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Effects of alloying elements, manganese and chromium, on corrosion resistance of carbon steel were examined using weight loss test and electrochemical tests (polarization test and electrochemical impedance spectroscopy (EIS)) in synthetic seawater at 60 ℃. The results from the weight loss test showed that chromium effectively improved corrosion resistance of carbon steel during the entire immersion time, but manganese improved corrosion resistance after the lowered corrosion resistance at the beginnings of immersion. Unlike the weight loss test, the electrochemical tests showed that the corrosion resistance did not increase with immersion time, in all the specimens. This disagreement is explained by the presence of rust involved in electrochemical reaction during electrochemical tests. The analysis of rust with transmission electron microscopy (TEM)-energy dispersive spectroscopy (EDS) showed that the amorphous-like rust layer located at the metal/rust interface with enriched alloying element (Cr, Mn) prevents diffusion of corrosive species into a metal/rust interface effectively, which leads to increased corrosion resistance. The initial corrosion behaviour is also affected by the rust types. In other words, manganese accelerated the formation of spinel oxides, negatively affecting corrosion resistance. Meanwhile, chromium accelerated the formation of goethite but impeded the formation of spinel oxides, positively affecting the corrosion resistance. From the above results, the corrosion resistance of steel is closely related with a rust type.(Received May 12, 2015)

keyword : alloys, annealing, corrosion, transmission electron microscopy, TEM, X-ray diffraction

Black deposits (smut) are created on MIG welds in cryogenic Al alloys. The smut should be removed because it ruins the appearance of the end product and affects surface treatments such as painting. It was recently reported that plasma-MIG hybrid (PMH) welding controls the formation of smut duringwelding. In order to determine the reason for this, smut formation using both MIG and PMH welding was investigated through metallurgy and arc phenomena analysis. Smut on MIG welds is a Mg-Al-O amorphous layer that includes nano-sized MgO particles less than 100 nm in diameter and MgO particles 1-2 μm in diameter. Smut on MIG welds is created by large amounts of metal vapor from the arc explosion generated between the welding wire and the weld pool after a short circuit transfer. However, smut on PMH welds is not created owing to the small amount of metal vapor produced from a stable globular transfer rather than a short circuit transfer and arc explosion.(Received April 28, 2015)

keyword : metals, arc welding, oxidation, transmission electron microscopy, smut

Herein, we describe a study on the recovery of copper from a nitric acid solution containing copper,lead and iron. We removed the iron using a neutralization precipitation method after adjusting the pH of the solution to 1.8 at 80 ℃. After the iron was removed, we used a solvent extraction method for recovery of copper using LIX 84 as an extractant. The experiment was conducted by changing various conditions such as the equilibrium pH, concentration of the extractant and the phase ratio. The results of the experiment confirmed that over 99% of the copper can be extracted using 10% LIX 84 at an equilibrium pH 2.0. Adjusting the phase ratio (A/O) to 4.0 when the concentration of the copper was 4.0 g/L through the McCabe-Thiele Diagram confirmed that over 99% of the copper was extracted by a 3-stage operation. Meanwhile, adjusting the phase ratio (O/A) to 3.0 using 2.0 M sulfuric acid as a stripping agent stripped 99% of the copper. Finally, we suggest the optimal process for recovering copper from a nitric waste solution.(Received April 7, 2015)

keyword : nitric acid solution, recovery, recycling, copper, solvent extraction, LIX84

To develop a process for the selective extraction of Hf (IV) over Zr (IV) from a strong sulfuric acid solution, we investigated the stripping of Zr (IV) and Hf (IV) from loaded D2EHPA using alkaline reagents and various acid solutions. Since both Zr (IV) and Hf (IV) were quantitatively stripped by oxalic acid as well as by alkaline reagents (Na2CO3 and (NH4)2CO3), it was difficult to separate the two metals during the stripping step. Among the tested inorganic acids (HCl, HNO3 and H2SO4), only sulfuric acid could strip Zr (IV) and Hf (IV) and the stripping behavior was dependent on the sulfuric acid concentration employed in the extraction. When the extraction of the two metals by D2EHPA was conducted with a 0.5 M sulfuric acid solution, Zr (IV) was selectively stripped from the loaded D2EPA with a sulfuric acid solution of 3-5 M. A separation factor of 10 resulted from the stripping with a 4 M sulfuric acid solution.(Received June 16, 2015)

keyword : zirconium, hafnium, stripping, D2EHPA, sulfuric acid

This study examined methods to increase the production of Mg crown and minimize the amounts of solid impurities using the thermodynamic commercial package Factsage. A thermodynamic calculation was carried out to predict the degree of reduction of Mg vapor depending on the operating parameters through a single-stage calculation method involving the use of the CaO/MgO molar ratio, ferrosilicon/ dolime mass ratio and the pressure and temperature during the Pidgeon process. The results indicate that the CaO/MgO molar ratio was 1.4~1.5 to increase the degree of the reduction of Mg vapor in a non- equilibrium state. The thermodynamic calculations were designed to examine the effect the ferrosilicon had on specific ferrosilicon/dolime ratios. A good effect was observed between 25 and 30%. Moreover, it was determined that the optimum operating conditions which offer a high purity level of magnesium and reduce the degree of vapor was the case 5 (1200 ℃, 0.1 ~ 0.01 torr). In addition, the distribution of solid impurities in the Mg crown was calculated by a multi-stage calculation method while decreasing the temperature. Solid impurities existed as compounds in the Mg crown depending on the condensation temperature range in retort. The compound was composed of Mg2Si under 700 ℃ and CaAl2 under 500 ℃, also FeAl3, MnB under 400 ℃. A comparison of the thermodynamic calculations and experimental results regarding the types of impurities were in good agreement.(Received July 2, 2015)

keyword : Mg crown, intermetallics, solidification, recovery, computer simulation

