Abstract
Newly synthesized nanocomposite coatings containing polypyrrole (Ppy), silanes, and CoO nanoparticles (polypyrrole/silane/CoO nanocomposite) for magnesium alloy (AZ91) protection in 3.5% NaCl solution were investigated by electrochemical techniques and mechanical studies. Electrochemical impedance spectroscopic (EIS) analysis displayed a significant increase in the charge transfer (Rct: 7516.67 kΩ cm2) and coating resistances (Rc: 4825.32 kΩ cm2) for Ppy/MES/CoO nanocomposite coating compared to polypyrrole coating (Rct: 545.88 kΩ cm2 and Rc: 9.86 kΩ cm2) at 80 days of immersion. Potentiodynamic polarisation studies exhibited a significant reduction in the corrosion current for the Ppy/silane/CoO nanocomposite. The passive layer formed by the studied nanocomposite prevented the diffusion of aggressive ions into the coating. The addition of silane functionalized CoO nanoparticles into the polypyrrole coating slowed down the diffusion of ions by forming an enclosed pathway. This resulted in charge transfer inhibition at the Mg alloy/electrolyte interface which suppressed the dissolution of Mg alloy. Scanning electrochemical microscopic (SECM) analysis confirmed the presence of the lowest corrosion current of 2.5 nA for Ppy/MES/CoO coated Mg alloy and a higher corrosion current of 13.6 nA for polypyrrole coating at 80 days immersion. Surface morphological studies of synthesized nanocomposite coatings were investigated by scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX) and X-ray diffraction (XRD) technique. SEM/EDX analysis displayed the formation of passive corrosion product layers that hindered the dissolution of magnesium alloy. The improved mechanical properties were noticed for the nanocomposite coatings containing silane-modified CoO nanoparticles and polypyrrole.
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