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For the applications in automotive, aircraft, aerospace, and electronic industries, the lightest structural Mg alloys have received much attention since 2000. There has been some progress for the improvement of the mechanical properties such as room temperature strength, formability and mechanical anisotropy. However, the high temperature strength of Mg alloys is very low to be used for the parts and structures of high temperature conditions. For the last decade, considerable efforts are concentrated for the development of Mg alloys to be used at high temperature. Newly developing Mg-RE alloys are the good examples for the high temperature use. In this regard, this review paper introduces the recent research trends for the development of Mg-RE alloys strengthened with some precipitates and the long period stacking ordered (LPSO) structures related RE elements. (Received September 13, 2016: Accepted September 23, 2016)

keyword : Mg-RE alloys, LPSO, texture, mechanical anisotropy, mechanical property

An AlCrTiSiN film composed of 31Al-15Cr-1.7Ti-0.5Si-51.8N (at%) was deposited on a steel substrate by arc ion plating to a thickness of 1 μm. It consisted of nano crystalline hcp-AlN and fcc-CrN. Its corrosion behavior in Ar-1%SO₂ gas at 800 ℃ for 5-50 h was studied. The resulting scales consisted primarily of Al₂O₃ and Cr₂O₃, which effectively suppressed the corrosion. No sulfides formed, because Al and Cr oxidized competitively from the surface. The film was primarily corroded by the inward diffusion of oxygen and a much smaller amount of sulfur. (Received July 26, 2016; Accepted October 25, 2016)

keyword : thin films, vapor deposition, corrosion property, transmission electron microscopy (TEM), AlCrTiSiN

The effects of particle size on the surface properties of HVOF spray coating were studied to improve of the durability of metal components. Micro and nano sized WC-12Co powders were coated on the surface of Inconel718, and the effects of particle size on surface properties were studied. Surface hardness was reduced when the particle sizes of the powder were decreased, because the larger specific surface area of the smaller particles caused greater heat absorption and decomposition of the hard WC to less hard W2C and graphite. Porosity was increased by decreasing the particle size, because the larger specific surface area of the smaller particles caused a greater decomposition of WC to W2C and free carbon. The free carbon formed carbon oxide gases which created the porous surface. The friction coefficient was reduced by decreasing the particle size because the larger specific surface area of the smaller particles produced more free carbon free Co and Co oxide which acted as solid lubricants. The friction coefficient increased when the surface temperature was increased from 25 to 500 ℃, due to local cold welding. To improve the durability of metal mechanical components, WC-Co coating with the proper particle size is recommended. (Received August 22, 2016; Accepted October 28, 2016)

keyword : surface properties, powder, HVOF coating

To improve the sensitivity of impact sensor modules for automotive air bag systems, we developed a flexible module. The impact sensor was soldered with Sn-3.0Ag-0.5Cu (SAC305) solder on a flexible printed circuit board (FPCB) with an organic solderability preservative (OSP) surface finish. Thermal shock (TS) is one of the test methods used to accelerate the degradation of solder joints. To evaluate the solder joint fatigue life of the proposed flexible impact sensor module experienced with/without TS, TS test was conducted from -40 to 90 ℃ with a dwell time of 10 min for 1000 cycles. Then, high cycle fatigue tests were sequentially performed at a force range from 0 N and 20 N with a 1 Hz frequency sine wave. From these results, we determined that the mean life and B₁₀ life of the solder joint fatigue after 1000 TS cycles were 4188.9 and 1864.8 cycles, respectively. Finally, we found that the fatigue life of the solder joint decreased with increasing TS cycles due to the growth of Cu₆Sn₅ + Cu₃Sn, the thickness and the dispersion of Ag₃Sn at the solder joint and matrix. Even though the mean life and B₁₀ life of the solder joint fatigue life were reduced by 60% and 13.8% respectively, compared to their initial values, we confirmed the feasibility of using the flexible modules for automobile air bag systems. (Received September 19, 2016; Accepted October 19, 2016)

keyword : fatigue life, solder joint, flexible, air bag, automotive electronics

The effect of ultrasonic melt treatment (UST) on the microstructure and mechanical properties of Al-7Si-0.35Mg (A356) casting alloys was investigated. The particular aim of this study was to analyze the mechanism involved in the strengthening of the A356 alloys when fabricated by UST. The UST had little effect on the sizes of the α-Al grain and eutectic Si at a melt temperature of 750 ℃, and the yield strength of the A356 alloy was increased by UST by approximately 16%. After T6 heat treatment, however, both alloys prepared with and without UST had similar levels of yield strength. These results are possibly associated with a change in the type and the volume fraction of intermetallics due to UST. UST greatly reduced the volume fractions of the intermetallics which were formed upon solidification, resulting in alloys with predominantly β-Al5FeSi instead of π-Al₈FeMg₃Si₆. However, T6 heat treatment, especially a solid solution treatment at 530 ℃ for 8 hours, led to the dissolving of intermetallics such as Mg₂Si and π -Al₈FeMg₃Si₆ and as a result their volume fractions were further reduced to similar levels in both alloys with and without UST. (Received May 4, 2016; Accepted October 5, 2016)

keyword : hypoeutectic Al-Si alloy, casting, ultrasonic melt treatment, microstructure, mechanical properties

