• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.5
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• pp.16-22
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• 2023

In this study, a salt water immersion test was performed on concrete specimens simulating the concrete mix design of the nuclear power plant, and the correlation between the amount of chloride and the XRF component according to the depth of the concrete was analyzed. The amount of chloride on the surface of the nuclear power plant concrete increased slightly with increasing immersion time in salt water, but the amount of chloride in the depth of 5.5 mm or more showed a clear tendency to increase with increasing immersion time in salt water. As a result of analyzing the correlation between the amount of chloride in concrete and the XRF component, the concrete with 20% FA substitution compared with the OPC concrete showed a very high correlation between the composition ratio of Cl ions and the evaluation result of salt damage resistance by XRF component analysis. Accordingly, it was confirmed that chlorine ion analysis and salt damage resistance performance evaluation by XRF component analysis were possible through repeated data accumulation in the nuclear power plant concrete mix with 20% fly ash replacement.

• Journal of the Korea Institute of Building Construction
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• v.24 no.3
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• pp.285-295
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• 2024

This study investigated the impact of accelerated carbonation on Ordinary Portland Cement(OPC) paste that had undergone steam curing at 500℃·hr. Two carbonation environments were examined: atmospheric carbonation(1atm, 20% CO₂) and pressurized carbonation(5atm, 99% CO₂). Chemical analysis using X-ray diffraction(XRD) and Fourier-Transform Infrared spectroscopy(FT-IR) were conducted, along with physical characterization via scanning electron microscopy(SEM) and compressive strength testing. Results indicated that atmospheric carbonation with 20% CO₂ concentration significantly densified the internal microstructure of the OPC paste, leading to enhanced compressive strength. Conversely, pressurized carbonation at 5atm with 99% CO₂ concentration resulted in rapid densification of the surface structure, which hindered CO₂ diffusion into the sample. This limited the extent of carbonation and prevented the improvement of physical properties.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.1
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• pp.66-78
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• 2004

The objective of this study was to apply the vibration technique to reduce the viscosity of bonding adhesives and thereby compare the bond strength and resin penetration in enamel and dentin achieved with those gained using the conventional technique and vibration technique. For enamel specimens, thirty teeth were sectioned mesio-distally. Sectioned two parts were assigned to same adhesive system but different treatment(vibration vs. non-vibration). Each specimen was embedded in 1-inch inner diameter PVC pipe with a acrylic resin. The buccal and lingual surfaces were placed so that the tooth and the embedding medium were at the same level. The samples were subsequently polished silicon carbide abrasive papers. Each adhesive system was applied according to its manufacture's instruction. Vibration groups were additionally vibrated for 15 seconds before curing. For dentin specimen, except removing the coronal part and placing occlusal surface at the mold level, the remaining procedures were same as enamel specimen. Resin composite(Z250. 3M. U.S.A.) was condensed on to the prepared surface in two increments using a mold kit(Ultradent Inc., U.S.A.). Each increments was light cured for 40 seconds. After 24 hours in tap water at room temperature, the specimens were thermocycled for 1000cycles. Shear bond strengths were measured with a universal testing machine(Instron 4465, England). To investigate infiltration patterns of adhesive materials, the surface of specimens was examined with scanning electron microscope. The results were as follows: 1. In enamel the mean values of shear bond strengths in vibration groups(group 2, 4, 6) were greater than those of non-vibration group(group 1, 3, 5). The differences were statistically significant except AQ bond group. 2. In dentin, the mean values of shear bond strengths in vibration groups(group 2, 4, 6) were greater than those of non-vibration groups(group 1, 3, 5). But the differences were not statistically significant except One-Up Bond F group. 3. The vibration group showed more mineral loss in enamel and longer resin tag and greater number of lateral branches in dentin under SEM examination.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.3 s.32
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• pp.37-45
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• 2004

