钛酸钡-明胶复合含水弹性胶体电控力学行为

将无机钛酸钡颗粒分散到含水明胶体系中,在有、无电场作用下分别胶凝得到了两种类型的复合弹性水凝胶。通过对胶体的内部颗粒分散情况分析和压缩模量的测试,研究了该胶体体系对电场的响应。结果表明,两种类型的弹性水凝胶分散相颗粒的分布有明显不同,对电场的响应程度也有很大差异。分析认为,电场作用使颗粒有序分布于连续相的胶联网络中,并形成链状结构。颗粒的有序分布使胶体的压缩模量增强,对电场作用的响应程度增大,在钛酸钡质量分数为1.5% 时胶体压缩模量出现一个极大值,并对电场响应最强。      

Motion of paramagnetic particles in a viscous fluid under a uniform magnetic field: benchmark solutions

Numerical simulations of the two-dimensional motion of multiple paramagnetic particles suspended in a viscous fluid subjected to a uniform magnetic field are presented. Both the magnetic field and flow field can be described efficiently with simple series in local coordinates attached to each particle. The coefficients of the series can be obtained with fast convergence when only a few leading coefficients are treated implicitly. Numerical results for the flow field are validated by comparing the data with those given by an asymptotic solution for a pair of particles separated by a small distance. The numerical results of the magnetic field are validated by comparison with the solutions in bipolar coordinates. Simulations of the motion of multiple particles reveal interesting phenomena and shed light on the fundamental mechanism of particles clustering into a straight chain. The data presented in this paper can be used as a benchmark solution for verifying codes for simulating the motion of paramagnetic particles in a magnetic field.     

A device for measuring the concentration and dispersion quality ofmagnetic particle suspensions

A technique, called rheomagnetic measurement, for studying the concentration and orientation of magnetic particles through inductance measurement is presented. The particles are oriented in a predominantly extensional flow field, and, because they are magnetic, their orientation can be detected with a weak magnetic sensing field. Because flocs of magnetic particles orient differently in a flow field than primary particles do, this method can be useful in obtaining information about the particle flocculation aspect of dispersion quality. A magnetic sensing field can also be used to detect the particle concentration in a quiescent flow. Experimental data on the effects of particle concentration and milling for rod-like γ-Fe₂O₃ and plate-like Ba-ferrite suspensions are discussed. The results for Ba-ferrite magnetic markedly contrast with those for the rod-like magnetic particles but showed similarity with those for rod-like γ-Fe₂O₃     

Numerical simulation of chainlike cluster movement of feeble magnetic particles by induced magnetic dipole moment under high magnetic fields

In this paper, the motion of a chainlike cluster of feeble magnetic particles induced by high magnetic field is discussed on the basis of the results of numerical simulations. The simulations were performed on glass particles with a diameter of 0.8 mm; and the viscosity, applied magnetic field and magnetic properties of the surrounding medium were changed. In addition to the magnetic field and the difference in magnetic susceptibility between the particles and the surrounding medium, the obtained results indicate that the viscosity is an essential factor for the formation of the chainlike alignment of feeble magnetic particles. We also carried out simulations using glass particles with a smaller diameter of 0.1 mm. Chainlike clusters were produced similar to those of ferromagnetic particles formed in a ferromagnetic fluid.     

Magnetic forces on monocomponent toner

The magnetic field strengths and magnetizations of an assembly of magnetic (monocomponent) particles in a constant external field has been calculated. Due to the equilibrium configuration of the particles, forming chains or treelike structures, a one-dimensional approach has been employed. Using the dipole approximation, the problem can be cast as an eigenvalue problem, whose solution yields the magnetizations and field strengths, where the nonlinear interaction between particles has been explicitly accounted for in the formalism.     

Physical Simulation of Nonmetallic Particle Movement in Al Melt under Electromagnetic Field

Physical simulation is used to study the movement of nonmetallic particles in AI melt in electromagnetic field. It is found that the terminal velocity of particles in different Reynolds number range has different functions. By confirming drag force coefficient of nonmetallic particles with Reynolds number in the range of 0.2～10 and 10～25 respectively, two functions of terminal veIocity for spherical nonmetallic particles have been got accordingly, which provide a theoretical basis for separating nonmetallic inclusions from AI melt in electromagnetic field.     

