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Effect of Sodium Phosphate and Calcium Nitrate Sealing Treatment on Microstructure and Corrosion Resistance of Wire Arc Sprayed Aluminum Coatings

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Department of Architectural Engineering, Hanyang University, 1271 Sa 3-dong, Sangrok-gu, Ansan 15588, Korea
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Department of Chemistry, Sri Baldeo Post Graduate College-Baragaon, Mahatma Gandhi Kashi Vidyapeeth University, Varanasi 221204, India
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Intelligent Construction Automation Center, Kyungpook National University, 80, Daehak-ro, Buk-gu, Daegu 41566, Korea
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Innovative Durable Building and Infrastructure Research Center, Department of Architectural Engineering, Hanyang University, 1271 Sa 3-dong, Sangrok-gu, Ansan 15588, Korea
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Civil Engineering Department, College of Engineering, Prince Sattam Bin Abdul-Aziz University, Al-Kharaj 11942, Saudi Arabia
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Authors to whom correspondence should be addressed.
Coatings 2020, 10(1), 33; https://doi.org/10.3390/coatings10010033
Received: 28 November 2019 / Revised: 23 December 2019 / Accepted: 29 December 2019 / Published: 1 January 2020
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. View Full-Text
Keywords: aluminum; steel; coating; corrosion; cathodic protection; arc thermal spray; scanning electron microscopy; X-ray diffraction aluminum; steel; coating; corrosion; cathodic protection; arc thermal spray; scanning electron microscopy; X-ray diffraction
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Lee, H.-S.; Kumar, A.; Mandal, S.; Singh, J.K.; ASLAM, F.; Alyousef, R.; Albduljabbar, H. Effect of Sodium Phosphate and Calcium Nitrate Sealing Treatment on Microstructure and Corrosion Resistance of Wire Arc Sprayed Aluminum Coatings. Coatings 2020, 10, 33.

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