MATERIALS PROCESSING WITHAMAGNETIC LEVITATION FURNACE

强梯度磁场允许反磁性材料克服重力悬浮。这种悬浮状态相当于微重力，因为磁力抵消了重力。因此，磁悬浮有望为材料加工提供一种新的技术。无容器熔炼是磁悬浮技术最实用和最有用的应用之一。磁悬浮炉的设计需要几个特定的功能：首先是在高磁场中加热样品。第二种是将炉安装在具有52 mm孔径的混合磁体中的受限狭窄空间中。第三个是观察悬浮样品在炉中的行为。CO_2激光加热炉是满足上述要求的加热方法之一。激光束不受磁场的影响，并且仅在样品上的局部照射允许在样品附近使用CCD相机。然而，激光炉在加热悬浮样品方面也有缺点。当样品被不均匀地加热并且样品的热导率非常小时，样品被部分加热，导致热分解。当样品的抗磁化率随温度升高而增加时，样品向上移动，失去水平稳定位置，与磁体孔壁接触。采用电炉进行均匀加热。为了观察样品在炉中的行为，使用了耐热内径镜。这种新的炉能够观察悬浮样品高达800℃的混合磁体。我们进行了环烯烃聚合物的无容器熔融实验，并成功地制备了球形样品。我们研究了磁悬浮条件下水中的传热行为，发现强梯度磁场显著抑制了热对流。

Strong gradient magnetic fields allow levitation of diamagnetic materials against the gravity. This levitation state is equivalent to the microgravity because the magnetic force counterbalances the gravity. The magnetic levitation is thus expected to provide a novel technique for materials processing. Containerless melting is one of the most practical and useful applications of magnetic levitation. The design of a magnetic levitation furnace requires several specific features : The first is to heat samples in high magnetic fields. The second is to install the furnace in a confined narrow space in the hybrid magnet with a 52 mm bore. The third is to observe the behavior of a levitating sample in the furnace. A CO_2 laser furnace is one of heating methods satisfying above requirements. The laser beam is not affected by magnetic fields, and the local irradiation just on a sample allows use of a CCD camera near the sample. Laser furnaces, however, have also disadvantages in heating a levitating sample. When a sample was heated inhomogeneously and thermal conductivity of the sample was very small, the sample was partially heated, causing thermal decomposition. When the diamagnetic susceptibility of a sample increased with increasing temperature, the sample moved upward and lost the horizontal stable position, resulting in a contact with the wall of a magnet bore.We developed a new magnetic levitation furnace. An electric furnace was employed to get homogeneous heating. For the observation of the sample behavior in the furnace, a heat-proof bore scope was used. This new furnace enabled to observe the levitating sample up to 800℃ in the hybrid magnet. We performed containerless melting experiments of a cycloolefin polymer, and succeeded in preparing a spherical sample.We investigated the heat transfer behavior in water under the magnetic levitation conditions and found that strong gradient magnetic fields considerably suppress thermal convection.