先驱体转化氮化硼块体陶瓷的实现机制及其性能研究

Borzine derived bulk boron nitride (BN) ceramics with high purity and high relative density have been put forward to solve the problem of additive softening and precipitation at high temperatures in traditional sintered BN ceramics. Meanwhile, a systematic microstrucutre-property research on the current BN ceramics can lead to the understanding of the basic properties of BN matrix in those precursor derived BN matrix composites. The current BN ceramics are achived by firstly molding of the active and plastic precursor polymer, which is followed by the formation of a porous ceramic skeleton with a high-temperature treatment, and finally precursor infiltration and pyrolysis method is used to desify the ceramics. This project will focus on the reaction activity evolution of polyborazyne and the associated pyrolysing products, the fabrication of large size bulk ceramics and the integrated performance of the preapred BN ceramics. The mechanisms on contraction control, roles of microstructures, and thermal spectrum characteristiis of dielectric properties and ablative heat transfer behavior will be proposed. The results of this project can contribute to improving the applications of boron nitride ceramics in space thermal protection, ultra-high purity crucibles and high-temperature wave-transparent composites, as well as enriching the research method of precursor derived ceramics.

本项目提出了基于环硼氮烷转化的高纯度、高致密度的氮化硼块体陶瓷，以期解决目前氮化硼陶瓷高温应用受到助剂软化、析出限制的问题，同时用于先驱体转化氮化硼基复合材料中基体性能的系统研究。氮化硼块体陶瓷利用先驱体聚合物的高活性和可塑性进行模压成型，经高温预处理形成陶瓷骨架，进而采用先驱体浸渍裂解工艺实现致密化。本项目将重点开展环硼氮烷聚合物及其裂解产物的反应活性变化规律、大尺寸块体陶瓷制备工艺及块体陶瓷力热电综合性能等方面的研究，并在块体陶瓷收缩控制技术、微观结构影响机制、介电性能温谱特性及烧蚀传热行为等方面开展机理性探索。本项目的研究成果将有助于提高氮化硼陶瓷在航天热防护、超高纯度坩埚及高温透波复合材料等领域的应用水平；同时，可丰富和发展先驱体转化陶瓷材料的研究方法。

高纯度无烧结助剂氮化硼（BN）陶瓷在航天热防护材料、高温透波复合材料、超高纯度坩埚与电子元器件基底介质材料等领域有着广泛和迫切的应用需求，本项目提出了先驱体交联聚合物模压成型+先驱体浸渍裂解（PIP）工艺制备高纯高致密氮化硼块体陶瓷的新方法，深入研究了环硼氮烷先驱体高温裂解特性、块体BN陶瓷制备工艺优化及块体BN陶瓷热力电综合性能。首先，厘清了环硼氮烷先驱体交联固化和陶瓷化转变机理，建立了裂解温度与裂解产物成分、形貌及结晶性的内在关系，探明了先驱体无机化过程中裂解产物内部三维网络的形成过程与反应活性变化特点。其次，探索了先驱体聚合物粉体模压成型+PIP致密化制备工艺，优化的工艺参数包括聚环硼氮烷的固化温度为90℃、聚合物粉体的模压成型压力为80Mpa、聚合物坯体陶瓷化预烧结升温降温速率为3℃/min、采用3轮PIP进行致密化处理；采用该工艺成功在800℃—1800℃宽温度范围内实现了高纯高致密BN陶瓷的制备，制备全过程不发生开裂和弯曲，并可用于制备异形样件。最后，全面表征了块体陶瓷的室温及高温力学、热物理、介电、烧蚀等性能，获取了氮化硼陶瓷随制备温度变化的本征性能数据；建立了氮化硼陶瓷的高温介电、烧蚀传热等模型，深入分析了微观结构对陶瓷热力电综合性能的影响机制，探明了陶瓷的内在组成-结构—性能关系。本项目提出的模压成型+PIP致密工艺为先驱体转化陶瓷的设计和制备提供了一种新方法，可为先驱体转化氮化硼基涂层及复合材料的宽温域服役性能演变分析及新材料综合性能设计提供重要的基础数据支撑，促进先驱体转化氮化硼陶瓷的实际应用。