【作者】 杨勇；

【导师】 刘玉付； 张寿春；

【作者基本信息】 东南大学 ， 材料工程（专业学位）， 2016， 硕士

【摘要】 连续碳化硅纤维密度小、比强度大、比模量高、耐高温,含锆碳化硅纤维还具有优异的抗高温化学腐蚀性能,有望广泛应用于航空、航天、核能和化学化工等行业的耐高温腐蚀领域。国内报导的含锆碳化硅连续纤维的锆添加范围窄,锆含量低,本论文开展锆含量大幅度提升的SiC纤维研究具有重要意义。本论文以正丁醇锆为锆源,利用常压高温反应法,合成了碳化硅纤维陶瓷先驱体聚锆碳硅烷(PZCS),制备出理论锆含量为0.5wt％.3.8.wt％和9.5wt%的三种PZCS;经过连续熔融纺丝、不熔化处理以及纤维的热解烧成,制备出三种锆含量的碳化硅连续纤维,研究了烧结温度、烧结气氛、锆元素含量以及施加张力对纤维拉伸性能的影响；利用扫描电子显微镜(SEM)、X射线能谱分析、X射线衍射(XRD)、透射电子显微镜(TEM)对三种锆含量SiC纤维在空气中高温氧化前后的形貌、成分与结构进行表征分析,明确了氧化温度和氧化时间对纤维强度的影响及其与材料形貌、成分与结构的关系。研究主要结论如下：(1)锆含量0.5wt%先驱体的最佳合成温度300℃,保温时间2h,先驱体软化点210℃；3.8wt%先驱体的最佳合成温度2500C,保温时间2h,先驱体软化点210℃；9.5wt%先驱体的最佳合成温度2300C,保温时间7h,先驱体软化点165℃。(2)锆含量0.5wt%先驱体纺丝温度3100C,纺丝压力0.5MPa,最大纺丝速度15r/s；3.8wt%先驱体纺丝过程,纺丝温度300℃,纺丝压力0.6MPa,最大纺丝速度15r/s;9.5wt％先驱体纺丝温度210℃,纺丝压力0.8MPa,最大纺丝速度7.5r/s。原丝纤维在空气下200℃处理6h的不熔化处理后氧增重率10wt%左右,实现连续烧成而不发生并丝。(3)使用锆含量0.5wt%先驱体制备的纤维室温拉伸强度为2.2-2.3GPa,锆含量约为2.11wt%,氧含量约为9.16wt%,平均直径12～13μm；3.8wt%先驱体的纤维室温拉伸强度为2.6-2.7GPa,锆含量约为6.98wt%,氧含量约为7.68wt%,平均直径13～14μm；9.5wt%先驱体的纤维室温拉伸强度为2.4-2.5GPa,锆含量为15.51wt%,氧含量为12.73wt%,平均直径13～14μm。施加张力烧结得到的纤维强度明显提高,纤维柔软平直。(4)使用锆含量0.5wt％、3.8wt％和9.5wt%先驱体制备的纤维1000-C大气气氛下氧化100h后,平均剩余强度分别为1.5GPa、1.9GPa和1.8GPa,强度保留率分别为65%、74%和71%：在1250℃处理0.5h后,平均剩余强度分别为1.5GPa、1.9GPa和1.7GPa,强度保留率分别为65.5%、71%和68%。(5)含锆SiC纤维在经过大气气氛高温氧化后,在纤维表面形成了致密的Si02氧化层,出现了皮芯双层结构,氧化层随着氧化时间的延长和温度的增加而变厚；纤维氧化后,锆以ZrO2相的形式存在于纤维中；锆添加提升了SiC纤维的高温抗氧化性,但是锆含量从6.98wt%增加至15.51wt%后高温抗氧化性呈现下降趋势。更多还原

【Abstract】 As a heat-resistant low-density material with high specific strength and specific modulus, SiC continuous fibers, particularly zirconium-containing ones, have excellent resistance to chemical attack at high temperature and are promising for wide applications in many industries such as aeronautical, aerospace, nuclear and chemical engineering. However, domestic research on zirconium-containing SiC fibers is scarce and limited to low zirconium contents below 5wt%. It is, therefore, necessary to study high-performance silicon carbide fibers with various zirconium contents.In this thesis, synthesis of polyzirconocarbosilane (PZCS) was carried out by using polycarbosilane and zirconium n-butoxiden-butyl alcohol as starting materials at high temperature under atmospheric pressure argon flow. Three types of PZCS containing, in theory,0.5wt%,3.8wt% and 9.5wt% zirconium were fabricated, which were then melt-spun into three green SiC fibers, respectively. These green fibers were then cured in ambient air and pyrolysed to ceramic fibers. Also investigated were effects of pyrolysis temperature, atomosphere, contents of zirconium and fiber string tension on fiber tensile strength. Fiber morphology, microstructure and chemical composition were characterized by Scanning Electron Microscope (SEM) and Tunnelling Electron Microscope (TEM) with attached Energy Spectrum Analysis (EDX). X-ray Diffraction (XRD) was used for identifying phase compositions. Tensile strength at room temperature and after exposing to high-temperature oxidation conditions was measured and correlated with the fiber morphology, composition and structure. The main results are summarized as follows.(1) The synthesis temperatures of about 300℃ with a hold time 2h,250℃ holding for 2h, and 230℃ for 7h were shown to be the optimum conditions for the PZCS precursors with 0.5,3.8 and 9.5 wt% zirconium, respectively.And the softing point of the precursors is 210℃,210℃ and 165℃, respectively.(2) For the PZCS precursor with 0.5 wt% zirconium, green SiC fibers were processed at the spinning temperature of about 310℃ with a spinning pressure 0.5MPa to attain a maximum spinning speed 15 r/s, while the precursor with 3.8wt% zirconium needed a spinning temperature of about 300℃ under a pressure 0.6MPa to give the maximum spinning speed 15 r/s. The precursor with 9.5wt% zirconium saw a best fit condition of the spinning temperature at about 210℃ and pressure at 0.8MPa to yield a maximum spinning speed 7.5 r/s.(3) The tensile strength of the three types of SiC fibers is 2.2-2.3GPa,2.6-2.7GPa and 2.4-2.5GPa, respectively. The tension during the pyrolysis process is very helpful to improve the fibers’tensile strength. The three types of SiC fibers are observed as no obvious defect on fiber surface by SEM. The SiC fibers with 0.5wt% zirconium content contain 9.16wt% oxygen and have average dimeters of 12～13μm. The SiC fibers with 3.8wt% zirconium content contain7.68wt% oxygen and have average dimeters of 13～14μm. The SiC fibers with 9.5wt% zirconium content contain 12.73wt% oxygen and have average dimeters of 13-14um.(4) The results of the high-temperature oxidation tests are as follows. After high temperature oxidation treatment at 1250℃ for 0.5h in ambient air, the residual tensile strength of the three types of fibers are 1.5GPa,1.9GPa and 1.7Gpa, respectively. The strength retention rates are 65.5%,71% and 68%. Moreover, after high temperature oxidation treatment in 1000℃ for 100h under air atmosphere, the strength retention rates of the three types of SiC fibers containing diferent zirconium are 65%,74% and 71%, respectively.(5) After the high temperature treatment under air atmosphere, the SiC fibers containing diferent zirconium have formed a dense oxidation layer of SiO2. The thickness of the oxidation layer will improve with the increase of the oxidation time and temperature.更多还原