Adsorption and corrosion inhibition of carbon steel in hydrochloric acid medium by hexamethylenediamine tetra(methylene phosphonic acid)

On the corrosion inhibition of carbon steel in 1 M HCl with a pyridinium-ionic liquid: chemical, thermodynamic, kinetic and electrochemical studies

“…In this respect, it is commonly agreed in literature that free energy values equal or less than 20 kJ mol À1 are indicative a physisorption process while those equal or higher than 40 kJ mol À1 reveal its chemisorption nature. 7,[32][33][34]53,55,56 The value of (DG ads ¼ À33.037 kJ mol À1 ) obtained in the current work shows that a rather complex mixed-type adsorption is involved [32][33][34]49,53,57 and that is a predominantly physisorption. 32,58 This implies a predominant electrostatic interaction (physisorption) between NR3 and carbon steel in addition to electrons transfer or sharing (chemisorption) between NR3 molecules and the metal surface affecting most probably both anodic and cathodic sites.…”

“…The latter is then proven to be involved in a dissociation-type activation process. 7,32,52 Furthermore, the observed increase of DS a is suggestive of water molecules replacement during NR3 adsorption onto the metal surface 53 as discussed in the previous section.…”

“…8 reveals parallel cathodic Tafel lines which indicate that HER is under activation (charge-transfer) control. 7,49,61 Also, there is no signicant change in the values of both anodic and cathodic Tafel slopes upon addition of various concentrations of NR3 compound suggesting that the inhibition mechanism of the latter proceeds through blocking the active anodic and cathodic sites on the carbon steel surface. [62][63][64] The inhibitory effect of NR3 is also revealed as current densities decrease in both cathodic and anodic branches 50 though this effect is slightly more pronounced on the latter.…”

“…Adsorption isotherm enables the elucidation of the investigated ionic liquid inhibition mechanism through understanding its adsorptive strength and behaviour. 7,48,49 The data is usually analyzed via common adsorption isotherms tting, namely: Freundlich, Temkin, Flory-Huggins, Frumkin and Langmuir. 7,34,48,49 In this work, the experimental data was best tted to the Langmuir isotherm (R 2 ¼ 0.999) where the ratio of NR3 concentration and surface coverage (q) is plotted against the concentration [NR3] (cf.…”

“…[1][2][3][4] This results in the chemical attack of less noble metals, for instance steel, which leads to its corrosion occurring generally via electrochemical anodic dissolution 5 and causes several economical and safety problems. [6][7][8] The use of corrosion inhibitors, mainly organic compounds, was revealed to be one of the most effective methods for corrosion control and, hopefully, its prevention. [9][10][11][12][13][14][15][16] Higher inhibition efficiencies are generally achieved with compounds comprising in their molecular structures P, O, S, N, p-electrons and aromatic rings.…”