Preparation Of Biochar Composite Coating And Its Anti-corrosion Performance On Carbon Steel Surface

Coating protection is one of the effective measures to prevent metal corrosion.Anti-corrosion materials are often added to coating fillers.Many anti-corrosion materials are expensive and unfriendly to the environment,which is an urgent problem for anti-corrosion researchers to solve.In this study,renewable,widely sourced and low-cost biochar was used as coating filler,and epoxy resin and sol-gel film were used as base coatings to study the anti-corrosion properties of composite coatings.（1）First,biochar with different sonication durations were prepared and added to epoxy resin substrates to prepare composite coatings.The mechanical properties and acid resistance tests showed that the biochar composite coating with ultrasonic for 0.5 h had the best adhesion（3.03 MPa）and the highest impact strength（14 Kg·cm）to the steel substrate,and remained stable after being soaked in an acid solution.It can maintain the lowest corrosion weight loss rate of 0.35%.This is attributed to the better lamellar structure of the biochar material after ultrasonication for 0.5 h,which can be dispersed uniformly in the epoxy resin substrate and form a stronger chemical cross-linking effect with the surface of the steel substrate.Then,biochar with different carbonization temperatures were prepared.Electrochemical tests showed that the biochar（T900）composite coating carbonized at 900℃could still maintain good corrosion resistance after soaking for 14 days(impedance modulus value of|Z|_0.01Hz=3.2110×10¹⁰Ω·cm²).This is because,compared with other lower carbonization temperatures,T900 biochar has higher stability,can reduce the volume expansion during the coating curing process,form a relatively smooth and dense coating,and the bonding force with the steel substrate is also relatively stable.（2）Biochar materials were modified by adding ammonium oxalate and zinc chloride,carbonization at temperatures of 600°C（T600）,700°C（T700）and 800°C（T800）,and added to sol-gel substrate to prepare composite coatings.XRD test showed that zinc oxide was present in T600 and T700 modified biochar,and the presence of zinc oxide increased the density of the coating and improved the defects of the surface structure of the coating.T700composite coating can resist 3H pencil hardness and maintain the lowest corrosion weight loss rate（0.89%）after immersion in acid solution.This shows that the coating can provide an effective anti-corrosion barrier for the steel matrix,reduce the corrosion rate of the steel matrix,and thus improve the protection effect of the steel matrix.