• 한국주조공학회지
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• 제30권3호
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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.

• 한국분무공학회지
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• 제20권1호
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• pp.35-42
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• 2015

This study is to investigate the spray behavior of DME-LPG blended fuels in common rail injection system for diesel engines. The visualization experiment was performed to analyze the macroscopic spray behavior of test fuels. In addition, the experiment using BOS(Background Oriented Schlieren) method is performed to compare liquid phase and gas phase. The test fuels are injected in high pressure chamber. The ambient pressure of high pressure chamber was formed by nitrogen gas. Spray tip penetration, spray cone angle and spray area were measured using high speed camera. SMD(Sauter Mean Diameter) and spray particle velocity were measured using the PDPA(Phase Doppler Particle Analyzer) system to analyze the microscopic properties of test fuels. The results of this experiment showed that spray tip penetration, spray cone angle and spray area of DME-LPG fuels are similar to those of DME fuel. When compared to results of experiment using BOS, significant differences of spray tip penetrations, spray cone angle and spray area are showed because of gas phase. The results of experiment using BOS method showed higher values. SMD of DME-LPG blended fuels is smaller than that of DME fuel. Velocity of DME-LPG blended fuels is faster than that of DME fuel.

• 열처리공학회지
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• 제26권6호
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• pp.306-316
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• 2013

Microstructure and fracture behavior of a multi-phase low-density steel were investigated. After hot-rolling and heat treatment, the microstructure of low-density steel was composed of coarse ferrite grains and elongated bands which include second phases such as austenite, martensite and ${\kappa}$-carbide depending on holding time during isothermal heat treatment. After tensile test, microcracks were observed at martensite or ${\kappa}$-carbide interface in the elongated bands. Coarse ferrite grains showed cleavage fracture behavior regardless of second phase. The cleavage fracture of ferrite could be attributed to their coarse grain size and solute atoms that increase ductile-to-brittle transition temperature of ferrite. Despite of the tendency of cleavage fracture in coarse ferrite grains, a specimen having coarse spheroidized ${\kappa}$-carbide particles in the elongated bands showed high total elongation of 30%. Thus, the easiness of plastic deformation in the elongated band seems to play an important role in retardation of cleavage crack formation in coarse ferrite grains.

• 공업화학
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• 제8권2호
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• pp.246-251
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• 1997

당류를 친수기로 한 슈크로오스 모노팔미테이트에 대한 3성분계 즉, 슈크로오스모노팔미테이트/알칸올/물계에서의 상거동을 각 조성에 따라 조사하였다. 미셀영역에서 여러 액정영역에 이르기까지 각 성분의 조성을 변화시키면서 정온 및 변온하에 여러 상의 구조를 온도조절기와 카메라가 부착된 편광현미경으로 비교 관찰하였다. 극성물질인 알칸올의 탄소수 증가에 따른 3성분계에서의 상거동을 관찰한 결과, 헥산올<옥탄올<데칸올 순으로 비교적 넓은 영역에서 비등방성의 여러 액정상이 존재하였으며, 이를 토대로 에멀젼이나 가용화계의 포뮬레이션에 적용할 수 있다.

• Nuclear Engineering and Technology
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• 제47권7호
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• pp.827-837
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• 2015

Following a severe accident in a nuclear power plant, iodine is a major contributor to the potential health risks for the public. Because the amount of iodine released largely depends on its volatility, iodine's behavior in containment has been extensively studied in international programs such as International Source Term Programme-Experimental Program on Iodine Chemistry under Radiation (EPICUR), Organization for Economic Co-operation and Development (OECD)-Behaviour of Iodine Project, and OECD-Source Term Evaluation and Mitigation. Korea Institute of Nuclear Safety (KINS) has joined these programs and is developing a simplified, stand-alone iodine chemistry model, RAIM (Radio-Active Iodine chemistry Model), based on the IMOD methodology and other previous studies. This model deals with chemical reactions associated with the formation and destruction of iodine species and surface reactions in the containment atmosphere and the sump in a simple manner. RAIM was applied to a simulation of four EPICUR tests and one Radioiodine Test Facility test, which were carried out in aqueous or gaseous phases. After analysis, the results show a trend of underestimation of organic and molecular iodine for the gas-phase experiments, the opposite of that for the aqueous-phase ones, whereas the total amount of volatile iodine species agrees well between the experiment and the analysis result.

