• Journal of Technologic Dentistry
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• v.7 no.1
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• pp.13-18
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• 1985

Casting alloys, both precious and non-precious, were by heat in order to observe the change in HB and the results were : 1. The hard treatment showed 1.4 - 1.5 times as high as the soft treatment in HB. 2. The experiment shows that Au-Pt should be contained more than 75% to prevent color change. 3. Cu by hard teatment played the greatect part in creasing the solidity of Ag-Cu alloy. 4. Casting Co-Cr alloys showed little difference of HB in heat treatment.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.286-293
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• 2002

Microstructure and the electrical porperties of a ZnO-based multilayered chip-type varistor(abbreviated as MLV) with Ag/Pd(7:3) inner electrode have been studied as a function of firing of temperature. At 1100$^{\circ}$C, inner electrode layers began to show nonuniform thickness and small voids, which resulted in significant disappearance of the electrode pattern and delamination at 1100$^{\circ}$C. MLVs fired at 950$^{\circ}$C showed large degradation in leakage current, probably due to incomplete redistribution of liquid and transition metal elements in pyrochlore phase decomposition. Those fired at 1100$^{\circ}$C and above, on the other hand, revealed poor varistor characteristics and their reproductibility, which are though to stem from the deformation of inner electrode pattern, the reaction between electrode materials and ZnO-based ceramics, and the volatilization of $Bi_2O_3$. Throughout the firing temperature range of 950∼1100$^{\circ}$C, capacitance and leakage current increased while breakdown voltage and peak current decreased with the increase of firing temperature, but nonlinear coefficient and clamping ratio kept almost constant at ∼30 and 1.4, respectively. In particular, those fired between 1000$^{\circ}$C and 1050$^{\circ}$C showed stable varistor characteristics with high reproducibility. It seems that Ag/Pd(7:3) alloy is one of the electrode materials applicable to most ZnO-based MLVs incorporating with $Bi_2O_3$ when cofired up to 1050$^{\circ}$C.

• Journal of the Microelectronics and Packaging Society
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• v.7 no.3
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• pp.45-54
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• 2000

The effect of electropolishing far stamped leadframe on the removal of the edge burr and residual stress relief was examined. The present study showed that the electropolishing could be used for enhanced surface quality of stamped leadframes. The electropolishing was performed at the condition of 60% phosphoric acid electrolyte, 5 ampere of current and 3 cm electrode gap at $70^{\circ}C$ for 2 minutes for Alloy42 type leadframe, and $50^{\circ}C$ for 1.5 minutes for C-194 type leadframe. The FWHM values from X-ray diffraction showed that residual stress of electropolished leadframe recovered to the level of as-received raw materials and surface roughness measured by using AFM tuned out to be improved by 0.079 $\mu\textrm{m}$ and 0.014 $\mu\textrm{m}$ ($R_{rms}$) far alloy 42 and C-194 type leadframes, respectively. The plated thickness using XRF showed the improved uniformity in thickness variation by 0.4~0.5 $\mu\textrm{m}$ and grain growth, which is favorable for interface adhesion, was also observed from the bake test samples. We could certify dimensional stability of leadframe with inspection by means of 3D-topography and hardness measurements.

• The Journal of Korean Academy of Prosthodontics
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• v.54 no.3
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• pp.259-266
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• 2016

In edentulous mandible, implant supported overdenture was considered as a first treatment option. Konus type attachment supplies rigid support and cross arch stabilization so that more favorable force transmission and distribution can be attained. In the dentistry, computer aided design-computer aided manufacturing (CAD-CAM) system makes it possible to fabricate restorations with high precision and effectiveness. Recently, Palladium-silver (Pd-Ag) alloy which is millable has been developed. This article presents that application of CAD-CAM Konus type attachment can be provide satisfactory stability and function on four-implant supported mandibular overdenture.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.26-34
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• 2016

Automotive today has been transforming to an electronic product by adopting a lot of convenience and safety features, suggesting that joining materials and their mechanical reliabilities are getting more important. In this study, a Sn-Cu-Cr-Ca solder composition having a high melting temperature ($>230^{\circ}C$) was fabricated and its joint properties and reliability was investigated with an aim to evaluate the suitability as a joining material for electronics of engine room. Furthermore, mechanical properties change under complex environment were compared with several existing solder compositions. As a result of contact angle measurement, favorable spreadability of 84% was shown and the average shear strength manufactured with corresponding composition solder paste was $1.9kg/mm^2$. Also, thermo-mechanical reliability by thermal shock and vibration test was compared with that of the representative high temperature solder materials such as Sn-3.5Ag, Sn-0.7Cu, and Sn-5.0Sb. In order to fabricate the test module, solder balls were made in joints with ENIG-finished BGA and then the BGA chip was reflowed on the OPS-finished PCB pattern. During the environmental tests, resistance change was continuously monitored and the joint strength was examined after tests. Sn-3.5Ag alloy exhibited the biggest degradation rate in resistance and shear stress and Sn-0.7Cu resulted in a relatively stable reliability against thermo-mechanical stress coming from thermal shock and vibration.

