• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.8 s.350
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• pp.13-18
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• 2006

[ $SnO_2$ ] and ZnO nanostructures were grown on the surface of thin film by heat treatment of metal Sn, Zn under Ar gas flow and $O_2$ at atmospheric pressure, respectively. The sensitivity of the $SnO_2$ thin film device on which grown nanowires to CO gas(5,000 ppm) was 50 % at the operating temperature of $200^{\circ}C$. In case of using Pt as catalysts, the sensitivity was enhanced and operating temperature was reduced(73 % at $150^{\circ}C$ ). The sensitivity of the ZnO nanorods device using Cu as catalysts to NOx gas was 90 % at the operating temperature of $200^{\circ}C$. It was found that the sensitivity to CO and NOx gases for the device on which grown nanostructures was much higher than those for general thin film device.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.2
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• pp.200-213
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• 2000

Lasers have given dentistry a new rapid, economic, and accurate technique for metal joining. Although laser welding has been recommended as an accurate technique, there are some limitations with this technique. For example, the two joining surfaces must have a tight-fitting contact, which may be difficult to achieve in some situations. The tensile samples used for this study were made from a custom-made pure titanium and type III gold alloy plates. 27 of 33 specimens were sectioned perpendicular to their long axis with a carborundum disk and water coolant. Six specimens remained and served as the control group. A group of 6 specimens was posed as butt joints in custom parallel positioning device with a feeler gauge at each of three gaps : 0.00, 0.25. and 0.50mm. All specimens were then machined to produce a uniform cross-sectional dimension, none of the specimens was subjected to any subsequent form of heat treatment. Scanning electron microscopy was performed on representative tested specimens at fractured surfaces in both the parent metal and the weld. Vickers hardness was measured at the center of the welds with a micropenetrometer using a force of 300gm for 15 seconds. Measurement was made at approximately $200{\mu}m\;and\;500{\mu}m$ deep from each surface. One-way analysis of variance (ANOVA) and Scheffe's test was calculated to detect differences between groups. The purpose of this study is to compare the strength and properties of the joint achieved at various butt Joint gaps by the laser welding of type III gold alloy and pure titanium tensile specimens in an argon atmosphere. The results of this study were as follows : 1. When indexing and welding pure titanium, there was no decrease in ultimate tensile strength as compared with the unsectioned alloys for indexing gaps of 0.00 to 0.50mm, although with increasing gap size may come increased distortion (p>0.05). 2. When indexing and welding type III gold alloy, there were significant differences in ultimate tensile strength among groups with weld gaps of 0.00mm, 0.25 and 0.50mm, and the control group. Group with butt contact without weld gap demonstrated a significant higher ultimate tensile strength than groups with weld gaps of 0.25 and 0.50mm (p<0.05). 3. When indexing and welding the different metal combination of type III gold alloy and pure titanium, there were significant differences in ultimate tensile strength between groups with weld gaps of 0.00, 0.25, and 0.50mm. However, the mechanical properties of the welded joint would become too brittle to be acceptable clinically (p<0.05). 4. The presence of large pores in the laser welded joint appears to be the most important factor in controlling the tensile strength of the weld in both pure titanium and type III gold alloy.

• Journal of the Korean Electrochemical Society
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• v.11 no.4
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• pp.313-318
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• 2008

The influence of the particle size of platinum(Pt) on the stability and activity was studied. The particle size of platinum was controlled in the range of $3.5{\sim}9\;nm$ by heat treatment of commercial Pt/C and confirmed by XRD and TEM. An accelerated degradation test was performed to evaluate the stability of platinum catalysts. Oxygen reduction reaction was monitored for the measurement of activity. As increasing the Pt particle size, the stability of Pt/C electrode was enhanced and the activity was reduced. It was confirmed that the stability of Pt/C electrode was in inverse proportion to the activity. PtCo/C alloy catalyst was used to improve the activity and stability of large-sized platinum particle. The maximum power density of commercial Pt/C was $507.6\;mV/cm^2$ and PtCo/C alloy catalyst was $585.8\;mV/cm^2$. The decrement of electrochemical surface area showed Pt/C(60%) and PtCo/C alloy catalyst(24%). It was possible to enhance both of stability and activity of catalyst by the combination of particle size control and alloying.

