• 한국결정성장학회지
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• 제20권3호
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• pp.113-116
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• 2010

본 논문에서는 Sb를 촉매제로 이용하는 경우의 InGaN 나노구조의 성장과 구조적 특징 및 광학적 특성에 대해서 연구하였다. 결정성장에 있어서 촉매제의 사용은 성장 모드의 변화와 결정 결함의 감소 등을 위한 목적으로 많이 사용되어왔다. 본 연구에서는 혼합소스 HVPE(hydride vapor phase epitaxy) 사용하여 (0001) 사파이어 기판 위에 InGaN 나노구조를 성장하였고, 구조적 및 광학적 특성은 scanning electron microscope(SEM)과 photoluminescence(PL)를 통해 평가하였다. Sb이 첨가되지 않은 경우에는 InGaN 나노구조가 c-축 방향으로 정렬되는 경향을 보이지만 Sb이 첨가된 경우에는 InGaN 나노구조의 c-축 방향이 기판에 대해 평행하거나 경사진 방향으로 정렬되고 있는 것을 관찰할 수 있었다. In의 조성은 Sb 의 첨가 여부에 관계없이 약 3.2% 정도로 계산되었다. 이러한 결과들로부터 측면 배향된 나노입자를 활성층으로 하는 광소자에 적용할 경우 압전 전계를 완화할 수 있기 때문에 광소자의 발광 성능을 향상시킬 수 있을 것으로 기대된다.

• 한국분말재료학회지
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• 제13권5호
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• pp.327-335
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• 2006

In the development of new hydrogen absorbing materials for a next generation of metal hydride electrodes for rechargeable batteries, metastable Mg-Ni-based compounds find currently special attention. Amor phous-nanocrystalline $Mg_{63}Ni_{30}Y_7$ and $Mg_{50}Ni_{30}Y_{20}$ alloys were produced by mechanical alloying and melt-spinning and characterized by means of XRD, TEM and DSC. On basis of mechanically alloyed Mg-Ni-Y powders, complex hydride electrodes were fabricated and their electrochemical behaviour in 6M KOH (pH=14,8) was investigated. The electrodes made from $Mg_{63}Ni_{30}Y_7$ powders, which were prepared under use of a SPEX shaker mill, with a major fraction of nanocrystalline phase reveal a higher electrochemical activity far hydrogen reduction and a higher maximum discharge capacity (247 mAh/g) than the electrodes from alloy powder with predominantly amorphous microstructure (216 mAh/g) obtained when using a Retsch planetary ball mill at low temperatures. Those discharge capacities are higher that those fur nanocrystalline $Mg_2Ni$ electrodes. However, the cyclic stability of those alloy powder electrodes was low. Therefore, fundamental stability studies were performed on $Mg_{63}Ni_{30}Y_7$ and $Mg_{50}Ni_{30}Y_{20}$ ribbon samples in the as-quenched state and after cathodic hydrogen charging by means of anodic and cathodic polarisation measurements. Gradual oxidation and dissolution of nickel governs the anodic behaviour before a passive state is attained. A stabilizing effect of higher fractions of yttrium in the alloy on the passivation was detected. During the cathodic hydrogen charging process the alloys exhibit a change in the surface state chemistry, i.e. an enrichment of nickel-species, causing preferential oxidation and dissolution during subsequent anodization. The effect of chemical pre-treatments in 1% HF and in $10\;mg/l\;YCl_3/1%\;H_2O_2$ solution on the surface degradation processes was investigated. A HF treatment can improve their anodic passivation behavior by inhibiting a preferential nickel oxidation-dissolution at low polarisation, whereas a $YCl_3/H_2O_2$ treatment has the opposite effect. Both pre-treatment methods lead to an enhancement of cathodically induced surface degradation processes.