Effect of combined magnetic field on the eliminating inclusions from liquid aluminum alloy

The effect of electromagnetic field on the removal of inclusions in the aluminum alloy was investigated. Primary silicon particles precipitating from the solidification of Al-Si hypereutectic alloy were regarded as inclusions. An experimental apparatus applied with both rotating magnetic field (RMF) and traveling magnetic field (TMF) was employed to study the distribution of silicon particles in Al-Si alloy under magnetic field. The results showed that combined magnetic field (CMF) consisting of RMF and TMF eliminated the silicon particles from the molten alloy. Compared with TMF or RMF, CMF increased the separating effectivity substantially. It was proposed that CMF provided a highly effective approach for metal purification.     

Numerical simulation of chainlike cluster movement of feeble magnetic particles by induced magnetic dipole moment under high magnetic fields

Abstract

In this paper, the motion of a chainlike cluster of feeble magnetic particles induced by high magnetic field is discussed on the basis of the results of numerical simulations. The simulations were performed on glass particles with a diameter of 0.8 mm; and the viscosity, applied magnetic field and magnetic properties of the surrounding medium were changed. In addition to the magnetic field and the difference in magnetic susceptibility between the particles and the surrounding medium, the obtained results indicate that the viscosity is an essential factor for the formation of the chainlike alignment of feeble magnetic particles. We also carried out simulations using glass particles with a smaller diameter of 0.1 mm. Chainlike clusters were produced similar to those of ferromagnetic particles formed in a ferromagnetic fluid.     

Vacuum electric discharge initiated by accelerated nanoparticles

A static breakdown induced by the impact of particles detached from a point anode in a strong electric field, corresponding to the athermal field evaporation threshold, was studied by field ion microscopy. Under these conditions, the particle size threshold for the vacuum discharge initiation decreases by one order of magnitude as compared to the case of flat electrodes and falls within a nanometer range of the average radius of bombarding charged particles. The threshold energies of particles initiating a static electric discharge also exhibit a significant decrease.     

Magnetic coupling properties of multiple metal wear particles for high-precision electromagnetic debris detection applications

The electromagnetic wear particle detector is one of effective method to monitor wear debris in lubricating oil for assessing the wear condition of mechanical equipment. However, the motion of wear particles, especially the aggregation behavior in both fluid field and magnetic field, may make the particle detector generate false wear signals. Therefore, to estimate the impact on the detection accuracy of wear debris by the particle aggregation effect, the magnetic coupling model of multiple wear particles is established for studying the magnetic coupling effect between adjacent metal particles. The research results show that the effect changes the total magnetic energy variation induced by the particles and then affects the amplitude of particle signal. Meanwhile, the variation degree is closely associated with the frequency of magnetic field of particle detectors. Overall, the aggregation of wear particles with the same magnetic properties (both ferromagnetic or non-ferromagnetic) leads to false alarms of particle detectors; and the aggregation of wear particles with different magnetic properties causes missing alarms of particle detectors. Meanwhile, increasing the field frequency may increases the probability of missing alarm failure of particle detectors.     

Particle characterization and separation by a coupled acoustic-gravity field

A coupled acoustic-gravity field is proposed as a novel external field for particle separation and characterization. When a standing plane ultrasound wave is generated, particles move to the node of the wave along the ultrasound force gradient. If the particles also undergo a sedimentation force, they aggregate at the equilibrium position, where these two forces are balanced. The equilibrium position, which is determined by the density and compressibility of a medium and particles, characterizes the particles. The local ultrasound energy, which is necessary for quantitative discussions, is evaluated by using a standard particle, the physical parameters of which are unambiguously determined; aluminum particles are used in the present study. The local ultrasound energy makes possible the determination of the compressibility of unknown materials. Nonporous particles of inorganic and polymeric materials, the particle sizes of which range from 3 to 100 microm, follow a derived model, suggesting that the local ultrasound energy and a derived model be valid. The proposed external field can be used for separation of particles having different acoustic natures.     

Effect of an electrostatic field on the optical properties of a cloud of dielectric particles

The optical properties of a cloud of anisotropic dielectric particles when the orientational distribution is made nonrandom by interaction with an electrostatic field are studied. Since the interaction energy is determined by the polarizability of the particles, a general expression for the polarizability of nonspherical particles is worked out. In particular, we investigated the response to the electrostatic field of two different dispersions whose component particles are built as clusters of four identical spheres. Although in one cloud the clusters were shaped as linear chains, and in the other cloud the clusters were shaped as squares, the optical properties of both dispersions as a function of the static field are rather similar. There are, however, noticeable ranges of size within which the optical response of the two kinds of particles is substantially different.     

