Roles of Chloride Ions in the Formation of Corrosion Protective Films on Copper

Abstract

Unambiguous evidence is presented that the chloride ions play a dual role in the formation of a micrometre thick film of polymerized [Cu-Cl-MBI] n . This occurs when the copper is exposed to 3 wt.% NaCl solution containing 1 mM of mixture of inhibitors 2-mercaptobenzimidazole, MBI, and octylphosphonic acid, OPA, in the molar ratio MBI:OPA of 9:1. The chloride ions act simultaneously as a promoter of polymerized [Cu–MBI] n /[Cu–Cl–MBI] n film formation and a reactant that is incorporated in the film, as confirmed by time-of-flight secondary ion mass spectrometry. Also, formation of a Cu2O film under the Cu-inhibitor film was proven by focused ion beam microscopy, with chemical analysis being employed at the cross-section of the thick polymerized film. The Cu(I) oxide underlayer, together with the porous straw-like morphology of the [Cu–Cl–MBI] n overlayer, is believed to be responsible for the excellent corrosion protection of copper, even in a chloride environment without the reservoir of MBI+OPA. We also report a new insight into the mechanism of degradation of the Cu–MBI/Cu–Cl–MBI film that results in the formation of (MBI)2 dimers. The inhibitor layer, formed in NaCl solution and containing the synergistic combination of MBI and OPA, showed outstanding resistance to degradation.

Small Concentrations of Nacl Help Building Stable Inhibiting Layers from 2,5-Dimercapto-1,3,4-Thiadiazole (Dmtd) on Aa2024-T3

“…The XPS results hence reveal the capability of DMTD (due to acidity increase) and NaCl to remove the native (hydro)oxide layer followed by DMTD deposition with or without oxidation. The observed trend is in good agreement with the EPN and pH evolution shown in Table1 suggesting the dissolution of the native Al (hydro)oxide and its effect on an increased deposition of DMTD at the surface as previously suggested for other alloys [37][38][39] and other inhibitors e.g. MBT [16,17].…”

Effect of refrigerant absorbent combinations in the corrosion resistance of copper as structural material in absorption refrigeration systems (ARS)

“…However, this compound can form normalCnormalunormalO2−, CuO and Cu(OH) 2 , which are highly protective, explaining the lower I corr (Table 2 and Figure 3c) and the high R p observed (Figures 4 and 5). It means that the Cl − ions act as promotors for forming the passive layer, as reported by Kozlica et al, who find that the Cl − dissolves the Cu − , producing cuprous chloride, forming complexes highly protective [39]. Finally, the S4 solution follows a typical degradation trend since Cu´s R p decreased to lower values (Table 3).…”

Studies of Benzotriazole on and into the Copper Electrodeposited Layer by Cyclic Voltammetry, Time-of-Flight Secondary-Ion Mass Spectrometry, Atomic Force Microscopy, and Surface Enhanced Raman Spectroscopy

“…Polymeric forms of Cu-BTA-Cl complexes were postulated previously for benzotriazole [90]. Furthermore, polymeric chloride complexes for 2-mercaptobenzimidazole (MBI) were also reported [91]. On the other hand, the occurrence of cuprous intermediates Cu + /Cu(I)BTA/CuCl that partially eliminate the inhibition properties of BTA was recently postulated [20].…”