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구상 페놀수지 분말과 푸르프릴 알코올로부터 주형성형에 의한 매크로 다공성 카본 폼의 제조
정현덕,김세기,Jeong, Hyeondeok,Kim, Seiki 한국분말야금학회 2019 한국분말재료학회지 (KPMI) Vol.26 No.6
Macro-porous carbon foams are fabricated using cured spherical phenolic resin particles as a matrix and furfuryl alcohol as a binder through a simple casting molding. Different sizes of the phenolic resin particles from 100-450 ㎛ are used to control the pore size and structure. Ethylene glycol is additionally added as a pore-forming agent and oxalic acid is used as an initiator for polymerization of furfuryl alcohol. The polymerization is performed in two steps; at 80℃ and 200℃ in an ambient atmosphere. The carbonization of the cured body is performed under Nitrogen gas flow (0.8 L/min) at 800℃ for 1 h. Shrinkage rate and residual carbon content are measured by size and weight change after carbonization. The pore structures are observed by both electron and optical microscope and compared with the porosity results achieved by the Archimedes method. The porosity is similar regardless of the size of the phenolic resin particles. On the other hand, the pore size increases in proportion to the phenol resin size, which indicates that the pore structure can be controlled by changing the raw material particle size.
볼밀 공정 중 점도와 음향 데이터의 실시간 수집 및 상관관계 분석
정현덕,김영범,류성수,김세기,Jeong, Hyeondeok,Kim, Young-Beom,Ryu, Sung-Soo,Kim, Seiki 한국분말재료학회 (*구 분말야금학회) 2020 한국분말재료학회지 (KPMI) Vol.27 No.6
In this study, acoustic and viscosity data are collected in real time during the ball milling process and analyzed for correlation. After fast Fourier transformation (FFT) of the acoustic data, changes in the signals are observed as a function of the milling time. To analyze this quantitatively, the frequency band is divided into 1 kHz ranges to obtain an integral value. The integrated values in the 2-3 kHz range of the frequency band decrease linearly, confirming that they have a high correlation with changes in viscosity. The experiment is repeated four times to ensure the reproducibility of the data. The results of this study show that it is possible to estimate changes in slurry properties, such as viscosity and particle size, during the ball milling process using an acoustic signal.
Effect of MgO-CaO-Al2O3-SiO2 glass additive on densification of Al2O3 ceramics
Dagyeong Lee,Hyun Seon Hong,Hyeondeok Jeong,Sung-Soo Ryu 한양대학교 세라믹연구소 2022 Journal of Ceramic Processing Research Vol.23 No.2
We investigated the effect of the MgO-CaO-Al2O3-SiO2 (MCAS) additive on the densification of Al2O3 ceramics. MCAS wassynthesized using a polymeric-complex method. We analyzed the densification behavior, using dilatometric analysis up to1600 oC, and the results showed that sinterability increased with increasing MCAS content. Al2O3 samples were prepared byisothermal sintering at 1400, 1500, and 1600 oC. The microstructure, phase formation, and hardness of the samples wereanalyzed and discussed in relation to both the MCAS content and sintering temperature. The density of the MCAS-dopedsamples sintered at 1500 and 1600 oC was over 98%, and the maximum relative density was 99.7%. The highest hardness (18GPa) was achieved for the sample prepared with 3 wt.% MCAS and sintered at 1500 oC for 1 h because further dopingresulted in excessive grain growth. These results elucidate the conditions required for pressure-free sintering.
MgB<sub>4</sub>와 Mg 분말을 원료로 사용하여 고상반응법으로 제조한 MgB<sub>2</sub> 초전도체의 상생성과 초전도 특성
정현덕,김찬중,전병혁,김설향,박해웅,Jeong, Hyeondeok,Kim, Chan-Joong,Jun, Byung-Hyuk,Kim, Seolhyang,Park, Hai-Woong 한국분말야금학회 2015 한국분말재료학회지 (KPMI) Vol.22 No.5
$MgB_2$ bulk superconductors are synthesized by the solid state reaction of ($MgB_4$+xMg) precursors with excessive Mg compositions (x=1.0, 1.4, 2.0 and 2.4). The $MgB_4$ precursors are synthesized using (Mg+B) powders. The secondary phases ($MgB_4$ and MgO) present in the synthesized $MgB_4$ are removed by $HNO_3$ leaching. It is found that the formation reaction of $MgB_2$ is accelerated when Mg excessive compositions are used. The magnetization curves of $Mg_1+_xB_2$ samples show that the transition from the normal state to the superconducting state of the Mg excessive samples with x=0.5 and x=0.7 are sharper than that of $MgB_2$. The highest $J_c-B$ curve at 5 K and 20 K is achieved for x=0.5. Further addition of Mg decreases the $J_c$ owing to the formation of more pores in the $MgB_2$ matrix and smaller volume fraction of $MgB_2$.
