铜石墨材料导电性能研究

以镀铜石墨粉为原料，用压制－烧结的工艺制备了不同铜含量的铜石墨材料，研究其电导率随铜含量变化的规律，并与传统的铜石墨材料的导电能力进行比较。研究发现，用镀铜石墨粉制备的铜石墨材料的电导率与铜体积分数呈简单线性关系，拟合曲线外推到铜体积分数为100％时与纯铜电导率相近，说明铜的导电能力几乎得到充分发挥。含铜量为75％的镀铜石墨试样的导电性能优于含铜量为85％的传统铜石墨材料。     

碳纳米管导电剂对硅复合电极初始裂纹的调控作用

硅作为新型高容量锂离子电池最具潜力的负极材料,具有极高的能量密度。然而,硅材料在充放电过程中的巨大体积变形,导致电极的严重损伤和快速退化,使得硅基电池的循环寿命普遍较低,难以同时满足高容量与长寿命的设计要求,是高容量锂离子电池研发的核心难题。导电剂作为锂离子电池复合电极活性层的主要构成之一,传统上认为主要起到提高电极电导率的作用。通过研究导电剂(以碳纳米管为例)的组分含量,实验揭示了导电剂对硅复合电极的初始裂纹密度存在调控作用,得到了碳纳米管含量的最优值,并发现了碳纳米管的加入会引入缺陷的负面机制,此机制在电化学循环中也起到重要作用。以上实验结果对指导高容量长寿命硅复合电极的设计和制备具有重要意义。     

基于Ag-PDMS复合导电材料的微流控芯片3D电极的制备

提出一种利用Ag粉和聚二甲基硅氧烷(Polydimethylsiloxane,PDMS)制成的复合材料加工微流控芯片3D电极的方法。选取导电性良好的银粉作为填料物,透明性良好和生物兼容的PDMS作为基体。将Ag颗粒表面改性后,用超声法、机械共混法相结合的方法与PDMS混合加工形成一种新型Ag-PDMS复合导电材料。分析了Ag粉的形貌、粒径、填料比例与复合材料电阻率的关系,结果表明当选取粒径为1μm片状Ag颗粒作为填料物,填料质量分数为86%时,Ag-PDMS复合导电材料的导电性能最好。最后利用软光刻方法,经过曝光、显影、填充、固化和剥离等过程,制备了3D电极。实验证明,该方法可以成功制备Ag-PDMS复合导电材料微流控芯片3D电极,对微流控芯片电极的制备有重要意义。     

原位聚合法制备环氧树脂／纳米炭黑复合导电材料的性能研究

采用原位聚合法制备了环氧树脂／纳米炭黑复合导电材料,并对其力学性能、电阻率和抗弯断面形貌进行了分析。结果表明,环氧树脂／纳米炭黑复合导电材料的邵氏硬度和抗弯强度随纳米炭黑含量而变化,当其含量为3％（质量分数）附近时两者出现最大值,抗弯强度可达到43．86MPa,邵氏硬度可达到5．34HD;纳米炭黑的加入使复合材料的电性能得到较大的提高。     

碳纤维增强酚醛树脂/石墨复合材料双极板的性能

研究了碳纤维表面处理方法及其含量对碳纤维增强酚醛树脂／石墨复合材料导电性能与力学性能的影响。结果表明：空气氧化处理碳纤维表面形成微孔和刻蚀沟槽，容易形成应力集中，复合材料的强度不高；空气加液相氧化处理填充了碳纤维表面的微裂纹，对复合材料有一定的补强作用；液相氧化处理有利于提高碳纤维表面活性以及碳纤维的均匀分散性，使材料表现出较好的力学性能与导电性能；随碳纤维含量增多，材料电导率变小，材料强度开始增大，达到最大值后材料强度下降。对碳纤维进行液相氧化处理，碳纤维含量在3％～4％时复合材料的力学性能与导电性能最好。     

微型电导率仪的研制

介绍了一种笔型微电导率仪。仪器能自动进行温度补偿。特制的电导电极体积小，寿命长，克服了玻璃电极易碎的缺点。在室温下测定了不同浓度ＫＣＬ溶液的电导率，测量精度能满足要求。     

基于原子力显微镜的四电极微探针局域电导率测量技术

开发了基于原子力显微镜(Atomic force microscope,ArM)的四电极微探针局域电导率测量技术.四电极AFM探针最小的电极间距为300 nm,安装了这种新型四电极微探针的AFM系统既保持表面微观形貌测量能力,又可以在实施表面形貌扫描的同时测定局域电导率.利用该技术精确测量了厚度为6.0μm的铝薄膜和厚度为350nm的透明导电氧化铟薄膜(Indiumtin oxide,ITO)的局域电导率,试验结果证明基于AFM的四电极微探针技术在亚微米局域电导率测量方面的能力.     

