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.

Direct observation of the plasmon-enhanced palladium catalysis with single-molecule fluorescence microscopy

Plasmonic nanostructures have been proved effective not only in catalyzing chemical reactions,but also in improving the activity of non-plasmonic photocatalysts.It is essential to reveal the synergy between the plasmonic structure and the non-plasmonic metal photocatalyst for expounding the underlying mechanism of plasmon-enhanced catalysis.Herein,the enhancement of resazurin reduction at the heterostructure of silver nanowire(AgNW)and palladium nanoparticles(PdNPs)is observed in situ by single-molecule fluorescence microscopy.The catalysis mapping results around single AgNW suggest that the catalytic activity of PdNPs is enhanced for~20 times due to the excitation of localized surface plasmon resonance(LSPR)in the vicinity of the AgNW.This catalysis enhancement is also highly related to the wavelength and polarization of the excitation light.In addition,the palladium catalysis is further enhanced by~10 times in the vicinity of a roughened AgNW or a AgNW-AgNW nanogap because of the improvement of catalytic hotspots.These findings clarify the contribution of plasmon excitation in palladium catalysis at microscopic scale,which will help to deepen the understanding of the plasmon-enhanced photocatalysis and provide a guideline for developing highly efficient plasmon-based photocatalysts.

Air plasma-sprayed high-entropy (Y_(0.2)Yb_(0.2)Lu_(0.2)Eu_(0.2)Er_(0.2))_(3)Al_(5)O_(12) coating with high thermal protection performance

High-entropy rare-earth aluminate(Y_(0.2)Yb_(0.2)Lu_(0.2)Eu_(0.2)Er_(0.2))_(3)Al_(5)O_(12)(HE-RE_(3)Al_(5)O_(12))has been considered as a promising thermal protection coating(TPC)material based on its low thermal conductivity and close thermal expansion coefficient to that of Al2O3.However,such a coating has not been experimentally prepared,and its thermal protection performance has not been evaluated.To prove the feasibility of utilizing HE-RE_(3)Al_(5)O_(12) as a TPC,HE-RE_(3)Al_(5)O_(12) coating was deposited on a nickelbased superalloy for the first time using the atmospheric plasma spraying technique.The stability,surface,and cross-sectional morphologies,as well as the fracture surface of the HE-RE_(3)Al_(5)O_(12) coating were investigated,and the thermal shock resistance was evaluated using the oxyacetylene flame test.The results show that the HE-RE_(3)Al_(5)O_(12) coating can remain intact after 50 cycles at 1200℃ for 200 s,while the edge peeling phenomenon occurs after 10 cycles at 1400℃ for 200 s.This study clearly demonstrates that HE-RE_(3)Al_(5)O_(12) coating is effective for protecting the nickel-based superalloy,and the atmospheric plasma spraying is a suitable method for preparing this kind of coatings.

Atomic-resolution investigation of structural transformation caused by oxygen vacancy in La_(0.9)Sr_(0.1)TiO_(3+δ)titanate layer perovskite ceramics

Perovskite functional ceramics have been widely applied for thermal protection owing to their unique physical properties.However,formation of oxygen vacancies under external stimuli usually limits their performance in practical applications.Therefore,the mechanism of the effect of oxygen vacancy on the layer structure of perovskite La_(0.9)Sr_(0.1)TiO_(3+δ)was investigated by experiments and first-principles simulations.The experimental results showed that the lattice distortion occurred in oxygen-deficient environment to give a longer c-axis,along with a significant adjustment in the modes of A/B–O bond vibration,resulting in lower reflectivity.Advanced transmission electron microscopy studies revealed that oxygen vacancies induced localized atomic rearrangements via[TiO_(6)]layer movements to adapt to the lattice distortion.This eventually restructured a part of the layer interfaces by expanding the overlapping projection of atoms in the c-axial direction.The specific transformation process was described as a compendious process,while geometric phase analysis effectively clarified how oxygen vacancies can inhibit reflectivity on the layer structure.Thus,this study provides effective approaches for researching the effects of oxygen vacancy on the physical properties of orthorhombic layer perovskite structures,which may facilitate the development of perovskite-based functional devices.