THE ELECTROMAGNETIC FIELD CALCULATION AND ANALYSIS OF LEVITATION MELTING WITH COLD CRUCIBLE

In this paper, using the quasi-3D coupled current method, the influences of structure of cold crucible, the power frequency, the electricity property of melt, the coil position and current on the electromagnetic field (EMF) and the levitation characteristics in the melting processes are analyzed. It is shown that in the processes of levitation melting with cold crucible, the power frequency and cold crucible structure are the decisive factors for the ability of magnetic flux penetrating into cold crucible. The magnetic flux density in cold crucible is reduced as the increasing of power frequency, and this tendency becomes stronger when the power frequency is higher than 100kHz. The segmented structure of cold crucible can reduce the induction eddy in itself effectively, and the higher the power frequency is, the better the result is. So, a cold crucible can be segmented into 16-20 sectors for high frequency electromagnetic field and/or 8-12 sectors for lower frequency one. It is also shown that the levitation force of melting charge is related to coil current as a parabolic function.

Vacuum Electromagnetic Levitation Melting and Undercooling of Peritectic Terfenol-D

For the first time, the undercooling of a magnetostrictive material a near peritectic Tb 0.27 Dy 0.73 Fe 1.90 alloy was realized by vacuum electromagnetic levitation melting and 60 K undercooling was obtained. There is one recalescence behavior during solidification of the undercooled melt,which can attribute to the priority precipitation of REFe 2 phase instead of REFe 3 phase, due to preferential nucleation and higher crystal growth rate of REFe 2 phase and the suppression of peritectic reaction. According to the crystal structural characteristics of REFe 2 and REFe 3, REFe 2 is a Laves phase intermetallics with MgCu 2 type structure, which has similar polytetrahedral structure with short range ordered structure in undercooled melt and has lower potential barrier for nucleation than that of REFe 3,which lead to the preferential nucleation of REFe 2 phase directly from the undercooled melt. Also, the similarity of structures between REFe 2 phase and undercooled melt leads to higher crystal growth rate of REFe 2 phase than that of REFe 3.

Effect of sample radius on stability of electromagnetic levitation melting

Based on the power dissipating model of spherical sample in free convection gas medium and the expression of input power, the model of temperature calculation for electromagnetic levitation melting sample was established. Considering the limitation of levitation force and levitation sample temperature,the principle of stability levitation zone computation was determined. A spherical sample （ThDy）Fe2 under the protection of argon gas was examined, and the effect of radius of levitation sample and perturbation on the stable levitation zone was investigated. The results show that longitudinal perturbation and transverse perturbation can shorten the length of stable levitation zone and the range of levitation sample radius. By increasing the sample radius and weakening the perturbation the electromagnetic levitation melting stability of sample can be improved.

Effect of Transition Metal on the Electrochemical Performances of Some Intermetallic Anodes for Lithium Ion Batteries

Some transition metal antimonides were prepared by levitation melting and subsequent ball-milling. The electrochem-ical behaviors of these materials as new candidate negative electrode materials in lithium ion secondary batteries wereinvestigated. It was found that they exhibited significantly larger volumetric capacity than carbon-based materi-als. The formation and composition of solid electrolyte interface (SEI) film were characterized by electrochemicalimpedance spectroscopy (EIS) and Fourier transform infra-red (FTIR) spectroscopy.

New Two-Frequency Method and Devices for Electromagnetic Levitation Drip- and Leakage-Free Melting of Metals

A new method and devices for the electromagnetic levitation melting of metallic samples with greater weights and axisymmetrically stabilized positions is presented in this paper.The new method is applying two homogeneous magnetic fields of different frequencies,whose field lines are in absence of a charge horizontally and reciprocally normal in order to exert electromagnetic lift forces also on the axis of the levitated sample.Therefore the weight of the charge can be increased and the charge can be drip- and leakage-free melted.The method can be used in a melting furnace with or without a cold protective wall,as well as for the coreless induction valves applied for flow rate control,e.g.in the continuous casting of molten metals.The applicability of the method was experimentally examined and proved by tests conducted with three types of laboratory setups.

Fabrication and thermoelectric properties of Yb-doped ZrNiSn half-Heusler alloys

Half-Heusler(HH)alloys constitute an important class of materials that exhibit promising potential in high-temperature thermoelectric(TE)power generation.In this work,we synthesized Zr_(1−x)Yb_(x)NiSn(x=0,0.01,0.02,0.04,0.06 and 0.10)HH alloys using a time-efficient levitation melting and spark plasma sintering procedure.X-ray diffraction showed that the samples were predominantly single phased,and that the lattice constant increased systematically with increasing Yb doping ratio.The doping effects of Yb on the thermoelectric properties were studied.It was found that Yb doping consistently decreased the electrical and thermal conductivities.On the other hand,the effects of Yb doping on the Seebeck coefficient were found to be non-monotonic.The magnitude of the Seebeck coefficient(n-type)was increased upon Yb doping up to x=0.02,above which Yb doping introduced notable p-type conduction.As a result,the room-temperature Seebeck coefficient of the x=0.10 sample became positive although the magnitude was not high.The thermoelectric figure of merit,ZT,reached a maximum of∼0.38 at 900 K for the x=0.01 sample.Selective doping on the Ni and Sn sites are necessary to further optimize the TE performance of Zr_(1−x)Yb_(x)NiSn alloys.

Preparation and Thermoelectric Properties of Zr_(1-x)Ti_xNiSn_(0.975)Sb_(0.025) Half-Heusler Alloys

Zr1-xTixNiSn0.975Sb0.025 （x=0, 0.15, 0.25, 0.5） half-Heusler thermoelectric materials have been prepared by levitation melt, melt spinning and hot pressing. X-ray diffraction analysis and scanning electron microscopy observation showed that nearly single phase half-Heusler compounds were obtained for the levitation-melted ingots. The effects of Ti substitution and grain refinement by melt spinning have been studied. It is found that both the Ti substitution on the Zr site and the grain refinement can reduce the lattice thermal conductivity and total thermal conductivity. The maximum figure of merit ZT value achieved is about 0.47, which is comparable with the previously reported value of ,-0.5 for Zr0.5Ti0.5NiSn.

Innovative Inductive Cold Crucible Configurations With Improved Efficiency

The inductive cold crucible is a very interesting tool for processing materials by magnetic field without pollution.It is more and more used in various areas like in aeronautic,photovoltaic,waste recycling industries and also for medical applications.As the cold cracible in its current state of art has a low energetic efficiency,the better comprehension of this process thanks to recently improved multiphysic modeling tools and experimental measurements gives some guidelines for experimenting new kinds of cold crucibles.These elements are presented in this paper, especially the numerical modeling and first tests operated on a'thin shaped cold crucible'which seems very promising concerning the efficiency improvement and also a better overheating of liquid charge.