几种纳米微粒作为锂基脂添加剂对钢-钢摩擦副摩擦磨损性能的影响研究

采用四球摩擦磨损试验机考察了纳米SiO2、纳米LaF3及纳米Ni等3类纳米微粒作为锂基脂添加剂对钢-钢摩擦副摩擦磨损性能的影响;采用扫描电子显微镜、X射线能量色散谱仪及X射线光电子能谱仪分析了含纳米微粒添加剂的锂基脂润滑下的钢球磨损表面形貌、元素面分布及典型元素的化学状态.结果表明:3种纳米微粒作为添加剂均能够显著提高锂基脂的减摩抗磨能力;锂基脂及含不同纳米添加剂的锂基脂润滑下的钢球磨损表面形貌及其表面保护膜的性质存在明显差异,这种差异决定了钢-钢摩擦副在相应脂润滑条件下的摩擦磨损性能差异;含纳米SiO2的锂基脂润滑下的钢球磨损表面形成的含纳米SiO2的表面保护膜均匀且厚度适中,故其相应的减摩抗磨效果最佳.     

表面修饰SiO2纳米微粒对锂基脂抗磨性能影响的研究

合成了表面修饰SiO2纳米微粒,利用四球摩擦磨损试验机考察了SiO2纳米微粒作为锂基脂添加剂的摩擦磨损行为,用扫描电子显微镜、能量色散谱仪和X射线光电子能谱仪对钢球磨损表面进行了分析.结果表明:SiO2纳米微粒作为锂基脂添加剂具有良好的抗磨损性能,能够显著提高锂基脂的失效载荷.这是由于在摩擦过程中,SiO2纳米微粒富集在磨损表面并形成边界润滑膜,对磨损表面起到修复作用,从而使得锂基脂的抗磨和承载能力明显提高.     

纳米Fe_3O_4在板带钢冷轧轧制液中的摩擦学性能

在超声波作用下,将经油酸表面修饰平均粒径为20 nm的纳米Fe3O4微粒分散于板带钢冷轧轧制液中,在MRS-10A四球摩擦磨损试验机上考察了其对钢/钢摩擦副摩擦磨损性能的影响;利用X射线衍射仪和透射电镜分析了纳米Fe3O4的相组成和微结构,采用光学显微镜观察了磨损表面形貌.利用四辊冷轧试验机进行了轧制液润滑下的板带钢冷轧试验,考察了纳米Fe3O4添加剂对板带钢冷轧润滑的效果.结果表明:纳米Fe3O4作为轧制液添加剂能有效提高钢/钢摩擦副的抗磨性能、降低摩擦系数,同时表现出良好的板带钢冷轧润滑效果;含纳米Fe3O4的轧制液可明显降低带钢最小可轧厚度,并改善轧制带钢板面质量.     

油酸表面修饰PbO纳米微粒作为润滑油添加剂的摩擦学性能研究

利用四球摩擦磨损试验机考察了油酸修饰PbO纳米微粒作为润滑油添加剂的摩擦学行为,并用X射线光电子能谱仪（XPS）、扫描电子显微镜（SEM）和能量散射谱仪（EDS）等现代分析工具对钢球磨损表面进行了分析,摩擦磨损试验结果表明,油酸修饰PbO纳米微粒作为润滑油添加剂能够明显提高基础油的减摩抗磨能力,当添加质量分数为0.30%时,与基础油相比可以使摩擦系数和钢球磨厂主 直径降低30%左右。XPS、SEM及EDS分析结果表明,钢球表面在摩擦过程中形成了一层富含PbO的边界润滑膜,这使得油酸修饰PbO纳米微粒作为润滑油添加剂表现出良好的摩擦学性能。     

水溶性纳米二氧化硅添加剂的制备及摩擦学性能研究

本文制备了不同粒径的水溶性纳米二氧化硅,用TEM和XRD对其形貌进行了表征,采用SRV-IV微动摩擦磨损试验机研究了其作为水基添加剂的摩擦学性能。通过SEM和XPS对磨斑表面进行了分析,简单探讨了摩擦机理。结果表明,小颗粒水溶性纳米二氧化硅作为水基添加剂是具有良好的抗磨减摩性能和极压性能,摩擦过程中形成的沉积膜起到了非常重要的作用。     