• Journal of the Mineralogical Society of Korea
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• v.27 no.4
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• pp.263-270
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• 2014

This paper was researched that provenance of the raw material for bronze relics excavated Cheonghaejin using the distribution of lead isotope ratio based on galena ores of South Korea. Also we want to make sure that the trace elements appearing as a by-product can be used as a secondary indicator for provenance research. In the case of the galena map of the East-North Asia (Mabuchi, 1985), data are plotted in China area. Therefore it is estimated that most bronzes were produced with lead ore from China. On the other hand, the same data are plotted in the Okcheon Metamorphic Belt and Yeongnam Massif of the galena map of South Korea (KOPLID, 2012). Also the contents of Ag and Sb are available as indicator due to separate ores from similar zone in lead isotope ratio.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.112-112
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• 2018

알루미늄 합금은 내구성과 내식성이 우수한 경량 재료이다. 그 중 Al-Mg계 5083 Al 합금은 가공성 및 용접성이 우수하여 선체 재료로 널리 이용되고 있다. 이는 선체 중량의 경량화로 인해, 연료비 절감과 빠른 선속 등 다양한 이점을 지니기 때문이다. 그러나 선박의 고속화에 따라 선체에 가해지는 유체충격이 증가하고, 압력 저하에 기인하여 캐비테이션-침식 손상이 증가할 뿐만 아니라, 염소이온이 존재하는 해수환경에서는 침식과 부식의 시너지효과로 인하여 재료의 손상이 더욱 가속화된다. 이에 대한 다양한 방지책들이 제안되고 있으나, 강한 충격압을 동반한 캐비테이션 침식-부식 복합 손상 환경에서는 다소 한계가 있다. 따라서 본 연구에서는 알루미늄 5083에 대하여 캐비테이션 환경 하에서 일정 전위를 인가하며 침식-부식 손상이 최소화 되는 전위 구간을 규명하고자 하였다. 먼저, 분극 실험을 선행하여 재료의 전기화학적 거동을 파악 한 후 적용 전위구간을 선정하여, 해당 전위를 인가한 상태에서 캐비테이션 실험을 실시하였다. 전기화학적 분극실험과 캐비테이션-전기화학 복합 실험은 $25^{\circ}C$의 해수 하에서 실시하였으며, 시험편의 노출면적은 $3.24cm^2$으로 하였다. 분극 실험은 개로전위로부터 +3 V까지 2 mV/s의 분극속도로 전위를 인가하였고, 기준전극으로 Ag/AgCl, 대극으로 백금전극을 사용하였다. 캐비테이션-전기화학 복합 실험은 정전위를 인가한 상태에서 대향형 진동법으로 진동수 20 kHz, 진폭 $30{\mu}m$ 진동을 20분간 가하였으며, 혼팁과 시험편 사이의 거리는 1 mm로 일정하게 유지하였다. 실험 후 표면 손상의 정량적 분석을 위해 인가된 전위별 전류밀도를 비교하고, 무게감소량을 측정하였으며, 손상경향 파악을 위하여 3D광학현미경과 주사전자현미경(SEM)을 통해 표면을 분석하였다.

• Restorative Dentistry and Endodontics
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• v.18 no.2
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• pp.431-445
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• 1993

