Comparative Study of the Corrosion Resistance of Air-Plasma-Sprayed Ca2SiO4 and Al2O3 Coatings in Salt Water

Abstract

In this study, Ca 2 SiO 4 coating was sprayed on stainless steel substrate and the corrosion resistance of the as-sprayed coating was studied in salt water. At the same time, Al 2 O 3 coatings were produced by air-plasma-sprayed technology as comparison. Immersion test was carried out to evaluate the protection performance of coatings. Potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) plots were also analyzed. The results indicated that Ca 2 SiO 4 coatings showed a better protection performance than Al 2 O 3 coatings. During the immersion, various calcium carbonate crystals appeared on the surface of Ca 2 SiO 4 coatings. Ca(OH) 2 was released from Ca 2 SiO 4 coatings into NaCl aqueous solution, increasing the alkalinity, which is in favor of the formation of passivation film, and thus improves the corrosion resistance. Ca 2 SiO 4 coatings became denser after immersion due to the fact that the pores and micro cracks were filled with hydration products i.e., hydrated calcium silicate (C-S-H) gel. On the contrary, the microstructure of Al 2 O 3 coatings became loose and obvious rusty spots were observed on the surface after the immersion test.