溶胶-凝胶法制备镍纤维及其电磁性能研究

以碱式碳酸镍和柠檬酸为原料,通过络合反应形成具有良好可纺性的溶胶,经过干法纺丝纺成前驱体纤维,再经高温热处理还原制得了直径约为10～20μm的金属镍纤维.研究了不同原料、添加剂的加入对溶胶前驱体可纺性的影响,探讨了不同热处理气氛对纤维物相的影响.制得的镍纤维在2～18GHz范围内其复介电常数、复磁导率随测试频率的增大而降低,表现了较好的频散特性.     

PVA-PEG/SiO_2-TiO_2杂化纤维的制备与表征

以聚乙烯醇(PVA)与聚乙二醇(PEG)共混,并以正硅酸乙(酯TEOS)和钛酸四丁酯(TBT)为无机前驱体,采用溶胶-凝胶法制备了不同(SiO_2-TiO_2)含量的PVA-PEG/SiO_2-TiO_2杂化溶胶,陈化后用提拉法制得杂化纤维.研究了杂化溶胶的可纺性,并使用IR、光学显微镜、UV-Vis和TG对杂化纤维的结构与性能进行了研究.结果表明:随硅钛摩尔比的增加或随有机相中PEG/PVA质量比的增加,溶胶的可纺性变好;有机相与无机相之间通过化学键连接;纤维直径为50μm左右;TiO_2的引入增加了其抗紫外性,杂化纤维的耐热性优于纯PVA-PEG.     

溶胶-凝胶燃烧合成法制备γ-LiAlO2

研究了以硝酸锂、硝酸铝和尿素为原料,用溶胶-凝胶燃烧合成法制备γ-LiAlO2粉体的工艺.采用热重分析(TG-DTA)、X射线衍射(XRD)、红外光谱(IR)、扫描电镜(SEM)对反应前驱体、反应过程、燃烧产物进行了表征测试.分析了原料配比、溶胶前驱体pH值对反应产物特性的影响,并初步探讨了反应的历程.     

PEG/SiO2-TiO2杂化纤维的制备与表征

以正硅酸乙酯(TEOS)和钛酸四丁酯(TBT)为无机前驱体,采用溶胶-凝胶法制备了PEG/SiO2-TiO2杂化溶胶,通过提拉法制得杂化纤维,并对其进行了简单表征.结果表明,随钛硅物质的量比的增加或有机相质量的增加,溶胶的可纺性变好;有机相与无机相之间通过化学键连接;纤维直径为40μm左右;TiO2的引入增强了其抗紫外性,杂化纤维的耐热性优于纯PEG.     

Al2O3-SiO2-B2O3连续纤维的制备及力学性能

本实验采用溶胶-凝胶法结合干法纺丝制备了氧化铝基凝胶连续纤维,煅烧后得到含12.92％B2O3、24.56％SiO2和62.50％(均为质量分数)Al2O3的氧化铝基陶瓷连续纤维.通过TG-DSC、SEM、TEM、XRD和强度拉伸仪等分析手段研究了前驱体溶胶的微观结构、纤维晶相组成以及纤维表面和内部结构.结果表明,通过溶胶-凝胶法制备的前驱体溶胶可纺性优良,性质稳定.采用干法纺丝得到的氧化铝基凝胶连续纤维长度可达上千米,将凝胶纤维进行陶瓷化后形成的含硼氧化铝基陶瓷连续纤维直径均匀,为14～15 μm,经1 000℃煅烧后纤维主晶相为莫来石相,拉伸强度最高可达1.35 GPa.本实验所制备的氧化铝基陶瓷连续纤维具有优良的力学性能,在热防护领域具有广阔的应用前景.     

