• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.574-574
• /
• 2012

We report a simple way of fabricating high-quality carbon nanoscrolls (CNSs) by taking advantage of strain relief due to large difference in strain at the interface of graphene and underlying layer. This method allows strain-controlled self rolling-up of monolayer graphene during etching process at predefined positions on SiO2/Si substrates by photolithography. The size and the length of the CNSs can be easily controlled by adjusting the thickness of the underlying layer and by pre-patterning. Raman spectroscopy studies show that the CNSs is free of significant defects, and the electronic structure and phonon dispersion are slightly different from those of two-dimensional graphene. The preparation of high-quality CNSs may open up new opportunities for both fundamental and applied research of CNSs.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2005.05a
• /
• pp.360-363
• /
• 2005

본 연구에서는 인듐 액체금속이온원을 제작하여 빔 특성에 대해 연구를 하였으며, 기존의 연구를 하였던 갈륨 액체금속 이온원의 빔특성과 비교분석 하였다. 빔특성 분석을 위해 빔 안정도, 전류-전압특성곡선, 에너지 퍼짐을 측정하였다. 액체금속이온원에 사용되는 액체금속 저장소 및 바늘전극(tip)은 $500{\mu}m$의 직경을 갖는 텅스텐을 사용하였으며, 국내에서 제작된 제품을 사용하였다. 액체금속 저장소의 구조는 이전에 구상하여 연구가 이루어진 6개의 pre-etching된 텅스텐와이어(wire)가 묶여진 형태를 사용하였다.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 2003.11a
• /
• pp.227-232
• /
• 2003

Anodizing film was prepared by anodic oxidation of pure aluminum(purity > 99.50) using DC power supply for constant current mode in an electrolytic solution of surface of sulfuric acid. Effects of pre-treatment process such as chemical polishing, acid cleaning, alkali etching before anodic oxidation, were studied to microstructures and surface morphologies. A roughness on surface of anodizing film had to be decreased for amorphous phase by anodic oxidation. A roughness on surface of anodizing film decrease as annealing temperature increased in chemical polishing.

• Corrosion Science and Technology
• /
• v.15 no.2
• /
• pp.84-91
• /
• 2016

The transport and deposition of corrosion products in pressurized water nuclear reactor (PWR) steam generators have led to corrosion (SCC, denting etc.) problems. Lancing, mechanical cleaning and chemical cleaning have been used to reduce these problems. The methods of lancing and mechanical cleaning have limitations in removing corrosion products due to the structure of steam generator tubes. But high temperature chemical cleaning (HTCC) with EDTA is the most effective method to remove corrosion products regardless of the structure. However, EDTA in chemical cleaning aqueous solution and chemical cleaning environments affects the integrity of materials used in steam generators. The nuclear power plants have to perform the pre-test (also called as qualification test (QT)) that confirms the effect on the integrity of materials after HTCC. This is one of the series studies that assess the effect, and this study determines the effects of 20 % EDTA aqueous solution on defective tubes in high temperature chemical cleaning environments. The depth and magnitude of defects in steam generator (SG) tubes were measured by eddy current test (ECT) signals. Surface analysis and magnitude of defects were performed by using SEM/EDS. Corrosion rate was assessed by weight loss of specimens. The ECT signals (potential and depth %) of defective tubes increased marginally. But the lengths of defects, oxides on the surface and weights of specimens did not change. The average corrosion rate of standard corrosion specimens was negligible. But the surfaces on specimens showed traces of etching. The depth of etching showed a range on the nanometer. After comprehensive evaluation of all the results, it is concluded that 20 % EDTA aqueous solution in high temperature chemical cleaning environments does not have a negative effect on defective tubes.

• Restorative Dentistry and Endodontics
• /
• v.32 no.3
• /
• pp.222-235
• /
• 2007

