新型耐超高温碳化锆（ZrC）陶瓷先驱体分子设计、合成及裂解机理研究

In order to solve the difficulty in synthesizing the proper precursor for zirconium carbide (ZrC), a novel method is presented for preparing high-preformance ZrC precursor with Zr element dispersed uniformly at the molecular level by the method of chemical synthesis in this project. With the technique of molecular design, ZrOCl2•8H2O will be used to react with salicyl alcohol in the presence of triethylamine to produce Zr-containing polymer with excellent solubility, and this polymer is for ZrC precursor. In this project, we mainly study synthesis conditions, precursor structures, solution properties of precursor, cross-linking and pyrolysis mechanism. Single-crystal XRD、FTIR、NMR and GPC are employed to characterize the structures of the precursor, analyzing the influnce of synthesis conditions (molar ratio, reaction temperature, reaction time and solvents) on the structures and properties of ZrC precursor, and controlling the structures and properties of ZrC precursor by controlling the synthesis process. We also pay our attention to the thermodynamic and rheological properties of the solution of ZrC precursor, establishing the methods of processing. The cross-linking behavior of ZrC precursor is studied by rising temperatures set by programme, establishing the condition of cross-linking. Pyrolysis process and mechanism of ZrC precursor will also be studied by high-temperature tube furnace, TGA and thermal analysis, determing its optimal pyrolysis conditions and controlling ceramics compositions and structures by controlling the pyrolysis conditions. This study offers a new idea and a novel method for preparing ZrC precursor and provides scientific basis and crucial technical support for the application of ZrC precursor in C/C, C/SiC composites with good ablation resistance and ceramic matrix composites (CMCs) with ultra-high temperature resistance via PIP method.

针对目前ZrC陶瓷先驱体合成遇到的难题，本课题拟采用化学合成方法，制备Zr元素分子级均匀分散的新型高性能ZrC陶瓷先驱体。从分子设计出发，通过一种新型的合成方法-氯氧化锆与水杨醇之间的缩聚反应，合成Zr-O主链的可溶有机锆聚合物，作为ZrC陶瓷先驱体。拟深入研究先驱体合成、分子结构、先驱体溶液性能、交联固化及裂解机理。利用单晶XRD、FTIR、NMR及GPC等分析手段对先驱体结构进行表征，研究反应条件（原料配比、反应温度、反应时间和溶剂）对先驱体结构的影响，通过对合成条件的调控，实现对先驱体组成和性能的调控。研究先驱体溶液热力学性质和流变性能，建立先驱体成型的评价方法。采用程序升温研究先驱体交联固化特性，确定先驱体交联固化条件。利用高温管式炉、TG和热分析法等技术研究先驱体裂解过程及机理，确定先驱体最优裂解条件，通过对裂解条件的控制达到对最终陶瓷产物结构和组成的控制，制备高性能ZrC陶瓷。

碳化锆（ZrC）因具有低密度、高熔点（3540 oC）及化学稳定性好等优点，且可有效提高C/C、C/SiC等复合材料的抗烧蚀性能，而成为航空航天等极端环境下急需的超高温陶瓷材料。本项目利用化学合成方法，成功制备了碳化锆陶瓷先驱体。采用FTIR及GPC等表征了先驱体的分子结构。该先驱体的数均分子量1050-1600 g/mol，重均分子量为3200-4600 g/mol，分子量分布为2.5-3.7。结果说明先驱体是以Zr-O-Zr为主链，水杨醇为配体的聚合物，Zr原子以化学键形式引入聚合物主链。研究了先驱体的溶解性及溶度参数，发现先驱体可溶于醇类等有机溶剂，溶度参数是13.40 cal1/2/cm3/2。研究了先驱体的交联固化过程，确立了其固化条件。将固化的先驱体分别在900 ℃ -1400 ℃裂解，利用等速升温热失重分析及高温管式炉法研究了先驱体的陶瓷化过程；确立了裂解程序。采用X射线衍射、扫描电子显微镜、拉曼光谱、透射电子显微镜和能谱等对裂解产物进行了表征。先驱体的分解主要经历4个阶段的失重，通过碳热还原反应，形成碳化锆陶瓷，1400 ℃ 陶瓷产率为40%-56 %。不同温度热解产物中均含有Zr, C和O三种元素，且C和O的含量随温度升高而降低。研究表明，1300 ℃裂解产物是典型的面心立方的碳化锆结构，且XRD锋线很尖锐，说明XRD结晶性很好。根据XRD结果和Rietveld修正，碳化锆的晶格参数是4.686 Ǻ，比纯相的ZrC0.98 (4.698 Ǻ) 数值小。ZrC呈不规则多面体结构，晶粒平均尺寸为100-300 nm。1300 ℃热解产物中含有16.42 wt% 的C，高于纯相ZrC中的C含量（11.6 wt %）。提出了先驱体的热解机理，即基于碳热还原的气相反应机理。先驱体原位裂解先形成ZrO2和C，ZrO(g) 和CO(g)之间化合形成ZrCxOy 中间相。中间相ZrCxOy 经碳热还原进一步转化成ZrC。本项目的研究不仅为设计和合成新型高性能ZrC陶瓷先驱体分子提供重要的理论支持，也将大大促进其在耐超高温陶瓷基复合材料中的实际应用。