MgB<sub>2</sub> 초전도체의 임계특성에 대한 Fe 입자 크기의 영향
정현덕,이동건,류성수,박해웅,김찬중,전병혁,Jeong, Hyeondeok,Lee, Dong-Gun,Ryu, Sung-Soo,Park, Hai-Woong,Kim, Chan-Joong,Jun, Byung-Hyuk 한국분말야금학회 2019 한국분말재료학회지 (KPMI) Vol.26 No.5
This study demonstrates the effect of addition of Fe particles of different sizes on the critical properties of the superconductor $MgB_2$. Bulk $MgB_2$ is synthesized by ball milling Mg and B powders with Fe particles at $900^{\circ}C$. When Fe particles with size less than $10{\mu}m$ are added in $MgB_2$, they easily react with B and form the FeB phase, resulting in a reduction in the amount of the $MgB_2$ phase and deterioration of the crystallinity. Accordingly, both the critical temperature and the critical current density are significantly reduced. On the other hand, when larger Fe particles are added, the $Fe_2B$ phase forms instead of FeB due to the lower reactivity of Fe toward B. Accordingly, negligible loss of B occurs, and the critical properties are found to be similar to those of the intact $MgB_2$.
광개시제 함량과 노광 시간이 DLP기반 알루미나 3D 프린팅 공정에 미치는 영향
김경민,정현덕,한윤수,백수현,김영도,류성수,Kim, Kyung Min,Jeong, Hyeondeok,Han, Yoon Soo,Baek, Su-Hyun,Kim, Young Do,Ryu, Sung-Soo 한국분말야금학회 2019 한국분말재료학회지 (KPMI) Vol.26 No.4
In this study, a process is developed for 3D printing with alumina ($Al_2O_3$). First, a photocurable slurry made from nanoparticle $Al_2O_3$ powder is mixed with hexanediol diacrylate binder and phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide photoinitiator. The optimum solid content of $Al_2O_3$ is determined by measuring the rheological properties of the slurry. Then, green bodies of $Al_2O_3$ with different photoinitiator contents and UV exposure times are fabricated with a digital light processing (DLP) 3D printer. The dimensional accuracy of the printed $Al_2O_3$ green bodies and the number of defects are evaluated by carefully measuring the samples and imaging them with a scanning electron microscope. The optimum photoinitiator content and exposure time are 0.5 wt% and 0.8 s, respectively. These results show that $Al_2O_3$ products of various sizes and shapes can be fabricated by DLP 3D printing.
메모리 분석 기반의 암호화폐 트랜잭션 정보 추출 방안 연구
임민택(MinTaek Lim),강정윤(JeongYoon Kang),박준성(JunSung Park),이문규(MoonGyu Lee),정현덕(HyeonDeok Jeong),서정택(JungTaek Seo) 한국디지털포렌식학회 2022 디지털 포렌식 연구 Vol.16 No.1
암호화폐는 P2P 네트워크에서 암호화 알고리즘에 따라 채굴되며, 채굴자를 포함한 네트워크 참가자들은 거래소를 통하여 현금화하기도 한다. 익명성을 보장하는 암호화폐의 특성상 범죄 자금의 은닉 및 세탁에 자주 사용되며 특히 암호화폐를 직접 점유 및 소유할 수 있는 하드웨어 지갑의 사용률이 증가하고 있다. 하지만 이러한 하드웨어 지갑 사용을 분석하고 추적하기 위한 포렌식 도구가 없기 때문에 암호화폐와 관련된 수사에 어려움이 있다. 따라서 본 논문은 하드웨어 지갑 사용의 추적 및 분석을 위해 디스크와 메모리에 기록된 암호화폐 거래 관련 아티팩트를 분석하고 이를 추출하는 포렌식 도구를 개발 및 제안한다. 추출된 암호화폐 거래 행위를 분석하는 것은 디지털 포렌식적으로 유의미한 자료가 될 것이며, 이러한 하드웨어 지갑의 아티팩트들은 암호화폐 추적 관련 수사에 활용될 수 있을 것이다. Cryptocurrency is mined according to a cryptographic algorithm in a P2P network, and network participants, including miners, sometimes cash out through exchanges. Due to the peculiarity of cryptocurrencies that guarantee anonymity, they are often used for hiding and laundering criminal funds, and in particular, the usage rate of hardware wallets that can directly occupy and own cryptocurrencies is increasing. However, there are no forensic tools to analyze and track the use of these hardware wallets, it is difficult to investigate cryptocurrency. Therefore, in this paper, we develop and propose a forensic tool that analyzes and extracts artifacts related to cryptocurrency transactions recorded on disk and memory for tracking and analysis of hardware wallet usage. Analyzing the extracted cryptocurrency transaction behavior will be a meaningful digital forensic data, and these hardware wallet artifacts can be utilized for investigations related to cryptocurrency tracking.