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- 저자 : Haiqing Bai (검색결과 2 건)
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Haiqing Bai,Wang Qin,Shikui Jia,Li Ren,Yiwei An,Jun Bao 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.10
Considering the problems faced by Fused Deposition Modeling (FDM) 3D printing equipment, including limited consumables choices and unstable extrusion rate as well as difficult prints precision control, etc., a new type of 3D printing molding equipment was designed following the current screw extrusion technology combined with 3D printing molding mechanism. Also, the optimal matching relation between the rotational speed of the screw, which is the core of the equipment, and the feed rate of the nozzle was determined. The POLYFLOW, the software of finite element numerical simulation, was employed for analyzing the performance of the screw module under different working conditions. The result revealed that the outlet fluid pressure derived from the theoretical calculation (1.48 MPa) was close to the simulation value of 1.51 MPa, and the volumetric flow rate at the outlet derived from theoretical calculation 3.51 × 10 –8 (m 3 /s) was close to the value obtained from simulation (3.18 × 10 –8 (m 3 /s). Those findings indicated that the material could be extruded at a constant output rate; with the increase of the screw lead size, the pressure build-up capacity of screw improved, and the pressure fluctuation and velocity change became more intensive; therefore, the lead within the range of 24 ~ 36 mm should be the suitable choice for the application in actual production; the reduction of the rational speed resulted a lower shear rate, therefore, the screw rotational speed should be optimized within the reasonable range of 8 ~ 15r/min ( N max ~ N min ) and the feed rate of nozzle should be selected within the range of 1043.33 ~ 746.24 mm/min ( V Fmax ~ V Fmin ).
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KAI-GUO MA,JIN-YI BAI,TAN FANG,Haiqing Guo 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2013 NANO Vol.8 No.5
4-Mercaptovaleric acid (4MVA) and 3-mercaptovaleric acid (3MVA), two branched isomers of 5-mercaptovaleric acid (MVA), were designed and synthesized. They were used as capping agents in the aqueous synthesis of CdTe quantum dots (QDs) by a modified hydrothermal method with sodium tellurite as Te source. Compared with MVA-CdTe, either 4MVA-QDs or 3MVA-QDs exhibited higher fluorescent quantum yield (QY) and sharper absorption peak, which confirmed the superiority of using branched mercapto acids in the aqueous synthesis of QDs for improved optical properties. The fluorescence of QDs capped with 4MVA was higher than that of QDs capped with 4-mercaptobutyric acid (MBA) but lower than that of QDs capped with 3-mercaptobutyric acid (3MBA), which further confirmed the advantage of designing methyl side group rather than methylene group in the main chain for desired optical properties. However, the lower fluorescence, less sharp absorption peak and faster growth rate of 3MVA-QDs than that of 3MBA-QDs indicated adverse effect of side group on the aqueous synthesis of QDs if the size of side group is very bulky. Our results are helpful for selecting and designing appropriate capping agents for QDs with excellent properties.
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