Cerium Oxide Nanoparticles as an Accelerating Agent for Zinc Phosphate Coatings with Enhanced Corrosion Resistance

Cerium oxide (ceria, CeO۲) is a biocompatible ceramic oxide with a wide range of applications as catalysts, fuel cell systems, and sensors. In the present study, CeO۲ NPs were added to a zinc phosphate bath as an accelerator. The microstructural, morphological, and phase studies of coatings formed in the phosphating bath with and without CeO۲ NPs, were performed by scanning electron microscopy (SEM), field emission-SEM (FE-SEM), and X-ray diffraction spectroscopy (EDS). Besides, the corrosion behavior of phosphate coatings containing ۰, ۰.۰۴, ۰.۰۷, and ۰.۱ g/L of CeO۲ NPs was evaluated using the Tafel polarization method and electrochemical impedance spectroscopy (EIS). The results showed significant differences in the microstructure, roughness, and phase structure of phosphate coatings with and without CeO۲ NPs. The optimum addition of CeO۲ NPs to the phosphating bath was equal to ۰.۰۷ g/L, in which, as compared to typical phosphate coating, the coating weight increased from ۰.۵۱ to ۱.۷۳ mg/cm۲ while the corrosion current density decreased from ۱۲.۵ to ۲.۲ µA/cm۲. Furthermore, the coating porosity decreased from ۱۳.۹ to ۱.۷ percent due to creating a denser coating with much better coverage by CeO۲ NPs.

Keywords:

Zinc phosphate coating , Ceria nanoparticle , Phosphating bath accelerator , Phosphate coating morphology , Corrosion behavior study