Abstract
Aluminum coating was deposited by arc thermal spraying process onto the steel substrate for the corrosion protection in aggressive environment. However, the arc thermal sprayed coating possesses defects in the coating. Thus, it is important to reduce the defects and enhance the corrosion resistance properties of the deposited coating using post-treatment. In the present study, we have used different concentrations of sodium phosphate mono basic (NaH2PO4) with 0.1 molar (M) calcium nitrate [Ca(NO3)2] as post-treatment solution to fill out the defects of the Al coating. It was observed by scanning electron microscopy (SEM) that 1 M NaH2PO4 with 0.1 M Ca(NO3)2 treated sample exhibited 71% reduction in defects compared to as coated samples. X-ray diffraction (XRD) was performed to determine the phases formed on the coating surface after treatments. XRD confirms the formation of sodium aluminum hydrogen phosphate (Na3Al(OH)(HPO4)(PO4)) and brushite (Ca(HPO4)(H2O)2) as composite oxides on the Al coating. Electrochemical results show that 0.5 M NaH2PO4 with 0.1 M Ca(NO3)2 treated sample has exhibited the highest charge transfer resistance and the lowest corrosion current density after 89 days of exposure in 3.5 wt.% NaCl solution. The enhancement in corrosion resistance of 0.5 M NaH2PO4 with 0.1 M Ca(NO3)2 treated sample attributed to the formation of adherent, sparingly soluble, and stable corrosion products. The volume fraction result of the corrosion products formed on 0.5 M NaH2PO4 with 0.1 M Ca(NO3)2 treated sample after 89 days of exposure in 3.5 wt.% NaCl using XRD confirms the highest amount of Bayerite (α-Al(OH)3) deposition, thus, the corrosion rate of this sample was the lowest.
Highlights
The economic loss of the most advanced countries due to corrosion is estimated to be about3%–4% of gross domestic product [1,2,3]
We have found that adding 0.1 M calcium nitrate in a 0.5 M SP solution dramatically enhances the morphological and corrosion resistance properties of Al coating deposited by an arc thermal spray coating process
Nc/t value of as coated (AC), SPCN1, and SPCN2 is gradually increased with exposure periods and it is found that SPCN2 shows 0.79 after 89 days of exposure which reveals that the coating becomes homogenous
Summary
The economic loss of the most advanced countries due to corrosion is estimated to be about3%–4% of gross domestic product [1,2,3]. The economic loss of the most advanced countries due to corrosion is estimated to be about. Coatings 2020, 10, 33 corrosion using a barrier type of coating, galvanization, cathodic and anodic coating, inhibitor, corrosion resistance alloys, etc. The coating can be deposited onto the substrate depending on applications and requirements. Organic coating is being used which helps to isolate the metallic substrates from the solution. Such type of coating is called passive coating. This type of coating is used for failure, owing to mechanical damages, but it can be minimized using inorganic anticorrosion pigment [5,6]
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