• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.305-311
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• 1998

최근들어 고려된 LBB(Leak Before Break) 적용요건중 동적파괴시힘 절차에는 울진 3&4호기 이후 파단전누설개념이 적용되는 배관이 탄소강으로 제작될 경우. 이 배관이 Dynamic Strain Aging (DSA)에 의해 파괴저항치가 감소되지 않는다는 것이 정량적으로 입증되지 않는 한, 동 배관의 파괴 물성치 결정시 DSA의 영향이 고려되어야 하며, DSA 영향을 평가하기 위해서는 동적과괴시험이 수행되어야 함을 요건화 하고 있다. 본 연구에서는 DSA 효과에 의한 파괴저항(J-R) 특성의 저하가차세대원전 원자로냉각재배관 파단전누설개넘(LBB) 적용시 설계 안전여유도에 영향을 미치지 않는 정도임을 평가하는데 있다. 따라서 ASME Section III에서 탄소강으로 분류하고 있는 강종별 파괴인성 변화를 고찰하고, 차세대원전 주냉각재배관 재료인 SA508 Class la의 최대 파괴인성 감소치를 예측하여, 울진 3&4호기에서 측정된 엘보우용 SA516-Gr.70 강의 DSA 영향 평가 결과와 비교 분석하여 차세대원전 주냉각재배관의 DSA영향을 평가하였다. 도출된 결론으로는 DSA 영향을 고려한 SA508 Class la의 J 및 dJ/dA 값은 극히 보수적으로 추정할 때 50% 이상 감소하는 것으로 예측된다. 이러한 DSA 영향을 고려하였을 경우 배관재 모재의 파괴인성치는 Weld-SAW의 J/T 값 수준으로 감소하였다. 그러나 현 LRB 해석이 가장 낮은 J/T값을 갖는 Weld-SAW Auto의 균열길이 2a인 J/T선도에 의거하여 수행되고 있다는 점을 고려한다면 비록 DSA가 배관재에 영향을 주는 가장 보수적인 값(J 및 dJ/dA값을 50% 이상)을 사용한다고 하더라도 차세대원전 LBB 적용에 문제가 되지 않음을 알 수 있다. 즉 차세대원자로 주냉각재배관에 LBB를 적용하는데는 DSA 영향은 상대적으로 중요하지 않다는 결론을 얻었다. 표면에 수소화물이 농축되어 있는 hydride layer가 형성됨을 관찰하였으며 ～5,000ppm 이상의 경우에는 수소화물의 방향성이 random하였으며 특히, ZIRLO$^{TM}$ 시편의 경우에서는 원주방향으로 길게 이어진 수소화물과 기계적 성질에 치명적인 반경방향의 수소화물이 평행하게 배열된 것을 관찰하였다.하였을 때는 Li$_2$O의 첨가에 의해 치밀화가 주로 일어났고, 반면에 $N_2$-7vol.%H$_2$ 분위기에서 소결하면 Li$_2$O의 첨가에 의해 작은 기공은 소멸되고 큰 기공이 생성되었다.지나치게 모국어의 영향만 강조하고 다른 요인들에 대해서는 다분히 추상적인 언급으로 끝났지만 이 분석을 통 해서 배경어, 목표어, 특히 중간규칙의 역할이 괄목할 만한 것임을 가시적으로 관찰할 수 있 다. 이와 같은 오류분석 방법은 학습자의 모국어 및 관련 외국어의 음운규칙만 알면 어느 학습대상 외국어에라도 적용할 수 있는 보편성을 지니는 것으로 사료된다.없다. 그렇다면 겹의문사를 [-wh]의리를 지 닌 의문사의 병렬로 분석할 수 없다. 예를 들어 누구누구를 [주구-이-ν가] [누구누구-이- ν가]로부터 생성되었다고 볼 수 없다. 그러므로 [-wh] 겹의문사는 복수 의미를 지닐 수 없 다. 그러면 단수 의미는 어떻게 생성되는가\ulcorner 본 논문에서는 표면적 형태에도 불구하고 [-wh]의미의 겹의문사는 병렬적 관계의 합성어가 아니라 내부구조를 지니지 않은 단순한 단어(minimal $X^{0}$ elements)로 가정한다. 즉, [+wh] 의미의 겹의문사는 동일한 구성요 소를 지닌 병렬적 합성어([$[W1]_{XO-}$ $[W1]_{XO}$ ]$_{XO}$)로

