Licheng Dong

Effect of a static magnetic field on the preparation of MnOOH and Mn3O4 by a hydrothermal process

In this paper, manganese oxides/oxyhydroxides were prepared by a low-temperature hydrothermal process in a static magnetic field. The products were analyzed with XRD, TEM, HRTEM and VSM. Single-crystalline nanowires (20 nm in diameter and 1 μm in length) of MnOOH were obtained under zero magnetic fields. However, some cubic particles of Mn3O4 were formed when a static magnetic field was applied. Furthermore, the quantity of Mn3O4 increased with the increase of the magnetic flux density. Quantitative thermodynamic calculation results showed that the magnetic Gibbs energy would change the direction of the chemical reaction to obtain Mn3O4.

Orientation of Magnetized MnBi in a Strong Static Magnetic Field

Solidification of Bi-4.5xa0wt pct Mn alloy was investigated in the presence and absence of a strong static magnetic field (SSMF). A cooling rate (R) of 60xa0K/min caused MnBi to orient with the SSMF, owing to the force moment and attractive force. The attractive force and magnetic gradient force induced formation of multilayered MnBi when R was 5xa0K/min. The magnetic gradient force was damped when R was 60xa0K/min. Low cooling rates favored the aggregation process.

An Electromagnetic Compounding Technique for Counteracting the Thermoelectric Magnetic Effect During Directional Solidification Under a Transverse Static Magnetic Field

An external direct current (DC) was introduced to counteract the thermoelectric magnetic effect during the directional solidification of Sn-10xa0wtxa0pct Bi alloy under a 0.5xa0T transverse static magnetic field. The results show that the single-side Bi segregation induced by the thermoelectric magnetic effect gradually becomes weakened, disappeared, and then reversed with the increasing current density of the external DC. Therefore, a new method for counteracting the thermoelectric magnetic effect during materials processing under the magnetic field was proposed. In order to verify this method, the absolute thermoelectric power of Sn-10xa0wtxa0pct Bi alloy and the internal thermoelectric current under the experimental conditions were measured and calculated, respectively. A 2D numerical simulation was established to simulate the evolution of the solid–liquid interface morphology, flow field, and composition segregation with the increasing current density of the external DC during directional solidification under a transverse static magnetic field. The present study not only facilitates the understanding of the effects of the forced flows on the directionally solidified microstructures and composition segregation, but also provides a new way for eliminating segregation and obtaining the higher-quality solidification structure by using the electromagnetic compounding technique.