Solvent extraction was employed to recover precious metals (Au (III), Pd (II) and Pt (IV)) from the leach solution of spent electronic wastes containing Cu (II), Cr (III) and Fe (III). First, pure Fe (III) and Au (III) were recovered by simultaneous extraction with Cyanex 923 followed by selective stripping with HCl and Na₂S₂O₃. Second, Pt (IV), Pd (II) and Cu (II) were extracted by Alamine 336 from the raffinate. After the removal of Cu (II) by stripping with weak HCl, Pd (II) and Pt (IV) were separately stripped by controlling the concentration of thiourea in the mixture with HCl. A process flow sheet for the separation of precious metals was proposed. (Received August 18, 2016; Accepted November 2, 2016)

keyword : gold, platinum, palladium, separation, solvent extraction

In this study, zinc oxide (ZnO) nanostructures were grown on a ZnO-buffered fluorine-doped tin oxide (FTO) substrate using a microwave chemical bath deposition method with different zinc oxide precursor concentrations from 0.01 to 0.5 M. We investigated the effects of the zinc oxide precursor concentration on the morphological, structural, optical and photoelectrochemical properties of the ZnO nanostructures. From this work, we found that ZnO one-dimensional structures mainly grew along the (002) plane, and the nanorod length, diameter, surface area and photoelectrochemical properties were largely dependent on the precursor concentration. That is, the photoelectrochemical properties were affected by the morphological and structural properties of the ZnO. The morphological, structural, optical and photoelectrochemical properties of the ZnO nanostructure were investigated by field emission scanning electron microscopy (FE-SEM) and atomic force microscope (AFM), X-ray diffraction (XRD), UV-visible spectroscopy and 3-electrode potentiostat. We obtained the highest photocurrent density of 0.37 mA/㎠ (at 1.1 V vs. SCE) from the precursor concentration of 0.07 M, which resulted in ZnO nanostructures with proper length and diameter, large surface area and good structural properties. (Received April 21, 2016; Accepted July 22, 2016)

keyword : ZnO nanorods, microwave chemical bath deposition, photoelectrochemical, photocurrent density, precursor concentration

In this study, a spray drying system was used to prepare macroporous titania micro-particles for applications including UV blocking materials and photocatalysts. To synthesize the macroporous particles a colloidal templating method using polymeric beads as sacrificial templates and a titania nano-colloid as precursor material was adopted. The resulting porous titania particles were mixed with distilled water to measure their light transmittance, and to assess their UV blocking performance. To demonstrate another application, the organic dye Rhodamine B was decomposed using the macroporous titania micro-particles as a photocatalyst for water purification. The spray drying system was also utilized to fabricate porous iron oxide particles using iron chloride liquid precursor. Following a reduction reaction, the porous iron oxide particles fabricated in this study are also potentially applicable as intermediates for the synthesis of porous metal particles, which have various applications including porous surface burners, artificial bones, thermal insulation, and sound absorbers. (Received June 28, 2016; Accepted September 21, 2016)

keyword : porous titania particles, spray dying, UV blocking property, photocatalyst, porous iron oxide particles

High speed and large capacity optical communication networks are needed to meet the demands of increased traffic being created by mobile services. Advanced optical communication systems are based on high performance optical device modules that have small footprints and low power consumption. A microlens with a short coupling length and high coupling efficiency is an essential component of these compact optical modules, and silicon is the most widely studied material for this purpose because of its large refractive index at optical communication wavelengths. We used CODE V to simulate the coupling efficiency and the coupling tolerance of an optical system composed of a laser diode and an optical fiber coupled through a silicon lens. The maximum coupling efficiency for spherical lenses varied from -0.4 to -0.8 dB depending on the radius of curvature while -0.2 dB coupling loss was obtained with an optimized aspherical lens. Aspherical lenses exhibited larger coupling efficiencies while their coupling tolerance was slightly degraded. (Received May 18, 2016; Accepted August 5, 2016)

keyword : silicon lens, plano convex lens, optical coupling system, coupling efficiency, align tolerance

In this study, quaternary phosphate-based sol-gel derived glasses were synthesized from a P₂O₅-CaO-Na₂O-TiO₂ system with a high TiO2 content of up to 50 mol%. The sol-gel method was chosen because incorporating a high percentage of titanium into a phosphate network via traditional melt-quench methods is non-trivial. The structure and thermal properties of the obtained stabilized sol-gel glasses were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). The XRD results confirmed the amorphous nature of all of the stabilized sol-gel derived glasses. The FTIR results revealed that added TiO₂ enters the network as (TiO₆), which likely acts as a modifier oxide. Consequently, the number of terminal oxygen atoms increases, leading to an increase in the number of P-OH bonds. In addition, DSC results confirmed a decrease in glass transition and crystallization temperatures with increasing TiO₂ content. This is the first report of a sol-gel synthesis strategy combined with enameling to prepare glass at low processing temperatures and the first use of such a system for both hydrophilic and chemical resistance purposes. (Received July 26, 2016, Accepted November 1, 2016)

keyword : phosphate glass, sol-gel, enamel, hydrophilic, chemical durability