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The effect of thiourea on the nano-mechanical and chemical properties of Ni-P foil was studied to develop a high performance Ni-P deposit for automobile and machinery parts. The Ni-P deposit was prepared by electroforming in a modified sulphate bath with different amounts of thiourea. Chemical analysis of the electrodeposited Ni-P foils by energy dispersive spectroscopy showed that phosphorous in the foil was reduced with thiourea. Structural analysis by X-ray diffractometry revealed that the (111) plane of the Ni-P deposits grew preferentially with increasing crystallinity. Surface analysis by atomic force microscopy and fieldemission scanning electron microscopy showed that the surfaces of the Ni-P electrodeposited with 0 and 0.01 g/L thiourea were relatively smooth and clean showing no nodules, whereas, the cauliflower-like nodules were observed on the surfaces of the deposits prepared with 0.03, 0.05, 0.07 and 0.1 g/L thiourea. The surface roughness (RRMS) of the deposits increased by addition of 0.1 ppm of thiourea from 6 to 54 nm. Nanomechanical properties of the Ni-P foil such as elastic modulus, hardness and stiffness determined by tribonano- indenter were tended to increase by addition of 0.1 ppm of thiourea from 77 to 156 GPa, 6.6 to 8.9 GPa and 109.6 to 186.6 μN/nm, respectively. (Received September 16, 2019; Accepted November 30, 2019)

keyword : electrodeposition, Ni-P, thiourea

The effects of heat treatment conditions on the mechanical properties and energy absorption capacity of 7003 (Al-6Zn-0.6Mg) aluminum alloy were studied. The extruded material was heat treated at various temperatures to prepare annealed or aged specimens. Tensile tests, hardness measurements, electron backscatter diffraction characterizations, and differential scanning calorimeter analyses were carried out to investigate the mechanical properties and microstructures of the as-extruded or heat treated specimens. Axial compression tests of circular tube samples were also performed to characterize their energy absorption behavior. Specific energy absorption was calculated by measuring the absorbed energy per unit weight of the tube specimen. The peak reaction force was defined as the maximum force applied during the compression test. The as-extruded material with high strength and low elongation exhibited fracture failure during the axial compression test. After a low temperature annealing at 200 or 250 oC, the material had low strength and low energy absorption capacity. In contrast, the high temperature (300 to 400 oC) heat treatment resulted in an increase in strength and enhancement of energy absorption capacity. The aging treatment effectively increased the strength and the energy absorption capacity. After artificial aging, fine and uniform precipitates were formed. The artificially aged specimens showed the highest yield strength and therefore exhibited the highest energy absorption capacity among the heat treated specimens. Specific energy absorption and peak reaction force were linearly proportional to the flow stress of the material. (Received October 18, 2019; Accepted December 3, 2019)

keyword : Al-Zn-Mg alloy, heat treatment, energy absorption capacity, mechanical properties, microstructure

Studies of effective furnace cooling technology and refractory materials have extended the lifetime of a blast furnace to more than 15 years. On the other hand, the replacement of refractories in the blast furnace results in considerable cost and time loss for stopping the blast furnace operation. Various kinds of refractories are used inside a blast furnace, and SiC-based refractories, which are resistant to abrasion and thermal shock, are used in the area where frequent friction of charged materials occurs. However, these SiCbased refractories are quite vulnerable to an oxidizing atmosphere and alkali gases, and it is difficult to prevent corrosion by alkali gases generated from the impurities of the raw materials only by controlling the composition of the refractories and raw materials. Therefore, this study was carried out to investigate the alkali gas corrosion behavior of the blast furnace refractory as a fundamental study. Experimental results showed that the SiC and Si3N4 refractories used in the bosh part of the blast furnace were corroded by alkali gas even in an inert atmosphere. The alkali corrosion progressed gradually with time, and the alkali element and numerous pores and liquid precipitates were observed in the section of the corrosion layer. It was confirmed that the alkali gas corrosion reaction occured according to the well-defined conventional reaction mechanism. In addition, it was found that the corrosion rate of the SiC castable was 30 times faster than that of the SiC brick. (Received October 4, 2019; Accepted November 15, 2019)

