• Journal of Surface Science and Engineering
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• v.49 no.2
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• pp.218-224
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• 2016

Thermal radiation pastes were prepared by dispersing carbon materials as fillers with a content of 1 weight percent in an acrylic resin. The kind of fillers was as follows; $25{\mu}m$ graphite, $45{\mu}m$ graphite, $15{\mu}m$ carbon nanotube(CNT), a 1:1 mixture of $25{\mu}m$ graphite and $15{\mu}m$ CNT, and a 1:1 mixture of $45{\mu}m$ graphite and $15{\mu}m$ CNT. Thermal emissivity was measured as 0.890 for the samples with graphite only, 0.893 for that with CNT only, and 0.892 for those containing both. After coating prepared pastes on a side of 0.4 mm thick aluminium plate and placing the plate over an opening of a box maintained at $92^{\circ}C$ with the coated side out, the temperatures on the uncoated side of the plates were measured. The samples containing graphite and CNT showed the lowest temperatures. The paste with mixed fillers was coated on the back side of the PCB of an LED module and thermal analysis was carried out using Thermal Transient Tester (T3ster) in a still air box. The thermal resistance of the module with coated PCB was measured as 14.34 K/W whereas that with uncoated PCB was 15.02 K/W. The structure function analysis of T3ster data revealed that the difference between junction and ambient temperatures was $13.8^{\circ}C$ for the coated case and $18.0^{\circ}C$ for the uncoated. From the infrared images of heated LED modules, the hottest-spot temperature of the module with coated PCB was lower than that of the uncoated one for a given period of LED operation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.126-127
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• 2007

Sn-filled and Fe-doped $CoSb_3$ skutterudites were synthesized by encapsulated induction melting. Single ${\delta}$-phase was successfully obtained by subsequent annealing and confirmed by X-ray diffraction analysis. Temperature dependences of Seebeck coefficient, electrical resistivity and thermal conductivity were examined from 300 K to 700 K. The positive Seebeck coefficient confirmed the p-type conduction. Electrical resistivity increased with increasing temperature, which shows that the $Sn_zCo_3FeSb_{12}$ skutterudite is highly degenerate. Thermal conductivity was reduced by Sn-filling because the filler atoms acted as phonon scattering centers in the skutterudite lattice. Thermoelectric figure of merit was enhanced by Sn filling and its optimum filling content was considered to be z=0.3 in the $Sn_zCo_3FeSb_{12}$ system.

• Polymer(Korea)
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• v.26 no.5
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• pp.623-633
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• 2002

The flame retardant and thermal properties of ortho-cresol novolac (OCN) and biphenyl epoxy blends containing red-phosphorus were investigated. For five types of compounds designed with the volume ratio of OCN and biphenyl epoxy, thermal properties were analysed by TGA or DTC, and flame retardancy effectiveness was estimated through UL-94V test. While the flame retardant and thermal properties were improved with the content of filler and red-phosphorus, the excessive amount of red-phosphorus caused to deteriorate those properties. Using the blends of OCN/biphenyl rather than pure OCN or biphenyl epoxy as a matrix the flame retardancy of composites could be improved by the synergic effects of high thermal resistance of OCN and intumescent property of biphenyl. The flame retardant me chanism of epoxy compound containing red-phosphorus could be thought of the heat-insulating effect of intumescent char-layer formed in the surface of composites.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.46 no.5
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• pp.79-87
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• 2014

The enrichment with nutrients in rivers and lakes becomes serious problems in Korea. As the environmental friendly solution, the phytoremediation are getting more attention and the water hyacinth could be a strong candidate plant for this. Water hyacinth is a free floating freshwater plant proven to be a effective plant used for a purification of a polluted lakes, sewage wastewater, and livestock wastewater. The biggest obstacles for application of water hyacinth in Korea could be the disposal of the water hyacinth before winter, because there is no feasible use for the water hyacinth until now. In this study, the characteristics of water hyacinth were deeply investigated for providing background data to develop appropriate application of the water hyacinth. The water hyacinth was fractioned three parts, leaf, air blader, root of which morphological properties were evaluated with microscope and field emission scanning electron microscope (FE-SEM). The water contents of each parts of the water hyacinth were 87% for leaf, 96.5% for air bladder, 94.6% for root. The chemical compositions of each parts were also measured and showed around 29% of hot water extract in leaf and air bladder, 42% holocellulose for leaf, 47% holocellulose for air bladder. The application of water hyacinth biomass without root parts to papermaking provided bulkier structure, but the tensile strength was decreased.

• Restorative Dentistry and Endodontics
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• v.39 no.4
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• pp.310-318
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• 2014

Objectives: This study examined the influence of the resin thickness on the polymerization of silorane- and methacrylate-based composites. Materials and Methods: One silorane-based (Filtek P90, 3M ESPE) and two methacrylate-based (Filtek Z250 and Z350, 3M ESPE) composite resins were used. The number of photons were detected using a photodiode detector at the different thicknesses (thickness, 1, 2 and 3 mm) specimens. The microhardness of the top and bottom surfaces was measured (n = 15) using a Vickers hardness with 200 gf load and 15 sec dwell time conditions. The degree of conversion (DC) of the specimens was determined using Fourier transform infrared spectroscopy (FTIR). Scratched powder of each top and bottom surface of the specimen dissolved in ethanol for transmission FTIR spectroscopy. The refractive index was measured using a Abbe-type refractometer. To measure the polymerization shrinkage, a linometer was used. The results were analyzed using two-way ANOVA and Tukey's test at p < 0.05 level. Results: The silorane-based resin composite showed the lowest filler content and light attenuation among the specimens. P90 showed the highest values in the DC and the lowest microhardness at all depth. In the polymerization shrinkage, P90 showed a significantly lower shrinkage than the rest two resin products (p < 0.05). P90 showed a significantly lower refractive index than the remaining two resin products (p < 0.05). Conclusions: DC, microhardness, polymerization rate and refractive index linearly decreased as specimen thickness linearly increased. P90 showed much less polymerization shrinkage compared to other specimens. P90, even though achieved the highest DC, showed the lowest microhardness and refractive index.

