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The influence of electron beam irradiation on the catalytic activity of Pt/C for polymer electrolyte membrane fuel cell (PEMFC) was investigated using a 2.5 MeV electron beam. Pt catalysts supported on Vulcan XC-72R were synthesized by a polyol method using chloroplatinic acid hydrate (H2PtCl6·6H2O) as a Pt precursor. Before and after e-beam irradiation, all synthesized catalysts were characterized by various physical and electrochemical techniques. Crystallinity change before and after e-beam irradiation was investigated by X-ray diffraction (XRD). Transmission electron microscopy (TEM) was utilized to examine the particle size of Pt. Pt loading amounts were determined by thermal gravimetric analysis (TGA). The catalytic activity for PEMFC was measured by both a half cell test and full cell test. The results show that the proper e-beam irradiation significantly improved the electrochemical activity of Pt/C. (Received March 3, 2014)

keyword : PEMFC, Pt/C catalyst, e-beam, electrode

Metal atoms in rare-earth oxides (REOs) have a different electronic structure, where the unfilled 4f orbitals are shielded from interactions with the surrounding environment by the full octet of electrons in the 5 s2 p6 outer shell. Thus, these metal atoms would have a lower tendency to exchange electrons and form a hydrogen bond with interfacial water molecules. In this study, we have prepared (10+x)CeO2-30Na2O- (60-x)SiO2 (in mol%, x=0,5,10) glass system and examined the characterization of hydrophobicity behavior of crystallized Na2O-SiO2 glass containing CeO2. In addition, we confirmed the change in the wettability of the glass surface due to change the heat treatment time for crystallization and a change amount of CeO2. It was found that the contact angles of crystallized specimens (CNS glasses) got higher by about 40~50° by the addition of CeO2 and 0~18 hr-heating, compared with the specimens without CeO2 and 0~8 hr heat treatment. In order to explain the hydrophobicity behavior of CNS glasses, surface structure through FT-IR ATR ranging from 3000 cm-1 to 4000 cm-1 was examined. The band characteristic of -OH bridges at about 3200 cm-1, 3400 cm-1 and 3600 cm-1 are attributed to the existence of hydrogen bond. At 3700 cm-1, as the intensity of peaks (0.006~0.036) gets higher, the contact angles increase by 51° to 73°. (Received July 1, 2013)

keyword : glasses, crystal growth, wetting, scanning electron microscopy, SEM, CeO2

The work was made to investigate how the amount of glass particles affected the microstructure and magnetic properties of Fe-6.5 wt%Si alloy subjected to metal injection molding (MIM) technique. The high-temperature sintering treatments at 1350 ℃ for 2 hrs were carried out on the present samples containing various glass particle contents, such as 0, 1, 2, and 3 wt%. Microstructural observations revealed that the ferrite grain size of the sample without glass particle was much larger than those with glass particle. This was attributed to the uniform incorporation of glass particles which inhibited the grain growth of the ferrite phase during sintering. Moreover, both the size and fraction of the micro pores present in the sintered microstructures were increased by the addition of glass particles which was dissolved completely due to lower melting temperature of glass particles (~800 ℃) than the sintering temperature (1350 ℃). As the amount of glass particle increased up to 2 wt%, the eddy current loss decreased considerably while the hysteresis loss increased slightly after sintering, causing the reduction in the total magnetic loss of the present sample. It is also observed that the appreciable amount of glass particle appeared to be segregated locally within the micro pores when the amount of glass particle exceeded 2 wt%. Consequently, the glass content of 2 wt% would be most beneficial for enhancing the magnetic properties of Fe-6.5 wt%Si alloy sample via MIM. (Received May 13, 2014)

keyword : magnetic materials, sintering, magnetic properties, scanning electron microscopy, metal injection molding

We report on the effect of solvent type on the synthesis of Sn nanoparticles via a modified polyol method at room temperature in an ambient atmosphere. In the synthesis, tin (II) 2-ethylhexanoate, sodium borohydride (NaBH4), and polyvinylpyrrolidone (PVP) were used as a precursor, reducing agent, and capping molecule, respectively. Transmission electron microscopy confirmed by that the Sn nanoparticles obtained in 1,5-pentanediol were smaller (9.2 nm) than 10 nm for an average diameter and had a narrow size distribution. We also observed that the average diameter of Sn nanoparticles obtained in 1,5-pentanediol increased slightly with a decreasing PVP molecular weight. The result can explain the synthesis mechanism in which Sn ions are not only preferential in forming a complex with the PVP but also preferentially reduced in a solvent, and the movement of reduced particles is influenced by the PVP. Consequently, an increase in PVP molecular weight may more effectively inhibit coalescence between nanoparticles, which are surrounded by a longer molecular chain and are highly viscous in the synthesis solution, all of which finally results in a decrease in the average particle size. On the basis of Fourier-transform infrared spectroscopy result, we demonstrated that the PVP on the Sn surface could be removed using an acetone/methanol mixed solvent. (Received January 20, 2014)

keyword : nanostructured materials, powder processing, surface treatment, transmission electron microscopy, TEM, Sn nanoparticles

