• Journal of the Korea Concrete Institute
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• v.22 no.2
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• pp.149-158
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• 2010

Recently, numerous construction techniques for repairing and strengthening methods for above ground or air exposed concrete structure have been developed. However repairing and strengthening methods for underwater structural members under continuous loading, such as piers and steel piles need the further development. Therefore, this study develops an aqua epoxy, which can be used for repairing and strengthening of structural members located underwater. Moreover, using the epoxy material and strengthening fibers, a fiber reinforced composite sheet called Aqua Advanced FRP (AAF) for underwater usage is developed. To verify and to obtain properties of the material and the performance of AAF, several tests such as pull-off strength test, bond shear strength test, and chemical resistance test, were carried out. The results showed that the developed aqua epoxy does not easily dissolve in wet conditions and does not create any residual particle during hardening. In spite of underwater conditions, it showed the superior workability, because of the high viscosity over 30,000 cps and adhesion capacity over 2 MPa, which are nearly equivalent to those used in dry conditions. In case of the chemical resistance test, the developed aqua epoxy and composite showed the weight change of about 0.5~1.0%, which verifies the superior chemical resistance.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.120-127
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• 2006

The hammer-milled characteristics of waste wood materials such as lumber, plywood, particleboard(PB), MDF and railroad tic were investigated in this study. The physical and mechanical properties of recycled boards according to types of recycled particle and the mixing ratios were also studied. The hammer-milled, waste wood materials had the dimensional distributions suitable for the core layer panicle. Bending strengths of recycled boards (one layer) were shown in order of plywood, PB(laboratory-fabricated with particles used in the PB factory), lumber, tego film-overlaid plywood, MDF, waste railroad tie, PB(factory-made) and LPL-overlaid PB. Cured resin and creosote containing waste wood contributed to dimensional stability of reconstituted boards. Considering the mixing effects between lumber and plywood with recycled PB particle, lumber particle was contributive to bending strength, MOE and internal bond(IB) strength, whereas plywood particle was contributive to dimensional stability. The bending and IB strength of 3 layer boards composing only recycled waste wood particles in core layer of board were in order of lumber, plywood, PB and MDF. On the other hand, the thickness swelling was in order of PB, lumber, plywood and MDF. Bending strength of the 3 layer boards mixed with recycled PB-particle in the core layer had a decreasing tendency, as the mixing ratios of recycled PB-particles increased. The dimensional stability of 3 layer recycled board was improved as the mixing ratio of recycled PB-particle increased same as in one layer. Formaldehyde emission of boards fabricated with recycled PB-particles in the core layer of the PB was in the range of E2 grade (below 5.0mg/l).

• Journal of Korean Dental Science
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• v.5 no.1
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• pp.7-12
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• 2012

Purpose: To examine the antibacterial effectiveness of silver nanoparticles (SNP) mixed with commercial orthodontic adhesives. Materials and Methods: SNP was prepared by dissolving silver perchlorate in an organic solvent and reducing it with ultraviolet radiation. SNP was then mixed with four commercial orthodontic adhesives (Light Bond, Blugloo, Transbond XT, and Fuji Ortho LC) (0.05 wt %), which were then formed into disc-shape specimens ($8.0mm{\times}3.0mm$). Commercial orthodontic adhesives containing no SNP were used as the control groups. Specimens of the four experimental and four control groups were incubated with streptococcus mutans and the medium turbidity was assessed at 3, 6, 9, 12, and 24 hours after incubation. The agar diffusion test was also performed to examine the growth inhibition zone of these groups. The data were statistically analyzed using a Wilcoxon rank sum test and t-test with a Bonferroni's correction (P<0.05). Result: The SNP containing groups had a superior antibacterial effect compared to the control groups. In the agar diffusion test, the control groups without SNP did not produce an inhibition zone, whereas the SNP containing groups showed inhibition zone of 10~13 mm. Conclusion: The incorporation of SNP into orthodontic adhesives can inhibit cariogenic bacterial growth.

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.499-504
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• 2005

Polymer concrete shows excellent mechanical properties and chemical resistance compared with conventional normal cement concrete. The polymer concrete Is drawing a strong interest as high-performance materials in the construction industry Resins using recycled PET offer the possibility of a lower source cost of materials for making useful polymer concrete products. Also the recycling of PET in polymer concrete would help solve some of the solid waste problems Posed by plastics and save energy. An objective of this paper is to estimate the damage of sulfuric acid, through investigating recycled PET polymer concrete, immersed at sulfuric acid solution for 84 days. As a result of testing, recycled PET PC, used $CaCO_3$ as filler, makes a problem of appearance and strength if they are exposed for long term at corrosion environment. On the other hand, recycled PET PC, used fly-ash as filler, had less effect on decrease in weight and strength. Recycled PET PC is excellent chemical resistance, resulting in the role of unsaturated polyester resin which consists of polymer chain structure accomplishes bond of aggregates and filler strongly. Also, recycled PET PC, used fly-ash as filler, is stronger resistance of sulfuric acid corrosion than $CaCO_3$, because it is composed of $SiO_2$ and very strong glassy crystal structure. Therefore, recycled PET PC, used fly-ash as filler, is available under corrosion circumstances like sewer pipe or waste disposal plant.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.3
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• pp.57-62
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• 2020

