Thermophysical properties of moist disperse materials in a magnetic field

Results are shown of an experimental study concerning the thermal conductivity and the thermal diffusivity of grade KSK-2 silica gel and of Glukhovets kaolin with various levels of moisture content in a constant nonuniform magnetic field varying from 0 to 6000 Oe.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 24, No. 5, pp. 876–880, May, 1973.     

Drying of materials in magnetic high-frequency field

A theoretical analysis is made of energy relations which determine the efficiency of drying granular materials in a magnetic high-frequency field.     

Low temperature growth of carbon nanotubes in a magnetic field

We report on the growth of carbon nanotubes on a glass substrate at a low temperature of 450 °C by plasma-enhanced chemical vapor deposition in the presence of a magnetic field. The growth of carbon nanotubes can be realized at 450 °C only when a magnetic field is applied to the substrate. Carbon nanotubes cannot be grown in the absence of a magnetic field at the same temperature. An NH₃ plasma pretreatment significantly improved the uniformity of the grain size of the Ni catalyst under the magnetic field. The enhancement in the growth of CNTs at low temperature can be attributed to the magnetic moment pre-alignment of the ferromagnetic catalyst film under high magnetic field. A high emission current density of 20 mA/cm² was obtained at 6 V/μm and a stable emission current was observed. This method permits the growth of carbon nanotubes directly on glass substrate at much more reliable low temperatures for the fabrication of high-density field emitter arrays.     

Processing of non-ferromagnetic materials in strong static magnetic field

Static magnetic field processing of non-ferromagnetic materials has been of broad interest and been applied in such fields as drug delivery, colloid chemistry and engineering of materials containing particles. A ‘strong’ magnetic field refers to a ‘strong’ response from the manipulated material and can vary in definitions. The response is corresponding to a local interaction between the material and the local magnetic field, being influenced by the magnetic susceptibilities of the material and the surrounding/coated medium. By carefully designing the medium, a significantly ‘strong’ response from a weakly magnetic material can even be generated by a traditional magnet, i.e. magnetic flux density ∼0.01 T. Therefore, the ability to manipulate materials by using a magnetic field depends critically on the understanding of the principles of the magnetic properties of materials and their magnetic responses. This paper provides a critical discussion on the principles including magnetic field effect thermodynamics, magnetic energy, magnetic anisotropy and different magnetic forces during ’strong’ magnetic field processing of weakly magnetic materials (focusing on metallic materials). A series of case studies and the related magnetic field effect are subsequently integrated and discussed. Overall this review aims to provide a better understanding and efficient overview on the phenomenon principles in the field of magnetic field processing.     

Heat conductivity of thin-layer polymeric materials treated by a magnetic field

The influence of a constant magnetic field on the heat conductivity of thin-layer polymeric materials with a ferromagnetic filler at the stage of their hardening has been investigated. It is shown that multicomponent fillers and a pulsating magnetic field do a good job for obtaining polymeric materials possessing a high heat conductivity. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 3, pp. 583–586, May–June, 2008.     

Excitonic phase in a strong magnetic field. I. Phase diagram

The transition temperature of the excitonic phaseT _c is calculated for various band configurations in the mean field approximation.T _c depends on two quantities, the band gap (or the band overlap)2G between unstable Landau subbands andE ₀ , which denotes a configuration of those subbands relative to the Fermi energy.T _c takes the maximum value 0.45W _B , provided that the number of electrons equals that of holes(E ₀ =0) and the band overlap is2G=1.85W _B (W _B is the binding energy of an electron-hole pair). The region of finiteT _c is shown on the(G, E ₀ ) plane, which gives the excitonic phase region in a magnetic field.T _c is reduced by impurity scattering and vanishes at a critical electron lifetime _cr : / _cr =1.1k _B T _c0 forE ₀ =0 andG=0, whereT _c0 denotesT _c in the absence of impurities.     

Chromogenic smart materials

Smart materials cover a wide and developing range of technologies. A particular type of smart material, known as chromogenics, can be used for large area glazing in buildings, automobiles, planes, and for certain types of electronic display. These technologies consist of electrically-driven media including electrochromism, suspended particle electrophoresis, polymer dispersed liquid crystals, electrically heated thermotropics, and gaschromics.     

