Hyun-Seon Hong

Study on the cavitation erosion behavior of hardfacing alloys for nuclear power industry

Abstract The cavitation erosion behavior of wear resistant hardfacing alloys for nuclear power industry Co-base Stellite 6 and new Fe-base alloy was investigated using 20xa0kHz vibratory cavitation erosion test equipment. Although the crack was initiated at the carbide-matrix interfaces, the matrix hardened by strain-induced phase transformation from austenite to martensite effectively repressed the crack propagation. The cumulative weight loss of new Fe-base alloy was about 2.40xa0mg/cm2 after exposing to cavitation for 150xa0h and the cavitation erosion characteristic was similar to that of Stellite 6 on the whole range. The improved cavitation erosion resistance of new Fe-base alloy was due to the matrix hardening by the strain-induced phase transformation and to the small volume fraction of the carbide-matrix interface acting as crack initiation sites.

Effects of alloying elements on the tensile properties and oxidation behavior of modified Zircaloy-4 in 360°C water

Abstract The effects of oxygen and tin contents on the tensile properties and oxidation behavior of modified Zircaloy-4 (Zry-4) were investigated. The modified alloys were prepared by changing the chemical compositions of Zry-4; the tin contents were decreased from 1.0 wt% to zero while oxygen increased from 0.1 to 0.8 wt%, 0.1 wt% Nb was added and the amounts of Fe and Cr were kept 0.1 and 0.2 wt%, respectively. The UTS increased significantly with the oxygen content. 0.2 wt% oxygen could compensate the decrease in strength resulted from the reduction of tin content from 1.0 wt% to zero. The weight gain in water at 360°C under a pressure of 180 bar increased with tin and oxygen contents. The alloy with tin and oxygen contents of zero and 0.1 wt% showed the lowest weight gain for 120 days of oxidation test.

Overview and Future Concerns for Lithium-Ion Batteries Materials

이차전지는 일차전지와 달리 충전과 방전이 가능 하기 때문에 환경 친화성 및 경제성(고용량 및 장수 명)의 관점에서 경쟁력을 바탕으로 새로운 응용분야 로 사업 영역이 확대되고 있는 추세이다. 이차전지의 개발 및 발달로 인해 휴대전화, 노트북 PC, PMP (portable multimedia player) 등 휴대용 기기의 확대 가 활발해 지는 계기가 됐으며, 최첨단 산업인 하이 브리드 전기자동차(HEV), 모바일 IT, 지능형 로봇 산업, 친환경 에너지 산업 등의 발전에 따라 이들 산 업의 핵심부품인 이차전지 산업의 기술적 산업적 발 전이 절실히 요구되고 있다[1, 4]. 리튬이온전지는 기존의 니켈을 기반으로 하는 전지 (니켈 카드뮴 전지, 니켈 수소 전지)에 비해 용량, 중량 및 자가 방전과 메모리 효과 등에 있어서 탁월한 장점 을 갖추고 있어 이차 전지 시장의 전반을 지배하고 있 다. 또한 이러한 장점으로 인해 빠르게 수요와 응용분 야가 증가하고 있으며, 고용량과 경량화 요구가 강한 노트북, 휴대폰 등에 주로 적용되고 있다. 현재 리튬이차전지의 최대 수요처는 노트북 PC, 휴대전화 및 휴대용 전자기기이며, 특히 간헐적이고 반복적인 충전에도 성능감소 없이 사용이 가능하므 로 모바일 IT나 미래형 자동차 분야의 용도에 가장 최적의 특성을 구현할 수 있다[2]. 리튬이차전지를 구성하는 핵심소재는 양극소재, 음 극소재, 전해질, 분리막 등을 들 수 있는데, 양극소재 로는 리튬코발트산화물 또는 리튬망간산화물 등을 주 로 사용하며 음극소재로는 금속/산화물계 소재 또는 탄소재료가 적용되고 있다. 층상구조의 리튬이차전지 에 주로 사용하는 양극 및 음극소재는 사이클 안정 성, 고밀도화, 열적 안정성, 전극 가공성, 고에너지밀 도, 반응성 등의 장점을 갖는 소재를 채택하여 적용 하고 있으며, 전지 가격의 저가화 및 안정성을 향상 시키는 방향으로 연구개발이 진행되고 있다[3]. 최근 리튬이차전지의 기술개발은 점차 소재 쪽으 로 이동되고 있으며, 새로운 고용량 신소재 및 설계 기술 개발 등의 부품소재 기술이 산업 경쟁력의 핵 심요소로 부상하여 경제성장을 주도할 것으로 전망 되고 있다. 양극소재인 리튬코발트산화물의 경우는 전지의 부품소재 부분 중 가장 많은 가격적 비중을 차지하고 있음에도 불구하고, 한국은 양극소재의 대 부분을 수입에 의존하고 있는 실정이다. 이에 본고에서는 최근 각광을 받고 있는 리튬이차 전지의 최근 산업동향과 함께 이차전지용 소재 중 전 극재료인 양극과 음극을 중심으로 소재의 기술개발 현황 및 향후 전망에 대하여 소개하고자 한다.

