A magnetic transducer with a permanent magnet

Conclusions At present the development of magnetic transducers of the type described is in its infancy.The investigation carried out cannot be considered as exhaustive, since a complete evaluation of the possibilities of the new system can only be made after considerable experimental material has been accumulated and the theory developed still further. The outlines method of designing magnetic transducers, however, may be found useful.     

Surface effects on the mechanical properties of nanoporous materials

Using the theory of surface elasticity, we investigate the mechanical properties of nanoporous materials. The classical theory of porous materials is modified to account for surface effects, which become increasingly important as the characteristic sizes of microstructures shrink to nanometers. First, a refined Timoshenko beam model is presented to predict the effective elastic modulus of nanoporous materials. Then the surface effects on the elastic microstructural buckling behavior of nanoporous materials are examined. In particular, nanoporous gold is taken as an example to illustrate the application of the proposed model. The results reveal that both the elastic modulus and the critical buckling behavior of nanoporous materials exhibit a distinct dependence on the characteristic sizes of microstructures, e.g. the average ligament width.     

Microtensile tests of mechanical properties of nanoporous Au thin films

The mechanical properties of nanoporous Au (NPG) thin films were investigated by uniaxial microtensile tests. Such mechanical parameters as Young’s modulus, tensile strength, and breaking strain were obtained from the recorded force–displacement curves. Through observations on the microstructure and fracture surface morphology of the samples after the tension tests by a scanning electronic microscope (SEM) and an optical microscope, we analyzed the physical mechanisms underlying the mechanical behavior of NPG thin films. It was found that the NPG films exhibit mechanical properties distinctly different from its bulk counterpart.     

Microstructure and magnetic properties of the permanent magnet material FeAIC

The relationship between microstructure and magnetic properties of a series of permanent magnets based on the composition Fe₉₀Al₈C₂ (wt%) has been studied using X-ray diffractometry and transmission electron microscopy. We have used various fabrication methods, heat treatments and alloying elements in order to optimize the magnetic properties of these alloys and the properties obtained were found to compare favourably with commercially available cobalt steels.     

放电等离子烧结制备块状纳米晶SmCo5烧结磁体

采用放电等离子烧结（SPS）技术制备了致密纳米晶SmCo5烧结磁体，研究了磁体的结构和磁性能。X衍射结果表明，烧结磁体具有CaCu5结构，说明SPS过程可以获得稳定的1：5相。TEM观察显示，磁体由平均晶粒尺寸约为30nm的1：5相构成。室温时磁体的矫顽力高达2208kA/m，而剩磁比高达0，7，说明在纳米晶之间存在强烈的晶间交换耦合作用。烧结磁体具有良好的高温性能，773K时的矫顽力为456kA/m，矫顽力温度系数β为-0．212％/K。     

Characterization of magnetic dispersions: Rheological, mechanical and magnetic properties

The rheological properties of magnetic oxide dispersions have been studied, varying dispersing agent, magnetic oxide, milling time and oxide loading level. Magnetic properties of handcoats as well as mechanical and magnetic properties of free films prepared from these dispersions have also been studied. The results show a good correlation between rheological, magnetic and physical properties. As a result, rheological measurements can be a convenient and powerful tool for evaluating the dispersibility of a magnetic oxide and the efficiencies of formulation components such as dispersing agents. Rheological measurements can also determine optimum oxide loading, optimum dispersant level, and optimum milling time. Results show that for a given oxide, there exists an oxide-binder ratio where mechanical, rheological and magnetic properties are optimized. This optimum suggests the existence of a well-defined oxide-binder structure. Results at oxide loadings lower and higher than the optimum can be explained, respectively, on the basis of individual particles with no long range structure formation and on the basis of possible clustering of particles.     

ALD functionalized nanoporous gold: thermal stability, mechanical properties, and catalytic activity

Nanoporous metals have many technologically promising applications, but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only 1 nm thick oxide films can stabilize the nanoscale morphology of np-Au up to 1,000°C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO(2) ALD coatings. Our results open the door to high-temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications.     

