Deposition and corrosion studies of plasma arc thermal sprayed Zn and 85Zn-15Al films on steel surface

Abstract

The corrosion of the structural steel exposed in coastal area is a big challenge for the researchers. Therefore, researchers are using different coating processes. The thermal spray coating is a convenient and easy process being used in thermal barrier coatings, electromagnetic pulse (EMP), wear and corrosion resistance. In plasma thermal spray technology, inert gas is used to create plasma, while in the present studies, we have considered normal air to deposit a 100 mu m thick pure Zn and 85Zn-15Al film by plasma arc thermal spray process to control the corrosion of steel immersed in artificial ocean water and their properties are assessed by different techniques. The scanning electron microscopy (SEM) results of 85Zn-15Al deposited film show the dense and around 3 times reduced porosity compared to pure Zn attributed to the higher melting point and surface tension of Al, which make the substrate soften compared to Zn as well as exhibits hydrophobicity and, enhance the bond adhesion. The open-circuit potential (OCP) of the 85Zn-15Al film is found to be nobler and stabilized compared to pure Zn with immersion periods in artificial ocean water. The electrochemical impedance spectroscopy (EIS) results reveal that the film resistance (R-f) and charge transfer resistance (R-ct) of the 85Zn-15Al are greater than pure Zn attributed to the compact and regular morphology of the film, which stifle the ingress of solution. Therefore, the corrosion rate of 85Zn-15Al film is found lower compared to pure Zn after 552 h of immersion in artificial ocean water solution might be attributed to the formation of Zn-5(OH)(8)Cl-2 (simonkolleite), Zn-5(OH)(6)(CO3)(2) (hydrozincite) and Zn-Al layered double hydroxide (Zn6Al2(OH)(16)CO3: Zn-Al LDH) where Al in alloy film facilitates to form these corrosion products in alkaline solution by direct precipitation reaction and make the film impervious for penetration of solution.