熔融纺丝制备聚碳硅烷有机先驱体纤维

运用超声手段将碳纳米管(CNTs)掺混到聚碳硅烷(PCS)中,在先驱体转化法的基础上,通过熔融纺丝、空气不熔化等工艺过程制备出了直径18~20μm的有机混合纤维。研究了掺混CNTs后PCS纤维纺丝工艺的变化,并通过红外光谱及热分析的手段将掺混CNTs的PCS纤维与原PCS纤维进行对比,研究了掺混CNTs后PCS纤维在活化能、反应速率常数及预氧化程度上的变化。结果表明:相同的升温制度下,随着CNTs的加入,PCS纤维的预氧化程度提高了7.51%,PCS纤维的熔融纺丝温度提高了约5℃,压力增加约5个单位。     

聚碳硅烷制备SiC纤维的热化学交联研究

以异丙醇锆(ZIP)为交联剂、聚碳硅烷(PCS)为先驱体,在Ar气氛的保护下通过干法纺丝、热化学交联工艺使PCS从热塑性转变热固性结构.研究了该工艺对PCS纤维质量变化、Si-H反应程度、溶解性及氧含量等性能的影响.实验结果表明:在不熔化过程中,PCS结构中的Si-H键与ZIP反应,在PCS分子间形成Si-O-Zr交联结构,随着交联温度和保温时间的升高,Si-H反应程度和纤维失重率相应提高;在测试范围内最大Si-H反应程度为73.06%,失重率2.678%,氧含量低于2.0%.     

静电纺聚碳硅烷制备SiOC超细纤维

以聚碳硅烷(PCS)为先驱体, 采用静电纺丝法和先驱体转化法制备SiOC超细纤维, 研究PCS溶液浓度和表面活性剂对纤维形貌和直径的影响。实验结果表明: 添加表面活性剂后, 纤维分布均匀, 串珠现象消失; 通过调节溶液中PCS比例, 纤维直径分布范围为500~900 nm。力学性能测试表明SiOC纤维毡的抗拉强度可达8.88 MPa。SiOC超细纤维毡也展现出优异的热稳定性和抗化学腐蚀性能, 在苛刻环境中可以作为催化剂载体和过滤材料使用。     

聚碳硅烷纤维的不熔化与SiC纤维制备研究

以聚二甲基硅烷(PDMS)为原料,在高压釜内高温高压反应制备了聚碳硅烷(PCS)先驱体,经熔融纺丝制备了PCS纤维,研究了在190 C下不同不熔化时间对PCS纤维氧化增重、Si-H键反应程度、凝胶含量、氧含量及最终SiC纤维氧含量与性能的影响.研究表明,在不熔化过程中,PCS结构中的Si-H键与氧反应,在PCS分子间形成Si-O-Si交联结构.随着不熔化时间的延长,PCS纤维发生氧化增重、Si-H键反应程度提高、凝胶含量增加,SiC纤维中氧含量也逐渐增加.在不熔化保温3h,制备的SiC纤维强度可达2.52GPa.随着不熔化时间的进一步延长,SiC纤维氧含量增加,其强度逐渐降低.     

干法纺丝法制备低氧含量SiC纤维

通过粘度、凝胶含量和XRD等手段研究了聚碳硅烷(PCS)纺丝原液的干法纺丝性能和干纺PCS纤维的自交联过程, 并对所制得的低氧含量SiC纤维的组成、结构和性能进行了表征. 结果表明, PCS/二甲苯纺丝原液的最佳纺丝粘度范围在18.0～22.0Pa·s; 干纺PCS纤维在烧成温度超过250℃后开始发生自交联反应, 在烧成温度超过550℃后, 干纺PCS纤维完全交联形成了“不熔不溶”的网状结构; 干法纺丝法制备得到的SiC纤维与空气不熔化法制得的SiC纤维相比, 氧含量大幅降低, 仅在3.6wt%左右, 结晶度较高, 其耐高温抗氧化性也有明显的改善.     

聚碳硅烷纤维氧化交联机理的研究

对聚碳硅烷(PCS)原丝在不同氧化交联温度区间生成的逸出产物进行红外、核磁和GC-MAS分析,并结合交联丝的红外分析,推测氧化交联的机理。结果表明,PCS的氧化交联主要是其Si—H氧化生成Si—OH,后者进而彼此缩合生成Si—O—Si交联结构;氧化交联温度高于150℃时,其部分Si—CH3也开始氧化生成Si—OH并进而交联;同时,在氧化交联过程还发生PCS侧链的热裂解,所形成小分子也通过Si—OH彼此结合,形成较大分子,且其分子量随交联温度的提高而提高。因此,要及时排除氧化交联过程废气,以免逸出产物黏附在纤维表面而导致粘结。     

活性填料钼在聚碳硅烷转化陶瓷中的应用

研究了活性填料钼(Mo)在聚碳硅烷(PCS)先驱体转化陶瓷中的应用.研究表明,活性填料Mo能有效降低陶瓷素坯的气孔率.Mo可与PCS气态裂解碳氢产物、游离碳和N2气氛反应生成新的化合物,可明显提高PCS的陶瓷产率.当Mo/PCS为25%(vol)时, 坯体的陶瓷产率为100%.Mo还能有效地提高烧成体的强度.     

