Magnetorheological (MR) fluids: Principles and applications

In the relatively well established family of smart materials such as those based on ferroelectricity, piezoelectricity, magnetostriction, electrostriction and the shape memory effect, there resides another sub-set of materials known as ‘field responsive fluids’. These include magnetorheological (MR), magnetic liquids or ferrofluids and electrorheological (ER) fluids. This article provides a summary of the properties and applications and recent advances concerning MR fluids and devices. Applications of MR fluids in the automotive and other sectors of technology are also outlined.     

Magnetic carbonyl iron nanoparticle based magnetorheological suspension and its characteristics

Magnetic nano-sized carbonyl iron (CI) particle was prepared and adopted as an additive for micron-sized CI based magnetorheological (MR) fluid, in which the magnetic nanoparticle was fabricated via decomposition of pentacarbonyl iron (Fe(CO)₅). Magnetic property and morphology of the nanoparticle were confirmed via vibration sample magnetometer (VSM) and transmission electron microscopy (TEM), respectively. MR fluids, consisting of micron-sized CI and carrier fluid, were investigated under different external magnetic field strengths via a rotational rheometer. Their flow behaviors at a steady shear mode were examined with and without a nano-sized magnetic additive under magnetic field strength. The MR fluid with magnetic CI nanoparticle added demonstrated slightly higher yield behaviors, suggesting that micron-sized CI and magnetic CI nanoparticle particle were being oriented in magnetic field direction under applied magnetic field and with strengthened structure.     

磁流变材料及其在振动控制中的应用

磁流变材料是由悬浮于载体液中的可磁化粒子构成,它是一种新型的智能材料,在建筑结构防震和机械振动控制领域有较大的应用前景。在外加磁场的作用下,磁流变装置能产生连续可控的阻尼力对振动系统的振动特性进行控制。对磁流变材料的发展及磁流烃装置在振动控制中的应用作了介绍,并讨论了发展趋势。     

磁流变液机理及行为描述的理论研究现状

概述了解释磁流变液链化机理的3种理论即磁畴理论、相变理论和偶极矩理论,以及链化机理的定量分析和数值模拟.同时介绍了3种描述磁流变液行为的理论方法和途径即宏观本构描述、微观分析描述和数值模拟描述.上述磁流变液的基础理论研究对优化磁流变材料的配置和设计高性能磁流变装置具有重要意义.     

铁粒子多分散系统磁流变液的制备和性能研究

磁流变液是铁磁性颗粒分散到低粘度的油中形成的稳定的悬浊液。其扩散特性主要由颗粒本身的物性和颗粒间的相互作用而决定。为了更好的控制颗粒间的相互作用,我们加入同样物性,但尺寸更小的颗粒,以调控悬浊液的流动特性。研究显示,在高体积百分比的磁流变液中加入亚微米尺寸的铁颗粒可以显著改善流体在没有外加磁场情况下的流动特性。受范得华力影响,加入的小颗粒首先附着在大颗粒周围,形成组装体,组装体间范得华力较小,从而有效降低了流体粘度。流体的粘度随着小颗粒在大颗粒上附着的比例不同而变化。随着小颗粒的增加,流体中铁颗粒的体积百分比增加,从而提高了磁流变液在磁场中的屈服应力,增强了磁流变液的磁流变效果。     

磁性聚合物粉的制备及在磁流变液中的应用初探

采用化学镀的方法制备磁性聚合物粉,初步考察其在磁流变液中的应用。研究了在聚合物粉表面进行化学镀镍、钴的工艺条件,并对其物理性能和化学结构进行了表征。将磁性聚合物粉分散于硅油中制成磁流变液,结果发现不需加防沉剂,该磁流变液就具有较高的稳定性,其它磁流变性能也得到改善,有望解决磁流变液普遍存在的沉降问题。     

Magnetorheology of single-walled nanotube dispersions

Stable homogeneous aqueous colloidal dispersion of single-wall carbon nanotubes (SWNTs) was prepared by using sodium salt dodecylbenzene sulfateas dispersing agent. Both strain amplitude and frequency sweep modes were employed to investigate the effect of magnetic fields on their viscoelastic properties by using a parallel-plate rheometer. The experimental results demonstrated that such materials exhibit magnetorheology, whose storage modulus and loss modulus show an increasing trend with magnetic field. The network microstructure was employed to explain the effect of magnet field on the magnetorheological properties. In addition, these results are expected to develop novel SWNT based magnetorheological fluids.     

