Effects of Bivalent Cations on Corrosion Inhibition of Steel by 1‐Hydroxyethane‐1,1‐diphosphonic Acid

Abstract

The influence of calcium and zinc ions on the corrosion inhibition effect of 1‐hydroxyethane‐1,1‐diphosphonic acid (HEDP) on carbon steel has been investigated by electrochemical techniques, X‐ray photoelectron spectroscopy, and atomic force microscopy. Addition of calcium or zinc ions greatly increased the inhibition efficiency of HEDP in a synergistic manner. The highest inhibition effect was obtained for molar ratios of Ca/HEDP = 0.5 and Zn/HEDP = 3 for 3×10−4 mol dm−3HEDP . The corrosion inhibition mechanism in the presence of these additives proved to be different from that with HEDP alone and was related to the formation of different complex species between HEDP and cation additives. The frequency response of the studied system was described by a transfer function containing two relaxation time constants corresponding to the charge‐transfer process and the porous oxide layer. Higher zinc and phosphorous content in the inhibitor layer and a continuous change in the O‒Fe and HO‒Fe ratio were achieved by increasing zinc concentration in the solution (in the range Zn/HEDP = 0.5–3) as supported by XPS measurements. Changes in the chemical structure were established in the oxide‐hydroxide layer developed spontaneously on the steel surface. The synergistic effect of inhibitor compounds appeared also in surface morphology, leading to the development of smooth, i.e., dense, protective layers as revealed by atomic force microscopy. © 1999 The Electrochemical Society. All rights reserved.

Surface Analysis of Carbon Steel Protected from Corrosion by a New Ternary Inhibitor Formulation Containing Phosphonated Glycine, Zn<sup>2+</sup> and Citrate

“…All these results indicate that there is formation of a protective film in the presence of the ternary inhibitor formulation. Several authors, who studied the inhibitory effects of phosphonate-based corrosion inhibitors, also reported that there is formation of thick and less permeable protective film on the metal surface [5,6,8]. They also concluded that the protective film consists of phosphonate-metal complexes.…”

“…Nakayama obtained a P 2p peak at 133.0 eV and attributed it to the presence of phosphonate compounds [48]. Felhosi et al observed a P 2p peak at 132.1 eV in the XPS of the surface film formed on carbon steel when immersed in a solution containing Zn 2+ and HEDP [5]. They interpreted this peak due to the presence of [Zn-HEDP] complex in the surface film.…”

“…It was also mentioned in their paper that such hydrous ferric oxides consist of Fe(OH) 3 and FeOOH. Felhosi et al studied the effects of bivalent cations on corrosion inhibition of steel by HEDP [5]. They mentioned that the O 1s peak at 531.4 eV is due to Fe-OH bond.…”

“…It was reported in literature that the Zn 2p 3/2 peak at 1022.8 eV was due to the presence of Zn(OH) 2 in the surface film [56]. Felhosi et al interpreted from the XPS analysis that there is formation of [Zn-HEDP] complex on the mild steel surface when immersed in a solution consisting of a mixture of HEDP and Zn 2+ [5]. Along with the elements discussed above, the survey spectrum (not included in the paper) in case of the control has a low intensity chlorine peak at 200.0 eV.…”

“…Phosphonate-based formulations are well-known for corrosion inhibition of carbon steel [2][3][4][5][6][7][8][9][10][11][12] and the impact of phosphonic acids on environment was reported to be negligible at the concentration levels used for corrosion inhibittion [13,14]. Phosphonic acids show synergistic effect with zinc ions and form complexes [1,[4][5][6]9,10]. A phosphonated aminoacid namely N,N-bis (phosphonomethyl) glycine (BPMG), was reported to be an environmentally friendly compound and also an effective corrosion inhibitor in combination with metal ions like Zn 2+ [12,15].…”