表面修饰油溶性BaSO_4@SiO_2-OTMS纳米微粒的制备及作为油基钻井液添加剂的研究

采用原位表面修饰和溶胶-凝胶法制备了十八烷基三甲氧基硅烷(OTMS)修饰的油溶性BaSO_4@SiO_2-OTMS纳米微粒;利用透射电子显微镜、X射线衍射仪、傅里叶变换红外光谱仪分析了产物的形貌及结构,采用热分析仪评价了其热稳定性,用往复摩擦磨损试验机和六速旋转黏度计研究了产物对油基钻井液润滑性能及流变性能的影响.结果表明:所制备的Ba SO_4@Si O_2纳米微粒由直径为30 nm的Ba SO_4内核和厚约8 nm的Si O_2外壳组成,经OTMS修饰后,Ba SO_4@Si O_2-OTMS纳米微粒在液体石蜡中具有良好的分散稳定性.与此同时,Ba SO_4@Si O_2-OTMS纳米微粒作为添加剂可以降低油基钻井液的流动阻力,减轻钻头磨损,提高钻井速度.当添加剂浓度较低时,随着添加剂含量的增加,油基钻井液的黏度降低;当添加剂质量分数为0.8%时,钻井液的黏度以及钢球-页岩摩擦副的摩擦系数和页岩磨痕宽度最小.     

新型水溶性润滑添加剂的研究进展

在工业润滑领域中,水溶性润滑添加剂决定着水基润滑体系的性能.近年来一些具有特殊结构与组成的新型水基润滑添加剂表现出了优异的使用性能和广阔的应用前景.本文作者从摩擦学特性和润滑机理出发,分别综述了国内外关于纳米微粒、含氮杂环化合物、高分子聚合物和离子液体等材料作为水溶性润滑添加剂的研究进展,分析了当前研究中存在的问题,并对其发展趋势进行了展望.     

ZrO_2纳米微粒的制备、表征及作为MACs添加剂的摩擦学性能

制备了氧化三辛基膦表面修饰的油溶性ZrO2纳米微粒,用透射电镜(TEM)、X-射线衍射仪、红外光谱仪对其进行表征,研究了其作为多烷基环戊烷(MACs)添加剂的摩擦学性能及润滑机理.结果表明:ZrO2纳米微粒粒径大约为7～8 nm,分布比较均匀,无明显团聚,在非极性溶剂中能很好地溶解和稳定分散;作为MACs添加剂,在摩擦过程中,无机ZrO2纳米微粒以沉积膜形式沉积在摩擦副表面,有机修饰剂中的活性P元素在摩擦副表面发生了化学反应,形成了FePO4极压润滑膜,ZrO2沉积膜和FePO4极压润滑膜的协同作用起到了良好的抗磨和抗极压作用.     

2，5—二巯基—1，3，4—噻二唑—聚乙二醇共聚物纳米微粒的制备及其摩擦学行为

合成了大分子主链中含噻二唑环的共聚物纳米微粒，并用高分辨透射电子显微镜、傅立叶红外光谱仪和热分析系统等对该纳米微粒进行了表征，用MRSl—J型和MRS—10A型四球摩擦磨损试验机考察了共聚物纳米微粒作为高水基润滑添加剂的摩擦学性能．结果表明，该共聚物纳米微粒能分散于水中，且具有较好的极压抗磨性能．     

季铵盐修饰磷钼酸铵纳米微粒作为液体石蜡添加剂的摩擦学性能

采用共沉淀法在溶液中原位合成了季铵盐修饰磷钼酸铵[(NH4)3PMo12O40]纳米微粒,采用透射电子显微镜、X射线衍射仪、示差扫描热分析仪及热重分析仪等观察分析了表面修饰(NH4)3PMo12O40纳米微粒的形貌和热稳定性,并在四球摩擦磨损试验机上考察了其作为液体石蜡添加剂的摩擦学性能。结果表明：表面修饰(NH4)3PMo12O40纳米微粒大小均匀,平均粒径约为20nm;(NH4)3PMo12O40纳米核在300℃左右分解;(NH4)3PMo12O40。纳米微粒作为液体石蜡添加剂,在中低负荷下具有较好的抗磨性和一定的减摩作用,并可提高液体石蜡的极压负荷,采用扫描电子显微镜和X射线光电子能谱对磨斑表面形貌和化学组成进行观察分析发现,(NH4)3PMo12O40纳米微粒在摩擦副接触表面发生了摩擦化学作用,并形成由多种含氧化合物组成的表面保护膜,从而起到减摩抗磨作用。     

Heat- and mass-transport in aqueous silica nanofluids

Using the transient hot wire and pulsed field gradient nuclear magnetic resonance methods we determined the thermal conductivity and the solvent self-diffusion coefficient (SDC) in aqueous suspensions of quasi-monodisperse spherical silica nanoparticles. The thermal conductivity was found to increase at higher volume fraction of nanoparticles in accordance with the effective medium theory albeit with a smaller slope. On the other hand, the SDC was found to decrease with nanoparticle volume fraction faster than predicted by the effective medium theory. These deviations can be explained by the presence of an interfacial heat-transfer resistance and water retention by the nanoparticles, respectively. We found no evidence for anomalous enhancement in the transport properties of nanofluids reported earlier by other groups.     

