발간논문

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In this study, Zn-Mg alloys with various Mg contents were manufactured by the casting method using an induction melting furnace. Then microstructure analysis and mechanical property tests were carried out. In the Zn-Mg alloy with a content of less than 7 wt%Mg, the hardness of the Zn-Mg alloys gradually increased as the Mg content increased but in the alloy with more than Zn-7 wt%Mg, the hardness was almost the same. Enhanced hardness is induced by the intermetallic compounds phase of Mg2Zn11 and MgZn2. In the compression test, Zn-3 wt%Mg had the best compression strength at 610 MPa, but Zn-7 wt%Mg and Zn-10 wt%Mg had a low compression strength at 343 Mpa and 111 MPa, respectively, although these alloys have excellent hardness. This study verified that Zn-Mg alloys containing a Zn phase have more toughness than those composed of only intermetallic compounds such as Mg2Zn11 and MgZn2. (Received November 19, 2012).

keyword : alloys, casting, microstructure, hardness test, compression test

The degradation behavior of vulcanized rubber in elevator cabins for reducing vibrations was investigated by morphological and spectroscopy analysis. Thermal (85℃) and hydrothermal aging (85℃ and 85% relative humidity) was performed to determine the effects of heat and humidity on the mechanical properties of rubber materials. The international rubber hardness degree (IRHD), tensile strength, and elongation percentage of rubber materials were measured to better understand the stiffening of the surface with the degradation time. The degradation mechanism of rubber materials was classified into two types: an increase in cross-links and chain scission. When rubber components were used for 96 hr under hydrothermal stress conditions, their mechanical characteristics deteriorated rapidly according to the results of the thermal aging test due to complex degradation behavior. Hydrothermal aging affects the increase in not only cross-links but also chain scission of the polymer segment. Fourier transform infrared (FT-IR) spectroscopy of the specimens of hydrothermal aging revealed improvement in C-H bonding at 2916 and 2848 cm?1, and an increase in the peak intensity in the 1080 cm?1 due to C-O-C bonding. The reduced C-C bonding was associated with the decomposition of cross-links and elastic modulus, which affected the degradation of the matrix near the surface. Therefore, the mechanical properties decreased more rapidly after hydrothermal degradation than after thermal degradation. (Received December 28, 2012).

keyword : rubber materials, hydrothermal aging, microstructure, degradation behavior, cross-links, chain scission

Magnesium (and its alloys) is of considerable interest as a structural material, especially in the aerospace and automotive industries thanks to its low density. Plasma electrolytic oxidation (PEO) is a promising novel process for forming ceramic-like coatings with a thickness ranging from tens to hundreds of microns on light metals (Al, Mg, and Ti) and their alloys for corrosion protection, wear resistance, biomimetic and thermal barrier properties. The AZ91D magnesium alloys with and without treatment by PEO was investigated by reflectance, scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS) measurements. (Received Setember 10, 2012).

keyword : magnesium alloy, AZ91D, plasma electrolytic oxidation, surface treatment

In this study, the corrosion resistance of pure Zn, Mg2Zn11, and MgZn2 single phases was investigated using an electrochemical test and surface analysis. The electrochemical test showed clearly that alloying with Mg significantly increased the corrosion resistance of Zn-Mg alloys. This study confirms that the Mg2Zn11 phase has the most outstanding corrosion resistance among these phases. The improved corrosion resistance of the Mg2Zn11 phase is attributed to the formation of an intermediate corrosion product. Intermediate corrosion products, which are formed on the surface of the specimen, have a role in preventing direct exposure from corrosion environments. In particular, among these products, Zn5(OH)8Cl2· H2O (simonkolleite) contributes to the improvement of corrosion resistance, probably because it delays the formation of ZnO, the final corrosion product in the generative process. (Received July 3, 2012).

keyword : alloys, casting, corrosion, X-ray diffraction, electrochemical test.

