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( Soyeon Choi ),( Kyungho Chung ),( Seunghyuk Kwon ),( Hyoungjin Choi ) 한국고무학회 2016 엘라스토머 및 콤포지트 Vol.51 No.2
Magneto-rheological elastomer (MRE) is a material which shows reversible and various modulus under magnetic field. Comparing to conventional rubber vibration isolator, MREs are able to absorb broader frequency range of vibration. These characteristic phenomena result from the orientation of magnetic particle (i.e., chain-like formation) in rubber matrix. In this study, silicone rubber was used as a matrix of MREs. Carbonyl iron particle (CIP) was used to give magnetic field reactive modulus of MRE. The surface of the CIP was modified with chemical reactants such as silane coupling agent and poly(glycidyl methacrylate), to improve interfacial adhesion between matrix and CIP. The mechanical properties of MREs were measured without the application of magnetic field. The results showed that the tensile strength was decreased while the hardness was increased with the addition of CIP. Also, surface modification of CIP resulted in the improvement of physical properties of MRE, but the degree of orientation of CIP became decreased. The analysis of MR effect was carried out using electromagnetic equipment with various magnetic flux. As the addition of CIP and magnetic flux increased, increment of MR effect was observed. Even though the surface modification of CIP gave positive effect on the mechanical properties of MRE, MR effect was decreased with the surface modification of CIP due to decrease of CIP orientation. Throughout this study, it was found that the loading amounts of CIP affected the mechanical properties of MRE, and surface property of CIP was an important factor on MR effect of MRE.
높은 수율의 임계값 스위칭 특성을 위한 CMOS 호환 전극을 갖는 NbO<SUB>x</SUB> 층에서 산화물 장벽의 역할
최현식(Hyeonsik Choi),김윤서(Yunsur Kim),박형진(Hyoungjin Park),정지애(Jiae Jeong),우지용(Jiyong Woo) 대한전자공학회 2023 대한전자공학회 학술대회 Vol.2023 No.11
This study shows how the threshold switching (TS) characteristics of a NbOx layer with noninert W electrodes can be improved by introducing an oxide barrier. The ~10-nm-thick NbOx layer exhibits TS, which is known to originate from NbO₂, after electroforming. However, through X-ray photoelectron spectroscopy, a Nb₂O<SUB>5</SUB> layer, which is known to cause resistive memory switching, is formed mainly at the top interface as well. This results in a worsening TS yield. Therefore, thin oxides were introduced to improve the TS behavior and systematically investigate the role of the oxide barrier by considering their location and material properties. The barrier inserted at the bottom interface makes the formation of NbO₂ difficult, preventing TS. When the barrier was introduced at the top interface, the unwanted Nb₂O<SUB>5</SUB> created through reaction with the W electrode can be mitigated, promoting the occurrence of TS. Note that when an AL₂O₃ (or HfO₂) barrier is used, which prefers to scavenge (or provide) oxygen from (or to) the NbOx, a dielectric (or weak TS) behavior is shown. As a result, excellent cell-to-cell uniformity of the TS is achieved in the ZrO₂/NbOx stack, which not only prevents the formation of Nb₂O<SUB>5</SUB> but also stabilizes the NbO₂ in the NbOx layer. Through examining the temperature dependence of the TS obtained from the W/NbOx/W and W/ZrO₂/NbOx/W stacks, it was found that the suppression of the Nb₂O<SUB>5</SUB> at the top interface is indirectly shown as a strengthened Schottky barrier from an electrical measurement perspective.
Lim, SungTaek,Choi, HyoungJin,Jhon, MyungS 한국공업화학회 2003 Journal of Industrial and Engineering Chemistry Vol.9 No.1
Ultrasonication was used to control the dispersibility of organophillic montmorillonite (OMMT) and the rheological properties of poly(ethylene oxide) (PEO)/OMMT nanocomposites, which were prepared via the solvent casting method using chloroform as a cosolvent. X-ray diffraction analysis showed that the application of ultrasound to OMMT dispersions prior to the mixing with polymer solution increases the layer spacing in clay particles. We systematically developed the ultrasonification preparation procedure by establishing the relationship between dispersion quality and rheological properties of polymer/clay nanocomposites. Dispersion quality was compared with both thermal properties obtained from TGA and rheological properties measured in steady shear and dynamic oscillatory tests. To analyze the non-Newtonian flow behavior, we analyzed shear viscosity data via the Carreau model. We found that the steady shear viscosity and power-law index increase with the dispersion quality for a fixed OMMT content. The microstructure of PEO/OMMT nanocomposite having enhanced dispersibility through sonication was also examined using transmission electron microscopy.
최재성(Jaesung Choi),이충희(Choonghee Lee),임재일(Jaeil Lim),이형진(Hyoungjin Lee) 한국추진공학회 2017 한국추진공학회지 Vol.21 No.5
Extinguishment of a burning solid propellant is difficult, however, dynamic extinction can be induced by fast depressurization in combustion chamber. This paper describes experimental results for the characteristics of extinguishment for composite solid propellants by rapid depressurization. For various composition of solid propellants, depressurization ratio which can induce extinguishment of combustion was obtained using experimental apparatus with rupture disk. Experimental results showed that particle size of oxidizer, mixing ratio of oxidizers with different particle size and contents of metal fuel can affect on the characteristics extinguishement for solid propellant.
Gao, Tianming,Na, Bokgyun,Choi, Hyoungjin,Chung, Kyungho North-Holland 2018 Materials letters Vol.214 No.-
<P><B>Abstract</B></P> <P>The metal-ligand complex (sacrificial bonds) that exist in the mussels, bone and silk can dissipate energy and reinforce mechanical strength. Inspired by the high performance of metal-ligand complex, we introduced a kind of metal-ligand crosslink into the rubber network. In this work, ethylene acrylic elastomer (AEM) was filled with ZnO, and was cured by the amine cure system. The metal-ligand crosslink structure was verified by FTIR and XPS, and the tensile strength and dynamic properties were examined with a universal testing machine and rubber process analyzer (RPA). The results showed that coordination crosslink formed in the AEM matrix and exhibited outstanding tensile strength and unexpected dynamic properties due to the coordination bonds between Zn<SUP>2+</SUP> and amine group.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Zinc oxide (ZnO) filled AEM and reacted with the amine group to achieve the coordinated bonds. </LI> <LI> The coordinated bonds had been verified by FTIR and XPS. </LI> <LI> The coordinated bonds can dissipate energy and preserve the structure integrity of elastomer. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>The zinc oxide (ZnO) filled AEM and reacted with the amine group to achieve the coordinated bonds. The dynamic properties of AEM exhibit that the coordinated bonds can dissipate energy and preserve the structure integrity of elastomer.</P> <P>[DISPLAY OMISSION]</P>