| 题名 | 有机前驱体法BN陶瓷纤维及BNf/BN复合材料的制备 |
| 作者 | 陈明伟 |
| 学位类别 | 博士 |
| 答辩日期 | 2012-06-02 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 张伟刚 |
| 关键词 | 聚硼氮烷 有机前驱体法 BN原丝 陶瓷纤维 介电性能 抗氧化性能 |
| 其他题名 | Polyborazine, Organic precursor, BN green fibers, Ceramic fibers, Dielectric property, Oxidation resistance. |
| 学位专业 | 化学工程 |
| 中文摘要 | 本论文针对在强气动载荷、气动热等恶劣环境下工作的导弹天线罩对高温透波材料，特别是透波陶瓷连续纤维的迫切需要，开展BN纤维与BN复合材料的研究。氮化硼（BN）纤维具有低密度、低热膨胀系数、耐高温和低介电性，是制备高温透波复合材料理想的连续陶瓷纤维，有机前驱体法是目前制备 BN陶瓷纤维较为有效的途径。本论文通过分子结构设计合成三甲胺基硼烷(B(CH3NH2)3)和三甲胺基环硼氮烷([CH3(H)N]]3B3N3H3)两种BN分子前驱体，并对其聚合机理及聚合物可纺性进行研究，合成了化学稳定性、在有机溶剂中溶解度高、聚合过程可控、纺丝温度区间较宽，综合性能优异的BN聚合物前驱体，进而通过熔融纺丝、不熔化处理、高温裂解工艺，成功制备透波性能和抗氧化性能优异的BN陶瓷纤维。探讨了聚环硼氮烷的裂解机理以及影响BN原丝和BN陶瓷纤维结构和性能的因素，并对BN纤维增强BN陶瓷基体复合材料(BNf/BN复合材料)的制备进行初步探索。主要工作内容和结果如下：（1）通过1H-NMR 、11B-NMR、13C-NMR、GPC、MS、FTIR等技术对TCB及三甲胺基环硼氮烷进行表征。实验表明，三甲胺基环硼氮烷的聚合产物具有较高的陶瓷产率，但聚合反应过程中易形成硬质的B、N六元环直接相连接的结构，导致聚合物粘度的增加，降低了可纺性，其单一聚合物不适宜作为熔融纺丝原料。（2）通过11B-NMR、13C-NMR、GPC、FTIR等技术对三甲胺基硼烷进行表征。该分子前驱体在200℃聚合过程中，形成BN六元环为骨架，以B-N(CH3)-B为桥键的BN聚合物前驱体-聚环硼氮烷，其粘流活化能为=56.83 KJ/mol，具有聚合过程可控，化学性质稳定，在有机溶剂中溶解度高，纺丝温度区间宽的特点。通过TG/TGA-FTIR-MS联用分析技术，分析了聚环硼氮烷在N2下裂解的机理。发现在裂解过程中，三甲胺基硼烷通过胺解缩合、交联、开环、环化等反应，释放出CH4、CH3NH2、CH3CN等小分子气体，生成以BN六元环为骨架的三维网络结构，完成有机物向无定型态无机物，无定型结构向晶体结构的转变。在聚环硼氮烷在N2气氛中裂解机理分析的基础上，研究聚环硼氮烷高温裂解制备BN陶瓷的过程。实验表明，聚环硼氮烷热解过程应采取两段式热处理工艺：室温-1000℃阶段，应采用NH3为载气，聚合物中的有机基团以小分子形式逸出体系，实现产物的无机化，同时促进BN六元环结构转化及规整；1000-1600℃阶段，采用氮气为载气，提高产物的结晶度。（3）在聚环硼氮烷熔融纺丝制备BN原丝过程中，纺丝温度、纺丝压力和收丝速率必须相协调，才能获得性能优异的BN连续长丝。实验表明，聚环硼氮烷体系较适宜的纺丝温度范围为125-145℃，纺丝压力范围为0.3-0.8MPa，收丝速率应高于8.0m/s。在上述工艺条件下，成功制备了直径为10-40μm，连续长度达500米BN原丝。（4）通过SEM、TEM、XRD、Raman、FTIR、元素分析等测试技术研究了BN不熔化纤维高温裂解制备陶瓷纤维的过程。热处理温度和无机化阶段的升温速率对BN陶瓷纤维的组成、结构和性能影响较大。随着热处理温度的升高，有机基团以小分子形式逸出体系，导致纤维质量减少及晶体化程度提高。当热处理温度升至600℃时，中空结构逐渐形成,继续升温至1000℃及1600℃，纤维形貌保持基本不变。无机化阶段升温速率是影响BN纤维结构另一个的重要因素，随着升温速率的降低，BN中空结构的BN中空结构孔径逐渐减小，当升温速率为0.1℃/min时，中空结构消失，可以得到实心BN陶瓷纤维。BN纤维沿径向的粘度梯度导致中空结构的出现，通过控制升温速率，可以调节BN纤维的孔隙率。 BN陶瓷纤维表现出较好的抗氧化性能，氧化温度为900℃，BN纤维的介电常数和介电损耗正切值分别小于3.30和0.00064（7-18GHz），介电性能性能优异，是高温透波复合材料理想的候选增强纤维材料。（5）以传统的硼酸氮化法氮化硼连续纤维编制体为增强纤维，以实验室自制的聚环硼氮烷甲苯溶液为浸渍液，采用前驱体浸渍-裂解(PIP)工艺制备BNf/BN复合材料，并对复合材料的结构、物相、抗氧化性能、力学性能及介电性能进行研究和探索。 BNf/BN复合材料的起始氧化温度为830℃，抗氧化性能略逊于本实验由有机前驱体法制备的BN纤维，主要因为后者具有纯度高、晶化度高等特性。实验表明，复合材料在受到外力冲击时，纤维的存在使得基体所承受的应力得到释放和缓冲，能够避免复合材料发生脆性断裂，起到对基体增强增韧的效果。材料的介电常数介于3.50-3.70之间，介电损耗正切值介于0.0013-0.0085之间（2-18GHz），透波性能优异。 |
| 英文摘要 | Envisioned for the urgent need of high temperature wave-transparent materials，especially continuous ceramic fibers，for the hypersonic missile，it is necessary to study on the on preparation and properties of boron nitride ceramic fibers and BNf/BN composites. Boron nitride (BN) ceramic fiber is an ideal candidate as high temperature wave-transparent composite because of its radome under abominable working environment such as strongaerodynamicload and heatinglow density, low thermal expansion coefficient, high temperature resistance and low dielectric properties; moreover, polymer-derived ceramics technique is the most effective method for the preparation of high performance BN fibers. Two kinds of molecular