Steady laminar mixed convection stagnation-point flow of a nanofluid over a vertical permeable surface in the presence of a magnetic field

A similarity solution for a steady laminar mixed convection boundary layer flow of a nanofluid near the stagnation point on a vertical permeable plate with a magnetic field and a buoyancy force is obtained by solving a system of nonlinear ordinary differential equations. These equations are solved analytically by using a new kind of a powerful analytic technique for nonlinear problems, namely, the homotopy analysis method (HAM). Three different types of nanoparticles, namely, copper (Cu), alumina (Al₂O₃), and titanium oxide (TiO₂), with water as the base fluid are considered. The influence of the volume fraction of nanoparticles, permeability parameter, magnetic parameter, and mixed convection parameter on the surface shear stress and surface heat transfer, as well as on the velocity and temperature profiles, is considered. It is observed that the skin friction coefficient and the local Nusselt number increase with the nanoparticle volume fraction for all types of nanoparticles considered in this study. The greatest values of the skin friction coefficient and the local Nusselt number are obtained for Cu nanoparticles.     

Synthesis and thermal conductivity of microfluidic copper nanofluids

A microfluidic chemical solution method is developed for the synthesizing Cu nanofluids.The method replaces batch-based macroreactors in the conventional chemical solution method by continuous-flow microfluidic microreactors,thereby enabling the synthesis of nanofluids with various microstructures.The Cu nanofluids synthesized by this technology show a better stability,remaining stable even after more than 100h standing.The measured thermal conductivity shows that the presence of nanoparticles can either upgrade or downgrade fluid conductivity,a phenomenon predicted by the recent thermal-wave theory of nanofluids.     

原位生成MoB增强Cu-Sn-Al合金复合材料的摩擦学性能研究

采用快速热压烧结方法成功制备了原位生成MoB增强的Cu-Sn-Al合金复合材料,研究了增强体添加含量对复合材料体系摩擦学性能的影响,并对其摩擦磨损机制进行了分析. 研究表明:在Cu-5Sn合金基体中添加MoAlB陶瓷颗粒后,烧结过程中,层状结构MoAlB陶瓷中的Al元素能够扩散到基体中,生成原位MoB增强Cu-Sn-Al合金复合材料. 此外,复合材料体系的硬度随着MoAlB添加量的增加逐渐提高,与Cu-5Sn合金相比,当添加MoAlB质量分数为30%时,复合材料硬度值提高了约5倍. 同时,随着添加MoAlB陶瓷颗粒含量的增加,复合材料体系摩擦系数和磨损率逐渐降低,当添加的MoAlB陶瓷颗粒质量分数为30%时,复合材料摩擦系数和磨损率分别低至0.33和5.4×10?5 mm3/(N·m). 由于原位生成MoB颗粒的钉扎效应,在摩擦过程中能够抑制基体材料的塑性变形,使得材料体系的硬度显著提高,磨损率明显降低,摩擦过程中表面生成的摩擦氧化物,能够降低材料体系的黏着磨损和二体磨粒磨损,可以起到优异的抗磨减摩效应.      

Computer simulation of Cu: AlOOH/water in a microchannel heat sink using a porous media technique and solved by numerical analysis AGM and FEM

Extensive improvements in small-scale thermal systems in electronic circuits, automotive industries, and microcomputers conduct the study of microsystems as essential. Flow and thermic field characteristics of the coherent nanofluid-guided microchannel heat sink are described in this perusal. The porous media approximate was used to search the heat distribution in the expanded sheet and Cu: γ - AlOOH/water. A hybrid blend of Boehme copper and aluminum nanoparticles is evaluated to have a cooling effect on the microchannel heat sink. By using Akbari Ganji and finite element methods, linear and non-linear differential equations as well as simple dimensionless equations have been analyzed. The purpose of this study is to investigate the fluid and thermal parameters of copper hybrid solution added to water, such as Nusselt number and Darcy number so that we can reach the best cooling of the fluid. Also, by installing a piece of fin on the wall of the heat sink, the coefficient of conductive heat transfer and displacement heat transfer with the surrounding air fluid increases, and the efficiency of the system increases. The overall results show that expanding values on the NP (series heat transfer fluid system maximizes performance with temperatures) volume division of copper, as well as boehmite alumina particles, lead to a decrease within the stream velocity of the Cu: AlOOH/water. Increasing the volume fraction of nanoparticles in the hybrid mixture decreases the temperature of the solid surface and the hybrid nanofluid. The Brownian movement improves as the volume percentage of nanoparticles in the hybrid mixture grows, spreading the heat across the environment. As a result, heat transmission rates rise. As the Darcy number increases, the thermal field for solid sections and Cu: AlOOH/water improves.     

