高导热金刚石/玻璃复合材料的制备和性能研究

首先对金刚石颗粒进行化学镀Cu,并控制氧化,从而在金刚石颗粒表面获得Cu-Cu2O复合结构。然后,在800℃无压烧结制备了金刚石/玻璃复合材料,观察了其表面和界面形貌,并测定了其相对密度和热导率。结果表明,通过对镀Cu金刚石的控制氧化,明显改善了玻璃对金刚石颗粒表面的润湿性,避免了玻璃对金刚石颗粒表面的侵蚀,提高了复合材料的热导率;复合材料的热导率随金刚石含量的增加而增加,当金刚石质量分数为70%时,热导率最高达到了14.420W/(m·K)。     

Ordered Mesoporous Carbon/Fused Silica Composites

A series of novel, dense, and interesting ordered mesoporous carbon (OMC)/fused silica composites with different carbon contents has been prepared by a controllable but simple sol‐gel method followed by hot‐pressing. In the as‐sintered OMC/fused silica composites the carbon particles still exist in the form of perfectly ordered carbon nanowires. Conductivity measurements on the composites indicate that these novel composites are electrically conductive and have a typical percolation threshold of 3.5–5 vol% OMC. The electromagnetic interference (EMI) shielding efficiency (SE) of an OMC/fused silica composite containing 10 vol% OMC is as high as 40 dB in the X band which is higher than that of a carbon nanotube (CNT)/ fused silica composite with the same carbon content (～30 dB). This indicates that these conductive OMC/fused silica composites are very suitable for an application as EMI shielding materials. Upon increasing the volume content of OMC in the composite the overall contribution as well as the increase rate of the microwave absorption are larger than those of the microwave reflection, which suggest that OMC/fused silica composites may also be promising electromagnetic (EM) wave absorbing materials. Based on the promising properties of these composites this work will hopefully lead to the development of new low‐cost and highly efficient EMI shielding or EM wave absorbing materials.     

不同粒径的SiO_2纳米粒子与PVK分子复合体系的发光性质研究

通过溶胶-凝胶的方法,在乙醇溶液中合成了40nm和60nm两种不同粒径的SiO2纳米粒子,并将其分别与聚乙烯咔唑(PVK)混和,得到了不同粒径、不同质量分数配比的PVK/SiO2纳米粒子复合体系;利用光致发光光谱、吸收光谱和喇曼光谱,深入研究了PVK分子在不同状态条件下的发光特性和PVK/SiO2纳米粒子复合体系的光学性质;在复合体系中,观察到PVK与SiO2纳米粒子之间的界面能量转移过程,且不同粒径的SiO2纳米粒子对PVK分子的发光性质影响也不同。通过喇曼光谱的进一步研究表明,SiO2纳米粒子的存在,使PVK分子的振动能量明显减小,表明PVK分子与SiO2纳米粒子表面存在较强的相互作用。     

Defect Engineering Activates Schottky Heterointerfaces of Graphene/CoSe2 Composites with Ultrathin and Lightweight Design Strategies to Boost Electromagnetic Wave Absorption

To tackle the increasingly complex electromagnetic (EM) pollution environment, the application-oriented electromagnetic wave (EMW) absorption materials with ultra-thin, light weight and strong tolerance to harsh environment are urgently explored. Although graphene aerogel-based lightweight EMW absorbers have been developed, thinner thickness and more effective polarization loss strategies are still essential. Based on the theory of EMW transmission, this work innovatively proposes a high attenuation design strategy for obtaining ultra-thin EMW absorption materials, cobalt selenide (CoSe₂) is determined as animportant part of ultra-thin absorbers. In order to obtain a dielectric parameter range that satisfies the ultra-thin absorption characteristics and improve the lightweight properties of EMW absorption materials, a composite of CoSe₂ modified N-doped reduced graphene oxide (N-RGO/CoSe₂) is designed. Meanwhile, the controllable introduction of defect engineering into RGO can activate Schottky heterointerfaces of composites to generate a strong interfacial polarization effect, achieving ultra-thin characteristics while significantly improving the EM loss capability. In addition, infrared thermal images and anti-icing experiments show that the composite has good corrosion resistance, infrared stealth, and thermal insulation properties. Therefore, this work provides an effective strategy for obtaining thin-thickness, light-weight, and high-performance EMW absorption materials, embodying the advantages of N-RGO/CoSe₂ composites in practical applications.     