SiBNC陶瓷纤维前驱体的结构及流变性能

以三氯化硼(BCl_3)、甲基二氯硅烷(SiHMeCl_2)和六甲基二硅氮烷(HMDZ)为初始原料、甲胺(NH_2Me)为交联剂合成的SiBN(C)前驱体分子为基础,聚合得到聚硼硅氮烷(PBSZ)前驱体聚合物。通过FTIR、NMR等对其结构进行分析发现,PBSZ除Si-B-N骨架结构外,还包含硼氮六元环状结构及局部交联结构。流变分析表明,PBSZ具有良好的可纺性,其流变性能对于纺丝工艺的设定具有重要作用。采用熔融纺丝对前驱体聚合物的可纺性进行了验证,制得的前驱体纤维表面光滑、结构致密,无明显孔洞结构,直径约18μm。     

由醋酸锆前驱体制备ZrO2连续纤维的过程及研究

为了制得耐高温、高强度的氧化锆连续纤维,利用新制醋锆作为前驱体,通过溶胶-凝胶法合成含有Zr-O长链的溶胶,干法纺丝,制备ZrO2连续纤维。研究了醋酸锆的光谱和热学性质,并对烧结后的纤维做扫描电镜观察、XRD分析和纤维抗拉强度的测试。测试结果表明醋酸锆前驱体溶胶中含有以Zr-O为骨架的长链,具有良好的可纺性和稳定性。直径在十几个径微米以下的连续纤维具有一定的强度和韧性,添加5mol%的Y2O3可将ZrO2的晶相稳定在四方相。     

由醋酸锆前驱体制备ZrO_2连续纤维的过程及研究

为了制得耐高温、高强度的氧化锆连续纤维,利用新制醋酸锆作为前驱体,通过溶胶－凝胶法合成含有Ｚｒ－Ｏ长链的溶胶,干法纺丝,制备ＺｒＯ２连续纤维．研究了醋酸锆的光谱和热学性质,并对烧结后的纤维做扫描电镜观察、ＸＲＤ分析和纤维抗拉强度的测试．测试结果表明醋酸锆前驱体溶胶中含有以Ｚｒ－Ｏ为骨架的长链,具有良好的可纺性和稳定性．直径在十几个微米以下的连续纤维具有一定的强度和韧性,添加 ５ｍｏｌ％的 Ｙ２Ｏ３可将 ＺｒＯ２的晶相稳定在四方相．     

柠檬酸-醋酸盐溶胶-凝胶过程制备3Y-TZP纤维的可纺性研究

以ZrOCl2·8H2O为原料,通过柠檬酸盐-醋酸盐溶胶-凝胶法制备了3Y-TZP可纺性溶胶。醋酸/ZrOCl2、柠檬酸/ZrOCl2的物质的量比分别是1.5~2.0和0.3~0.5时,溶胶具有可纺性。用理论计算、IR和流变性分析考察了可纺性溶胶中化合物的类型。结果表明,溶胶中主要是羧酸与锆低聚物形成的桥合双齿配位结构,使溶胶在制备过程中保持稳定并具有可纺性。     

聚合物前驱体法合成铌酸锶钡铁电薄膜

采用聚合物前驱体法制备铌酸锶钡(Srx Ba1-x Nb2O6,SBN)铁电薄膜.以柠檬酸为配位剂与金属离子配合,水作为溶剂,用乙二醇加速溶液聚合形成稳定的前驱体溶胶.采用旋转法在Si/SiO2/Ti/Pt基片上镀膜.研究了柠檬酸(CA)/乙二醇(EG)(质量比)、pH值对前驱体溶胶稳定性的影响.结果表明,当Sr-Ba-Nb前驱体溶胶的pH值为7,CA/EG=40:60时,可以获得稳定性好的溶胶.薄膜经750℃热处理,可以获得单相、表面均匀、无裂纹的铌酸锶钡铁电薄膜.     