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.2
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• pp.62-67
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• 2015

The carbon microspheres of a core-shell type were grown by the method of mixed-source hydride vapor phase epitaxy (HVPE). The surface and the cross section of the carbon microsphere grown by a new method were observed by scanning electron microscope (SEM). The characteristics of the carbon microsphere were investigated by X-ray photoelectron spectroscopy (XPS) and a high resolution-transmission electron microscope (HR-TEM). From these measurements, the diameters of carbon sphere were about few hundred micrometers. Furthermore, we show that the carbon microsphere of the core-shell type by mixed-source HVPE method can be grown successfully with the larger size than those of the existing one. This mixed-source HVPE method is proposed a new method for making of carbon microsphere.

• Korean Journal of Materials Research
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• v.8 no.3
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• pp.268-273
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• 1998

Standard Zircaloy-4 sheets, charged with 230-250ppm hydrogen by the gas-charging method and homogenized at $400^{\circ}C$ for 72hrs in a vacuum, were corroded in pure water and aqueous LiOH solutions using static autoclaves at $350^{\circ}C$. Their corrosion behaviors were characterized by measuring their weight gains with the corrosion time and observing their microstructures using an optical microscope and a scanning electron microscope. The elemental depth profiles for hydrogen and lithium were measured using a secondary ion mass spectrometry(S1MS) to confirm their distributions at the oxidelmetal interface. The normal Zircaloy-4 specimens corroded abruptly and heavily at the concentration of Li ions more than 30ppm in the aqueous solution. This is due to accelerations by the rapid oxidation of many Zr- hydrides formed by the large amount of absorbed hydrogen, resulting from the increased substitution of $Li^{+}$ ions with $Zr^{4+}$-sites in the oxide as the Li ion concentration increased. The specimens that had been charged with amounts of hydrogen greater than its solubility corroded early with a more rapid acceleration than normal specimens, regardless of the corrosion solutions. At longer corrosion times. however, normal specimens showed a rather accelerated corrosion rate compared to the hydrogen-charged specimens. These slower corrosion rates of the hydrogen-charged specimens at the longer corrosion times would be due to the pre-existent Zr-hydride in the matrix, which causes the hydrogen pick- up into the specimen to be depressed, when the oxide with an appropriate thickness formed.

• Korean Journal of Materials Research
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• v.10 no.7
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• pp.464-470
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• 2000

The compacting and sintering behavior of titanium powders containing oxygen in the range of 1980~8450 ppm was examined. The powders were prepared by the hydride-dehydride (HDH) and by the deoxidation by solid state(DOSS) methods. Their compaction density ranged from 69.0% to 62.3% and decreased with the increase in the oxygen content. It was explained by the effect of oxygen on the hardness of powders. Unlike the compaction density, the oxygen content did not affect the apparent density greatly being 90.5$\pm$0.5% after sintering at $1100^{\circ}C$ for 2 hours. Their average grain size was $60\mu\textrm{m}$ and the size and distribution of pores were about the same for all cases. The hardness of sintered samples showed a linear increase with oxygen and could be expressed as VHN(sintered)= 135.5+64.3$\times$$(wt{\%}O_2)$ The exami-nation of fracture surface revealed that the ductile-brittle transition occurs at oxygen contents of 2987~5582 ppm.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.72-72
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• 2012