卧式螺旋卸料离心机转鼓与螺旋间差转速的液压无级调节

一、问题的提出“差转速”是卧式螺旋卸料离心机的重要参数之一。它选择的是否得当,不仅关系到机器能否顺利出料,还关系到沉渣内液相含量以及清液中固相含量的多少。从实验或理论分析说明,悬浮液中固相含量多、颗粒尺寸较大时,宜采用较高的差转速。相反,如果悬浮液中固相含量少、颗粒尺寸较小,或希望得到较干的沉渣时,应采用较低的差转速。总之,为了获得好的分离效果,对于不同品种、不同浓度的悬浮液,要选择一个适当的差转速。     

金属相在复相陶瓷刀具材料中体积含量的研究

依据陶瓷刀具材料晶粒的结构,建立了四种晶粒模型,通过理论计算,得出了金属相在陶瓷刀具材料中体积分数的合理取值范围(3.5%-13%);以3.6vol.%、5.1vol.%、6.6vol.%、8.1vol.%的Ni作为金属粘结相,制备了TiB2-TiC-WC复相陶瓷刀具材料,用扫描电镜分析了材料的微观结构,陶瓷晶粒呈六棱体状或方体,金属相包覆在陶瓷晶粒周围,并且当Ni的含量为5.1vol.%时,可以获得力学性能优良的复相陶瓷刀具材料。     

MEMS方法制造小型PEM燃料电池电极

小型PEM燃料电池电极有着比较复杂的细微结构,电极担负了收集电荷,传输燃料,催化剂载体和构架支撑的功能.介绍了一种新的带有燃料传输孔的硅片电极制造方法,并且在它的表面上生长了一层多孔硅薄膜,以利于燃料传输,扩散和渗透.多孔硅孔径分布和深度范围从百纳米到几十纳米.当催化剂Pt溅射到它表面时,受多孔硅形状的限制,Pt就形成了不连续微小颗粒,对乙醇有比较强的催化作用.用此电极组装的电池,使用乙醇或甲醇燃料时分别有0.55V和0.6V的输出电压.     

Computer aided simulation of mesoscale particles mixing for direct printable ink

Conductivity is an important property of nano ink when considering printable electrical devices need low current loss and high frequency application. Some of the mechanical, chemical and physical characteristics that can affect the conductivity of nano ink are contact resistance, impurity, void volume, aspect ratio, particle shapes, and packing density. Increasing the packing density is one of the most important factors in increasing nano ink conductivity. A computer modeling code was developed to simulate 2 dimension packing factor (2D-PF: covered area by circle/total area of domain, %) using statistics and probability theory. The values calculated in the 2D-PF were similar to empirical 3 dimension PF (3D-PF; volume of occupied by particles/total volume of system, %) values. The observed volume fraction of voids using spherical balls could be applied to printable ink. The highest 2D-PF calculated by 2D particles model simulation was 60% (binary) when the ratio of large to small particles size was 6. The fraction of void volume was observed empirically for binary packing systems using various ball sizes. The highest 3D-PF observed was 75.5% when the ratio of large particle to small particle was 10 and the volume fraction of small particles was 0.3. The 2D-PF results calculated using 2D computer simulation agreed with the results found in actual experiments. This work studies the relationship of how packing-density and surface-contact affects conductivity of patterns using printable nano inks.     

Cross-sectional capacitance measurement of particle concentration in a microchannel with multi-layered electrodes

In the present study, cross-sectional capacitance is measured in a microchannel with 12 multi-layered electrodes. The cross-sectional capacitances of microparticles of three different diameters are measured upstream and downstream. Based on these measurements, the particle concentration in terms of particle volume fraction is calculated. The particle volume fractions at three configuration areas of electrode pairs, namely, at ones containing adjacent, horizontal, and vertical pairs, are considered for ease of understanding of the particle concentration for different electrode pairs. The particle volume fraction shows an increment of 1.0–9.3% for electrode pairs near the channel walls, but decreased by 0.4–0.96% for center electrode pairs from the upstream cross-section to the downstream cross-section. Moving from the inlets to the outlet, the particles drift away from the center of the microchannel and approach the channel walls and the number of particles that migrate toward the channel walls increases clearly in the outlet area.     

The effects of particle size and volume fraction of Al2O3 on electronic thermal conductivity of α-Al2O3 particulate reinforced aluminum composites (Al/Al2O3MMC)

The effects of particle size and volume fraction of Al₂O₃ on the thermal conductivity properties of α-Al₂O₃ particulate reinforced aluminum composites (Al/Al₂O₃MMC) are investigated herein. It is found that the thermal conductivity of composites is higher with an Al₂O₃ particle size of 15 μm than with a particle size of 30 μm. The increase in the thermal conductivity could be due to the greater stability of thermal conductive paths with smaller Al₂O₃ particles.     

