Phosphate glass doped with niobium and bismuth oxides as an eco-friendly corrosion protection matrix of iron steel in HCl medium: Experimental and theoretical insights

A phosphate glass (PG) composite based on the ternary system 75 mol% P2O5–15 mol% Nb2O5–10 mol% Bi2O3 was fabricated via the one-step melt-quench method and its anti-corrosion performance was evaluated using systematic experimental and theoretical approaches. XRD, Raman spectroscopy, AFM and SEM-EDX techniques were used to confirm the successful synthesis of PG. XRD and DSC disclosed the amorphous nature of the fabricated glass. Weight loss method, Tafel polarization and EIS revealed high inhibition performance of the doped PG toward low carbon steel in the aggressive 1 M HCl medium at different temperatures. Tafel polarizations demonstrated the superior corrosion protection of PG via a mixed-type mechanism with anodic predominance. The protection efficiency, obtained from EIS, increased with increasing the PG concentration, reaching up to 87 % for 250 ppm PG, which agrees with the Tafel analysis result. Further, SEM and AFM images verified that the steel surface is effectively protected by a robust layer of PG. Adsorption isotherms revealed that both physisorption and chemisorption are involved at the steel-electrolyte interface. Ab initio simulations were performed, for the first time on phosphate glass, and unraveled a shielding effect and high electron donating ability of PG, reflecting its strong adsorption, hence explaining its protection effectiveness at the molecular level.