SmCo6.6Nb0．4块状纳米晶烧结磁体的结构和磁性能

采用SPS技术制备了纳米晶SmCo6．6Nb0.4烧结磁体，研究了磁体的结构和磁性能．X衍射结果表．4明烧结磁体具有TbCu7结构，说明SPS过程可以获得稳定的1：7相．TEM观察显示，磁体由平均晶粒尺寸约为30nm的1：7相构成．室温时磁体的矫顽力高达2．8T，而剩磁比高达0．74，说明在纳米晶之间存在强烈的晶间交换耦合作用．烧结磁体具有良好的高温性能，矫顽力温度系数β为-0.169％/K。     

Mechanism of reversible effect of hydrogen on mechanical properties of steel

By analyzing the experimental data on the influence of gaseous hydrogen on physicomechanical properties of steels, we consider the mechanism of reversible hydrogen embrittlement, focus our attention on the processes of surface interaction, and explain the surface-active properties of hydrogen. The low solubility, high mobility, and affinity to metals characterize hydrogen as the most efficient surface-active element with respect to metals. We propose to consider the ability of hydrogen to concentrate in certain microvolumes of metal as the main point for explanation of the mechanism of reversible hydrogen embrittlement. The actual behavior of the material is determined by hydrogen localized in defects of the structure, but its total concentration cannot characterize the degree of danger of hydrogen degradation. Depending on the deformation conditions, the interaction of a metal with hydrogen either promotes plastic flow or leads to selective fracture. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 4, pp. 29–36, July–August, 1999.     

Micro-patternable nanoporous polymer integrated with microstructures for molecular filtration

This paper proposes a facile method to fabricate nanoporous microstructures by a photo-patternable SU-8 photoresist, to serve as a molecular filter in microfluidic systems. The fabrication process involves solvent-controlled nanoporous structure formation combined with standard photolithography steps for microstructure fabrication. The self-formed nanoporous morphology embedded inside the microstructure exhibits a sufficient mechanical strength and eliminates complex processes or protocols for integration/assembly of nano-?and microstructures. Field emission gun scanning electronic microscopy (FEGSEM) images showed the fabricated nanoporous morphologies with embedded nanogaps of about 6-10?nm. Atomic force microscopy (AFM) images also depicted a clear difference on the degree of porosity between the solvent-controlled SU-8 and the standard resist. Fluorescent dyes, namely Rhodamine-B and Rhodamine-6G, were employed to estimate the diffusivity of the fabricated SU-8 based nanofilter and demonstrated that the Rhodamine based fluorescent molecules can penetrate these nanosized filtration structures. The fabricated nanofilter was capable of providing a molecular weight cut-off range up to 70?kDa, estimated roughly for a molecule with a diameter of 6-10?nm. This simple process provides a novel way to integrate the nanofiltration capability into microstructures while maintaining a sufficient mechanical strength for molecular level filtration in lab-on-chip (LOC) systems.     

3D magnetic printing of bio-inspired composites with tunable mechanical properties

In the natural composites, the reinforcement particles are subtly organized into complex structures in matrix, and its various microstructures endow the biomaterials with a variety of excellent mechanical behaviors. Among the various reinforcement building blocks used in biomaterials, short fibers are the most ubiquitous reinforcement elements. Unfortunately, because of the limitation of fabrication technique, replication of these fiber-reinforced biological composites can be extremely difficult in practice. In this paper, we developed a fiber assembly 3D printing process, which can manipulate the orientation of fibers during 3D printing procedure. Benefiting from this technology, the reinforcement particles were manipulated remotely and the arrangement of reinforcement particles with higher degree of freedom was achieved. Subsequently, based on the herringbone-modified helicoidal architecture of mantis shrimp, the bio-inspired composites with various microstructures were reconstructed by 3D magnetic printing. In addition, the influence of microstructure type and parameters of bio-inspired composites on the properties of composites was studied systematically, and the quantitative relationship between microstructure and properties of the composites was established. The results show that the impact resistance and compression resistance of the composites can be significantly improved by the simple internal microstructures design, and the regression model established in this article can be used for accurate prediction of composites properties and the reliability is higher. In a word, this study opens a new route for the design of composites with unusual features.     

