微粒团聚的尺度效应及其分形表征

利用全自动激光粒度分析仪，研究了乙醇分散液中羟基磷灰石微粒团聚过程中粒径分布、微粒的平均团聚粒径和比表面积随微粒团聚时间的变化关系，以及微粒质量分数对平均团聚粒径和比表面积的影响，对微粒团聚平均粒径、比表面积及团聚速率与微粒质量分数及微粒团聚时间的关联性进行了分形表征。结果表明：随微粒团聚时间的延长，所测微纳米微粒的最大分布粒径值、最小分布粒径值逐渐增大，分布曲线有逐渐向正态分布发展的趋势；随团聚时间增加，或微粒质量分数的增大，微粒团聚平均粒径逐渐增大，而比表面积逐渐减小，并都在一定的时间内达到动态平衡；微粒团聚速率分形维数可以客观地描述微粒团聚基本规律，当微粒质量分数一定时，微粒团聚分形维数越大，其团聚速度越大，当微粒团聚分形维数一定时，微粒质量分数越大，团聚速率越大。     

纳米ZnO填充PTFE复合材料的力学及摩擦学性能

通过机械搅拌和超声分散制备纳米ZnO填充PTFE复合材料,研究纳米ZnO填充量对复合材料力学及摩擦磨损性能的影响。结果表明:当ZnO质量分数小于3%时,复合材料的拉伸强度与纯PTFE相比略有增高;复合材料的密度、硬度、摩擦因数随ZnO填充量的增加而逐渐增大;当ZnO填充质量分数为1%～3%时,复合材料的磨耗量大幅下降,但若继续增加ZnO填充量,复合材料的磨耗量却变化不大。     

锰元素对铜基CuZnNi合金钎料性能的影响

通过在CuZnNi合金钎料中添加不同含量的锰元素,研究了锰元素对CuZnNi合金钎料的液相线温度、润湿性能和钎料与接头力学性能的影响。结果表明:随着钎料中锰含量的增加,钎料的液相线温度逐渐降低,当锰的质量分数为4.5%时,钎料的液相线温度下降了54℃;钎料的铺展面积随钎料中锰含量的增加而逐渐增大,当锰的质量分数为4.5%时,钎料的铺展面积达到了298mm~2;随着钎料中锰含量的增加,钎料的抗拉强度逐渐增大,而伸长率呈先上升后略下降的趋势;钎焊接头的抗剪强度随钎料中锰含量的增加而显著提高,当锰的质量分数为4.5%时,抗剪强度达到了221 MPa,比基体钎料的提高了16.1%。     

漂珠/AZ91D镁合金复合材料的显微组织与力学性能

以AZ91D镁合金为基体,以不同粒径(45128μm)的漂珠为颗粒增强相,采用搅拌铸造法制备了漂珠质量分数为010%的AZ91D镁合金基复合材料,并研究了复合材料的显微组织和力学性能。结果表明:复合材料中的漂珠分布均匀,主要由α-Mg、Mg17Al12、Mg2Si、MgO等物相组成;复合材料的硬度随漂珠含量增加而增大;当漂珠的质量分数为6%、平均粒径为60μm时,复合材料的硬度最高,为82.1HBW;当漂珠的平均粒径为90μm、质量分数为6%时,复合材料的抗压强度最高,为348.3 MPa;复合材料的断裂方式是以解理断裂为主的脆性断裂,漂珠在复合材料断裂过程中发生破损。     

Al_2O_3-H_2O纳米流体冻结过程的数值模拟和试验研究

纳米流体作为强化换热介质,是目前的研究热点,但关于其相变过程的研究较少。利用当量比热法,在COMSOL有限元模拟软件中对质量分数为5%,不同粒径(10、20、50、100、500nm)的Al2O3-H2O纳米流体和去离子水的冻结过程进行数值模拟,并将模拟结果和试验结果进行了对比。二者具有较好一致性,表明烧杯中心和壁面附近的温度变化趋势有较大区别,中心处的温度变化更能反映样品的冻结过程;当质量分数为5%时,Al2O3-H2O纳米流体的相变时间与去离子水相比较短,且纳米流体的相变时间随Al2O3粒径的增大而增加。     

基于分子动力学的纳米轴承动压润滑研究

采用分子动力学方法建立了纳米轴承分子动力学模型,研究了不同剪切速度、不同主轴偏心率、不同势能参数下轴承承载力的变化。研究结果表明,纳米轴承具有临界速度,在临界速度以下,轴承承载力随剪切速度增大而增大,超过临界速度,承载力产生突降;纳米轴承承载力随主轴偏心率增大而逐渐增大;当势能参数增大时,轴承承载力逐渐增大,但增幅趋缓。     

电镀废液回收纳米铜粉作为润滑添加剂的摩擦学性能研究

以化学还原法从电镀铜废液中回收的纳米铜粉为固体润滑油添加剂,在四球式摩擦磨损试验机上研究纳米铜粉的加入量对润滑油摩擦学性能的影响。采用SEM、EDAX等分析磨斑表面,初步探讨纳米铜粉抗磨减摩机制。结果表明:纳米铜粉的添加显著提高基础油的抗磨减摩性能,当纳米铜粉加入量为0.3%(质量分数)时,其摩擦因数和磨斑直径分别比基础油减小33.4%和19%。含纳米铜粉润滑油在高载荷下具有更好的抗磨减摩性能。纳米铜粉在摩擦过程中抗磨减摩机制主要为填充作用和沉积自修复膜作用机制。     

