The crystal alignment behavior of bismuth particles in the presence of an imposed static magnetic field was examined in situ by X-ray diffraction. Because the c-plane of a bismuth crystal is aligned perpendicular to the direction of a magnetic field, the temporal variation in the (110) peak intensity of bismuth was measured by X-ray diffraction to determine the crystal alignment. The alignment time decreased as the magnetic field strength increased. This tendency is similar to that calculated for the relaxation time. The difference in the magnetic susceptibility between the magnetically easy and hard axes is the driving force for the crystal alignment, and aggregation of the bismuth particles decreases this driving force. The effective difference in magnetic susceptibility for aggregated bismuth particles was estimated by measuring the alignment time of the particles under magnetic fields of various strengths. The estimated effective difference in magnetic susceptibility generally increases with a decreasing magnetic field strength. Furthermore, the interference to crystal rotation caused by the interaction between the induced current and the imposed magnetic field is negligible in this study. To decrease the strength of the magnetic field required for alignment of crystals, the number of small particles should be reduced.
Crystal alignment of a Bi-10mass%Sn alloy solidified under different electromagnetic field imposing condition has been experimentally investigated in this study. Simultaneous imposition of a static magnetic field and an alternating current excited an electromagnetic vibration and it promoted nucleation, and resulted in decrease of undercooling, though imposition of the static magnetic field alone did not affect the undercooling. Furthermore, grain size of the solidified structure under the simultaneous imposition of the static magnetic field and the alternating current was smaller than that solidified with the magnetic field alone or solidified without the electromagnetic field imposition. XRD pattern of the sample solidified without the electromagnetic field imposition was similar to that of bismuth powder. On the contrary, only specific crystal plane peaks were observed when the electromagnetic field was imposed on the sample during the solidification. That is, crystal alignment of bismuth rich primary phase was achieved not only by the static magnetic field imposition alone but also the simultaneous imposition of the static magnetic field and the alternating current. However, degree of the crystal alignment solidified under the latter electromagnetic condition was slightly higher than that solidified under the former electromagnetic condition.
A force and/or torque are induced in a material under the imposition of a magnetic field. Their magnitudes are different from those acting on the surrounding materials because of the difference in their physical properties. Therefore, a magnetic field is a powerful tool for controlling a second phase in a mother phase such as particles suspended in a liquid. In this paper, we focus on two processes. The first one is a novel method of magnetic filtration in which schwertmannite particles in wastewater are controlled using a magnetic field. The second one is a refining process for a metallic alloy structure during solidification in which solid particles suspended in the liquid phase are controlled using the force excited by the simultaneous imposition of a magnetic field and alternating current.
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