Synergistic effect of rare earth salts conversion coating with phytic acid conversion coating was studied. Rare-earth salts were used as post-treatment to modify the phytic acid coated steel. The corrosion resistance properties of different coatings was investigated with electrochemical impedance spectroscopy in 3.5 wt.% NaCl solution. The corrosion resistance of phytic acid coated steel on steel was further enhanced with cerium nitrate post-treatment. The corrosion rate of phytic acid coated steel was seriously impaired by cerium nitrate post-treatment. But scanning electron microscopy (SEM) images indicated that there are also some micro-cracks on the coating surface when phytic acid coated steel was post-treated with cerium nitrate conversion bath. X-ray photoelectron spectroscopy (XPS) results demonstrated that the phytic acid could bind to the steel surface through the formation of -P-O-Fe and the cerium salts on the steel surface existed in the forms of both Ce 3+ and Ce 4+ .
This paper aims to overcome the adverse influence of intrinsic micropores and microcracks in the micro-arc oxidation (MAO) layer by creating a hydrophobic cerium-based conversion top layer through a vacuum-assisted post-treatment. The electrochemical results reveal that the corrosion current density ( j c ) and impedance modulus at the low-frequency region of the duplex protective coating system are significantly lower and higher than that of the bare magnesium alloy and MAO coating without modification. The unprecedentedly low j c and high impedance of the as-prepared coating are attributed to the notable improvement in hydrophobicity , sealing effect to micropores, and self-healing function of the outer cerium-based film.
Micro-arc oxidation (MAO) enhances the corrosion resistance of magnesium alloys, but the resulting porous property of the MAO layer facilitates the ingress of corrosive media. This study presents a synergistic sealing treatment using cerium nitrate and stearic acid under ambient conditions to improve MAO-treated magnesium alloy's corrosion resistance, durability, and hydrophobicity. The impact of varying immersion times in cerium nitrate solution on sealing morphologies was also assessed. Results indicate that the specimen with a two-hour immersion shows the fewest micrometer-sized pores, smallest pore sizes, and minimal microcracks. Further sealing treatment with stearic acid, the charge transfer resistance of composite coating ( R ct ) was 186 times greater than the unsealed MAO coating, reaching 24.6 MΩ cm 2 . Additionally, the corrosion current density j corr after 15 days of immersion was three orders of magnitude lower than that of the unsealed coating, down to 1.88 nA cm −2 . These findings introduce a novel strategy for sealing micro-arc oxidized magnesium alloys, highlighting a promising approach to enhance their corrosion resistance, durability, and hydrophobicity, expanding their potential applications.
A simple and facile co-calcination strategy of Beta molecular sieves and cerous nitrate is proposed. Based on the results of XRD , UV–Vis, in-situ FTIR, and 29 Si MAS NMR techniques, open-site configurations of Ce(III)O 4 and Ce(IV)O 4 tetrahedrons are observed due to a large ionic radius of Ce 3+ and Ce 4+ ions. Open-site configurations result in a low ratio of BrØnsted and Lewis acid sites in HBeta-Ce-6. In the isomerization of α- pinene, a higher amount of Lewis acid sites increases the yield for camphene . BrØnsted acids are accessible for α- pinene to form limonene due to a high surface area and low coke deposition. Isomorphous incorporation of Ce 3+ occurs and a decreasing selectivity for limonene are observed using regenerated catalysts. These results indicate that co-calcination strategy protects Beta molecular sieves from thermal destruction, endows Beta molecular sieves with a higher relative crystallinity and porosity during calcination .
Xu Yan,Miao Yu,Wen-Peng Han,Ming-Hao You,Jun-Cheng Zhang,Rui-Hua Dong,Hong-Di Zhang,Yun-Ze Long
Electrospun nanofibers with designed or controlled structures have drawn much attention. In this study, we report an interesting new closed-loop structure in individual cerium nitrate/polyvinyl alcohol (Ce(NO3)3/PVA) and NaCl/PVA fibers, which are fabricated by electrospinning with a nail collector. The electrospinning parameters such as voltage and Ce(NO3)3 (or NaCl) concentration are examined for the formation of the closed-loop structure. The results suggest that the increase of the spinning voltage or addition of Ce(NO3)3 (or NaCl) is favorable for the formation of the closed-loop structure, and the increase of loop numbers and the decrease of loop size. Further analyses indicate that the formation mechanism of the closed-loop fibers can be predominantly attributed to the Coulomb repulsion in the charged jets.
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