Zn-Ceramic Composite Coatings oil Carbon Steel

Abstract

Zn-ceramic composite coatings on carbon steel were prepared by a process consisting of two steps. The Zndiffusing coating was produced by a Zn-slurry process, followed by sol-gel deposition of Si0 2 or S1O2/AI2O3 layers. A Zn-Si0 2 or a Zn-Si02/Al 2 0 3 composite coating was formed on carbon steel. The sol-gel solutions used in these experiments were modified by dispersion of Si0 2 and α-Α1 2 0 3 powders. Microstructural studies showed that the top porous surface of Zn-diffusing coating on carbon steel was covered fully with the fine powders of Si0 2 and Si0 2 /Al 2 0 3 . The properties of the composite coatings were improved with the combined advantages of Zn and ceramic coatings. Erosion-corrosion, high-temperature oxidation and sulphidation tests were carried out, indicating that the corrosion resistance of the composite coatings in water and in 3.5 mass % NaCl solution was significantly improved. The composite coatings also showed greatly improved resistance to high-temperature oxidation in air and sulphidation in H 2 S atmosphere at 773K (500°C).