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Dongfeng Li,Bangwen Yin,Yue Lei,Shengdan Liu,Yunlai Deng,Xinming Zhang 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.2
By means of the end-quenching technique, we investigated the relationship between quenching rate and hardness as well as exfoliation corrosion rating for Al-2.21 Zn-3.59 Mg-0.45 Cu-0.038 Zr (at%) alloy plate. In order to achieve an exfoliation corrosion rating of P or EA, the quenching rate must be greater than approximately 460 °C/min and 300 °C/min, respectively, and the drop degree in hardness should simultaneously be lower than approximately 2.0% and 3.5%, respectively. The results of microstructural and microchemical examination using a scanning transmission electron microscope indicate that a lower quenching rate leads to a higher content of Zn, Mg, and Cu in the grain-boundary particles and a greater width of precipitate-free zones near grain boundaries; therefore, grain-boundary particles with Zn and Mg contents less than approximately 13.39% and 10.23% (at%), respectively, and precipitate-free zones near grain boundaries with widths less than about 107 nm can contribute to an exfoliation corrosion rating better than EA. The amount of quench-induced η- phase particles, which lead to lower hardness, increases with decreasing quenching rate, and the area fraction of these particles is approximately 2.9% at a quenching rate of 300 °C/min.
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Chaoke Bulin,Ting Guo,Ruichao Zhao,Rongxiang Zheng,Bangwen Zhang,Fang Liu 한국화학공학회 2023 Korean Journal of Chemical Engineering Vol.40 No.1
Heavy metals discharged into water by industrial activity give rise to severe environmental pollution. Herein, graphene oxide (GO) was prepared based on an improved Hummers method and utilized as adsorbent to remove aqueous Cu(II). The “species resolved” adsorption mechanism was deeply inspected via combining multiple explorations extracted from Cu(II) species distribution, GO surface charge, adsorption experiment and fitting, hard-soft acid-base (HSAB) theory, FTIR and XPS spectra. Different adsorption mechanism resolved by Cu(II) species was proposed, corresponding to different pH range. (1) When pH<8, bare Cu2+ is the dominant Cu(II) species, ion exchange and chemical complexation are the adsorption mechanism. (2) When pH=8, Cu(OH)2 is the dominant Cu(II) species, precipitation, ion exchange and chemical complexation are the adsorption mechanism. (3) When pH>8, Cu(OH) − 3 is the dominant Cu(II) species, electrostatic attraction is the adsorption mechanism. Electron transfer and energy lowering calculated based on the HSAB theory demonstrates, OH is stronger than COOH regarding binding affinity towards Cu(II). As for adsorption efficiency, adsorption of Cu(II) onto GO equilibrated in 12 min, with adsorption percent and quantity 92.32% and 553.90 mg·g−1, respectively. Findings of this work may shed light on the interaction mechanism of graphene oxide with heavy metals. Accordingly, these as clarified mechanisms may provide guidance for developing efficient adsorbent based on graphene for heavy metal scavenging.
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