Papers by Author: Kwang Chul Jung

Abstract: Metal sulfide (MeS) is well known and widely used an additive for enhancing machinability, but the problems is extremely sensitive to reaction with moisture and thermal decomposition during sintering. In this study, micron or nano size compound powders of FeS were produced by mechano-chemical process. The machinability was also evaluated at the metal sulfide added sintered steel. Compared with the MnS additive, addition of the FeS powders to the iron resulted the formation of the sintering materials containing a spherical shape of pore, partly remained FeS rich-phase in iron matrix. Relative machinability behavior of sintering materials was investigated by the lathe manufacturing. Mechanical properties of sintering material with 1.2%FeS powders were improved rather than its using MnS powders.

Abstract: To improve the fracture strength and wear resistance of WC-Co cemented carbide, various technologies have been developed related producing the nano crystalline. There have been extensive studied conducted to retard grain growth during liquid phase sintering. However, when this inhibitor is added by simple mixing, a micro-pores forms during sintering In this study, WC-Co nanocrystalline powders with grain growth inhibitor in the site were prepared by MTP (Mechano-Thermic carburizing Process) to minimize this formation of micro pores and to retard grain growth effectively during sintering. In addition, then the phase and grain size of WC-Co nanocrystalline powders were evaluated according to the condition of MTP.

Abstract: As the electrodes of secondary battery are made with sulfide composite powders, excellent electrode system of environmental non-toxicity and with high specific energy density and low material cost can be obtained. In this study, the (Fe, M)S2 composite powders was synthesized by mechanochemical processes (MCP) in order to improve of the cycle life in bettery. The formation of pyrite phase appreared at the case which adds nickel, but it was not observed in the case where the transition metal was does not add but the transition metal such as cobalt, molybdenum was added in stead. From charge-discharge test results, the initial discharge capasity of (Fe, Ni)S2 electrode was 845 mAh/g. The initial discharge capasity of (Fe, Co)S2 electrode was 500mAh/g, but it showed a better cycle perfoemance than the case where the diffrent transition metal was added.