Lithium rechargeable batteries have been widely used as key power sources for portable devices for the last couple of decades. Their high energy density and power have allowed the proliferation of ever more complex portable devices such as cellular phones, laptops and PDA's. For larger scale applications, such as batteries in plug-in hybrid electric vehicles (PHEV) or power tools, higher standards of the battery, especially in term of the rate (power) capability and energy density, are required. In PHEV, the materials in the rechargeable battery must be able to charge and discharge (power capability) with sufficient speed to take advantage of regenerative braking and give the desirable power to accelerate the car. The driving mileage of the electric car is simply a function of the energy density of the batteries. Since the successful launch of recent Ni-MH (Nickel Metal Hydride)-based HEVs (Hybrid Electric Vehicles) in the market, there has been intense demand for the high power-capable Li battery with higher energy density and reduced cost to make HEV vehicles more efficient and reduce emissions. However, current Li rechargeable battery technology has to improve significantly to meet the requirements for HEV applications not to mention PHEV. In an effort to design and develop an advanced electrode material with high power and energy for Li rechargeable batteries, we approached to this in two different length scales - Atomic and Nano engineering of materials. In the atomic design of electrode materials, we have combined theoretical investigation using ab initio calculations with experimental realization. Based on fundamental understanding on Li diffusion, polaronic conduction, operating potential, electronic structure and atomic bonding nature of electrode materials by theoretical calculations, we could identify and define the problems of existing electrode materials, suggest possible strategy and experimentally improve the electrochemical property. This approach often leads to a design of completely new compounds with new crystal structures. In this seminar, I will talk about two examples of electrode material study under this approach; $LiNi_{0.5}Mn_{0.5}O_2$ based layered materials and olivine based multi-component systems. In the other scale of approach; nano engineering; the morphology of electrode materials are controlled in nano scales to explore new electrochemical properties arising from the limited length scales and nano scale electrode architecture. Power, energy and cycle stability are demonstrated to be sensitively affected by electrode architecture in nano scales. This part of story will be only given summarized in the talk.

• Korean Journal of Food Science and Technology
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• v.31 no.2
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• pp.273-279
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• 1999

Forty plants used as tea materials were chosen for determining the contents of total phenolics, selenium (Se), ${\beta}-carotene$, ${\alpha}-tocopherol$ and ascorbate. Total phenolics and ascorbate contents were analyzed colorimetrically. The Se contents were measured by hydride-atomic absorption spectrometry. The contents of ${\beta}-carotene$ and ${\alpha}-tocopherol$ were simultaneously determined by high performance liquid chromatography using separate detectors, UV for ${\beta}-carotene$ and FL for ${\alpha}-tocopherol$ analyses. The contents of these antioxidants were as follows (per 100 g dry plant); Contents of total phenolics in green tea leaf, black tea leaf, oolong tea leaf and instant coffee were about 7 g and the Se contents in corni fructus and arrowroot were found to be about $4{\mu}g$, which were the highest among all plants used. Contents of ${\beta}-carotene$ in eucommiae cortex, persimmon leaf and green tea leaf were 8587, 6222 and $3652\;{\mu}g$ respectively. The persimon leaf contained the highest ${\alpha}-tocopherol$ content (33 mg) and then followed by eucommiae cortex (26 mg), green tea leaf (16 mg) and black tea leaf (13 mg) in order. Ascorbate contents were found to be high in green tea leaf (199 mg) and black tea leaf (117 mg).

• Transactions of the Korean hydrogen and new energy society
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• v.13 no.3
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• pp.181-189
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• 2002

A series of multicomponent $Zr_{0.8}Ti_{0.2}Mn_{0.4}V_{0.6}Ni_{1-x}Fe_{x}$ (x=0.00, 0.08, 0.15, 0.22, and 0.30) alloys are prepared and their oystal structure and P-C-T curves are examined. The electrochemical properties of these allqys such as activation conditions, discharge capacity, cycling performance are also investigated. $Zr_{0.8}Ti_{0.2}Mn_{0.4}V_{0.6}Ni_{1-x}Fe_{x}$ (x=0.00, 0.08, 0.15, 0.22 and 0.30) have the C14 Laves phase hexagonal structure. The electrode was activated by the hot-charging treatment. The best activation conditions were the current density 120 mA/g and the hot-charging time 12h at $80^{\circ}C$ in the case of the alloy with x=0.00. The discharge capacity increased rapidly until the fourth cycle and then decreased. The discharge capacity increased again from the 13th cycle, arriving at 234 mAh/g at the 50th cycle. The discharge capacily just after activation decreases with the increase in the amount of the substituted Fe but the cycling performance is improved. The discharge capacity after activation of the alloy with x=0.00 is 157 mAh/g at the current density 120 mA/g. $Zr_{0.8}Ti_{0.2}Mn_{0.4}V_{0.6}Ni_{0.85}Fe_{0.15}$ is a good composition with a medium quantity of discharge capacities and a good cycling performance. The ICP analysis of the electrolyte for these electrodes after 50 charge-discharge cycles shows that the concentrations of V and Zr are relatively high. Another series of multicomponent $Zr_{0.8}Ti_{0.2}Mn_{0.4}V_{0.6}Ni_{0.85}M_{0.15}$ (M = Fe, Co, Cu, Mo and Al) alloys are prepared. They also have the C14 Laves phase hexagonal structure. The alloys with M = Co and Fe have relatively larger hydrogen storage capacities. The discharge capacities just after activation are relatively large in the case of the alloys with M = Al and Cu. They are 212 and 170 mAh/g, respectivety, at the current density 120mA/g. The $Zr_{0.8}Ti_{0.2}Mn_{0.4}V_{0.6}Ni_{0.85}Co_{0.15}$ alloy is the best one with a relatively large discharge capacity and a good cycling performance.

