Shigeo Asai

Recent development and prospect of electromagnetic processing of materials

Abstract Application of electromagnetic force to materials processing, so called Electromagnetic Processing of Materials (EPM) has been recognized as a cutting edge technology, especially in the fields of advanced materials processing. The backgroundto promote EPMis described. The present state of EPMis given through a brief introduction of several examples of the applications of a high frequency magnetic field, a DC magnetic field, DC magnetic and electric fields, and a traveling magneticfield. Furthermore, a high static magnetic field has been applied to generate compression waves in molten metals. As otherexamples of the application of a high static field, the crystal orientations in thin films in vapordeposition and electrodeposition processes and those in carbon fibers in a graphitization process are described. Finally the future view of EPM is revealed.

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

Abstract 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.

Alignment of Titania Whisker by Colloidal Filtration in a High Magnetic Field

Whisker alignment is one possible way in order to improve the properties of whisker reinforced materials. Susceptibility is very small in diamagnetic ceramics such as titania and alumina, etc.; therefore, the effects of a high-magnetic field on these ceramics had been generally neglected. Recently, superconducting magnet technologies have been developed and used for applications for such feeble magnetic materials. We demonstrate that the alignment of titania whiskers can be controlled by colloidal filtration of a well-dispersed suspension of the whiskers in a high magnetic field (10 T) when the direction of the magnetic field was perpendicular to the direction of the fluid.

The Effect of a Magnetic Field on a RAPET (Reaction under Autogenic Pressure at Elevated Temperature) of MoO(OMe)4: Fabrication of MoO2 Nanoparticles Coated with Carbon or Separated MoO2 and Carbon Particles

In this article, we present results of the RAPET dissociation of MoO(OMe)4 at 700 degrees C in a closed Swagelok cell. The reaction produces molybdenum dioxide nanoparticles (20 nm) coated with carbon (20 nm). We have also carried out the same reaction under an applied magnetic field of 10 T. This reaction yielded different products. It produces a mixture of comparatively larger (50 nm) molybdenum dioxide nanoparticles and separated uncoated carbon particles (20-30 nm).

Application of a high magnetic field in the carbonization process to increase the strength of carbon fibers

Carbon fibers produced from PAN (polyacrylonitrile) as a precursor are generally subjected to the three heat treatment processes of stabilization and carbonization followed by graphitization. Stabilized fibers were carbonized in a high magnetic field of 5 T imposed parallel to the fiber axis at a temperature of 1445 K and graphitized without a magnetic field at 2273 K. The tensile strength of these treated fibers is increased by 14% in comparison with those of no magnetic treatment. The reason why the imposition of the magnetic field could improve the strength of the fibers has been studied through microscopic observation of the fiber surface as well as a statistical analysis by use of Weibull distributions.

Application of high magnetic fields in inorganic materials processing

Application of high magnetic fields in materials processing has started. A high magnetic field enhances not only a Lorentz force in a weak electric current but also a magnetization force in non-magnetic materials. The main results obtained from the application of a high magnetic field to the processing of several materials is reviewed. These include the alignment of particles in a composite coating as an example of a Lorentz force and the separation of inclusions in a molten metal for mass transport using magnetic force. Orientation of crystals of non-magnetic materials using magnetization force is mentioned. The orientation was conducted in such processes as electro-deposition, vapour-deposition, solidification, baking, slip-casting and precipitation.

Effect of Process Parameters on Ultrasonic Separation of Dispersed Particles in Liquid

The effects of process parameters on ultrasonic separation of dispersed particles in a liquid using a standing-plane-wave field are discussed on the basis of experimental and theoretical results. Numerical solution of the equation of motion of a fine particle in a standing-wave field indicates that the inertia term can be neglected during conventional ultrasonic separation of fine particles. Analytical solutions for the particle speed, the position at which particles are coagulated, and the minimum power for separation, have then been derived to incorporate key process parameters. Experiments are carried out to observe transitional coagulation of polystyrene particles in an aqueous sugar solution with the incidence of standing ultrasonic plane wave, in terms of the density difference as well as the acoustic energy density exerted. Experimental results agree well with the theoretical predictions. The time required for coagulating and for the separation of particles is shortened in the case that particles coalesce.

Transient characteristics of convection and diffusion of oxygen gas in an open vertical cylinder under magnetizing and gravitational forces

Abstract A simplified model was derived for magnetizing force convection of oxygen gas and solved for transient characteristics of oxygen gas in a vertical open pipe. Oxygen gas in the cylindrical pipe initially flows out downward since oxygen gas is heavier than air. However, the magnetizing force works to attract the oxygen gas in the lower half of the vertical pipe, and the oxygen gas rises back to the central part of the pipe where the magnetic field is strongest. After a long time, all the oxygen gas in the pipe is replaced with air due to diffusion. This model represented moderately well the transient concentration of oxygen gas measured experimentally in a similar system.

Application of a strong magnetic field on materials fabrication and experimental simulation

Abstract A magnetic field has a lot of useful functions. We focus on two of these functions. The first one is alignment of crystals with magnetic anisotropy. We aligned hydroxyapatite crystals and graphite whiskers during slip casting process under the imposition of the high magnetic field. In the case of the hydroxyapatite crystals, the sample was rotated in the magnetic field. The second function we focus on is Lorentz force induced by an electrically conductive material motion submerged in the magnetic field. We experimentally simulated bubble motion in a liquid metal by using argon bubble in a sodium chloride solution.

Orientation of Fibers in Liquid by Ultrasonic Standing Waves

The orientation of fibers in a liquid irradiated with ultrasound is studied to realize the noncontact directional control of reinforcing fibers in the molten matrix of a composite material. The equations of translational and rotational motions of a fiber in a standing wave field are derived. The numerical solutions show the movement of the fibers at various initial positions and their stable positions and directions. Experiments are performed using polystyrene fibers of various lengths suspended in an aqueous sugar solution. Both numerical and experimental results indicate that polystyrene fibers shorter than one-fourth of the wavelength are constrained at the pressure node and are oriented in the direction perpendicular to that of wave propagation. On the other hand, fibers ranging from one-fourth to one-half of the wavelength have orientation either parallel to the direction of wave propagation at the pressure loop or perpendicular to that at the pressure node depending on their initial positions and directions.