• The Korean Journal of Ceramics
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• 제4권2호
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• pp.90-94
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• 1998

Self diffusion coefficients of $^{67}$Co and impurity diffusion coefficients of $^{51}$Mn and $^{65}$Zn in single crystalline CoO have been measured by applying different radioactive isotopes simultaneously. To compare the residual activity method and the tracer sectioning method we analyzed our tracer diffusion experiments by using both methods simultaneously. According to our experimental results, the diffusion coefficients obtained from both methods are identical within experimental error, demonstrating the relibility of our experimental procedures. The diffusion coefficients of all the isotopes obtained during these test experiments for the methodology are similar in magnitude and show similar dependences on oxygen partial pressure. These first observations indicate that impurity diffusion of Mn and Zn occur via a vacancy mechanism as known for self diffusion of cobalt.

• Bulletin of the Korean Chemical Society
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• 제35권12호
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• pp.3475-3481
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• 2014

This paper describes how primary contaminants in ambient air affect the performance of the cathode in fuel cell electric vehicle applications. The effect of four atmospheric pollutants ($SO_2$, $NH_3$, $NO_2$, and CO) on cathode performance was investigated by air impurity injection and recovery test under load. Electrochemical analysis via polarization and electrochemical impedance spectroscopy was performed for various concentrations of contaminants during the impurity test in order to determine the origins of performance decay. The variation in cell voltage derived empirically in this study and data reported in the literature were normalized and juxtaposed to elucidate the relationship between impurity concentration and performance. Mechanisms of cathode degradation by air impurities were discussed in light of the findings.

• 한국건설순환자원학회논문집
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• 제1권1호
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• pp.72-80
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• 2005

건설폐기물 발생량이 급증함에 따라, 폐콘크피트를 파쇄가공한 순환골재를 구조체 콘크리트용으로 사용할 필요성이 증대하고 있다. 그러나 순환골재에는 콘크리트의 물리적 특성에 악영향을 미치는 각종 이물질이 포함되어 있어, 사전에 이물질 함유량을 적절히 판단하기 위한 시험방법이 요구된다. 본 연구에서는 순환잔골재와 순환굵은골재에 포함되어 있는 각종 이물질 함유량을 육안관찰에 의하여 선별하기 위한 시험방법을 개발하였으며, 그 결과는 다음과 같다. 1. 현행 KS F 2576(재생골재의 이물질 함유량 시험방법)은 시험대상 순환골재의 종류, 용어의 정의, 시료량, 시험방법 등의 전반적인 개정이 필요하다. 2. 순환골재에 포함된 이물질은 시료의 입경이 1.2mm 이상이면 육안선별이 가능하며, 입경이 클수록 측정 소요시간이 크게 단축된다. 3. 육안선별 방법에 의한 이물질 함유량 시험을 위하여 순환잔골재는 입경 2.5~5mm의 시료 30g, 순환굵은골재는 입경 5mm 이상의 시료 1kg을 대상으로 하면 시험의 용이성 및 정밀도 확보가 가능하다.

• 한국수소및신에너지학회논문집
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• 제19권4호
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• pp.291-298
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• 2008

Carbon monoxide(CO) is one of the contamination source in reformed hydrogen fuel with an influence on performance of polymer electrolyte membrane fuel cell(PEMFC). The studies of CO injection presented here give information about poisoning and recovery processes. The aim of this research is to investigate cell performance decline due to carbon monoxide impurity in hydrogen. Performance of PEM fuel cell was investigated using current vs. potential experiment, long time(10 hours) test, cyclic feeding test and electrochemical impedance spectra. The concentrations of carbon monoxide were changed up to 10 ppm. Performance degradation due to carbon monoxide contamination in anode fuel was observed at high concentration of carbon monoxide. The CO gas showed influence on the charge transfer reaction. The performance recovery was confirmed in long time test when pure hydrogen was provided for 1 hour after carbon monoxide had been supplied. The result of this study could be used as a basis of various reformation process design and fuel quality determination.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1996년도 추계학술대회 논문집
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• pp.329-333
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• 1996

In this Paper, the streaming electrification of transformer oils generated at the interface of transformer oils and the AC breakdown with impurity is studied. The electrification current is measured by the electrometer connected the faraday cage. And a oil velocity is maintained equally. In case of the AC breakdown test, the temperature are 30[$^{\circ}C$], 50[$^{\circ}C$], 80[$^{\circ}C$] and 90[$^{\circ}C$], repetitively. As a result of breakdown experiment, the dielectric breakdown strength is decreased in low temperature region and is increased in high temperature region according to increase of contained sodium. In case of streaming electrification experiment, the streaming current is more increased with the specimen contained sodium than the original specimen.

