聚酰亚胺薄膜气相沉积的研究进展

综述了气相沉积聚合设备、制备过程、影响因素、性能表征方法及近年来国内外的研究现状.气相沉积聚合聚酰亚胺薄膜相比于传统湿法成型具有纯度高、无溶剂、膜厚可控、致密均匀、可在复杂表面成型等优点.展望了气相沉积的应用以及今后的发展前景.     

Transport properties of 1,1,1,2-tetrafluoroethane (R134a)

New equations for the thermal conductivity and the viscosity of R134a that are valid in a wide range of pressures and temperatures are presented. They were obtained through a theoretically based, critical evaluation of the available experimental data, which showed considerable inconsistencies between data sets, in particular in the vapor phase. In the critical region the observed enhancement in the thermal conductivity is well represented by a crossover model for the transport properties of fluids. Since thermodynamic properties enter into the calculation of the critical enhancement of the transport properties, a new fundamental equation for the critical region was developed also.Paper dedicated to Professor Joseph Kestin.     

Preparation and characterization of foamed polyurethane/silicone rubber/graphite nanocomposite as radio frequency wave absorbing material: The role of interfacial compatibilization

A novel method for the preparation of radio frequency (RF) wave absorber polyurethane foam (PU) has been developed by impregnation of PU foam in n-hexane solution of room temperature vulcanizing (RTV) silicone rubber (SR) hybridized with graphite nanosheets (GNs) called doping solution. Extent of the GNs dispersion was optimized by the incorporation of a specific type of bifunctional compatibilizer. Insulator to conductive transition threshold as well as electromagnetic wave absorption characteristics of the fabricated nanocomposites was shown to be dependent upon the compatibilizer functionality. All PU/SR/GN nanocomposites generated from bifunctional compatibilizer exhibited higher electrical conductivity with enhanced permittivity implying enhanced formation of conductive networks by GN platelets. Permittivity of the PU/SR/GN nanocomposite based on bifunctional compatibilizer showed to be higher than uncompatibilized counterpart. Electromagnetic reflection loss behavior of the PU/SR/GN nanocomposites exhibited a non-linear correlation with the electrical conductivity. Although all PU/SR/GN prepared nanocomposites exhibited electromagnetic wave reflection loss behavior, but this revealed to be affected by the GN level as well as the size and dispersion state of the graphite nanosheets.     

Oxidation and Mechanical Properties of SiC/SiC-MoSi2-ZrBa Coating for Carbon/Carbon Composites

To improve oxidation resistance of carbon/carbon （C/C） composites, a SiC/SiC-MoSi2-ZrB2 double-layer ceramic coating was prepared on C/C composites by two-step pack cementation. The phase compositions and microstructures of as-prepared multilayer coating were characterized by X-ray diffraction and scanning electron microscopy. The oxidation resistance at 1773 K and the effect of thermal shock between 1773 K and room temperature on mechanical performance of coated specimens were investigated. The results show that the SiC/SiC-MoSi2-ZrB2 coating exhibits dense structure and is composed of SiC, Si, MoSi2 and ZrB2. It can protect C/C composites from oxidation at 1773 K for more than 510 h with weight loss of 0.5%. The excellent anti-oxidation performance of the coating is due to the formation of SiO2-ZrSiO4 complex glassy film. The coating can also endure the thermal shocks between 1773 K and room temperature for 20 times with residual flexural strength of 86.1%.     

Optical and surface morphological properties of triethylamine passivated lead sulphide nanoparticles

The triethylamine capped lead sulphide (PbS) nanoparticles were successfully synthesized by simple wet chemical method. The synthesized product has been characterized by powder X-ray diffraction (XRD), UV–vis spectrophotometry, FTIR spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) and photoluminescence studies. The size of the PbS nanoparticles was determined from AFM, TEM, XRD and from these studies it is found that the size of the particles of the order of 10–15 nm. Significant “blue shift” from bulk material was observed on the PbS nanoparticles using UV–vis and photoluminescence spectrum.     

炭/炭刹车副表面硬度对摩擦磨损性能的影响

对等温CVD沉积所得两种不同结构的炭/炭复合材料,不同表面硬度下的摩擦磨损性能进行了研究.其中A材料是光滑层结构,B材料是粗糙层和光滑层的混合结构.摩擦试验在实验室规模的MM-1000摩擦试验机上进行.试验表明:随着热处理温度的提高,不同材料的表面硬度均在下降;但在经历相同热处理温度后,B材料的表面硬度比A材料的低;表面硬度较低的B材料塑性较强,摩擦面上的磨屑易于形成致密、连续的摩擦膜,有利于保持稳定而较高的摩擦系数.     

多孔材料缓冲吸能特性表征方法

分析了多孔材料缓冲吸能机理，综述了多孔缓冲材料吸能特性的几种表征方法：缓冲曲线、缓冲系数、Janssen因子、Rusch曲线、能量吸收率曲线和能量吸收图，并分析了各种表征方法的优缺点。能量吸收图汇集了应变率和材料结构特征等信息，且能够模型化，对于不同密度多孔材料吸能特性的表征具有一定的普适性。     

镍基单晶高温合金研究进展

单晶高温合金因具有较高的高温强度、优异的蠕变与疲劳抗力以及良好的抗氧化性、抗热腐蚀性、组织稳定性和使用可靠性,广泛应用于涡轮发动机等先进动力推进系统涡轮叶片等部件。由于采用定向凝固工艺消除了晶界,单晶高温合金明显减少了降低熔点的晶界强化元素,提高了合金的初熔温度,能够在较高温度范围进行固溶和时效处理,其高温强度比等轴晶和定向柱晶高温合金也大幅度提高。经过几十年的发展,单晶高温合金已经在合金设计方法、组织结构与力学性能关系、纯净化冶炼工艺和定向凝固工艺等方面取得了重要进展。从单晶高温合金成分特点、合金元素作用、强化机理、力学性能各向异性、凝固过程及缺陷控制、单晶制备工艺等方面,简要介绍了单晶高温合金的主要研究进展。     

双随机分布细观分析模型与复合材料性能预报

发展了一种细观力学有限元分析方法——拟真实的参数化双随机分布模型, 该模型综合考虑了纤维增强树脂基复合材料的真实微结构特点和纤维单丝综合力学性能测试结果的离散性特征, 模拟了复合材料中纤维排列和强度分布的随机性。借助移动窗口法研究了该参数化双随机分布模型的可靠性, 确定了其代表性体积单元的尺寸。基于能量法原理推导了单向复合材料的弹性模量预测公式, 结合能量法和渐进失效分析方法, 利用该细观力学有限元方法分别预测了单向纤维增强树脂基复合材料T300/5228的弹性模量和强度性能。数值模拟结果和大部分试验结果吻合良好, 表明发展的细观力学有限元方法能够较好地预测复合材料的力学性能。      

分离膜表面光接枝结构及特性研究进展

介绍了膜表面光接枝技术的研究进展,并对接枝表面结构：表面形态和接枝链长度和密度作了综述．列举了接枝表面的性质,如接触角、吸附性、功能化、蛋白质固定化、环境敏感性等的变化．