LAUSR

ABSTRACT Corrosion is a major cause of economic failures and environmental concerns in industries. This study evaluated the corrosion rates of mild steel (MS), stainless steel (SS), aluminium (Al), and copper (Cu) in sodium silicate using potentiodynamic polarisation (PDP) and electrochemical impedance spectroscopy (EIS) at temperatures of 25, 50, and 70°C. Corroded metal samples at 25°C were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The PDP results revealed that SS had the lowest corrosion rates (CR) of 0.0002 mm/y at 25°C and 0.0085 mm/y at 70°C, while also maintaining a moderate CR of 0.0018 mm/y at 50°C, indicating superior corrosion resistance. MS recorded the lowest CR (0.0007 mm/y) at 50°C. Most corroded materials in NaSiO3 at 25, 50 and 70°C was Al with CR of 0.1245, 0.138 and 3.2817 mm/y. Corrosion rates and current densities (icorr) for all metals increased with temperature. The EIS analysis supported the PDP findings. XRD identified FeMnSiO4 as dominant phase in MS, phases of FeSiO3 and FeSi4O6 in SS, Al2O3 and aluminium complexations discovered on Al while Cu8H6O27Si8 was corrosion product on Cu. SEM analysis showed micrographs in SS having denser and more compact corrosion layer than that of MS, dimple-like spots were discovered on micrographs of Al while Cu surface was almost unaffected. In conclusion, stainless steel is suitable for both low and high-temperature applications in sodium silicate environments though mild steel is more appropriate for medium temperatures application.