• Polymer(Korea)
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• v.24 no.5
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• pp.646-655
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• 2000

Polymerizations of higher $\alpha$-olefins were carried out in toluene by using highly isospecific catalyst, rac-(EBI)M(NMe$_2$)$_2$ (EBI=1,2-ethylenebis-(1-indenyl); M=Zr(rac-1); M=Hf(rac-2)) In the presence of Al(i-Bu)$_3$/[Ph$_3$C][B($C_{6}F_{5}$)$_4$]. The polymerization of high $\alpha$-olefin showed high activity and similar polymerization behavior. The polymerization activity was affected by both monomer size and lateral size of polymer chain. The conversion of monomer to polymer decreases with the increased lateral size in the order of 1-pentene>1-hexene>1-octene>1-decene. The same dependences of melting behavior and intrinsic viscosity of polyolefin on lateral size were observed according to the results obtained by differential scanning calorimetry and intrinsic viscosity. All poly($\alpha$-olefin)s showed very high isotacticity (triad) and the isotacticity increases in the order of poly(1-pentene)$^1H$ NMR and Raman spectra analysis showed that chain transfer to cocatalyst, which generates saturated methyl groups, Is a main chain termination. The $\beta$-hydride eliminations, which generate unsaturated vinylidene, tri-substituted, and vinylene end group. are found to be minor chain terminations.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.3
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• pp.89-94
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• 2016

In this study, the crystalline property of a-plane GaN epitaxial layer grown on r-plane sapphire by a HVPE method has been investigated according to the V/III ratio and the growth time of multi-step growth. Furthermore, these results were compared with the previous result obtained from the single-step growth of a-plane GaN on r-plane sapphire substrate. In the multi-step growth for a-plane GaN epitaxial layer on r-plane sapphire, the FWHM values of rocking curve in GaN epitaxial layer were decreased as the HCl source flow rate and the growth time were increased. The void formed in epitaxial layer was continuously decreased as the growth time in first step and second step using a higher HCl flow rate was increased. As a result, the GaN layer obtained with the longest growth time on the first step and second step exhibited the lowest FWHM values of 584 arcsec and the smallest dependence of azimuth angle.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.4
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• pp.127-134
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• 2015

Aluminum nitride (AlN) single crystals have attracted much attention for a next-generation semiconductor application because of wide bandgap (6.2 eV), high thermal conductivity ($285W/m{\cdot}K$), high electrical resistivity (${\geq}10^{14}{\Omega}{\cdot}cm$), and high mechanical strength. The bulk AlN single crystals or thin film templates have been mainly grown by PVT (sublimation) method, flux method, solution growth method, and hydride vapor phase epitaxy (HVPE) method. Since AlN suffers difficulty in commercialization due to the defects that occur during single crystal growth, crystalline quality improvement via defects analyses is necessary. Etch pit density (EPD) analysis showed that the growth misorientations and the defects in the AlN surface exist. Transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD) analyses were employed to investigate the overall crystalline quality and various kinds of defects. TEM studies show that the morphology of the AlN is clearly influenced by stacking fault, dislocation, second phase, etc. In addition EBSD analysis also showed that the zinc blende polymorph of AlN exists as a growth defects resulting in dislocation initiator.