Synthesis and characterization of corrosion-resistant hydrophobic Ca-Zn nanocomposite coatings on SAE 1020 steels

The present research focuses on preparation and characterization of calcium-oxide nanoparticles (CaO-NPs) using eggshell waste. Moreover, an electro-deposited calcium-zinc nanocomposite coating was applied to a steel substrate (SAE-1020), thereby creating a high-performance hydrophobic coating on the steel surface to mitigate corrosion. In the current research, the steel substrate was submerged in an electro-deposition bath and connected to a power source, with varying coating time intervals from 10 to 40 min to control the coating characteristics. The dried eggshell, Ca (OH)2 gel, CaO-NPs, steel substrate and coated samples were characterized using OES, XRF, TGA, UV-Vis, FTIR, SEM, XRD, coating adhesion, surface wetting and corrosion testing. The OES results confirm the steel grade as SAE-1020. The FT-IR confirmed the presence of required hydrocarbon groups for CaO-NPs. The UV-Vis and XRD peaks were used to verify the successful formation of CaO-NPs. Moreover, XRD peaks revealed the presence of CaZn13, Ca5Zn3 and CaZn3 compounds in the coated samples. Moreover, a coating duration of 40 min resulted in improved properties, including a hydrophobic contact angle of 132°, an adhesion strength of 46 N, and a reduced corrosion rate of 0.0248 mmpy. Similarly, electrochemical impedance spectroscopy confirmed that ED-40 exhibited the highest corrosion resistance, showing the largest Nyquist semicircle and the greatest Rc and Rct values. Immersion testing further supported this, as the ED-40 sample maintained the lowest and most stable pH over 14 days, indicating minimal corrosion, which was attributed to the presence of CaZn3 and CaZn13 compounds.