• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1427-1430
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• 2014

A thermal barrier coating (TBC) prevents heat directly transferring from a high-temperature flame to a substrate. The TBC system comprises a top coating and bond coating. TBC technology reduces the substrate surface temperature by about $100{\sim}170^{\circ}C$. In the TBC system, internal stress is generated by the difference in thermal expansion coefficients of the substrate and coating. The internal stress also differs according to the shape and position of the blade. In this study, finite element analysis was performed for different curvatures of coin-shaped specimens, which are commonly used for thermal fatigue tests, and the changes in internal stress of the TBC system were compared. Based on the results, the curvature at which the minimum stress occurs was derived, and the thermal stress was confirmed to increase with the difference between a given curvature and the curvature with the minimum stress.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1093-1098
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• 2013

A single-crystal sapphire is used as a transparent bulletproof window material; however, few studies have investigated the dynamic behavior and fracture properties under high-speed impact. High-speed and high-resolution sequential images are required to study the interaction of the bullet with the brittle ceramic materials. In this study, a device is developed to capture the sequence of high-speed impact/penetration phenomena. This system consists of a speed measurement device, a microprocessor-based camera controller, and multiple CCD cameras. By using a linear array sensor, the speed-measuring device can measure a small (diameter: up to 1 2 mm) and fast (speed: up to Mach 3) bullet. Once a bullet is launched, it passes through the speed measurement device where its time and speed is recorded, and then, the camera controller computes the exact time of arrival to the target during flight. Then, it sends the trigger signal to the cameras and flashes with a specific delay to capture the impact images sequentially. It is almost impossible to capture high-speed images without the estimation of the time of arrival. We were able to capture high-speed images using the new system with precise accuracy.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.42-47
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• 2017

In this study,we conducted an injection molding analysis of metal powder materials for the development of flanges, which are necessary adapters for optical communication. The metal powder injection molding process is a technique for producing an injection molded article having a complicated shape by mixing ceramic or stainless powder and binders. It is used to produce products which require complex processing technology or for which the productivity is low. The purpose of this study is to minimize the manufacturing processing of products which are manufactured through existing mechanical processing procedures. For the injection molding analysis, we mixed stainless STS316 metal powder with binders at a ratio of 6 to 4 to make molding materials consisting of granular pellets. Then, three-dimensional modeling and meshing were carried out to obtain the optimal injection molding analysis conditions(molding temperature, melting temperature, injection time, injection temperature, injection pressure, packing time and cooling time). As a result of the analysis, it was discovered that the inlet became available 13.29 seconds after the first injection. Also, as the flowing and packing in the melt through the sprue, runner and gate were stable, it is expected that good molds can be manufactured.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.4
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• pp.153-159
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• 2015

Inorganic pigments have been received a great attention for various applications including paint, glazed ceramic ink, art tile, and building exterior due to their excellent thermal and chemical stability. Traditionally, the compositions of $PbCrO_4$, CdS and CdSe have been widely used as a yellow inorganic pigment. However, the use of these compositions has been restricted in recent years, because they contain harmful elements such as Cd, Cr, Pb and Se. In this study, new environment-friendly ceria-based pigment was synthesized using solid state reaction. Crystal structure and morphology of the obtained $Ce_{1-x}Zr_xBi_yO_{2-y/2}$ yellow pigment were analyzed using XRD and SEM, respectively. Substitutional effect of Zr and Bi on the pigment color was analyzed using UV-vis. spectrophotometer and CIE $L^*a^*b^*$ analysis. The crystal structure of the obtained pigments was dependent on the calcination temperature. The color characteristics and absorption band of the pigments were dependent on the calcination temperature and Zr, Bi contents. As a result, all the obtained yellow pigments showed the effective absorption ranged from ultraviolet to visible light, and $Ce_{0.44}Zr_{0.36}Bi_{0.20}O_{0.19}$ (x = 0.36, y = 0.20) pigment showed the most brilliant yellow color.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.9
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• pp.481-487
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• 2019