precursors, tris(methylamino)borane (B(CH3NH2)3) and 2,4,6-tri(methylamino)borazine ([CH3(H)N]]3B3N3H3), were synthesized through molecular design, and both the polymerization mechanism and spinnability were studied in detail, then BN polymeric precursors (polyborazine), with good chemical stability, high solubility in organic solvents, controlled polymerization process and broad spinning temperature range, were obtained. Further, the BN fibers with excellent wave-transparent property and oxidation resistance were prepared through melting spinning, curing process and pyrolysis. The polymerization mechanism of polyborazine and the influencing factors on the microstructures and properties of BN green fibers and BN ceramic fibers were investigated systematically; moreover, BN fiber reinforced BN ceramic matrix composites (BNf/BN composites) were discussed. The obtained main conclusions are as follows: (1) B-trichloroborazine (TCB) and 2,4,6-tri(methylamino)borazine were synthesized, then characterized through NMR, GPC, MS and FTIR. The result showed that direct inter-cyclic bonds were possibly formed, leading to the increase of viscosity and the decrease in spinnability. Therefore, the polymer of 2,4,6-tri(methylamino)borazine were considered unsuitable as raw material for melting spinning in spite of its high ceramic yield. (2) Tris(methylamino)borane and its polymerization mechanism were characterized through NMR, GPC and FTIR. The results showed that the polymer of tris(methylamino)borane (polyborazine) was composed of borazinic ring as backbone and methyamino bridges (B-N(CH3)-B) as linkage, which had good chemicalstability, high solubility in organicsolvents, controlled polymerization process and broad spinning temperature range. Furthermore, the flow activation energy of polyborazine was estimated at 56.83 KJ/mol. The polymerization mechanism，NH2CH3 and CH3CN were released from the precursors and three-dimensional network with borazinic ring as backbone was formed. During the pyrolysis of polyborazine, organic compounds were converted into inorganic ones and an amorphous structure was changed into a well-obvious hexagonal crystalone. of polyborazine under N2 was characterized by TG-DSC-FTIR-MS online coupling analysis. Through deamine condensation, cross-link, ring-opening and cyclization reactions, CH4 On the basis of the study mentioned above, true pyrolysis of polyborazine was performed in two stages. At the first temperature stage (room temperature to 1000℃), polyborazine was first heated in NH3 to remove carbon and hydrogen with the releasing of some small molecules, and borazinic ring backbones were gradually shaped and regularized. At the second temperature stage (1000 to 1600℃), pyrolysis took place under N2 to improve the crystallization of pyrolysized precursors. (3) BN continuous green fibers could be obtained with spinning temperature, pressure, speed rate matched to each other during melting spinning. The experimental result showed the optimal technical parameters