金属杂化新型Si-B-N-C-Zr多元陶瓷先驱体拓扑结构的构建与性能导向的结构控制

To pave the way for advanced multinary materials, the reliable method to synthesis multinary precursors with well-defined topological structures and tailoring to desined properties should be developed. A novel multinary ceramic precursors and the synthetic strategy are proposed in this project. Metal hybrid multinary ceramic precursors are organometallic polymers containing several covalently bonded elements, which can be pyrolyzed to multinary ceramics with appropriate structures and properties. The multinary Si-B-N-C-Zr ceramic precursors with linear, necklace-shaped, network and hyperbranched architectures will be constructed and synthesized, by means of tailoring interlinkage and branches via atom-economic hydrosilylation and hydroboration reaction and aminolysis.The reliable knowlage of this class of maltinary materials is still limited to date. Based on the mechanism of the co-condensation of the highly reactive monomers, the chemical structures of the polymer chains can be controlled under suitable reaction conditions and tunable for special properties. The pyrolysis of the polymers and the high-temperature behavior of the multinary systhems will be studied by characterize the microstructures during the whole process of polymer to ceramic. The rheology and the phase conversion of the preceramic polymers in unstable complex fields will be investigated in this project, understanding the agglomeration and the defects in polymer molding. The method of tailoring appropriate topological structure will be developed for durability at elevated temperature and spinning to fibers. The fundamental topological features and structure-property relation proposed by this project are of benefit to design and prepare brand-new functional materials. And the multinary ceramic precursors can be used for fibers, films, coatings and so on with great potential for extreme environment applications.

多元先驱体拓扑结构的构建方法与性能导向的结构控制方法是实现多元陶瓷材料结构与功能的预先设计和精确制备的关键科学技术问题。本项目拟利用硅氢化和硼氢化等原子经济性反应，通过可支化单体的裁剪和模块化组装，构筑具有线形、项链形、网络和超支化等拓扑结构的金属杂化新型Si-B-N-C-Zr多元先驱体。尚未见文献报道。本项目通过研究高活性低温缩聚反应机理，建立多元先驱体高效、可控的程序化合成方法；探索先驱体拓扑结构热解演化规律和耐高温机制，建立超高温性能导向的拓扑结构模型及其控制方法；研究先驱体在复杂外场下的流变特性和非平衡态的相变行为，揭示先驱体成型过程凝聚态结构和微缺陷的形成机理，建立流变性和成型性导向的拓扑结构模型及其控制方法。本项目对揭示有机金属聚合物"构效关系"规律和发展新型功能材料具有重要意义，获得的多元先驱体可制备纤维、薄膜和涂层等，有望在航空航天、耐热电子器件和高温熔炼等方面获得应用。

本项目利用硅氢化和硼氢化等原子经济性反应，通过可支化单体多官能团的裁剪和模块化组装，构筑了Zr-C-B、Zr-N -B、Zr-Si-B-N-C等多元陶瓷先驱体。锆杂化先驱体陶瓷的主要组成元素有Si、B、C、N、Zr、O等，其中Zr和B的含量则与先驱体中Zr和B的含量基本成线性关系。锆杂化先驱体陶瓷在1200℃以下仍为无定形，温度高于1600℃，基体中主要存在有Zr2CN、ZrC、BN、SiC、Si3N4以及游离碳等物相。其中Zr2CN在温度高于1800℃后转化为ZrB2。锆杂化陶瓷中弥散分布有直径范围为50-500nm纳米颗粒，且其尺寸随锆含量的增加而减小。Zr2CN以直径为10nm左右的尺寸均匀分散于陶瓷中。经1800℃高温热解1h后，锆杂化先驱体陶瓷的质量保持率可以达到74.3%， XRD结果表明锆的加入对陶瓷基体中SiC的结晶具有抑制作用。锆杂化先驱体陶瓷具有优异的抗高温氧化性能，其在1550℃经空气气氛氧化1h后表面会生成氧化物，内部相均未发生明显变化，质量保持率接近100%。由于锆杂化陶瓷表面Zr的富集，生成的ZrO2能够更加有效抑制氧气对基体内部的氧化。通过研究高活性低温缩聚反应机理，建立了多元先驱体高效、可控的合成方法，研究了多元复合陶瓷的组成结构和耐高温抗氧化性能，制备了几种具有可溶解、可熔融的金属有机聚合物，初步研究了其熔融纺丝的成纤性能，为后续制备连续细直径陶瓷纤维奠定了基础。通过本项目的实施，实现了Si-B-N-C-Zr多元陶瓷材料结构与功能的预先 设计和制备，具有很好的推广应用价值。

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