The objectives of this study was to evaluate the effect of thermocycling on the ${\mu}TBS$ (microtensile bond strength) to dentin with four different adhesive systems to examine the bonding durability. Freshly extracted $3^{rd}$ molar teeth were exposed occlusal dentin surfaces, and randomly distributed into 8 adhesive groups 3-steps total-etching (Scotchbond Multi-Purpose Plus; SM, All Bond-2; AB), 2-steps total-etching (Single Bond; SB, One Step plus; OS), 2-steps self-etching (Clearfil SE Bond; SE, AdheSE AD) and single-step self-etching systems (Promp L-Pop; PL, Xeno III; XE) Each adhesive system in 8 adhesives groups was applied on prepared dentin surface as an instruction and resin composite (Z250) was placed incrementally and light-cured. The bonded specimens were sectioned with low-speed diamond saw to obtain $1\times1mm$ sticks after 24 hours of storage at $37^{\circ}C$ distilled water and proceeded thermocycling at the pre-determined cycles of 0, 1,000 and 2,000. The ${\mu}TBS$ test was carried out with EZ-tester at 1mm/min. The results of bond strength test were statistically analyzed using one-way ANOVA/ Duncan's test at the a < 0.05 confidence level. Also, the fracture mode of debonded surface and the interface were examined under SEM. The results of this study were as follows ; 1. 3-step total etching adhesives showed stable, but bond strength of 2-step adhesives were decreased as thermocycling stress. 2. SE showed the highest bond strength, but single step adhesives (PL, XE) had the lowest value both before and after thermocycling. 3 Most of adhesives showed adhesive failure. The total-etching systems were prone to adhesive failure and the single-step systems were mixed failure after thermocycling. Within limited results of this study, the bond strength of adhesive system was material specific and the bonding durability was affected by the bonding step/ procedure of adhesive Simplified bonding procedures do not necessarily imply improved bonding performance.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.37 no.4
• /
• pp.422-428
• /
• 2010

Giomer is fluoride-releasing, resin-based dental materials that comprise PRG(pre-reacted glass ionomer) filler. The purpose of this study was to evaluate the shear bond strength of Giomer using self-etching primer systems to bovine dentin. Bovine incisors were mounted in self-curing orthodontic resin and the facial surfaces were wet ground on SIC paper to expose the dentin. Total 100 samples were made and divided randomly into 4 groups, Giomer group(I), Composite resin group(II) and Compomer group(III), Giomer and single bottle adhesive group(IV). The shear bond strengths of 25 samples per each group were measured using universal testing machine. And data were analyzed statistically with One-way ANOVA and Scheffe test. Giomer group(I) showed the significantly higher bond strength than Compomer group(III)(p<0.05). There was no significant difference between Giomer group(I) and Composite resin group(II)(p>0.05). And there is no significant difference between gourp(I) and group(IV). Based on the results of present study, the use of Giomer as an esthetic restorative material for primary teeth might be justified. It is considered that more study about the fluoride releasing ability is needed to evaluate the anticariogenic effect of giomer.

• Journal of the Korean Ceramic Society
• /
• v.41 no.10 s.269
• /
• pp.728-734
• /
• 2004

The effect of microstructure of WC-Co substrates which have different WC grain sizes from submicron to 5 $\mu$m on the diamond-substrate adhesion strength was investigated. The substrates were pre-treated by two methods : chemical etching with Murakami's solution and subsequently with $H_2SO_4$, and thermal heat-treatment. The adhesion strength was estimated by degree of peeling after Rockwell indentation. Diamond films of 20 $\mu$m thickness deposited on the heat-treated substrates showed an excellent adhesion strength at the load of 100 kg, which ascribed to the large and elongated WC grains. However, the cutting edge of insert was deformed after heat treatment and the surface morphology of heat treated substrate strongly affected on the surface roughness of the deposited diamond films. On the contrary, the diamond film of 10 $\mu$m in thickness on the chemically etched substrates of average WC grain size over 2 $\mu$m showed good adhesion strength enough not to peel-off under a load of 60 kg. Especially, the substrate of average WC grain size over 5 $\mu$m exhibited much improved reliability of adhesion comparing with the substrate of average grain size under 2 $\mu$m. No substrate deformation was observed in this case after the chemical etching, which is more advantageous and more practical in terms of precious machining than the heat treatment case.

• Restorative Dentistry and Endodontics
• /
• v.27 no.1
• /
• pp.34-43
• /
• 2002