Modeling of multi-layered structure containing heterogeneous material layer with randomly distributed particles using infinite element method

In the electronics industry, filler particles are added to the epoxy to form a composite material in order to adjust the elastic modulus and the coefficient of thermal expansion (CTE). This paper enhances the infinite element method (IEM) for modeling and analyzing a multi-layered structure such as flip-chip assembly containing a heterogeneous material layer reinforced with randomly distributed multiple particles under thermal loading. The proposed method provides a straightforward and efficient means of modeling multiple particles since only one IE stiffness matrix of particle needs to be calculated for all of the other particles. Moreover, in analyzing the material interface problem, the proposed technique could put many number of element layers to measure the high stresses close to the edge of the multi-layered structure, and was easily applied to compare the maximum interfacial stresses near the corner.A series of problems relating to multi-layered structures containing heterogeneous materials are investigated. Initially, this study investigates the effect of varying the volume fraction of randomly arranged particles in the heterogeneous layer on the effective properties of the layer. The results obtained for the effective properties of the heterogeneous material and their influence on the interfacial stress are compared to those obtained from the Mori-Tanaka analytical method. Finally, in addition to equivalent models, three-dimensional finite element models containing multiple randomly distributed particles were built and studied. It is shown that at the free edge the interfacial stresses decrease when the number of particles close to the interface increases.     

太赫兹复合材料无损检测技术及其应用

随着材料科学的迅速发展,复合材料、高分子材料在航空航天领域得到了广泛应用。由于这些材料的特殊性质,现有的较为成熟的探伤手段都不能有效对其进行检测。但对于太赫兹波来说,许多非极性、非金属材料都是半透明,可以有效探测到这些材料的内部缺陷。本文简要介绍了太赫兹的性质及太赫兹无损探伤原理,并以航天领域应用较广的几种复合材料为例对太赫兹无损检测应用做了简介。     

Statistical Characterization of Complex Random Media in Random Fields

The statistical macroscopic characterization of composite materials in simple and complex electromagnetic environments is addressed. Based on the central limit theorem applied to the random parameters that characterize the microscopic constituents, the probability density function, mean, uncertainty and confidence intervals of various macroscopic effective constitutive material and wave parameters are derived. The implications ofthe randomness of the external field on these parameters are also investigated.     

Effects of particle shape on the effective permittivity ofcomposite materials with measurements for lattices of cubes

The effects of inclusion shape on the quasi-static effective permittivity of a two-phase periodic composite material are discussed in this paper. The lattice is formed from complex-shaped conducting inclusions suspended in a host medium. The effective permittivity is computed using an accurate moment-method-based technique. Numerical results are presented for a variety of particle shapes including circular, square, and "rounded square" cylinders (two dimensional) as well as lattices of spheres and cubes (three dimensional). It was found that among these shapes, lattices of square cylinders and cubes produced nearly the minimal polarization per unit volume possible (a` la Maxwell/Maxwell Garnett). It appears that the strong mutual interaction between edges and corners of these particles is responsible for this effect. That is, it was observed that the mutual interaction between square cylinders and cubes caused a decrease in their dipole moments and, hence, the effective permittivity, which is opposite to the usual expectation from mutual interaction between circular cylinders and spheres. Experimental verification of this effect is provided by quasi-static conductivity measurements     