• 한국세라믹학회지
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• 제48권5호
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• pp.426-432
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• 2011

The oxidation behavior of CVD ${\beta}$-SiC was investigated for Very High Temperature Gas-Cooled Reactor (VHTR) applications. This study focused on the surface analysis of the oxidized CVD ${\beta}$-SiC to observe the effect of impurity gases on active/passive oxidation. Oxidation test was carried out at $950^{\circ}C$ in the impurity-controlled helium environment that contained $H_2$, $H_2O$, CO, and $CH_4$ in order to simulate VHTR coolant chemistry. For 250 h of exposure to the helium, weight changes were barely measurable when $H_2O$ in the bulk gas was carefully controlled between 0.02 and 0.1 Pa. Surface morphology also did not change based on AFM observation. However, XPS analysis results indicated that a very small amount of $SiO_2$ was formed by the reaction of SiC with $H_2O$ at the initial stage of oxidation when $H_2O$ partial pressure in the CVD ${\beta}$-SiC surface placed on the passive oxidation region. As the oxidation progressed, $H_2O$ consumed and its partial pressure in the surface decreased to the active/passive oxidation transition region. At the steady state, more oxidation did not observable up to 250 h of exposure.

• 한국수소및신에너지학회논문집
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• 제27권6호
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• pp.670-676
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• 2016

Hydrogen town in Republic of Korea was established in 2013. Hydrogen as a byproduct produced by various processes of factories is used in hydrogen town facilities. As cell performance is affected by contaminations in fuel gas, various standards about impurities of fuel have been determined by many countries. This study shows performance degradation of single cell with impurities concentrations. Traces of carbon monoxide (CO) and hydrogen sulfide ($H_2S$)can cause considerable cell performance losses. For comparing the performances by poisoning of CO, acceleration test, I-V curve, constant current are performed. Both the CO and $H_2S$ poisoning rate are a function of their concentration. With the higher concentrations the higher poisoning rates are observed. And, it was confirmed that, oxidation behavior and side reaction generation are not affected. Under the lower $H_2S$ concentration condition, the poisoning rate is much higher than that of CO because of its different adsorption intensity. It can be possible that the result of this study can be used for enacting regulation as a baseline data.

• 한국추진공학회지
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• 제22권2호
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• pp.59-65
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• 2018

AP(Ammonium Perchlorate, $NH_4ClO_4$)를 포함하는 복합화약조성의 등온가열시험시, 일정 순도 이하의 AP를 사용하는 경우 "bulged"현상으로 인해 등온가열시험 결과를 얻을 수 없었다. 본 연구는 품질 혹은 순도에 따른 AP의 열적 안정성 차이에 대해 규명하기 위해 LOT 별 AP에 대해 DSC 결과를 분석하고, 그 분석결과를 등온가열시험 결과 및 ARC결과와 비교분석하였다. 또한 순도가 낮은 AP에 대해서는 재결정을 통해 포함된 불순물을 제거한 후 분석한 결과, 열적 안정성이 높아졌음을 확인하였다. DSC 고압팬을 사용하여 AP 순도를 결정하는 정량적 분석방법을 확립하였다.

• 대한금속재료학회지
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• 제48권2호
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• pp.122-132
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• 2010

Higher strength and fracture toughness of reactor pressure vessel steels can be obtained by changing the material specification from that of Mn-Mo-Ni low alloy steel (SA508 Gr.3) to Ni-Mo-Cr low alloy steel (SA508 Gr.4N). However, the operation temperature of the reactor pressure vessel is more than $300^{\circ}C$ and the reactor operates for over 40 years. Therefore, we need to have phase stability in the high temperature range in order to apply the SA508 Gr.4N low alloy steel for a reactor pressure vessel. It is very important to evaluate the temper embrittlement phenomena of SA508 Gr.4N for an RPV application. In this study, we have performed a Charpy impact test and tensile test of SA508 Gr.4N low alloy steel with changing impurity element contents such as Mn and P. And also, the mechanical properties of these low alloy steels after longterm heat treatment ($450^{\circ}C$, 2000hr) are evaluated. Further, evaluation of the temper embrittlement by fracture analysis was carried out. Temper embrittlement occurs in KL4-Ref and KL4-P, which show a decrease of the elongation and a shifting of the transition curve toward high temperature. The reason for the temper embrittlement is the grain boundary segregation of the impurity element P and the alloying element Ni. However, KL4-Ref shows temper embrittlement phenomena despite the same contents of P and Ni compared with SC-KL4. This result may be caused by the Mn contents. In addition, the behavior of embrittlement is not largely affected by the formation of $M_3P$ phosphide or the coarsening of Cr carbides.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 봄 학술발표회 논문집
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• pp.253-260
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• 2002

Chemical weathering processes related with mineralogical characters and ground water condition are very essential engineering problems in soluble rock masses. Detailed geological mapping were performed and 8 samples were collected from the 2 formations including various rock faces to deduce the possibility of the limestone cavity formation and their mechanism. Petrological descriptions and various petro-mineralogical experiments such as XRD analysis, clay mineral analysis, absorptivity test, impurity analysis were conducted to evaluate the cavity making processes. Laboratory solubility test for rock specimen were also carried out under the strong acid (pH=1) condition. From the experimental data and geological mapping data, it is found that the formation of limestone cavities in limestones are strongly related with geological structures such as beddings, cleavages and the contents of impurities rather than CaCO$_3$contents. In case of dolomites, rock textures, grain size, amounts and types of clay minerals as well as geological structures are major controlling factors of cavity forming processes