• 한국항공우주학회지
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• 제41권3호
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• pp.233-239
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• 2013

화학수소화합물 수소저장방법을 이용한 100 W 급 연료전지 시스템을 소형 무인항공기의 추진시스템으로 적용하는 연구를 수행하였다. 소형/경량 수소 발생 제어장치와 연료전지/배터리 하이브리드 전력 공급 방법으로 효율성 및 안정성을 증대하였다. $NaBH_4$ 수용액을 이용한 수소 발생장치와 Dead-end 형식의 PEMFC를 이용한 연료전지 시스템의 지상, 비행 시험이 수행되었다. 연료전지 스택을 안정적으로 운전하고, 높은 효율을 얻기 위해 45 kPa의 압력을 가하는 방법을 적용하였다. 수소 발생 시스템 내부 압력을 이용한 수소 발생 제어 장치는 45~55 kPa 사이에서 유지되며 안정적으로 수소가 공급되는 것을 확인하였다. 그 결과, 100 W 연료전지 시스템이 소형 무인항공기 적용하기에 무게 및 소비 전력을 만족함을 확인하였고, 시험비행을 통해 성능을 입증하였다.

• Nuclear Engineering and Technology
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• 제47권6호
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• pp.678-699
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• 2015

Although the harsh space environment imposes many severe challenges to space pioneers, space exploration is a realistic and profitable goal for long-term humanity survival. One of the viable and promising options to overcome the harsh environment of space is nuclear propulsion. Particularly, the Nuclear Thermal Rocket (NTR) is a leading candidate for nearterm human missions to Mars and beyond due to its relatively high thrust and efficiency. Traditional NTR designs use typically high power reactors with fast or epithermal neutron spectrums to simplify core design and to maximize thrust. In parallel there are a series of new NTR designs with lower thrust and higher efficiency, designed to enhance mission versatility and safety through the use of redundant engines (when used in a clustered engine arrangement) for future commercialization. This paper proposes a new NTR design of the second design philosophy, Korea Advanced NUclear Thermal Engine Rocket (KANUTER), for future space applications. The KANUTER consists of an Extremely High Temperature Gas cooled Reactor (EHTGR) utilizing hydrogen propellant, a propulsion system, and an optional electricity generation system to provide propulsion as well as electricity generation. The innovatively small engine has the characteristics of high efficiency, being compact and lightweight, and bimodal capability. The notable characteristics result from the moderated EHTGR design, uniquely utilizing the integrated fuel element with an ultra heat-resistant carbide fuel, an efficient metal hydride moderator, protectively cooling channels and an individual pressure tube in an all-in-one package. The EHTGR can be bimodally operated in a propulsion mode of $100MW_{th}$ and an electricity generation mode of $100MW_{th}$, equipped with a dynamic energy conversion system. To investigate the design features of the new reactor and to estimate referential engine performance, a preliminary design study in terms of neutronics and thermohydraulics was carried out. The result indicates that the innovative design has great potential for high propellant efficiency and thrust-to-weight of engine ratio, compared with the existing NTR designs. However, the build-up of fission products in fuel has a significant impact on the bimodal operation of the moderated reactor such as xenon-induced dead time. This issue can be overcome by building in excess reactivity and control margin for the reactor design.

• 분석과학
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• 제25권6호
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• pp.402-409
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• 2012

연속흐름 수소화물 생성-유도결합 플라스마 원자 방출 분광기(FI-HG-ICP-AES) 이용하여 플라스틱 소재에 함유된 비소를 정량하기 위한 조건을 얻었다. 플라스틱 시료를 습식 산 분해 방법 및 마이크로파 산 분해 방법으로 전처리하여 시험 용액을 조제하였다. 인증표준물질(CRM)인 CRM-EC680k 및 CRM-EC681k를 사용하여 측정한 값과 인증값을 비교하여 분석 방법의 재현성 및 정확성을 확인하였다. 습식 산 분해 방법 및 마이크로파 산 분해 방법으로 전처리하여 FI-HG-ICP-AES로 측정한 결과 CRM-EC680k의 경우에는 4.1~4.3 mg/kg (인증값 $4.1{\pm}0.5$ mg/kg)이고, CRM-EC681k의 경우에는 28.9~30.6 mg/kg (인증값 $29.1{\pm}1.8$ mg/kg)이었다.

