• Journal of the Korean institute of surface engineering
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• v.26 no.6
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• pp.291-298
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• 1993

In order to substitute for porous nickel anode in Molten Carbonate Fuel Cell(MCFC), porous cermet elec-trode was fabricated with Ni and Ni-P coated ceramic powder. Ni and Ni-P were coated by electroless plat-ing method in the nickel solution containing of hydrazine and sodium hypophosphate as a reducing agent. The plating solution was stirred by air and mechanical agitator. Ultrasonic irradiation was applied to the plating bath to improved the effect of agitation and coating speed. Electorde was formed by pressing method and doc-tor blade method followed by sinterd at$ 800^{\circ}C$ for 6 hours in H2 environment. Anode performance test carried out by potentiodynamic polarization technique in the MCFC operating condition and 154-161mA/$\textrm{cm}^2$ as ob-tained as a anode current density at the+100mV overpotential.

• Analytical Science and Technology
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• v.33 no.3
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• pp.115-124
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• 2020

Marker pens belong to school things that are controlled by the regulation system called safety confirmation under special act on the safety of products for children with the formaldehyde criteria of 20 mg/kg. With nine marker pens available commercially, formaldehyde in marker pen ink was analyzed by present test standard where marking on a fabric swatch with a pen and extracting the swatch in water and derivatization with Nash reagent followed by UV/Vis spectrophotometeric measurement (Nash-UV/Vis method), giving not detected results or a false positive result in case of a colored water extract. However, the contents of formaldehyde in ink of nine marker pens were determinded to range between 3.2 ~ 93.2 mg/kg with three results above the safety criteria of 20 mg/kg by HPLC/DAD measurements on DNPH derivatives of formaldehyde (DNPH-HPLC/DAD method) in ink dissolved directly in water using an ultrasonic bath. Therefore, the DNPH-HPLC/DAD method with the extraction of ultrasonic dissolving ink in water is proposed as a proper method for analyzing formaldehyde in ink. The proposed method has advantages of lower detection limit and accuracy with colored extracts as well as a simple and fast extraction. The accuracy and precision of this method was estimated to be 90.1 ~ 105.4 % and 0.6 ~ 3.3 %, respectively by spiking tests in the ranges of 20 mg/kg and 40 mg/kg using matrixes such as highlighter pen ink, board marker ink, chalk marker pen ink and painter marker ink.

• Journal of Life Science
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• v.21 no.1
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• pp.56-61
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• 2011

This study was performed to investigate effective extract conditions in fronds of the Ostrich fern (Matteuccia struthiopteris) to increase antioxidant compound contents and antioxidant capacity. Powder (1 g) of lyophilizated fronds were mixed with 3 kinds of solvents (MeOH, 80% EtOH and water). Extractions were carried out using not only immersion (room temp.), heating ($60^{\circ}C$) and stirring (200rpm) for 6 hr, but also through sonication in a 42 kHz ultrasonic bath for 15, 30 and 45 min. Extracts were filtrated and measured for contents of soluble solids (SS), total polyphenols (TP; tannic acid as a standard) and total flavonoids (TF; Naringin as a standard). Antioxidant activity was expressed as $RC_{50}$ for DPPH and ABTS radical scavenging. SS (0.317 $g{\cdot}g^{-1}$ db), TP (70.90 $mg{\cdot}g^{-1}$ db) and TF (41.53 $mg{\cdot}g^{-1}$ db) contents reached their highest levels when 30 minute sonication extraction with 80% EtOH was performed, and the highest DPPH and ABTS scavenging activity was observed in the same extraction conditions ($RC_{50}$=0.14 $mg{\cdot}ml^{-1}$ and 0.09 $mg{\cdot}ml^{-1}$, respectively). From the present investigation, it can be concluded that fronds of the ostrich fern can be used as a natural material for antioxidants, and sonication for 15-30 min with 80% EtOH is an ideal extraction method for increasing their antioxidant effects and saving extraction time.