分子沉积膜的力学特性研究

在金衬底上制备了分子沉积膜。用原子力显微镜研究了它的摩擦力,结果表明沉积膜能明显地减小摩擦力。用纳米压痕仪研究它的纳米力学特性,结果表明在金表面沉积一层膜后,弹性模量、硬度和载荷都减小,说明分子沉积膜能改善金衬底的纳米力学特性。     

Synthesis, magnetic properties and formalism of magnetic properties of high-quality refined Nd2Fe14B powders for permanent magnet devices

Stable Nd2Fe14B powders of refined grain size of 0.1–1.0 μm were prepared using a combination of the rapid quenching (of the melt into thin ribbons), mechanical attrition and grain-surface passivation (or surface hardening) and coating by a thermally rigid, adhesive and corrosion-proof material in air. The ribbons (of 15–30 μm thickness) were cut, crushed and milled under H2 gas at approximately 1 bar and room temperature to give hydrided Nd2Fe14BHx, x≲5, flakes of 1–5 μm sizes, which are brittle and easily obtained in powder form by high-energy ball milling. The interstitial H atoms in the hydride sample were desorbed by slowly heating (5°C min-1) the sample between 25 and 600°C in N2 gas (which helps the desorption of the H atoms without decomposition of the sample) in a reactor and then pumping off the total gas at 600°C. The H-desorbed specimen, when annealed at 600–800°C under a dynamic vacuum, results in a refined powder, showing a characteristically high remanence, Jr of 9–12 kG, together with a high intrinsic coercivity, Hci, of 10–28.3 kOe, depending on the size and surface structure of the grains. This powder is highly pyrophoric and catches fire in open air but can be stabilized by passivating and coating the grain surfaces with a mixture of carbon, AIN and Nd2O3 by milling the mixture in a suitable organic liquid (to allow the additives to adhere the sample without excess oxidation) followed by annealing at an elevated temperature in N2 gas at approximately 1 bar. In this process, the separated Nd2Fe14B grains acquire a thin nitride–carbide (probably amorphous) stabilized surface passivation layer which prevents further oxidation of the sample in air at room temperature. The passivation layer, in combination with a thin film of the Nd-rich intergranular phases, if any, peculiarly appears to be non-magnetic compared with the main ferromagnetic Nd2Fe14B phase. It keeps the ferromagnetic Nd2Fe14B grains separated and thus inhibits mixing between the local magnetic lines of forces confined to them. As a result, they behave like ideal single-domain particles and therefore exhibit a reasonably improved Hci value, without a significant decrease in the high Jr or the high saturation magnetization Ms which are useful for the high-energy-density magnets and related devices and components. The results are modelled and discussed with microstructures, magnetic properties, thermal stability and loss, if any, in the mass of the specimens during exposure to ambient atmosphere. This revised version was published online in November 2006 with corrections to the Cover Date.     

Permanent magnetic materials with low reversible temperature coefficient

Permanent magnets made from SmCo5exhibit negative reversible change in magnetization with increasing temperature, typically of the order of 0.04% per deg C between -100 and +200°C. For certain special applications in precision instruments such as gyros and accelerometers, it is highly desirable to improve this property. Earlier studies have shown that ternaries of the composition RxSm1-xCo5(where R = Gd, Ho, Er, or Dy and x is nearly 0.4) exhibit improved temperature compensation. A systematic investigation of the temperature coefficients of magnetization of a number of quaternaries in the temperature range 100-400 K has been undertaken. The effect of variation of the cobalt concentration on the temperature compensation of one typical system has also been examined. The results indicate that good temperature compensated magnets can be synthesized with composition Sm0.6Gd0.3DY0.1Co5(α = 0.0056 at 200-300 K; 0.002 at 300-350 K and ∼0 at 350-400 K). Slight variation of cobalt concentration does not have significant effects on the temperature compensation. Lattice constants, saturation magnetization, and the theoretical energy products of a number of quaternaries are also reported.     