Predicting thermal conductivity of liquid suspensions of nanoparticles (nanofluids) based on rheology

A methodology is proposed for predicting the effective thermal conductivity of dilute suspensions of nanoparticles (nanofluids) based on rheology.The methodology uses the rheological data to infer microstructures of nanoparticles quantitatively,which is then incorporated into the conventional Hamilton-Crosser equation to predict the effective thermal conductivity of nanofluids.The methodology is experimentally validated using four types of nanofluids made of titania nanoparticles and titanate nanotubes dispersed in water and ethylene glycol.And the modified Hamilton-Crosser equation successfully predicted the effective thermal conductivity of the nanofluids.     

The direct effect of interfacial nanolayers on thermal conductivity of nanofluids

One of the most important features of nanofluids is their thermal conductivity. In this article, a new model for thermal conductivity is proposed based on the combination of a statistical model and thermal convection caused by Brownian motion of nanoparticles with considering the effect of interfacial nanolayers among nanoparticles and base fluids. This model is compared with Al₂O₃ in deionized water and CuO in deionized water (based nanofluids of spherical particles) using a number of theoretical and experimental thermal conductivity models, after that the experimental results have been made available in the open literature. In this model, an interfacial nanolayer is influenced directly on both parts of static and dynamic effective thermal conductivity. The present model shows good agreement with the experimental result of nanofluids and gives better predictions compared to models used for nanofluids in this article. This model is purely theoretical and in order to achieve it, experimental results have no effect.     

The role of several heat transfer mechanisms on the enhancement of thermal conductivity in nanofluids

A modelling of the thermal conductivity of nanofluids based on extended irreversible thermodynamics is proposed with emphasis on the role of several coupled heat transfer mechanisms: liquid interfacial layering between nanoparticles and base fluid, particles agglomeration and Brownian motion. The relative importance of each specific mechanism on the enhancement of the effective thermal conductivity is examined. It is shown that the size of the nanoparticles and the liquid boundary layer around the particles play a determining role. For nanoparticles close to molecular range, the Brownian effect is important. At nanoparticles of the order of 1–100 nm, both agglomeration and liquid layering are influent. Agglomeration becomes the most important mechanism at nanoparticle sizes of the order of 100 nm and higher. The theoretical considerations are illustrated by three case studies: suspensions of alumina rigid spherical nanoparticles in water, ethylene glycol and a 50/50w% water/ethylene glycol mixture, respectively, good agreement with experimental data is observed.     

Effect of temperature on the effective thermal conductivity of n-tetradecane-based nanofluids containing copper nanoparticles

Nanofluids were prepared by dispersing Cu nanoparticles(~20nm) in n-tetradecane by a two-step method.The effective thermal conductivity was measured for various nanoparticle volume fractions(0.0001-0.02) and temperatures(306.22-452.66 K).The experimental data compares well with the Jang and Choi model.The thermal conductivity enhancement was lower above 391.06 K than for that between306.22 and 360.77 K.The interfacial thermal resistance increased with increasing temperature.The effective thermal conductivity enhancement was greater than that obtained with a more viscous fluid as the base media at 452.66 K because of nanoconvection induced by nanoparticle Brownian motion at high temperature.     

Predicting thermal conductivity of liquid suspensions of nanoparticles （nanofluids） based on rheology

A methodology is proposed for predicting the effective thermal conductivity of dilute suspensions of nanoparticles （nanofluids） based on rheology. The methodology uses the rheological data to infer microstructures of nanoparticles quantitatively, which is then incorporated into the conventional Hamilton-Crosser equation to predict the effective thermal conductivity of nanofluids. The methodology is experimentally validated using four types of nanofluids made of titania nanoparticles and titanate nanotubes dispersed in water and ethylene glycol. And the modified Hamilton-Zrosser equation successfully predicted the effective thermal conductivity of the nanofluids.