有机前驱体法制备BN纤维过程中的结构演变与控制研究

Boron nitride (BN) is an excellent high-temperature resistant microwave-transmitting material which can work in the oxidizing atmosphere below 900℃ and inert atmosphere below 2800℃ for a long term. Through spinning, curing,low-temperature decarburization and high-temperature nitridation processes, the polymeric precursor consisted of B, N, C and H atom was converted into a ceramic material containing B and N elements. At the same time a number of complex physical and chemical changes occur in these processes. However，study on the structure of BN fibers and their porosity and defect control was not enough, which restricted the research of high-performance BN fibers and their wide use. Using as-obtained polymer derived ceramic precursor as raw material, the project will center on the structural evolution of green fibers during the curing, decarburization and high-temperature nitridation processes and its control, to investigate physical and chemical changes during the curing of green fibers，decarburization kinetics and the correlation of fibers' composition and structural evolution with their mechanical and dielectric properties. Then BN fibers with decarburization thoroughly,high ceramic yield as well as compact structure can be obtained, which will lay the foundation for the preparation of the high-performance BN fibers.

氮化硼(BN)是一种综合性能优良的耐高温透波材料，可以在900℃以下的氧化气氛和2800℃以下的惰性气氛中长期使用。采用有机前驱体法制备BN 纤维的过程中，前驱体经过不熔化、低温脱碳、高温烧成处理，由含有B、N、C和H的多原子化合物转变为以B、N元素为主体的陶瓷产物，发生了复杂的物理和化学变化。然而，目前关于BN纤维在结构、缺陷与孔隙控制等方面的机理研究还远远不够，制约着高性能BN纤维的研制和广泛应用。本项目以自制的聚硼氮烷前驱体为原料，围绕BN原纤维在不熔化、低温脱碳及高温烧成过程中的结构演变与控制这一主题，深入研究BN原纤维不熔化过程中的物理化学变化机理、低温脱碳反应的动力学规律及BN纤维的组成、结构演变与性能的相关性，以获得脱碳彻底、陶瓷收率高、结构致密的BN纤维，为高性能BN纤维的制备奠定基础。

针对强气动载荷、气动热等恶劣环境下工作的天线窗、罩对高温透波材料的迫切需求，开展了高性能氮化硼（BN）纤维的研制。本项目主要研究了BN原纤维在不熔化、低温脱碳及高温氮化过程中的组成、形貌、微结构变化过程。结果表明，BN原纤维通过氨气辅助热交联方式或电子束交联方式均可得到凝胶程度达90%、低氧含量的不熔化BN纤维；在低温脱碳（0-1100℃）过程中，氨气气氛下、600℃时纤维中95%以上的碳和氢被脱除，经1000℃热处理后纤维中的碳含量降低至0.45%，所得的BN纤维呈短程有序二维结构结构，纤维直径变细。在高温氮化（1100-1600℃）过程中氮气气氛有利于BN纤维的晶体结构的完善，升高温度、施加适当的牵伸力有利于提高BN纤维的力学性能。本项目的完成，深化了对有机前驱体法研制陶瓷纤维在不熔化、低温脱碳、高温氮化过程中组成、结构演变规律的认识，实现了对BN纤维在缺陷与孔隙的控制，为高性能连续的BN纤维的研制奠定基础。