• Toxicological Research
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• 제29권2호
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• pp.137-142
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• 2013

Arsenic (As) is a well-known human carcinogen and its dietary exposure has been found to be the major route of entry into general population. This study was performed to assess the body levels of As and their associated factors in Korean adults by analyzing total As in urine. Urine and blood samples were collected from 580 adults aged 20 years and older, who had not been exposed to As occupationally. Demographic information was collected with the help of a standard questionnaire, including age, smoking, alcohol intake, job profiles, and diet consumed in the last 24 hrs of the study. Total As, sum of As(III), As(V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), in urine was determined using atomic absorption spectrometer involving hydride generation method. The geometric mean concentration of total As in urine was $7.10{\mu}g/L$. Urine As was significantly higher in men ($7.63{\mu}g/L$) than in women ($6.75{\mu}g/L$). Age, smoking, alcohol consumption, and job profiles of study subjects did not significantly affect the concentration of As in urine. No significant relationship was observed between body mass index (BMI), Fe, and total cholesterol in serum and urinary As. Urine As level was positively correlated with seaweeds, fishes & shellfishes, and grain intake. A negative correlation between urinary As level and HDL-cholesterol in serum and meat intake was observed. Overall, these results suggest that urinary As concentration could be affected by seafood consumption. Therefore, people who frequently consume seafood and grain need to be monitored for chronic dietary As exposure.

• 한국수소및신에너지학회논문집
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• 제20권4호
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• pp.300-308
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• 2009

In a pursuit of the development of alternative mobile power sources with a high energy density, a planar and air-breathing PEMFCs with a new type of hydrogen cartridge which uses onsite $H_2$ generated from sodium borohydride ($NaBH_4$) hydrolysis have been investigated for use in advanced power systems. Two types of $H_2$ generation through $NaBH_4$ hydrolysis are available: (1) using organic acids such as sulphuric acid, malic acid, and sodium hydrogen carbonate in aqueous solution with solid $NaBH_4$ and (2) using solid selected catalysts such as Pt, Ru, CoB into the stabilized alkaline $NaBH_4$ solution. It might therefore be relevant at this stage to evaluate the relative competitiveness of the two methods mentioned above. The effects of flow rate of stabilized $NaBH_4$ solution, MEA (Membrane Electrode Assembly) improvement, and type and flow control of the catalytic acidic solution have been studied and the cell performances of the planar, air-breathing PEMFCs using $NaBH_4$ has been measured from aspects of power density, fuel efficiency, energy density, and fast response of cell. In our experiments, planar, air-breathing PEMFCs using $NaBH_4$ achieved to maximum power density of 128mW/$cm^2$ at 0.7V and energy efficiency of 46% and has many advantages such as low operating temperature, sustained operation at a high power density, compactness, the potential for low cost and volume, long stack life, fast star-up and suitability for discontinuous operation.

• 한국환경보건학회지
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• 제47권5호
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• pp.496-503
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• 2021

Background: Considering the expenses of and difficulties in arsenic speciation by high performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS), alternative measurement methods should be useful, especially for large-scale research and projects. Objectives: A measurement method was developed for arsenic speciation using HPLC-atomic fluorescence spectrometry (HPLC-AFS) as an alternative to HPLC-ICP-MS. Methods: Total arsenic and toxic arsenic species in some seafoods were determined by atomic absorption spectrometry coupled with hydride vapor generation (AAS-HVG) and HPLC-AFS, respectively. Recovery rate of arsenic species in seafood was evaluated by ultra sonication, microwave and enzyme (pepsin) for the optimal extraction method. Results: Limits of detection of HPLC-AFS for As³⁺, dimethylarsinate (DMA), monomethylarsonate (MMA) and As⁵⁺ were 0.39, 0.53, 0.60 and 0.64 ㎍/L, respectively. The average accuracy ranged from 97.5 to 108.7%, and the coefficient of variation was in the range of 1.2~16.7%. As³⁺, DMA, MMA and As⁵⁺ were detected in kelp, the sum of toxic arsenic in kelp was 40.4 mg/kg. As³⁺, DMA, MMA and As⁵⁺ were not detected in shrimp and squid, but total arsenic (iAS and oAS) content in shrimp and squid analyzed by AAS-HVG were 18.1 and 24.7 mg/kg, respectively. Conclusions: HPLC-AFS was recommendable for the quantitative analysis method of arsenic species. As toxic arsenic species are detected in seaweeds, further researches are needed for the contribution degree of seafood in arsenic exposure.