This study investigated the effect of powder granulation on the mechanical properties of sintered alumina ceramics. 2 wt% MgO was added to enhance the sintering process, and the effect of Y2O3 addition was investigated at various sintering temperatures (1450 ℃, 1550 ℃ and 1650 ℃) with a granulation process. The sintered density, flexural strength and Vicker``s hardness were analyzed according to the amount of Y2O3 addition and the sintering temperature. The sintered density and mechanical properties of the sintered specimens with powder granulation was higher than the as-received commercial Al2O3 powders because granule powders uniformly filled the mold. The mechanical properties of strength and hardness for the sintered Al2O3 specimens increased with addition of Y2O3 up to 1 wt%, and then decreased beyond that. The 1 wt% Y2O3-added Al2O3 samples (sintered at 1650 ℃) had the maximum flexural strength of 363.53 MPa and a Vicker``s hardness of 20.1 GPa. (Received April 9, 2014)

keyword : ceramics, sintering, mechanical properties, X-ray diffraction

One of the candidates for metallic interconnects of solid oxide fuel cells is a ferritic stainless steel, Crofer 22 APU. By grinding with different grit SiC grinding paper, Crofer 22 APU specimens with various surface roughness were prepared. The specimens were then thermally cycled by heating them to 1,073 K at a rate of 10 K min-1, holding at 1,073 K for 25 h, and cooling to 298 K at a rate of 10 K min-1. Examinations of the resulting microstructures, measurements of the area specific resistances (ASRs), and analyses of the atomic percentages of elements via energy dispersive X-ray (EDX) spectroscopy were performed. The particle size decreased as the grit number of the grinding paper used to grind the sample surfaces increased. A polished sample exhibited the smallest particle size. Plots of ln (ASR/ T) vs. 1/ T for the samples ground with grit 80 and grit 400 and the polished sample after 40 thermal cycles exhibited good linearity. At the same measuring temperature, the ASR increased as the surface of the sample became rougher. This suggests that the polished Crofer 22 APU is better than those with rougher surfaces for application as interconnect of SOFC. (Received May 9, 2014)

keyword : fuel cells, oxidation, microstructure, X-ray diffraction, ferritic stainless steel interconnect

The effect of insulators in a Czochralski furnace on the power consumption and the oxygen content in the melts as well as in the Si ingots was investigated with no radiation shield by using a commercial software, Femag-Cz. Location and thickness of the insulator were changed. The calculated results with no radiation shield were compared to those with radiation shield. The top insulator showed better results than the top-side and bottom insulators for the power consumption and Si melt temperature in the calculations of separately installed insulators. The oxygen content in the melt decreased with increasing the thickness of insulators for the top and top-side insulators. Installation of insulators at the three locations at the same time, the power consumption and the oxygen content in the melt and the Si ingot were improved compared to those of separately installed insulators. (Received March 10, 2014)

keyword : semiconductors, crystal growth, solidification, computer simulation, Czochralski

Ni-YSZ (Y2O3-stabilized ZrO2) core-shell structures were prepared by a high-speed mixing method, starting from Ni particles of three different average sizes of 0.2, 0.4, and 1.8 μm. The Ni-YSZ core-shell structures prepared using Ni particles of size 0.2, 0.4, and 1.8 μm exhibited dense core, porous core, and random-morphology core, respectively. Subsequently, nanostructured cermet anodes were fabricated using the prepared Ni-YSZ core-shell powders. During the formation of cermet, the heat treatment of Ni-YSZ core-shell powder results in the eruption of Ni core out of the YSZ shell layers, thereby facilitating the formation of nanostructured Ni-YSZ cermet. Systematic studies indicated that the morphology and electrical conductivity of the prepared Ni-YSZ core-shell powders and the cermet anode varied, depending on the initial particle size of the Ni particles. Of the different samples prepared in this study, the Ni-YSZ cermet prepared using Ni particles of size 0.4 μm showed the highest electrical conductivity at 750 ℃. (Received May 15, 2014)

keyword : fuel cells, powder processing, electrical properties, scanning electron microscopy, SEM, ohmic resistance

Anodic aluminum oxide (AAO) templates have drawn much interest because they can be applicable to form carbon nanotubes, nanowires and nanorods. For the aim of nanowire fabrication, infiltration behaviors of metal containing solution into pores in AAO template were investigated. In this paper, nickel nitrate solution [Ni(NO3)2·6H2O] was used as metal containing solution (marker solution). The infiltration behavior of marker solution into the pores (diameter: 30 nm) in AAO template was observed by scanning electron microscopy. The samples which had been processed by plasma treatment or pressure change showed a favorable influence on the infiltration properties of marker solution into the pores. Compared to plasma treatment, the pressure change in the chamber showed a little effect on infiltration behavior of marker solution. From this study, we conclude that the change in surface energy of the AAO surface is more effective than pressure change for the infiltration of marker solution into the holes in AAO template. The weak effect of pressure change on infiltration is due to large value of Knudsen number resulted from very small diameter of pores in the AAO template. (Received June 3, 2014)

keyword : porous materials, infiltration, surface, scanning electron microscopy, nanowires

N-type electrode optimization of GaN-based vertical light-emitting diode (VLED) single chip with 3-W output power is reported. The various n-type electrode designs were proposed and simulated to optimize the output power and operating voltage. In addition, the LED chip with optimized n-type electrode design was fabricated in the form of a vertical-injection structure with chip dimensions of 2×2 mm2. Electrical and optical characteristics of the VLED were measured up to 3 A injection current under pulsed operation condition. Output power and forward voltage at 2.7 A were obtained to be 3.1 W and 3.67 V, respectively. (Received May 21, 2014)

keyword : optoelectronic materials, vapor deposition, electrical/optical properties, computer simulation, current spreading