The Effect of TiO2 as a Pigment in a Polyurethane/Polysiloxane Hybrid Coating/Aluminum Interface Based on Damage Evolution

The effect of titanium oxide as an additive on the performance of a polyurethane/polysiloxane hybrid coating was characterized by an electrochemical approach. The performance evolution was quantified by exposing the hybrid coating on an aluminum substrate to NaCl solution at pH 5 over time. Real-time measurements were performed to quantify and correlate the mechanisms that occur at the coating/substrate interface. Electrochemical impedance spectroscopy (EIS) quantified the hybrid coating/substrate interface performance over the course of the 263 days of exposure, and electrically passive elements described and characterized the degradation/performance stages upon exposure to the acidic NaCl solution. The addition of TiO2 produced hydrophobicity functionality, and TiO2 acted as a physical barrier layer that influenced the initial damage stage. Different exposure times were associated the different stages of damage evolution for the hybrid coating and coating/substrate interfaces. Electrochemical testing with high-resolution techniques such as AFM (atomic force microscope) and IFM (infinite focus microscope) characterized the coating surface and the interface performance and resolved the surface and defect formation observed with different levels of TiO2 content. Of the systems tested, the system with 10 wt% TiO2 provided the best corrosion inhibition

Transpassivity Characterization of the Alloy Uns N08367 in a Chloride-containing Solution

We investigate the transpassivity of super-austenitic stainless steel UNS N08367 in 2.5 M LiCl solution by using cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The CPP curve exhibits negative hysteresis, which indicates a transpassive dissolution process instead of pitting corrosion. The transition from the passive region to the transpassive region is characterized by EIS and equivalent circuit analysis. During the transpassive dissolution of the N08367 alloy, two reactions of adsorbed intermediates are dominant, as indicated by the two inductive loops at the transpassive region. The first inductive loop is associated with the faster reaction, i.e., the adsorption of Fe intermediates. This fast reaction is significantly influenced by the preferential dissolution of Fe during the transpassive dissolution. The second inductive loop is correlated with the adsorption of the Cr intermediate. In contrast to Fe, the Cr content on the surface increases in the transpassive region compared with the content in the passive region. The XPS spectra support the time and frequency domain approach for the preferential dissolution, and the dominant species resulted from the interfacial processes at the transpassive regio