Growth characteristics and corrosion resistance of micro-arc oxidation coating on pure magnesium for biomedical applications

Effect of pulse frequency on the microstructure, phase composition and corrosion performance of a phosphate-based plasma electrolytic oxidation coated AM50 magnesium alloy

We have synthesized boron-doped single wall carbon nanotubes in a high vacuum chemical vapor deposition (CVD) system using a new boron precursor. Transmission electron microscopy was used in order to confirm the presence of single wall carbon nanotubes and field emission scanning electron microscopy to allow a qualitative characterization of the produced tubes. To estimate the doping level, we compared the Raman spectra with pure single wall carbon nanotubes and we found an upshifted G band as an evidence of doping. X-ray photoelectron spectroscopy analysis and ab initio electronic structure calculations reveals the presence of substitutional boron atoms incorporated on the tubes. We have also developed a simple method to determine quantitatively in which temperature range the carbon nanotubes are produced more efficiently by high vacuum CVD.

Production and Characterization of Boron-Doped Single Wall Carbon Nanotubes

Improvement in corrosion characteristics of AZ31 Mg alloy by square pulse anodizing between transpassive and active regions

Pulsed current hard anodizing procedures have been applied to the widely used heat treated aluminum alloys AA2024-T3, AA6082-T6 and AA7075-T6. The influence of frequency and of current amplitude on anodic oxide thickness, hardness, defectiveness, volumetric expansion ratio and on process faradic efficiency has been studied. Higher frequencies generate a decrease in coating electric resistance and in general they are less effective in order to overcome typical critical issues arising in alloys difficult to be anodized. In AA2024-T3 and AA6082-T6 higher frequencies led to slight increase in thickness, decrease in compactness and faradic efficiency while hardness remained almost constant or a bit higher. With higher frequencies in AA2024-T3 defective state significantly got worse, in AA6082-T6 it improved. In AA7075-T6 an almost frequency independent behavior occurred. The highest wave amplitude with a slightly cathodic “off” current (reverse pulse) allowed to obtain greater thickness, hardness and compactness while other current amplitudes did not show significant influence on properties analyzed; a very low, but still anodic, “off” current however induced slight hardness decreases.

Di Li

Papers

Formation mechanism of pulse current anodized film on AZ91D Mg alloy