基于熔融沉积成型的多层石墨烯吸波体的快速制备及其性能

在制备石墨烯/聚乳酸(PLA)复合材料的基础上,利用熔融沉积成型技术快速制备了单层均质样件,研究了石墨烯含量对其电磁参数的影响规律,并基于传输线理论计算分析了其吸波效果;选择石墨烯含量较低的复合材料作为透波层的打印材料,石墨烯含量较高的复合线材作为吸收层和再次吸收层的打印材料,并基于四分之一波长匹配理论确定了吸收层、再次吸收层的匹配厚度范围。设计制造了由不同石墨烯/PLA复合材料组合而成的三层吸波体,测试结果表明:三层吸波体的吸波效果远优于单层均质吸波体,且当选取石墨烯质量分数分别为5%、7%、8%的复合材料作为透波层、吸收层和再次吸收层打印材料时,可以获得最佳的吸收效果,此吸波体在13.3~18GHz频段内的反射率均小于-10dB,在17GHz时有-30dB的最大吸收峰值。     

Analyzing carbon-fiber composite materials with equivalent-Layer models

The purpose of this paper is to investigate the use of equivalent-layer models for the analysis of carbon-fiber composite materials. In this paper, we present three different models for the electromagnetic characterization (effective material properties) of fiber composites that are commonly used in aircraft and EMC/EMI shielding materials. These three models represent various orders (or levels) of detail in the fiber composite structure and, hence, capture various physical aspects of the composite. These models can be used to efficiently calculate the reflection and transmission coefficients, as well as the shielding effectiveness, of these fiber composites. We compare results of the reflection coefficient and shielding effectiveness obtained from these effective-property models to results obtained from a full numerical solution based on the finite-element (FE) method of the actual periodic fiber composite. We show that, as expected, as more of the geometric detail of the fiber composite is captured with the different models, the upper frequency limit of validity increases.     

Theoretical and experimental characterization of theEMP-interaction with composite-metallic enclosures

A numerical procedure is developed for the prediction of the electric and magnetic field distribution inside an enclosure having aluminum and carbon-fiber reinforced composite (CFRC) walls, illuminated by a transient electromagnetic plane wave. The composite panel is simulated by an effective layer model; time-domain surface impedance boundary conditions are enforced on the external faces of the composite slab, to express the relations among the tangential electric and magnetic field components. A coupling model for the calculation of the current induced along thin wires inside the enclosure is presented. The proposed models are implemented in a three-dimensional (3-D) finite-difference time-domain (FDTD) procedure, which is applied to the analysis of the shielding performances of an aluminum box with one CFRC face, illuminated by a transient electromagnetic wave. The computed results are compared with measured data obtained by using a full scale EMP generator     

高导热聚合物基复合封装材料及其应用

微电子封装密度的提高对传统环氧塑封料的导热性能提出了更高的要求,将高导热的陶瓷颗粒/纤维材料添加到聚合物塑封材料中可获得导热性能好的复合型电子封装材料。文章结合高导热环氧塑封材料的研究工作,评述了高热导聚合物基复合封装材料的材料体系、性能特点和在微电子封装中的应用情况。分析讨论了影响聚合物基复合电子封装材料导热性能和介电性能的因素,提出了进一步提高聚合物基复合电子封装材料导热性能的途径。     

Creep Properties of Composite Solders Reinforced with Nano- and Microsized Particles

In the present work the creep properties of Sn37Pb- and Sn0.7Cu-based composite solders reinforced with metallic nano- and microsized Cu and Ag particles have been studied. First, a series of volume percentages of reinforcements were selected to optimize the content of reinforcing particles. Then, the composite solder with optimum volume fraction of reinforcement particles, corresponding to the maximum creep rupture lifetime, was selected to investigate the effect of applied stress and temperature on the creep rupture lifetime of the composite solder joints. In the creep rupture lifetime test, small single-lap tensile-shear joints were adopted. The results indicate that composite solders reinforced with microsized particles exhibit better creep strengthening than composite solders reinforced with nanosized particles, although the mechanical tensile shear strength of composite solder joints reinforced with nanosized particles may be higher than those reinforced with microsized particles. Moreover, the creep strengthening action of the reinforcement particles is more obvious under conditions of lower applied stress or lower test temperature. Strengthening by metallic Cu or Ag reinforcement particles decreases with increasing temperature or applied stress. The Sn0.7Cu-based composite solder reinforced with microsized Ag particles is a low-cost lead-free solder that is easy to process and may have good market potential.     

