• Journal of the Korea Concrete Institute
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• v.20 no.4
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• pp.431-437
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• 2008

The concrete pavement at Seohae Expressway in Korea has suffered from serious distress, only after four to seven years of construction. The deterioration of ASR has seldom been reported per se in Korea, because the aggregate used for the cement concrete has been considered safe against alkali-silica reaction so far. The purpose of this study is to examine the expansion behavior of aggregates of Korea due to alkali-silica reaction by ASTM C 1260 standard method of the accelerated mortar bar test (AMBT), stereo microscopic analysis, scanning electronic microscope (SEM) analysis, and electron dispersive X-ray spectrometer (EDX) analysis. The results are presented as it follows. The accelerated mortar bar test (AMBT) showed that mica granite and felsite of igneous rocks, aroke, red sandstone and shale of sedimentary rocks, slate of metamorphic rock, and dendrite and quartz of mineral rock showed more expansion than 0.1% at 14 days. But, some sedimentary rocks and metamorphic rocks expanded more than 0.1% at 28 days even though they were less than 0.1% at 14 days. The mortar bars, which showed more than occurred 0.1% expansion, resulted in cracking on surface. SEM and EDX analysis confirmed that the white gel was a typical reaction product of ASR. The ASR gel in Korea mainly consisted of Silicate (Si) and Potassium (K) from the cement. The crack in the concrete pavement was caused by ASR. It seems that Korea is no longer safe zone against alkali-silica reaction.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.17 no.2
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• pp.127-137
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• 2019

Zr electrorefining is demonstrated herein using Zirlo tubes in a chloride-fluoride mixed molten salt in the presence of $AlF_3$. Cyclic voltammetry reveals a monotonic shift in the onset of metal reduction kinetics towards positive potential and an increase in intensity of the additional peaks associated with Zr-Al alloy formation with increasing $AlF_3$ concentration. Unlike the galvanostatic deposition mode, a radial plate-type Zr growth is evident at the top surface of the salt during Zr electrorefining at a constant potential of -1.2 V. The diameter of the plate-type Zr deposit gradually increases with increasing $AlF_3$ concentration. Scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) and X-ray photoelectron spectroscopy (XPS) analyses for the plate-type Zr deposit show that trace amount of Al is incorporated as Zr-Al alloys with different chemical compositions between the top and bottom surface of the deposit. Addition of $AlF_3$ is effective in lowering the residual salt content in the deposit and in improving the current efficiency for Zr recovery.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.297-304
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• 2008

It is well known that cracks in concrete decrease permeability and durability of concrete because cracks enhance the penetration of water or corrosive chemicals like as chlorides, carbon dioxides, sulfates and some others. But some of cracks in hardened cements may be sealed in case of contacting water. This phenomenon is called "self healing" and it has a close relation to hydration products newly formed on surfaces of cracks. Many studies on self healing in concretes commonly showed that CSH gel has been observed on crack surfaces. And some studies have reported that calcium hydroxides and ettringite were observed as well as CSH gel on crack surfaces. This study was carried out to investigate hydration products formed by self healing process and also examine the influence of waterproof admixture for concretes on self healing of cement. As a result of XRD, DSC, SEM and EDX analysis of crack surfaces, it was found that self healing of cement was related to CSH gel, calcium hydroxides and ettringite. And waterproof admixture increased fibrous (needle-like) hydration products which were in network form. It is estimated that such fibrous products are effective for self healing process of cement system.

• Composites Research
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• v.37 no.3
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• pp.238-245
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• 2024

In this study, as part of the development of a monitoring system for the efficient maintenance of steel pipes, an experimental study was conducted to evaluate the performance of steel pipes treated with modified polyethylene coating. In the case of the conventional mechanical pre-coating method, there was a deterioration in polyethylene adhesion during expansion testing, which led to the application of a chemical pre-treatment process using a calcium-mixed phosphate zinc film to resolve this issue. SEM and EDX analyses showed that the densest structure was observed at a Zn/Ca ratio of 1.0, and improved heat resistance compared to the conventional method was confirmed. Additionally, to prevent coating detachment during expansion, an evaluation of adhesion and elongation was conducted on steel pipes with modified polyethylene coating, incorporating materials such as elastomers based on maleic anhydride grafting, metal oxides, blocking agents, and slip agents. Experimental results showed that the specimen (S4) containing all modified materials exhibited more than a 25% performance improvement compared to the specimen (S2) containing only metal oxides. Lastly, the development and performance evaluation of wedge-shaped socketing and pressing wheels, which are part of the pipe fixing accessories, were conducted to prevent surface coating damage on the completed pipes.

