【作者】 尹静；

【导师】 于杰；

【作者基本信息】 哈尔滨工业大学 ， 材料科学与工程， 2008， 硕士

【摘要】 氮化硼纤维兼备了氮化硼材料和纤维材料各自所特有的多种优良性,极具良好的应用前景。本研究以氧化硼为原料,采用溶液静电纺丝技术制备了高质量的氮化硼连续纳米纤维。首先,本研究采用静电纺丝技术制备了氧化硼/聚乙烯缩丁醛(B2O3/PVB)复合纤维,并较为系统地考察了静电纺丝工艺参数对B2O3/PVB纤维形貌的影响,主要包括聚合物(PVB)浓度、B2O3的浓度及电纺电压三个参数。本论文进而研究了B2O3/PVB初级复合纤维的聚合物脱除工艺和氮化工艺条件对氮化硼纳米纤维产品的形貌和成份的影响规律。研究结果表明,聚合物的脱除与否对氮化硼纳米纤维产品的纯度具有明显的影响。没有脱除聚合物的产品,由于聚合物在高温处理过程中发生碳化,所以产品中含有较多的碳杂质;反之,脱除了聚合物后,氮化硼纤维中的碳杂质含量很低。研究还表明,在进行聚合物脱除过程中,采用NH3气氛保护是必要的。氮化工艺可以将B2O3转变为BN,本研究制备得到了纯度较高的氮化硼纳米纤维产品,其氧元素的摩尔含量低于1.5%,说明所用氮化工艺条件能够将B2O3彻底地氮化生成BN。与文献中得到的皮包芯结构不同,本论文得到了实心的氮化硼纤维,此与本研究采用静电纺丝技术得到的初级纤维具有纳米尺度的直径,NH3和N2分子易于扩散至纤维中心密切相关。SEM和TEM表征的结果表明,氮化硼纳米纤维产品的直径可控制在200nm以下,且纤维表面比较光滑、直径分布均匀。SEM结果还表明,氮化硼纳米纤维产品对B2O3/PVB初级纤维的形貌有较大的继承性。本论文采用FTIR、EDX、EELS及TGA等手段对氮化硼纤维产品的成份和抗氧化性能进行了表征。FTIR、EDX和EELS分析的结果证实,脱除聚合物后得到的氮化硼纳米纤维产品中的主要成份是B和N两种元素,不含或含微量的碳元素。FTIR和EELS结果还表明氮化硼主要以六方的形式存在。TGA结果显示,氮化硼纳米纤维具有良好的抗氧化性能,其在空气氛中的起始氧化温度约为890℃,而碳杂质的存在使其起始氧化温度下降约95℃。此外,本论文对电纺纤维的收集装置进行了研究,采用点电极收集装置制备了大量的、具有良好定向性的B2O3/PVB初级纤维,将其进行高温处理后得到氮化硼连续纳米纤维仍保持了良好的定向性。更多还原

【Abstract】 Boron nitride fibers which possess the excellent properties of both born nitride material and fibrous material, show a very high promising in some applications. In this work, continuous boron nitride nanofibers (BNFs) with high quality were prepared via solution-electrospinning technique by adopting B2O3 as precursor.Firstly, B2O3/polyvinylbutyral (B2O3/PVB) composite fibers (BOFs) were prepared by solution electrospinnig. And the influences of the electrospinning parameters on the morphology of BOFs were studied, including the concentration of PVB ethanol solution, the concentration of B2O3 ethanol solutiono and the electrospinning voltage. Secondly, we studied the process of removing the PVB from the as-spun B2O3/PVB composite fibers and the nitridization, and the effects of the used conditions on the morphology and structures of BNFs final products. The results showed that the removal of the PVB greatly affected the purity of the boron nitride nanofibers. The BNFs had not treated by removing PVB and the PVB would be converted into carbon impurity at high temperature. Contrarily, the BNFs treated by removing PVB had very low carbon content. The research results also showed that the protection of NH3 during the elimination of PVB was necessary. In this paper, BNFs with high purity were prepared via nitridization processing during which B2O3 were transformed into BN. The molar content of oxygen element in obtained BN fibers was about 1.5%, strongly suggesting that most B2O3 had been converted into BN under the used nitridization conditions. Be different from the reported boron nitride fibers with a structure of bark encapsulated core, the whole BN fibers even the core could be nitrdized, because the as-spun BOFs have nano-diameters and thus NH3 and N2 molecules could diffuse into the core of BOFs. The SEM and TEM results showed that the average diameter of the BNFs could be controlled below 200 nm, and the fibers had smooth and unfirom diameters. The SEM results also showed that BNFs final products inherited the morphology to a great extent.In this work, FTIR, EDX, EELS and TGA characterization methods were used to investigate the components and resistance to oxidation of BNFs products. The results of FTIR, EDX and EELS proved that the BNFs after the removal of PVB mainly composed of B and N elements, and little or no C elment was detected. FTIR and EELS results also showed that the BN mainly existed in the form of hexagonal structure. TGA analysis revealed that the BNfs without carbon impurity exhibited good resistance to oxidation, and their initiate oxidation temperature in air was about 890℃. But carbon impurity would cause this initiate oxidation temperature decrease about 95℃.Additionally, in this work, the electrospinning collector was also studied. And well-aligned B2O3/PVB composite fibers and boron nitride fibers were prepared by using a tip electrode collector.更多还原