The purpose of this study was to compare microleakage and marginal hybrid layer in class V restorations using two one-bottle adhesives and one self-etching adhesive. Class V cavity preparations with occlusal margins in enamel and gingival margins in dentin were pre-pared on buccal and lingual surfaces of 30 extracted human molar teeth. Prepared teeth were randomly divided into three treatment groups (n=30) and restored with three adhesives and composites: Single Bond/Filtek Z-250 (Group 1), Prime&BondNT/Esthet.X (Group 2), UniFil Bond/UniFil F (Group 3). For microleakage, samples were stored in room temperature water for 24 hours, thermocycled stained with 2% methylene blue dye, sectioned into halves, scored and analysed using Mann-whitney test and Wilcoxon signed rank sum test. For marginal hybrid layer, samples were sectioned into halves, treated with 10% phosphoric acid for 5 seconds, stored in 5% NaOCL solution for 24 hours, dried and gold coated. Occlusal and gingival margins of each sample were inspected under SEM. The results of this study were as follows ; 1. Microleakage at the occlusal margins was not evident in group 1 and group 2, but it showed in group 3 (p<0.05). 2. Microleakage in group 1 and group 3 was significantly lower than in group 2 at gingival margins (p<0.05). 3. Microleakage at gingival margins was greater than at occlusal margins in group 1 and group 2, but microleakage at occlusal margins was greater than at gingival margins in group 3 (p<0.05). 4. In group 1 and group 2, no gaps at occlusal margins showed. But gaps showed in group 3. Occlusal margins were free from a hybrid layer in all groups 5. The thickness of the marginal hybrid layers was 2.5~5 $\mu\textrm{m}$ thick in group 5 $\mu\textrm{m}$ thick in group 2 and 1.5 $\mu\textrm{m}$ thick in group 3. 6 There was no corelation between microleakage and thickness of marginal hybrid layer. In coclusion, the effect of dentin adhesives on microleakge in class V composite restorations was excellent when one-bottle adhesives were applied on enamel margin, and it was good when a self-etching adhesive was applied on dentinal margin. There was no corelation between microleakage and thickness of marginal hybrid layer.

• Restorative Dentistry and Endodontics
• /
• v.41 no.2
• /
• pp.106-113
• /
• 2016

Objectives: This study evaluated the effects of different surface conditioning methods on the bond strength of orthodontic brackets to glazed full-zirconia surfaces. Materials and Methods: Glazed zirconia (except for the control, Zirkonzahn Prettau) disc surfaces were pre-treated: PO (control), polishing; BR, bur roughening; PP, cleaning with a prophy cup and pumice; HF, hydrofluoric acid etching; AA, air abrasion with aluminum oxide; CJ, CoJet-Sand. The surfaces were examined using profilometry, scanning electron microscopy, and electron dispersive spectroscopy. A zirconia primer (Z-Prime Plus, Z) or a silane primer (Monobond-S, S) was then applied to the surfaces, yielding 7 groups (PO-Z, BR-Z, PP-S, HF-S, AA-S, AA-Z, and CJ-S). Metal bracket-bonded specimens were stored in water for 24 hr at $37^{\circ}C$, and thermocycled for 1,000 cycles. Their bond strengths were measured using the wire loop method (n = 10). Results: Except for BR, the surface pre-treatments failed to expose the zirconia substructure. A significant difference in bond strengths was found between AA-Z ($4.60{\pm}1.08MPa$) and all other groups ($13.38{\pm}2.57-15.78{\pm}2.39MPa$, p < 0.05). For AA-Z, most of the adhesive remained on the bracket. Conclusions: For bracket bonding to glazed zirconia, a simple application of silane to the cleaned surface is recommended. A zirconia primer should be used only when the zirconia substructure is definitely exposed.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2003.03a
• /
• pp.53-53
• /
• 2003

There has been increasing interest in the fabrication of nano-sized structures because of their various advantages and applications. Anodic Aluminum Oxide (AAO) is one of the most successful methods to obtain highly ordered nano pores and channels. Also It can be obtained diverse pore diameter, density and depth through the control of anodization condition. The three types of substrates were used for anodization; sheets of Aluminum on Si wafer and Aluminum on Mo-coated Si wafer. In Aluminum sheet, a highly ordered array of nanoholes was formed by the two step anodization in 0.3M oxalic acid solutions at 10$^{\circ}C$ After the anodization, the remained aluminum was removed in a saturated HgCl$_2$ solution. Subsequently, the barrier layer at the pore bottom was opened by chemical etching in phosphoric acid. Finally, we can obtain the through-channel membrane. In these processes, the effect of various parameters such as anodizing voltage, anodizing time, pore widening time and pre-heat treatment are characterized by FE-SEM (HITACH-4700). The pore size. density and growth rate of membrane are depended on the anodizing voltage and temperature respectively. The pore size is proportional to applied voltage and pore widening time The pore density can be controlled by anodizing temperature and voltage.