Biochar nanoparticles in zinc epoxy coatings: Dual-function as conductive filler and inhibitor carrier for enhanced anticorrosive performance

In this work, the potential of utilizing biochar nanoparticles (BCN) as a dual-function component in zinc epoxy coatings (ZEP): serving as both a conductive pigment and a carrier for corrosion inhibitors, was unleashed. Tannins (TA) and benzotriazole (BTA) were loaded into BCN, with loading capacities at 13.5 wt% and 9.0 wt% calculated based on thermogravimetric analysis (TGA). Release tests indicated a pH-dependent behavior favoring alkaline conditions for both inhibitors. Approximately 35 wt% and 67 wt% of the loaded inhibitors were released at pH = 12 for TA@BCN and BTA@BCN, respectively. Open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) demonstrated that incorporating BCN enhanced the conductivity between zinc particles, thereby improving galvanic protection. The charge transfer resistance (Rct) at the coating/steel substrate interface of TA@BCN or BTA@BCN remained more stable after 25 days of immersion in the 3.5 wt% NaCl solution compared to those with neat BCN, indicating improved inhibition protection. Reduced steel corrosion was observed at the artificial scribe during neutral salt spray testing ascribed to the released inhibitors. This study introduced a facile, cost-effective, and environmentally friendly approach to boosting the performance of ZEP in a neutral corrosive environment.