电纺十二酸十二酯@聚乙烯醇蓄热调温纤维的制备及性能

以十二酸十二酯作为相变材料(PCM),以聚乙烯醇(PVA)作为支撑材料,通过乳液静电纺丝技术制备十二酸十二酯@PVA蓄热调温纤维。应用SEM、TEM、DSC、TGA、迷你温度记录仪和红外热成像仪等研究了纺丝液组成及静电纺纤维的表面形貌、潜热值、热稳定性、调温性能、力学性能和水溶性。结果表明,当PVA浓度为10.0wt%、十二酸十二酯∶PVA质量比为50%时,纺丝液具有较好的稳定性和可纺性。十二酸十二酯@PVA静电纺纤维具有明显的芯-鞘结构,纤维中PCM的热分解温度比纯PCM提高了20℃,具有良好的热稳定性。十二酸十二酯@PVA静电纺纤维的潜热值在63 J/g左右,在降温冷却和热红外成像测试中,显示出良好的蓄热调温性能。经戊二醛交联后,静电纺纤维中支撑材料的热稳定性显著增强,而且,纤维的力学性能和水溶解性得到明显改善。      

Preparation and properties of silicon oxycarbide fibers

Silicon oxycarbide fibers have been prepared from vinyl trimethoxysilane (VTMS) by a modified sol–gel method and with secondary cellulose acetate (SCA) as the fiber-forming aid. Its main advantage over a normal sol–gel fiber processing is that the spinning dope remains spinnable for a long period of time. The effect of the pre-hydrolysis of VTMS on the dope spinnability is studied. At H₂O/VTMS = 4, the resultant sol transforms into gel very quickly, unsuitable to obtain a spinnable dope; at H₂O/VTMS = 2, too much un-reacted VTMS exists in the sol, making the extruded fiber difficult to solidify; at H₂O/VTMS = 3, a dope with good spinnability and stability, and thus high ceramic yield is obtainable. Pyrolysis at 1,000 °C in argon/5% hydrogen results in silicon oxycarbide fibers with the maximum tensile strength (940.0 MPa), moderate Young’s modulus (63.2 GPa) and high carbon content (33.2%).     

Preparation and properties of silicon oxycarbide fibers

Silicon oxycarbide fibers have been prepared from vinyl trimethoxysilane (VTMS) by a modified sol-gel method and with secondary cellulose acetate (SCA) as the fiber-forming aid. Its main advantage over a normal sol-gel fiber processing is that the spinning dope remains spinnable for a long period of time. The effect of the pre-hydrolysis of VTMS on the dope spinnability is studied. At H₂O/VTMS = 4, the resultant sol transforms into gel very quickly, unsuitable to obtain a spinnable dope; at H₂O/VTMS = 2, too much un-reacted VTMS exists in the sol, making the extruded fiber difficult to solidify; at H₂O/VTMS = 3, a dope with good spinnability, stability and high ceramic yield is obtainable. Pyrolysis at 1000^∘C in argon/5% hydrogen results in silicon oxycarbide fibers with the maximum tensile strength (940.0 MPa), moderate Young’s modulus (63.2 GPa) and high carbon content (33.2%).     

Sol-gel dry spinning of mullite fibers from AN/TEOS/AIP system

Continuous mullite ceramic fibers were fabricated by a sol-gel dry-spinning technique. The sol was prepared from an aqueous solution of aluminum nitrate, aluminum isopropoxide and tetraethylorthosilicate. The sol-gel transition was investigated by measuring the volume, the solid content, the viscosity and the rheological properties of the solution. Shear viscosity η of the mullite sol varied dynamically with concentrating time and temperature of the sol. Combined with size analysis of sol particles and TEM analysis, the growth characteristics of sol particle agglomeration and its structural evolution were examined. By adjusting the temperature, the gelation degree could be stabilized at a certain value, and the sol-gel transition could be transferred to the spinning line. Continuous fibers were obtained from such sols using a laboratory dry-spinning apparatus. Sintering of the precursor fibers at 1100 °C yielded crack-free mullite ceramic fibers when the solid content of spinnable sol was above 50%.     

