Dual-functional anti-corrosion coatings with surface hydrophobicity and internal smart-releasing Ce3+ loaded in bentonite on carbon steel

Water-based coatings are gradually replacing traditional oil-based coatings for environmentally friendly applications, which creates a new paradigm in corrosion control of metallic components. In this work, water-based ZrO2–SiO2 sol-gel coatings were prepared for corrosion protection of carbon steel. The effects of the sol-gel ZrO2 to SiO2 ratio, coating thickness, corrosion inhibitor content and surface hydrophobicity on the coating physicochemical and anti-corrosion properties were investigated. The results showed that, compared to the pure silica coating, coating with 1/9 wt% ZrO2 in SiO2 matrix and coating thickness of 25 μm provided about 7 times higher corrosion resistance (impedance modulus 1.38 × 108 Ω cm2). A smart-releasing corrosion inhibitor containing Ce3+ ions (0.91 wt%) loaded into the layered structure of bentonite showed ability to delay the corrosion of substrate by 9 orders of magnitude by trapping Cl− ions from the environment and releasing Ce3+ ions at the cracked substrate surface. By applying a hydrophobic top layer, the water contact angle increased from 89° to 115°, which further increased the impedance modulus of the coating from 2.42 × 109 to 3.60 × 109 Ω cm2. The optimized coating passed salt spray standard corrosion test for 720 h (on scribed coating) due to the cathodic protection by corrosion inhibitor and shielding effects of a top hydrophobic layer. This work provides an enhanced strategy of dual-functional anti-corrosion coatings with surface water repellency and internal smart-releasing corrosion inhibitor for steel against environmental corrosion and damages with efficient self-healing functionality.