• Korean Journal of Materials Research
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• v.16 no.10
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• pp.647-651
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• 2006

A new class of compounds in the form of skutterudite structure, Fe doped $CoSb_3$ with a nominal composition of $Fe_xCo_{4-x}Sb_{12}$ ($0{\leq}x{\leq}2.5$), were synthesized by mechanical alloying of elemental powders followed by vacuum hot pressing. Nanostructured, single-phase skutterudites were successfully produced by vacuum hot pressing using as-milled powders without subsequent heat-treatments for the compositions of $x{\leq}1.5$. However, second phase was found to form in case of $x{\geq}2$, suggesting the solubility limit of Fe with Co in this system. Thermoelectric properties including thermal conductivity from 300 to 600 K were measured and discussed. Lattice thermal conductivity was greatly reduced by introducing a dopant up to x=1.5 as well as by increasing phonon scattering in nanostructured skutterudite, leading to enhancement in the thermoelectric figure of merit. The maximum figure of merit was found to be 0.32 at 600 K in the composition of $Fe_xCo_{4-x}Sb_{12}$.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.2
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• pp.171-175
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• 2014

In this study, we suggest a method to measure the thickness of thin films nondestructively using the dispersion characteristics of a surface acoustic wave propagating along the thin film surface. To measure the thickness of thin films, we deposited thin films with different thicknesses on a Si (100) wafer substrate by controlling the deposit time using the E-beam evaporation method. The thickness of the thin films was measured using a scanning electron microscope. Subsequently, the surface wave velocity of the thin films with different thicknesses was measured using the V(z) curve method of scanning acoustic microscopy. The correlation between the measured thickness and surface acoustic wave velocity was verified. The wave velocity of the film decreased as the film thickness increased. Therefore, thin film thickness can be determined by measuring the dispersion characteristics of the surface acoustic wave velocity.

• Applied Chemistry for Engineering
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• v.23 no.2
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• pp.138-142
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• 2012

The ${\epsilon}$ type copper phthalocyanine (${\epsilon}$-CuPc), called as a pigment blue 15 : 6, is a significant material to produce a blue pixel in LCD (Liquid Crystal Display) panel. In this study, ${\epsilon}$-CuPc sample was synthesized at various reaction conditions by applying the seed method using ${\epsilon}$-CuPc nanoparticles as a seed. Adequate synthetic conditions of the samples were selected by analyzing and comparing crystalline structure, crystalline purity, microstructure, and synthetic yield of the samples with ${\alpha}$ and ${\beta}$ crystalline CuPc samples. The chemical and crystalline structure of the samples were tested using FT-IR spectrometer and X-ray diffractometry, respectively. The shape of the particle was examined using field emission scanning electiron microscope while the thermal property was tested utilizing thermogravimetric analysis.

• Journal of Radiation Industry
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• v.9 no.1
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• pp.9-13
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• 2015

Epoxy resin is widely used as aerospace, automobile, construction and electronics due to their good mechanical and electrical properties and environmental advantages. However, the inherent flammability of epoxy resin has limited its application in some field where good flame retardancy is required. Nano clay can enhance the properties of polymers such as flames retardancy and thermal stability. In this study, we have investigated the nanoclay filled epoxy composite, which has good flame retardancy while maintaining high mechanical properties. The cured epoxy resins were obtained using an electron beam curing process. The nano clays were dispersed in epoxy acrylate solution and mechanically stirred. The prepared mixtures were irradiated using an electron beam accelerator. The composites were characterized by gel content and thermal/mechanical properties. Moreover, the flammability of the composite was evaluated by limited oxygen index (LOI). The flame retardancy of nano clay filled epoxy composite was evidently improved.

• Korean Journal of Metals and Materials
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• v.50 no.1
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• pp.71-77
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• 2012

We studied the effect of heat treatment on the microstructures and mechanical strength of the solder joints in the Light Emitting Diode (LED) packages. The commercial LED packages were mounted on the a flame resistance-4 (FR4) Printed Circuit Board (PCB) in the reflow process, and then the joints were aged at $125^{\circ}C$ for 100, 200, 300, 500 and 1000 hours, respectively. After the heat treatment, we measured the shear strength of the solder joints between the PCB and the LED packages to evaluate their mechanical property. We used Pb-free Sn-3.0Ag-0.5Cu solder to bond between the LED packages and the PCBs using two different surface finishes, Electroless Nickel-Immersion Gold (ENIG) and Electroless Nickel-Electroless Palladium-Immersion Gold (ENEPIG). The microstructure of the solder joints was observed by a scanning electron microscope (SEM). (Cu,Ni)6Sn5 intermetallic compounds (IMCs) formed between the solder and the PCB, and the thickness of the IMCs was increased with increasing aging time. The shear strength for the ENIG finished LED package increased until aging for 300 h and then decreased with increasing aging time. On the other hand, in the case of an ENEPIG finished LED package, the shear strength decreased after aging for 500 h.