• Journal of the Korean Electrochemical Society
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• v.5 no.2
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• pp.52-56
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• 2002

Tin oxide was coated on graphite particle by sol-gel method and an electrode with this material having microcrystalline structure for lithium ion battery was obtained by heat treatment in the range $400-600^{\circ}C$. The content of tin oxide was controlled within the range of $2.25wt\%\~11.1wt\%$. The discharge capacity increased with the content of tin oxide and also initial irreversible capacity increased. The discharge capacity of tin oxide electrode showed more than 350 mAh/g at the initial cycle and 300 mAh/g after the 30th cycle in propylene carbonate(PC) based electrolyte whereas graphite electrode without surface modification showed 140 mAh/g. When the charge and discharge rate was changed from C/5 to C/2, The discharge capacity of tin oxide and graphite electrode showed $92\%\;and\;77\%$ of initial capacity, respectively. It has been considered that such an enhancement of electrode characteristics was caused because lithium $oxide(Li_2O)$ passive film formed from the reaction between tin oxide and lithium ion prevented the exfoliation of graphite electrode and also reduced tin enhanced the electrical conduction between graphite particles to improve the current distribution of electrode.

• Journal of Conservation Science
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• v.36 no.5
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• pp.405-420
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• 2020

A convergence research was conducted on glass beads excavated at the ruins of Hapgang-ri, Sejong, using the archeology and conservation approach. The period of appearance of Jugu Towangmyo in the ruins of Hapgang-ri can be estimated to begin in the late 2^nd century; for Jugu Towangmyo No. 15, the period spans from the late 2^nd to early 3^rd century. Form, color, and manufacturing techniques of complete glass beads were examined, and the cross-sections and chemical composition of 16 samples were observed. Based on these analyses, the glass beads were divided into blue, purple, and red colors. The blue-colored beads could be further sub-divided based on their gloss and brightness; in contrast, the red-colored beads were highly uniform with regard to these parameters. Based on the stripe and bubble arrangement on the surface of the glass beads, their drawing technique was identified. Traces of heat treatment or polishing were observed at the ends of the beads. According to their chemical composition, the 16 samples were classified into 3 potash glass and 13 soda glass groups; in the latter, the properties of the stabilizers were divided according to the blue and red bead colors. The stabilizers of the red beads are unique in that they allow the distinction among beads excavated in other areas in South Korea owing to their compositional differences. Colorants in blue- and red-colored beads are cobalt (containing MnO), and copper and iron, respectively.

• Clean Technology
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• v.26 no.2
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• pp.122-130
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• 2020

The isotherm, kinetic, and thermodynamic parameters of reactive blue 4 adsorbed by activated carbon were investigated for activated carbon dose, pH, initial concentration, contact time, and temperature data. The adsorption of the RB 4 dye by activated carbon showed a concave shape in which the percentage of adsorption increased in both directions starting from pH 7. The isothermal adsorption data were applied to Langmuir, Freundlich, and Temkin isotherms. Both Freundlich and Langmuir isothermal adsorption models fit well. From determined Freundlich separation factor (1/n = 0.125 ~ 0.232) and Langmuir separation factor (R_L = 1.53 ~ 1.59), adsorption of RB 4 by activated carbon could be employed as an effective treatment method. The constant related to the adsorption heat (B_T = 2.147 ~ 2.562 J mol^-1) of Temkin showed that this process was physical adsorption. From kinetic experiments, the adsorption process followed the pseudo second order model with good agreement. The results of the intraparticle diffusion model showed that the inclination of the first straight line representing the surface diffusion was smaller than that of the second straight line representing the intraparticle pore diffusion. Therefore, it was confirmed that intraparticle pore diffusion is the rate-controlling step. The negative Gibbs free energy change (ΔG = -3.262 ~ -7.581 kJ mol^-1) and the positive enthalpy change (ΔH = 61.08 kJ mol^-1) indicated the spontaneous and endothermic nature of the adsorption process, proving this process to be spontaneous and endothermic.