各向异性不同含量羟基铁粉颗粒/磁性聚氨酯泡沫的可控力学和声学性能

聚氨酯泡沫(PUFs)被广泛应用于飞机、车辆和许多其他设施中的噪声控制。本文研究的磁性聚氨酯泡沫(MPUFs)是一种新型智能泡沫,其力学和声学特性可通过磁场控制。采用一步全水法制备了添加羟基铁粉颗粒的磁性聚氨酯泡沫(CIPs/MPUFs),在发泡过程中施加一定强度的磁场,磁颗粒沿着外加磁场方向排列成链状有序结构,得到各向异性磁性泡沫。在外加磁场作用下,CIPs/MPUFs内部磁性颗粒发生迁移,材料的力学和声学性能发生改变。实验研究了外加磁场对CIPs/MPUFs力学性能和吸声性能的影响。实验结果表明:在外加磁场条件下,CIPs/MPUFs的储能模量和损耗模量随磁性颗粒含量的增加而增加;CIPs/MPUFs的平均吸声系数变化幅度在1%~7%之间,当颗粒含量为5wt%、制备磁场为200 mT、测试施加1.5 A电流时,CIPs/MPUFs的平均吸声系数增加幅度最大,为6.5%。      

Some magnetic and mechanical properties of fibre-reinforced nickel and nickel-iron alloys

Composites containing tungsten wires reinforcing nickel and nickel-iron alloy matrices have been fabricated by a filament winding-electroplating technique and a considerable improvement in the tensile strength was achieved relative to the unreinforced matrix. The presence of the fibres was found to have a significant influence on the magnetic properties of the composites measured in the direction of the fibre axes. In composites having a matrix with a negative magnetostriction, the maximum permeability decreased with increasing volume fraction, V _f, and was also dependent on the fibre diameter and the magnitude of the magnetostriction. In cases where the matrix had a positive magnetostriction the maximum permeability was observed to increase with increasing V _f, reaching a peak value at V _f0.1. It was suggested that the presence of stresses induced in the matrix during cooling from the heat-treatment temperature, due to the difference in the thermal expansion between the fibre and matrix, could explain this magnetic behaviour. By theoretical considerations, the peak was shown to coincide approximately with the volume fraction at which the maximum, uniaxial elastic stress was expected to form in the matrix. Above this volume fraction the uniaxial and transverse stresses became sufficiently high to cause plastic deformation in the entire matrix leading to the observed fall in the maximum permeability, although in all cases the value remained above that shown by the unreinforced matrix.     

Fabrication of nanoporous networks with tunable triangular cavities with a molecular template

Herein we report a systematic construction of highly regular 2D triangular nanoporous networks by host-guest interaction. All molecular building blocks have the same four carboxylic acids groups, while the lengths of the blocks increase from 1.94 nm up to 2.90 nm. By using a suitably designed guest molecule, called coronene, we have fabricated steady porous network with tunable size of the edge length of the triangular pores of 3.2 nm, 3.7 nm and 4.1 nm at the liquid-solid interface. The results clearly demonstrate this approach may be also an efficient method to form the porous structures stable and controllable both in shape and in size.     

Processing and properties of nanoporous hydroxyapatite ceramics

Method for fabrication and properties of nanoporous hydroxyapatite (HA) ceramic were described in the present work. The nanoporous hydroxyapatite was derived from nano hydroxyapatite powder and polyvinyl alcohol (as a pore former). The HA nanopowder was obtained from vibro-milling for 4 h. The nanoporous ceramics were sintered at 1200 °C. Properties of the nanoporous ceramics were investigated using various methods. Average porosity of the final product was found to be 64.6 ± 1.4%. Open and interconnected pores were obtained with an average pore size less than 100 nm, confirming the nanoporous structure of this ceramic. A high bending strength of 14.7 ± 3.2 MPa for the nanoporous ceramic, shows significant promise as a potential bone repairing material.