• Journal of Biomedical Engineering Research
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• v.19 no.3
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• pp.285-290
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• 1998

There are various reports on the fracture of mechanical heart valves implanted in human or animal, and they are pointed out that problems are induced by an erosion of disk surface, due to a cavitation effect. We have been investigating this mechanism using accelerated fatigue tester, and it was found that erosion was enhanced by a compliance effect in the test circuit. In this study, effects of compliance value and location on erosion were discussed, while disk closing velocity was measured by a high speed video camera. It was clarified that faster closing velocity was resulting in a enhancement of erosion on the disk surface.

• Journal of the Korean institute of surface engineering
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• v.40 no.3
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• pp.149-158
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• 2007

Of all components of MCFC(molten carbonate fuel cell), corrosion of separator is one of the most decisive factor for commercializing of MCFC. In order to provide better understanding of corrosion behavior and morphology for gas channel of separator plate, post-analysis after cell operation for 1200 hours at $650^{\circ}C$ was performed by optical microscope, SEM and EPMA. Intergranular corrosion was observed on gas channel of separator plate. Corrosion product layer was identified as Fe-oxide, Cr-oxide and Ni-oxide by EPMA, and oxide thickness was measured with a $60{\mu}m-150{\mu}m$. Also, gas channel of separator was damaged by severe intergrannular attack with post analysis in consistent with immersion test. Moreover, pitting on the channel plate was observed with a depth of $18{\sim}24{\mu}m$. The results of immersion method are well agreement with post analysis measurements.

• Corrosion Science and Technology
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• v.15 no.4
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• pp.189-197
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• 2016

It is a common practice to conduct periodic washes at designated intervals in order to prevent the atmospheric corrosion of aircraft. The wash interval depends on the atmospheric conditions, but the wash intervals set by the U.S. Air Force were widely adopted in Korea without detailed knowledge of the background data. Therefore, it is necessary to determine our own wash intervals representing the atmospheric and geographical conditions in Korea. This study analyzed previous wash interval algorithms and atmospheric data in Korea. New wash intervals are then proposed based on the corrosion rate equation in ISO-9223:2012. Atmospheric corrosion testing was conducted using 7075 and 1050 aluminum alloy specimens to verify the accuracy of the corrosion rate equation in ISO-9223:2012. Test results showed a reasonable agreement with the corrosion rates predicted by the equation.

• Corrosion Science and Technology
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• v.17 no.4
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• pp.183-192
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• 2018

Stainless steel can be classified into three categories depending on the microstructure as austenitic stainless steel, ferritic stainless steel and martensitic stainless steel. Generally, stainless steel is extremely resistant to corrosion as the name implies. However, under specific environments, susceptibility to localized corrosion such as pitting, intergranular corrosion and stress corrosion cracking increases. This paper reviewed the state of arts on intergranular corrosion mechanisms, countermeasures on intergranular corrosion and intergranular corrosion test methods. Intergranular corrosion is mostly related with chromium depletion at the grain boundary and sometimes with segregation of electroactive elements in solution annealed stainless steel. Countermeasures on intergranular corrosion include avoiding chromium depletion by heat treatment and the addition of alloying elements. Sensitization evaluation of stainless steel was performed either through acid immersion test or electrochemical test. The methods were standardized in (Japanese Industrial Standards). Even though are useful in evaluating the degree of sensitization for industrial purpose but do not provide detailed information about sensitization mechanism, cause and chromium profile.

• Corrosion Science and Technology
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• v.17 no.1
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• pp.6-11
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• 2018

Outdoor exposure tests using of 7B04 aluminium alloy samples including plate, tensile and various SCC samples were carried out in Tuandao station, Shandong province (East of China) and Wanning station, Hainan province (South of China). Corrosion characteristics including weight loss, microstructure, tensile strength and SCC susceptibility were investigated. The corrosion rates in Tuandao and Wanning showed high to low and the corrosion rates changed to the following equation of $w=at^b$ (b<1). The corrosion of 7B04 aluminium alloy in Wanning was more serious than that in Tuandao. Pitting appeared at early stage of expose test, and it can be changed to general corrosion with test time extension. The 7B04 aluminium alloy of which specimen shapes are forging and thick plate also showed SCC (Stress corrosion cracking) in the marine atmosphere. The higher SCC sensitivity was observed in Wanning station than in Tuandao station. The 7B04 aluminium alloy with a high stress level was more sensitive to SCC. Intergranular and transgranular or a mixed mode of cracking can be observed in different marine exposure.

