In this study, cobalt nanopowder is fabricated by sonochemical polyol synthesis and magnetic separation method. First, sonochemical polyol synthesis is carried out at 220oC for up to 120 minutes in diethylene glycol (C4H10O3). As a result, when sonochemical polyol synthesis is performed for 50 minutes, most of the cobalt precursor (Co(OH)2) is reduced to spherical cobalt nanopowder of approximately 100 nm. In particular, aggregation and growth of cobalt particles are effectively suppressed as compared to common polyol synthesis. Furthermore, in order to obtain finer cobalt nanopowder, magnetic separation method using magnetic property of cobalt is introduced at an early reduction stage of sonochemical polyol synthesis when cobalt and cobalt precursor coexist. Finally, spherical cobalt nanopowder having an average particle size of 22 nm is successfully separated.

In this study, in order to improve the efficiency of n-type monocrystalline solar cells with an Alu cell structure, we investigate the effect of the amount of Al paste in thin n-type monocrystalline wafers with thicknesses of 120 μm, 130 μm, 140 μm. Formation of the Al doped p+ layer and wafer bowing occurred from the formation process of the Al back electrode was analyzed. Changing the amount of Al paste increased the thickness of the Al doped p+ layer, and sheet resistivity decreased; however, wafer bowing increased due to the thermal expansion coefficient between the Al paste and the c-Si wafer. With the application of 5.34 mg/cm2 of Al paste, wafer bowing in a thickness of 140 μm reached a maximum of 2.9 mm and wafer bowing in a thickness of 120 μm reached a maximum of 4 mm. The study’s results suggest that when considering uniformity and thickness of an Al doped p+ layer, sheet resistivity, and wafer bowing, the appropriate amount of Al paste for formation of the Al back electrode is 4.72 mg/cm2 in a wafer with a thickness of 120 μm.

In this study, modified catalytic chemical vapor deposition (CCVD) method was applied to control the CNTs (carbon nanotubes) growth. Since titanium (Ti) substrate and iron (Fe) catalysts react one another and form a new phase (Fe2TiO5) above 700℃, the decrease of CNT yield above 800℃ where methane gas decomposes is inevitable under common CCVD method. Therefore, we synthesized CNTs on the Ti substrate by dividing the tube furnace into two sections (left and right) and heating them to different temperatures each. The reactant gas flew through from the end of the right tube furnace while the Ti substrate was placed in the center of the left tube furnace. When the CNT growth temperature was set 700/950℃ (left/right), CNTs with high yield were observed. Also, by examining the micro-structure of CNTs of 700/950℃, it was confirmed that CNTs show the bamboo-like structure.

Translucent alumina is a potential candidate for high temperature application as a replacement of the glassor polymer. Recently, due to the increasing demand of high power light emitting diode (LED), there is a growing inter-est in the translucent alumina. Since the translucent property is very sensitive to the internal defect, such as voids insideor abnormal grain growth of sintered alumina, it is important to fabricate the defect-free product through the fabricationprocess. Powder injection molding (PIM) has been commonly applied for the fabrication of complex shaped products.Among the many parameters of PIM, the flowability of powder/binder mixture becomes more significant especially forthe shape of the cavity with thin thickness. Two different positions of the gate were applied during PIM using the disctype of die. The binder was removed by solvent extraction method and the brown compact was sintered at 1750oC for3 hours in a vacuum. The flowability was also simulated using moldflow (MPI 6.0) with two different types of gate.The effect of the flowability of powder/binder mixture on the microstructure of the sintered specimen was studied withthe analysis of the simulation result.

Pt has been widely used as catalyst for fuel cell and exhausted gas clean systems due to its high catalytic activity.Recently, there have been researches on fabricating composite materials of Pt as a method of reducing the amount of Pt due toits high price. One of the approaches for saving Pt used as catalyst is a core shell structure consisting of Pt layer on the core ofthe non-noble metal. In this study, the synthesis of Pt shell was conducted on the surface of TiO2 particle, a non-noble material,by applying ultraviolet (UV) irradiation. Anatase TiO2 particles with the average size of 20~30 nm were immersed in the eth-anol dissolved with Pt precursor of H2PtCl6·6H2O and exposed to UV irradiation with the wavelength of 365 nm. It was con-firmed that Pt nano-particles were formed on the surface of TiO2 particles by photochemical reduction of Pt ion from the solution.The morphology of the synthesized Pt@TiO2 nano-composite was examined by TEM (Transmission Electron Microscopy).

This paper describes the surface modification effect of a Ti substrate for improved dispersibility of the cat-alytic metal. Etching of a pure titanium substrate was conducted in 50% H₂SO₄, 50˚C for 1h-12h to observe the sur-face roughness as a function of the etching time. At 1h, the grain boundaries were obvious and the crystal grains weredistinguishable. The grain surface showed micro-porosities owing to the formation of micro-pits less than 1 µm in diam-eter. The depths of the grain boundary and micro-pits appear to increase with etching time. After synthesizing the cat-alytic metal and growing the carbon nano tube (CNT) on Ti substrate with varying surface roughness, the distributiontrends of the catalytic metal and grown CNT on Ti substrate are discussed from a micro-structural perspective.

In this study, gradient porous Al-Cu sintered body was fabricated by powder metallurgy processing. Al-Cu powder mixtures were prepared by low energy ball milling with various milling time. After ball milling for 3h, the shape of powder mixtures changed to spherical type with size of 100~500 . Subsequently, Al-Cu powder mixtures were classified (under 150, 150~300 and over 300 ) and compacted (20, 50 and 100 MPa). Then, they were sintered at for various holding time (10, 30, 60 and 120 min) in atmosphere. The sintered bodies had 32~45% of porosity. As a result, the optimum holding time was determined to be 60 min at and sintered bodies with various porosity were obtained by controlling the compacting pressure.