聚锆碳烷/聚碳硅烷杂化先驱体转化制备ZrC-SiC复相陶瓷EI

采用聚锆碳烷PZC和聚碳硅烷PCS作为杂化先驱体聚合物,通过脱氢耦合反应制备富含活性交联位点的ZrC-SiC复相陶瓷先驱体PZCS,研究先驱体陶瓷化机理及最终陶瓷的组成结构。结果表明:PZCS先驱体由于促进了陶瓷化过程中活性基团的交联,850℃下其陶瓷产率(71.84%,质量分数,下同)显著高于PZC(51.40%)或PCS(53.46%)先驱体。同时,在Zr-Cp的催化下,通过先驱体之间的协同作用近程碳与Zr,Si元素直接转化生成碳化物陶瓷,避免了碳热还原反应对陶瓷的损伤,并有效降低了烧结温度。PZCS先驱体经陶瓷化处理后生成兼具耐高温组元和抗氧化组元的ZrC-SiC纳米复相陶瓷,ZrC相和SiC相可以相互抑制结晶、细化晶粒,其中ZrC晶粒尺寸为25.4 nm,纳米复相结构的生成有利于提升超高温陶瓷的综合性能。     

聚锆碳烷/聚碳硅烷杂化先驱体转化制备ZrC-SiC复相陶瓷EI北大核心

采用聚锆碳烷PZC和聚碳硅烷PCS作为杂化先驱体聚合物,通过脱氢耦合反应制备富含活性交联位点的ZrC-SiC复相陶瓷先驱体PZCS,研究先驱体陶瓷化机理及最终陶瓷的组成结构。结果表明:PZCS先驱体由于促进了陶瓷化过程中活性基团的交联,850℃下其陶瓷产率(71.84%,质量分数,下同)显著高于PZC(51.40%)或PCS(53.46%)先驱体。同时,在Zr-Cp的催化下,通过先驱体之间的协同作用近程碳与Zr,Si元素直接转化生成碳化物陶瓷,避免了碳热还原反应对陶瓷的损伤,并有效降低了烧结温度。PZCS先驱体经陶瓷化处理后生成兼具耐高温组元和抗氧化组元的ZrC-SiC纳米复相陶瓷,ZrC相和SiC相可以相互抑制结晶、细化晶粒,其中ZrC晶粒尺寸为25.4 nm,纳米复相结构的生成有利于提升超高温陶瓷的综合性能。     

熔融纺丝过程优化制备细直径碳化硅纤维及其对力学性能的影响

强度、模量和柔顺性作为碳化硅(SiC)纤维重要的力学性能受到纤维直径大小的影响, 而制备工艺中的熔融纺丝过程对纤维直径起决定作用。本工作研究了纺丝温度、纺丝压力和卷绕速度对聚碳硅烷(Polycarbosilane, PCS)原纤维直径的影响, 分析了纺丝过程中纤维断裂的原因, 并初步探究了SiC纤维直径与力学性能的关系。结果表明, 在一定范围内降低纺丝温度、降低纺丝压力和提高卷绕速度均能显著减小原纤维的直径。在连续纺丝的前提下, 最优纺丝工艺下得到的PCS原纤维直径为13.5 μm。随着PCS纤维直径由18.3 μm减小至13.5 μm, SiC纤维直径则由13.8 μm减小至9.5 μm, 而SiC纤维的强度与模量分别由1.7、181 GPa提高至2.9、233 GPa, 强度分布更为集中, 柔顺性得到显著提高。     

Preparation of silicon carbide fibers from the blend of solid and liquid polycarbosilanes

A highly branched liquid polycarbosilane (LPCS) was added into a solid polycarbosilane (PCS) to give a polymer blend. It was then melt-spun into precursor fibers, oxidation-cured in hot-air, and converted into ceramic fibers by pyrolysis under nitrogen. It was found that the addition of the LPCS resulted in a significant drop on the spinning temperature from 285 °C (without LPCS) to 225 °C (with 15% LPCS), while the spinning ability of the polymer blend was also markedly improved over the solid PCS. Furthermore, the LPCS enhanced the oxidation curing, reducing the curing temperature and hence the tendency for fiber partial melting and sticking. However, the strength of the silicon carbide fibers decreased owing to the presence of the LPCS. The effects of the LPCS addition and their mechanisms on the fiber processing and properties were studied using FTIR, NMR, GPC, XRD, SEM, and elemental analysis.     

