Mg?1Zn?0.5Ca alloys were prepared by traditional steel mould casting and water-cooled copper mould injection casting at higher cooling rate. Microstructure, mechanical properties and bio-corrosion resistance of two alloys were contrastively investigated. Grain size reduces remarkably and microstructure becomes homogenous when raising cooling rate. The bio-corrosion behaviour in 3.5% sodium chloride solution (3.5% NaCl) and Hank’s solution at 37°C was investigated using electrochemical polarization measurement and the results indicate that the alloy prepared at higher cooling rates has better corrosion resistance in both types of solution. Further mass loss immersion test in Hank’s solution reveals the same result. The reason of corrosion resistance improvement is that raising cooling rate brings about homogeneous microstructure, which leads to micro-galvanic corrosion alleviation. The tensile test results show that yield strength, ultimate tensile strength and elongation are improved by raising cooling rate and the improvement is mainly due to grain refinement.
Graphene is a promising material as both active components and additives in electrochemical energy storage devices. The properties of graphene strongly depend on the fabrication methods. The applications of reduced graphene oxide as electrode materials have been well studied and reviewed, but the using of "pristine" graphene as electrode material for energy storage is still a new topic. In this paper, we review state-of-the-art progress in the fabrication of "pristine" graphene by different methods and the electrochemical performance of graphene-based electrodes. The achievements in this area will be summarized and compared with the graphene oxide route in terms of cost, scalability, material properties and performances, and the challenges in these methods will be discussed as well.
Nanoscale europium（Ⅲ） metal-organic frameworks, Eu（BTC）（H20）.DMF, were synthesized by rapid microwave-assisted method. The components of the as-prepared products were confirmed by the elemental analysis, X-ray powder diffraction （XRD）, thermal gravimetric analysis （TGA） and Fourier-transform infrared spectra （FTIR） analyses. Eu（BTC）（H20）.DMF with various morphologies, including particle-like, rod-like, straw-sheaf-like nanostructures, could be simply prepared by con- trolling the concentrations of the starting reactants. The optical measurements on the obtained Eu（BTC）（H20）- DMF indicated that all the nanomaterials show the characteristic emissions of the Eu3＋ ions at 578, 590, 612, 650, and 699 nm, which were at- tributed to 5Do→7FJ （J=0-4） transitions of the Eu3＋ ion, respectively. It was also noticed that the luminescent properties of the as-prepared products were heavily dependent on the morphologies and sizes of the nanomaterials. The assembled straw-sheaf-like architectures displayed the strongest emissions and the longest luminescence lifetime, which was mainly due to the fewest surface defects.
The search of electrode materials with high electrochemical activity is one of key solutions to actualize both high energy density and high power density in a supercapacitor. Recently, we have developed one novel kind of rare earth and transitional metal colloidal supercapacitors, which can deliver higher specific capacitance than electrical double-layer capacitors(EDLC) and traditional pseudocapacitors. The electrode materials in colloidal supercapacitors are in-situ formed electroactive colloids, which were transformed from commercial rare earth and transitional metal salts in alkaline electrolyte by chemical and electrochemical assisted coprecipitation. In these colloidal supercapacitors, multiple-electron Faradaic redox reactions can be utilized, which can deliver ultrahigh specific capacitance often larger than one-electron capacitance. Multiple-valence metal cations used in our designed colloidal supercapacitors mainly include Ce3+, Yb3+, Er3+, Fe3+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Sn2+ and Sn4+. The colloidal supercapacitors can be served as the promising next-generation high performance supercapacitors.
