Tungstate as a synergist to phosphonate-based formulation for corrosion control of carbon steel in nearly neutral aqueous environment

Abstract

Synergistic inhibition of corrosion of carbon steel in low chloride aqueous medium using tungstate as a synergist in combination with N,N-bis(phosphonomethyl) glycine (BPMG) and zinc ions is presented. The synergistic action of tungstate has been established through the present studies. The new ternary inhibitor formulation is effective in neutral and slightly acidic as well as slightly alkaline media. Potentiodynamic polarisation studies inferred that the formulation functions as a mixed inhibitor. Impedance studies of the metal/solution interface revealed that the surface film is highly protective. Characterisation by X-ray photoelectron spectroscopy (XPS) of the surface film formed in presence of the inhibitor revealed the presence of iron, phosphorus, nitrogen, oxygen, carbon, zinc and tungsten in the surface film. The chemical shifts in the binding energies of these elements inferred that the surface film is composed of iron oxides/hydroxides, zinc hydroxide, heteropolynuclear complex [Fe(III), Zn(II)-BPMG] and WO 3 . Reflection absorption FTIR spectroscopic studies also supported the presence of these compounds in the surface film. Morphological features of the metal surface studied in the absence and presence of the inhibitor by scanning electron microscopy (SEM) are also presented. Based on all these results, a plausible mechanism of corrosion inhibition is proposed.

Synergistic Inhibition Effect of Sodium Tungstate and Hexamethylene Tetramine on Reinforcing Steel Corrosion

“…[43][44][45] The fitting curves were also shown in Figure 3, and the parameters from fitting the EIS data and the corrosion inhibition efficiency (η) of Na 2 WO 4 are listed in Table IV. η values can be calculated by the following equation: 26,33 …”

“…26 The former peak corresponded to W 4f 5/2 , which shifted from characteristic elemental binding energy of 33.6 eV, and the latter peak corresponded to W 4f 7/2 electron, which shifted from 31.0 eV. 52 Such large shifts in the binding energy indicated that W existed in the +6 oxidation state (in the form of WO 3 ) in the surface film.…”

“…52 Such large shifts in the binding energy indicated that W existed in the +6 oxidation state (in the form of WO 3 ) in the surface film. 26,53,54 It has been reported that the composition of the passive film of reinforcing steel is mainly composed of ferric compounds. [55][56][57][58] From the deconvoluted XPS spectra of Fe shown in Figures 9C and 9D, we obtained the atomic percentage of Fe 3+ (at about 710 eV) in total Fe for the solution with the mixed inhibitor was 54.4% by estimating the component peak areas ( Figure 9C), which was higher than that (about 49.9%) without inhibitors ( Figure 9D).…”

“…[5][6][7] In recent years, increasing attention has been paid to the environment-friendly corrosion inhibitors and natural products such as plant extracts, amino acids, some inorganic salts, proteins and bio-polymers. [8][9][10][11][12][13][14][15][16][17][18][19] Tungstate has been extensively studied in the protection of iron as an environmental-friendly anodic type inorganic corrosion inhibitor, [20][21][22][23][24][25][26][27] and is one of the most effective corrosion inhibitor. However, tungstate is not feasible to be used alone for corrosion protection of carbon steel due to its low oxidizing ability, high cost and low efficiency at a low concentration.…”

“…Therefore, many co-inhibitors are used, such as polyaspartic acid, [28][29][30] metaborates and metaphosphates, 22,24,31 sodium silicate, 27 sodium tartrate, 32 phosphates and zinc salts. 26 The compounds of tungstate synergistically in combination with small molecule compounds (such as amine) for the protection of steel are supposed to be good corrosion inhibitors. Hexamethylene tetramine (HMTA) is a potential corrosion inhibitor for iron and mild steel due to its low cost, good water solubility.…”