Additive manufacturing is a state-of-the-art manufacturing process technology in which three-dimensional structures are fabricated by laminating two-dimensional sections of a structure using various materials such as plastic, ceramics, and metals. The additive manufacturing technology has the advantage of high design freedom, while the surface property (roughness) of the finished product varies depending on the process conditions, which necessitates performing a post-process after the products are manufactured. In this study, the surface roughness of a structure made of polyamide 12, which was manufactured by SLS (Selective Laser Sintering) and MJF (Multi Jet Fusion) process was compared. The processing condition was classified by the building orientation of structure as 0, 45, and 90 degrees, which is the angle between the analytical surface and the horizontal plane of the fabrication platform. Structures with a hole of various diameters ranging from 1mm to 10mm were manufactured and the hole characteristics (ratio of hole depth to diameter) and results of the specimens were compared. As a result of the surface characteristics analysis, the surface roughness value of the specimens manufactured with a building orientation of $45^{\circ}$ was the highest in both technologies. In the case of the through-hole structure fabrication, the shape was maintained with 5mm and 10mm diameter holes regardless of the building orientation, although the hole forming was difficult for the smaller holes.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.3
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• pp.116-126
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• 2021

Diesel particulate filter (DPF) is a typical application field of cordierite (Mg₂Al₄Si₅O₁₈) honeycomb. Green body for DPF honeycomb was extruded using slurry paste and sintered at the temperature range of 980~1450℃. Quantitative crystal phase analysis was carried out by using Rietveld refinement method for powder XRD data. In conjunction with the quantitative Rietveld analysis, SEM-EDS analysis was carried for the crystal phases (indialite, cordierite, cristobalite, alumina, spinel, mullite, pro-enstatite). After removing amorphous phase on the sintered surfaces by chemical etching method, the shape and composition of the crystal phases can be clearly identified by SEM-EDS method. By combining the Rietveld refinement method and SEM-EDS analysis, crystal phase evolution process in DPF cordierite ceramics could be clarified. In addition, the coefficient of thermal expansion (CTE) of the DPF honeycombs were measured and compared with the calculated CTEs based on the quantitative crystal phase analysis results.

• Clean Technology
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• v.28 no.2
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• pp.154-162
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• 2022

Microstructured Al@Al₂O₃ and Al@Ni-Al LDH (LDH = layered double hydroxide) core-shell metal-ceramic composites are prepared by hydrothermal reactions of aluminum (Al) metal substrates. Controlled hydrothermal reactions of Al metal substrates induce the hydrothermal dissolution of Al ions at the Al-substrate/solution interface and reconstruction as porous metal-hydroxides on the Al substrate, thereby constructing unique metal-ceramic core-shell composite structures. The morphology, composition, and crystal structure of the core-shell composites are affected largely by the ions in the hydrothermal solution; therefore, the critical physicochemical and surface properties of these unique metal-ceramic core-shell microstructures can be modulated effectively by varying the solution composition. A Ni/Al@Al₂O₃ catalyst with highly dispersed catalytic Ni nanoparticles on an Al@Al₂O₃ core-shell substrate was prepared by a controlled reduction of an Al@Ni-Al LDH core-shell prepared by hydrothermal reactions of Al in nickel nitrate solution. The reduction of Al@Ni-Al LDH leads to the exolution of Ni ions from the LDH shell, thereby constructing the Ni nanoparticles dispersed on the Al@Al₂O₃. The catalytic properties of the Ni/Al@Al₂O₃ catalyst were investigated for CO₂ methanation reactions. The Ni/Al@Al₂O₃ catalyst exhibited 2 times greater CO₂ conversion than a Ni/Al₂O₃ catalyst prepared by conventional incipient wetness impregnation and showed high structural stability. These results demonstrate the high effectiveness of the design and synthesis methods for the metal-ceramic composite catalysts derived by hydrothermal reactions of Al metal substrates.

• Clean Technology
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• v.20 no.4
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• pp.375-382
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• 2014

