Papers by Author: Jae Kyo Yang

Abstract: The influence of relative density on the thermal stability of CNTs-dispersed Al2O3 nanocomposites has been investigated by using thermogravimetric analysis (TGA). TGA revealed that the onset temperature for weight loss increased with an increasing sintering temperature and CNT content. By taking account of the XRD and SEM results, it is suggested that the weight loss is caused by a decomposition of CNTs phase by oxidative atmosphere. The difference in thermal stability was explained by the porosity effect on the oxidation and decomposition behavior of CNTs, because the open pores promote the chemical reaction and gas flow of reactants.

Abstract: The microstructure and electrical conductivity of CNTs dispersed Al2O3 nancomposites depending on the powder processing and CNTs content were demonstrated. The composite powders with homogeneous dispersion of CNTs could be synthesized by a catalytic route for direct formation of CNTs on nano-sized Fe dispersed Al2O3 powders. The sintered nanocomposite using the composite powder with directly synthesized CNTs showed homogeneous microstructure and enhanced elelctrical conductivity. The influence of powder processing on the properties of sintered nanocomposites was discussed by the observed microstructural features.

Abstract: Fe/MgO nanocomposites, which are applicable to high frequency electronic devices, were fabricated by ultrasonic spray pyrolysis and selective reduction processes. Transmission electron micrographs showed that nano ferromagnetic Fe particles were isolated by MgO insulating matrix. With the increase of the reduction temperature, the particle size and saturation magnetization of the nanocomposites increased, which resulted in the decrease of the coercive force and the increase of the permeability. Furthermore, the ferromagnetic resonance peak of the nanocomposites was not observed up to 9 GHz.

Abstract: As the oxygen permeation flux of La0.7Sr0.3Ga0.6Fe0.4O3-δ (LSGF) membranes is lower than commercial membranes, we coated the nano porous La0.6Sr0.4CoO3-δ (LSC) particles to enhance the oxygen permeation flux. The nano porous LSC particles were synthesized in an advanced process to increase the volume fraction of nano pores by ultrasonic spray pyrolysis. The synthesized LSC particles consisted of nano sized primary particles and pores. They also had remarkably high surface area (22 m2/g). It was found that the LSGF membrane coated by the nano porous LSC resulted in significant improvement in the oxygen permeability.

Abstract: Au coated γ-Fe2O3 nanoparticles were prepared by the changing of surface charge of Au and γ-Fe2O3 nanoparticles with pH. Well Au coated γ-Fe2O3 nanocomposite particles developed in the range between isoelectric point of Au and that of γ-Fe2O3 nanoparticles. Immobilization of glutathione (GSH), crystalline polypeptide containing mercapto group, was successfully performed on the well Au coated γ-Fe2O3 nanocomposite particles. Properties of nanoparticles and GSH immobilized Au/γ-Fe2O3 were characterized by UV-vis, LPA, XRD, and TEM.

Abstract: A layer consisting of La0.6Sr0.4CoO3-d particles with inner nano-pores is coated on the La0.7Sr0.3Ga0.6Fe0.4O3-d oxide to improve the surface reaction resulting in high oxygen permeability. The La0.6Sr0.4CoO3-d particles with inner nano-pores are synthesized by an ultrasonic spray pyrolysis method. The permeated oxygen contents from air to helium gas were measured using gas chromatography after the synthesized particles were coated on the La0.7Sr0.3Ga0.6Fe0.4O3-d oxide by the conventional screen-printing. The results demonstrated that the reactive free surfaces of the nano-pores are an important factor in determining the oxygen permeation for application such as gas separation membrane and ceramic fuel cell.