Zirconia-based coatings on mild steel fabricated by atmospheric-pressure plasma processing for corrosion protection

Corrosion mitigation of steel by coatings produced from benign and environmentally-friendly alternatives to the toxic and carcinogenic hexavalent chromium systems remains a critical challenge. Here, we demonstrate that zirconia-based coatings can be produced by initially depositing a film from a precursor solution, and subsequently converted to a functional coating using an atmospheric-pressure microwave-powered plasma. The effects of processing parameters including microwave power, precursor concentration, pass spacing, and repetitions were studied by characterizing the morphology and chemical composition of the fabricated coatings using scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. Results show that changing the processing conditions has a complex effect on aspects of the coating including defects and degree of precursor conversion. From our parametric study, we found that the coatings could be optimized by multiple treatment repetitions, small pass spacing, lower precursor concentration in the solution, and higher plasma power. The ability of the coatings to prevent corrosion was assessed by linear polarization resistance measurements. We find six-fold decrease in the corrosion rate compared to a blank test, indicating that our approach is a promising candidate for the creation of corrosion-protective conversion coatings on steel that minimizes the use of harmful chemicals and chemical waste.