Papers by Author: Jong Hyun Lee

Abstract: Several micrmeter-size Cu powders were synthesized by a simple and green wet-chemical process. Moreover, changes in particle size are examined with different synthesis temperatures and amounts of gelatin reducing agent. All powder samples synthesized in this study were indexed as a Cu phase despite the synthesis was performed in air. The particle size decreased with increasing the gelatin content in principle, indicating that gelatin is an effective agent in suppressing aggregation between synthesized particles. The smallest average particle size was 1.53 μm.

Abstract: SnO₂ powders were prepared using a modified polyol synthesis method and subsequent calcinations. Well-dispersed spherical 2SnO∙(H₂O) particles could be synthesized at room temperature through the modified polyol method using tin (II) 2-ethylhexanoate as the precusor, 1,2-propanediol as the solvent, PVP as the capping agent, and sodium borohydride as the reducing agent. The 2SnO∙(H₂O) nanoparticles agglomerated to form larger particles during the drying step, and most of these larger nanoparticles coalesced with one another. Finally, these 2SnO∙(H₂O) nanoparticles were successfully transformed into the SnO₂ phase by calcination for 1 h at 500 °C.

Abstract: Spherical Bi particles were fabricated through a polyol synthesis using a zinc bismuth(III) carbonate precursor, and the effects of processing temperature and time on the morphology and composition of the resulting particles were evaluated. It was determined that longer processing times or higher processing temperatures resulted in the gradual conversion of as-formed bismuth hydroxide into spherical elemental bismuth via bismuth glycolate. The temperature for the effective synthesis of spherical Bi particles under these conditions was 230 °C

Abstract: The transient liquid-phase sintering behavior of micro-Zn/nano-Sn-3.0Ag-0.5Cu (SAC) pastes was examined at a temperature of 190 °C as a function of the volume of ultrafine (~12.4 nm) SAC nanoparticles present. SAC nanoparticles have lower melting point drop than the bulk SAC particles. Although successful linkage at the interface between all Zn particles was not accomplished in all sintered samples, the number of linkages increased marginally with a decrease in the SAC content. As a result, the electrical resistivity of the sintered samples decreased with the decrease in the SAC content; however, the resistivities were still very high in all samples. Microstructural observations indicated that the observed results were mainly due to the short lifespan of the liquid phase caused by the coarsening of SAC nanoparticles during heating.

Abstract: Tin nanoparticles were synthesized through compulsive reduction using a Tin(II) 2-ethylhexanoate precursor, and the effect of reductant (sodium borohydride) amount on the size distribution of the particles was surveyed. Issues caused by the absence of a capping agent (polyvinyl pyrrolidone) were similarly examined. An excessive amount of dissolved sodium borohydride caused variations in the tin nanoparticle sizes, from a few nanometers to several tens of nanometers. The formation of abnormally large particles was attributed to the vigorous coagulation among smaller tin particles. In the tin nanoparticles synthesized without polyvinyl pyrrolidone, an exceptionally wide size distribution was observed owing to irregularly coagulated and aggregated large particles.