Preparation of the Nano Cobalt Powder by Wet Chemical Reduction Method

Spherical nanosized cobalt powder with an average size of 150-400 nm was successfully prepared at room temperature from cobalt sulfate heptahydrate (). Wet chemical reduction method was adopted to synthesize nano cobalt powder and hypophosphorous acid () was used as reduction agent. Both the HCP and the FCC Co phase were developed while concentration ranged from 0.7 M to 1.1 M. Secondary phase such as and were also observed. Peaks for the crystalline Co phase having HCP and FCC structure crystallized as increasing the concentration of , indicating that the amount of reduction agent was enough to reduce . Consequently, a homogeneous Co phase could be developed without second phase when the ratio exceeded 7.

Motion analysis and control of the hybrid multi-DOF motor with taking account on design of motor shape

This paper proposes new type multi-DOF motor called Hybrid multi-DOF motor. Unlike spherical motor, this multi-DOF motor has cylindrical shape. Also it has two separated motors to handle the rotating and tilting motion independently. The outer motor is used for rotating movement, and the inner motor is used for tilting movement. The hybrid motor and its two separated motors are shown. A hybrid multi-DOF motor is shown. It is composed of an outer motor and an inner motor. The outer motor is for 1-DOF rotating motion and it is outer-rotor type 3-phases BLDC motor. Also the design of the outer motor is not difficult because it is totally separated from the inner motor. Another motor in the hybrid multi-DOF motor is the inner motor. This motor is for tilting motion with 2-DOF. For the 2-DOF motion, it has 2-pairs of PMs(Permanent Magnets) and coils. The PMs is on the rotor. Also, the coils is on the support plate(stator). The rotor and the stator are connected by an universal joint. The universal joint helps the 2-DOF tilting motion smooth. Meanwhile, two opposite coils and PMs can make same direction torque.

Coating of Cobalt Over Tungsten Carbide Powder by Wet Chemical Reduction Method

Cobalt coated tungsten carbide-cobalt composite powder has been prepared through wet chemical reduction method. The cobalt sulfate solution was converted to the cobalt chloride then the cobalt hydroxide. The tungsten carbide powders were added in to the cobalt hydroxide, the cobalt hydroxide was reduced and coated over tungsten carbide powder using hypo-phosphorous acid. Both the cobalt and the tungsten carbide phase peaks were evident in the tungsten carbide-cobalt composite powder by X-ray diffraction. The average particle size measured via scanning electron microscope, particle size analysis was around 380 nm and the thickness of coated cobalt was determined to be 30~40 nm by transmission electron microscopy.

