• 한국전기전자재료학회논문지
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• 제17권2호
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• pp.236-241
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• 2004

New electrolytes of cubic L $a_2$M $o_2$-x Nbx $O_{9-}$$\delta$/(x=0, 0.05, 0.1, 0.2) were fabricated by a solid-state reaction method and their sintered densities were approximately 93％ of theoretical density. X-ray diffraction analysis and microstructure observation for the sintered specimens were performed. The at complex impedance were measured at 34$0^{\circ}C$ to 93$0^{\circ}C$ in air and fitted with a Solatron ZView program. Their impedance spectra showed big difference below and over the phase transition temperature (58$0^{\circ}C$). The electrical conductivity of L $a_2$M $o_2$ $O_{9}$ was 1.36${\times}$10$^{-2}$ S$cm^{-1}$ / at 817$^{\circ}C$. Comparing to undoped L $a_2$M $o_2$ $O_{9}$ , Nb-doped specimen showed the increase of electrical conductivity due to the aliovalent doping effect..

• Journal of Periodontal and Implant Science
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• 제37권4호
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• pp.767-777
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• 2007

The present study was performed to evaluate the effect of Tetracycline-HCI on the change of implant surface microstructure according to application time. Anodic oxidation surface were utilized. Implant surface was rubbed with 50mg/ml Tetracycline-HCI solution for ${\frac{1}{2}}min.$, 1min., $1{\frac{1}{2}}min.$, 2min., $2{\frac{1}{2}}min.$, and 3min. respectively in the test group. Then, specimens were processed for Ra Value test and scanning electron microscopic observation. The results of this study were as follows. 1. The anodic oxidation surface roughness tests don't show significant difference on conditioning with saline and Tetracycline-HCI. 2. The anodic oxidized surfaces showed the craterous structures. The surface conditioning with Tetracycline-HCI didn't influence on its micro-morphology. In conclusion, Anodic oxidation implant surface is stable to detoxificate with 50mg/ml Tetracycline-HCI of implant surface.

• Journal of Periodontal and Implant Science
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• 제37권4호
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• pp.779-789
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• 2007

The present study was performed to evaluate the effect of Tetracycline-HCI on the change of implant surface microstructure according to application time. Implant with hydroxyapatite surface was were utilized. Implant surface was rubbed with 50mg/ml Tetracycline-HCI solution and sterilized saline for ${\frac{1}{2}}min.$, 1min., $1{\frac{1}{2}}min.$, 2min., $2{\frac{1}{2}}min.$, and 3min. respectively in the test group. Then, specimens were processed for scanning electron microscopic observation and measured surface roughness by optical interferometer. The results of this study were as follows. 1. Hydroxyapatite surface showed that round particles were deposited irregularly. 2. The roughness of surfaces conditioned with Tetracycline-HCI and saline was lessened and the cracks were increased relative to the application time. In conclusion, the detoxification with 50mg/ml Tetracycline-HCI must be applied respectively with appropriate time according to hydroxyapatite implant surfaces.

• 마이크로전자및패키징학회지
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• 제16권2호
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• pp.27-31
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• 2009

Sn whiskers can grow from the pure Sn and high Sn-based finish and cause the electrical shorts and failures. Even with the wealth of information on whiskers, we have neither the clear understanding of whisker growth nor methods for its prevention. In this study, the whisker grain roots which connected with intermetallic layer were analyzed by high-resolution transmission electron microscopy (HR-TEM). In the Sn-Cu plated leadframe (LF) that was stored at ambient condition for 540 days, filament-shaped whiskers were grown on the Sn-plated surface and ${\eta}'-Cu_6Sn_5$ precipitates were widely distributed along the grain boundaries at the Sn matrix. The measured of the lattice fringes at the ${\eta}'-Cu_6Sn_5$ was $4.71{\AA}$ at the coarse grain and $2.91{\AA}$ at the fine grain. The $Cu_3Sn$ which generates the tensile stresses was not observed. The formation of $Cu_6Sn_5$ precipitates and intermetallic layer were strongly related to whisker growth, but, the whisker growth tendency does not closely relate with the geometric morphology of irregularly grown intermetallic compound (lMC).

• 한국표면공학회지
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• 제19권3호
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• pp.92-108
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• 1986

An electroplating on the lead frame fabricated from domestic copper plate was studied experimentally. In this study, nickel was plated on the thin copper lead frame and silver layer was coated on the nickel film in the cyanide electrolyte. The effect of process variables such as current density, plating time, coating thickness and flow rate of electrolytic solution on the properties of coating was investigated. Some samples on each step were fabricated during electroplating. The results obtained from polarization measurement, observation of SEM photograph, adhesion test of coating and microhardness test are as follows. On silver plating, polarization resistance of potentiostatic cathodic polarization curve is reduced as the flow rate of Ag electrolytic solution increases. And above resistance is also reduced when the minor chemicals of sodium cyanide and sodium carbonate are added in potassium silver cyanide bath. The reduced polarization resistance makes silver deposition on the cathode easy. An increase in the current density and the coating thickness causes the particle size of deposit to coarsen, and consequently the Knoop microhardness of the coating decreases. On selective plating an increase in the flow rate of plating solution lead to do high speed plating with high current density. In this case, the surface morphology of deposit is of fine microstructure with high Knoop hardness. An increasing trend of the adhesion of coating was shown with increasing the current density and flow rate of electrolytic solution.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.39-40
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• 2006

