Research was conducted on the microstructure, composition, and properties of a ceramic coating deposited on the surface of an aluminium matrix composite (10Al2O3f –ZL109) using microarc oxidation. The influence of different matrixes and reinforcements on the microstructure, properties, and deposition parameters of the ceramic coatings was studied. Both factors showed considerable effects, though the matrix composition had more influence. The results also showed that mullite ceramic coatings can be successfully deposited on the surfaces of aluminium matrix compos ites. The coating was composed of two layers, a porous layer and a dense layer.
The effects of adding Na2 WO4. 2H2O and SiC powder to the electrolyte on the characteristics of ceramic coatings on Al based alloys formed by microarc oxidation were studied. The ceramic coating quality was improved by the two additives, but the addition of Na2 WO4. 2H2O was more effective, as it improved the formation of Al2O3 phase in the ceramic coating, increased the ratio of the internal dense region to the whole ceramic coating, optimised the ceramic coating phase structure, and improved its wear resistance. The SiC powder was able to enter into the ceramic coating and improve its wear resistance, at the same time increasing the friction coefficient of the coating.
The effects of pre-charged hydrogen on electrochemical behavior of Alloy 690 in solutions of various bicarbonate concentrations were investigated by measurements of open circuit potential, anodic polarization curves and electrochemical impedance spectroscopy. Charged-hydrogen shifted the open circuit potential in the negative direction, decreased the electrochemical impedance, increased the anodic current density. In general, charged hydrogen accelerated the interfacial reaction kinetics for Alloy 690 in bicarbonate solutions.
At present passive hydrogen recombiners (PAR) are used to prevent hydrogen explosion. Hydrogen removal catalyst is the core component of PAR. The adsorption of hydrogen on the solid catalyst surface is the premise of catalytic hydrogen removal and is of great significance for deeper understanding of hydrogen removal mechanism. The adsorption behavior of H2-Pt Pd/γ-Al2O3 system has been studied by using density functional theory and periodic slab model. The results of different adsorption sites indicate the adsorption energy of top site is highest, which is -1.2584eV. Higher adsorption energy means stronger interaction between H2 and catalyst substrate, which elongates H-H bond and increases the negative charge on H2. With increasing doping content of Pd, the adsorption energy of substrate decreases gradually. The adsorption energy absolute value of Pt4/γ-Al2O3 is highest and its H-H bond is longest, arriving at 0.0967nm. After adsorbed on substrate, the energy gap of H2 decreases drastically with the lowest energy gap of H2-Pt4/γ-Al2O3 that is 0.5197eV, and the peaks of density of state pattern move to lower energy level. This is because that the d orbital of Pt/Pd atoms interacts with the τ* anti-bond orbital of H2 strongly, transferring electrons to the τ* anti-bond orbital of H2. Doping Pd increases the energy gap of molecule orbital.
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