Optimization of Wet Reduction Processing for Nanosized Cobalt Powder

Abstract Nano-sized cobalt powder was fabricated by wet chemical reduction method at room temperature. Theeffects of various experimental variables on the overall properties of fabricated nano-sized cobalt powders have beeninvestigated in detail, and amount of NaOH and reducing agent and dropping speed of reducing agent have been prop-erly selected as experimental variables in the present research. Minitab program which could find optimized conditionswas adopted as a statistic analysis. 3D Scatter-Plot and DOE (Design of Experiments) conditions for synthesis of nano-sized cobalt powder were well developed using Box-Behnken DOE method. Based on the results of the DOE process,reproducibility test were performed for nano-sized cobalt powder. Spherical nano-sized cobalt powders with an averagesize of 70-100 nm were successfully developed and crystalline peaks for the HCP and FCC structure were observedwithout second phase such as Co(OH) 2 .Keywords: Nano-sized cobalt powder, Wet chemical reduction, Design of experiments, Reproducibility

Recovery of Copper Powder form MoO 3 Leaching Solution Using Cementation Reaction System

Recovery of copper powder from copper chloride solution used in leaching process was carried out using a cementation method. Cementation is a simple and economical process, necessitating less energy compared with other recovery methods. Cementation utilizes significant difference in standard reduction potential between copper and iron under standard condition. In the present research, Cementation process variables of temperature, time, and added amount of iron scraps were optimized by using design of experiment method and individual effects on yield and efficiency of copper powder recovery were investigated using bench-scale cementation reaction system. Copper powders thus obtained from cementation process were further characterized using various analytical tools such as XRF, SEM-EDS and laser diffraction and scattering methods. Cementation process necessitated further purification of recovered copper powders and centrifugal separation method was employed, which successfully yielded copper powders of more than 99.65% purity and average in size.

Synthesis of Nano Sized Cobalt Powder from Cobalt Sulfate Heptahydrate by Liquid Phase Reduction

Nanostructured cobalt materials have recently attracted considerable attention due to their potential applications in high-density data storage, magnetic separation and heterogeneous catalysts. The size as well as the morphology at the nano scale strongly influences the physical and chemical properties of cobalt nano materials. In this study, cobalt nano particles synthesized by a a polyol process, which is a liquid-phase reduction method, were investigated. Cobalt hydroxide (), as an intermediate reaction product, was synthesized by the reaction between cobalt sulphate heptahydrate () used as a precursor and sodium hydroxide (NaOH) dissolved in DI water. As-synthesized was washed and filtered several times with DI water, because intermediate reaction products had not only but also sodium sulphate (), as an impurity. Then the cobalt powder was synthesized by diethylene glycol (DEG), as a reduction agent, with various temperatures and times. Polyvinylpyrrolidone (PVP), as a capping agent, was also added to control agglomeration and dispersion of the cobalt nano particles. The optimized synthesis condition was achieved at for 4 hours with 0.6 of the PVP/ molar ratio. Consequently, it was confirmed that the synthesized nano sized cobalt particles had a face centered cubic (fcc) structure and with a size range of 100-200 nm.

Research and Development Status of Low-Cost Fe-based Cathode Materials for Lithium Secondary Batteries

이차전지(Secondary battery)는 사용 후 다시 충전 하여 재사용이 가능하고 전기에너지를 고효율로 저 장, 사용함으로써 에너지 효율성을 극대화하고 온실 가스 배출량을 감소시킬 수 있어 다양한 산업군의 동 력원으로 사용되고 있다. 이차전지에는 납축전지 (Lead-acid), 니켈카드뮴전지(Ni-Cd), 니켈수소전지(NiMH), 리튬이차전지(Lithium secondary battery)가 있 는데, 이중 리튬이차전지는 액상 전해액을 사용하는 리튬이온전지(Lithium ion battery), 젤(Gel)상의 고분 자 전해액을 사용하는 리튬폴리머전지(Lithium polymer battery)로 분류된다. 이차전지 중 리튬이차 전지는 고출력이면서 부피/중량당 에너지밀도가 가장 우수한 경쟁력을 바탕으로 새로운 응용분야로 사업 영역이 확대되고 있는 추세이다[1]. 현재 리튬이차전지의 최대 수요처는 소형 에너지 저장시스템을 사용하는 노트북 PC, 휴대전화 및 휴 대용 전자기기로 2010년 94억