Modification of Nano-α-Al2O3 and Its Influence on the Surface Properties of Waterborne Polyurethane Resin Composite Passivation Films

Silane coupling agent KH560 was used to modify the surface of nano-α-Al2O3 in ethanol-aqueous solution with different proportions. The particle size of nano-α-Al2O3 was determined by nano-particle size analyzer, and the effects of nano-α-Al2O3 content, ethanol-aqueous solution ratio and KH560 dosage on the dispersion and particle size of nano-α-Al2O3 were investigated. The material structure before and after modification was determined by Fourier transform infrared spectroscopy (FTIR). Aqueous polyurethane resin and inorganic components are combined with modified nano-α-Al2O3 dispersion to form chromium-free passivation solution. The solution is coated on the galvanized sheet, the adhesion and surface hardness are tested, the bonding strength of the coating and the surface hardness of the substrate are discussed. The corrosion resistance and surface morphology of the matrix were investigated by electrochemical test, neutral salt spray test and scanning electron microscope test. The chromium-free passivation film formed after the modification of nano-α-Al2O3 increases the surface hardness of galvanized sheet by about 85%. The corrosion resistance of the film is better than that of a single polyurethane film. The results show that the surface hardness and corrosion resistance of polyurethane resin composite passivation film are significantly improved by the introduction of nano-α-Al2O3.

Preparation of crystalline rare earth carbonates with large particle size from the lixivium of weathered crust elution-deposited rare earth ores

Crystalline rare-earth(RE)carbonates having large particle size were prepared from the lixivium of weathered crust elution-deposited rare-earth ores using the precipitation method with ammonium bicarbonate as the precipitant.Their chemical composition was studied using elemental and thermogravimetric analyses(TGA),and their structure and morphology were characterized using Fourier transform infrared(FTIR)spectroscopy,X-ray diffraction(XRD),and scanning electron microscopy(SEM).The results demonstrate that the crystalline rareearth carbonate is a hydrated basic carbonate or oxycarbonate and not astable intermediate carbonate in the process of thermal decomposition.The particle size of crystalline rare-earth carbonates with large particle size is in the range of 50–200μm.With an RE2O3 content of up to 95wt%,the quality of crystalline rare-earth carbonates is higher compared to the Chinese National Standard(GB/T 28882–2012).The quality of the product is superior to the Chinese National Standard.

Fabrication and Manipulation of Magnetic Composite Particles with Specific Shape and Size

The fabrication of microscale polyethylene glycol diacrylate（PEGDA） hydrogel particles was demon-strated via magnetic property ultraviolet（UV） lithography techniques, polydimethylsiloxane（PDMS） soft stamp pre-paration techniques and micro-nano imprint technology in this paper. The results of compositional and morphologicalcharacterizations of magnetic microparticles show that the Fe304 nanoparticles with an average diameter of 100 nmare uniformly dispersed in hydrogel. Owing to the excellent magnetism of Fe304 nanoparticles, the fabricated hydro-gel microparticles with different sizes and shapes were manipulated in water via applying an external magnetic fields.Three types of motions, translation, rotation and flip, were demonstrated with the manipulator. These microscalemagnetic PEGDA hydrogel particles have a great application potential in manufacturing process, micro/nanomotors,and machines.

Chemical synthesis and characterization of SmCo_(5)/Co magnetic nanocomposite particles

Magnetic nanocomposite material has been widely focused for the potential to become the next generation of magnetic material.In this paper,two kinds of chemical coating methods were used to prepare SmCo_(5)/Co nanocomposite particles which were further characterized and compared.The two methods were carried out by using different materials and at different temperatures.In Method I,oleylamine(OAm),oleic acid and Ca(acac)2 were used and the reaction was carried out at the temperature of 300℃.In MethodⅡ,anhydrous isopropanol,polyvinylpyrrolidone(PVP),N_(2)H_(4)·H_(2)O and CoCl_(2)·6 H_(2)O were used and the reaction temperature was~55℃.It was found that by using the two methods,the growth and the crystal structure of the Co nanoparticles(NPs)are different.In Method I,epitaxial growth on the surface of SmCo_(5) NPs was observed and the Co NPs were in a facecentered close packing crystal structure.While in Method II,the coated Co NPs were self-nucleated with a crystal structure of hexagonal close packing.Using MethodⅡwith the addition of surfactant,anisotropic nanocomposite particles were achieved with an enhanced saturated magnetization of 84.2 A·m^(2)·kg^(-1).And the coercivity change of the NPs illustrates that a nonmagnetic interlayer between the hard and soft magnetic phase is beneficial to maintain the coercivity.