Non-Settling Super-Strong Magnetorheological Fluids

A magnetorheological (MR) fluid is generally called a suspension in which magnetic particles are dispersed in a non-magnetic medium. When an external magnetic field is applied, a pseudo-phase transition occurs within a short time to generate yield stress, and when the magnetic field is released, it returns to the suspended state. Due to these unique characteristics, it is classified as a smart material to be widely applied in various industries. High performance MR fluids require high yield stress and stability for long-term use. However, it is very difficult to improve performance and stability simultaneously due to the limited amount of magnetic particles in the suspension and particle sedimentation caused by the density mismatch between the suspending particles and the liquid phase. In this study, an MR slurry is developed that is completely different from the MR suspension, starting from the opposite concept. An innovative non-settling (i.e., permanently stable) magnetorheological slurry is successfully created that exhibits unprecedented ultra-high yield stress. This result is expected to be a turning point for applying MR fluids to more diverse industries. In addition, a simple fitting equation expressing the yield stress as a function of the particle volume fraction is proposed.     

静磁场下磁流变液微结构形态稳定性分析

作为磁偶极流体系统,磁流变液丰富的微结构形态及构成这些微结构的基本胞元决定了磁流变液在磁场-力场作用下的磁流变效应.对外加静磁场下具有单链、多链密排、正方、面心立方和体心立方胞元的微结构系统的磁势能进行了分析,结果表明具有体心立方胞元的微结构的平均磁势能较低,而具有正方胞元的微结构的平均磁势能较高.基于最小势能原理可知,静磁场下磁流变液中的颗粒容易形成具有体心立方胞元和多链密排胞元的微结构.     

磁性离子液体的制备与应用研究进展

磁性离子液体是一种新型的功能化离子液体材料,具有优良的热稳定性、优异的电化学性能、良好的溶解性能以及可回收性等特性,使其在萃取分离、反应催化和复合材料等领域具有较好的应用前景。对目前合成的磁性离子液体做了概述并根据构效关系对主要的磁性离子液体进行了分类。综述了磁性离子液体的主要制备方法,主要有一步合成法、二步合成法和辅助合成法。介绍了磁性离子液体在萃取分离、反应催化及碳纳米管复合材料领域应用研究进展。最后根据磁性离子液体在合成和应用中的不足做了展望。     

Magnetic particles stabilized by chemically adsorbed monolayers for use in functional fluids

Chemically adsorbed monolayers were applied to magnetic particle surfaces for preparing functional fluids. Fluorocarbon silanes were used to form the monolayers, as the methoxysilyl groups of fluorocarbon silanes can form a strong chemical bond with the surface of a magnetic particle without degrading its properties. Fluorocarbon oils were used as the carrier liquid because of their high affinity with the fluorocarbon group of the monolayers, enabling the particles to disperse easily in it. Also, fluorocarbon oils can sustain high temperature and low pressure. The functional fluids prepared using these materials showed magnetorheological characteristics and can be used under high-vacuum and/or high-temperature conditions like those encountered in space.     

A new class of magnetic fluids: bmim[FeCl/sub 4/] and nbmim[FeCl/sub 4/] ionic liquids

The responses to a magnet of two room-temperature ionic liquids containing tetrachloroferrate(III) ions, 1-butyl-3-methylimidazolium tetrachloroferrate (bmim[FeCl/sub 4/]) and 1-butyronitrile-3-methylimidazolium tetrachloroferrate (nbmim[FeCl/sub 4/]) are compared. Although their magnetic susceptibilities are similar, the observed responses are distinct from each other, suggesting that the response is determined not only by the magnetic susceptibility but also by the other factors including density, viscosity, and surface tension. The two magnetic ionic liquids constitute a new class of magnetic fluids that hold many attractive physical properties for practical applications.     

圆筒式磁流变离合器的设计分析

磁流变离合器是通过磁流变液的剪切应力传递转矩的器件.本文建立了圆筒式磁流变离合器的几何设计方法,得到了磁流变液传递的转矩和两圆筒间能产生磁流变效应的最小间隙的设计计算公式,为离合器的几何设计奠定了理论基础.研究结果表明:转矩可由外加磁场连续控制;选择磁饱和时高屈服应力和零磁场时低粘度的磁流变液材料,能使设计的离合器的尺寸小而紧凑.     

基础油对羰基铁磁流变液摩擦性能的影响

采用四球摩擦磨损试验机,在有外加磁场和无外加磁场条件下,考察了基础油对羰基铁磁流变液的摩擦系数的影响,记录了试验时间内摩擦系数随时间的变化曲线.结果表明,在较低载荷下,基础油的运动黏度值与磁流变液的流变性能有直接关系;基础油的摩擦性能决定了磁流变液的摩擦性能.     

