No abstract

No abstract

A titanate conversion coating was made on AZ31 magnesium alloys in a titanium chloride and hexafluorosilicic acid solution. The titanate conversion coating formation proceeded via the formation of a porous magnesium hydroxide and fluoride layer. Compact silicon hydroxide and titanium hydroxide were then formed locally on top of the porous layer. The fluorine ion dissociated from hexafluorosilicic acid contributed to the incorporation of magnesium fluoride in the porous layer. Moreover, a pH rise due to hydrogen discharge caused the precipitation of silicon hydroxide and titanium hydroxide. With continued immersion, the porous layer thickened and the coverage of the compact silicon hydroxide and titanium hydroxide proceeded to a larger extent, which, in turn, reduced the corrosion area fraction and enhanced the polarization resistance of the AZ31. However, prolonged immersion resulted in more cracks with larger openings, which reduced the corrosion resistance of the titanate conversion coating. As a result, the titanate conversion coating formed at immediate immersion times provided the best corrosion protection on the AZ31.Eco-awareness has been gradually raised in recent years, such as the need for energy saving and carbon reduction in transportation systems. Magnesium alloys are known as one of the green materials in the 21th century. They have excellent physical and mechanical properties, including low density, high specific strength and stiffness, excellent damping effects, and good electromagnetic shielding characteristics. 1-3 Because magnesium resource is abundant on earth, magnesium alloys have the potential to be used widely in the industry. However, magnesium has a low reduction potential (-2.37 V) and is readily oxidized in nature. According to the Pourbaix diagram of magnesium, 4 magnesium ion stably exists in the aqueous solution with pH value less than 8.5, signifying its poor corrosion resistance in the atmosphere. To enhance the corrosion resistance of magnesium alloys is thus crucial before their extensive applications. 2,3,5,6 Several surface modification treatments on magnesium alloys have been developed, including chemical conversion coating, anodization, electroplating, electroless plating, and nitrogen ion implantation. 7-12 Among them, chemical conversion coating treatment is known as an efficient and low-cost process. Moreover, the conversion coating improves the corrosion resistance of magnesium alloys and the adhesion of the organic paint. Chromate conversion coating is known for its excellent corrosion resistance and unique self-healing properties. 13,14 However, its usage has been banned by several environmental directives due to the toxicity to human health and ecological environment. Several non-chromate conversion treatments have thus been studied, including phosphate, phosphate/permanganate, rare-earth metal salt, stannate, and the solution containing transition metal compounds such as vannadate, molybdate, zirconate, and titanate. 7, 8, 15-36 Among the various conversion coating t...

Detection of heavy metals is of great importance for food safety and environmental analysis. Among various heavy metal ions, mercury ion is one of the most prevalent species. The methods for detection of mercury were numerous, and the T-Hg-T based assay was promising due to its simplicity and compatibility. However, traditional T-Hg-T based methods mainly relied on multiple T-Hg-T to produce enough conformational changes for further detection, which greatly restrained the limit of detection. Hence, we established a branch-migration based fluorescent probe and found that single T-Hg-T could produce strong signals. The sensing mechanism of our method in different reaction modes was explored, and the detection limits were determined to be 18.4 and 14.7 nM in first-order reaction mode and mixed reaction mode, respectively. Moreover, coupled with Endonuclease IV assisted signal amplification, the detection limit could be 1.2 nM, lower than most DNA based fluorometric assays. For practicability, the specificity of our assay toward different interfering ions was investigated and detection of Hg in deionized water and lake water was also achieved with similar recoveries compared to those of atomic fluorescence spectrometry, which demonstrated the practicability of our method in real samples. Definitely, the proposed branch migration probe would be a promising substitution for current DNA probes based on recognition of multiple T-Hg-T and we anticipate it to be widely adopted in food and environmental analysis.

High‐performance rechargeable Zn‐air batteries with long‐life stability are desirable for power applications in electric vehicles. The key component of the Zn‐air batteries is the bifunctional oxygen electrocatalyst, however, designing a bifunctional oxygen electrocatalyst with high intrinsic reversibility and durability is a challenge. Through density functional theory calculations, it is found that the catalytic activity originated from the electronic and geometric coordination structures synergistic effect of the Fe and Co dual‐sites with metal‐N4 coordination environment, assisting the stronger hybridization of electronic orbitals between Co (dxz, dz2) and OO* (px, pz), thus making the stronger O2 active ability of Co active site. These findings enable to development of a fancy dual single‐atom catalyst comprising adjacent FeN4 and CoN4 sites on N‐doped carbon matrix (FeCo‐NC). FeCo‐NC exhibits extraordinary bifunctional activities for oxygen reduction and evolution reaction (ORR/OER), which displays high half‐wave potential (0.893 V) for the ORR, and low overpotential (343 mV) at 10 mA cm−2 for the OER. The assembled FeCo‐NC air‐electrode works well in the flexible solid‐state Zn‐air battery with a high specific capacity of 747.0 mAh g−1, a long‐time stability of more than 400 h (30 °C), and also a superior performance at extreme temperatures (−30 °C–60 °C).