MATERIALS PROCESSING WITHAMAGNETIC LEVITATION FURNACE

点击翻译按钮获取中文摘要

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.