SiO2包裹纳米Cu粒子/环氧树脂复合材料及其在芯片封装领域的应用

为提高微电子封装材料的散热性能并保留其良好的电绝缘性能,以环氧树脂为基体,二氧化硅包裹纳米铜粒子(SiO2-Cu)为填料,采用机械混炼法制备了芯片封装用SiO2-Cu环氧树脂复合材料。采用SEM和TEM研究了SiO2-Cu纳米粒子在环氧树脂中的分散情况;研究了填料对复合材料导热系数、热膨胀系数(CTE)和力学性能的影响。结果表明:SiO2-Cu纳米粒子在环氧树脂中分散性良好;复合材料的导热系数随SiO2-Cu纳米粒子填充量的增加而增大,填充量(体积分数)超过25%时导热系数开始下降,SiO2-Cu纳米粒子适宜用量为总体积的25%;随着填料的增加,复合材料的CTE减小;当SiO2-Cu纳米粒子填充量为25%时,用于芯片封装材料时具有良好的抗冲击性能和较长的电迁移失效时间。     

Interfacial effect on thermal conductivity of diamond-like carbon films

Diamond-like carbon (DLC) has been of interest as a promising coating for protection and insulating layer in micro-electromechanical systems due to high hardness, wear resistance, transparency in IR range, chemical inertness and biocompatibility. The interfacial effect on thermal transport is studied for DLC films deposited on Al₂O₃ substrates with an ion gun method. Thermal conductivity of DLC thin films is measured with a 3ω method. DLC films show the thickness-dependent thermal conductivity, which is understood with the interfacial thermal resistance between DLC thin film and Al₂O₃ substrate. The interfacial thermal resistance and thermal conductivity of bulk DLC are determined with the measured thickness-dependent thermal conductivity of DLC films.     

Apparent thermal conductivity approach at high-temperature measurements of porous materials

The apparent thermal conductivity approach for high-temperature investigations of porous materials taking into account moisture transport, convective and radiative modes of heat transport, phase-change processes and chemical reactions is presented. Methods for the measurement of apparent thermal conductivity as a material characteristic are analyzed. An example of the practical application of the approach is given, for a hybrid-fiber reinforced cement composite exposed to high temperatures up to 1000 °C. The aspects of the utilization of apparent thermal conductivity as a tool in an assessment of porous materials and their multi-layered systems exposed to high temperatures are discussed.     

石墨烯–铝复合冷板散热性能试验研究

传统散热冷板以铝合金为主,其导热能力有限且本身密度较大,已无法满足嵌入式计算机对高效散热及轻量化的需求。针对该问题,文中提出将具有超高导热性能的石墨烯散热片粘贴在铝合金表面得到石墨烯–铝复合冷板,以石墨烯–铝复合冷板代替传统散热材料的方法,并对不同厚度、不同功耗下的石墨烯–铝复合冷板的导热效果进行了试验研究。测试结果表明,在铝合金表面贴石墨烯散热片可保证在整体质量增加较小的情况下显著提高冷板的导热能力,在3 mm厚的铝合金表面粘接2 mm厚的石墨烯散热片时导热性能最佳,导热系数达到360 ~ 370 W/(m·K),而质量仅占6 mm厚铝板质量的66.5%。因此石墨烯–铝复合冷板可应用于高性能、高集成、小型化嵌入式计算机的散热设计。     

