Kazuhiko Iwai

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.

Analysis of Uni-Axial Alignment Behavior of Nonmagnetic Materials under Static Magnetic Field with Sample Rotation

A high magnetic field is a useful tool to control crystal alignment of non-magnetic materials such as metals, ceramics and polymers. However, uni-axial alignment of hexagonal crystals with a magnetic susceptibility of χc<χa, cannot be achieved under a static magnetic field, because the c-axis can be in arbitrary direction in the plane perpendicular to the direction of the magnetic field. For a uni-axial alignment of these materials, an application of the rotating magnetic field during a slip casting (process) has been proposed. In this study, both theoretical analysis and model experiment have been carried out for elucidation of crystal alignment phenomena under rotating magnetic field and for quantitative clarification of optimum operating parameters such as magnetic field strength and viscosity of the medium surrounding the crystals. It has been found that the alignment time was shortened by decreasing the magnetic field strength and/or increasing the viscosity of the surrounding medium. This relation is opposite in the case of crystal alignment under the static magnetic field. The result of the model experiment well agrees with that obtained by the theoretical analysis.

Microstructural, magnetic and magnetostrictive properties of Tb0.3Dy0.7Fe1.95 prepared by solidification in a high magnetic field

The microstructure evolution and magnetization and magnetostriction properties of Tb0.3Dy0.7Fe1.95 alloy solidified in a high magnetic field were investigated. A cellular microstructure was produced, with the grains highly aligned along the direction of the magnetic field. The (Tb,Dy)Fe2 phase was highly oriented, with its ?1?1?1? axis along the magnetic field direction. The easy magnetization direction of the alloy lay along the magnetic field direction. The magnetostriction at room temperature significantly increased to double that of the sample prepared without high magnetic field; in addition, a sharp rise in the initial magnetostriction at low fields was observed. Applying a high magnetic field during the solidification process is proposed as an effective route for fabricating ?1?1?1? oriented Tb?Dy?Fe compounds, and improving their magnetic and magnetostrictive properties.

Superconducting Magnetic Filter: Performance, Recovery, and Design

Due to the development of superconducting magnets, the magnetic filtration process is now undergoing its biggest evolution since its conception. In Japan, the first industrial superconducting magnetic filter has been successfully applied for factory wastewater treatment. Much effort in both theory and practice is needed to further contribute to the new developments of this high gradient magnetic filtration process. In this substantial review, we have collected the most important theoretical and practical data about magnetic filtration, its recovery and design to establish a good framework for further development of this amazing technology.

Alignment of HAp Crystal Using a Sample Rotation in a Static Magnetic Field

Formation of crystallographically orientaed hydroxyapatite (HAp) is one of the promising ways to utilize their anisotropic nature of chemical and biological properties. On the other hand, the development of super conducting magnet technology enables to introduce a high magnetic field which can control crystal orientation of non-magnetic materials with magnetic anisotropy. In this study, a high magnetic field and sample rotation are simultaneously imposed on the hydroxyapatite during a slip casting process in order to align its c-plane within a horizontal plane. From X-ray diffraction, it has been found that the HAp crystals in the sample treated with the magnetic field and the sample rotation were oriented to a particular direction in the slip casting process and it was enhanced by the subsequent sintering process, while the c-axis crystal orientation of the sample treated without the magnetic field and with the sample rotation was not observed before and after the sintering.

Structure control of hydroxyapatite using A magnetic field

A high magnetic field is a useful tool to control the crystal alignment of ceramic materials. In this study, a horizontal 10T static magnetic field was imposed on slurry containing hydroxyapatite (HAp) crystals under the horizontal mold rotation during slip casting process so as to introduce uni-axial alignment for some amount of crystals in the sample, and then it was sintered in atmosphere without the magnetic field. From X-ray diffraction, it has been found that the HAp crystals in the sample treated with the mold rotation under the magnetic field were aligned its c-axis to a particular direction.

The effect of design parameters on the magnetic field distribution around a cold crucible and the heat generation rate in it

To clarify the characteristics of cold crucibles, experimental and numerical analyses were conducted. An electrical circuit model for cold crucible was developed to evaluate the inductance corresponding to the coil voltage and the resistance corresponding to the heat loss in the charge, the coil and crucibles with different slit widths. It was found that a narrow slit width was favourable for decreasing the coil voltage under a constant coil current. The boundary element method was adopted for calculation of the three-dimensional magnetic field distribution around the cold crucible. The computed results agree well with the measured values. The heat generation rates in the charge, the crucible and the coil were estimated from the magnetic field calculated by the BEM. Increasing the radius of the charge and the inner radius of the crucible results in a higher energy efficiency and a decrease in the heat generation rate per unit volume in the charge. Local heating of the top part of the charge is available when the tops of the charge, the crucible and the coil are adjusted at the same level.

Formation of c-Axis Aligned Polycrystal Hydroxyapatite Using a High Magnetic Field with Mechanical Sample Rotation

It is possible to control the crystal alignment of non magnetic materials such as anisotropic ceramics and polymeric materials using a high magnetic field. However, alignment of the c-axis direction in hexagonal crystals, with a magnetic susceptibility of χc<χa=χb, is uncontrollable under a static magnetic field, because the c-axis can be in arbitrary direction in the plane perpendicular to the direction of the magnetic field. In this study, a high magnetic field and mold rotation are simultaneously imposed on a sample in order to align crystals parallel to the c-axis that has small magnetic susceptibility. This process was applied to hydroxyapatite crystals and a sample, in which the c-axis of the crystals aligned in a particular direction, was successfully obtained.

Bubble Rising Velocity in Sodium Chloride Aqueous Solution under Horizontal DC High Magnetic Field

In a continuous casting of steel, argon bubbles are injected from a nozzle to prevent nozzle clogging. However, this sometimes causes a problem of the entrapment of inclusions in a solidifying metal front. On the other hand, an electromagnetic brake has been utilized to control molten metal flow in the continuous casting process. Therefore, the understanding of bubble behavior in molten steel under the electromagnetic brake in which inertial force, Lorentz force and buoyancy force play an important role is essential for the optimization of the continuous casting process of steel. A water model experiment is one of the typical methods for direct observation of bubble behavior while it is impossible to use the water model experiment for this purpose because the Lorentz force is not induced by the bubble motion in the water. The Lorentz force is excited when a molten metal with low melting temperature is used instead of the water, however, the direct observation of the bubble motion is impossible because of ...

Different properties exhibited on the two typical crystal faces of hydroxyapatite in a simulated body environment

Hydroxyapatite is a main mineral constituent of hard tissues and is extensively used as a biomaterial in the medical field. Hydroxyapatite exhibits anisotropic chemical properties on its two typical crystal faces, the a-face and c-face, due to its hexagonal crystal structure. In polycrystalline bodies, such anisotropy can be enhanced by controlling the crystal orientation. Hydroxyapatite nanocrystals that constitute long bones also form a crystal oriented structure. Therefore, clarification of the difference between the properties of a-face and c-face in hydroxyapatite using in vitro experiments is useful to understand the structure and function of actual hard tissues. Hydroxyapatite ceramics with controlled crystal orientation were prepared by a slip casting method under application of a magnetic field. The fabricated hydroxyapatite ceramics had surfaces consisting mainly of a-face, or otherwise c-face hydroxyapatite. These hydroxyapatite ceramics were immersed into simulated body fluids to investigate the difference in bioactivity. The precipitation behavior observed on the surface of each hydroxyapatite ceramic was different. The thickness of the precipitate was increased and formed earlier on the HAp c-face compared to that on the a-face.