取向吸波贴膜电磁性能研究

提高吸波材料的电磁性能,是新型电磁波吸收材料的重要研究内容。采用朗道-利夫希兹-吉尔伯特(LLG)方程、等效媒介理论和传输线理论,分别对随机取向和一致取向吸波贴膜的本征磁导率、等效磁导率和反射损耗进行了计算。计算结果表明当微波吸收剂一致取向时吸波材料的本征磁导率、等效磁导率和反射损耗均有显著提升。通过改变吸波贴膜内部吸收剂空间排布的方式,可以有效地提高吸波贴膜的电磁性能。针对流延法制备吸波贴膜的过程,对刮刀下流延浆料速度曲线和微波吸收剂取向之间的关系进行了分析,通过微波吸收剂的取向张量对吸波贴膜的取向程度进行了表征。通过改变流延过程中的物理参数,可以调控吸波贴膜的取向状态。     

利用等效电容计算复合材料的有效介电常数

为克服经典理论不适合计算高占空比复合材料的情况,提出了一种利用等效电容计算复合材料的有效介电常数的方法。对于颗粒弥散型复合材料,将其看成是电容器内的填充介质。通过求解电容器的等效电容,进一步导出复合材料有效介电常数的计算公式。将此模型与MG模型以及EMA模型对比,其计算结果非常接近,表明这种方法原理正确、适应性强,并且在高占空比的时候与文献给出的实验值吻合得更好。     

Electric conductivity of composite materials based on phenylon matrices and nickel particles

Nanocomposites based on nickel-containing particles and phenylon matrices have been developed and investigated. The size and compositions of the particles are determined. The conductivity of composite polymer materials containing nickel particles is studied in the vicinity of the percolation threshold. It is found that, below this threshold, the experimental dependence of the electric conductivity on the content of nickel nanoparticles in these materials differs from the dependence calculated in accordance with the percolation theory.     

掺杂铁电纳米粉的液晶的电光特性

铁电纳米粒子悬浮在向列相液晶母体中，增强介电各向异性，而且对施加的电场信号敏感。本文也展示了纳米粒子对所述复合材料可实现的总的相变的作用。这种方法也许可应用于设计新型显示材料。     

Homogenization of 3-D Periodic Bianisotropic Metamaterials

A novel homogenization technique, combining an asymptotic multiscale method with wave-field conception, is proposed for computing the quasi-static effective parameters of three-dimensional lattices of general bianisotropic composite materials. This technique is based on the decomposition of the fields into an averaged nonoscillating part and a corrected term with microoscillation. This paper provides an original and accurate way to model the electromagnetic fields in fine microstructures of bianisotropic particles with complex inclusion shapes when the wavelength is larger than the periodicity of the microstructure. The effects of the interaction between edges and corners of adjacent inclusions on the macroscopic effective parameters have been studied, and numerical results and verifications have been presented     

Recent applications of polyimide to micromachining technology

In this paper, applications of polyimide materials to micromachining technology are reviewed. First, the use of polyimide-based materials as sensor materials are discussed. In this case, the polyimide material is used as an integral part of the micromachined devices. Emphasis is given to the development and characterization of a piezoresistive composite of polyimide and graphite particles. The composite material is characterized for the mechanical properties (Young's modulus, residual stress) and the electromechanical property (piezoresistive coefficient). Second, the use of both photosensitive and nonphotosensitive polyimides as electroplating molds for the fabrication of thick and high aspect ratio metallic microstructures is presented. Extensions of the basic micromolding process, which enable the fabrication of controlled gaps between metallic microstructural components and higher aspect ratio microstructures, are presented. Electroplated metallic microstructures realized using these technologies are shown. In addition, various applications of the polyimide micromolding technologies are discussed