Papers by Keyword: Coating Time

Abstract: This paper reports the silica density, surface structures and optical properties of gold nanoparticles coated with different thickness of silica shells. The gold nanoparticles encapsulated with amorphous silica shells were prepared in a slight modification of Stǒber method. The silica-shell thickness could be varied from 20 to 50 nm by controlling the experimental conditions, such as reaction time. Transmission Electron Microscopy (TEM) and UV-Visible absorption spectroscopy were employed to characterize the size, shell density, surface structures and the optical properties of these silica-coated gold nanoparticles. The TEM images demonstrated that the density of the silica shell were depended on the reaction time, and the surface morphology was changed from porous structures in the initial coating to the final continuous and smooth silica surface. With the increasing of the reaction time, the silica-coated gold nanoparticles became more and more round and monodispersed. UV-Vis spectra showed that surface plasmon absorption peak had a red-shifted of 3~12 nm on increasing the thickness of silica shell from 20 to 50 nm. A possible mechanism of silica formation on gold nanoparticles was proposed on the basis of silica shell density and the shift of absorption peak of coated gold nanoparticles.

Abstract: Tensile properties of AZ91D magnesium alloy coated by Plasma Electrolytic Oxidation method for various coating times were investigated. The coatings on AZ91D magnesium alloy showed porous microstructure, and became thicker with increasing the coating time. After tensile test, the coated AZ91D magnesium alloy had lower tensile strength and elongation than the uncoated one. The tensile strength and elongation decreased with increasing the coating time, while the proof stress was almost no changed. The uncoated AZ91D magnesium alloy revealed ductile fracture surface. As the coating time increased, however, the fracture surface was changed to brittle fracture morphologies.

Abstract: Ceramic coatings were synthesized on pure magnesium, binary Mg-Al and Mg-Zn alloys by plasma electrolytic oxidation (PEO) technique, and their mechanical and electrochemical properties were investigated. The coatings showed porous microstructure and some volcano top-like pores on the surface. The coatings on Mg-Al alloys consisted of MgO, MgAl2O4 and Al2O3. In the coatings on Mg-Zn alloys, MgO and ZnO were detected. The hardness and wear resistance showed slight dependence on Al content but no tendency to increase with increasing Zn content. The coated Mg alloys with Al, Zn showed better corrosion resistance in 3.5%NaCl solution but poor corrosion resistance in methyl alcohol, compared to the coated pure Mg.

Abstract: Plasma electrolytic oxide coatings were produced on both pure magnesium and binary Mg-Al alloys containing 3, 6, 7 wt% Al, and the effect of Al on the characteristics of coatings was investigated under the processing conditions of various coating times and current. The coatings on Mg-Al alloys showed porous microstructure and some volcano top-like pores on the surface, and they consist of MgO and Al2O3. The surface roughness became larger with increasing coating time, while it was unchanged with increasing Al content. The thickness increased with increasing coating time and showed slight dependence on Al content. The hardness was almost unchanged with increasing coating time and Al content in the coatings grown with the ratio of current, C1:C2=100:75.