干法室温振动制备纳米铜粉

将粒径为1～5μm的原料铜粉置入辊压振动磨中,经振动研磨后得到纳米铜粉,通过X射线多晶衍射仪和扫描电子显微镜对其进行了分析.结果表明:得到的纳米铜粉晶格类型仍为面心立方晶格,结构参数和化学成分没有发生变化;随着研磨时间的增加,粉末的平均粒径越来越小,粒度分布趋于均匀,研磨6 h以后,平均粒径在100 nm左右.     

纳米CaCO_3添加量对其改性聚丙烯复合材料发泡效果及力学性能的影响

采用超临界流体技术制备出纳米CaCO3改性聚丙烯复合材料,研究了纳米CaCO3添加量对复合材料发泡效果、力学性能以及CaCO3和聚丙烯共混物流变性能的影响。结果表明:随纳米CaCO3添加量的增多,复合材料的发泡效果先变好再变差,而拉伸强度和冲击韧度均先升后降,当纳米CaCO3质量分数为5%时,复合材料的发泡效果最佳,拉伸强度和冲击韧度最大,分别为16MPa和37kJ·m-2;在250℃时,随着纳米CaCO3添加量的增大,共混物的表观黏度逐渐减小。     

多晶金刚石微粉的制备及其得率和耐磨性

以土状石墨粉和铜粉为原料,采用粉末冶金法制备了铜/石墨材料,然后采用冲击波合成工艺制备了多晶金刚石微粉;研究了铜含量、石墨粒径、热处理以及复压工艺对其得率和耐磨性的影响。结果表明:多晶金刚石微粉的得率随铜含量的增加而增大,随石墨粒径的增大而先增后降,粒径为70μm时的得率最高;复压前,多晶金刚石微粉的得率随热处理温度的升高先略增加后又急剧降低,复压后,得率随热处理温度的升高而增大;制备工艺对多晶金刚石微粉耐磨性能的影响较小。     

Microstructural characterization of mechanicallyactivated ZnO powders

In this paper, changes of microstructural characteristics of disperse systems during mechanical activation of zinc oxide (ZnO) have been investigated. ZnO powder was activated by grinding in a planetary ball mill in a continuous regime in air during 300 min at the basic disc rotation speed of 320 rpm and rotation speed of bowls of 400 rpm but with various balls‐to‐powder mass ratios. During ball milling in a planetary ball mill, initial ZnO powder suffered high‐energy impacts. These impacts are very strong, and large amounts of microstructural and structural defects were introduced in the milled powders. The morphology and dispersivity of particles and agglomerates of all powders were investigated by scanning electron microscopy and scanning transmission electron microscopy. The specific surface area of initial ZnO powder was determined as 3.60 m² g^?1 and it increased to 4.42 m² g^?1 in mechanically activated powders. An increase of the ball‐to‐powder mass ratio led to a decrease of particle dimensions as well as increased the tendency for joining into quite compact agglomerates, that is aggregates, compared with the very loose, soft initial agglomerates. The obtained results pointed out that activation of ZnO powders produces a highly disperse, nano‐scaled mixture of small particles, that is crystallites with sizes in the range of 10–40 nm. Most of these particles are in the form of aggregates with dimensions of 0.3–0.1 μm. The crystallite and aggregate size strongly depend on milling conditions, that is ball‐to‐powder mass ratio, as shown in this investigation.     

纳米铜在润滑油中烷基苯三唑分散剂的制备和性能研究

为提高铜纳米颗粒在润滑油中的分散性能,以苯并三氮唑和卤代烃为原料,合成烷基苯并三氮唑分散剂,并通过红外光谱和核磁共振确定化合物的结构;通过沉降试验、流变性能的测试考察了分散剂的烷基链长、分散剂的用量对分散性能的影响,并通过热分析和TEM对分散剂的分散性能做进一步考察。结果表明：分散剂的链长为十八时,分散剂质量分数为0.1%-0.2%时分散剂的分散性能最好;并且分散剂的质量分数小于0.2%时对润滑油流变性能的影响很小;分散剂与纳米铜的结合不仅有物理吸附还有化学吸附。在四球摩擦磨损试验机上进行的摩擦学性能试验结果表明,采用所合成的分散剂分散的铜纳米微粒添加剂能够显著提高基础油的极压性能,同时具有良好的减摩性能。     

Sol-Gel法制备氧传感器用纳米TiO_2材料

以钛酸丁酯为前驱物,乙醇为溶剂,采用Sol-Gel法合成了颗粒尺寸约十几nm、分散良好的纳米TiO_2粉体.经测试,采用厚膜工艺用该粉体制成的元件较传统粉体制作的元件在灵敏度上提高50%以上.     

