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Hwang D.K.,Small and Medium Business Corporation | Shul Y.G.,Yonsei University | Chu Y.H.,Sangji University
Polymer Composites | Year: 2015

Photocatalytic degradation mechanism of the polycarbonate(PC)/TiO2 composite films was studied under the ambient air condition in order to investigate the feasibility of the PC/TiO2 composite as a photodegradable polymer. TiO2 composition in the PC/TiO2 composite was changed from 0 wt% to 4 wt%. Photodegradation behaviors of the composite films were compared with that of the pure PC films by performing the weight loss monitoring under UV irradiation, FTIR spectroscopy, color measurement analysis, SEM, and XPS analysis. The weight loss rate of the PC/TiO2 composite film (33% weight loss after 300 h) with 4 wt% TiO2 was twice as high as the pure PC films (14% weight loss after 300 h). The increase in the FTIR hydroxyl peak, and carbonyl peak intensity and the yellowing observation during the photodegradation were due to the formation of the photoproducts (aliphatic, aromatic chain-ketones, aromatic, and OH radical) and the structural modification of polycarbonate. XPS analysis of composite film showed the photodegradation of the polymer surface and TiO2 particles exposure on the surface of the composite films matrix. © 2014 Society of Plastics Engineers.

Son J.-Y.,Kyungpook National University | Kim J.-H.,Small and Medium Business Corporation | Kim W.-B.,Korea Technology Credit Guarantee Fund | Ye B.-J.,Kyungpook National University
Metals and Materials International | Year: 2010

In this study, the effect of the microstructure and mechanical properties of austempered high-carbon (0.9 %C) high-silicon (2.3 %Si) cast steel were investigated. The specimens were austenitised for 60 min. at 900 °C, and austempered at 260 °C, 320 °C, and 380 °C for periods of time ranging from 30 min to 240 min. After receiving this heat treatment, the mechanical properties were measured using both a tensile test and hardness test. To analyze the microstructure, an optical microscope was used and an X-ray diffraction (XRD) analysis was carried out. In this study, high carbon high silicon cast steel without graphite and with higher tensile strength (1300 MPa to 2200 MPa) and elongation (~25 %), when compared to austempered ductile cast iron (ADI), was developed. When the austempering temperature was at 260 °C, the microstructures were low ausferrite, but at 380 °C, an upper ausferrite structure was formed. As the austempering temperature increased from 260 to 380 °C, the ultimate tensile strength and hardness decreased, but the elongation and retained austenite volume fraction increased. In addition, the microstructures were coarser. © KIM and Springer.

Kim H.-J.,Korea Institute of Industrial Technology | Jung R.,Korea Institute of Industrial Technology | Jung R.,Samsung | Hwang D.-K.,Small and Medium Business Corporation | And 2 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2014

The surface of commercial carbon black was modified by pyrolysis of acetonitrile in attempt to obtain the graphitic carbon coating layer. It was confirmed that the surface of carbon black was partially graphitized, having 0.23 of graphitization index and 1.87 nm of mean stack height. From the electrochemical oxidation test of carbon, the carbon-coated carbon black showed higher corrosion resistance than the untreated carbon black although the core of the carbon black support still remained untreated. When it was applied to the support for platinum electrocatalyst, the enhanced stability was observed. From those corrosion tests as well as XPS results, it can be suggested that the partially crystalline graphitic carbon surface facilitates the relatively more reduced surface of platinum. Copyright © 2014 American Scientific Publishers.

Hwang D.K.,Small and Medium Business Corporation | Shul Y.-G.,Yonsei University | Oh K.,Inha Technical College
Industrial and Engineering Chemistry Research | Year: 2013

Nanosize Au-TiO2 is becoming popular to photocatalytic application in visible light. A new fabrication process of photocatalyst is introduced for the purpose of its potential utilization under sunlight. A mixture of photocatalyst and polycarbonate (PC) was cast on a glass substrate to form a film. The photocatalytic experiment was performed in the UV region and visible region separately with powdery samples first, followed by composite films. When powdery Au-TiO2 was applied to decompose of acetaldehyde, activity inferior to Degussa P-25 was observed in UV light, but superior activity was observed in visible light. In the case of Au-TiO2 in PC composite film, evidence of acetaldehyde decomposition was observed, unlike the case of P-25 in PC composite, which showed negligible traces of acetaldehyde decomposition. © 2013 American Chemical Society.

Hwang D.K.,Small and Medium Business Corporation | Lee H.S.,Dong - A University | Kim H.J.,Korea Institute of Industrial Technology | Shul Y.G.,Yonsei University | Oh K.,Inha Technical College
Polymer Engineering and Science | Year: 2014

Crystallization of polycarbonate (PC) was attempted by a precipitated method in a ternary system of PC/solvent/nonsolvent. Chloroform was used as a solvent, and isopropanol was used as a nonsolvent. Crystallization of PC was clearly observed as a powdery state when chloroform/isopropanol mixtures were prepared by 68/32 and 61/39 vol%. Crystallinity of PC was evaluated by differential scanning calorimeter and X-ray diffractometer. As the difference of solubility parameters between PC and binary solvent/nonsolvent mixtures became smaller, the relative crystallinity of PC was increased. The highest degree of PC crystallization was obtained when chloroform/isopropanol was mixed by 61/39 vol%. Subsequently, crystallized PC was used as a filler to high-density polyethylene (HDPE) composite. HDPE composite incorporated by crystallized PC filler improved its mechanical and thermal properties. Flexural modulus was increased from 620 to 990 N/mm2, and flexural strength was increased from 720 to 1080 N/mm2. And heat deflection temperature measurement and flammability test supported the enhancement of thermal property when crystallized PC was added to HDPE composite up to 40 wt%. POLYM. ENG. SCI., 54:1893-1899, 2014. © 2013 Society of Plastics Engineers.