Electroless Ni(P) has been widely used for under bump metallization (UBM) of flip chip and surface finish layer in microelectronic packaging because of its excellent solderability, corrosion resistance, uniformity, selective deposition without photo-lithography, and also good diffusion barrier. However, the brittle fracture at solder joints and the spatting of intermetallic compound (IMC) associated with electroless Ni(P) are critical issues for its successful applications. In the present study, the mechanism of IMC spatting and microstructure change of the Ni(P) film were investigated with varying P content in the Ni(P) film (4.6,9, and $13 wt.\%$P). A reaction between Sn penetrated through the channels among $Ni_3Sn_4$ IMCs and the P-rich layer ($Ni_3P$) of the Ni(P) film formed a $Ni_3SnP$ layer. Thickening of the $Ni_3SnP$ layer led to $Ni_3Sn_4$ spatting. After $Ni_3Sn_4$ spatting, the Ni(P) film directly contacted the molten solder and the $Ni_3P$ phase further transformed into a $Ni_2P$ phase. During the crystallization process, some cracks formed in the Ni(P) film to release tensile stress accumulated from volume shrinkage of the film.

• KSBB Journal
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• v.23 no.5
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• pp.439-444
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• 2008

In this study, hair care effects of the hair cosmetics including low molecular weight silk peptide, hydrolysate which is produced from cocoon were investigated. After producing the hair cosmetics including silk peptide which has 300-500 molecular weight, we measured its hair care effects through the various tests; change of the hair weight, hair thickness, absorbance rate and hair moisture value and micro structure analysis. As a result, S.P.T. (Silk peptide Treatment) was effectively penetrated into the hair which has been damaged by chemical treatments, increased the hair weight, thickness and hair moisture value and also recovered the cuticle of the hair. Thus, the treatment of hair with silk peptide hydrolysate would be effective to recover the damaged hair into the normal conditions.

• Polymer(Korea)
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• v.34 no.6
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• pp.540-546
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• 2010

In this manuscript, in order to reduce methanol permeability and, at the same time, to increase proton conductivity THS-PSA containing silica compound, responsible for methanol permeability reduction, and sulfonic acid, responsible for proton conductivity enhancement, was applied onto PVA/PSSA-MA membranes. And in order to improve durability, the resulting membranes, PVA/PSSAMA/THS-PSA, were exposed to 500ppm F2 gas at varying reaction times. The surface-fluorinated membranes were characterized through the measurement of contact angles, thermo-gravimetric analysis, and X-ray photoelectron spectroscopy to observe the physico-chemical changes. For the evaluation of the electro-chemical changes in the resulting membranes, its water contents, ion exchange capacity, proton conductivity, and methanol permeability were measured and then compared with the commercial membrane, Nafion 115. Finally, the membran electrode assembly(MEA) was prepared and the cell voltage against the current density was measured. As fluorination time increased, the contents of F2 increased up to maximum 4.3% and to depth of 50 nm. At 60 min of fluorination, the proton conductivity was 0.036 S/cm, larger than Nafion 115 at 0.024 S/cm, and the methanol permeability was $9.26E-08cm^2/s$, less than Nafion 115 at $1.17E-06cm^2/s$.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.585-593
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• 2007

This paper presents a model for durability evaluation of concrete structures exposed to marine environment, considering mainly a build-up of surface chloride $(C_s)$ as well as diffusion coefficient (D) and chloride threshold level $(C_{lim})$. In this study, time dependency of $C_s$ and D were extensively studied for more accurate evaluation of service life of concrete structures. An analytical solution to the Fick's second law was presented for prediction of chloride ingress for time varying $C_s$. For the time varying $C_s$, a refined model using a logarithm function for time dependent $C_s$ was proposed by the regression analysis, and averaging integrated values of the D with time over exposed duration were calculated and then used for prediction of the chloride ingress to consider time dependency of D. Durability design was also carried out for railway concrete structures exposed to marine environment to ensure 100 years of service life by using the proposed models along with the standard specification on durability in Korea. The proposed model was verified by the so-called performance-based durability design, which is widely used in Europe. Results show that the standard specification underestimates durability performances of concrete structures exposed to marine environment, so the cover depth design using current durability evaluation in the standard specifications is very much conservative. Therefore, it is found that utilizing proposed models considering time dependent characteristics of $C_s$ and D can evaluate service lift of concrete structures in marine environment more accurately.

