Enhance corrosion behavior of AZ31 magnesium alloy by tailoring the anodic oxidation time followed by heat treatment in simulated body fluid

Purpose This paper aims to investigate the impact of anodizing time and heat treatment on morphology, phase and corrosion resistance of formed coating. To characterize the anodic oxide layer, X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) that was equipped with energy dispersive spectroscopy (EDS) was hired. The corrosion behavior of oxide-coated samples was estimated by electrochemical polarization test in simulated body fluid (SBF). Design/methodology/approach Anodic oxidation method is applied to reinforce the corrosion and biological properties of biomaterials in the biomedical industry. In this paper, the alkaline NaOH (1 M) electrolyte was used for AZ31 magnesium alloy anodizing accompanied by heat treatment in the air. Findings It can be concluded that the best corrosion resistance belongs to the 10 min anodic oxidized sample and among the heat-treated samples the 30 min anodized sample represented the lowest corrosion rate. Originality/value In this study, to the best of the authors’ knowledge for the first time, this paper describes the effect of anodizing process time on NaOH (1 M) electrolyte at 3 V on corrosion behavior of magnesium AZ31 alloy with an alternate method to change the phase composition of the formed oxide layer. The morphology and composition of the obtained anodic oxide layer were investigated under the results of SEM, EDS and XRD. The corrosion behavior of the oxide coatings layer fabricated on the magnesium-based substrate was studied by the potentiodynamic polarization test in the SBF solution.

The electrical current characteristics of thermally annealed Co/anodic oxide layer/n-GaAs sandwich structures

The Co/anodic oxide layer/n-GaAs MOS structures have been fabricated by us. The MOS structures have shown an excellent rectifying behavior before and after thermal annealing of 500[Formula: see text]C for 2 min. It has been stated in the literature that the thermal annealing at a relatively low-temperature can improve the quality and performance of the anodic MOS structure. The current–voltage (I–V) measurements of the annealed MOS structure have been attempted in the measurement temperature range 60–320 K with the steps of 20 K. The I–V plot at 300 K has given the diode parameter values as barrier height [Formula: see text] = 0.96 eV and ideality factor n = 1.22, diode series resistance R[Formula: see text] = 124 [Formula: see text] for the annealed sample, and [Formula: see text] = 0.87 eV and n = 2.11, R[Formula: see text] = 204 [Formula: see text] for the nonannealed structure. A mean tunneling potential barrier value of 0.59 eV for the anodic oxide layer at the Co/n-GaAs interface has been calculated from the current–voltage–temperature curves. Furthermore, [Formula: see text](T) versus (2kT)[Formula: see text] curve has followed a double Gaussian distribution (GD) of the barrier heights. It has been stated that the double GD may be originated from the presence of the surface patches and phases arisen at the anodic oxide layer/n-GaAs interface.

About nature of the effective surface charge on InAs crystals transformation during anode oxide layer growing

Dynamics of changes in fluorine atoms distribution through grown anodic oxide layer thickness and the effective surface charge on InAs crystals under such layers has been studied. Anodic oxidation was performed in alkaline electrolyte with fluorochemical additive component in galvanostatic mode at anode current densities 0.05 or 0.5 mA·cm−2. The layers thickness in boundes 32—51 nm varied by electrodes final voltage setting in range 15—25 V. The layer thickness and refractive index was measured by ellipsometric method, and distribution of fluorine atoms through thickness — by photoelectron−spectroscopy method, combined with ion etching. At the same time, based on grown layers there were produced MIS structures, and from calculation of theirs capacitance−voltage characteristics are determined effective surface charge and surface states density, corresponding to different layer thicknesses.Main results are reduced to the facts during layers growing despite of anodizing current density comes their sealing, the profile of fluorine atoms distribution shifts towards InAs, positive effective surface charge gradually decreases from 3.6 · 1011 to 2.0 · 1011 cm−2 at surface states density in (6—7) · 1011 eV·cm−2 range for all cases. Based on comparison of these data and theoretical concepts of MIS structure charge construction, there was made a conclusion about gradual built−in charge distancing from the border with InAs in the process of growing anodic oxide layer, which explains observed effective surface charge decrease during layer thickness increasing. This results indicates that the layer growth rate exceeds the built−in charge displacement rate towards InAs.