keyword : SiC, Si₃N₄, alkali corrosion, refractory element, SEM

The ability to form high quality nano-/micro- patterns is very important for the nanofabrication of high-density electronic devices. However, remaining challenges have yet to be resolved, including low quality roughness, low pattern resolution, and the highly complex process. In this study, we suggest a novel and simple method for creating high quality patterns, controlling the surface roughness of the target substrates with a polishing process. We systematically investigated the effect of surface roughness on pattern generation, using a nanotransfer printing (nTP) process on target Al2O3 substrates. We successfully formed highly ordered nanoscale functional patterns on well-defined surfaces, using a mirror-polishing process, compared to normally-polished substrates. In addition, we demonstrated well-printed Sn nanopatterns on various metal (Cu and Fe) substrates. Close-up scanning electron microscope (SEM) images clearly show welldefined patterns on the mirror-polished substrates. Based on these results, we expect that by mechanically modifying substrate surfaces, the yield and quality of pattern formation can be improved, and that this approach can be extended to other patterning methods. (Received October 17, 2019; Accepted November 26, 2019)

keyword : surface modification, polishing, nanotransfer printing

Laser surface heat treatment and laser nitriding processes were applied using selective surface modification techniques to investigate phase transformation, microstructural evolution, and surface hardening behaviors for two types of plastic injection mold steels, AISI 1045 and P21. During laser surface heat treatment, a 245% hardness increase compared to that of the base metal (290 HV) was achieved due to martensite transformation of the AISI 1045 steel. However, for the AISI P21 steel, hardness within the heat-treated zone was largely unchanged from that of the base metal (410 HV) despite being accompanied by martensite transformation. Compared to that of the base metal, this static hardness behavior of the heat treated P21 steel was due to coarsening of Cu particles induced by the laser irradiation. To overcome the static hardness behavior of P21 steel, laser nitriding was used. The laser-nitrided specimen (at 4500 J/mm heat input) was approximately 40% (577 HV) harder than the base metal (410 HV) and was highly correlated with nitride formation. Nitrogen successfully penetrated the surface of the specimen during laser irradiation and formed a nitrided layer mainly composed of an AlN phase. Thus, the surface hardening behavior of AISI P21 steel after laser nitriding could be largely attributed to the AlN phase development. (Received July 16, 2019; Accepted October 16, 2019)

keyword : plastic injection mold steels, surface modification, laser surface heat treatment, laser nitriding, nitride

Electroplating has many economic advantages in producing copper foils. The easiest way to manufacture electroplated copper foil with various properties is to add appropriate additives. This study evaluated the surface properties, mechanical and electrical properties of copper foil electroplated in electrolytes containing the leveler JGB (Janus Green B). When the leveler JGB was added as an additive, Cu crystals were distributed uniformly on the surface layer in an initial nucleation process. In the JGB-free group, dents and pinholes were observed on the surface of the electroplated Cu foil. Such surface defects were reduced with the addition of JGB. Surface roughness was decreased by 68% in the samples electroplated in electrolytes with 10 ~ 40 ppm JGB, when it is compared with a JGB-free sample. It was observed that the priority growth direction of crystal texture changed from (200), (111) to (220). Elongation decreased by 59%, while the tensile strength increased by 157% due to a decrease in crystal size by 69%. With the addition of 0 ~ 40 ppm JGB, resistivity increased due to the decrease in crystal size and changes in the crystal texture. Based on a linear regression approximation between 0 and 40 ppm the value of R2 was 91.4%. There was no statistically significant difference between 40 and 60 ppm, and the resistivity was 37.7% higher than in the JGB-free sample. (Received October 4, 2019; Accepted November 22, 2019)