Hwang D.K.,Small and Medium Business Corporation | Oh K.,Inha Technical College
Iranian Polymer Journal (English Edition) | Year: 2014

Reducing cycle time in injection molding process is important because it can save operational cost and increase product yield. Cycle time can be categorized by six criteria, which are metering time, time for closing a mold, packing time, holding time, cooling time, and the time needed to open a mold and to eject the molded product. It was found that the metering time is crucial to predict the cycle time of glass fiber reinforced syndiotactic polystyrene (sPS/GF, 60/40 by weight). In many cases, however, cycle time could be reduced by saving cooling time. This study is motivated by the demand to reduce the cycle time of sPS/GF composite. Since the increase of thermal conductivity leads to the reduction of cooling time, silicon carbide (SiC) is employed to evaluate if it can increase the thermal conductivity of sPS/GF composite. When SiC is added to replace entire GF in sPS/GF composite, the mechanical property of the resulting sPS/SiC (60/40 by weight) composite was not satisfied even though its thermal conductivity was enhanced to about 62 %. Within tolerable ranges in mechanical properties, SiC was added to replace a half amount of existing GF filler. sPS/GF/SiC (60/20/20 by weight) composite achieved the enhancement of thermal conductivity from 0.230 to 0.308 W/m K (34 %) which resulted in the effective reduction of both cooling time and cycle time from 16 to 10 s and from 47 to 38 s, respectively. It should be noted that additional time saving was obtained by 3 s between 6 s in cooling and 9 s in overall cycle time. It can be interpreted by the fact that the increase of thermal conductivity also accelerated the heating rate of sPS/GF/SiC composite. © 2014 Iran Polymer and Petrochemical Institute.

Hwang D.K.,Small and Medium Business Corporation | Lee H.S.,Dong - A University | Oh K.,Inha Technical College
Polymer - Plastics Technology and Engineering | Year: 2014

Criteria of cycle time include metering, closing a mold, packing, holding, cooling, opening a mold and ejecting. Interestingly, metering time was found relatively lengthy in the composite of glass fiber (GF)-reinforced syndiotactic polystyrene (sPS) during injection molding. It was motivated by the ideas that analyzing dynamic thermal property may provide the correlation with metering time because differential scanning calorimeter does not fully provide dynamic thermal property. We created new measuring system to examine thermal behavior in the presence of pressure loading. The method was very effective to determine the melting rate of thermoplastics in the presence of pressure loadings. © 2014 Copyright Taylor & Francis Group, LLC.

Lee H.-N.,Korea Institute of Industrial Technology | Shin C.-H.,Korea Institute of Industrial Technology | Hwang D.K.,Small and Medium Business Corporation | Kim H.,Yeungnam University | And 2 more authors.
Journal of Alloys and Compounds | Year: 2015

In this study, a novel pressurized polyol method is proposed to synthesize aluminum-doped ZnO (AZO) nanoclusters without utilizing additional thermal treatment to avoid the merging of nanoclusters. The size of the AZO nanoclusters range from 100 to 150 nm with a resistivity of 204 Ω cm. The AZO nanoclusters primarily consist of approximately 10-nm nanocrystals that form a spherically clustered morphology. A two-stage growth model has been proposed based on the results of scanning electron microscopy and transmission electron microscopy images, nanocluster sizes, and X-ray diffraction patterns. The primary AZO nanocrystals first nucleate under pressurized conditions and then spontaneously aggregate into larger nanoclusters. Optically, the AZO nanoclusters exhibit a significant decrease in the near-infrared (NIR) transmittance compared to pure ZnO nanoparticles. The NIR blocking efficiency of AZO nanoclusters reached 85%. Moreover, the doping efficiency, resistivity, and NIR transmittance of AZO nanoclusters are influenced by the reaction time in the pressurized polyol solution. On the other hand, the reaction time has no effect on the particle size and crystallinity. An optically transparent coating for the AZO nanoclusters, which consisted of iso-propanol solvent and ultraviolet-curable acrylic binder, was also demonstrated. © 2015 Elsevier B.V. All rights reserved.

Kwon Y.-H.,Yeungnam University | Ahn S.-S.,Korea Institute of Machinery and Materials | Lee S.-J.,Small and Medium Business Corporation | Kwon K.-J.,Yeungnam University
Journal of the Optical Society of Korea | Year: 2015

This paper presents a hybrid single optical system for an LED surgical light that combines the advantages of both lens- and reflector-type single optical systems. The proposed hybrid single optical system includes a lens in the center and the LED light originating from the lens is redirected using a reflector to achieve a high beam spread. Iterative optical software simulations are used to provide data for the design of the lens and reflector for a single optical system, and for a complex optical system for the LED light assembly. The resulting data is also used to fabricate a prototype system. Experiments using the prototype of the hybrid single optical system and a mock-up LED surgical light confirm the system’s shadow dilution performance and its applicability to surgical operations. © 2015, Optical Society of Korea. All right reserved.

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