고온변형시 Alloy 718 의 동적 및 준동적 재결정 거동

나영상,김인수,박노광,손성만 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.10

Compression tests were carried out on Alloy 718 to investigate the microstructure development following dynamic recrystallization, meta-dynamic recrystallization and grain growth. Tests were performed in the temperature range of 927∼1066℃ and strain rate range of 5∼5×10^(-4)s^_(-1), with true strains up to 0.8. Dynamically recrystallized grain size decreases consistently with increasing Zener-Hollomon parameter (Z=ε exp(Q/RT)) which is function of strain rate and temperature. The extent of recrystallization increases with a decrease in Zener-Hollomon parameter due to an increase in the critical strain (ε_c) corresponding to the initiation of dynamic recrystallization. The fraction of meta-dynamically recrystallized grain, however, increases with increasing the strain rate from 0.01s^(-1) to 1s^(-1). This paper outlines the microstructural evolution of Alloy 718 during the high temperature deformation.

열처리에 따른 니켈기 초내열 713LC 합금의 인장 및 크리프-파단 특성

나영상,박노광,김종엽,염종택 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.11

Microstructure and creep-rupture property of Alloy 713LC were investigated to optimize the utility of Alloy 713LC. The applied heat treatment condition was 1170℃/2hours/air cooling followed by 650℃/16hours/air cooling. During the heat treatment at 1170℃, MC carbide on grain boundary of as-cast Alloy 713LC was partially dissolved and coarsening of γ' particles was contemporaneously taken place so that inhomogeneous distribution in size of γ' particles was observed in heat-treated Alloy 713LC. It was concluded from the high temperature tensile test that the equi-cohesive temperature(ECT) of Alloy 713LC is around 750℃. At higher temperature than ECT, stress-rupture time was not changed after heat treatment. On the other hand, at the temperature around ECT, stress-rupture time decreased by the factor of 10 after heat treatment. This was explained by relating it to the microstructural change of grain boundary and grain interior caused by heat treatment.

단조용 니켈기 초내열합금의 상태도 계산 및 검증

나영상,김인수,손성만,박노광 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.9

Thermodynamic phase calculation and its experimental confirmation were made on a series of wrought Ni base superalloys. The Gibbs free energy of the constituent phases such as γ, γ', σ, etc can be expressed by applying the Sublattice model. Minimum Gibbs free energy condition was selected as the criteria for determining the equilibrium state. The calculated phase fraction and the transition temperature were experimentally validated by comparing the calculated value with the measured one. Isothermal aging treatment followed by electrochemical extraction and quantitative X-ray diffraction was employed for experimental validation of the calculated phase fraction, and the differential thermal analysis for the phase transition temperature. The calculated values for both phase fraction and transition temperature are well matched with the measured values. The calculated phase diagrams offer lots of useful information such as solution treatment temperature, TCP(Topologically Close Packed) phase formation, γ' phase fraction and driving force for precipitation, etc.

Udimet 720 Li 합금에서 시그마상의 모양 및 형성 기구

나영상,박노광 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.3

The precipitation kinetics of the detrimental sigma phase in Udimet 720Li has been characterized and quantified by varying exposure temperatures between 725℃ and 775℃ and exposure period up to 5000 hours. The electrochetemiyal extraction and the X-ray diffraction combined with the Rietveld analysis have been employed for the quantification of sigma precipitation. The sigma formation rate is increased and the incubation time for sigma nucleation is decreased with increasing temperatures. Sigma formation behavior has been analyzed by comparing the activation energy for sigma formation with the activation energy for the diffusion of sigma forming elements such as Cr, Co, Mo. Sigma precipitation is controlled by the diffusion of Cr segregated in the γ matrix adjacent to the primary γ′ in the early stage. and then controlled by the diffusion of Mo in the steady state. Sigma morphology was also investigated by observing the extracted residue. As the aging time increases, sigma morphology is changed from the globular shape to the dendritic. From the analysis mentioned above. a model of sigma precipitation behavior was schematically suggested.

Dieulafoy 양 병변에 의한 십이지장게실 출혈 1 예

김상현,김경환,이동현,송철수,정노원,박상제,김은규,하홍성,나일환,황윤이,성은영,최익수,신영기 대한소화기내시경학회 2001 Clinical Endoscopy Vol.23 No.1

Duodenal diverticula are first reported by Chomel in 1710. Duodenal diverticula are relatively common in adults with a prevalence of 23% in SRCP. The most duodenal diverticulum is asymptomatic. Complications such as obstruction, cholangitis, blliary stones, ulceration, perforation and hemorrhage can occur in approximately 10%. However, relatively few cases of bleeding from a duodenal diverticulum have been reported. The cause of bleeding from a duodenal diverticulum is uncertain and various suspected etiologies were suggested, such as ectopic gastric mucosa, stasis-induced ulceration, erosion into major vessels, aortoenteric fistuias, intradiverticujar polyp, aspirin-induced erosion. We report a case of a bleeding duodenal diverticulum by a Dieulafoy-like lesion and suggest this 1esion as one of posslble causes of blee4ng in duodenal diverticulum.