磁性颗粒含量对磁性液体润滑性能的影响

利用分子动力学模拟的方法研究磁性颗粒含量对磁性液体固液界面润滑性能的影响,建立体积分数为5％、9.6％和14.7％的Fe3O4的磁性液体模型,构建磁性液体固液界面润滑模型,并对润滑模型进行结构优化与退火处理,对优化后的模型进行模拟.模拟结果显示:随着磁性颗粒含量的增大,会使摩擦因数降低,从而提高磁性液体的润滑性能;其中...     

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。     

两相流离心泵水力输送性能计算分析

为探索一台固液两相流离心泵的水力性能与磨损特性,基于代数滑移混合物模型(Algebraic slip mixture model,ASMM)对其内部流场进行三维不可压缩定常流动数值计算,其中转子与定子之间的动静耦合采用"冻结转子法"实现。多相位定常流动计算结果与水力试验结果的对比确定最佳的转动位置,并确认数值计算方法的准确性。预测结果表明,颗粒属性对模型泵水力性能影响的次序为固相体积分数、颗粒密度和粒径。随着颗粒直径、密度和固相体积分数的增加,预测扬程均下降;效率总体上也呈现下降趋势,但在固相体积分数为10%时输送效率最高。在靠近隔舌的叶轮出口处存在由低、中、高三种速度组合的双剪切层射流—尾流结构。总体而言,模型泵叶片吸力面的磨损程度比压力面更为严重。固相体积分数对叶片表面磨损程度的影响比较明显,颗粒密度影响较小,颗粒直径仅对吸力面磨损程度影响显著,对压力面影响不明显。     

Evidence for the importance of particle distribution in effective medium theory: a model study

This study investigates the fundamental effects of particle distribution in a heterogeneous composite, which has never been revealed before. This work is based on the Laplace equation in cylindrical coordinates and shows that the effective thermal conductivity has a different value even at the same volume fraction depending on the particle distribution configuration. Consequently, applying the effective medium approximation without using detailed information about the particle spatial distribution can result in considerable error. This is especially true for the case of augmented conduction by insertion particles.     

SURFACING ELECTRODE WITH CRACKING RESISTANCE AND WEARABILITY

A new surfacing electrode is developed with cracking resistance and wearability based on high microhardness of TiC and VC, carbides of Ti and V are formed in deposited metal by means of high temperature arc metallurgic reaction. The results show the hardness of surfacing metal increases with the increase of ferrotitanium (Fe-Ti), ferrovanadium (Fe-V) and graphite in the coat. However, when graphite reaches the volume fraction of 11%, the hardness reaches its peak value, and when beyond 11%, the hardness falls off. As Fe-Ti, Fe-V and graphite increase, the cracking resistance of deposited metal and usability of electrode declines. Carbides are dispersedly distributed in the matrix structure. The matrix microstructure of deposited metal is lath martensite. Carbides present irregular block. When using the researched surfacing electrode to continue weld with non-preheated, no seeable crack or only a few micro-cracks can be observed in the surface of deposited metal. The hardness is above 60 HRC. The wear res     

Abrasive wear of cast aluminium alloy-zircon particle composites

The abrasive wear rates of particulate composites of an Al-11.8Si-4Mg alloy containing up to 0.35 volume fraction of zircon particles (average size, 100 μm) were measured on an 80 grit aloxide cloth sheet as a function of the volume fraction of zircon, the applied load and the number of passes over the abrasive paper. When the volume fraction of zircon is above a critical value of 0.09, the abrasive wear resistance (reciprocal of the wear rate) increases with the volume fraction of zircon according to the rule of mixtures. When the volume fraction is fixed, the abrasive wear resistance increases with the number of passes possibly because of blunting of the alumina particles of the abrasive cloth. No improvement in the abrasive wear resistance of composites over the matrix alloy was observed when the volume fraction of zircon was below 0.09. Scanning electron microscopy studies of the abraded surfaces of composites revealed fractured zircon particles but no evidence of filler particle pull-outs or debonding at the interface was obtained.     

Description and performance of a fully automatic device for the study of the sedimentation of magnetic suspensions

In this paper we describe an experimental setup for the automatic determination of the sedimentation behavior of magnetic suspensions (i.e., disperse systems consisting on ferro- or ferri-magnetic particles in a suitable fluid) of arbitrary volume fraction of solids. The device is based on the evaluation of the inductance of a thin coil surrounding the test tube containing the sample. The inductance L is evaluated from the measurement of the resonant frequency of a parallel LC circuit constructed with the coil and a capacitor of known capacitance. The coil can be moved vertically along the tube at specified steps and time intervals, and from the knowledge of L as a function of the vertical position and time, one can get an image of the particle concentration profiles at given instants of time. The performance of the device is tested against suspensions of spherical iron particles in the micrometer size range dispersed in silicone oil, with various initial concentrations of solids. The sedimentation profiles are then compared with the predictions of existing models for the settling of disperse systems of non-interacting particles.