4）引入适量（3.6wt.%）二茂铁催化剂不仅可以改善硅树脂基耐高温胶的液态性质，而且可在1100~1500℃范围内成功催化高长径比碳化硅纳米线在耐高温胶内的原位生长，强度提高率高达59.2%；（5）气态反应源参与的莫来石晶须（V-S）与碳化硅纳米线（V-L-S）原位生长可实现对微裂纹和孔洞的架桥修补，而S-L-S机制原位生长莫来石晶须的分布更加紧密，胶基体结构演致密性高；（6）晶须原位生长的主要增韧机制包括桥接、搭接、拔出、承载应力和诱发裂纹偏转；（7）晶须原位生长技术更适用于同质陶瓷胶接结构件的强韧化，而对于CTE高度不匹配的陶瓷与高温合金胶接接头内的热应力缓和作用不佳，强韧化效果有限。