Na₂S 하부층을 이용한 Cu(In,Ga)Se₂ 광흡수층의 저온증착 및 Cu(In,Ga)Se₂ 박막태양전지에의 응용

신해나라(Hae Na Ra Shin),신영민(Young Min Shin),김지혜(Ji Hye Kim),윤재호(Jae Ho Yun),박병국(Byung Kook Park),안병태(Byung Tae Ahn) 한국태양광발전학회 2014 Current Photovoltaic Research Vol.2 No.1

High-efficiency in Cu(In,Ga)Se₂ (CIGS) solar cells were usually achieved on soda-lime glass substrates due to Na incorporation that reduces deep-level defects. However, this supply of sodium from sodalime glass to CIGS through Mo back electrode could be limited at low deposition temperature. Na content could be more precisely controlled by supplying Na from known amount of an outside source. For the purpose, an Na₂S layer was deposited on Mo electrode prior to CIGS film deposition and supplied to CIGS during CIGS film. With the Na₂S underlayer a more uniform component distribution was possible at 350°C and efficiency was improved compared to the cell without Na₂S layer. With more precise control of bulk and surface component profile, CIGS film can be deposited at low temperature and could be useful for flexible CIGS solar cells.

Na₂S 하부층을 이용한 Cu(In,Ga)Se₂ 광흡수층의 저온증착 및 Cu(In,Ga)Se₂ 박막태양전지에의 응용

신해나라,신영민,김지혜,윤재호,박병국,안병태,Shin, Hae Na Ra,Shin, Young Min,Kim, Ji Hye,Yun, Jae Ho,Park, Byung Kook,Ahn, Byung Tae 한국태양광발전학회 2014 Current Photovoltaic Research Vol.2 No.1

High-efficiency in $Cu(In,Ga)Se_2$ (CIGS) solar cells were usually achieved on soda-lime glass substrates due to Na incorporation that reduces deep-level defects. However, this supply of sodium from sodalime glass to CIGS through Mo back electrode could be limited at low deposition temperature. Na content could be more precisely controlled by supplying Na from known amount of an outside source. For the purpose, an $Na_2S$ layer was deposited on Mo electrode prior to CIGS film deposition and supplied to CIGS during CIGS film. With the $Na_2S$ underlayer a more uniform component distribution was possible at $350^{\circ}C$ and efficiency was improved compared to the cell without $Na_2S$ layer. With more precise control of bulk and surface component profile, CIGS film can be deposited at low temperature and could be useful for flexible CIGS solar cells.

Effects of Sunghyangchungisan(SHCS) on Cellular Ion Contents and Metabolism in Cat Brain Cortical Slices under Hypoxic Insult

Kim, Na-Ri,Kim, Young-Kyun 동의대학교 한의학연구소 2001 동의ㆍ경산 한의학 학술대회 Vol.5 No.-

星香正氣散은 腦卒中을 가진 患者에 대해 有益한 處方이라고 알려져 있다. 이번 硏究에서 는 고양이 大腦 皮質 切片을 사용하여 低酸素 發作을 誘發한 뒤, 星香正氣散이 細胞의 이온環境과 代謝의 變化와 關聯하여 效果가 있는지 硏究하였다. 고양이의 大腦 皮質 切片이 低酸素症에 露出되었을 때, 細胞內에 Na+는 增加하고 K+는 減少한다. 星香正氣散은 低酸素症으로 誘發된 細胞內의 K+와 Na+의 含量의 變化를 현저하게 遲延시켰다. 星香正氣散의 效果는 0.3-2 mg/ml의 濃度에서 投與量에 依存的이었다. 星香正氣散은 低酸素 期間의 前이나 그동안에 適用했을 때만 效果가 있었고, 이미 低酸素 發作으로 인해 損傷된 組織에 適用했을 때는 이온 障害를 바꾸는 어떤 效果도 나타나지 않았다. 星香正氣散은 Na-K-ATPase의 抑制劑인 와바인 또는 代謝 抑制劑인 2,4-DNP로 誘發된 細胞內 K+ 含量의 變化에 어떤 效果도 보이지 않았다. 또한, 正常 狀態의 切片뿐만 아니라 低酸素 狀態의 切片에서 分離된 顆粒體의 分屑에 있어서 Na-K-ATPase의 活動度에 影響을 미치지 않았다. 星香正氣散은 低酸素 發作下에서 酸素 消費量과 細胞의 ATP含量이 떨어지는 것을 현저하게 막았다. 또한 ATP를 生産하는 機能을 保護하는 低酸素 組織의 絲粒體를 돕는데 效果的이었다. 結論的으로 星香正氣散은 大腦 組織의 低酸素 發作下에서 細胞의 이온 環境과 代謝를 保護하는 有益한 效果가 있다는 것을 알 수 있다.

