基于加成固化型Si－Zr－B－C近化学组成陶瓷先驱体的构建及结构演变机制

The development of solid rocket engine nozzle throat insert involved national security and the peaceful use of space, which is the focus of the international race for space technology. Near-stoichiometric polycarbosilane preceramic with heterogenic element Zr and B (abbreviated for PSZB) was synthesized based on molecular design theory. Molecular level uniform distribution corresponding to carborane, Zr and polymer was achieved through chemical bond with high Zr content and without impurity oxygen atom. PSZB possesed good procssing and high ceramic conversion rate（>88%） could be obtained with the formation of three-dimensional net structure by addition polymerization. Near- stoichiometric SiC ceramic was gained through in suit pyrolysis, therefore, oxidation and creep resistance were obviously improved. Ultra high temperature ablation of 3000℃ for composites could be achieved attributing to the formation of ZrC and ZrB2. The micro-crack owing to ablation were filled and repaired by B2O3 corresponding to the oxidation of B4C, so called, with self-healing and anti-oxidation ability. Moreover, fracture toughness of composites was enhanced to prevent the catastrophic destroy. Study of ceramic evolution mechanism was the main line of this project, meanwhile, both microscopic structure and performance of the ceramic materials could be tailored by means of the design and optimization of the composition and structure of the precursor, which established the solid theoretical basis for the preparation and application of ablation resistant ceramcis.

固体火箭发动机喉衬材料的发展涉及国家安全与和平利用空间，是目前国际竞相争夺的焦点空间技术之一。本项目以分子设计为基础，构建一种含异质元素锆、硼的近化学组成聚碳硅烷先驱体（Si－Zr－B－C）（简称PSZB）。PSZB结构中碳硼烷、锆元素和聚合物通过化学键达到分子级均匀分布、无杂质氧原子、锆含量高。PSZB具有良好的成型工艺，通过加成聚合形成三维网络结构，产物具有很高的陶瓷转化率（>88%）。热解形成近化学组成SiC可明显改善材料的耐氧化和抗蠕变性；原位生成的ZrC、ZrB2使得复合材料能够承受3000℃的超高温烧蚀；热解形成的B4C氧化为B2O3，可以填补和修复烧蚀形成的微裂纹，具有自愈合能力，同时提高SiC的断裂韧性，防止发生灾难性破坏。本项目以研究陶瓷演变机制为主线，通过对聚合物组成和结构的设计与优化，实现陶瓷材料微观结构和性能的可裁剪性，为耐烧蚀陶瓷的制备和应用奠定扎实的理论基础。

先进导弹飞行器的发展，涉及国家安全与和平利用空间，是目前国际竞相争夺的焦点技术之一，体现了综合国力。本项目围绕含异质元素锆、硼的先驱体PZBS的设计合成、分子结构与耐热性能之间的关系展开，探讨了Si－Zr－B－C陶瓷演变机制。前驱体PZBS在100℃至250℃之间有两个明显的放热峰，峰值分别为151.0℃和224.5℃，分别对应于Si-H键与C≡C键的硅氢加成反应和C≡C与C≡C的加成反应，固化过程中形成致密的三维网状结构，保证其在高温热解过程结构与形状的稳定。PZBS固化物具有优异的耐热及热氧化性能，TGA研究结果表明，氮气与空气气氛下1000℃的质量保留率均在90%以上。热力学研究表明，前驱体PZBS在室温至1600℃范围内，生成ZrB2反应的吉布斯自由能比ZrC低。因此，前驱体在热解过程中优先生成ZrB2陶瓷相，同时也说明在该温度下，ZrB2具有更好的热稳定性能。PZBS的陶瓷化研究结果表明：热解温度1400℃是陶瓷产物由无序状态变为有序晶体结构的转折点。在氩气条件下，经过1600℃陶瓷化处理后，前驱体PZBS转化为由B、Zr、Si、C组成的高度晶化的SiC、ZrC、ZrB2陶瓷相，陶瓷转化率为66.2%。纳米尺寸（50~100 nm）的SiC、ZrC、ZrB2晶体颗粒均匀的分布在基体中。在该温度下，随着石墨微晶的形成，热解碳微观结构的有序性有所改善，热解碳内部的缺陷得到修复。本项目通过无机、金属材料与高分子材料进行实质性的学科交叉研究，增强此类材料的源头创新能力，为解决我国国防和国民经济建设急需的关键技术提供合适的材料，为未来火箭发动机的发展奠定技术创新基础。