• Bulletin of the Korean Chemical Society
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• v.35 no.12
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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.

• Journal of the Korean Applied Science and Technology
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• v.29 no.4
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• pp.594-598
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• 2012

Polymer electrolyte membrane fuel cell(PEMFC) performance degrades seriously when sulfur dioxide and hydrogen sulfide are contaminated in the fuel gas at anode and air source at cathode, respectively. This paper reveals the effect of the combined sulfur impurity poisoning on both PEMFC cathode and anode parts through measuring electrical performance on single FC operated under 1 ppm to 10 ppm impurity gases. The severity of $SO_2$ and $H_2S$ poisoning depended on concentrations of impurity gases under optimum operating conditions($65^{\circ}C$ of cell temperature and 100 % relative humidity). Sulfur adsorption occured on the surface of Pt catalyst layer on MEA. In addition, MEA poisoning by impurity gases were cumulative. After four consecutive poisonings with 1, 3, 5 to 10 ppm, the fuel cell performance of PEMFC was decrease upto 0.54 V(76 %) from 0.71 V.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.526-529
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• 2008

The effect of air impurities on PEMFC performances were studied using electrochemical analysis, such as OCV monitoring, polarization, constant current operation, and electrochemical impedance spectroscopy. The nitrogen dioxide in air lowered the operation voltage at 1 A/$cm^2$ by 160 mV (10 ppm) and 227 mV (100 ppm), while the carbon monoxide effect was relatively not significant (30 mV at 100 ppm). For both nitrogen dioxide and carbon monoxide, the performances were largely recovered when pure air was provided again. Further study for additional air impurities and simulated air are under progress to provide fundamental data for the design of fuel cell vehicles.

• Carbon letters
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• v.6 no.1
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• pp.31-40
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• 2005

The carbon nanofibers (CNFs) were synthesized through the catalytic decomposition of hydrocarbons in a quartz tube reactor. The CNFs prepared from $C_3H_8$ at $550^{\circ}C$ was selected as the purification sample due to the higher content of impurity than that prepared from other conditions. In this study, we carried out the purification of CNFs by oxidation in air or carbon dioxide after acid treatment, and investigated the influence of purification parameters such as kind of acid, concentration, oxidation time, and oxidation temperature on the structure of CNFs. The metal catalysts could be easily eliminated from the prepared CNFs by liquid phase purification with various acids and it was verified by ICP analysis, in which, for example, Ni content decreased from 2.51% to 0.18% with 8% nitric acid. However, the particulate carbon and heterogeneous fibers were not removed from the prepared CNFs by thermal oxidation in air and carbon dioxide. This result can be explained by that the direction of graphene sheet in CNFs is vertical to the fiber axis and the CNFs are oxidized at about the similar rate with the impurity carbon.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.277-284
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• 2004

Low carbon steels containing Si of up to $1.2\;wt\%$ were oxidized in air at 1373 K and 1523 K, i.e. below and above the eutectic temperature of FeO and $Fe_2SiO_4$. The influence of a impurity element, S on behavior of scale formation during oxidation was investigated by using $M\"{o}chssbauer$ spectroscopy and EDS. This allowed establishment of an interface oxidation model of Si-added steel depending on temperature and an impurity element. A compound of FeO and FeS was formed in the scale/matrix interface of low carbon steels containing S of up to $0.03\;wt\%$ oxidized above 1213 K of the eutectic temperature. This was flat formed between $Fe_2SiO_4$ nodules along the scale/matrix interface without selective oxidation. It is due to low viscosity and high wettability of the compound of FeO and FeS in liquid. Conventional metallographic examinations revealed that roughness of the scale/matrix interface in Si-added steels became flat as the content of S increased. It was independent of oxidizing temperature and Si content. Effects of oxidizing temperature and an impurity element content on descaling characteristics in Si-added steels were evaluated by using a hydraulic descaling simulator. Good descaling characteristics was attributable to this flatness of the scale/matrix interface.

• Nuclear Engineering and Technology
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• v.43 no.5
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• pp.429-436
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• 2011

The corrosion of materials exposed to high temperature helium in a very high temperature reactor is caused by interaction with the impurities in the helium. This interaction then induces high temperature mechanical deterioration. By considering the effect of the impurity concentration on material corrosion, a long-term coolant chemistry guideline can be determined for the range of impurity concentration at which the material is stable for a long time. In this work, surface reactions were investigated by analyzing the thermodynamics and the experimental results for Alloy 617 exposed to controlled impure helium at $950^{\circ}C$. Moreover, the surfaces were examined for the Alloy 617 crept in air and in uncontrolled helium, which was explained by possible surface reactions.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.3
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• pp.278-283
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• 2013

While Built-in Spindle is working in machining center, the tool is changed by ATC(Automatic Tool Changer) automatically. However, impurities could be stacked in front of spindle because of chips formation while machining, and positional error between spindle and tool could be generated. Compressed air holes are necessary for removal of the impurities. But, the diameter and number of compressed air hole are different for each built-in spindle in market. In this paper, flow analysis is carried out to find out the efficient figuration of the compressed air hole by using velocity and pressure distributions.

• Journal of the Korean Geophysical Society
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• v.4 no.4
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• pp.251-256
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• 2001

Korean natura1 zeolite with fe1dspar and illite as impurities was purified by an air c1assification method. X-ray powder diffraction ana1yses showed that the air c1assification effectively separated zeolite and impurities, and reduce the amount of impurity of the natura1 zeolite. The zeolite with air c1assification was treated with 1N NaOH solutions at temperatures at 100, 150, 200 ℃ for 17hours. The obtained hydrotherma1 treatment of phase change to philli1site and ana1cime from mordenite and clinopti10lite.

• The Journal of Engineering Research
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• v.5 no.1
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• pp.57-62
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• 2004

Korean natural zeolite with feldspar and illite as impurities was purified by an air classification method. X-ray powder diffraction analyses showed that the air classification effectively separated zeolite and impurities, and reduce the amount of impurity of the natural zeolite. The zeolite with air classification was treated with 1N NaOH solutions at temperatures at 100, 150, $200^{\circ}C$ for 17hours. The obtained hydrothermal treatment of phase change to phillilsite and analcime from mordenite and clinoptilolite.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.607-612
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• 2006

A pressure-type rapid automatic filter of 2000mm diameter and 170 ton/h filtering capacity was fabricated. In case of no external impurity inflow, the turbidity removal efficiency on raw water was experimented and the numbers of impurities of each sizes were analyzed by particle counter. As the result of circulated filtering, the raw water of 40 NTU was filtered to 0.44 NTU and the numbers of impurities above $1{\mu}m$ were removed by approximately 95%. With the filtering efficiency experimented and the mathematical method, the turbidity change of circulation water were calculated according to the inflow rate of external impurity and water treatment method of blow-down or filtering. The cost of blow-down water was calculated from above results. And simple payback period for this filter is calculated as about one year. Nowadays, as the cost of water is continuously increasing and environment regulations will be more strict, the water quality control using this filter will be expected to satisfy the user requirement.