High resolution SEM imaging of gold nanoparticles in cells and tissues

The growing demand of gold nanoparticles in medical applications increases the need for simple and efficient characterization methods of the interaction between the nanoparticles and biological systems. Due to its nanometre resolution, modern scanning electron microscopy (SEM) offers straightforward visualization of metallic nanoparticles down to a few nanometre size, almost without any special preparation step. However, visualization of biological materials in SEM requires complicated preparation procedure, which is typically finished by metal coating needed to decrease charging artefacts and quick radiation damage of biomaterials in the course of SEM imaging. The finest conductive metal coating available is usually composed of a few nanometre size clusters, which are almost identical to the metal nanoparticles employed in medical applications. Therefore, SEM monitoring of metal nanoparticles within cells and tissues is incompatible with the conventional preparation methods. In this work, we show that charging artefacts related to non‐conductive biological specimen can be successfully eliminated by placing the uncoated biological sample on a conductive substrate. By growing the cells on glass pre‐coated with a chromium layer, we were able to observe the uptake of 10 nm gold nanoparticles inside uncoated and unstained macrophages and keratinocytes cells. Imaging in back scattered electrons allowed observation of gold nanoparticles located inside the cells, while imaging in secondary electron gave information on gold nanoparticles located on the surface of the cells. By mounting a skin cross‐section on an improved conductive holder, consisting of a silicon substrate coated with copper, we were able to observe penetration of gold nanoparticles of only 5 nm size through the skin barrier in an uncoated skin tissue. The described method offers a convenient modification in preparation procedure for biological samples to be analyzed in SEM. The method provides high conductivity without application of surface coating and requires less time and a reduced use of toxic chemicals.     

One-step preparation and characterization of zinc tungstate–carbon nanoparticles with application to lithium-ion batteries

Zinc tungstate–carbon nanoparticles were synthesized by a one-step hydrothermal process followed by heat treatment. X-ray diffraction results indicated that the addition of glucose prevented grain growth of zinc tungstate during the hydrothermal process and subsequent heat treatment. Transmission electron microscopy images showed that the zinc tungstate nanoparticles were coated by carbon with a thickness of 1 nm following heat treatment at 550°C and a diameter of 10 nm with a homogeneous morphology. Electrochemical measurements showed that the zinc tungstate–carbon nanoparticles reached an initial discharge capacity of 990 mAh g^?1 at a current density of 50 mA. g^?1. The specific capacity of the zinc tungstate-carbon nanoparticles was maintained at approximately 400 mAh g^?1 after 50 cycles, exhibiting better stability than pure zinc tungstate due to the carbon coating providing high conductivity with the zinc tungstate nanoparticle.     

Sliding wear performance of nano-SiO2/short carbon fiber/epoxy hybrid composites

In the present work, epoxy based composites filled with hybrid nano-SiO₂ particles and short pitch based carbon fiber were prepared. Copolymer of styrene and maleic anhydride was grafted onto the nanoparticles prior to the compounding so that the nanoparticles can be covalently connected to the composites’ matrix through the reaction between anhydride and epoxide groups during curing. Consequently, the nano-SiO₂/matrix interfacial interaction was enhanced. By evaluating sliding wear properties of the composites as a function of the components concentrations, positive synergetic effect was found. That is, both wear rate and friction coefficient of the hybrid composites were significantly lower than those of the composites containing individual nano-SiO₂ or short carbon fiber. The composite with 4 wt.% nano-SiO₂ and 6 wt.% carbon fiber offered the greatest improvement of the tribological performance. Compared to the results of hybrid composites reported so far, the above composite is characterized by relatively lower filler content, which would facilitate processing in practice. Increased surface hardness, lubricating effect of the sheet-like wear debris reinforced by nano-SiO₂ and rapidly formed transfer film were believed to be the key issues accounting for the remarkable wear resisting and friction reducing behaviors.     