• Journal of Korea Foundry Society
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• v.44 no.4
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• pp.97-102
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• 2024

In this study, the properties of Zr-14Cu-7.5Ni-2.6Al wide ribbon with amorphous structure and properties were analyzed using Hall effect, SEM-EDX, and XRD. Made by melt spinning method, this Zr-14Cu-7.5Ni-2.6Al based alloy ribbon is not more than 96 ㎛ thick and 100 mm wide. This amorphous alloy exhibited tensile strength of 1,641 MPa, yield strength of 1,541 MPa, elongation of 1% and elastic modulus of 98GPa. The bulk concentration, resistivity, and mobility values are midway between general heavy doping ceramics and metals, and they are about 100 times weaker than ordinary metals, so they are close to Si and have good electrical conductivity. In addition, folding tests were conducted at extreme temperatures, withstanding 150,000 times at -20℃, 300,000 times at 24℃, and 150,000 times at 60℃, with no folding defects observed. These results demonstrate the excellent durability and reliability of the Zr-14Cu-7.5Ni-2.6Al wide ribbon alloy and suggest the possibility of developing electronic products using this alloy.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.231-231
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• 2010

GaN는 상온에서 3.4 eV의 넓은 밴드갭을 갖는 직접천이형 반도체로 우수한 전기적/광학적 특성 및 화학적 안정성으로 발광 다이오드 및 레이저 다이오드 등과 같은 광전소자 응용을 위한 소재로 많은 연구가 진행되어왔다. 특히, GaN 나노구조의 경우 낮은 결함밀도, 빠른 구동 및 고집적 특성 등을 가지기 때문에 효과적으로 소자의 광학적/전기적 특성을 향상시킬 수 있어 나노구조 성장을 위한 연구가 활발히 진행되고 있다. 최근에는 Metal organic vapor deposition (MOCVD), hot filament chemical vapor deposition (CVD), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE) 등 다양한 방법을 통해 성장된 GaN 나노구조가 보고되고 있다. 하지만 고가 장비 사용 및 높은 공정 온도, 복잡한 공정과정이 요구되며 크기조절, 조성비, 도핑 등과 같은 해결되어야 할 문제가 여전히 남아있다. 본 연구에서는 나노구조를 형성하기 위하여 보다 간단한 방법인 전기화학증착법을 이용하여 GaN 나노구조를 ITO 및 FTO가 증착된 전도성 glass 기판 위에 성장하였고 성장 메커니즘 및 그 특성을 분석하였다. GaN 나노구조는 gallium nitrate와 ammonium nitrate가 혼합된 전해질 용액에 Pt mesh 구조 및 전도성 glass 기판을 1cm의 거리를 유지하도록 담가두고 일정한 전압을 인가하여 성장시켰다. Pt mesh 구조 및 전도성 glass 기판은 각각 상대전극 (counter electrode) 및 작업전극 (working electrode)으로 사용되었고 전해질 용액의 농도, 인가전압, 성장시간 등의 다양한 조건을 통하여 GaN 나노구조를 성장하고 분석하였다. 성장된 GaN 나노구조 및 형태는 field emission scanning electron microscopy (FE-SEM)를 이용하여 분석하였고, energy dispersive X-ray (EDX) 분석을 통하여 정량 및 정성적 분석을 수행하였다. 그리고 성장된 GaN 나노구조의 결정성을 조사하기 위해 X-ray diffraction (XRD)을 측정 및 분석하였다. 또한, photoluminescence (PL) 분석으로부터 GaN 나노구조의 광학적 특성을 분석하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.131-131
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• 2018