Crystal orientation of non-magnetic materials by imposition of a high magnetic field

From the view point of learning from the nature, the controlling of crystal orientation is accounted to be a major subject for materials processing. This paper reviews the researches on the crystal orientation by use of a high magnetic field and belongs to the category of researches for mimicking structures, namely the crystal orientation, which nature or living bodies are forming. Regarding to the crystal orientation, several methods such as unidirectional solidification and epitaxial growth and so on have been developed hitherto. On the other hand the magnetization force that is familiar with the force to attract iron to a magnet, has been recognized to be effective even in non-magnetic materials when those are placed under a high magnetic field, which has become rather conveniently available by developing super-conducting technologies in these days. In this paper, main results obtained when the imposition of a high magnetic field was accompanied to several materials processing such as electrodeposition, vaperdeposition, solidification, baking, slip-casting and precipitation, are reviewed from the view point of crystal orientation of non-magnetic materials.     

Crystal orientation of non-magnetic materials by imposition of a high magnetic field

From the view point of learning from the nature, the controlling of crystal orientation is accounted to be a major subject for materials processing. This paper reviews the researches on the crystal orientation by use of a high magnetic fieldand belongs to the category of researches for mimicking structures, namely the crystal orientation, which nature or livingbodies are forming. Regarding to the crystal orientation, several methods such as unidirectional solidification and epitaxial growth and so on have been developed hitherto. On the other hand the magnetization force that is familiar with the force to attract iron to a magnet, has been recognized to be effective even in non-magnetic materials when those are placed under a high magnetic field, which has become rather conveniently available by developing superconducting technologies in these days. In this paper, main results obtained when the imposition of a high magnetic field was accompanied to several materials processing such as electrodeposition, vaperdeposition, solidification, baking, slip-casting and precipitation, arereviewed from the view point of crystal orientation of non-magnetic materials.     

Analytic treatment of field diffusion into hysteretic magnetic materials

This paper reapproaches the very classic problem of the analytic study of nonlinear diffusion of electromagnetic fields in conducting media. Significant contributions that appeared in the literature on this topic are cited in order to highlight the interest and the efforts provided by the scientific community on this topic as well as the aim and the main results of this work. The capabilities of two analytic procedures for estimating the energy losses in magnetic materials with hysteresis are shown and discussed. One formulation reduces the full nonlinear diffusion problem to a linear problem through an optimization procedure and is suited for thick cores. A second formulation approximates the magnetic field behavior by means of polynomials and provides good results for thin laminations. Energy losses are evaluated for magnetic materials with different B-H relations operating in wide frequency intervals. A scalar Preisach model, numerically treated, is used as a benchmark and, finally, calculations are compared with experimental data provided by other authors.     

Grain boundary motion and grain growth in zinc in a high magnetic field

The motion of grain boundaries in zinc bicrystals (99.995 %) driven by the “magnetic” driving force was measured. An in situ technique for observations and continuous recording the boundary migration was applied. Planar symmetrical and asymmetrical $ \left\langle {10\overline{1} 0} \right\rangle $ tilt grain boundaries with rotation angles in the range between 60° and 90° were studied. The boundary migration was measured in the temperature regime between 330 and 415 °C. The mobility of $ \left\langle {10\overline{1} 0} \right\rangle $ tilt boundaries in zinc and its temperature dependence were found to depend on the misorientation angle and the inclination of the boundary plane. An application of a magnetic field during the annealing of cold rolled (90 %) zinc–1.1 % aluminum alloy sheet specimens substantially affected the texture and microstructure evolution. This effect is attributed to the additional magnetic driving force for grain growth arising due to the magnetic anisotropy of zinc.     

How to characterize soft magnetic materials by measuring magneticflux density in a rotating field apparatus

This paper deals with the characterization of the magnetic permeability of soft magnetic materials under a rotating magnetic field. The paper reviews the principle of the rotating-flux-density device used for measurement of flux density, then describes the mathematical method used to calculate permeability from the measurements. The method combines direct and inverse solutions and is based on a functional minimization sequence. An example demonstrates the validity of the method. Finally, the paper discusses the uniqueness of the solution and its sensitivity     

Colorimetric biosensing using smart materials

In recent years, colorimetric biosensing has attracted much attention because of its low cost, simplicity, and practicality. Since color changes can be read out by the naked eye, colorimetric biosensing does not require expensive or sophisticated instrumentation and may be applied to field analysis and point-of-care diagnosis. For transformation of the detection events into color changes, a number of smart materials have been developed, including gold nanoparticles, magnetic nanoparticles, cerium oxide nanoparticles, carbon nanotubes, graphene oxide, and conjugated polymers. Here, we focus on recent developments in colorimetric biosensing using these smart materials. Along with introducing the mechanisms of color changes based on different smart materials, we concentrate on the design of biosensing assays and their potential applications in biomedical diagnosis and environmental monitoring.     

