Preparation and Research on 2-Methylimidazole-Lanthanum Nickel-Based Sol-Gel Conversion Coating for Oxide Scale Reinforcement Bars

Corrosion induced by defective oxide scales severely compromises the durability of concrete structures. This study develops a dual-mechanism sol-gel protection strategy based on La3+/Ni2+/2-Methylimidazole (2-MI). First, 2-Methylimidazole-catalyzed epoxy ring-opening constructs defect-minimized Si–O–Si/C–O–C networks through 60 °C low-temperature curing, reducing microcrack formation and curing energy consumption compared to conventional 130 °C processing. Second, utilizing 400 °C waste heat from hot-rolled steel triggers pH-modulated La2O3/NiO co-deposition within oxide scale defects, enhancing corrosion resistance. After a 40-day immersion in SCP + 0.1 M NaCl, the coated reinforcement exhibits a low-frequency impedance modulus of 25.6 kΩ·cm2, achieving a 10.4-fold increase over untreated steel. Specimens embedded in 3.5 wt% NaCl mortar demonstrate a 120-day impedance modulus of 74.63 kΩ·cm2, exceeding the control by 8.03-fold. This strategy integrates efficient industrial waste heat utilization with energy-saving low-temperature curing, providing long-term corrosion protection for marine concrete structures.