The effect of super- and nanodispersed powders of zinc and copper alloys in plastic greases on the structure and triboengineering properties of steel surfaces

It is demonstrated that the wear rate of tribocouples can be reduced significantly with the use of lubricating compositions obtained by added super- and nanodispersed zinc or Cu-Sn powders to the Lithol-24 plastic grease. When the superdispersed powders of copper alloys interact with tribosurfaces, the copper and tin diffuse into the base metal, producing secondary composite superdispersed structures. The alloyed elements penetrate into the base metal more deeply if the powder contains the nanodispersed fraction. The films of polyfluorinated oligomers based on particles of zinc and copper alloy powders with functional substitutes reduce substantially the friction coefficient of kinematic couples when they are lubricated with these lubricating compositions and expand the temperature range of application of plastic greases.     

纳米金属粉在润滑中的应用

介绍了纳米金属粉的特性、制备以及其在润滑油中的分散、稳定悬浮等几个方面的内容，分析了纳米金属粉作添加剂的摩擦学性能，并指出了纳米金属粉作为润滑油添加剂在摩擦学中的研究进展和发展趋势。     

制备工艺对PTFE复合材料硬度的影响

采用溶剂蒸发法和固体纳米粉末混合法制备两种工艺制备了PTFE复合材料。结果表明：在填料含量相同时，溶剂蒸发法制备的PTFE复合材料的硬度显著高于固体纳米粉末混合法制备的PTFE复合材料的硬度；使用纳米颗粒作填料时，用偶联剂处理表面对硬度没有显著影响。其作用机理为：当用固体纳米粉末填料时，由于纳米粉末的团聚作用，丧失了部分纳米颗粒的表面特性，界面结合较差，硬度较低；而使用液体纳米硅溶胶制备PTFE复合材料时，纳米颗粒在搅拌蒸发的过程中被PTFE大分子包裹，可以有效防止团聚的发生。     

纳米粉体的团聚与分散

纳米粉体的团聚一直是困扰纳米材料制备和粉末纳米材料应用的关键问题。从纳米粉体团聚机理入手，综述了纳米粉体团聚行为的影响因素、克服纳米粉体团聚现象和纳米粉体分散的技术途径。     

纳米级金属粉改善润滑油摩擦性能的研究

在MPX200实验机上考察了粒径为20～30hm的铜粉和锡粉加入Q030润滑油后的摩擦性能,结果表明该铜粉能够提高Q030润滑油的极压性能,而将铜粉和锡粉一起加入该润滑油则效果更佳。     

On the compressive behavior of sintered porous coppers with low-to-medium porosities—Part II: Preparation and microstructure

A polymer space-holder method was used in this study to prepare porous coppers with low-to-medium porosity within the range 5–50%. This provides the possibility to control the pore size, distribution and structure. Optical microscopy and scanning electron microscopy (SEM) with energy dispersion spectrum (EDS) were utilized to characterize the porous samples. Two different sizes of copper powders, 5 and 45 μm, were used to investigate the effect of raw materials powder size. Microstructure results have shown that there exist two different types of pore in the sintered samples: round-shaped macro-pores left over by the burnout of the space holder and irregular micro-pores or the intervals among metal powders. No matter which size powder was used, the size of the macro-pore falls into a range 200–500 μm, but the pore structures are different in the two cases, interconnected or open pores for the 45 μm raw powders and closed pore for the 5 μm powders. The sizes of the micro-pores among the copper powders in the two cases are also different, several microns for the 5 μm powders and 10–20 μm for the 45 μm powders, though all micro-pores are interconnected for both powder sizes. From the viewpoint of pore structure, it is concluded that the 45 μm powder is more appropriate for use to prepare the porous metal. In addition, the effect of the binder was also investigated. It is suggested that a binder that can be easily and completely removed should be used in order to induce the residue. This paper, as Part II of the publication, focuses on the fabrication of the porous samples where Part I [Lemons JE, editor. Quantitative characterization and performance of porous implants for hard tissue application. ASTM STP 953; 1985] has been published earlier for the mechanical properties of the material.     

Effects of Powder Characteristics on Electrodischarge Machining Efficiency

This paper presents the effects of various powder characteristics on the efficiency of electrodischarge machining (EDM) SKD-11. The additives examined include aluminium (Al), chromium (Cr), copper (Cu), and silicon carbide (SiC) powders that have significant differences in their thermophysical properties. The machining mechanism with the addition of the foreign particles, the tool wear rate (TWR), and the material removal rate (MRR) have been investigated. It was found experimentally that the particle concentration, the particle size, the particle density, the electrical resistivity, and the thermal conductivity of powders were important characteristics that significantly affected the machining performance in the EDM process. Proper addition of powders to the dielectric fluid increased the MRR and, thus, decreased the TWR. Under the same particle concentration experiments, the smallest suspended particle size led to the greatest MRR and, thus, the lowest TWR. Of the additives investigated, chromium powder produced the greatest MRR and the lowest TWR, whereas the process without foreign particles has the converse effects. The addition of copper powder to the dielectric fluid was found to make almost no difference to the pure kerosene EDM system.