碳纤维增强碳化硅陶瓷复合材料的研究

使用ＣＶＤ技术提高纤维增强陶瓷基复合材料的密度是很困难的,因为它很难使反应气体完全渗入到基体里面,这是由于“瓶颈”效应所致,即ＣＶＤ过程阻塞了基体表面的小气孔,进而封闭了通向大气孔的入口,为此提出了一种新的方法位控ＣＶＤ（ＰＣＣＶＤ）,来克服上述通过控制反应气体通道位置试样的加热位置,从而达到控制沉积位置,使沉积界面始终处于开孔状态,使用ＰＣＣＶＤ技术制造的Ｃ／ＳｉＣ复合材料,实际密度可达到其理论     

Responsive Liquid‐Crystal‐Clad Fibers for Advanced Textiles and Wearable Sensors

A simple process to clad conventional monofilament fibers with low‐molecular‐weight liquid crystals (LCs) stabilized by an outer polymer sheath is demonstrated. The fibers retain the responsive properties of the LCs but in a highly flexible/drapable format. The monofilament core makes these fibers much more rugged with a magnified response to external stimuli when compared to previously reported LC‐core fibers produced by electrospinning or airbrushing. The microscopic structure and the optical properties of round and flattened fibers are reported. The sensitivity of the response of individual fibers can be tuned over a broad range by varying the composition of the LCs. Complex fabrics can be easily woven from fibers that respond to different external stimuli, such as temperature variation, chemical concentrations, and pressure. The fabrics can be fashioned into garments that can sense and report the state of health of the wearer or the status of their environment.     

等离子喷涂纳米陶瓷涂层的显微组织及结构分析

热障涂层由绝热陶瓷层和金属底层组成,是目前保证高温合金在火箭发动机热端部位正常工作的主要技术.应用等离子喷涂方法成功备了纳米氧化锆陶瓷涂层,并对其微观组织形貌及相结构等进行观察分析,探讨了纳米陶瓷涂层的沉积机理.研究表明,涂层中的孔隙主要为长条形和近球形,无贯穿性孔洞;纳米陶瓷涂层裂纹较为细小,无明显的方向性;纳米粉末和涂层均为四方相(t-ZrO2)氧化锆组成的熔融或者部分熔融状态的纳米结构.     

聚合物共混制备纳米和多孔碳纤维及性能研究

聚丙烯腈(PAN)和聚甲基丙烯酸甲酯(PMMA)共混膜的结构和尺寸可由两组分比例和分子量调整。以PAN为碳前驱体,PMMA为热分解聚合物,并控制m(PAN)/m(PMMA)为30/70和70/30,通过湿法纺丝制备了PAN/PMMA共混纤维。以m(PAN)/m(PMMA)为30/70和70/30的共混纤维为原丝经碳化后获得了纳米碳纤维(CNFs)和多孔碳纤维(PCFs)。利用扫描电镜观察了所得CNFs和PCFs的形貌,发现单根CNFs的直径为50～150nm,PCFs中孔的直径为0.1～1μm。由CNFs和PCFs的拉曼光谱分析了不同碳化温度对CNFs和PCFs石墨化程度的影响,结果表明随碳化温度升高,石墨化程度也增加,同时电导率也随之提高。     

Liquid‐Phase Transmission Electron Microscopy for Studying Colloidal Inorganic Nanoparticles

For the past few decades, nanoparticles of various sizes, shapes, and compositions have been synthesized and utilized in many different applications. However, due to a lack of analytical tools that can characterize structural changes at the nanoscale level, many of their growth and transformation processes are not yet well understood. The recently developed technique of liquid‐phase transmission electron microscopy (TEM) has gained much attention as a new tool to directly observe chemical reactions that occur in solution. Due to its high spatial and temporal resolution, this technique is widely employed to reveal fundamental mechanisms of nanoparticle growth and transformation. Here, the technical developments for liquid‐phase TEM together with their application to the study of solution‐phase nanoparticle chemistry are summarized. Two types of liquid cells that can be used in the high‐vacuum conditions required by TEM are discussed, followed by recent in situ TEM studies of chemical reactions of colloidal nanoparticles. New findings on the growth mechanism, transformation, and motion of nanoparticles are subsequently discussed in detail.     

Poly(P‐Phenylene Terephthalamide) Fibers Reinforced with Ultrathin Ceramic Coatings

The poly(p‐phenylene terephthalamide) (PPTA) fibers are engineering polymer materials with high strength and stiffness, lightweight, and outstanding fatigue characteristics. However, these materials exhibit drawbacks, namely, anisotropic mechanical strength along the tensile and compressive directions. In particular, they show low compressive strength, and mismatched thermal expansion as well as moisture uptake and oxidative stability along the axial and radial directions. Here, the authors describe a hybrid material approach by integrating ultrathin ceramic coatings (alumina or silica) onto PPTA fibers to enhance their compressive modulus by 2.5 times. In addition, these ceramic coating improve the energy absorption, thermal conductivity, and chemical stability of PPTA fibers, while their flexibility and lightweight are preserved. This strategy provides a new route for the preparation of high performance polymer fibers for advanced engineering applications.

