Changbum Lee

Effect of Heating Rate on the Refining of Metallurgical-Grade Silicon during Fractional Melting

Silicon was purified using fractional melting (FM), which is a more effective refining method than fractional solidification. Changes in the silicon microstructure during FM were observed using a scanning electron microscope (SEM) and an electron probe microanalyzer (EPMA). Purity of each sample was investigated using inductively coupled plasma atomic emission spectrometry (ICP-AES) to determine the effects of various heating rates on the efficiency of FM. A refining ratio of 97.28% was the best result that could be obtained for the sample that was heated at a rate of 15 °C/min. For the samples that were heated below 1390 °C lower heating rate resulted in higher refining efficiency. Acid-leaching yielded 99.98% pure silicon samples after FM.

Refining of Silicon Using an Induction Furnace in the Fractional Melting Process

A new fractional melting process using an induction furnace and a centrifugal system has been developed for metallurgical-grade silicon (MG-Si) refining. An induction furnace enables rapid heating and therefore reduces the total refining process time. Impurity-rich liquids can be ejected effectively from the MG-Si by the centrifugal force induced by a motor. The impurity behaviors of the refined samples are observed by scanning electron microscope (SEM). The refining efficiency, which depends on sample size and centrifugal force, is evaluated using inductively coupled plasma atomic emission spectroscopy (ICP-AES) and inductively coupled plasma mass spectroscopy (ICP-MS). The purity of the refined silicon increases with the centrifugal force. The correlation between the centrifugal force and silicon purity is rationalized using the surface tension of impurity-rich liquids. In spite of the rapid heating rate by induction furnace, the MG-Si is refined and 96.7% of the impurities are removed at rotation speeds of 3000 rpm.

Analysis of Solid-Liquid Interface Behavior during Continuous Strip-Casting Process Using Sharp-Interface Technique

Continuous strip casting (CSC) has been developed to fabricate thin metal plates while simultaneously controlling the microstructure of the product. A numerical analysis to understand the solid-liquid interface behaviors during CSC was carried out and used to identify the solidification morphologies of the plate, which were then used to obtain the optimum process conditions. In this study, we used a modified level contour reconstruction method and the sharp-interface method to modify the interface tracking, and we performed a simulation analysis to identify the differences in the material properties that affect the interface behavior. The effects of the process parameters such as the heat transfer coefficient and extrusion velocity on the behavior of the solid-liquid interface are estimated and also used to improve the CSC process.