• The Journal of Korean Medicine Ophthalmology and Otolaryngology and Dermatology
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• v.10 no.1
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• pp.357-366
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• 1997

Urticaria is an erythematous or white non-pitting edematous plague that changes in size and shape by peripheral extention or regression during the few hours or days. Urticaria is classified as acute or chronic type. The etiology of acute urticaria has been determined in many case, but the cause of chronic urticaria has been determined in only $5\%\;to\;20\%$ of cases. This observation was aimed to evaluate the clinical manifestations and clinical indence of urticaria seen between June, 1995 and November, 1996(18months) at the Department of Dermatology, Oriental Medical Hospital, Kyung Hee University. The results were summarized as follows ; 1. In the cases of 106 patients, $43\%\;were\;male\;and\;51\%$ were female. 2. The pick incidence of age group was 20 to 29($32\%$). 3. The most frequent duration of urticaria was from 2 months to 6 months. 4. In this study, the inciting causes could not be found in $61\%\;of\;acute\;patients,\;60\%$ of chronic patients. 5. Among 107 patients, $5\%$ of all patients had personal history of atopic diseases and $9\%$ of all patients had familly history. 6. Angioedema was founded in 7 patients, and the most common involved site were lips, eyelids and tongue. 7. The most frequently treated prescription was Chhunggisan which occupied $51\%$ of all, Gyakhangjunggisan(41\%$) and Gosamhomasan($25\%$), Bangpoongtongsungsan($22\%$) in that order of frequency.

• Journal of Welding and Joining
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• v.32 no.2
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• pp.14-17
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• 2014

Ferritic stainless steels are widely used in the construction industry and in exhaust manifolds due to their low cost and relatively superior stress corrosion cracking resistance and pitting corrosion resistance compared to austenite stainless steels. Ferritic stainless steels are currently welded by various welding process including gas tungsten arc welding (GTAW), electron resistance welding (ERW) and laser beam welding. However, when these stainless steels are welded by fusion welding, some problems occur in the fusion zone (FZ) and heat affected zone (HAZ). First, the ductility of the weld is reduced due to the grain growth in the FZ and HAZ. Second, as its HAZ is frequently sensitized during welding, corrosion resistance deteriorates in this region due to the Cr depletion zone. To prevent these problems, it is recommended that ferritic stainless steels be welded with a low heat input. In this study, recent researches in the view of friction stir welded ferritic stainless steels are briefly reviewed.

• Journal of Powder Materials
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• v.9 no.4
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• pp.227-234
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• 2002

For the austenitic stainless steel (304L) manufactured by metal injection molding(MIM), the effects of copper content and sintering temperature on the mechanical properties, antibacterial activities, corrosion resistance, and electric resistances were investigated. The specimens were prepared by injection molding of the premixed powders of water-atomized 304 L and Cu with poly-acetyl binders. The green compacts were prepared with various copper contents from 0 to 10 wt.% Cu, which were debound thermally at 873 K for 7.2 ks in $N_2$gas atmosphere and subsequently sintered at various temperatures from 1323 K to 1623 K for 7.2 ks in Ar gas atmosphere. The relative density and tensile strength of the sintered compacts showed the minimum values at 5 and 8 wt.% Cu, respectively. Both the relative density and the tensile strength of the specimen with 10 wt.% Cu sintered at 1373 K showed the highest values, higher than those of copper-free specimen. Antibacterial activities investigated by the plastic film contact printing method for bacilli and the quantitative analysis of copper ion dissolved in water increased as the increase of the copper content to stainless steels. It was also verified by the measurement of pitting potential that the copper addition in 304 L could improve the corrosion resistance. Furthermore the electric conductivity increased with the increase of copper content.

• Corrosion Science and Technology
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• v.7 no.6
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• pp.301-306
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• 2008

Surface composite layers of 1.9~2.9 mm in thickness were fabricated by depositing metamorphic powders on a carbon steel substrate and by irradiating with a high-energy electron beam. In the surface composite layers, 48~64 vol.% of $Cr_{2}B$ or $Cr_{1.65}Fe_{0.35}B_{0.96}$ borides were densely precipitated in the austenite or martensite matrix. These hard borides improved the hardness of the surface composite layer. According to the otentiodynamic polarization test results of the surface composites, coatings, STS304 stainless steel, and carbon steel substrate, the corrosion potential of the surface composite fabricated with 'C+' powders was highest, and its corrosion current density was lowest, while its pitting potential was similar to that of the STS304 steel. This indicated that the overall corrosion resistance of the surface composite fabricated with 'C+' powders was the best among the tested materials. Austenite and martensite phases of the surface composites and coatings was selectively corroded, while borides were retained inside pits. In the coating fabricated with 'C+' powders, the localized corrosion additionally occurred along splat boundaries, and thus the corrosion resistance of the coating was worse than that of the surface composite.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.4
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• pp.245-252
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• 2016

Girth gears are applied in the mining, cement, and mineral processing industries and used in various types of horizontal mills, rotary dryers and kilns, and other heavy-gear ring applications. The large ring gears are normally fitted outside mills or kilns to provide the primary rotational drive. Recently, an external pinwheel gear set (e-PGS) was introduced to overcome manufacturing problems associated with girth gears. e-PGS is also suitable for low-speed, heavy-duty mechanical transmission and dusty and poor-lubrication conditions. This paper first presents a new profile modification of root relief for the e-PGS cam pinion. We then investigate load-stress factors to estimate the surface fatigue life by varying the shape design parameters. The results show that the contact fatigue life of an e-PGS can be extended significantly by increasing the profile shift coefficient. However, support bearing life of the pinwheel depends more on the contact force distribution than the profile shift coefficient.