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Ji‑Eun Ahn,Young‑Kyun Kim,Sang‑Hoon Yoon,Kee‑Ahn Lee 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.7
An equiatomic CoCrFeMnNi high entropy alloy (HEA) coating layer was prepared via a cold spray (CS) process. In orderto control the microstructure and nano-indentation properties of the CS HEA, heat treatments were employed. CS HEAcoating layer showed a heterogeneous microstructure where ultra-fine grains were formed at the particle interfaces, whilecoarse grains were formed inside the particles. Furthermore, deformation twins (DTs) were also formed inside the particlesdue to severe plastic deformation (SPD) in each particle generated during the CS deposition. For the 550 °C heat treatment(HT), fine Cr-rich precipitates were additionally formed at the grain boundary and particle boundary. By contrast, recrystallizationoccurred during 850 °C HT, while the size of the Cr-rich precipitate increased. The nano-indentation hardness ofthe CS HEA coating layer was 10.9 GPa, which was ~ 3 times higher than that of the conventional cast HEA. The superiorhardness of the CS HEA might has been enabled due to the combination of the high dislocation density, DTs, and ultra-finegrains. Based on the results above, the strategy to control the microstructure and mechanical properties through HT of theequiatomic CoCrFeMnNi HEA coating layer prepared via the CS process has been discussed.
기계적합화법으로 제조된 TiNi 분말의 방전플라즈마 소결에 관한 연구
김윤호,강지훈,김지순,안인섭,권영순 울산대학교 1999 공학연구논문집 Vol.30 No.2
기계적합금화법(MA)에 의해 제조된 TiNi 분말을 사용하여 방전플라즈마 소결법(SPS)으로 소결체를 제조하고 치밀화 거동을 조사하기 위하여 미세조직의 관찰 및 상분석을 행하였다. SPS법으로 소결체를 제조한 결과, 통상적인 소결법으로 소결체를 제조하였을 때 보다, 낮은 온도와 짧은 시간의 유지시간에서 이론 밀도의 99% 가까운 소결체 밀도를 얻을 수 있었고, 소결체의 상은 B2구조의 cubic과 2차상으로 Ti₂Ni가 존재함을 확인하였다. Mechanically-alloyed TiNi powders were densified by Spark-Plasma Sintering(SPS) method. The densififcation behavior was investigated throgh the microstructural observation, the phase analysis and the measurement of change in devsity, linear shrinkage and densification rate as a function of temperature. Sintered body with close to 99% relative density was obtained at lower sintering temperature for shorter holding time in comparison to the conventional sintering methods. TiNi with B2 structure was confirmed as the major phase and Ti₂Ni as the second phase.
문창기,박상준,조민구,김영중,김소연,김윤권,정준오,안석진,김은실,서승오,김지훈,최원제,이윤영,박형기,최규영,김현근 대한감염학회 2006 감염과 화학요법 Vol.38 No.6
Background: The purpose of this study was to document the incidence and clinical characteristics of patients with tuberculosis (TB) in combat and auxiliary police, living in a group, in Korea where the incidence rate of active TB in a general population is higher than in Western countries. Materials and Methods:We retrospectively reviewed the medical records of all tuberculosis patients diagnosed at National Police Hospital from January 2002 through December 2004. Results:In 2002-2004, a total of 156 cases of tuberculosis were identified with the mean (Standard deviation) age of 20.6 (±1.0) years. Of these, 134 (85.9%) patients were registered as new cases, 11 (7.1%) as relapse, 2 (1.3%) as failure, 5 (3.1%) as treatment-after-default cases whereas 4 (2.6 %) patients were not included in any categories. Average annual new TB rate and smear-positive TB rate were 86.5/10^(5) and 17.4/10^(5) person-years, respectively. In 12 of 31 smear-positive cases, time from onset of symptoms to diagnosis was more than 30 days. Two multidrug-resistance TB cases were identified and two suspected outbreak episodes of TB had occurred during 3 years. Conclusion:There was no statistically significant difference in the incidence rate of new cases of TB between the general population aged 20 to 29 years and combat and auxiliary police in Korea. 배경 : 국내 결핵의 발생은 감소 추세에 있으나 여전히 후진국형 발생양상을 보이고 있다. 특히 집단생활을 하는 젊은이들에서 발생하는 결핵의 유행이 간헐적으로 알려지고 있어 우려를 낳고 있다. 이에 저자들은 최근 전경대원의 결핵 발병 양상에 대해 알아보고자 본 연구를 시행하였다. 재료 및 방법 : 2002년 1월부터 2004년 12월까지 3년간 경찰병원에서 결핵 진료를 받은 전경대원의 의무기록을 후향적으로 분석하여 연도별 결핵 신환발생률, 도말양성결핵 신환율, 진단 지연, 집단발병, 다제내성결핵을 조사하였다. 결과 : 연도별 결핵 신환자 수(10만명당 발생추정치)는 2002년 50명(83.6명), 2003년 42명(83.7명), 2004년 42명(93.5명)이었고 도말양성 폐결핵 신환자 수는 2002년 10명(16.7명), 2003년 11명(21.9명), 2004년 6명(13.4명)이었다. 3년간 도말양성 폐결핵 환자는 31명이 있었고 그 중 12명은 호흡기 증상 발생 30일이 지나서 진단을 받았다. 다제내성 결핵은 2명이 있었으며 결핵의 집단발병이 의심되는 사례는 2차례 있었다. 결론 : 전경대원과 20-29세 연령군 일반인의 결핵 신환발생률, 도말양성 폐결핵 발생률의 통계적으로 유의한 차이는 없었다.