基础油中金刚石纳米颗粒润滑性能和导热性能的分子动力学分析*

为了研究纳米颗粒对基础油液热导率的影响,在基础油蓖麻油酸中加入不同体积分数和粒径的纳米金刚石颗粒,采用LAMMPS和分子动力学的研究方法,对粒子数密度以及粒子的径向分布规律、导热系数进行研究。结果表明:加入纳米颗粒的纳米流体的热物理性质受到多方面的影响,其中包括纳米颗粒体积分数及粒径等;随纳米粒子体积分数的提高纳米流体的热导率呈近似线性增加,随着纳米粒子粒径的减小,纳米粒子润滑膜的承载能力增强。纳米润滑膜能承受很高的外界冲击力,这有助于减小两作用面之间的摩擦,减小表面磨损;加入纳米颗粒的润滑油会减小摩擦副之间的摩擦和增强散热,提高热导率。     

碳纳米管增强铜基复合材料的研究进展

综述了碳纳米管增强铜基复合材料的预处理和制备方法,探讨了复合材料的组织、力学性能与摩擦学性能、电学性能和热学性能;最后指出了碳纳米管增强铜基复合材料今后的研究方向。     

Comparative evaluation of machinability characteristics of Nimonic C-263 using CVD and PVD coated tools

Machining of Nimonic C-263 has always been a challenging task owing to its hot strength, low thermal conductivity, tendency to work harden and affinity towards tool materials. Although coated tools have been used to overcome some of these challenges, selection of coated tool with appropriate deposition technique is of immense significance. The current study attempts to comparatively evaluate various performance measures in machining of Nimonic C-263 such as surface roughness, cutting force, cutting temperature, chip characteristics, and tool wear with particular emphasis on different modes of tool failure for commercially available inserts with multi-component coating deposited using chemical vapour deposition (CVD) and physical vapour deposition (PVD) techniques. Influence of cutting speed (V_c) and machining duration (t) has also been investigated using both coated tools. The study demonstrated remarkable decrease in surface roughness (74.3%), cutting force (6.3%), temperature (13.4%) and chip reduction coefficient (22%) with PVD coated tool consisting of alternate layers of TiN and TiAlN over its CVD coated counterpart with TiCN/Al₂O₃ coating in bilayer configuration. Severe plastic deformation and chipping of cutting edge and nose, abrasive nose and flank wear along with formation of built-up-layer (BUL) were identified as possible mechanisms of tool failure. PVD coated tool successfully restricted different modes of tool wear for the entire range of cutting speed. Superior performance can be attributed to the hardness and wear resistance properties, thermal stability due to presence of TiAlN phase and excellent toughness owing to PVD technique and multilayer architecture.     

纳米铜对蓖麻油酸流体热导率提升机制的分子动力学模拟*

为了研究铜纳米粒子对蓖麻油酸基础流体热导率提升的作用机制,基于分子动力学模拟(MD)方法,以铜纳米粒子直径、添加量、形状、布朗运动及系统温度为变量,对纳米流体热导率的影响机制进行研究。结果表明:纳米粒子的布朗运动会提高纳米流体的热导率;纳米铜(Cu)的加入改变了蓖麻油酸基流体的部分区域密度,产生的液体吸附层对基础流体导热性有阻碍作用;纳米流体的热导率随纳米粒子直径、添加量、系统温度的增加而增加;当纳米粒子体积相同时,表面积大的形状会提高热导率。     

多壁碳纳米管改性UHMWPE的热膨胀和摩擦学性能研究

为了降低摩擦副用聚合物的热膨胀系数,用多壁碳纳米管(MWCNTs)改性超高分子量聚乙烯(UHM-WPE),通过热压成型法制备MWCNTs/UHMWPE复合材料.通过测量电导率计算渗流阈值来表征分散性;用热膨胀仪(DIL)测试复合材料的热膨胀率,并在干摩擦环境下,测试不同MWCNTs含量复合材料的摩擦学性能.结果表明:通...     

固体吸附制冷吸附床数值分析及强化传热技术

建立了固体吸附制冷吸附床的物理模型和数学模型,通过数值分析得到床层温度分布及其各点温度随时间的变化情况,并分析吸附剂的物性参数、换热流体流速、温度和床层初始温度参数变化对床层温度分布的影响.结果表明,吸附剂的物性参数对床层温度分布影响显著;换热流体流速、温度和床层初始温度对床层温度影响不大,但影响换热效率和传热速率.在径向上床层温度存在着较大的温度梯度,但在轴向上温度分布比较均匀.在吸附剂的物性参数中,导热系数影响最大,其次是密度和比热容.因此为了提高传热效率,应增大吸附剂的导热系数,选取具有较小密度和比热容的吸附剂.     

