• 한국재료학회지
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• 제29권7호
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• pp.412-424
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• 2019

Global fitting functions for Fe-selective chlorination in ilmenite($FeTiO_2$) and successive chlorination of beneficiated $TiO_2$ are proposed and validated based on a comparison with experimental data collected from the literature. The Fe-selective chlorination reaction is expressed by the unreacted shrinking core model, which covers the diffusion-controlling step of chlorinated Fe gas that escapes through porous materials of beneficiated $TiO_2$ formed by Fe-selective chlorination, and the chemical reaction-controlling step of the surface reaction of unreacted solid ilmenite. The fitting function is applied for both chemical controlling steps of the unreacted shrinking core model. The validation shows that our fitting function is quite effective to fit with experimental data by minimum and maximum values of determination coefficients of $R^2$ as low as 0.9698 and 0.9988, respectively, for operating parameters such as temperature, $Cl_2$ pressure, carbon ratio and particle size that change comprehensively. The global fitting functions proposed in this study are expressed simply as exponential functions of chlorination rate(X) vs. time(t), and each of them are validated by a single equation for various reaction conditions. There is therefore a certain practical merit for the optimal process design and performance analysis for field engineers of chlorination reactions of ilmenite and $TiO_2$.

• 한국재료학회지
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• 제29권3호
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• pp.167-174
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• 2019

To improve the performance of carbon nanofibers as electrode material in electrical double-layer capacitors (EDLCs), we prepare three types of samples with different pore control by electrospinning. The speciments display different surface structures, melting behavior, and electrochemical performance according to the process. Carbon nanofibers with two complex treatment processes show improved performance over the other samples. The mesoporous carbon nanofibers (sample C), which have the optimal conditions, have a high sepecific surface area of $696m^2g^{-1}$, a high average pore diameter of 6.28 nm, and a high mesopore volume ratio of 87.1%. In addition, the electrochemical properties have a high specific capacitance of $110.1F\;g^{-1}$ at a current density of $0.1A\;g^{-1}$ and an excellent cycling stability of 84.8% after 3,000 cycles at a current density of $0.1A\;g^{-1}$. Thus, we explain the improved electrochemical performance by the higher reaction area due to an increased surface area and a faster diffusion path due to the increased volume fraction of the mesopores. Consequently, the mesoporous carbon nanofibers are demonstrated to be a very promising material for use as electrode materials of high-performance EDLCs.

• Smart Structures and Systems
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• 제22권6호
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• pp.675-687
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• 2018

In the previous studies on the porous rock strength the effect of pore number and its diameter is not explicitly defined. In this paper crack initiation, propagation and coalescence in Brazilian model disc containing a single cylindrical hole and or multiple holes have been studied numerically using PFC3D. In model with internal hole, the ratio of hole diameter to model diameter was varied between 0.03, 0.17, 0.25, 0.33, and 0.42. In model with multiple hole number of holes was different in various model, i.e., one hole, two holes, three holes, four holes, five holes, six holes, seven holes, eight holes and nine holes. Diameter of these holes was 5 mm, 10 mm and 12 mm. The pre-holed Brazilian discs are numerically tested under Brazilian test. The breakage load in the ring type disc specimens containing an internal hole with varying diameters is measured. The mechanism of cracks propagation in the wall of the ring type specimens is also studied. In the case of multi-hole Brazilian disc, the cracks propagation and b cracks coalescence are also investigated. The results shows that breaking of the pre-holed disc specimens is due to the propagation of radially induced tensile cracks initiated from the surface of the central hole and propagating toward the direction of diametrical loading. In the case of disc specimens with multiple holes, the cracks propagation and cracks coalescence may occur simultaneously in the breaking process of model under diametrical compressive loading. Finally the results shows that the failure stress and crack initiation stress decreases by increasing the hole diameter. Also, the failure stress decreases by increasing the number of hole which mobilized in failure. The results of these simulations were comprised with other experimental and numerical test results. It has been shown that the numerical and experimental results are in good agreement with each other.

