• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.37-38
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• 2022

During the past decades, the corrosion of the steel rebar embedded in concrete structure surrounding marine environment is actually problematic and required the suitable preventive method. An eco-friendly corrosion inhibitor mix is investigated to stifle the active corrosion in comparison with other commercial corrosion inhibitors. The hybrid inhibitor enhances the corrosion resistance and the workability of concrete. However, it reduces the compressive strength slightly after 28-day-age. The electrochemical studies and mechanical studies are pointed out the corrosion resistance property, corrosion kinetics, and the mechanical properties of all concrete samples. H-3 is the optimum dose of hybrid inhbitor that meets the demand of both electrochemical property and mechanical property. It performs the noble features due to the formation of optimum amount of P-Zwitterions-(Cl)-Fe complex onto the steel rebar surface.

• Progress in Superconductivity and Cryogenics
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• v.8 no.1
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• pp.45-48
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• 2006

In the response to the demand for electrical energy , much effort was given to develop and commercialize high temperature superconducting (HTS) power equipments has been made around the world. Especially, HTS transformer is one of the most promising devices . but the cryogenic insulation technology should be established during development Hence many types of dielectric tests should be carried out to understand the dielectric phenomena at cryogenic temperature and to gather various dielectric data. Among the many types dielectric tests . the characteristic of barrier effect were conducted using simulated electrode after analysing the insulating configuration of HTS transformer main winding. The influence of a barrier on the dielectric strength was measured according to the position of the harriet the number of the barrier and thickness or the barrier. It was shown that the effectiveness . namely the ratio of the breakdown voltage in presence of barrier to the voltage without barrier, is highest when the barrier is placed at the needle electrode side. On the contrary, in the case of having the barrier between the electrodes, the harrier was placed between the electrodes the characteristic was even improved slightly.

• Korean Journal of Materials Research
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• v.32 no.12
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• pp.528-532
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• 2022

Recently, the necessity of designing and applying tool materials that perform machining of difficult-to-cut materials in a cryogenic treatment where demand is increasing. The objective of this study is to evaluate the performance of cryogenically treated WC-5 wt% NbC hard materials fabricated by a pulsed current activated sintering process. The densely consolidated specimens are cryogenically exposed to liquid nitrogen for 6, 12, and 24 h. All cryogenically treated samples exhibit compressive stress in the sintered body compared with the untreated sample. Furthermore, a change in the lattice constant leads to compressive stress in the specimens, which improves their mechanical performance. The cryogenically treated samples exhibit significant improvement in mechanical properties, with a 10.5 % increase in Vickers hardness and a 60 % decrease in the rupture strength compared with the untreated samples. However, deep cryogenic treatment of over 24 h deteriorates the mechanical properties indicating that excessive treatment causes tensile stress in the specimens. Therefore, the cryogenic treatment time should be controlled precisely to obtain mechanically enhanced hard materials.

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.1
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• pp.59-68
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• 2023

The column-tree type steel beam-column connections are commonly used in East Asian countries, including Korea. The welding detail between the stub beam and column is similar to the WUF-W connection; thus, it can be expected to have sufficient seismic performance. However, previous experimental studies indicate that premature slip occurs at the friction joints between the stub and link beams. In this study, for the accurate seismic performance evaluation of column-tree type moment connections, a moment-slip model was proposed by investigating the previous test results. As a result, it was found that the initial slip occurred at about 25% of the design slip moment strength, and the amount of slip was about 0.15%. Also, by comparing the analysis results from models with and without the slip element, the influence of slip on the performance of overall beam-column connections was examined. As the panel zone became weaker, the contribution of slip on overall deformation became greater, and the shear demand for the panel zone was reduced.

• Transactions of Materials Processing
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• v.33 no.1
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• pp.36-42
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• 2024

Additive manufacturing with 3XX austenitic stainless steels has been widely investigated during a decade due to its high strength, good corrosion resistance, and fair weldability. However, in recently, Ni price drastically increased due to the high demand of secondary battery for electric mobilities. Thus, it is essential to substitute the Ni with Mn for reducing stainless steels price. Meanwhile, the chemical composition changes in stainless steels not only affect to its properties but also change the optimal processing parameters during additive manufacturing. Therefore, it is necessary to optimize the processing parameters of each alloy for obtaining high-quality product using additive manufacturing. After processing optimization, mechanical properties and microstructure of the laser-powder bed fusion processed Fe-15Cr-7Ni-3Mn alloy were investigated in both room (298 K) and cryogenic (77 K) temperatures. Since the temperature reduction affects to the deformation mechanism transition, multi-scale microstructural characterization technique was conducted to reveal the deformation mechanism of each sample.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.2
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• pp.119-132
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• 2024

Dielectric ceramic capacitors present high output power density due to the fast energy charge and discharge nature of dielectric polarization. By forming dense ceramic films with nano-grains through the Aerosol Deposition (AD) process, dielectric ceramic capacitors can have high dielectric breakdown strength, high energy storage density, and leading to high power density. Dielectric capacitors fabricated by AD process are expected to meet the increasing demand in applications that require not only high energy density but also high power output in a short time. This article reviews the recent progress on the dielectric ceramic capacitors with improved energy storage properties through AD process, including energy storage capacitors based on both leadbased and lead-free dielectric ceramics.