This work investigated the plasma-catalytic decomposition of isopropyl alcohol (IPA) and the behavior of the byproduct compounds over monolith-supported metal oxide catalysts. Iron oxide ($Fe_2O_3$) or copper oxide (CuO) was loaded on a monolithic porous ${\alpha}-Al_2O_3$ support, which was placed inside the coaxial electrodes of plasma reactor. The IPA decomposition efficiency itself hardly depended on the presence and type of metal oxides because the rate of plasma-induced decomposition was so fast, but the behavior of byproduct formation was largely affected by them. The concentrations of the unwanted byproducts, including acetone, formaldehyde, acetaldehyde, methane, carbon monoxide, etc., were in order of $Fe_2O_3/{\alpha}-Al_2O_3$ < $CuO/{\alpha}-Al_2O_3$ < ${\alpha}-Al_2O_3$ from low to high. Under the condition (flow rate: $1L\;min^{-1}$; IPA concentration: 5,000 ppm; $O_2$ content: 10%; discharge power: 47 W), the selectivity towards $CO_2$ was about 40, 80 and 95% for ${\alpha}-Al_2O_3$, $CuO/{\alpha}-Al_2O_3$ and $Fe_2O_3/{\alpha}-Al_2O_3$, respectively, indicating that $Fe_2O_3/{\alpha}-Al_2O_3$ is the most effective for plasma-catalytic oxidation of IPA. Unlike plasma-alone processes in which tar-like products formed from volatile organic compounds are deposited, the present plasma-catalyst hybrid system did not exhibit such a phenomenon, thus retaining the original catalytic activity.

• The korean journal of orthodontics
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• v.28 no.1 s.66
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• pp.43-49
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• 1998

The aim of this study were to measure and compare the stress level on three type brackets and each other material (stainless steel, ceramic) with tipping and torquing forces by using the finite element analysis and to design biomechanically favorable brackets. For this study, three kinds of brackets were selected(A:Transcend-RMO, B:Signature-Unitek, C:PAW: plain archwire appliance-applied for a patent in Yonsei Udiversity). The slot size of bracket was 0.022inch and the size of archwire was 0.0175x0.025inch and taper shaped archwire was used in PAW. Loading force in tipping was 4.27N and torquing force was 32.858N applied by archwire torsion with 19.7degree and 11.3 degree in C type bracket. The conclusions were that (1) The finite element method proved to be a useful tool in the stress analysis of orthodontic bracket subjected to various forces. (2) With tipping, the stresses were concentrated at the gingival wall of the wire slot where it meets the mesial bracket surface and the incisal wall of the wire slot where it meets the distal bracket surface and with torquing, the stresses were concentrated at the junction of the gingival or incisal wall and base of the slot. (3) The maximum stress value was higher in torquing force than tipping force and therefore it is desirable to design on the basis of torquing force. (4) It was considered that the change in material might be affect on the diminish of stress value in the place of stess concentration. (5) The maximum stress value was highest on PAW bracket when the tipping and torquing force was applied and therefore it would be desirable to use mechanically favorable material on PAW bracket.

• Korean Journal of Dental Materials
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• v.45 no.4
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• pp.257-274
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• 2018

The purpose of this study was to evaluate the effect of acid-treatment conditions on the surface properties of the RBM (Resorbable Blast Media) treated titanium. Disk typed cp-titanium specimens were prepared and RBM treatments was performed with calcium phosphate ceramic powder. Acid solution was mixed using HCl, $H_2SO_4$ and deionized water with 4 different volume fraction. The RBM treated titanium was acid treated with different acid solutions at 3 different temperatures and for 3 different periods. After acid-treatments, samples were cleaned with 1 % Solujet solution for 30 min and deionized water for 30 min using ultrasonic cleanser, then dried in the electrical oven ($37^{\circ}C$). Weight of samples before and after acid-treatment were measured using electric balance. Surface roughness was estimated using a confocal laser scanning microscopy, crystal phase in the surface of sample was analyzed using X-ray diffractometer. Surface morphology and components were evaluated using Scanning Electron Microscope (SEM) with Energy Dispersive X-ray spectroscopy (EDX) and X-ray Photoemission Spectroscopy (XPS). Values of the weight changes and surface roughness were statistically analyzed using Tukey-multiple comparison test (p=0.05). Weight change after acid treatments were significantly increased with increasing the concentration of $H_2SO_4$ and temperature of acid-solution. Acid-treatment conditions (concentration of $H_2SO_4$, temperature and time) did not produce consistent effects on the surface roughness, it showed the scattered results. From XRD analysis, formation of titanium hydrides in the titanium surface were observed in all specimens treated with acid-solutions. From XPS analysis, thin titanium oxide layer in the acid-treated specimens could be evaluated. Acid solution with $90^{\circ}C$ showed the strong effect on the titanium surface, it should be treated with caution to avoid the over-etching process.