Bao-jia Li

Microstructure characterisation of alumina coating on steel by PEO

Abstract Alumina ceramic coating was prepared on Q235 carbon steel by plasma electrolytic oxidation. The discharge process was analysed according to the voltage–time curve. The microstructure of the ceramic coating was investigated by scanning electron microscopy, X-ray diffractometry and energy dispersive X-ray spectroscopy. The bonding strength, thickness, hardness, surface roughness and corrosion properties of the coatings were studied. The results indicated that coating on Q235 carbon steel mainly consisted of α-Al2O3 and γ-A12O3. The coating showed coarse and porous surface. The surface roughness of the coating was 1·8 μm, and the average diameter of the pores was 3–4 μm. The hardness of the coating was 1854 HV. The thickness of the coating was ∼28 μm, and the bonding strength was 23 MPa. The corrosion tests indicated that the corrosion current density of alumina coated Q235 in 3·5%NaCl was 8·289×10−7 A cm−2, which was decreased by two orders of magnitude compared with the uncoated one. The corrosion potential was increased to −0·379 V, which shifted positively by 0·303 V compared to the uncoated one.

Preparation and Spectral Analysis of Gold Nanoparticles Using Magnetron Sputtering and Thermal Annealing

Gold (Au) nanoparticles were prepared on Au-film-coated K9 glass and silicon substrates by direct current (DC) magnetron sputtering and thermal annealing treatment. The effects of substrate material, annealing temperature, and time on morphologies of Au nanoparticles were investigated, and the formation mechanism of Au nanoparticles was discussed. The experimental results indicate that silicon substrate is more suitable for the formation of Au nanoparticles. On a silicon substrate, Au nanoparticles formed with good spherical shapes at temperature over 700 °C. It was also found by spectral analysis that the field enhancement factor of the island-shaped Au particles was smaller than that of the granular Au particles; the better the spherical shape as well as the smaller the size and spacing of Au particles, the higher the light absorption rate; the absorption peak had a red shift with increasing particle size and spacing.