     

Single Carbon Fibers with a Macroscopic‐Thickness, 3D Highly Porous Carbon Nanotube Coating

Carbon fiber (CF) grafted with a layer of carbon nanotubes (CNTs) plays an important role in composite materials and other fields; to date, the applications of CNTs@CF multiscale fibers are severely hindered by the limited amount of CNTs grafted on individual CFs and the weak interfacial binding force. Here, monolithic CNTs@CF fibers consisting of a 3D highly porous CNT sponge layer with macroscopic‐thickness (up to several millimeters), which is directly grown on a single CF, are fabricated. Mechanical tests reveal high sponge–CF interfacial strength owing to the presence of a thin transitional layer, which completely inhibits the CF slippage from the matrix upon fracture in CNTs@CF fiber–epoxy composites. The porous conductive CNTs@CF hybrid fibers also act as a template for introducing active materials (pseudopolymers and oxides), and a solid‐state fiber‐shaped supercapacitor and a fiber‐type lithium‐ion battery with high performances are demonstrated. These CNTs@CF fibers with macroscopic CNT layer thickness have many potential applications in areas such as hierarchically reinforced composites and flexible energy‐storage textiles.     

Liquid‐Phase Exfoliated Indium–Selenide Flakes and Their Application in Hydrogen Evolution Reaction

Single‐ and few‐layered InSe flakes are produced by the liquid‐phase exfoliation of β‐InSe single crystals in 2‐propanol, obtaining stable dispersions with a concentration as high as 0.11 g L⁻¹. Ultracentrifugation is used to tune the morphology, i.e., the lateral size and thickness of the as‐produced InSe flakes. It is demonstrated that the obtained InSe flakes have maximum lateral sizes ranging from 30 nm to a few micrometers, and thicknesses ranging from 1 to 20 nm, with a maximum population centered at ≈5 nm, corresponding to 4 Se–In–In–Se quaternary layers. It is also shown that no formation of further InSe‐based compounds (such as In₂Se₃) or oxides occurs during the exfoliation process. The potential of these exfoliated‐InSe few‐layer flakes as a catalyst for the hydrogen evolution reaction (HER) is tested in hybrid single‐walled carbon nanotubes/InSe heterostructures. The dependence of the InSe flakes' morphologies, i.e., surface area and thickness, on the HER performances is highlighted, achieving the best efficiencies with small flakes offering predominant edge effects. The theoretical model unveils the origin of the catalytic efficiency of InSe flakes, and correlates the catalytic activity to the Se vacancies at the edge of the flakes.     

光聚合陶瓷先驱体裂解制备陶瓷涂层及其抗氧化性能

炭材应用广泛,但在高于500℃的有氧气氛中氧化迅速,其结构和性能受到严重影响.为此,采用光聚合巯基/乙烯基聚硅氮烷(PSN-1)陶瓷先驱体在炭材料表面裂解制备抗氧化陶瓷涂层,采用偏光显微镜和X射线衍射技术探讨了涂层对炭材抗氧化性能的影响.结果表明:先驱体溶液浓度为30%时浸渍效果最好;加入质量比(Ti/PSN-1)为1/10～1/5的钛粉时,制备的涂层抗氧化性能最佳,恒温氧化120 min后,失重率仅为18%;最佳的浸渍/裂解循环次数为3次,恒温氧化120 min,失重率为15%;聚硅氮烷经高温裂解后最终生成氮化硅陶瓷.     

SiC/PyC复合涂层碳纤维微观结构及氧化行为研究

采用两步法在碳纤维表面制备了碳化硅/热解碳(SiC/PyC)复合涂层,PyC内涂层的制备采用等温化学气相渗透法,SiC外涂层的制备采用碳热还原法.借助X射线衍射、场发射扫描电镜、透射电镜分析了SiC/PyC复合涂层碳纤维的物相组成以及微观结构,利用热重分析研究了SiC/PyC复合涂层、PyC涂层以及无涂层碳纤维的氧化行为.结果表明,在碳纤维表面制备的SiC/PyC复合涂层连续致密、厚度均匀,PyC内涂层厚度约为200nm,SiC外涂层厚度约为160nm,SiC层中存在大量孪晶面高度有序的SiC孪晶.SiC/PyC复合涂层能够有效地改善碳纤维的抗氧化性能,较无涂层碳纤维起始氧化温度提高了近250℃.