keyword : JGB, copper, electroplating, mechanical property, resistivity

In this study, we investigated the morphological, crystal structural, electronic structural, and electrocatalytic properties of the inverse spinel structured copper cobalt oxide (Cu_0.72Co_2.28O₄) catalysts. The materials were prepared by coprecipitation using various copper and cobalt precursors, and subsequent oxidation treatment. Electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Brunauer Emmett Teller (BET) analyses were employed to characterize the Cu_0.72Co_2.28O₄ catalysts. The Cu_0.72Co_2.28O₄ catalyst, synthesized with acetate based precursors, exhibited higher activity for the oxygen evolution reaction than commercial precious IrO₂ catalyst. This performance was attributed to its high surface area, sheet morphology and ratio of Co³⁺. The Cu_0.72Co_2.28O₄ catalyst also showed excellent stability with a performance of 99% after 300 hours. The Cu_0.72Co_2.28O₄ catalyst anode electrode was coupled with a Pt/C cathode electrode to construct an anion exchange membrane water electrolysis (AEMWE) cell. Our AEMWE cell achieved a current density of 644 mA/cm² and an energy efficiency of 85% at a cell voltage of 1.8 V in 1M KOH. (Received October 4, 2019; Accepted November 15, 2019)

keyword : water electrolysis, oxygen evolution reaction(OER), copper cobalt oxide, precursors, coprecipitation method, anion exchange membrane water electrolysis(AEMWE)

The photovoltaic properties of TiO₂/ZrO₂ double electron transport layered perovskite solar cells were investigated based on the ZrO₂ layer thickness. Samples were fabricated with a glass/FTO/TiO₂/ZrO₂/ perovskite structure. The TiO₂/ZrO₂ layer thickness ratio was confirmed to be 264/0, 228/168, 228/204, 270/ 242, and 282/288 nm, respectively, using an electron probe microanalyzer. To analyze the photovoltaic characteristics and transmittance of the ZrO₂ layer of the PSCs according to the ZrO₂ layer thickness, a solar simulator, incident photon-to-current conversion efficiency, and ultraviolet-visible-near-infrared spectroscopy were used, respectively. A field emission scanning electron microscopy and atomic force microscopy were used to analyze the microstructure of the ZrO₂ and perovskite layers. As the ZrO₂ layer thickness increased, the energy conversion efficiency (ECE) increased initially, reached a maximum ECE of 14.24% at 204 nm ZrO₂, and then decreased thereafter. The increase in ECE was due to the enhanced electrical conductivity of the ZrO₂, while the decrease was attributed to the reduced transmittance as the thickness of the ZrO₂ increased. In addition, we confirmed that the surface valley spacing in the ZrO₂ layer might affect the grain size and thickness of the perovskite layers, influencing the ECE. (Received November 1, 2019; Accepted December 4, 2019)

keyword : electron transport layer, ZrO₂ layer, perovskite grain, perovskite solar cells

ZnO nanorods are one of the most studied materials because it can be facilely grown on a wide range of substrates at low temperature. ZnO exhibits piezoelectricity as well as semiconducting properties, and hence is applicable to piezoelectric nanogenerators and sensors. In the present work, the effect of ZnO nanorods’ size on piezoelectric performance was systematically studied using conductive atomic force microscopy (C-AFM). We measured the total C-AFM signal for an observing area and evaluated the piezoelectric performance of the ZnO nanorods based on this total C-AFM signal. First, five samples of ZnO nanorod with distinct aspect ratios were hydrothermally grown on silicon substrates. Afterwards, two types of AFM tips with different spring constants were used to conduct C-AFM as a function of aspect ratio. When the AFM tip with a 42 N/m spring constant was used for the C-AFM measurement, the total C-AFM signal continuously increased with increasing aspect ratio. The total C-AFM signal increased with increasing normal force, but fluctuated with increasing scan rate. The results of the C-AFM experimental measurements were compared with the open-circuit voltage and short-circuit current of ZnO-nanorod based piezoelectric nanogenerator. We show that using C-AFM is a facile and effective method for investigating the optimized aspect ratio of ZnO nanorods for piezoelectric power generation. (Received November 20, 2019; Accepted December 11, 2019)

keyword : nanorod, zinc oxide, size effect, piezoelectric, conductive AFM, nanogenerator