최근 절삭공구산업은 자동차, 항공기, IT, 선박, 에너지 등 첨단산업의 증가로 인해 CGI, CFRP, 내열합금 등 난삭재의 수요가 증가하고 있다. 난삭재는 고내열, 고경도, 초경량 같은 특성을 지니며 우수한 기계적 물성을 갖지만 가공의 어려움이 있어 산업에 적용하는데 한계가 있다. 이러한 한계를 극복하기 위해 개발된 가공기술 중 하드 코팅은 공구코팅비용 대비 공구의 표면경도와 수명을 효율적으로 향상시킬 수 있다고 알려져 있다. 대표적인 하드코팅으로는 AlN계, TiN계 코팅이 있다. 이러한 코팅의 경우 높은 기계적 물성과 우수한 내마모성으로 인해 절삭공구의 성능을 향상시킬 수 있기 때문에, 많은 연구가 진행되고 있으며 절삭공구산업에서 각광받고 있다. 기존 선행연구 결과에 따르면 질화물 코팅의 우수한 물성은 질화물(Nitride) 생성 및 질화 공정에 의한 코팅층의 고밀도화에 의해 나타난다고 알려져 있다. 그 중에서 AlCrN coating은 우수한 내마모성 및 향상된 고온경도를 갖고 있다. AlCrN based coating에 미량의 원소를 첨가하여 기존 AlCrN coating의 기계적 특성을 더욱 향상 시킨 coating은 일반적인 고성능 코팅 대비 공구수명이 길다고 알려져 있으며, 전반적으로 우수한 특성에 의해 전 세계적으로 습식 및 건식 기계 가공 용도로 사용되고 있다. 본 연구에서는 AlCrN based coating에 미량의 원소를 첨가한 coating의 우수한 기계적 특성의 원인을 규명하기 위해 텅스텐카바이드(WC) 기판 위에 아크 이온 플레이팅 장비를 이용하여 AlCrN based coating을 증착 시킨 sample을 분석하였다. 결정구조 및 상 분석을 위해 X선 회절분석(XRD)을 실시하였으며, 미세 구조를 분석하기 위해 전계방출형 주사전자현미경(FE-SEM), 투과 전자현미경(TEM) 분석을 실시하였다. 또한 코팅층의 화학적 성분 분석을 위해 EDX분석을 실시하였으며 기계적 특성 평가를 위해 나노압입시험(Nano-indentation test)을 진행하였다.

• Journal of Korea Foundry Society
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• v.30 no.3
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• pp.100-110
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• 2010

The solidification sequence and formation of intermetallic phase of Fe-rich Al-Si-Cu alloy were investigated by using real-time imaging of synchrotron X-ray radiation. Effects of cooling rate during uni-directional solidification on the resultant solidification behavior was also studied in a specially constructed vacuum chamber in the SPring-8 facility. The series of radiographic images were complementarily analyzed with conventional analysis of OM and SEM/EDX for phase identification. Detailed solidification sequence and formation mechanisms of various phases were discussed based on real-time image analysis. The growth rates of $\alpha$-AlFeMnSi and ${\beta}-Al_5FeSi$ were measured in order to understand the growth behavior of each phase. It is suggested that real-time imaging technique can be a powerful tool for the precise understanding of solidification behavior of various industrial materials.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.10
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• pp.1966-1971
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• 2011

Generally, the characteristics of the conductor that was affected by forest fire can be analyzed only when the forest fire is accurately modeled and its effect is identified. Few studies have been conducted with a forest fire model for transmission lines, and no results of the examination of the actual test specimens that were exposed to forest fire have been reported. As the deterioration characteristics of a forest fire are difficult to analyze in the actual field, an environment that was similar to that in the field was used in this study. Deterioration was deposited on a wire using an artificial flame experiment device, to analysis the temperature, surface and component characteristics. It seems that this analysis data in this study can be used as the basic data for the database that can be utilized to analyze wires exposed to forest fire and deterioration and to predict the ACSR wire refurnishment life.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.848-851
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• 2009

석탄슬래그는 회분의 조성에 따라 고온에서 매우 상이한 슬래그 거동을 보여준다. 국내 가스화 대상탄으로 검토된 탄 중, 산성 산화물의 함량이 높아 고용융점을 갖는 7종의 석탄 회분을 가스화 조건인 고온, 환원분위기에서 점도 측정을 실시하였다. 4종의 탄에 대해서는 높은 점도를 낮추기 위하여 염기성 산화물인 CaO를 3가지 비율로 혼합하여 점도 측정을 실시하였다. 또한, flux의 혼합으로 인해 발생할 수 있는 결정체 형성을 FactSage 평형계산 프로그램과 CaO-SiO2-Al2O3 3성분계 상평형도를 이용하여 예측하였다. CaO가 첨가된 시료 모두에서 낮은 CaO 첨가비에서는 원래의 시료보다 낮은 점도를 보였으나, CaO첨가비가 20% 이상일 때는 anorthite이 형성되어 $T_{cv}$를 갖는 결정슬래그로 점도 거동이 변화하면서 실제조업 가능한 온도를 증가시켰다. 점도 측정 후 냉각된 시료의 SEM/EDX 분석을 통해 형성된 결정체를 관찰한 결과, FactSage와 상평형도에서 예측된 결정체와 유사하게 나타나 CaO-SiO2-Al2O3 3성분계 상평형도가 결정체 예측에 유용함을 확인하였다.