Improved corrosion resistance of permanganate-phosphate conversion coat on steel surface by surfactants

Abstract In the present work, we studied the effect of the presence of different concentrations of each of Triton-X-100 and Tween-80 surfactants in the bath of permanganate-phosphate conversion coating (PPC) on the corrosion resistance and the microstructure of the prepared coats. The coats were investigated using a scanning electron microscope (SEM), an energy dispersive X-ray spectrometer (EDX), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization techniques. The SEM results show that, on addition of the surfactants to the PPC bath, the porosity of the coat decreases and the coating layer becomes more compact. EIS results indicated that the presence of 0.01 M Triton-X-100 or 0.01 M Tween-80 in the coating solution caused an increase in the protection efficiency of the coat up to 93.7% and 84.1%, respectively. The potentiodynamic polarization results indicated that the two surfactants mainly act as anodic inhibitors due to the adsorption of their molecules at the anodic sites of the surface of steel and retard its oxidation reaction. The EDX and XPS results confirmed the results of the other techniques. A mechanism for the role of the surfactants in the coating process was proposed using the results of XPS and the other techniques

Corrosion behavior of AA2024-T6 and AA6065-T6 alloys in reline

Deep eutectic solvents have been widely acknowledged as ionic liquid analogues, since they share many characteristics and properties with ionic liquids. The two major application areas of deep eutectic solvents have been metal processing and synthesis media; however, plenty of other applications have already been reported and predicted for these liquids. Reline, an eutectic mixture of choline chloride and urea, is a well known representative of deep eutectic solvents. Despite their importance in the contemporary technologies, the knowledge about the corrosivity of deep eutectic solvents is remarkably scarce. This article reports the results on the corrosivity of reline towards two Al alloys, namely AA2024-T6 and AA6065-T6. To measure the corrosion rates and characterize the passive film on the alloys in reline, electrochemical impedance and inductively coupled plasma optical emission spectroscopy methods were used, and the corrosion product composition was analyzed by X-ray photoelectron spectroscopy. Surface morphology and Volta potential were imaged by scanning electron microscopy, atomic force microscopy and scanning Kelvin probe force microscopy. The corrosion tests show that the two alloys are extremely stable in reline, and the passive layer is formed in the first three hours of immersion in the corrosive media. There is no evidence that electrolyte species are incorporated into the Al oxide protective layer through chemical bonding