Immobilization of the Hyperthermophilic Archaeon Thermococcus onnurineus Using Amine-coated Silica Material for H₂ Production

배승섭,나정걸,이성목,강성균,이현숙,이정현,김태완,Bae, Seung Seob,Na, Jeong Geol,Lee, Sung-Mok,Kang, Sung Gyun,Lee, Hyun Sook,Lee, Jung-Hyun,Kim, Tae Wan The Korean Society for Microbiology and Biotechnol 2015 한국미생물·생명공학회지 Vol.43 No.3

초고온성 고세균 Thermococcus onnurineus NA1은 개미산, 일산화탄소, 또는 전분 등을 이용해서 수소를 생산하는 것으로 알려져 있다. 본 연구에서는 T. onnurineus NA1의 고정화 세포를 이용한 수소생산을 고찰하였다. 고정화 실험결과, T. onnurineus NA1은 표면에 아민기가 코팅된 규조토 담체에 정전기적 인력에 의해 효과적으로 고정화되었고, 1 g의 담체에 고정화 될 수 있는 최대 세포의 양은 71.7 mg-dcw로 확인되었다. 고정화 세포를 이용한 세 번의 반복회분식 배양을 통해 개미산으로부터 수소생산 특성을 고찰하였고, 그 결과 배양이 반복됨에 따라 고정화 세포 농도의 증가에 기인하여 초기수소생산속도가 2.3 에서 4.0 mmol l⁻¹ h⁻¹로 상당량 증가됨이 관찰되었다. 따라서, T. onnurineus NA1의 고정화세포 시스템은 수소생산을 위한 좋은 대안이 될 수 있을 것으로 사료된다. 본 연구는 초고온성 고세균의 고정화세포를 수소생산에 적용한 첫 번째 사례이다. Previously we reported that the hyperthermophilic archaeon, Thermococcus onnurineus NA1 is capable of producing hydrogen (H₂) from formate, CO or starch. In this study, we describe the immobilization of T. onnurineus NA1 as an alternative means of H₂ production. Amine-coated silica particles were effective in immobilizing T. onnurineus NA1 by electrostatic interaction, showing a maximum cell adsorption capacity of 71.7 mg-dried cells per g of particle. In three cycles of repeated-batch cultivation using sodium formate as the sole energy source, immobilized cells showed reproducible H₂ production with a considerable increase in the initial production rate from 2.3 to 4.0 mmol l⁻¹ h⁻¹, mainly due to the increase in the immobilized cell concentration as the batch culture was repeated. Thus, the immobilized-cell system of T. onnurineus NA1 was demonstrated to be feasible for H₂ production. This study is the first example of immobilized cells of hyperthermophilic archaea being used for the production of H₂.

Role of the oxidizing agent in the etching of 4H-SiC substrates with molten KOH

Na, M.,Kang, I. H.,Moon, J. H.,Bahng, W. 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.

<P>A novel etching solution using molten potassium hydroxide (KOH) for the identification of dislocation types in a silicon-carbide (SiC) epilayer is identified. Threading screw dislocations (TSDs) and threading edge dislocations (TEDs) are rarely useful for size-based differentiation of etch pits in highly nitrogen (N)-doped SiC through conventional KOH etching. In this study, we report the role of sodium peroxide (Na2O2) and potassium dioxide (KO2) as oxidizing agent additives to the etchant for identifying the dislocation types in highly N-doped 4H-SiC. A Na2O2-KOH phase diagram was calculated to predict the chemical composition of the etchant. Solid-phase Na2O2 remained in the system when added to the etchant at concentrations greater than 13-wt% Na2O2, and it provided excess oxygen to the etchant. We experimentally confirmed that etch pit shapes became more hexagonal and that the etch pit sizes of TSDs and TEDs differed more greatly when more than 20-wt% Na2O2 was added to the etchant. We also found that the size distribution of TEDs was much smaller than that of TSDs after etching using Na2O2-KOH. Dissolved oxygen played an essential role in enhancing the anisotropic etching of highly N-doped SiC and allowed the dislocation types to be identified.</P>