The relationship between the powder particle size change and a mechanical property of the Metal Injection Molding (MIM) product was examined in detail. The XRD results indicate that the diffraction peaks of BCC appeared in compacts of powder particle size of 4 to $10{\mu}m$ as well as the bulk SUS630. However, the diffraction peaks from both BCC and FCC were observed in the compact with powder size less than $3{\mu}m$. TEM observation revealed that the powder with those BCC/FCC two phase structure have a finely dispersed $SiO_2$ precipitates. Because the Si is ferrite stabilizing element, decrease of Si composition in the matrix phase by the $SiO_2$ precipitation resulted in formation of the retained austenite. Therefore, controlling the elements such as Si as well as oxygen decrease is very important to obtain a normal microstructure in ultra-fine powder $(<3{\mu}m)$ injection molding.

• 한국주조공학회지
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• 제17권5호
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• pp.494-501
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• 1997

In order to manufacture large rod preforms of 2014 Al alloy with a good mechanical property by spray forming method, it was spray-formed at a droplet temperature of $715^{\circ}C$, a droplet flight distance of 400mm, and a spraying angle of $35^{\circ}$. The rod preforms were extruded at $397^{\circ}C$ with the die temperature of $420^{\circ}C$ under the hot extrusion ratio 21:1 and T6 heat treatment was performed. The 2014 Al alloys cast by hot top process were also extruded and heat-treated at the same condition as a reference material. Microstructural observation and tensile test were carried out to investigate the effects of extrusion on microstructure and mechanical property of spray-formed Al alloy. Spray-formed Al alloys had many porosities due to inappropriate process conditions such as long droplet flight distance and low droplet temperature but have fine equiaxed grain. These porosities were reduced with decreasing in grain size by hot extrusion. Ultimate tensile strength and yield strength of spray formed-extruded 2014 Al alloy were inferior to those of the normal cast-extruded 2014 Al alloy, but elongations were superior. The control of porosity was important to get spray formed preform with a good mechanical property.

• 한국표면공학회지
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• 제43권2호
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• pp.57-63
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• 2010

In this study, thermal stability of the mechanical properties of Ni-P-B and Ni-P-Fe layers electroplated on Alloy 600 material was evaluated by measuring their microhardness, tensile strength, and elongation after heat treatment at $325^{\circ}C$ and $400^{\circ}C$. According to the results, there was no noticeable change in microhardness of the two electrodeposits before and after heat treatment at the temperatures for 30 days. In the case of a Ni-P-B electrodeposit, ultimate tensile strength (UTS) slightly increases with heat treatment time, while its elongation decreases, showing good thermal stability in the mechanical properties at high temperature. On the other hand, UTS and elongation of Ni-P-Fe decrease with heat treatment time, which is very unusual observation. This result was attributed to the bad microstructure of Ni-P-Fe having many defects in the deposit formed early stage of an electroplating process and their redistribution to link to become large ones during heat treatment.

• 자원리싸이클링
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• 제3권1호
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• pp.25-31
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• 1994

AZ91 마그네슘합금 절분 및 스크램외 재활용을 목적으로 절분 및 스크랩을 상온가압하여 빌렛을 얻었다. 이 압출용 벨렛을 압축비율 25:1로 고정하고, 압출온도를 $300~380^{\circ}C$로 변화시켜 가면서 시편을 제조하였으며, 비교재로 마그네슘합금 주조재도 열간압출을 행하였다. 마그네숨합금 절분 및 스크랩을 열간압출함에 따라 매우 미세한 재설정 조직을 얻었으며, 인장강도 및 연산률은 각각 330 MPa, 10%로 주조재를 열간압층한 재료와 거의 비슷한 기계적 특성을 나타내었다.

• 한국가스학회지
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• 제14권6호
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• pp.38-43
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• 2010

자원 부족과 환경규제의 강화에 따라 자동차 강판재의 고강도화와 박강판화가 주요 이슈로 대두되고 있다. 그러나 고강도 강판재 사용에 있어 수소취성은 기계적 성질 저하의 문제가 되고 있다. 본 연구에서는 개발중인 590MPa급 DP강을 대상으로 조성 및 조직특성에 따른 표면층에서의 수소의 거동에 대해 연구하였다. 수소주입은 음극전기분해법을 이용하여 강제 주입시켰고, 수소주입조건에 따른 수소주입량과 표면층 조직관찰 및 미소경도시험 결과의 관계로 부터 표면층의 수소거동을 평가하였다.