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.
The alignment behavior of a crystal has been investigated by numerical calculation and an in situ observation experiment with a process combining magnetic field imposition and sample rotation to form unidirectionally aligned crystals with a magnetic anisotropy of χ
c
< χ
a
. The experimentally observed alignment behavior of a polymeric fiber and its alignment time agreed with the numerically calculated ones. Crystal alignment under the out-of-step condition alternately repeats the alignment duration and the keeping of a constant duration, and finally the crystal aligns in a specific direction. The alignment time under the synchronous condition is longer than that under the out-of-step condition if the magnetic field intensity is constant. To reduce the alignment time, a strong magnetic field under the out-of-step condition is desirable in this process.
Synopsis : S45C carbon steel has been solidified under the simultaneous imposition of a static magnetic field in vertical direction and an alternating current having a horizontal component. Thus, an electromagnetic force was excited in the S45C steel sample and it affected structure formation during the solidification. The samples solidified under different electromagnetic conditions were cut and chemically etched for observation of the macro-and micro-structures. Solidified structure in the case neither the static magnetic field nor the alternating current was not imposed was dendritic structure. On the other hand, solidified structure under the simultaneous imposition of the 1 T static magnetic field and the alternating current of 80 A, 2 kHz was equi-axed structure. When the magnetic field intensity was decreased from 1 to 0.3 T, equi-axed structure and dendritic structure co-existed. As the frequency of the 80 A alternating current decreased from 2 kHz to 100 Hz under the constant magnetic field intensity of 1 T, solidified structure changed from equi-axed structure to dendritic one. Mechanism of the structure change is supposed to be breaking dendrites into pieces by convection induced in the sample by the non-uniform distribution of the electromagnetic force, which was intensified as the frequency of the alternating current increased.
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