Papers by Author: Jae Young Jung

Abstract: The titanium reduction from titanium tetrachloride (TiCl4) by molten magnesium pool, called the Kroll process, is regarded as a well-known process for the commercial-scale production of titanium sponge. Purified titanium tetrachloride vapor reduced by magnesium, forms sponge titanium with generating excessive heal. The heal transfer phenomena in a Kroll reactor should be thoroughly understood for productivity and quality enhancement. In this work, a computational modeling method to describe the thermal behavior in the TiCl4 reduction reactor was investigated and validated with the measured temperature distribution in a 500kg titanium sponge-capacity pilot-scale reactor in terms of various reduction ratios. The approach model for heat flow phenomenon in a reduction reactor could be utilized as a tool to predict the influence of operating process parameters on the optimization of Kroll process.

Abstract: The electrolytic production of magnesium from magnesium chloride containing sodium chloride-rich melts has been studied using mono-polar cell, where originally designed in consideration of current efficiency and energy consumption. The magnesium was formed well at the surface of cathode and floated at the free surface of the molten salt, and chlorine gas was generated at the anode without any inverse reaction between the magnesium which is produced electrolysis process. The magnesium was collected about 200 g/hr by operating an optimized mono-polar cell with 500 A for 24 hours. The metallic magnesium produced from this study had a high purity with 99.92 %.

Abstract: Ti-45.5Al-2Cr-4Nb-0.4B alloy was cast by vacuum arc melting at high purity Ar atmosphere using high purity sponge Ti, granular Al (99.99%), flake Nb (99.9%), lump Cr (99.9%) and TiB2 (99.5%) and subsequently heat-treated to obtain a couple of microstructures, i.e. lamellar and near γ. The heat treatment consisted of annealing at a high temperature (1200 ~ 1330oC) of different phase fields for 24 hrs and stabilizing at 900oC for 4 hrs followed by air cooling. Fracture toughness was measured on the specimens with different microstructures at room temperature. The value of KQ of specimen with fully lamella structure was obtained as 18.68 MPa √m, much higher than that of specimen with near γ structure (11.84 MPa √m). It was also revealed that the KQ value was decreased as the annealing temperature decreased.

Abstract: High temperature deformation behavior of a Ti-Al intermetallic compound has been investigated in this study. Specimens with a near gamma and a lamella structure were obtained by performing heat treatment at temperatures from 1200 to 1330°C for 24 hr, respectively, and stabilized at 900°C for 4 hr followed by air cooling. A series of load relaxation tests has been conducted on these samples at temperatures ranging from 850 to 950°C to construct flow curves in the strain rate range from 10^-6/s to 10^-3/s. Strain hardening was observed even at the temperature of 950°C in both the near gamma and the lamella structures. Further aging treatment for 12 hr at the test temperatures has been found to cause negligible softening in both microstructures, providing the strong applicability of this alloy system in the temperature range.