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

Abstract

Sodium tungstate (Na 2 WO 4 ) and hexamethylene tetramine (HMTA) are both eco-friendly corrosion inhibitors. In this work, their synergistic corrosion inhibition effects on reinforcing steel in the simulated polluted concrete pore solution containing Cl − were studied by electrochemical techniques including electrochemical impedance spectroscopy and potentiodynamic anodic polarization curve measurements. The morphologies and compositions of the steel surface were characterized by Electron Micro-Probe Analyzer, X-ray photoelectron spectroscopy, and Raman spectroscopy. The results showed that the serious steel corrosion took place in the solution with pH 11.00 and 0.5 M NaCl. However, a stable passive region occurred in the anodic polarization curve of the steel and its corrosion current density decreased dramatically after addition of a mixed inhibitor with 0.01 M Na 2 WO 4 and 0.01 M HMTA to the solution. The inhibition efficiency of the mixed inhibitor reached 97.1%. The surface analyses revealed that a protective composite film was formed on the steel in the solution with the mixed inhibitor, which indicated that the mixed inhibitor had a synergistic inhibition effect on the steel corrosion. Our study also indicated that the mixed inhibitor could effectively control corrosion of the reinforcing steel in cement mortar.Reinforcing steel in concrete is normally protected from corrosion by the passive film formed on its surface under high alkaline conditions of concrete. However, the passivity of the reinforcing steel may be destroyed and corrosion take place while aggressive species from the environment such as Cl − , CO 2 , SO 2 , etc., reach the steel-concrete interface through the porous concrete. 1-4 The damage of reinforced concrete structures and economic losses caused by reinforcing steel corrosion are still serious problems. Hence, many techniques have been developed to protect reinforcing steel from corrosion. The application of corrosion inhibitors is one of the most practical methods to control the corrosion of reinforcing steel. 5-7 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, 20-27 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, 28-30 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 inhibi...

Testing phosphate ions as corrosion inhibitors for construction steel in mortars

“…Other ions have been investigated as candidates to inhibit pitting corrosion of steel, namely chromates, phosphates, tungstates and molybdates [21][22][23]. Phosphates present some interesting advantages such as low cost and low toxicity.…”

Study on Synergistic Corrosion Inhibition Effect between Calcium Lignosulfonate (CLS) and Inorganic Inhibitors on Q235 Carbon Steel in Alkaline Environment with Cl−

“…The R film consists of the passivation film, precipitate film, and adsorption film. As the CLS concentration decreases, the barrier effect of adsorption film formed by organic inhibitor decreases, which is dominant in R ct value [ 15 , 18 ]. For three kinds of hybrid inhibitors, CLS compound with molybdate has the highest R ct and R film , which means molybdate has the best synergistic inhibition effect with CLS.…”

“…Similar to the CPP curves results, compound inhibitors act as a mix-type inhibitor. The decreases of OCP in the first 4 h might be owing to the adsorption of CLS onto the steel surface, which is much shorter than adding CLS alone and suggesting the inorganic inhibitor could promote the adsorption of CLS [ 15 , 18 ]. The increases of OCP from 4 h to the end of test are owing to the oxidation capacity of inorganic inhibitor [ 11 , 14 , 15 ], and the passivation film and deposition film formed on the steel surface could suppress the corrosion reactions.…”

“…However, tungstate, molybdate, and stannate are usually not used as corrosion inhibitor alone, which is owing to their low inhibition efficiency at low concentration, high cost, and low oxidizing ability. For instance, tungstate could act as an effective corrosion inhibitor for steel when the concentration exceeds 1200 ppm [ 18 ]. The effect of inhibition was obvious when the concentration of molybdate was very high (thousands of mg/L) [ 19 ].…”

The role of WO42−on surface passivation for Q235 carbon steel in tungstate solution

“…Like NO 2 − and MoO 4 2 − , WO 4 2 − is usually added into environmental electrolyte also to restrain the corrosion of steel material (Zuo et al , 2002; Jabeera et al , 2006; Gao et al , 2015), particularly to inhibit pitting corrosion (Abd et al , 2010; Javidi and Omidvar, 2019Abd et al , 2010). The addition of WO 4 2 − results in the positive shift of corrosion potential (E c ) (Zuo et al , 2002) and the decrease of corrosion current density (i c ) (Gao et al , 2015); with the increase of WO 4 2 − concentration, the initiation of pitting corrosion is inhibited effectively (Abd et al , 2010), and the pitting potential (E p ) moves to the positive direction obviously (Abd et al , 2010). According to the above statements (Zuo et al , 2002; Jabeera et al , 2006; Gao et al , 2015; Abd et al , 2010; Javidi and Omidvar, 2019; Abd et al , 2010), the effectiveness of WO 4 2 − is very closely related to its function on surface passivation.…”