• Journal of the Korean Wood Science and Technology
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• v.43 no.4
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• pp.518-527
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• 2015

In this study, nanocomposite mats consisting of cellulose nanocrystals (CNCs) and poly(lactic acide) (PLA) were electrospun from a suspension mixture consisting of tetrahydrofuran at room temperature. Morphology study showed that fibers of electrospun composite mats were aligned in three dimensional surface along the fiber long-axis. Average diameter of the electrospun fibers decreased with an increase in the CNC loading level. Tensile strength of the electrospun fibers mat decreased with an increase in the CNC loading level because of bead formation in the formed fibers and low interfacial bond strength between PLA and CNC. Meanwhile, thermal stability of the electrospun nanocomposite mats was effectively improved as the amount of CNC increased.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.283-283
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• 2011

The n-doping effect by doping metal carbonate into an electron-injecting organic layer can improve the device performance by the balanced carrier injection because an electron ohmic contact between cathode and an electron-transporting layer, for example, a high current density, a high efficiency, a high luminance, and a low power consumption. In the study, first, we investigated an electron-ohmic property of electron-only device, which has a ITO/$Rb_2CO_3$-doped $C_{60}$/Al structure. Second, we examined the I-V-L characteristics of all-ohmic OLEDs, which are glass/ITO/$MoO_x$-doped NPB (25%, 5 nm)/NPB (63 nm)/$Alq_3$ (32 nm)/$Rb_2CO_3$-doped $C_{60}$(y%, 10 nm)/Al. The $MoO_x$doped NPB and $Rb_2CO_3$-doped fullerene layer were used as the hole-ohmic contact and electron-ohmic contact layer in all-ohmic OLEDs, respectively, Third, the electronic structure of the $Rb_2CO_3$-doped $C_{60}$-doped interfaces were investigated by analyzing photoemission properties, such as x-ray photoemission spectroscopy (XPS), Ultraviolet Photoemission spectroscopy (UPS), and Near-edge x-ray absorption fine structure (NEXAFS) spectroscopy, as a doping concentration at the interfaces of $Rb_2CO_3$-doped fullerene are changed. Finally, the correlation between the device performance in all ohmic devices and the interfacial property of the $Rb_2CO_3$-doped $C_{60}$ thin film was discussed with an energy band diagram.

• Membrane Journal
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• v.24 no.4
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• pp.317-324
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• 2014

It is very well known that the conventional polyamide (PA) thin film composite (TFC) reverse osmosis (RO) membranes have excellent permselective properties, but their chlorine tolerance is not good enough. In this study, to improve such chlorine tolerance, microporous membranes containing hydrophilic functional groups such as -COOH were used as a support to prepare PA TFC RO membranes, employing the conventional interfacial polymerization method. Meta-phenylene diamine (MPD) and 2,6-diamine toluene (2,6-DAT) were used as diamine monomers and tri-mesoyl chloride (TMC) as an acid monomer. The membranes prepared were characterized using various instrumental analytical methods and permeation test set-up. The flux obtained from the membranes prepared so was more than $1.0m^3/m^2day$ at 800 psi of operating pressure, while the salt rejection was over 99.0%. The chlorine tolerance of them was also found to be better than that of the membrane prepared by using conventional polysulfone support without hydrophilic functional groups.

• Membrane Journal
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• v.30 no.3
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• pp.200-204
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• 2020

1,3,5-benzenetricarbonyl trichloride is a chemical substance in which three acyl chlorides are located at 1,3,5 position in the benzene ring, and is an important chemical for the area where the good physical and chemical properties are required through high degree of crosslinking. In particular, it is possible to form a three-dimensional structure having a certain pore size, it is used in various separation and purification fields. However, the high reactivity of acyl chloride has the advantage of a fast reaction rate, which means that it is difficult to control chemically to have a certain performance in other aspects. Therefore, in this study, we observed how the chemical change of 1,3,5-benzenetricarbonyl trichloride affected the membrane performance.

• Journal of Surface Science and Engineering
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• v.44 no.5
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• pp.173-178
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• 2011

Separator of stack in polymer electrolyte membrane fuel cell (PEMFC) is high cost and heavy. If we make it low cost and lighter, it will have a great ripple. In this study, low carbon steel is used as base metal of separator because the cost of low carbon steel is very cheaper commercial metal material than stainless steels, which is widely used as separator. Low carbon steel has not a good corrosion resistance. In order to improve the corrosion resistance and electrolytic conductivity, low carbon steel needs to be surface treated. We made Chromium electroplated layer of $5{\mu}m$, $10{\mu}m$ thickness on the surface of low carbon steel and it was nitrided for 2 hours at $1000^{\circ}C$ in a furnace with 100 torr nitrogen gas pressure. Cross-sectional and surface microstructures of surface treated low carbon steel are investigated using SEM. And crystal structures are investigated by XRD. Interfacial contact resistance and corrosion tests were considered to simulate the internal operating conditions of PEMFC stack. The corrosion test was performed in 0.1 N $H_2SO_4$ + 2 ppm $F^-$ solution at $80^{\circ}C$. Throughout this research, we try to know that low carbon steel can be replaced stainless steel in separator of PEMFC.

