Abstract
Corrosion of metals leads to high maintenance costs, as well as potential threats to structural health and safety. Here, we demonstrate the coating of cobalt tungstate (CoWO4) nanoparticles (NPS)/5-mercapto-1-phenyl-1 H-tetrazole derivative (MPT) used as a nano-composite film on Cu surface for the blocking of micropores to hinder the propagation of metastable pits in an aggressive NaCl medium. The mechanism of interaction between the nanoparticles and tetrazole derivative, in addition to the mode of anchoring to the metal surface and blocking the penetration of chloride ions (Cl−), are all investigated. In this investigation, CoWO4 is synthesized via a wet chemical route and thereafter, is combined with MPT at an optimized ratio thus formulating a nano-composite corrosion inhibitor which in solution gets coated on Cu surface. Atomic force and scanning electron microscopic images of the bare Cu reveal dip pits, which by the coating of the nano-composite are suppressed at the nucleation stage during exposure to the aggressive 3.5% NaCl electrolyte under flow conditions. Electrochemical analysis shows high protection of Cu up to 97% efficiency in the presence of the newly formulated nano-composite inhibitor film.
Highlights
Initiation of pits is usually attributed to film breakdown and passivity characteristics, whereas a pitting propagation process is influenced by factors, such as electrochemical potential, alloy composition, electrolyte concentration, and temperature [1,2,3,4]
Cobalt (II) acetate tetrahydrate [(Co(CH3 COO)2 ·4H2 O] with 98% purity, TX-100 surfactant (Polyethylene glycol tert-octylphenyl ether) (C14 H22 O(C2 H4 O)n ) 96%, Acetone (CH3 CoCH3 ) 99.0%, ethanol (CH3 CH2 OH) 96% sodium tungstate (Na2 WO4 ) 99%, and sodium chloride (NaCl) 99.8%, were all purchased from Sigma-Aldrich, Chennai, India. 5mercapto-1-phenyl-1H-tetrazole (C7 H6 N4 S) 98% was supplied by TCI chemicals, Chennai, India and a 99.999% pure copper rod was procured from Alfa Aesar, Chennai, India
Electrochemical methods and advanced surface techniques were employed to investigate the effectiveness of a wet chemical coating made of C-MPT nanocomposite inhibitor on Cu for corrosion mitigation
Summary
Initiation of pits is usually attributed to film breakdown and passivity characteristics, whereas a pitting propagation process is influenced by factors, such as electrochemical potential, alloy composition, electrolyte concentration, and temperature [1,2,3,4]. Studies performed on metastable and stable pit growth of metals and alloys have shown that the dissolution of metals via pitting corrosion tends to be stochastic rather than a visible catastrophic process, which makes the material failure more life-threatening than other corrosion damages [5,6,7]. Previous studies on pitting corrosion have shown that it is difficult to experimentally conclude on its mechanism due to the random nature and frequent breakdown of the protective film during the electrochemical corrosion reactions [5,7,8,9]. The degradation process starts with micro pits that later develop into big metastable holes [10]
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