Among the sewage pipes installed in Korea, the length of concrete pipes exceeding 20 years is 66,334 km (42.5%). Deteriorated concrete sewer pipes need to be repaired due to the leakage of internal sewage, which causes problems such as sink holes by expanding the cavity around the pipeline. In this study, we tried to apply anti-washout underwater mortar with ultra rapid hardening cement and segregation reducing agent to sewage pipe repair. As a result of the setting time test, the final set time was delayed by up to 172% by incorporating segregation reducing agent. In the test for measuring the degree of mortar segregation in water, it was measured at pH 12 or less under all mixing conditions. In addition, the suspension amount was measured to be 50 mg / l or less to satisfy the KCI-AD102 standard by incorporating a segregation reducing agent. In terms of the average value of mortar compressive strength, by incorporating segregation reducing agent, the strength of the specimens produced in air was more than 80% of that of the specimens produced in water. Conversely, the bond strengths of the specimens produced in water were measured to be higher than those of the specimens produced in air. Water resistance was evaluated by measuring water absorption and water permeability. Water absorption and water permeability were reduced by 42.6% and 36.6%, respectively, by mixing segregation reducing agent.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.493-496
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• 2005

비정질 실리콘 (a-Si)의 수소화를 통해 활성화 수소가 비정질 실리콘내의 댕글링본드 (dangling bond) 와 결합 하므로 에너지밴드의 국재준위(localized state)를 감소시켜 불순물 도핑이 가능하게 되므로 a-Si 이 전자소자로서 이용 가능하게 되었다. 이에 착안하여 본 연구에서는 경사($0^{\circ}$, $45^{\circ}$, $80^{\circ}$) 증착을 통해 비정질 칼코게나이드($a-As_{40}Ge_{10}Se_{15}S_{35}$) 박막을 제작하고 그 박막을 수소화처리 (15~20atm at $150\sim190^{\circ}C$)하여 처리 전 후의 surface morphology 변화 및 광학적 특성 변화를 고찰하였다. $a-As_{40}Ge_{10}Se_{15}S_{35}$ 박막의 SEM 측정을 통해 $40^{\circ}$와 $80^{\circ}$ 경사 증착된 $a-As_{40}Ge_{10}Se_{15}S_{35}$ 박막에서 각각 18.8nm 와 160nm의 transition layer와 박막의 기둥(columnar)구조가 형성됨을 관찰하였다. 특히, $80^{\circ}$ 증착박막의 경우 수소처리전 columnar구조는 약 $65\sim70^{\circ}$의 기둥 각을 가지고 형성되었고 수소화 처리를 통해 기둥구조가 붕괴 되었다. $70^{\circ}$ 경사 증착된 $a-As_{40}Ge_{10}Se_{15}S_{35}$ 박막은 $0^{\circ}$에 따른 박막 보다 흡수단 부근에서 약 20%의 투과도 증가와 광 에너지 갭 ($E_{op}$)의 증가를 관찰 할 수 있었다. $80^{\circ}$경사 증착된 수소처리 박막에서 흡수단 부근의 투과도가 약 10%증가 되었고, 광 에너지 갭은 약 0.07eV 증가 하였고, PL intensity는 흡수단 부근에서 증가한 것을 확인 할 수 있었다. 이러한 변화들은 경사 증착된 $a-As_{40}Ge_{10}Se_{15}S_{35}$ 박막 내의 상대적으로 원자 밀도가 큰 기둥(columnar)구조가 생성되고, 이 원자 밀도가 높은 기둥구조의 댕글링본드와 주입된 수소가 흡착하여 에너지대의 국재준위를 감소시키기 때문으로 판단된다.

• Korean Journal of Materials Research
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• v.8 no.4
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• pp.345-353
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• 1998

Metal organic chemical vapor deposition (MOCVD) of copper using three Cu( I ) precursors. (hfac)Cu (VTMS) (hfac= hexafluoroacetylacetonate, VTMS= vinyltrimethylsilane), (hfac)Cu(VTMOS) (VTMOS= vinyltri¬methoxysilane) and (hfac)Cu(A TMS) (A TMS= allyltrimethylsilane) was studied. The thermal stability and the gase¬ous phase reaction mechanism of Cu( I ) precursors were identified using $^1H$-, $^I3C$-NMR and Fourier transform infra¬red spectroscopy. It was found out that thermal stability of liquid phase (hfac)Cu(VTMS) and (hfac)Cu(VTMOS) were better than that of (hfac)Cu(A TMS) using FT - NMR. From in-situ FT - IR experiments, the disproportion reaction of Cu(hfac). the decomposition reaction of Cu(hfac), and cracking of free hfac ligand were observed. Also the effect of gaseous phase reaction on the deposition rates and film properties was investigated. The minimum temperature that deposition of copper films from (hfac)Cu(A TMS) was as low as 60$^{\circ}$C and such a low deposition temperature compared with those of other Cu( I ) precursors is believed to be related with weaken Cu- A TMS bond.