• Journal of Surface Science and Engineering
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• v.44 no.5
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• pp.226-231
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• 2011

Graphene was coated on STS 316L by electro spray coating method to improve its properties of corrosion resistance and contact resistance. Exfoliated graphite (graphene) was made of the graphite by chemical treatment. Graphene is distributed using dispersing agent, and STS 316L was coated with diffuse graphene solution by electro spray coating method. The structure of the exfoliated graphite was analyzed using XRD and the coating layer of surface was analyzed by using SEM. Analysis showed that multi-layered graphite structure was destroyed and it was transformed into fine layers graphene structure. And the result of SEM analysis on the surface and the cross section, graphene layer was uniformly formed with 3~5 ${\mu}m$ thickness on the surface of substrate. Corrosion resistance test was applied in the corrosive solution which is similar to the PEM fuel cell stack inside. And interfacial contact resistance test was measured to simulate the internal operating conditions of PEM fuel cell stack. The results of measurements show that stainless steel coated with graphene was improved in corrosion resistance and surface contact resistance than stainless steel without graphene coating layer.

• Journal of Korea Foundry Society
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• v.6 no.1
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• pp.12-19
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• 1986

This study was undertaken to understand the formation mechanism of the hard spots in high strength brass. To investigate the behavior of the hard spots in the isothermal liquid state with varying silicon content, the rapidly quenched specimens were obtained by suctioning the melt into the silica tube and water quenching. To examine the growth process of the hard spots with holding time, the unidirectional solidification technique was used. The results of this study are summarized as follows: 1) With the addition of Fe in order to get the effects of grain refinement in high strength brass, the two different type of Fe-rich phases are occurred, which are defined as dendritic and globular phase. The chemical composition of the globular phase was different from that of the dendritic phase in that the globular phase contained Si. 2) With increasing Si content, the Fe-rich phase had a tendency to form globular phase. 3) As the holding time increased in the liquid state, globular was also prone to coalesce. The further growth of globular phase to large size was due to reducing the interfacial energy. 4) The primary phase of copper alloy was nucleated preferentially on the dendritic phase. It was noticeable that the dendritic phase acted as a grain refiner. However, the agglomerate (hard spots) which was composed of the globular phase decreased the mechanical properties of high strength brass. 5) Once the hard spots formed in the high strength brass casting, it was very difficult to remove them. This is due to the fact that their meting temperature is higher than the pouring temperature of high strength brass.

• Journal of Technologic Dentistry
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• v.40 no.1
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• pp.41-47
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• 2018

Purpose: The purpose of this study was to analyze the biomechanical properties of the dental implants on the supporting bone using three-dimensional finite element method when three different abutment materials were applied to the implant system. Methods: Three different dental implant models were fabricated by applying Ti, PEEK, and CRE-PEEK (60% carbon-reinforced PEEK) to abutment material. The abutment and connecting screw from the fixture was applied with a tightening torque of 20 Ncm. And then, total loads of 150 N were applied in an $30^{\circ}oblique$ direction (to the vertical). The structural stability of dental implants on the supporting bone was analyzed using Von Mises stress and principal stress values. Results: The maximum tensile stress of the cortical bone was highest at 12.6 MPa in the PEEK abutment (Model-B). Ti abutment (Model-A) and CRE-PEEK abutment (Model-C) showed similar stress distributions (10.6 and 10.3 MPa, respectively). And the maximum compressive principal stress was similar in all models. The Von Mises stress value delivered to the bone around the implant was highest at 16.5 MPa in Model-B. On the other hand, Model-A and C showed similar stress distributions (14.0 and 13.8 MPa, respectively). In addition, the maximum equivalent stress applied to the abutment was highest at 629.8 MPa in Model-A. The stress distribution in Model-C was 573.9 MPa. Whereas, Model-B showed the lowest value at 165.6 MPa. Conclusion : The dental implant supporting bone system using PEEK material seems to have the possibility of supporting bone fracture. It was found that the CRE-PEEK abutment can reduce the elastic deformation and reduce the stress value of the interfacial bone.

• Journal of the Korean Magnetics Society
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• v.6 no.6
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• pp.411-416
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• 1996

We have studied the effect of a spin-dependence interface electron scattering on the giant magnetoresistance by adding a Fe magnetic material to the Co/Cu interfaces. The $Fe(50\;{\AA})/[Co(17\;{\AA})/Fe(t\;{\AA})/Cu(24\;{\AA})]_{20}$ multilayers are deposited on the Corning glass 2948 and 7059 substrates in a dc magnetron sputtering system. The magnetoresistance ratio is 22 % in the only Co/Cu multilayer, while it is increased to 26 % with inserted ultra thin Fe interface layer and reduced with increasing thickness of the Fe interface layer. It was investigated to the dependence of the magnetoresistance behaviors on annealing temperature. The magnetic properties of the multilayers were measured by vibrating sample magnetometer. Also, the structures and the surface roughness of samples were characterized by X-ray diffraction and atomic force microscope, respectively. The magnetoresistance ratio was increased to annealing temperature $300^{\circ}C$, but reduced at the temperature higher than $300^{\circ}C$ due to the interfacial diffuse.

• Journal of Adhesion and Interface
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• v.14 no.1
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• pp.36-42
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• 2013

To improve hydrolytic stability of polyurethane (PU) adhesives, a silane coupling agent (SCA) was added. 3-Isocyanatopropyl triethoxy silane (ITS) as a SCA has two functional groups in the main chain and it is used to improve an interfacial interaction between polymer and inorganic material or metal. In this study, PU adhesives with different amounts of ITS from 0 to 1 wt% were synthesized. Pot time, modulus, thermal stablilty, and adhesive force of the obtained samples were measured. The results showed that the adhesives with ITS showed better properties than that of pure one.