异型(三叶型)截面碳化硅纤维制备工艺研究

以聚碳硅烷（PCS）为原料,经不熔化和烧成制得三叶型碳化硅纤维,研究了纺丝温度,压力,收丝速度对纤维异形度和当量直径的影响,研究表明,较低的纺丝温度,适当高的纺丝压力和较低的转速有利于提高纤维的异形度,抗拉强度平均提高约30％。     

Fine SiC fiber synthesized from organosilicon polymers: relationship between spinning temperature and melt viscosity of precursor polymers

A very fine silicon carbide (SiC) fiber with diameter of 6 m, about a half of that of a commercially available SiC fiber, was synthesized from a polymer blend of polycarbosilane (PCS) and polyvinylsilane (PVS). The fine SiC fiber was obtained by optimizing the composition and the spinning temperature of PCS-PVS polymer blends. In order to determine these optimum conditions, the relationship between temperature and melt viscosities of the polymer blends was investigated. As a result, it was found that the optimum spinning temperature range was within a temperature range where the melt viscosity is 5–10 Pa · s. Moreover, by blending PVS with PCS, the spinning temperature of the polymer blends was lowered, the spinnability of polymer system was improved, and finer polymer fiber was obtained compared with PCS. The optimum content of PVS in the polymer blend was 15–20 wt%.     

具备吸收雷达波功能的三叶型碳化硅纤维研制

以聚碳硅烷(PCS)为原料,采用熔融纺丝制备三叶型PCS纤维后,经不熔化和烧成制得三叶型碳化硅纤维。研究了纺丝温度、收丝速度等对纤维异形度的影响,并对预氧化和烧成工艺以及吸波性能等进行了研究。研究表明,较低的纺丝温度、适当高的纺丝压力和较低的转速有利于提高纤维的异形度。与相同当量直径的圆形纤维相比,三叶型碳化硅纤维的抗拉强度平均提高约30%,三叶型碳化硅纤维在8~18 GHz范围内具有较好的吸收雷达波性能。      

High-temperature pyrolysis of ceramic fibers derived from polycarbosilane–polymethylhydrosiloxane polymer blends with porous structures

The polymer blends of PCS (polycarbosilane) and PMHS-h (polymethylohydrosiloxane with high molecular weight) were prepared by freeze-drying process of mixed benzene solution. Melt viscosity, mass loss, and gas evolution from prepared polymer blends were analyzed. A polymer blend of HSah15 (15 mass% PMHS-h to PCS) was melt-spun to fiber form, curing by thermal oxidation and pyrolyzed at various temperatures up to 1773 K. The obtained fibers were investigated by tensile tests, FE-SEM (field emission scanning electron microscope) observation, and XRD (X-ray diffraction) analysis. After pyrolysis at 1273 K, there were no pores in the cross section of the fiber derived from pure PCS; however, there were amounts of pores in the cross sections of the fiber derived from HSah15. After pyrolysis at 1773 K, the coarse β-SiC (silicon carbide) crystals were formed on the outside surface of the fiber derived from pure PCS; however, no remarkable β-SiC crystal were formed on the outside surface of the fiber derived from HSah15.     

Synthesis and properties of ceramic fibers from polycarbosilane/polymethylphenylsiloxane polymer blends

We synthesized ceramic fibers based on silicon carbide (SiC) from polymer blends of polycarbosilane (PCS) and polymethylphenylsiloxane (PMPhS) by melt-spinning and radiation curing. PMPhS was compatible with PCS up to 30 mass%, and formed a transparent melt at temperatures higher than 513 K. The softening point was also lowered by adding PMPhS and 15 mass% of PMPhS to PCS was the most suitable condition for obtaining thin fibers with an average diameter of 14.4 μm. Due to the lowered softening point of the PCS–PMPhS fibers, γ-ray curing in air was adopted. The ceramic yield of the cured fiber was 85.5% after pyrolysis at 1273 K. In spite of the small diameter, the resulting tensile strength at 1273 K was rather limited at 0.78 GPa. Blooming of the PMPhS component during pyrolysis may have caused surface defects. After high-temperature pyrolysis at 1673–1773 K, a porous nanocrystalline SiC fiber with a unique microstructure was obtained with surface area of 70–150 m²/g. When the fiber was pyrolyzed at the same temperature under a highly reductive atmosphere, wire bundle-shaped fibers were obtained by gas evolution and reactions.     

High-temperature stability of low-oxygen silicon carbide fiber heat-treated under different atmosphere

The effects of heat-treating atmosphere on the thermal stability of low-oxygen silicon carbide fiber were investigated. Heat-treatment of EB-cured PCS fiber were conducted at 1573 K in argon, nitrogen or vacuum of 10^–6 atm. Subsequently the fibers were exposed to 1873 K in argon. The strength of fibers were strongly influenced by the heat-treating atmosphere. When heat-treated in nitrogen, the fibers absorbed nitrogen. High-temperature exposure caused severe degradation of strength owing to the decomposition of silicon oxycarbonitride phase. When heat-treated in vacuum, the fiber surface was smooth and pore-free, minimizing the degradation of strength at high temperature.