• Clean Technology
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• v.21 no.4
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• pp.224-228
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• 2015

Phospholipase D (PLD) was immobilized on a submicro-porous membrane through covalent immobilization. The immobilization was conducted on the porous membrane surface with the treatment of polyethyleneimine, glutaraldehyde, and the anhydrase, in sequence. The immobilization was confirmed using X-ray photon spectrometer. The pH values of phosphatidylcholine (PC) dispersion solution with buffer were monitored with respect to time to calculate the catalytic activities of PC for free and immobilized PLD. The catalytic rate constant values for free PLD, immobilized PLD on polystyrene nanoparticles, and immobilized PLD on a porous cellulose acetate membrane were 0.75, 0.64, and 0.52 s^-1, respectively. Reusability was studied up to 10 cycles of PC hydrolysis. The activity for the PLD immobilized on the membrane was kept to 95% after 10 cycles, and comparable to the PLD on the nanoparticles. The stabilities for heat and storage were also investigated for the three cases. The results suggested that the PLD immobilized on the membrane had the least loss rate of the activity compared to the others. From these studies, the porous membrane was feasible as a carrier for the PLD immobilization in the production of phosphatidic acid.

• Journal of Conservation Science
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• v.27 no.1
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• pp.1-11
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• 2011

For the silver artifacts in the Koryo Dynasty excavated from Neungnae-ri Ganghwa island, the metallographic section analysis and hardness and chemical analysis were conducted. After making samples in the similar ratio of the composition concentration, the changes of the microstructure were checked according to the working method and temperature. The results show that those silver artifacts are Au-Cu alloys with 2 to 6 % of Cu. From the results it is judged that Cu was artificially alloyed with them to keep the proper hardness and identified that they were gilded by the amalgamation process seeing that mercury was included at the guilt layer. Also the porous texture on the surface of them could be formed at over $400^{\circ}C$, therefore, it is assumed the hot working or heat treatment at over $400^{\circ}C$ were performed. In silver artifacts made by the relief and repousse, they have the similar composition analysis to other 7 artifacts but the hardness is lower than pure silver. Consequently from differences in the hardness, it can be inferred that the low hardness of silver artifacts is concerned with manufacturing techniques.

• Journal of Adhesion and Interface
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• v.9 no.3
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• pp.20-26
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• 2008

It is well know that the structure of shape memory alloy (SMA) can change from martensite austenite by either temperature or stress. Due to their inherent shape recovery properties, SMA fiber can be used such as for stress or cure-monitoring sensor or actuator, during applied stress or temperature. Incomplete superelasticity was observed as the stress hysteresis at stress-strain curve under cyclic loading test and temperature change. Superelasticity behavior was observed for the single-SMA fiber/epoxy composites under cyclic mechanical loading at stress-strain curve. SMA fiber or epoxy embedded SMA fiber composite exhibited the decreased interfacial properties due to the cyclic loading and thus reduced shape memory performance. Rigid epoxy and the changed interfacial adhesion between SMA fiber and epoxy by the surface treatment on SMA fiber exhibited similar incomplete superelastic trend. Epoxy embedded single SMA fiber exhibited the incomplete recovery during cure process by remaining residual heat and thus occurring residual stress in single SMA fiber/epoxy composite.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.2
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• pp.92-98
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• 2012

The co-precipitation technique has been applied to synthesize biphasic calcium phosphate (BCP). $Ca(NO_3)_2{\cdot}4H_2O$, $(NH_4)_2HPO_4$, TEOS and $Mg(NO_3)_2{\cdot}6H_2O$ as the starting materials was used. After the heat treatment of powder crystalline phases HAp and ${\beta}$-TCP analysis showed a mixed phase. The overall spectra appear to have mainly two modes corresponding to characteristic $PO^{3-}_4$ and $OH^-$ groups. After immersion in Hanks' Balanced Salt Solution (HBSS) for 1 week a precipitation started to be formed with individual small granules on the specimen surface. An MTT assay indicated that ionic substituted BCP powders had no cytotoxic effects on MG-63 cells, and that they have good biocompatibility.