• Corrosion Science and Technology
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• v.23 no.1
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• pp.72-81
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• 2024

The Ti-6Al-4V alloy is widely used as an implant material due to its higher fatigue strength and strengthto-weight ratio compared to pure titanium, excellent corrosion resistance, and bone-like properties that promote osseointegration. For rapid osseointegration, the adhesion between the titanium surface and cellular biomolecules is crucial because adhesion, morphology, function, and proliferation are influenced by surface characteristics. Polymeric peptides and similar coating technologies have limited effectiveness, prompting a demand for alternative materials. There is growing interest in 2D nanomaterials, such as MoS₂, for good corrosion resistance and antibacterial, and bioactive properties. However, to coat MoS₂ thin films onto titanium, typically a low-temperature hydrothermal synthesis method is required, resulting in the synthesis of films with a toxic 1T@2H crystalline structure. In this study, through high-temperature annealing, we transformed them into a non-toxic 2H structure. The implant coating technique proposed in this study has good corrosion resistance and biocompatibility, and antibacterial properties.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.42 no.1
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• pp.30-37
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• 2006

Black rockfish and goldeye rockfish are commercially important fish species due to the increasing demand in Korea. When estimating the abundance of stocks for these species acoustically, it is of crucial importance to know the target strength(TS) to length dependence. In relation to these needs, TS measurement was conducted on black rockfish and goldeye rockfish in an acrylic salt water tank using 70kHz and 120kHz split beam echo sounders. The TS for these two species under the controlled condition was simultaneously measured with the swimming movement by DVR system and analyzed as a function of fish length(L). The results obtained are summarized as follows: The best fit regression of TS on fish length of black rockfish was TS=19.38 Log(L, cm)-70.46 ($r^2=0.71$) at 70kHz and TS=22.39 Log(L, cm)-70.40 ($r^2=0.64$) at 120kHz and in the standard form TS=20 Log(L, cm)-71.29 ($r^2 = 0.70$) at 70kHz and TS=20 Log(L, cm)-66.88 ($r^2=0.57$) at 120kHz. The best fit regression of TS on fish length of goldeye rockfish was TS=17.10 Log(L, cm)-68.28 ($r^2=0.37$) at 70kHz and TS=24.39 Log(L, cm)-73.74 ($r^2=0.59$) at 120kHz and in the standard form TS=20 Log(L, cm)-72.03 ($r^2=0.32$) at 70kHz and TS=20 Log(L, cm)-67.68 ($r^2=0.64$) at 120kHz. An empirical model for fish TS(dB) averaged over the dorsal aspect of 115 fishes of black rockfish and goldeye rockfish and which spans the fish length(L, m) to wavelength($\lambda$, m) ratio between 8 and 30 was derived : TS=34.12 Log(L)-14.12 Log($\lambda$)-23.83, ($r^2=0.90$).

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.589-594
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• 2006

The recycling of industrial wastes in the concrete manufacturing is of increasing interest worldwide, due to the high environmental impact of the cement and concrete industries and to the rising demand of infrastructures, both in industrialized and developing countries. The production of municipal wastes in the South Korea is estimated at about 49,902 ton per day and only 14.5% of these are incinerated and principally disposed of in landfill. These quantities will increase considerably with the growth of municipal waste production, the progressive closing of landfill, so the disposal of municipal solid waste incinerator(MSWI) ashes has become a continuous and significant issue facing society, both environmentally and economically. MSWI ash is the residue from waste combustion processes at temperature between $850^{\circ}C\;and\;1,000^{\circ}C$. And the main components of MSWI ash are $SiO_2,\;CaO\;and\;Al_2O_3$. The aim of this study is to find a way to useful application of MSWI ash(after treatment) as a structural material and to investigates the hydraulic activity, compressive strength development composition variation of such alkali-activated MSWI ashes concrete. And it was found that early cement hydration, followed by the breakdown and dissolving of the MSWI-ashes, enhanced the formation of calcium silicate hydrates(C-S-H). The XRD and SEM-EDS results indicate that, both the hydration degree and strength development are closely connected with a curing condition and a alkali-activator. Compressive strengths with values in the 40.5 MPa were obtained after curing the activated MSWI ashes with NaOH+water glass at $90^{\circ}C$.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.763-771
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• 2009

As the demand on long span structures increases more in recent years, the excessive deflection, in addition to the ultimate strength, in horizontal members becomes a very important issue. For this reason, as an alternative method to effectively solve the deflection problems, the application of post-tensioned structural system with unbonded tendon increases gradually. However, most of the existing researches on post-tensioned members with unbonded tendons (UPT) focused on the ultimate flexural strength, which would be impossible or improper to check serviceability such as deflections. Therefore, this study aims at proposing a stress prediction model for unbonded tendons that is applicable to the behavior of UPT members from the very initial loading stages, post-cracking states, and service to ultimate conditions. The applicability and accuracy of the proposed model were also evaluated comparing to the existing test results from literature. Based on such comparison results, it was verified that the proposed model provided very good predictions on tendon stresses of UPT members at various loading stages regardless their different characteristics; wide range of reinforcement index, different loading patterns, and etc. The proposed model especially well considered the effect of various loading types on stress increases of unbonded tendons, and it was also very suitable to apply on the over-reinforced members that easily happened during strengthening/repairing work.