Étude par microscopie et diffraction électroniques de particules pentagonales de nickel obtenu par réduction d'un sel en phase liquide

Nickel particles prepared by reduction of a nickel salt in organic liquid media were investigated by electron diffraction and electron microscopy. Various shapes were observed for these particles, the mean size of which is about 300 Å. In this paper we report on the structure and morphology of particles with a hexagonal elongated shape and a pentagonal section. From dark field and bright field images and from diffraction patterns it is shown that the particles have a decahedral shape with anisotropic growth in the Λ₅ direction.     

Stable oscillations and effective acceleration of charged particles at the electric field antinode of a standing electromagnetic wave

The phenomenon of the stable motion of charged particles at the electric field antinode of a standing electromagnetic wave is analyzed using the Hill equation derived from the equations of motion. The domains of parameters characterizing the field and charges are determined for the regime of stable oscillations. It is shown that the charged particles remaining at the electric field antinode can be accelerated to relativistic velocities.     

A simple method of forming small gold particles on a thin gold film

We have produced gold particles whose sizes range from several tenth nanometers up to about 1 μm. The small gold particles are distributed on a gold thin film of thickness 50–80 Å. The method for the formation is simple. We first evaporated the gold thin film, and then applied DC field along the film. When the field increases from 0 to 30 V, and the measured current increases from 0 to 650 mA, the particles were formed. The sizes and the distribution distances could be controlled by the applied DC field.     

取向磁场对钴颗粒填充硅橡胶磁流变弹性体动态黏弹性的影响

为了研究取向磁场强度对磁流变弹性体（MRE）动态黏弹性的影响规律及影响机制,采用溶剂热法制备球状钴颗粒,SEM和XRD表征结果显示,其粒径为1~2 μm,呈密排六方结构。以硅橡胶为基体,以钴颗粒为填充相,分别在0 mT、480 mT、1 154 mT取向磁场强度下制备MRE,并在不同工况下测试其动态黏弹性。实验结果表明,Co颗粒填充的MRE微观结构的有序性随取向磁场强度增大而增加,其储能模量G'、损耗模量G ″和磁流变效应也随之提高;当取向磁场强度增大到一定程度,由于有序结构趋于稳定,动态黏弹性随取向磁场的变化较小。     

Controlled formation of dielectric chain aggregates on material surfaces

This paper investigated the formation of chain aggregates from fine particles suspended in gas stream onto material surfaces under the action of electric field. The results showed that the shape of aggregate formed on material surface was greatly influenced by the field intensity and the surface condition of materials. In a weak electric field without corona discharge, particles tended to form clustered aggregates on a metal plate with smooth surface, but on a metal mesh and a porous alumina substrate, to form chain aggregate. On the other hand, in a corona discharge field, these surfaces were coated uniformly. Consequently, for forming chain aggregates on material surface, an electric field without corona discharge and a rough surface are necessary conditions. On rough surface, chain aggregates of dielectric particles or conductive particles grew from the protrusions of the surface and could form a rough and porous layer. When the external electric field was removed, the chain aggregates remained long time due to the Van der Waals forces. After sintered at proper temperature, the chain aggregates became fiber-like. The results indicate that the formation of chain aggregate can be controlled by electrostatic force, and sintering can be used as a method for increasing their mechanical strength.     

基于超声驻波场的水下颗粒操控研究

超声波产生的声辐射力可以实现对微小物体的操控。针对微米尺度颗粒在液体环境的操控问题,基于黏性介质中的声辐射力理论,建立由双凹球面聚焦超声换能器驱动下的水下颗粒操控模型。利用COMSOL软件仿真了模型的声场、声流场及颗粒操控动态过程,最后通过水下颗粒操控实验对仿真结果进行验证。研究发现,颗粒在水下操控过程受到声辐射力与声流曳力的共同作用,由声波干涉作用形成的局部驻波场主要依靠声辐射力将颗粒团聚在波节位置,但随着颗粒尺寸的减小,颗粒无法继续束缚,颗粒操控将由依靠声辐射力转变为声流曳力。此外声场强度的增加会增强颗粒操控的抗扰动能力。     

Electrorheological Fluids Based on Titania Particles Coated with Silica and Their Application in Smart Windows

The electrorheological (ER) fluids are colloidal suspension of highly polarizable particles in a non-conducting solvent.Chains of submicron-sized particles formed along an applied DC electric field by the so-called electrorheological effect.According to the obvious change of transmittance of the ER fluids in a DC electric field when the polarized particles arranged along the field,the model of smart window was proposed by sandwiching the ER fluids based on titania particles coated with silica between a pair of In-Sn oxide (ITO) coated glasses.The solar transmittance change as much as 48.0% was obtained with the wavelength of 500 nm at the maximum on applying and removing the electric field of 500V/mm.     

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。