• 한국콘텐츠학회논문지
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• 제19권1호
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• pp.463-471
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• 2019

테이프는 납치, 강도, 폭탄제조 등 강력범죄에 사용되며, 테이프 접착면에는 지문, DNA 등 수사에 필요한 증거가 남아있을 수 있다. 이러한 증거를 수집하기 위해서는 테이프 접착면을 박리하는 과정이 선행되어야 한다. 본 연구에서는 테이프가 다공성표면에 부착되어 있는 경우에 한 가지 시약을 사용하여 테이프를 손상없이 박리하면서 동시에 다공성표면에서 지문을 현출할 수 있는 새로운 조성의 이중목적시약을 탐색하였다. 실험 결과, 새로운 조성의 1,2-IND 농축용액과 HFE-7100의 비율이 1:2인 조성의 시약이 A4 용지에 테이프가 부착되어 있는 경우 테이프 접착면에 손상이 가지 않으면서, 박리한 종이에 열을 가하여 바로 지문을 현출할 수 있었다. 따라서 테이프가 다공성 표면에 부착되어 있는 경우에 본 연구에서 제시하는 새로운 조성의 1,2-IND(HFE-7100 기반, 1:2)를 사용할 것을 권장한다.

• 한국결정성장학회지
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• 제31권2호
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• pp.96-101
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• 2021

Developing effective and earth-abundant electrocatalyst for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is critical for the commercialization of a water splitting system. In particular, the overpotential of the OER is relatively higher than the HER, and thus, it is considered that one of the important methods to enhance the performance of the electrocatalyst is to reduce the overpotential of the OER. We report effects of incorporation of metalloid into Ni(OH)2 microcrystal on electrocatalytic activities. In this study, Te incorporated Ni(OH)2 (��Te-Ni(OH)2) were grown on three-dimensional porous NF by a facile solvothermal method with �� = 1, 3 and 5. Homogeneous microplate structure on the NF was clearly observed for the Ni(OH)2/NF and ��Te-Ni(OH)2/NF samples. However, irregular and collapsed nanostructures were found on the surface of nickel foam when Te precursor ratio is (��) over 3. Electrocatalytic OER properties were analysed by Linear sweep voltammetry (LSV) and Electrochemical impedance spectroscopy (EIS). The amount of Te incorporation used in the electrocatalytic reaction was found to play a crucial role in improving catalytic activity. The optimum Te amount (��) introduced into the Ni(OH)2/NF was discussed with respect to their OER performance.

• 한국재료학회지
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• 제29권10호
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• pp.617-622
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• 2019

In order to develop a process for manufacturing a composite structure of an intermetallic compound foam and a hollow material, the firing and pore form of the Al-Ni precursor in a steel pipe are investigated. When the Al-Ni precursor is foamed in a hollow pipe, if the temperature distribution inside the precursor is uneven, the pore shape distribution becomes uneven. In free foaming, no anisotropy is observed in the foaming direction and the pore shape is isotropic. However, in the hollow pipe, the pipe expands in the pipe axis direction and fills the pipe. The interfacial adhesion between $Al_3Ni$ foam and steel pipe is excellent, and interfacial pore and reaction layer are not observed by SEM. In free foaming, the porosity is 90 %, but it decreases to about 80 % in the foam in the pipe. In the pipe foaming, most of the pore shape appears elongated in the pipe direction in the vicinity of the pipe, and this tendency is more remarkable when the inside pipe diameter is small. It can be seen that the pore size of the foam sample in the pipe is larger than that of free foam, because coarse pores remain after solidification of the foam because the shape of the foam is supported by the pipe. The vertical/horizontal length ratio expands along the pipe axis direction by foaming in the pipe, and therefore circularity is reduced.

• 대한토목학회논문집
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• 제42권4호
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• pp.449-455
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• 2022