To investigate the effect of a Ni buffer layer on the structural, electrical and optical properties of GZO (Ga Doped ZnO) thin films, GZO single layer and GZO/Ni bi-layered films were prepared on poly-carbonate (PC) substrates by RF and DC magnetron sputtering without intentional substrate heating. GZO films had an optical transmittance of 87.1% in the visible wavelength region and an electrical resistivity of 1.0×10-2 Ωcm, while GZO/Ni films had a lower resistivity of 1.2×10-3 Ωcm and an optical transmittance of 82.4%. Based on the figure of merit, it is clear that a 2 nm thick Ni buffer layer enhanced the opto-electrical performance of GZO films for use as transparent conducting oxides in flexible display applications (Received December 24, 2014)

keyword : thin film, sputtering, electrical properties, optical properties, x-ray diffraction

Ga-doped ZnO (GZO) thin films were grown on muscovite mica substrates by sol-gel spin-coating. The effects of post-annealing on the optical properties and constants of the GZO thin films were investigated. All the films exhibited strong near-band-edge emission in the UV range, while the defect-related deep-level emission in the visible region was only observed at 600 ℃. The average transmittance of the films was about 75% in the visible region and the sharp absorption edges were shifted toward a higher wavelength and became sharper with an increase in the post-annealing temperature. The refractive index was measured for the as-grown and annealed GZO thin film at 500 ℃. The single oscillator energy, dispersion energy, M-1 and M-3 moments, average oscillator strength and wavelength, and the refractive index at an infinite wavelength were obtained from the refractive index values of the films. In addition, the real and imaginary parts of the dielectric constant and optical conductivity of the films were measured.(Received April 7, 2015)

keyword : zinc oxide, optical properties, optical constants, sol-gel, Ga doping

In this work, MgH2, which is brittle, and Ni-coated carbon were added to Mg in order to improve the hydrogen absorption and release properties of magnesium. Carbon has a relatively low density, and it is thus considered that the interfacial area between Mg and an added catalyst will increase when Ni-coated carbon is added to Mg. In this research, the quantity of added Ni-coated carbon was smaller than that in the previously reported studies. A mixture with a composition of 85 wt% Mg+10 wt% MgH2+5 wt% (Ni-coated carbon) was milled in a hydrogen atmosphere in a planetary ball mill (alloyed mechanically in a hydrogen atmosphere). The hydrogen absorption and release properties of the prepared sample were investigated. Mechanical alloying in a hydrogen atmosphere of Mg with MgH2 and Ni-coated carbon and hydrogen absorption-release cycling are believed to create defects on the surface and in the inside of the Mg particle, to make clean surfaces, to increase the interfacial area between Mg and additives, and to diminish the particle size of Mg. The sample released 0.03 wt% H for 2 min, 1.50 wt% H for 9 min, 2.69 wt% H for 16 min, and 2.86 wt% H for 60 min at 648 K under an initial hydrogen pressure of 0 bar.(Received May 8, 2015)

keyword : hydrogen absorbing materials, mechanical alloyin g/milling, scanning electron microscopy, SEM, X-ray diffraction, 85Mg+10MgH2+5(Ni-coated carbon).

We experimentally investigated the conditions for the enhancement of light extraction efficiency (LEE) in light-emitting diodes (LEDs) with cone patterned-sapphire substrates in terms of a base diameter of the cone pattern (d), pattern-to-pattern pitch (p), and pattern height (h). The LEE increased as both the base diameter of the cone pattern and height increase on the condition of the base diameter of the conepattern being a certain value or lower. However, after the base diameter of the cone pattern exceeded this value, the LEE did not increase as the cone height increased, but the maximum LEE was realized under the optimum condition of the pattern height being equal to half of the base diameter. We present specific numerical values of the patterns on two different conditions of the base diameter of the cone pattern.(Received July 13, 2015)

keyword : optoelectronic materials, light extraction efficiency, vapor deposition, optical properties, scanning electron microscopy

To estimate the infiltration potential in metal binders, a new parameter, the EII (Effective Infiltration Index), which can be determined with the surface tension and viscosity data of each liquid metal used in the binder, is introduced. The parameter was found to be closely related to the measured infiltration distance. As an infiltrant for core bits, the Cu-Sn alloy with a higher EII value was selected and compared with the conventional Cu-Zn alloy. For the formation of harder rock, a finer W size in the matrix is generally used to maintain the cutting rate. However, in such a case, the infiltration potential becomes lower and a fully infiltrated microstructure cannot be obtained. In this study, the matrix with the Cu-Sn alloy showed an evenly infiltrated and sound microstructure up to a W size of 1 μm and had a longer tool life than the conventional Cu-Zn alloy in a simulated drilling test.(Received March 30, 2015)

keyword : composites, infiltration, thermodynamic properties, hardness test, core bit