Extraction behavior of REEs (La, Pr, and Nd) from chloride solutions is investigated using Cyanex 272 and PC 88A. PC 88A had a greater extraction efficiency towards REEs than Cyanex 272. Adding EDTA to the aqueous solution depressed the extraction of Pr and Nd due to the formation of anionic complexes and had a negative effect on the separation of La from Nd and Pr. The extraction behavior of REEs in the presence of EDTA depended on the nature of the extractant. Extraction by Cyanex 272 in the absence of EDTA was better for separating La than extraction by PC 88A. (Received November 28, 2012).

keyword : Ethylenediaminetetraacetate, Neodymium, Praseodymium, solvent extraction

For improving anode materials in Li-ion batteries, the Si system has been noted by many researchers because it has higher energy density and capacity than the graphite anode material used currently. However, the life cycle of the Si anode tends to decrease due to the remarkable volume expansion which is caused by insertion of Li ions when the cell is charged. In this study, we controlled the size of active Si particles, which are dispersed in the inactive matrix, down to several tens of nm as active materials by adding heterogeneous elements. To understand the reaction mechanism of active Si dispersed in the inactive matrix, we analyzed the microstructure of the Si-Ti-Fe alloy using high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. The volume expansion behavior was improved by employing the TiFeSi2 matrix and refining the active Si particle size, and life performance of the Li-ion batteries was enhanced. (Received September 28, 2012).

keyword : Li-ion battery, Si-Ti-Fe alloy anode, solidification TEM, microstructure

Laser doping is used as an alternative to thermal annealing for formation of selective emitter Si solar cells. Laser processing has many advantages, such as a simple and low temperature process, high throughput, and low cost ownership. For fabrication of selectively low sheet resistance regions, we used a phosphosilicate glass layer as a dopant source, which was produced after furnace diffusion. We achieved an efficiency of 18.88% by using the laser doping with a PSG layer. (Received September 6, 2012).

keyword : solar cells, selective emitter, laser doping

This article describes how the flexural displacement-induced fracture strength of a lead-on-chip (LOC) package is influenced by a density change in SiC-fillers embedded in a package body of 60 wt% to 80 wt% and temperature variation of 25℃ to 300℃. The experimental results show that the fracture strength of LOC packages increases with an enhanced filler density at a temperature lower than 150℃, while it is not affected by a filler density change at a temperature higher than 200℃. Micro-structural examination indicates that the fracture results from crack initiation at the bottom surface of the plastic package body at a temperature lower than 150℃. On the other hand, at a temperature higher than 200℃, delamination between the silicon device and the plastic package body takes place first, and then chip cracking follows without package body damage. Thus, at the temperatures higher than 200℃, enhanced filler density in a package body does not contribute to the improvement of package fracture strength. Furthermore, this work shows that regardless of filler density variation, the fracture strength of the packages having the silicon devices with grinding-induced scratch marks is lower than that with no scratch marks at a temperature higher than 200℃. (Received September 7, 2012).

keyword : SiC filler, epoxy molding compound, silicon chip, lead-on-chip package, temperature

Acidic PEDOT: PSS anode buffer layers (ABLs) are widely used for improving efficiency in organic based solar cells. Recently, stable p-type metal oxides, such as NiO, MoO3, and V2O5, have been used to replace the commonly used acidic PEDOT:PSS ABL. Among these metal oxides, the thermally evaporated MoO3 anode buffer layer is largely used because it has appropriate optical and electrical properties. In this study, we used rapid thermal annealing (RTA) for fabricating polycrystalline MoO3 thin films. MoO3 thin films were fabricated by annealing 30 nm molybdenum in an oxygen atmosphere under 350℃-550℃ RTA conditions at intervals of 100℃. In particular, we suggest an optimized temperature of 450℃ for efficient ABL in organic based solar cells. The MoO3 thin film with 450℃ RTA conditions has the relatively highest RMS roughness (46.5 nm) and proper electrical resistance. The characteristics of MoO3 ABLs fabricated by the RTA process of Mo are compared with thermally evaporated MoO3 ABL. (Received September 25, 2012).

keyword : optoelectronic materials, sputtering, oxidation, X-ray diffraction, rapid thermal annealing

In this work, Mg-x wt% Fe2O3-y wt% Ni alloys were prepared by mechanical grinding under hydrogen (reactive mechanical grinding) using a planetary ball mill, and pressure-composition isotherms of the samples were subsequently obtained. By measuring the absorbed hydrogen quantity as a function of number of cycles, the cycling properties of a Mg-5 wt% Fe2O3-15 wt% Ni alloy was investigated. The Mg-10 wt% Fe2O3-5 wt% Ni alloy showed an equilibrium plateau pressure of 1.92 bar at 593 K and had a hydrogen storage capacity of 5.47 wt% at 593 K. The absorbed hydrogen quantity decreased as the number of cycles increased. The Ha value varied almost linearly with the number of cycles. The maintainability of absorbed hydrogen quantity at n = 150 was 73.8% for the hydriding reaction time of 60 min. (Received August 14, 2012).

keyword : hydrogen absorbing materials, mechanical alloying, milling, hydrogen, microstructure, Mg-x wt% Fe2O3-y wt% Ni alloys