Papers by Author: Kwang Ho Kim

Abstract: Aluminum dross is forms at the surface of the molten metal as the latter reacts with the furnace atmosphere and it was an unavoidable by-product of the aluminum production process. However, it has not been sufficiently recycled yet. Approximately 95% of the Al dross was land filled without innocent treatment. Therefore, Al-dross is positively necessary to recycling. The purpose of this study is to investigate the compressive strength of Selective Catalyst Reduction (SCR) prepares using recycled Al-dross and compared commercial SCR catalyst. Recycled Al-dross was as support material to increase strength. As to experimental procedures, Al dross was classified according to its size. The recycled Al dross was made into SCR catalyst by mixing with WO₃, V₂O₅, and TiO₂. After V₂O₅-WO₃-TiO₂-Al₂O₃ SCR strength was measured by Universal Testing Machine (UTM). And then NOx removal activity of V₂O₅-WO₃-TiO₂-Al₂O₃ SCR and commercial SCR catalyst were observed by MR(Micro-Reactor).

Abstract: Anodic oxide films were formed on titanium using an electrolyte solution containing phosphoric acid for dental implants by an electrochemical method. The parameters of the oxidation process were current density and electrolyte concentration. The micro structural morphology, surface roughness, thickness of the oxide layer and the behavior of voltage-time curves were examined. The results show that the surface roughness, porosity size and the thickness of the oxide layer showed similar trends as the process parameters were changed. The surface morphology of the samples was observed for different current densities at a constant electrolyte concentration. The pore size, thickness and roughness of the anodic oxide films are directly proportional to the maximum voltage and the slope of the voltage to time transient (dV/dt) curves during the growth of the galvanostatic anode oxide film on plate type Ti.

Abstract: CrN-based multi-component coatings were deposited by a hybrid coating system combining the arc ion plating (AIP) and sputtering technique. In this work, comparative studies on microstructure and mechanical properties of microhardness and wear behaviors among Cr-C-N, Cr-Si-N, and Cr-Si-C-N coatings were systematically conducted. Adding carbon and silicon atoms into CrN coatings had large effects on microstructural change and mechanical properties of CrN coatings. The hardness value of Cr-Si-C-N coatings showed about 44 GPa, while those of Cr-Si-N and Cr-C-N coatings were 34 and 23 GPa, respectively. The average friction coefficient of CrN-based coatings decreased from 0.65 to 0.4 with the incorporation of silicon and carbon content.

Abstract: Monodispersed and nano-sized Ni powders were synthesized from aqueous Ni sulfate hexahydrate (NiSO4· 6H2O) inside sucrose as a nonionic polymer network by using wet chemical reduction process. The influence of a nonionic polymer network on the particle size of the Ni powders were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA). The Ni powders obtained by adding of sucrose were nearly spherical in shape and seemed to be nano-sized, typically in the range of 100 nm with not being agglomerated. As the sucrose content increased, the particle size of Ni powders steeply decreased and reached the minimum value, however, the particle size increased again with a further increase of sucrose content. This is believed to be due to the pore size of the swollen polymer network. As a result, the particle size of the Ni powders prepared by the reduction inside polymer network was strongly dependent of the sucrose content.

Abstract: The Platinum catalysts on the carbon nanotubes(CNTs) supports of various diameters were prepared by wet impregnation method using H2PtCl6 precursor. The samples using 100nm, 15~20nm, 10~15nm and 5~10nm diameters of CNTs and carbon nanofibers(CNFs) are named Pt/t- CNFs, Pt/MWNTs20, Pt/MWNTs10 and Pt/MWNTs5, respectively. The effects of CNTs diameter on the Pt particle size and distribution were investigated by the means of powder XRD and TEM observation. In addition, the electro-catalytic characteristics for methanol electro-oxidation were estimated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. The average size of Pt particles increases as follows; Pt/MWNTs10 < Pt/MWNTs5 < Pt/MWNTs20 < Pt/t-CNFs. The electro-catalytic characteristics of Pt/MWNTs10 and Pt/MWNTs20 are found to be superior in comparison with the others. For preparation of the most effective supported Pt catalyst, the optimum diameter of CNTs support in the range of 10-20nm, is needed.

Abstract: High-temperature oxidation behaviors of Ti-Al-Si-N and Ti-Al-N films were comparatively investigated in this work. Two kinds of Ti0.75Al0.25N and Ti0.69Al0.23Si0.08N films were deposited on WC-Co substrates by a DC magnetron sputtering method using separate Ti3Al(99.9%) and Si(99.99%) targets in a gaseous mixture of Ar and N2. Si addition of 8 at.% into Ti-Al-N film modified its microstructure to a fine composite comprising, Ti-Al-N crystallites and amorphous Si3N4, and to a smoother surface morphology. While the solid solution Ti0.75Al0.25N film had superior oxidation resistance up to around 700
, the composite Ti-Al-Si-N film showed further enhanced oxidation resistance. Both Al2O3 and SiO2 layers played roles as a barrier against oxygen diffusion for the quaternary Ti-Al-Si-N film, whereas only the Al2O3 oxide layer formed at surface did a role for the Ti-Al-N film. Oxidation behavior and mechanical stability of the films after oxidation were compared between two films using instrumental analyses such as XRD, GDOES, XPS, and scratch test.

Abstract: In order to improve adhesion strength between TiN coatings and WC-Co substrate, two kinds of interlayer of Co and Ti were pre-deposited before TiN coating process. Thickness and postannealing effects of each interlayer on the adhesion property were investigated through scratch test in this work. Introduction of thin Ti interlayer largely enhanced the adhesion strength between TiN coatings and WC-Co substrate in scratch test. The critical load, Lc2 increased from 64 N without Ti interlayer up to 130N with Ti one of ~ 0.15
thickness. However, post-annealing of TiN/Ti/WCCo system at high temperature of 600 reduced the critical load again. The Ti interlayer caused a deficit of Co content in WC-Co substrate during annealing through diffusion of Co element into Ti interlayer. The reduction of critical load after post-annealing was believed due to diminution in mechanical properties of the substrate derived from the Co deficit in WC-Co substrate. On the other hand, introduction of thin Co interlayer of ~ 0.027
thickness also increased the critical load up to 84 N and improved failure mode, but did not reduce the critical load even after annealing, rather increased it. And, any Co deficit of the substrate was not found after annealing for TiN/Co/WC-Co system.

Abstract: Generally, solution nitriding (nitrogen permeation) is not applied to ferritic stainless steel, which has low nitrogen solubility in the ferrite phase. This study has investigated phase changes, nitride precipitations and hardness variations of Fe-11Cr-0.1Ti (409L) ferritic stainless steel following nitrogen permeation and tempering heat treatments. The strong affinity between nitrogen and Ti enabled the permeation of nitrogen to 409L ferritic stainless steel. The nitrogen-permeated surface changed to a martensitic phase with a hardness range of between 520 and 585Hv, depending on the nitrogen permeation temperature and time, while the surface nitrogen content was about 0.04%~0.05%. When tempering the NPSA (solution annealing after nitrogen permeation) treated specimen at 450 °C, a maximum hardness of 550Hv was obtained, probably due to the precipitation of very fine rod and square type titanium nitrides, while the minimum hardness of 365Hv was obtained at a tempering temperature of 650°C, owing to the precipitation of coarse TiN.