Taotao Ji,Jiahui Yan,Yongfu He,Wenjing Hu,Yuan Peng,Weishen Yang,Yi Liu
Despite their huge potential in C 3 H 6 refinement, ZIF-8 membranes still struggle to achieve stable production of high-purity C 3 H 6 , owing to their fluctuant performances under changing operating conditions. In this study, a previous low-temperature synthetic protocol was further optimized to improve the microstructure of ZIF-8 membranes for pressure-resistent C 3 H 6 /C 3 H 8 separation through precisely regulating the reaction temperature between −15 °C and 5 °C. The elevation of reaction temperature gave rise to reduced grain boundary defects at the cost of increased membrane thickness. Of particular note, carrying out reaction between −2.5 °C and 2.5 °C assured an exact balance between upward intergrowth and inner penetration and thus, the formation of well-intergrown semi-confined ZIF-8 membrane featuring pressure-resistant C 3 H 6 /C 3 H 8 separation even at operating temperature as high as 125 °C. At feed pressure of 7 bar, our membrane remained a separation factor approaching 190 with C 3 H 6 permeance up to 2.9×10 -8 mol m -2 s -1 Pa -1 , thus demonstrating the best separation performance under similar test conditions. Moreover, our membrane could maintain a stable separation capacity at C 3 H 6 feed fraction of 1%–99%, which has never been addressed in previous literature. The above stable and outstanding separation performance recommend our membrane a superb choice for reliable batch production of high-purity C 3 H 6 .
Zixian Wang,Yajun Li,Kai Yang,Yufan Gu,Mingxuan Gu,Limei Pan,Jian Gu,Jian Yang
In this work, high-continuity nano-Cr 2 O 3 films were fabricated on the Al 2 O 3 ceramic substrate surface via the evaporation-induced self-assembly (EIA) method, aiming at decreasing the secondary electron emission yield (SEEY) and increasing the vacuum withstand voltage performance of Al 2 O 3 ceramic for application in electric vacuum devices. The effects of ethylene glycol monomethyl ether (MOE) addition and calcination temperature on the composition, structure, and various properties of the nano-Cr 2 O 3 films were investigated, and the related mechanisms were discussed. Employing MOE and increasing its addition significantly mitigated internal stress during the liquid film formation and crack-free nano-Cr 2 O 3 films were achieved at 15% addition. With the calcination temperature increasing from 300 °C to 1000 °C, the crystallinity, uniformity, and compactness of the film were improved, while the defect states decreased, resulting in an increase in bandgap, surface resistivity, and decrease in SEEY, presenting the particularity of Cr 2 O 3 . When calcined at above 1000 °C, the Cr 2 O 3 film gradually dissolved into the Al 2 O 3 substrate, which led to the increase in bandgap, surface resistivity and SEEY, approaching the intrinsic characteristics of Al 2 O 3 at 1500 °C. The nano-Cr 2 O 3 film calcined at 1000 °C exhibits optimized comprehensive structure characteristics, moderate surface resistivity (1.30×10 16 Ω/□), the lowest SEEY (2.27), and presenting a much improved and impressive vacuum flashover voltage strength of 65 kV/cm.
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