• Nuclear Engineering and Technology
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• 제24권2호
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• pp.141-153
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• 1992

상온핵융합의 실험적 검증을 위하여 가공조건 및 기하학적조건이 다른 7종류의 팔라디움전극을 사용하여 24~28시간, 전류밀도 83~600 mA/$\textrm{cm}^2$의 조건하에 전기분해를 실시하였다. 상기조건 하에서 삼중수소의 농축에 기인한 분리팩타(separation factor)를 측정하였고 핵융합의 부산물일수도 있는 삼중수소 증가량을 측정하였다. 또한 초과열 계 산과 관련된 K(net Faradic efficiency)를 측정하여 산소/중수소 가스의 재결합정도를 조사하였다. 양전자소멸측정장치 및 일정체적 가스주입장치를 이용하여 팔라디움전극에서 격자결함과 수소의 반응 및 거동에 대하여 조사하였다. 전기분해하는 동안 삼중수소 농축현상이 관찰되었으나 핵융합의 증거가 될만한 삼중수소양은 검출되지 않았다. 한편 산소/수소 가스의 재결합 정도는 32%로 나타났다. 이는 재결합과정이 발열반응이므로 전기분해과정에서 핵반응과 관계없이 초과엔탈피가 발생할 수 있음을 의미한다. 양전자소멸측정장치를 이용하여 양전자수명, 양전자소멸밀도, P/W 및 R 파라메터의 측정을 통하여 전극의 격자결함(전위 및 공공)에 수소가 집적 (trap)되며 수소집적은 공공에서 보다 전위에 약간 더 선호하는 것으로 나타났다. 전극의 수소화물형성에 수반하여 대부분 전위가 발생한 것으로 나타났다. 또한 팔라디움수소화물의 등시소둔실험을 통하여 소량의 미소공동 형태의 결함이 존재하는 것으로 추정하였고 그 결함의 크기는 수 $\AA$정도인 것으로 생각된다.

• 한국환경보건학회지
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• 제37권5호
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• pp.348-357
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• 2011

Objectives: This study was conducted in order to examine the relationship between heavy metal concentrations in the soil and the level of heavy metals in the blood or urine of 216 local residents living near abandoned metal mines. Methods: Residents around abandoned metal mines were interviewed about their dietary habits, including seafood consumption, medical history, cigarette smoking, and drug history. Metal concentrations in the soil were determined by atomic absorption spectrophotometer (AA-7000, Shimadzu, Japan). Lead (Pb) and cadmium (Cd) contents in the blood or urine were analyzed by GF-AAS (AA-6800, Shimadzu). Mercury (Hg) contents in the blood were determined by means of a mercury analyzer (SP-3DS, NIC). Arsenic (As) content in the soil and urine were measured by a HG-AAS (hydride vapor generation-atomic absorption spectrophotometer). Results: The heavy metal concentrations in the soil showed a log normal distribution and the geometric means of the four villages were 8.61 mg/kg for Pb, 0.19 mg/kg for Cd, 1.81 mg/kg for As and 0.035 mg/kg for Hg. The heavy metal levels of the 216 local residents showed a regular distribution for Pb, Cd, Hg in the blood and As in the urine. The arithmetic means were 3.37 ${\mu}g$/dl for Pb, 3.07 ${\mu}g$/l for Cd and 2.32 ${\mu}g$/l for Hg, 10.41 ${\mu}g$/l for As, respectively. Conclusions: As a result of multi-variate analysis for the affecting factors on the bodily heavy metal concentrations, gender and concentration in the soil (each, p<0.01) for blood lead levels; gender and smoking status (each, p<0.01) for blood cadmium levels; gender (p<0.01) for urine arsenic levels; gender, age and concentration in the soil (p<0.01) for blood mercury levels were shown to be the affecting factors.