Corrosion inhibition at galvanized steel cut edges by phosphate pigments

Phosphate ions as corrosion inhibitors for reinforcement steel in chloride-rich environments

“…Some authors consider that phosphates are anodic inhibitors, being effective only in the presence of oxygen [14][15][16]. Other authors suggest that they act as cathodic inhibitors for [PO 4 -3 ]/[Cl -] ratios lower than 0.6 while they behave as mixed inhibitors for [PO 4 -3 ]/[Cl -] ratios higher than 0.6 [17,18].…”

Effect of Phosphate and Chromate Pigments on Sacrificial Corrosion Protection by Al–Zn Coating and Delamination Mechanism of Pre-painted Galvalume Steel

“…In phosphate or chromate containing solutions, a deposition layer composed of phosphates or Cr(III) oxyhydroxides was probably formed on steel substrate, inhibiting the oxygen reduction reaction. 4,18,21,26) However, the KPFM results of this study indicate that the corrosion potential of the steel substrates was not significantly influenced by the anti-corrosive pigments; as such, the pigments themselves appear to act as anodic inhibitors that suppress the dissolution rate of the Al-Zn layer.…”

“…Simões et al reported that a Zn 3 (PO 4 ) 2 film formed on the Zn layer was locally destroyed in a chloride-containing solution, and the anodic dissolution of Zn occurred even when the Zn surface was covered by the corrosion products. 18) It was concluded that the anodic dissolution of the Al-Zn was not inhibited due to the local breakdown of the layer of the corrosion products on the Al-Zn surface in the polarization measurements. The polarization measurements were performed in 0.1 M NaCl solution, and the cyclic wet/dry test (JASO M 609-91) was carried out using 0.856 M NaCl solution as the salt water.…”

“…[18][19][20][21][22][23] Simões et al studied the corrosion inhibition mechanism of sodium phosphate (Na 3 PO 4 ) at the cut edges of electrogalvanized steels using scanning vibration electrode technique (SVET) and electrochemical impedance spectroscopy (EIS) in phosphate-containing 0.1 M NaCl solution. They summarized that Zn 3 (PO 4 ) 2 , which was formed by the reaction between phosphate and Zn ions, inhibited the anodic dissolution of Zn; 18,19) however, the protective performance of Zn 3 (PO 4 ) 2 was lower than that of zinc chromate. 20) Zin et al reported that the deposition of compact calcium/zinc phosphate species on the Zn coating layer and the steel substrate highly improved the efficiency of the inhibition effect of phosphates on cut-edge corrosion.…”

Performance of a Magnesium-Rich Primer on Pretreated AA2024-T351 in Full Immersion: a Galvanic Throwing Power Investigation Using a Scanning Vibrating Electrode Technique

“…localized corrosion and its inhibition for steel, magnesium and aluminum substrates using organic and inorganic inhibitors. [36][37][38][39][40][41][42][43] The main advantage of using in-situ SVET over conventional electrochemical and non-electrochemical techniques is that it is capable of analyzing both the net anodic and cathodic behavior of the primer/defect galvanic couple and the local anodic activity associated with AA2024 micro-galvanic couples. The suppression of corrosion at artificial defects on AA2024 is somewhat different than that for a conventional galvanic couple in a stationary electrochemical system where anodic and cathodic kinetics are static with time.…”