• Polymer(Korea)
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• v.34 no.6
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• pp.534-539
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• 2010

Polystyrene (PS)/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared via latex technology and the effect of nanotube length on rheological properties were investigated. Monodisperse PS particle was synthesized by the emulsifier-free emulsion polymerization and two types of MWCNTs were used after surface modification to improve dispersion state and to remove impurities. Final nanocomposites were prepared by the freeze-drying process after dispersing the PS particles and the surface-modified MWCNTs in a ultrasonic bath. The effects of MWCNT content and nanotube length on rheological properties were evaluated by imposing the small-amplitude oscillatory shear flow. The PS/MWCNT nanocomposites showed that rheological properties were enhanced as the amount and length of MWCNT increased. It is speculated that the rheological characteristics of nanocomposites change from liquid-like to solid-like as the MWCNT amount increases, and the critical concentration to achieve network structure decreases as the nanotube length increases.

• Korean Chemical Engineering Research
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• v.53 no.1
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• pp.83-90
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• 2015

In this study, we investigated optimum conditions for the introduction of a lot of free radical polymerizable methacrylate groups on the multi-walled carbon nanotube (MWCNT) surface. Carboxyl groups were introduced first on MWCNT surfaces by treating with a mixture of sulfuric acid and nitric acid with ultrasonic bath for 2 hours, and oxidized MWCNTs were reacted further with thionyl chloride followed by triethylenetetramine (TETA) to introduce amino groups on the oxidized MWCNT surface, to make MWCNT-$NH_2$. To introduce free radical polymerizable methacrylate groups on the MWCNT-$NH_2$, MWCNT-$NH_2$ was reacted with 3-(acryloyloxy)-2-hydroxypropyl methacrylate (AHM) by Michael addition reaction. We investigated progress of modification reactions for MWCNT by fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and elemental analysis (EA). We found maximum degree of Michael addition reactions between AHM and TETA grafted on MWCNT-$NH_2$ for 10:1 mol ratio and 8 hour reaction time in our reaction conditions.

• Journal of Dental Rehabilitation and Applied Science
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• v.22 no.3
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• pp.211-220
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• 2006

Need of porcelain-repair system is largely demanding as dental porcelain restorations are increased in clinical dentistry. This study investigated shear bond strength of commercial porcelain-repair systems on dental porcelain and their reliability. Experimental groups were as follows; Group A Super Bond C&B, Group B Porcelain repair kit, Group C Ceramic repair, and Group D Spectrum system as a control. Porcelain disks were fired and embedded in epoxy resin. Porcelain surface were ground using 220 grit SiC disk, then cleaned in ultrasonic bath. Then porcelain specimens were treated with each repair system. A clear polystyrene cylinder 3.5 mm in internal diameter was filled with composite resin. Then the resin cylinder was polymerized with a visible light curing unit. Thirty one specimens at each group were prepared and stored at $37^{\circ}C$ distilled water for 48 h. Specimens were tested in an Instron testing machine according to ISO TR 11405. Mean shear bond strength and standard deviation of each group was $15.7{\pm}4.1MPa$ (Group A), $12.8{\pm}4.9MPa$ (Group B), $7.2{\pm}3.0MPa$ (Group C) and $9.6{\pm}2.2MPa$ (Group D). ANOVA and Tukey HSD post-hoc test showed that there were significant differences between groups (p<0.05). Data of bond strength were analyzed with two-parameter Weibull distribution. Confidence interval of Weibull modulus (m-parameter) at 95% of Group A (3.5-6.3) and Group D (3.6-6.0) were significantly higher than Group B (2.2-3.7) and Group C (2.0-3.4). There was little correlation between mean shear bond strength and Weibull modulus. Results indicated that acid-etching of porcelain surface increased porcelain-resin shear bonding strength.

• Journal of the Korean institute of surface engineering
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• v.50 no.5
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• pp.352-359
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• 2017

The growth of nanocrystalline diamond films on a p-type poly silicon substrate was studied using microwave plasma chemical vapor deposition method. A 6 mm thick poly silicon plate was mirror polished and scratched in an ultrasonic bath containing slurries made of 30 cc ethanol and 1 gram of diamond powders having different sizes between 5 and 200 nm. Upon diamond deposition, the specimen scratched in a slurry with the smallest size of diamond powder exhibited the highest diamond particle density and, in turn, fastest diamond film growth rate. Diamond deposition was carried out applying different DC bias voltages (0, -50, -100, -150, -200 V) to the substrate. In the early stage of diamond deposition up to 2 h, the effect of voltage bias was not prominent probably because the diamond nucleation was retarded by ion bombardment onto the substrate. After 4 h of deposition, the film growth rate increased with the modest bias of -100 V and -150 V. With a bigger bias condition(-200 V), the growth rate decreased possibly due to the excessive ion bombardment on the substrate. The film grown under -150V bias exhibited the lowest contact angle and the highest surface roughness, which implied the most hydrophilic surface among the prepared samples. The film growth rate increased with the apparent activation energy of 21.04 kJ/mol as the deposition temperature increased in the range of $300{\sim}600^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.371-372
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• 2005

