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- 저자 : Yiquan Qi (검색결과 2 건)
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Lignin Based Flexible Electromagnetic Shielding PU Synergized with Graphite
Jia Zhang,Yunxia Qi,Yumei Zhang,Jinchi Duan,Bairun Liu,Baijun Liu,Zhaoyan Sun,Yiquan Xu,Wei Hu,Niaona Zhang 한국섬유공학회 2021 Fibers and polymers Vol.22 No.1
In this paper, lignin (L)-based polyurethane (FeGLPU) with excellent electromagnetic shielding properties wasprepared and studied. The modified reduced iron powder was modified with KH550, and then the obtained modified reducediron powder (Fe) was mixed with lignin, polyethylene glycol 200 (PEG200), hexamethylene diisocyanate (HDI) and graphite(G) to in-situ synthesize the FeGLPU. The thermal stability, mechanical properties, electronic conductivity, and morphologyof the composite FeGLPU were characterized in detail. The electromagnetic interference shielding effectiveness (EMI SE) ofFeGLPU was tested in the frequency range of 8.2-26.5 GHz. When the content of Fe and G was fixed at 10 % and the lignincontent was 5 %, the maximum EMI SE was 21.6 dB, and the frequency width of EMI SE greater than 10 dB was 18.3 GHz. The conductivity was 4.27×10-4 S/m, and the tensile strength of Fe10G10L5PU reached 11.7 MPa. When the lignin contentincreased to be 20 %, the maximum EMI SE was 22.5 dB, and the frequency width of EMI SE greater than 10 dB was18.3 GHz. The conductivity was 1.06×10-2 S/m, and the thermal decomposition temperature T5 (5 % weight loss) reached234 °C. The obtained excellent EMI SE should be due to the synergistic effect of Fe, G and lignin. It can be observed fromthe SEM observation that the G and Fe are uniformly dispersed in PU matrix with strong interfacial interaction. It wasillustrated that the prepared FeGLPU was with efficient electromagnetic shielding properties, good mechanical properties,and high thermal stability. This lignin based electromagnetic shielding PU was proposed to have broad application prospectsdue to its low expenses and ecology friendliness.
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Shihao Luo,Zhiyou Jing,Yiquan Qi 한국해양과학기술원 2020 Ocean science journal Vol.55 No.2
Based on fine-resolution simulations, we present a case study of the frontogenetic generation of submesoscale flows associated with a convergence field inside an anticyclonic mesoscale eddy in the Kuroshio Extension. The results reveal that the generation of submesoscale flows on the edge of the eddy is closely related to the convergent zone in the ageostrophic secondary circulation (ASC) that develops from frontal sharpening. Diagnostic analysis of the frontal tendency based on flow decomposition shows that frontal sharpening is initiated by mesoscale strain and accelerated by submesoscale convergence. With convergence on the cold side and divergence on the warm side of fronts, submesoscale divergent fields contribute to the asymmetry of the frontal tendency because the fronts tend to be strengthened by convergent motions and weakened by divergent motions. During frontal sharpening, the cross-front ASCs generate additional positive vorticity in their downwardbranches characterized by convergence via vortex stretching, which involves neighboring submesoscale vortices. Moreover, the enhanced lateral buoyancy gradients and surface buoyancy loss are conducive to triggering symmetric instability (SI) and ageostrophic anticyclonic instability (AAI) on the edge of the eddy. In response to these submesoscale instabilities and the subsequent slumping of fronts, the removal of kinetic energy (KE) associated with shear flows is comparable to the source of submesoscale KE from the eddy, which indicates that mesoscale energy can be drained by submesoscale instabilities during frontal sharpening. This study focuses on and describes the frontogenetic generation of submesoscale flows in mesoscale eddies in the Kuroshio Extension.
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