A comparison of condensation heat transfer performance of MWCNT/Fe composite coatings on steel substrate

In the present study, the effect of MWCNT/Fe coatings on steel substrate was investigated using R134a vapor. Specifically, CNT and Fe₂O₃ powder were used as components in mechanically alloyed powder composites, which were used to fabricate surface coatings. There were two types of coatings used in the tests. The first one was pure Fe coating and the second one was the MWCNT/Fe composite coating. The powders were coated on a plain carbon steel plate by electrostatic spraying. This was followed by sintering at 900 °C. Results showed that the condensation heat transfer can be enhanced by MWCNT/Fe composite coatings, while a pure Fe coating can diminish the enhancement in comparison to the plain carbon steel plate.     

Heat and mass transfer enhancement of the bubble absorption for a binary nanofluid

The main objective of this study is to enhance the heat and transfer process of absorption using the nanofluids as the working medium. Carbon nanotubes—ammonia nanofluids (the binary nanofluids) are prepared. The thermal conductivity of the binary nanofluids and the bubble absorption process enhancement are examined experimentally. The results show the thermal conductivity of the carbon nanotubes—ammonia nanofluid is higher 16% than that of NH₃/H₂O solution. And the carbon nanotubes—ammonia nanofluid has a great enhanced effect to the NH₃/H₂O absorption.     

Preparation of Water-Soluble Lanthanum Fluoride Nanoparticles and Evaluation of their Tribological Properties

Water-soluble LaF₃ nanoparticles surface-capped by two kinds of dialkyl polyoxyethylene glycol thiophosphate ester (denoted as DTP-10 and DTP-20) were synthesized via a surface-modification method. The morphology and microstructure of resultant surface-modified LaF₃ nanoparticles (denoted as LaDTP-10 and LaDTP-20) were characterized by means of X-ray powder diffraction, transmission electron microscopy, and Fourier transform infrared spectrometry, and their thermal stability was examined by thermogravimetric analysis. Moreover, the tribological properties of as-synthesized LaF₃ nanoparticles as additives in distilled water were evaluated with a four-ball friction and wear tester, and the morphology of wear scar and the chemical states of some typical elements thereon were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. It has been found that as-prepared LaDTP-10 and LaDTP-20 nanoparticles have a size of 19.6 and 8.5 nm, respectively, and they have good dispensability in distilled water. Moreover, as-synthesized LaDTP-10 and LaDTP-20 nanoparticles as lubricant additives in distilled water exhibit good friction reducing, antiwear, and extreme pressure properties as well as high load-carrying capacity even at a concentration of 1 % (mass fraction). This is because LaF₃ nanoparticles can be deposited on sliding steel surfaces to afford a surface protective layer, and they may also tribochemically react with rubbing steel surfaces to generate a boundary lubricating film mainly composed of phosphate, sulfide, sulfate, La₂O₃, and LaF₃. Therefore, it is feasible for LaDTP-10 and LaDTP-20 nanoparticles to be used as water-soluble lubricant additives under harsh conditions.     