磁场作用下磁流变液剪切性能的实验分析

本文研究了磁流变液的力学性能,制备了羰基铁粉体积分数为20%的硅油基磁流变液,观察了磁流变液在磁场作用下的微观变化,测试了磁流变液的剪切性能。实验表明,无磁场作用下,磁流变液为牛顿流体;在磁场作用下,随着剪切速率的增加,剪切应力趋于稳定,表观粘度呈现指数式下降,磁流变液具有剪切稀化效应,符合广义Bingham模型。磁流变液剪切应力和外加电流的依赖关系为:在电流较小时,剪切应力表现为指数增长,指数值约为1.5;随着外加电流的增大,剪切应力表现为线性增长,最终达到稳定值。     

纳米Fe_3O_4/Fe复合磁流变液的流变性

用化学共沉淀法合成了纳米Fe3O4粒子,平均二次粒径为51.2nm,比表面积为109.6m2/g。以合成的纳米Fe3O4粒子与羰基铁粉复合配制了纳米复合磁流变(MR)液,并测定了其流变性。结果显示:纳米复合MR液对温度比较稳定;复合MR液在接近零场的低磁场强度下表现为牛顿流体,随着磁场强度提高转变为非牛顿流体;反复加载或撤除磁场,具有"开/关"特性,响应迅速,施加磁场时的响应时间Δt约为50～100ms,撤退磁场时约为100～150ms。     

取向磁场强度对磁流变弹性体力磁性能的影响

为探究制备过程中取向磁场对MRE力磁性能的影响,制备了相同磁敏颗粒夹杂的两种不同基体特性的MRE,分别对其微观组织和材料的力学性能进行了系统研究。结果表明:随着取向磁场与硅油含量的增大,磁敏颗粒在MRE中的链状排布更加明显;所制备材料的磁致剪切模量与磁流变效应均随着取向磁场的增大而增大,并且其增加趋势随着硅油含量的增加更加显著;磁流变弹性体的损耗因子随着取向磁场的增加逐渐增大,而当取向磁场高于250mT后,损耗因子几乎不变。相关结果可对磁流变弹性体的设计制备提供理论依据。     

Birefringence of maghemite-based magnetic fluid in the highly concentrated regime

The transmitted light intensity of a series of ionic magnetic fluid samples based on maghemite nanoparticles was investigated using the typical birefringence experimental setup. The field dependence of the transmitted light intensity evolves from a peak-like profile to a typical second-order Langevin profile as the nanoparticle volume fraction reduces from 2.4% to 0.9% volume fraction. The onset of the peak-like profile as the nanoparticle volume fraction increases is accounted for by two points, namely the transmitted light first scales with a sine function and second the birefringence signal appears in the argument of the sine function. The observed negative differential transmitted light is explained as one brings the above-mentioned sine dependence into the nowadays used model for the analysis of birefringence in magnetic fluids.     

磁性液体在均匀磁场中的瞬态双热线导热系数的测试

将封有聚α-烯烃合成油基磁性液体的两玻璃管放置于磁场中,为消除磁场力、重力所引起的磁性液体自然对流的影响,消除端部效应,研制了磁性液体在均匀磁场中瞬态双热线导热系数的实验测量系统,经与蒸馏水、乙醇标准样品的导热系数测量比较,实验装置有较高的测量精度。实验测量了不同方向的均匀磁场对不同体积浓度的磁性液体导热系数的影响。结果显示,当磁场方向与热通量方向一致时,磁场显著强化磁性液体的导热系数,其导热系数随磁场强度的增加而近似线性增加,且体积浓度越大增加量越大;当磁场方向与热通量方向垂直时,磁性液体的导热系数随磁场强度的变化不明显。     

Improved magnetorheological honing process for nanofinishing of variable cylindrical internal surfaces

Improved magnetorheological honing process is developed for nanofinishing of variable cylindrical internal surfaces with better surface integrity. In the present work, finishing performance of existing magnetorheological honing process is enhanced. The present improved process consists magnetorheological honing tool having curved permanent magnet end surfaces. When magnetic field is analyzed using Ansoft Maxwell, the improved magnetorheological honing process results in uniform and higher magnitude of magnetic flux density over its magnetic tool curved end surfaces as compared to the tool having magnetic flat end surfaces. Therefore, an improved magnetorheological honing process has been developed with tool having curved permanent magnet end surfaces. During experimentation, surface roughness values Ra, Rq, and Rz get decreased by 76.28%, 76.67%, and 75.20%, respectively, with improved magnetorheological honing tool having curved end magnetic surfaces, while 47.97%, 46.24%, and 47.08% decreased with tool having flat end magnetic surfaces in same 60 minutes of finishing time. This results in enhancement of finishing performance of the present improved magnetorheological honing process in terms of reduced finishing time and ability to produce good surface integrity. Hence, the present improved magnetorheological honing process performance with tool having curved end magnetic surfaces is found as comparatively better than the finishing tool having flat end permanent magnetic surfaces.