• Applied Chemistry for Engineering
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• v.32 no.2
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• pp.157-162
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• 2021

In this study, 3D printing filaments using recycled polypropylene (rPP) were produced by a single screw extruder. Graphene composite filament was also prepared using electrochemically exfoliated graphene (EEG) as a composite filler by adding 10, and 20 wt% of EEG to rPP. The graphene and rPP were successfully dispersed with great homogeneity, so that 3D filaments were uniformly produced, and their thermal properties increased as the graphene content increased. The mechanical property was also improved when EEG was 10 wt% but decreased when EEG was 20 wt% compared to that of rPP. 3D structures were successfully manufactured using prepared 3D filaments by a conventional 3D printer, and great advantages can be expected in terms of environmental and economical perspective by adopting plastic waste.

• Journal of the Microelectronics and Packaging Society
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• v.28 no.2
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• pp.51-57
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• 2021

This paper analyzed the effects of the concentration of nano-silica particles contained in epoxy resin on the thermomechanical properties of the composite materials. The 12nm sized nanoparticles were mixed with epoxy polymer by 5 different weight ratios for the test samples. The glass transition temperature, stress relaxation, and thermal expansion behaviors were measured using dymanic mechanical analyzer (DMA) and thermomechanical analyzer (TMA). It was shown that the nano particle mixing ratios had significant influences on the viscoelastic behaviors of the materials. As the content of the silica particles was increased, the elastic modulus was also increased, while the glass transition temperatures were decreased. Fourier Transform Infrared Spectroscopy (FTIR) results played an important role in determining the causes of the property changes by the filler contents in terms of the molecular structures, enabling the interpretations on the material behaviors based on the chemical structure changes.

• Steel and Composite Structures
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• v.37 no.6
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• pp.711-731
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• 2020

This paper deals with free vibration of FG sandwich annular sector plates on Pasternak elastic foundation with different boundary conditions, based on the three-dimensional theory of elasticity. The plates with simply supported radial edges and arbitrary boundary conditions on their circular edges are considered. The influence of carbon nanotubes (CNTs) waviness, aspect ratio, internal pores and graphene platelets (GPLs) on the vibrational behavior of functionally graded nanocomposite sandwich plates is investigated in this research work. The distributions of CNTs are considered functionally graded (FG) or uniform along the thickness of upper and bottom layers of the sandwich sectorial plates and their mechanical properties are estimated by an extended rule of mixture. In this study, the classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. The core of structure is porous and the internal pores and graphene platelets (GPLs) are distributed in the matrix of core either uniformly or non-uniformly according to three different patterns. The elastic properties of the nanocomposite are obtained by employing Halpin-Tsai micromechanics model. A semi-analytic approach composed of 2D-Generalized Differential Quadrature Method (2D-GDQM) and series solution is adopted to solve the equations of motion. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. Some new results for the natural frequencies of the plate are prepared, which include the effects of elastic coefficients of foundation, boundary conditions, material and geometrical parameters. The new results can be used as benchmark solutions for future researches.

• Imaging Science in Dentistry
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• v.52 no.3
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• pp.303-308
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• 2022

Purpose: This technical report aims to describe and detail the use of micro-computed tomography for a reliable evaluation of the bulk-fill composite/tooth interface. Materials and Methods: Bulk-fill composite restorations in tooth cavities were scanned using micro-computed tomography to obtain qualitatively and quantitatively valuable information. Two-dimensional information was processed using specific algorithms, and ultimately a 3-dimensional (3D) specimen reconstruction was generated. The 3D rendering allowed the visualization of voids inside bulk-fill composite materials and provided quantitative measurements. The 3D analysis software VG Studio MAX was used to perform image analysis and assess gap formation within the tooth-restoration interface. In particular, to evaluate internal adaptation, the Defect Analysis addon module of VG Studio Max was used. Results: The data, obtained with the processing software, highlighted the presence and the shape of gaps in different colours, representing the volume of porosity within a chromatic scale in which each colour quantitatively represents a well-defined volume. Conclusion: Micro-computed tomography makes it possible to obtain several quantitative parameters, providing fundamental information on defect shape and complexity. However, this technique has the limit of not discriminating materials without radiopacity and with low or no filler content, such as dental adhesives, and hence, they are difficult to visualise through software reconstruction.

• Applied Chemistry for Engineering
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• v.33 no.4
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• pp.381-385
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• 2022

It is very important to secure the adhesion durability between the base film and the conductive paste for the development of a sensor for detecting hazardous chemicals. In this study, an ester binder was used to improve the adhesive properties which can be a problem when applying the sensor to the cross cut 0B or 1B grade. This problem was found while evaluating the adhesive properties by coating the polyaniline/graphene nano plate (GNP) paste on the polyethylene terephthalate (PET) film. When 10 wt% or more of the ester-based binder was added, the cross cut grade to which the sensor can be applied was 3B or higher. It was confirmed that the excessive addition of the binder may affect the electrical properties of the conductive paste and actually decrease the reactivity to sulfuric acid. To improve the electrical property, a carbon black (CB) content was varied resulting in the optimum electrical property observed at 2 wt% of CB.