• 한국방재학회 논문집
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• 제8권5호
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• pp.71-76
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• 2008

본 연구는 재난에 특히 취약한 노인에게 재난 경고시의 행동 요령과 정보전달에 도움을 줄 수 있는 방안을 모색하기 위하여, 재난 시 경고시간(warning phase) 동안의 노인들의 대처행동을 분석하고 대처 행동에 영향을 미치는 요인을 살펴보고자 하였다. 연구대상자는 2006년 집중호우로 인해 직접적인 피해가 있었던 강원도 인제군과 평창군에 거주하는 60세 이상 노인 130명이었다. 조사결과를 살펴보면, 대부분의 노인들이 자연 징후를 보고 수해를 알게 되었다고 응답하였으며 대처행동을 6단계로 나타내는 Perry & Lindell(1997)'s index를 통해 재난시의 노인들의 대처행동이 높은 수준임을 알 수 있었다. 또한 노인의 일상생활 수행 능력(ADL)과 거주기간이 대처 행동에 영향을 주는 요인인 것으로 나타났는데, 수해 노인들은 ADL이 높을수록 높은 수준의 대처행동을 보였으며, 거주 기간이 길수록 낮은 수준의 대처행동을 보였다. 이러한 결과를 통하여 약 70%의 노인들이 재난시의 대처 행동에 충실하게 따랐으며, 노인들이 재난 시 비협력적이거나 비순응적인 집단이 아니라는 것을 보여주었다. 이는 노인에 대한 신속하고 정확한 경고의 발령과 전달의 중요성을 강조해주는 결과이며, 자연재해에 대한 사전 정보와 지식 전달, 그리고 대피에 대한 인식과 비상시의 대피계획 등에 관한 학습과 훈련의 필요성을 나타내 주었다.

• 한국세라믹학회지
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• 제25권5호
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• pp.502-508
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• 1988

The $\alpha$ to $\beta$ phase transformation of $\alpha$-Si3N4 whisker and related microstructural changes have been investigated. When only $\alpha$-Si3N4 whisker was heat treated in the range 1650~175$0^{\circ}C$, the $\alpha$ to $\beta$ phase transformation occured. In this case, it eas suggested that the oxygen content in $\alpha$-Si3N4 whisker affected the transformation behavior. Although $\alpha$-Si3N4 whisker with Si was heat treated under the same condition, however, the variation of $\beta$- fraction had a similar tendency with heat treating time. Therfore, it was considered that the oxygen content in $\alpha$-Si3N4 whisker affected the transformation behavior dominently rather than the content of added Si. The added $\beta$ phase did not affect the transformation behaviro of $\alpha$-Si3N4 whisker.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(2)
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• pp.537-542
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• 1996

In the present work the influence of various physical parameters on the two-phase flow behavior in a self-heated porous medium has been studied using a numerical model, that is, the effects of heat generation rate, of porosity, of particle size, and of system pressure on the dryout process. To analyze the effect of these parameters, the variation of both liquid volumetric fraction and liquid axial velocity is evaluated at the steady state or at the onset of a first boiled-out region. The analysis of computational results indicate that a qualitative tendency exists between the parameters such as heat generation rate, porosity, effective particle diameter and the temporal development of the liquid volumetric fraction field up to dryout. In addition to these parameters, a variation of fluid properties such as phase density, phase viscosity due to a change of system pressure can be used for gaining insight into the nature of two-phase flow behavior up to dryout.

• Korea-Australia Rheology Journal
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• 제16권3호
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• pp.153-160
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• 2004

Open microcellular foams having small-sized cell and good mechanical properties are desirable for many practical applications. As an effort to reduce the cell size, the microcellular foams combining viscosity improvers into the conventional formulation of styrene and water system were prepared via high internal phase emulsion polymerization. Since the material properties of foam are closely related to the solution properties of emulsion state before polymerization, the flow behavior of emulsions was investigated using a controlled stress rheometer. The yield stress and the storage modulus increased as viscosity improver concentration and agitation speed increased, due to the reduced cell size reflecting both a competition between the continuous phase viscosity and the viscosity ratio and an increase of shear force. Appreciable tendency was found between the rheological data of emulsions and the cell sizes of polymerized foams. Cell size reduction with the concentration of viscosity improver could be explained by the relation between capillary number and viscosity ratio. A correlative study for the cell size reduction with agitation speed was also attempted and the result was in a good accordance with the hydrodynamic theory.

• 한국결정학회지
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• 제12권2호
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• pp.81-87
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• 2001

We have studied the effect of sintering temperature and time on the cation ordering and second phase formation in Ba(Mg/sub 1/3/Nb/sub 2/3/)O₃(BMN) microwave ceramics by using transmission electron microscopy. The relationship between the structural-chemical behavior arid microwave dielectric properties has also been investigated. It is revealed that according to the sintering conditions the BMN ceramics show very diverse local ordering behavior, such as the development of domain twinning and "core-shell"-structured grains and the formation of local disordered domains, though having 1 : 2 cation ordering structure basically. The disordered structure is found in Mg-excess region. Such local chemical variation seems to be caused by the formation of BaNb₂O/sub 6/-like second phase in its neigh-boring grain boundary. The microwave dielectric quality factor of the ceramics decreases greatly with the increase of the structural-chemical inhomogeneity and diversity.