Development of a ta-C Wear Resistant Coating with Composite Interlayer for Recording Heads of Magnetic Tape Drives

The effect of two different surface modification methods on the wear life of the coating of magnetic tape drive heads has been studied. In this research, the heads were coated with 10 nm tetrahedral amorphous carbon (ta-C) film using filtered cathodic vacuum arc (FCVA) technique. The surface of the heads was pretreated by bombarding with energetic carbon ions or by developing a Si–Al–C composite interlayer before deposition of the coating. The coated heads were tested at a real head/tape interface of a tape drive. Surface characterization and tribological behavior of the head coatings with and without surface modification has been studied by transmission electron microscopy (TEM), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM). The results reveal that the ta-C coating without any surface modification is not durable and the coating fails due to delamination. Pre-treating the head surface with energetic carbon ions improves the durability of the coating, especially on the head read/write elements; however, the coating of the head ceramic substrate is still partially delaminated. The application of a Si–Al–C composite interlayer is shown to be able to solve the delamination problem effectively and increase the wear life of the coating up to six times in comparison with the sample pretreated with carbon ions. The formation of strong chemical bonds between the head surface and the overcoat is found to be an important factor in improving the durability of the ta-C head coating.     

碳纳米管压阻微悬臂梁红外热探测器的研究

研究了压阻复合层微机械悬臂梁红外探测器的热挠曲理论模型。利用IC工艺和微机械加工技术设计制作了一种硅/铝/碳纳米管三层微机械悬臂梁红外探测器,该探测器基于硅和铝两种材料热膨胀系数的差异,存在双物质效应,不同温度下梁的挠度不同,其形变可通过梁根部的压敏电桥检测。为提高探测器的红外吸收特性,实验探索出了在微机械悬臂梁上涂敷碳纳米管吸热层的工艺方法。实验研究了具有碳纳米管薄膜吸热层的三层微机械悬臂梁红外热探测器对红外辐射的响应规律,结果表明涂敷碳纳米管吸热层使响应灵敏度提高近一倍。     

Defect intelligent identification in resistance spot welding ultrasonic detection based on wavelet packet and neural network

Experimental correlation between varying processing and wear behaviour of ternary Ni-Co-SiO₂ composites coating was investigated. The parameter used in this research are: SiO₂ (5–25 wt%), thermal treatment (100–300 °C), applied load (5–15 N). The results show that novel ternary Ni-Co-SiO₂ nanoparticle composite coating was successful applied to mild steel. The addition SiO₂ nanoparticles in the coating Ni-Co bath lead to uniform microstructure. Thermal treatment of the coating at 300 °C decreased wear rate by (?0.031), increasing the wt% of SiO₂ from 0 to 25 decreased the wear rate by ?0.018, applied load increases from 5 to 15 N raises the wear rate raises (0.0097), The lower wear rate was obtained at 25 wt% SiO₂, applied load 5 N and thermal treatment at 300 °C. Validation of the results from pin on disc test with electro-hydraulic servo PV friction testing machine shows the same wear pattern. One can concluded in this work that the wear rate of the coated materials depend on the made up of the coating and not on the type of wear mechanism. It have be established in this work that thermal treatment and SiO₂ nanoparticle can be used to enhance the wear behaviour of Ni-Co coating of mild steel.     

Study of carbon fibres and carbon–carbon composites by scanning thermal microscopy

Scanning thermal microscopy (SThM) is a relatively new technique based on atomic force microscopy in which the tip is replaced by an ultra‐miniature temperature probe. This paper reports on a preliminary investigation of the application of SThM in the characterization of the thermal properties of carbon fibres and carbon–carbon (CC) composites. The technique enabled a comparative study to be made of discrete fibre and matrix thermal properties in a series of model unidirectional composites. The thermal images revealed a marked increase in thermal conductivity of the matrix with increasing temperature of treatment and hence confirmed the development of a highly ordered carbon matrix. The results were in qualitative agreement with previously determined values of thermal conductivity from which the separate values of fibre and matrix thermal conductivity had been derived. The technique was also applied to the characterization of samples of unknown processing history, enabling an estimation to be made of the heat treatment and type of the fibres and matrix present in the composite. It was concluded that SThM promises to be a powerful technique for the study of the thermal properties of CC composites and carbon fibres, as it uniquely enables variations in local thermal conductivity to be detected and resolved. Absolute quantification of the technique remains the key to its future widespread acceptance in materials characterization.