• Journal of Conservation Science
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• v.19
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• pp.19-30
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• 2006

Alteration of physical and chemical characteristics and the effect of removal of mineral substances in waterlogged archaeological woods by different cleaning processes were examined using oak wood(Quercus spp.) that was excavated from wetland near Gwangju, Korea. Cleaning methods employed in the present work were (1) tools, (2) deaeration, (3) EDTA and (4) ultrasonic cleaning, which are being currently applied in the field of preservation treatment. Cleaning process were performed independently or continuously. Composition of mineral substances in the waterlogged archaeological wood was almost same as the that of soil in which waterlogged archaeological woods were buried. In case of independent cleaning, tools cleaning efficiently removed the mineral substances on surface. Surface color become brighter after cleaning with EDTA. In contrast, deaeration and ultrasonic cleaning did not show any significant removal of mineral substances. In continuous cleaning process, tool cleaning as the first step treatment showed the same effect as shown in independent cleaning. Although deaeration as the second step cleaning did not remove the mineral substances, it could be assumed to contribute the infiltration of dimensional agents by homogenization of wood. EDTA treatment (the third step cleaning) removed the iron(Fe) and increased the whiteness of wood color. The ultrasonic treatment (the fourth step cleaning) removed the sodium(Na) remained after EDTA treatment and the fine mineral substances.

• Journal of Conservation Science
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• v.18 s.18
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• pp.89-96
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• 2006

Surface layers of stone cultural properties including the soluble salt need consolidation because they are mostly very weak. There is a lot of research on the penetration depth of consolidant in stone and the effect of consolidant on mechanical stability of deteriorated structure. But some conservation experiences show that consolidation with silicic acid ester is not successful on salt contaminated stone cultural properties. In this study, in order to assess the influence of soluble salts$(CaSO_4\;2H_2O,\;NaNO_3)$ on the efficiency of consolidation on the deteriorated stone cultural properties(Nationalgalerie, Berlin, Germany) sandstone samples have been soaked with the salts solution. The impregnation of consolidant based on ethyl filicate have been afterwards carried out on these samples. As a result, it confirms that the soluble salts act as a preventer or consolidation. They fill up the pores in the stone and prevent that sufficient amount of consolidant enter deeply into the stone. According to this result, if use silicic ethyl ester as a consolidant for the research object which is built by Nebra sandstone, desalination is necessary before the treatment with consolidant. But it is also reported by other researches that some soluble salts improve the consolidation effect. Therefore it should be necessary to pre-study about salt and its harmfulness before the consolidation treatment. In order to consolidate without the aggravative damage in salt contaminated stone cultural heritage, we must first of all study the relations among salt, stone and consolidant.

• Composites Research
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• v.12 no.6
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• pp.74-82
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• 1999

The static and fatigue characteristics of polyurethane foam cored sandwich structures are investigated. Three types of the specimens with the glass fabric faces and the polyurethane foam core are used; non-stitched. stitched, and stiffened sandwich specimen. Especially additional structural reinforcements with the twisted polyester and glass fiber for thickness direction are made to stitched sandwich structure panel to minimize the delamination of structure which is stitched the upper and lower faces through the core and the resin is impregnated Into stitched fiber with the characteristics of low viscosity of resin at resin flow temperature and cured together with during the curing process. Bending strength of stitched specimen which is 50 mm $50{\times}50{\;}mm$ pitched is improved by 50 % as com-pared with non-stitched specimen and stiffened specimen is improved 10 times more than non-stitched structure. After fatigue testing of $10^6$cycles by 20% of ultimate load under monotonic load, the bending fatigue strength of non-stitched specimen is decreased by 27% of monotonic bending strength, 39% for stitched structure and 20% for stiffened specimen. To verify the aging effect of polyurethane form core, Ultrasonic C-scanning equipment is used to detect the damage of skin laminate alone after fatigue test. From results of UT C-scan images, there is no defect that can be damaged occurred during fatigue test. It is concluded that the decrease of bending strength for foam cored sandwich specimen is caused by the decrease of stiffness due to the aging of polyurethane foam core during fatigue cycles.