Strong static magnetic field processing of metallic materials: A review

Metallic materials processing in an imposed strong static magnetic field (SSMF) has attracted widely attention in the last decade since a magnetic field of 10 T or higher becomes easily attainable. Fundamentals including magnetic energy, magnetic anisotropy and magnetic forces influence significantly the research and development of this technology by means of both scientific and engineering paths. The ability to control metallic materials processing depends crucially on the understanding of the fundamentals and subsequently the engineering of the strong magnetic field effects. This review provides a critical examination of different SSMF effects together with the fundamentals that can be used in liquid/solid metal controlling and the subsequent metallic materials preparation. These effects are discussed by integrating them into different technologies or experimental results and accompanied by theoretical considerations of the fundamentals. Comprehensive comparisons are then carried out for each series of SSMF effects. It is aiming to provide an overview of the recent progress in SSMF processing of metallic materials.     

Effect of a magnetic field on the hysteresis transitions during floating-zone crystal growth

The effect of a constant axial magnetic field on the thermosolutocapillary (TSC) convection in the floating liquid zone with an undeformed free surface under microgravity (MG) conditions has been studied. It is established that several stable flow regimes may coexist under such conditions in a certain range of parameters. The boundaries of transitions between various convection regimes under MG conditions with various Hartmann numbers have been determined. It is shown that the constant axial magnetic field suppresses TSC convection, so that the region of uncertainty decreases and shifts toward higher Marangoni numbers. The dependence of the structure and intensity of flow on the floating-zone length to radius ratio has been analyzed.     

新型智能材料:电活性聚合物的研究状况

电活性聚合物(electroactive polymer,EAP)是一种智能材料,具有特殊的电性能和机械性能。本文综述了不同类型电活性聚合物材料的国内外研究现状。按照作用机理的不同,电活性聚合物主要分为两大类:电子型和离子型。电子型EAP材料在直流电场作用下可产生诱导位移,但是需要较高的激励电场(>100V/μm);离子型EAP材料可以在较低电压下(1~2V)产生诱导弯曲位移,但是需要保持一定的湿润度,而且在直流电场激励下很难保持稳定的诱导位移。本文还介绍了电活性聚合物材料的应用领域和发展前景。由于其显著的电致伸缩响应,电活性聚合物被应用于驱动器和传感器,而且在仿生领域具有更广阔的应用。此外,透明度较高的EAP材料可被用于光学设备上。目前,电活性聚合物的应用还处于尝试阶段,但是,其独特的性能决定了这种材料具有不可估量的应用前景。     

Electrocodeposition of magnetic nickel matrix nanocomposites in a static magnetic field

The effect of an external magnetic field on the electrocodeposition of composites consisting of either Co or magnetite nanoparticles in a Ni matrix has been studied. An alkaline Ni pyrophosphate bath containing citrate was used. The magnetic particles were prepared by thermal decomposition (Co) or chemical precipitation (magnetite) and characterized by transmission electron microscopy, X-ray diffraction, dynamic light scattering, zeta potential and vibrating sample magnetometry measurements. The particle incorporation showed a distinct dependency on the orientation of an externally applied magnetic field. While the particle incorporation increased in a perpendicular field (perpendicular with regard to the electrode surface), it decreased in a parallel orientation. This result is explained with the dominating action of the magnetophoretic force. The structure and the properties of the Ni layers were significantly affected by the particle codeposition. A refinement of the Ni grains was found with increasing plating current density and as a result of the nanoparticle incorporation. The magnetic hardness and the Vickers microhardness of the films increased significantly due to the incorporation of the nanoparticles.     

On a new principle of a smart multisensor based on magnetic effects

In this paper, a new principle of a smart sensor is proposed, based on three different magnetic effects or operational modes, using the same sensor topology, which consists of a magnetic wire as sensing core, two coils as excitation or search means, and two electric contacts at the ends of the magnetic wire. The magnetic effects currently involved are magnetostriction, magneto-impedance and re-entrant flux reversal. Operating the sensor in these three different modes separately and sequentially, one can obtain the response of the sensor related to three different physical quantities, such as stress, temperature, and field. This paper refers to the first experimental results based on this principle, thus initiating the research work in this field. It has been experimentally observed that the total output of the sensor in each one of the three different modes is equal to the product of each corresponding physical quantity function concerned, provided that a given threshold of the ambient field and preloaded stress is used to bias the sensing element. Therefore, the three unknown parameters of stress, temperature, and field can be determined from a 3/spl times/3 matrix equation. Other magnetic effects may also be involved. Furthermore, other physical quantities may also be determined, such as position, pressure, load, etc.