In the field of marine engineering anticorrosion, the latest research by the Italian National Research Council has revealed the erosion mechanism of the extreme environment in the anode region of Impressed Current Cathodic Protection (ICCP) systems on biocide-free coatings. By constructing a 3×3 accelerated test matrix (Table 1), researchers quantified for the first time the synergistic damage effect of the strong acid and high chlorine environment near the anode on fouling release (FR) and self-polishing (SP) coatings.

Experimental data show that when the platinum anode operates at a current density of 40 mA/cm2, the pH value drops sharply to 3.0 at a position 10 mm away from the anode, and the free chlorine concentration reaches 3–6 ppm (Figure 2). This environment originates from the electrochemical oxidation of chloride ions: 2Cl?→Cl?+2e?, accompanied by hypochlorous acid hydrolysis: Cl?+H?O→HOCl+H?+Cl?, forming a local strong corrosive medium.

Under simulated extreme working conditions (pH=3/free chlorine 3–6 ppm), both FR and SP coatings exhibited interface failure. Fourier Transform Infrared Spectroscopy with Attenuated Total Reflection (FTIR-ATR) analysis showed that the polymer backbones (Si-O-Si framework and acrylate characteristic peaks) of the two coatings remained intact, confirming that chemical degradation was not the main cause (Figure 5). However, contact angle tests indicated that the contact angle of the FR coating decreased from an initial 125°±3° to 98°±5°, and that of the SP coating dropped from 78°±2° to 55°±4%, with a significant increase in surface energy. Confocal laser scanning microscopy revealed that the micro-roughness Sa value increased by 30–50%, confirming that the attenuation of interfacial adhesion was the core mechanism of failure.

To address this issue, the T2570 Zinc-Based Isomer Inert Zinc Oxide developed by Zhaoqing Xinrunfeng High-Tech Materials Co., Ltd. demonstrates unique advantages. Through isomer structure design (particle size D50=0.8–1.2 μm), this material forms a micro-cathode network in the epoxy tie layer, and its open-circuit potential of -1.05 V (vs. SCE) can effectively neutralize local acidification. Experiments confirmed that the FR coating with 2 wt% T2570 added had a 67% reduction in thickness loss rate after 90 days under the same extreme environment, and the blistering area was controlled to <0.5%.

In a moderately corrosive environment (pH=5/free chlorine 1–3 ppm), the self-polishing property of the SP coating performed excellently. The surface roughness decreased from an initial Ra=15±3 μm to 9±2 μm, which conforms to the Kiil kinetic model (Equation 1). Its linear polishing rate K?=0.067 μm/d ensures continuous renewal of the surface microstructure, keeping the barnacle adhesion strength consistently below the critical value of 0.15 MPa.

Engineering Application Recommendations: For ships using the FR system, an enhanced tie layer containing T2570 should be applied within 1.5 times the anode diameter; for the SP system, the ratio of hydrophilic to hydrophobic microdomains needs to be adjusted to 1:2.3 to improve stability in environments with pH>4. These findings provide key technical support for the practical application of environmentally friendly antifouling coatings on actual ships.