The purpose of this study was to observe corrosion characteristics of six dental amalgams and was to analyse corrosion products electrochemically. After each amalgam alloy and Hg was triturated as the direction of the manufacturer by using mechanical amalgamator, the triturated mass was inserted into the cylinderical metal mold ($12{\times}10mm$) and was condensed with 160kg/$cm^2$ by using the hydrolic press. The specimen was removed from the mold and was stored at room temperature for 1 week, and was polished with amalgam polishing kit. The anodic and cathodic polarization curve was obtained by using cyclic voltammetric method with 3-electrode potentiostat in saline for each amalgam and Ag, Sn, Cu plate specimen at $37{\pm}0.5^{\circ}C$. The potential sweep range was -1.7V~0. 4V(vs SCE) in working electrode and scan rate was 50mV/s and the exposed surface area of each specimen to the electrolytic solution was $0.79cm^2$. The results were as follows. 1. In anodic-cathodic polarization curve of amalgam specimens, two anodic current rising areas and two cathodic current peaks were obtained at the low Cu amalgam(CF, CS) specimen and three anodic current rising areas and three cathodic current peaks were obtained at the high Cu amalgam (TY, DS, HV) specimen. 2. As this compared with the anodic and cathodic current peak potentials of Sn, Cu and Ag specimen, the first cathodic current peak I c was caused by the reduction of divalent tin salt, second cathodic current peak IIIc results from the reduction of quadravalent tin salt, and third cathodic current peak me results from the reduction of copper salt. 3. As reverse potential sweeping was done repeatedly, anodic current was decreased slightly in all amalgam specimens.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.143-143
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• 2016

알루미늄 합금은 내구성과 내식성이 우수할 뿐만 아니라 다양한 표면개질을 통해 그 표면 특성을 더욱 향상시킬 수 있다. 특히 Al-Mg계 5083-H321 Al 합금의 경우 가공성 및 용접성이 우수하여 선체 재료로 널리 이용되는데, 이는 선체중량의 경량화가 가능하여 연료비 절감과 빠른 선속 등 다양한 이점을 지니기 때문이다. 그러나 선속의 고속화에 따라 선체에 가해지는 유체충격이 증가하고 정압 저하에 기인하여 캐비테이션-침식 손상이 증가할 뿐만 아니라 해수환경 특성 상염소이온의 존재로 부식이 가속화되는 등 침식 및 부식의 시너지효과로 손상은 크게 증가한다. 이에 대한 방지대책으로 다양한 표면개질 기법이 제안되고 있으나 강한 충격압이 동반된 캐비테이션 침식-부식 복합 손상 환경에서는 표면처리만으로는 불가능할 수 있다. 따라서 본 연구에서는 양극산화된 5083-H321을 대상으로 캐비테이션 환경 하에서 일정 전위를 인가하여 침식-부식 손상이 최소화되는 최적전위를 규명하고자 한다. 이를 위해 먼저 분극 실험을 통해 재료의 전기화학적 거동을 바탕으로 임의의 전위를 선정하고 해당 전위를 인가한 상태에서 캐비테이션 실험을 실시하였다. 이때 분극실험과 캐비테이션-전기화학 복합실험 모두 $25^{\circ}C$의 해수에서 실시하였으며, 전기화학적 분극실험은 유효면적이 $3.24cm^2$인 시편에 2 mV/s의 분극속도로 0 ~ -3 V 까지 인가하였고, Ag/AgCl 기준전극과 백금대극을 사용하였다. 캐비테이션-전기화학 복합 실험은 정전위를 인가한 상태에서 $30{\mu}m$의 진폭으로 20분간 실시하였으며, 혼팁과 시험편 사이의 거리는 1 mm로 일정하게 유지하였다. 실험 후 표면 손상의 정량적 분석을 위해 인가된 전위별 전류밀도를 비교하고, 무게감소량을 측정하였으며, 손상특성 분석을 위해 3D현미경과 주사전자현미경(SEM)을 통해 표면을 분석하였다.

• Journal of the Korean Electrochemical Society
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• v.7 no.2
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• pp.108-123
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• 2004

Imaging of surfaces and structures by near-field scanning optical microscopy (NSOM) has matured and is routinely used for studies ranging from biology to materials science. Of interest in this review paper is a versatility of modified or multi-functional NSOM (mf-NSOM) to enable high resolution imaging in several modes: (1) Concurrent fluorescence and Topographical Imaging (gases) (2) Microspectroscopy (gases) (3) Concurrent Scanning Electrochemical and Topographical Imaging (SECM) (liquids) (4) Concurrent Photoelectrochemical and Topographical Imaging (PEM) (liquids) The present study will summarize some of the recent advances in mf-NSOM work confirmed and supported by the results from several other imaging techniques of optical, fluorescence, electron and electrochemical microscopy. The studies are directed at providing local information on pitting precursor sites and vulnerable areas on metal and semiconductor surfaces, and at reactive sites on heterogeneous, catalytic substrates, especially on Al 2024 alloy and polycrystalline Ti. In addition, we will introduce some results related to the laser-induced nanometal (Ag) synthesis using mf-NSOM.