Investigation of Corrosion Resistance and Surface roughness of Carbon Steel Treated with Zinc Phosphate Coating in saline water

Abstract

Carbon steel is widely used in industrial applications due to its mechanical properties and high availability. In order to improve its corrosion resistance and promote better adhesion between metal surfaces and subsequent treatments, zinc phosphate conversion coating is commonly used for surface pretreatment in various industries.

In this study, two zinc phosphating solutions were prepared and carbon steel samples were treated with these solutions at a temperature of 90 °C. The solutions contained nitric acid, zinc oxide, phosphoric acid, and sodium carbonate. Nickel carbonate was added to the solution to create different zinc phosphate layers on the surface of the carbon steel samples.

The research focused on evaluating the corrosion resistance and surface roughness of the samples before and after exposure to corrosive media . Potentiodynamic polarization (Tafel) and electrochemical impedance spectroscopy techniques (EIS) were used for evaluation. Additionally, the surface properties, specifically surface roughness, were assessed using scanning electron microscopy (SEM) after exposure to seawater with 3.5% sodium chloride NaCl

The SEM analysis revealed the impact of the corrosive solutions on the zinc phosphate coating layer. In the presence of 3.5% NaCl solution, the coating dissolved, exposing the carbon steel surface and leading to localized corrosion with pits. This resulted in a rough surface with deposited pitting corrosion products. Furthermore, incorporating nickel carbonate in the treatment of carbon steel significantly improved its corrosion resistance.

In summary, this study demonstrated that the addition of nickel carbonate effectively enhanced the corrosion resistance of carbon steel samples treated with zinc phosphate coating. The evaluation was performed using potentiodynamic polarization, electrochemical impedance spectroscopy, and surface roughness analysis. These findings contribute to the understanding of surface pretreatment methods for improving the performance and durability of carbon steel in various industrial applications.