for melting spinning were as follows: spinning temperature 125-145℃, pressure 0.3-0.8MPa and speed rate above 8.0m/s. Then, BN continuous green fibers were obtained with 500m in length and 10-40μm in diameter. (4)The pyrolysis process of BN fibers from the cured BN fibers was investigated by SEM, TEM, XRD, Raman, FTIR and Elemental Analysis. Heating rate during the inorganic process and heat-treatmenttemperature had great influence on the composition, structure and performance of BN ceramic fibers. With heat-treatment，cylindrical hollow structures developed with diameter of 3.9 μm. The morphology of the BN fibers heated up to 1000℃ and 1600℃ was similar to that of the fibers heated at 600℃。The average hollow，so changing the heating rate is one efficient way to control the hollow structures of BN ceramic fibers.sizegradually decreased as the heating rates dropped, and the hollow structures disappeared completely when the heating rate was further decreased to 0.10℃/min. Viscosity gradientalong the direction of the diameter determined by temperature caused the development of hollow structurestemperature increasing, pyrolytic reactions gradually occurred with the release of a large quantity of gases, such as CH4, NH2CH3, and CH3CN, leading to reduction in fiber quality and increase in crystallization. When the heat-treatmenttemperature increasing up to 600℃, cylindrical hollow structures were developed. Microstructure of BN fibers was regularized and crystallization was improved gradually. At 600℃ BN ceramic fibers obtained had excellent oxidation resistance with incipient oxidationtemperature of 900℃ and excellent dielectric properties with ε′ and tanδ less than 3.30 and 0.000614 individually (7-18GHz). (5) BN fiber reinforced BN ceramic matrix composites (BNf/BN composites) were prepared through precursor infiltration and pyrolysis (PIP) process, using polyborazine as impregnant and BN fibers, obtained via inorganic precursors, as reinforced fibers. Structure, phase, mechanical property, oxidation resistance and dielectric property were studied in this paper. Oxidation，higher crystallization and lower carboncontent. When the composites received external force, the strain that ceramic matrix was subjected to wascushioned and released due to the existence of reinfored fibers; therefore it could not only avoided the brittle fracture but also strengthened and toughened the ceramic matrix. Futhermore, the dielectric properties of BNf/BN composites were excellent with with ε′ and tanδ in the range of 3.50-3.70 and of 0.0013-0.0085 individually (7-18GHz). resistance of BNf/BN composites, with incipient oxidationtemperature of 830℃,were slightly poorer than that of BN fibers prepared by organic precursors, because the latter had higher purity |
| 公开日期 | 2013-09-25 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1797]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 陈明伟. 有机前驱体法BN陶瓷纤维及BNf/BN复合材料的制备[D]. 北京. 中国科学院研究生院. 2012. |
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