Ahn, Ji Young,Kim, Sang Beom,Kim, Ji Hoon,Jang, Nam Su,Kim, Dae Hyun,Lee, Hyung Woo,Kim, Jong Man,Kim, Soo Hyung IOP 2016 Journal of micromechanics and microengineering Vol.26 No.1
<P>The interfacial contact area between the fuel and oxidizer components plays an important role in determining the combustion reactivity of nanothermite composites. In addition, the development of compact and reliable ignition methods can extend the applicability of nanothermite composites to various thermal engineering fields. In this study we report the development of a micro-chip initiator with controlled combustion reactivity using concepts usually applied to microelectromechanical systems (MEMS) and simple nanofabrication processes. The nanothermite composites fabricated in this study consisted of aluminum nanoparticles (Al NPs) as the fuel and copper oxide nanoparticles (CuO NPs) as the oxidizer accumulated on a silicon oxide substrate with a serpentine-shaped gold (Au) electrode. The micro-chip initiator rapidly ignited and exploded when minimal current was supplied. The effects of stacking structures of Al and CuO-based multilayers on the combustion properties were systematically investigated in terms of the pressurization rate, peak explosion time, and heat flow. Pressurization rates of 0.004–0.025 MPa <I>μ</I>s<SUP>−1</SUP> and heat flows of 2.0–3.8 kJ g<SUP>−1</SUP> with a commonly fast response time of less than 20 ms could be achieved by simply changing the interfacial structures of the Al and CuO multilayers. The controllability of combustion reactivity of micro-chip initiator can be made for general nanothermite composites composed of Al and various metal oxides (e.g. Fe<SUB>2</SUB>O<SUB>3</SUB>, CuO, KMnO<SUB>4</SUB>, etc). The micro-chip initiator fabricated in this study was reliable, compact, and proved to be a versatile platform, exhibiting controlled combustion reactivity and fast response time, which could be used for various civilian and military thermal engineering applications, such as in initiators and propulsion, welding, and ordinance systems.</P>
Ahn, Ji Young,Kim, Ji Hoon,Moon, Kook Joo,Park, So Dam,Kim, Soo Hyung RSC Pub 2013 Nanoscale Vol.5 No.15
<P>The existence of numerous interfacial boundaries among TiO2 nanoparticles (NPs) accumulated in the photoelectrode layer of dye-sensitized solar cells (DSSCs) hinders the effective transport of photogenerated electrons to an electrode. Therefore, as a replacement for TiO2 NPs, one-dimensional TiO2 nanowires (NWs) can be suggested to provide pathways for fast electron transport by significantly reducing the number of interfacial boundaries. In order to provide direct evidence for the better performance of such longer TiO2 NWs than shorter TiO2 NWs, we examine the effect of the controlled aspect ratio of the TiO2 NWs randomly accumulated in the photoelectrode layer on the photovoltaic performance of DSSCs. It is clearly found that longer TiO2 NWs significantly improve the electron transport by reducing the TiO2/dye/electrolyte interfacial contact resistance. Furthermore, the embedment of multi-walled carbon nanotubes (MWCNTs) as an effective charge transfer medium in longer TiO2 NWs is proposed in this study to promote more synergistic effects, which lead to significant improvements in the photovoltaic properties of DSSCs.</P>
Ahn, Ji Young,Kim, Ji Hoon,Kim, Jong Man,Lee, Deug Woo,Park, Jong Kweon,Kim, Soo Hyung American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.10
<P>We demonstrated that the size and morphology of an oxidizer have strong effects on the propulsion forces of nano-Al-based propellants. Enhanced propulsion forces could be obtained through the creation and addition of various oxidizer nanoparticles and nanowires in nano-Al-based propellants.</P>