Tailoring structures and properties of mesophase pitch-based carbon fibers based on isotropic/mesophase incompatible blends

Blends composed of isotropic and mesophase pitches in various proportions were used as precursors for carbon fibers. The effects of composition on the morphology of blends, precursor spinnability, transversal texture, and mechanical properties of the final carbon fiber were studied. The blends are binary incompatible phase-separation systems. When the content of isotropic pitch is ≤30 %, it is distributed uniformly in the mesophase matrix as spheres; whereas, complete phase inversion occurs when the content is ≥35 %. Blends containing isotropic pitch in dispersion phase show good spinnability and small-diameter fibers can be continuously drawn. The transversal texture of carbon fibers is transformed from a radial type with a crack along the fiber axis to an intermediate morphology between radial and random type by blending 20–30 % isotropic pitch. The tensile strength of carbon fibers with 20–30 % IPc is 2.5 times as high as the AR-based CF without the reduction of Young’s modulus.     

Preparation of Y-TZP ceramic fibers by electrolysis-sol-gel method

Polycrystalline yttria stabilized tetragonal Zirconia (T-ZrO₂) fibers were obtained by pyrolysis of gel fibers using zirconium oxychloride octahydrate as raw material. The spinnable zirconia sol was prepared by electrolyzing the zirconium oxychloride octahydrate solution in the presence of acetic acid and sugar (sucrose, glucose or fructose), in which the molar ratio of CH₃COOH/ZrOCl₂ · 8H₂O and sugar/ZrOCl₂ · 8H₂O was in the range of 1.0–4.0 and 0.2–0.4, respectively. The relation of spinnability to the shape of colloidal particle was discussed. The as-prepared zirconia fibers sintered at different temperatures show smooth and crack-free surface with the diameter of 5–10 μm. Slow heating rate below 600 °C and then sintering at 1,400 °C for 30 min were necessary to obtain the dense tetragonal zirconia ceramic fibers, the particles composed the fibers had the size of ∼150 nm.     

Importance of viscosity parameters in electrospinning: Of monolithic and core–shell fibers

Electrospun polymeric fibers are attractive candidates in the development of scaffolds for the tissue engineering and for providing new systems for delivery of bioactive molecules. Co-axial fibers have emerged as an efficient tool to protect the core material from the adverse conditions of electrospinning process, to spin difficult-to-process fluids and to generate fibers with much more control of the delivery of encapsulated bioactive molecules. Currently, there is very little reported work on the optimization of the processing parameters of electrospinning, especially core–shell electrospinning. This study extends the understanding of the role of solution viscosity as a vital material parameter for electrospinning of fibers. The spinning solutions were characterized for viscosity and optical imaging of the compound Taylor cone for spinnability, and the fibers were imaged by Scanning Electron Microscopy (SEM). Our experimental results, using PLGA as the model polymer, confirm that the solution concentration be above the entanglement concentration (C_e) to obtain uniform beadless monolithic fibers; for core–shell fibers, the shell solution must fulfill the above criterion for spinnability and, further, the ratio of the viscosities of core and shell solutions (η_core/η_shell) has to be greater than a threshold value to get a stable compound Taylor cone and therefore to obtain uniform beadless core–shell fibers. Addition of surfactant led to reduction of the threshold η_core/η_shell (from 0.55 to 0.18) for the PVA–PLGA system.     

Preparation and mechanical properties of silicon oxycarbide fibers from electrospinning/sol-gel process

Silicon oxycarbide (SiOC) fibers were produced through the electrospinning of the solution containing vinyltrimethoxysilane and tetraethoxysilane in the course of sol-gel reaction with pyrolysis to ceramic. The effect of the amount of spinning agent Polyvinylpyrrolidone (PVP) on the dope spinnability was investigated. At a mass ratio of PVP/alkoxides = 0.05, the spinning sol exhibited an optimal spinnable time of 50 min and generated a large quantity of fibers. Electrospun fibers were characterized by Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis-differential scanning calorimetry (TGA-DSC), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The SEM results revealed that the SiOC fibers had a smooth surface and dense cross-section, free of residue pores and cracks. The XPS results gave high content of SiC (13.99%) in SiOC fibers. The SiOC fibers prepared at 1000 °C had a high tensile strength of 967 MPa and Young's modulus of 58 GPa.