Supercapacitors are promising devices for delivering high power density. Digital communications, electric vehicles and other devices that require electrical energy at high power levels in relatively short pulses have prompted considerable research on supercapacitors. In recent years, solid electrolytes have been investigated for supercapacitors. Solid electrolytes are advantageous over liquid electrolytes in respect of easy handling and reliability without electrolyte leakage. In this preliminary study, an electrochemical supercapacitor in all solid configuration has been fabricated using CNF-DAAQ and poly-vinylidenefluoride(PVdF). A new type of Supercapacitor was constructed by using carbon nanofibers(CNFs) and DAAQ(l,5-diaminoanthraquinone) monomer. DAAQ was deposited on the carbon nanofibers by chemical polymerization with $(NH_4)_2S_2O_8$ as oxidant in the 0.1M $H_2SO_4$. Dried SPEEK powder was mixed with N-methyl pyrrolidone to make 10 wt.% solution in an ultrasonic bath, the slurry was cast over a glass substrate heated to $70^{\circ}C$ for solvent evaporation. And then we used solid electrolyte of SPEEK. The unit cell consist of DAAQ-CNF/electrolyte/Pt. From the analysis, it is clear that surface of carbon nanofibers was quite uniformly coated with DAAQ. The performance characteristics of the supercapacitors have been evaluated using Cyclic Voltammetry.

• Journal of the Korean institute of surface engineering
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• v.47 no.5
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• pp.263-268
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• 2014

Nanocrystalline diamond(NCD) coated SiC balls were applied in a ball-on-disk tribometer. After seeding in an ultrasonic bath containing nanometer diamond powders, $2.2{\mu}m$ thick NCD films were deposited on sintered 3 mm diameter SiC balls at $600^{\circ}C$ in a 2.45 GHz microwave plasma CVD system. Bare $ZrO_2$ and SiC balls were prepared for comparison as test balls. Tribology tests were performed in air with pairs of three different balls and mirror polished steel(SKH51) disk. The wear tracks on balls and disks were examined by optical microscope and alpha step profiler. Under the load of 3 N, the friction coefficients of steel against $ZrO_2$, SiC and NCD-coated balls were between 0.4 and 0.8. After a few thousands sliding laps, the friction coefficient of NCD-coated balls dropped from 0.45 to below 0.1 and maintained thereafter. Under a higher load of 10 N or 20 N with a long sliding distance of 2 km, $ZrO_2$ and SiC balls exhibited the similar friction coefficients as above. The friction coefficient of NCD-coated balls was less than 0.1 from the beginning and increased to above 0.1 steadily or with some fluctuations as sliding distance increased. NCD coating layers were found worn out after long duration and/or high load sliding test, which resulted in the friction coefficient higher than 0.1.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.32 no.2
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• pp.102-110
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• 2022

Objectives: The purpose of this study is to analyze the content of N,N-dimethylformamide(DMF) in polyurethane coated gloves(PU-gloves) and to assess the dermal exposure generated by wearing them. Methods: We analyzed the concentrations of DMF in 12 gloves by EN16778 standard. The samples cut into pieces of about 10 by 10 mm and extracted with methanol in flask in an ultrasonic bath at 70℃. An aliquot of the extract is analyzed with GC-MS. The dose of dermal exposure was calculated by ECETOC TRA consumer 3.1 and compared with derived no effect level(DNEL) for systemic effects due to long term exposure by workers. The extracted amount of DMF by saline solution was compared with that by EN16778 standard. Results: The mean concentration of DMF in PU-gloves was 1,377 mg/kg(range 13~3,948 mg/kg). The concentration of DMF showed significantly differences by packing type, manufacturer, and price(p<0.05). The dose of dermal exposure was 0.0007~0.572 mg/kg body weight/day when the DMF content was 10~4,000 mg/kg. The DMF extracted by saline solution was around 11% for 8 hours. Conclusions: The risk of dermal exposure due to the residual DMF in the PU-gloves was not signifiant. But, the limit of 1,000 mg/kg in PU-gloves can be recommended for international standard and trading systems.