• Korean Journal of Materials Research
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• v.9 no.3
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• pp.288-294
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• 1999

In the flip chip interconnection using solder bump, the Under Bump Metallurgy (UBM) is required to perform multiple functions in its conversion of an aluminum bond pad to a solderable surface. In this study, various UBM systems such as $Al 1\mu\textrm{m} / Ti 0.2\mu\textrm{m} / Cu 5\mu\textrm{m}, Al 1\mu\textrm{m} / Ti 0.2\mu\textrm{m} / Cu 1\mu\textrm{m}, al 1\mu\textrm{m}/Ni 0.2\mu\textrm{m} / Cu 1\mu\textrm{m} and Al 1\mu\textrm{m}/Pd 0.2\mu\textrm{m} / Cu 1\mu\textrm{m}$ for flip chip interconnection using the low melting point eutectic 63Sn-37Pb solder were investigated and compared to their metallurgical properties. $100\mu\textrm{m}$ size bumps were prepared for using an electroplating process. The effects of the number of reflows and aging time on the growth of intermetallic compounds(IMC) were investigated. $Cu_6Sn_5$ and $Cu_3Sn$ IMC were abserved after aging treatment in the UBM system with thick coper $(Al 1\mu\textrm{m}/Ti 0.2\mu\textrm{m}/Cu 5\mu\textrm{m})$. However only the $Cu_6Sn_5$ was detected in the UBM system with $1\mu\textrm{m}$ thick copper even after 2 reflow and 7 day aging at $150^{\circ}C$. Complete Cu consumption by Cu-Sn IMC growth gives rise to a direct contact between solder inner layer such as Ti, Ni and Pd, and hence to possibly cause reactions between two of them. In this study, however, only for the Pd case, IMC of PdSn. was observed by Cu consumption. UBM interfacial reactions with s이der affected the adhesion strength ot s이der balls after s이der reflow and annealing treatment.

• Journal of the Korean Chemical Society
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• v.36 no.4
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• pp.477-484
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• 1992

Using semiempirical molecular orbital method, ASED-MO of extended Huckel Theory, we were investigated chemical bonds and electronic properties of Cu atom in a chain and a layer for Y123 and Y124 superconductors from VEP (valence electron population), DOS (density of state), and COOP (crystal orbital overlap population). In order to investigate environmental effects of Cu atom for Y123 and Y124 superconductors, we introduced charged cluster models with point charge and without point charge into our calculations. As a result of ASED-MO calculations, the Cu atom in the layer acts as electron acceptor and the Cu atom in the chain acts as electron donor for Y123 and Y124 superconductors. The oxidation state of Cu atom for Y123 and Y124 superconductors without point charge is higher in the chain than in the layer. The oxidation state of Cu atom in the layer for Y123 superconductor is higher than that in the layer for Y124 superconductor. The Cu atom in the layer and the chain for Y123 superconductor does not largely affect on the environmental effect. However, the Cu atom in the layer and the chain for Y124 superconductor does largely affect on it. Also, electron population and chemical bonding of Cu1-O4, Cu2-O4, and Cu1-Cu2 for Y123 superconductor are far different from Y124 superconductor.

• Journal of Welding and Joining
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• v.28 no.3
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• pp.92-98
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• 2010

Ferritic stainless steels, which have relatively small thermal expansion coefficient and excellent corrosion resistance, are increasingly being used in vehicle manufacturing, in order to increase the lifetime of exhaust manifold parts. But, there are limits on use because of the problem related to cosmetic resistance, corrosions of condensation and high temperature salt etc. So, Aluminum-coated stainless steel instead of ferritic stainless steel are utilized in these parts due to the improved properties. In this investigation, Al-8wt% Si alloy coated 409L ferritic stainless steel was used as the base metal during Gas Tungsten Arc(GTA) welding. The effects of coated layer on the microstructure and hardness were investigated. Full penetration was obtained, when the welding current was higher than 90A and the welding speed was lower than 0.52m/min. Grain size was the largest in fusion zone and decreased from near HAZ to base metal. As welding speed increased, grain size of fusion zone decreased, and there was no big change in HAZ. Hardness had a peak value in the fusion zone and decreased from the bond line to the base metal. The highest hardness in the fusion zone resulted from the fine re-precipitation of the coarse TiN and Ti(C, N) existed in the base metal during melting and solidification process and the presence of fine $Al_2O_3$ and $SiO_2$ formed by the migration of the elements, Al and Si, from the melted coating layer into the fusion zone.