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확산 접합에 의해 제조된 텅스텐-레늄 합금/티타늄/그래파이트 접합체의 미세구조 및 고온 안정성
김주형,백창연,김동석,임성택,김도경,Kim, Joo-Hyung,Baek, Chang Yeon,Kim, Dong Seok,Lim, Seong Taek,Kim, Do Kyung 한국재료학회 2016 한국재료학회지 Vol.26 No.12
Graphite was diffusion-bonded by hot-pressing to W-25Re alloy using a Ti interlayer. For the joining, a uniaxial pressure of 25 MPa was applied at $1600^{\circ}C$ for 2 hrs in an argon atmosphere with a heating rate of $10^{\circ}C\;min^{-1}$. The interfacial microstructure and elemental distribution of the W-25Re/Ti/Graphite joints were analyzed by scanning electron microscopy (SEM). Hot-pressed joints appeared to form a stable interlayer without any micro-cracking, pores, or defects. To investigate the high-temperature stability of the W-25Re/Ti/Graphite joint, an oxy-acetylene torch test was conducted for 30 seconds with oxygen and acetylene at a 1.3:1 ratio. Cross-sectional analysis of the joint was performed to compare the thickness of the oxide layer and its chemical composition. The thickness of W-25Re changed from 250 to $20{\mu}m$. In the elemental analysis, a high fraction of rhenium was detected at the surface oxidation layer of W-25Re, while the W-25Re matrix was found to maintain the initial weight ratio. Tungsten was first reacted with oxygen at a torch temperature over $2500^{\circ}C$ to form a tungsten oxide layer on the surface of W-25Re. Then, the remaining rhenium was subsequently reacted with oxygen to form rhenium oxide. The interfacial microstructure of the Ti-containing interlayer was stable after the torch test at a temperature over $2500^{\circ}C$.
Biological Ferroelectret Property Based on β-Chitin Nanofibrils of Deep-Sea Tubeworms
김현승,이경자,Yu Ogawa,이예빈,이민구,백창연,정창규 한국전기전자재료학회 2024 Transactions on Electrical and Electronic Material Vol.25 No.1
The tubeworm ( Lamellibrachia satsuma ) exhibits unique characteristics, showcasing naturally occurring high orderliness and crystallinity in its chitin structure. Upon the removal of protein through a bleaching process, hydrogen bonds between the amide groups of β-chitin nanofibrils become apparent, alongside a spontaneous alignment in the c-axis direction. These factors contribute to the ferroelectret properties of the tubeworm, characterized by spontaneous polarization occurring within pores. Uniquely, these properties are expressed through the organism’s inherent high crystallinity and consistent directional arrangement, eliminating the need for external electric field application to achieve polarization alignment. In our study, we have successfully confirmed the mechano-electric coupling properties inherent to the tubeworm organism and have demonstrated the unique energy harvesting behavior of β-chitin in the low-frequency range.
Hf 도핑된 BaTiO<sub>3</sub> 나노입자 기반의 플렉서블 압전 소자 개발 및 특성평가
장학수 ( Haksu Jang ),박현준 ( Hyeon Jun Park ),김광현 ( Gwang Hyeon Kim ),이경자 ( Gyoung-ja Lee ),지재훈 ( Jae-hoon Ji ),이동훈 ( Donghun Lee ),정영화 ( Young Hwa Jung ),이민구 ( Min-ku Lee ),백창연 ( Changyeon Baek ),박귀일 ( K 한국센서학회 2024 센서학회지 Vol.33 No.1
Energy harvesting technology that converts the wasted energy resources into electrical energy is emerging as a semipermanent power source for self-powered electronics and wireless low-power sensor systems. Among the various energy conversion techniques, flexible piezoelectric energy harvesters (f-PEHs), using materials with piezoelectric effects, have attracted significant interest because they can harvest a small mechanical energy into electrical signals without constraints of time and space in various environments. In this study, we used a flexible piezoelectric composite film fabricated by dispersing BaHf<sub>x</sub>Ti<sub>(1- x)</sub>O<sub>3</sub> (x = 0, 0.01, 0.05, 0.1) piezoelectric powders inside a polymeric matrix to facilitate f-PEHs. The fabricated f-PEH with optimal Hf contents (x = 0.05) generated a maximum output voltage of 0.95 V and current signal of 130 nA with stable electrical/ mechanical disabilities under periodically bending deformations. In addition, we demonstrated a cantilever-type f-PEH and investigated its potential as a sensor by characterizing the output performance under mechanical vibrations at various frequencies. This study provides the breakthrough for realizing self-powered energy harvesting and sensing systems by adopting the lead-free piezoelectric composites under vibrational environments.