• Journal of Radiation Industry
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• v.6 no.1
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• pp.55-59
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• 2012

Polyacrylonitrile (PAN)-based carbon fibers have been widely used due to their unique chemical, electrical, and mechanical properties. Electron beam irradiation has been extensively employed as means of altering properties of polymeric materials. Electron beam irradiation can induce chemical reactions in materials without any catalyst. Electron beam irradiation may be useful in accelerating the thermal compression stabilization of PAN nanofibers. To investigate the irradiation effect on PAN fibers, PAN nanofibers were irradiated by electron beam at 1,000~5,000 kGy. Irradiated and non-irradiated PAN nanofibers were heated at 180 and $220^{\circ}C$ without applying pressure for 15 min. Then 1 metric ton has been applied for 5 min. SEM images have been found that the fiber kept its morphological behavior after the hot pressing up to electron beam irradiated 1,000 kGy. DSC thermograms showed that the peak temperatures of the exothermic reactions were found to decrease with increasing electron beam irradiation doses and temperature. FT-IR spectra have been found to decrease $C{\equiv}N$ stretch band with increasing the electron beam irradiation dose. These results indicate that the modification of PAN via reactions such as cyclization is significantly enhanced by electron beam irradiation and thermal compression technique.

• Journal of Adhesion and Interface
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• v.15 no.2
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• pp.63-68
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• 2014

Hollow mesoporous carbon nitride material with sphere shape was synthesized using polystyrene sphere as template and cyanamide as nitrogen and carbon atom sources via thermal treatment process. The process of the silica removal is not necessary because silica as template is not in use for the synthesis of hollow mesoporous carbon nitride material and any solvents are also not in use. The size of polystyrene spheres was about 170 nm. Hollow diameter and wall thickness were 82 nm and 13 nm, respectively, in hollow mesoporous carbon nitride sphere. Surface area, mesopore size and pore volume of hollow mesoporous carbon nitride material was $188m^2g^{-1}$, 3.8 nm and $0.35cm^3g^{-1}$, respectively. The wall in hollow sphere has graphitic structure. Hollow mesoporous carbon nitride material has potential applications in the area of fuel cell, catalysis, photocatalysis, electroemmision device, etc.

• Journal of the Korean Magnetics Society
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• v.21 no.5
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• pp.185-192
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• 2011

The technique of producing thin film plays a crucial role in modern science and technology as well as in industrial purposes. Numerous efforts have been made to get high quality thin film through surface treatment of materials. PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition) are two of the most popular deposition techniques used in both scientific study and industrial use. It is well known that the film deposited by PVD and CVD commonly possesses a columnar microstructure which affects many film properties. In recent years, various types of deposition sources which feature high material uses and excellent film properties have been developed. Electromagnetic levitation source appeared as an alternative deposition source to realize high deposition rate for industrial use. Complex film structures such as nano multilayer and multi-components have been prepared to achieve better film properties. Glancing angle deposition (GLAD) has also been developed as a technique to engineer the columnar structure of thin films on the micro- and nanoscale. In this paper, the trends and major issues of thin film technology based on PVD and CVD have been discussed together with the prospect of thin film technology.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.18 no.1
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• pp.83-90
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• 2019

LED lighting is spreading on the strength of LED lighting, and various government policies are being implemented. VLC research which is a wireless communication technology using lighting has been actively conducted, and it has been proven through many studies that a general LED light source such as a high-speed data transmitter can be used. But from now on, one of the main problems is the noise from side lights, which can be compared to the noise of radio broadcasts. So in this paper, we proposed a noise canceling model to remove the interference of ambient light by using an optical filter for a detachable VLC channel. In order to verify the proposed model, various high brightness RGB LED modules were used for comparative analysis. In addition, the applicability was verified through experiments using High Luminance LED lighting which is applied in real life.

• Korean Chemical Engineering Research
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• v.57 no.3
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• pp.432-437
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• 2019

An atmospheric pressure floating electrode-dielectric barrier discharge (FE-DBD) system having flexible electrodes was developed and its plasma characteristics was investigated. Polytetrafluoroethylene (PTFE), polydiemethylsiloxane (PDMS), and polyethylene terephthalate (PET) were used as flexible dielectrics for flexible powered-electrodes. The optical intensity and electron temperature of the atmospheric pressure FE-DBD plasma increased with the voltage applied to the powered electrode, and increased in the order of PTFE < PDMS < PET at a fixed voltage. This behavior was explained in terms of the change in the capacitance of the flexible dielectrics with the dielectric type and voltage, implying that the plasma characteristics of an atmospheric pressure FE-DBD having flexible electrodes can be controlled by modulating the flexible dielectrics for the flexible powered-electrode and the voltage applied to the powered electrode. Because an atmospheric pressure FE-DBD system can generate a plasma along the curvature of skins, it is expected to have useful applications in plasma medicine.