콘크리트는 가장 많이 사용되는 건설재료이다. 콘크리트의 비교적 높은 자중은 압축강도 발현과 수축저항성에서 이점을 갖지만, 초장대교량이나 초고층빌딩에 적용되기에는 구조물 자체의 무게가 큰 폭으로 증가하게 되어 거대 구조물의 형상을 제약하는 조건이 되기도 한다. 이러한 문제를 해결하고자, 경량골재를 사용하는 경량 콘크리트 개발이 많이 진행되어 왔으나, 경량 골재의 경우 다공질 구조로 인해 자체 강도가 작기 때문에, 일반적으로 경량 콘크리트는 일반 콘크리트에 비해서 낮은 강도를 가지게 된다. 본 연구에서는 기존의 경량 콘크리트의 한계점을 극복한 경량을 유지하면서 고강도를 만족시키는 건설재료를 개발하고자 하였다. 중공 유리 마이크로스피어를 낮은 물-시멘비율의 매트릭스에 다량으로 사용하는 방법을 적용해 보았으며, 네 가지 다른 종류의 마이크로스피어를 사용하여 그 적용성을 살펴보았다. 실험결과, 마이크로스피어의 종류와 관계 없이 밀도 1.7 g/cm³를 유지하면서 압축강도 60 MPa와 80 MPa를 각각 상온양생과 고온양생 조건에서 만족하는 것을 확인할 수 있었다.

• 공업화학
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• 제33권4호
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• pp.367-372
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• 2022

폴리염화비닐(polyvinylchloride, PVC)-tetrahydrofuran (THF) 용액에 PVC 비용매의 첨가와 박막 건조 공정이 PVC 박막에 미치는 영향을 분석하였다. 사용된 비용매는 알코올과 비알코올계로 구성되었으며, 첨가에 따른 PVC 박막의 표면 거칠기와 표면 형상의 차별성에 따른 소수성 성질을 비교하였다. PVC-THF 용액 제조과정에 발생하는 용액 내 기포 함유가 박막의 표면 구조에 미치는 영향이 큼을 확인하였다. 상대적인 고농도 PVC-THF 용액에서 코팅 박막의 정상적 표면 물성을 구현하기 위하여 적절한 박막 건조법의 선택이 요구된다. 알코올계 비용매를 첨가할 경우 과립형 형상의 다공성 표면을 갖는 PVC 박막이 얻어져 초소수성 특성을 보인다. 비용매에 대한 PVC-THF 용액의 부피 비는 코팅 박막의 표면 형상에 영향을 주며, 비용매 첨가량이 많을수록 초소수성 PVC 박막을 형성하는 데 유리하다.

• Steel and Composite Structures
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• 제43권1호
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• pp.91-106
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• 2022

This paper has focused on presenting a three dimensional theory of elasticity for free vibration of 3D-graphene foam reinforced polymer matrix composites (GrF-PMC) cylindrical panels resting on two-parameter elastic foundations. The elastic foundation is considered as a Pasternak model with adding a Shear layer to the Winkler model. The porous graphene foams possessing 3D scaffold structures have been introduced into polymers for enhancing the overall stiffness of the composite structure. Also, 3D graphene foams can distribute uniformly or non-uniformly in the shell thickness direction. The effective Young's modulus, mass density and Poisson's ratio are predicted by the rule of mixture. Three complicated equations of motion for the panel under consideration are semi-analytically solved by using 2-D differential quadrature method. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. Because of using two-dimensional generalized differential quadrature method, the present approach makes possible vibration analysis of cylindrical panels with two opposite axial edges simply supported and arbitrary boundary at the curved edges. It is explicated that 3D-GrF skeleton type and weight fraction can significantly affect the vibrational characteristics of GrF-PMC panel resting on two-parameter elastic foundations.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2020년도 봄 학술논문 발표대회
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• pp.148-149
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• 2020

Currently, the most commonly used EPS insulation material has been mainly used because its ease of adhesion with concrete. However, due to poor adhesion with wallpaper, separate adhesion needs to be strengthened and there are cases of breakage or grooves in the process of dismantling the mold. The biggest problem is that when a fire breaks out, various harmful substances are present and highly flammable. Cork used in this study is a truly eco-friendly building material that is taken from between the outer and inner bark of cork trees and does not damage the wood. Also, it is a porous material that is made up of countless cells and contains an air gap between the cells. It is very light in weight between 0.06 and 0.07 and has excellent insulation with a heat conductivity of 0.04W/mK. In addition, it has high stability in the topic of conversation because it does not produce harmful gas when burned and has self-sustaining properties. However, research on cork, an eco-friendly building material with excellent performance to date, is scarce Therefore, we encourage existing scholars to raise interest in new eco-friendly building materials through this study. It also aims to manufacture insulation boards with new inorganic properties using the low weight and heat conductivity held by the cork.