Structure-Corrosion Inhibition Performance Relationship: Application to Some Natural Free Acids and Antioxidants

Abstract

The inhibition of mild steel corrosion in a 1 M HCl solution by some natural free acids and antioxidants has been investigated by weight loss measurement, potentiodynamic polarization and DFT calculations. The experimental results have shown that these compounds exhibited a good corrosion inhibition. The inhibition efficiency increased with the inhibitor concentration. The adsorption of the inhibitor molecules onto the metal surface was found to respond to Langmuir adsorption isotherm for ascorbic, oleic and stearic acids, and to Temkin adsorption isotherm for palmitic acid. Tafel plot analysis revealed that these compounds acted as mixed type inhibitors, with more polarized cathodic than anodic curves. Regarding quantum chemical calculations, parameters such as energies of highest occupied molecular orbital and lowest unoccupied molecular orbital, energy gap, dipole moment, electronegativity, global hardness, softness, global electrophilicity, fraction of transferred electrons, ∆E Backdonation, Fukui and local softness indices have been performed on the tested inhibitors to investigate their structural and electronic properties, in order to provide an adsorption mechanism, and reveal the reactivity and selectivity of the molecules' centers. The experimental results were in good agreement with theoretical results. The results for the natural acids were used to predict the linoleic acid inhibition efficiency.

Corrosion protection of tin by some carboxylic acids in sodium chloride solution

“…The polarization curves shown in Figure 5 and the values of corrosion parameters shown in Table 3 once again have confirmed the protective effect of carboxylic acids on the corrosion of tin in the 0.5 mol/dm 3 NaCl electrolyte solution. It is also observed that the addition of the tested inhibitors retards both the cathodic and anodic reactions; however, the cathodic reactions are comparatively more affected than the anodic ones, suggesting that the investigated inhibitors are mixed type inhibitors and predominantly act as cathodic inhibitors [24,25]. Other films have also shown high efficiencies, so both deposition methods have shown to be effective for forming films that successfully prevent the corrosion of the tested tin electrode in this electrolyte.…”

“…where R is the universal gas constant, T is the absolute temperature, T = 298 K, and 55.5 is the concentration of water in the solution in mol dm -3 . The Langmuir adsorption isotherm has been reported for the adsorption of SA on metal surfaces [24]. The adsorption constant and Gibbs free energy were determined to be Kads = 2578 dm 3 mol -1 and Gads = −29.4 kJ mol -1 .…”

“…Other films have also shown high efficiencies, so both deposition methods have shown to be effective for forming films that successfully prevent the corrosion of the tested tin electrode in this electrolyte. The corrosion rate decrease is attributed to inhibitor adsorption on active metal sites [24], present on the tin surface, which is the primary step in achieving inhibition in the NaCl solution. The coating film provides corrosion protection to metallic substrates by acting as a barrier against electron and ion diffusion [18], thus reducing electrochemical reactions at the interface of Sn and electrolyte.…”

“…This result indicates that the adsorption of inhibitor onto the metal surface can occur on the basis of donor-acceptor interactions between inhibitors' π electrons and the vacant d-orbitals of the metal surface atoms. Investigated carboxylic acids have the highest density of electrons in the carboxylic group and it can be considered as a reaction canter for binding to the surface oxide [6,24].…”

Comparative Gravimetric Studies on Carbon Steel Corrosion in Selected Fruit Juices and Acidic Chloride Media (HCl) at Different pH

“…It is important to note that some of the organic acids and other chemical compounds present in foods can exert inhibitive effects on the corrosion of certain metals/alloys under acidic conditions consistent with foods such as: citric acid on aluminium in 2 M NaCl solution at pH 2 [ 16 ], ascorbic acid on mild steel in 0.01 M H 2 SO 4 solutions at pH = 2–6 and 0.3% NaCl solution at pH near neutral [ 9 , 17 ], folic acid on mild steel in 0.3% NaCl solution at pH near neutral [ 9 ], vitamins on mild steel in acidic media [ 9 , 17 , 18 , 19 , 20 , 21 ], antioxidant compounds normally present in foods on carbon steel in acidic medium [ 22 , 23 , 24 ], and amino acids on mild steel in acidic solutions [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Some peptides (compounds consisting of two or more amino acids) have been reported to bind strongly to aluminium and mild steel [ 36 , 37 , 38 , 39 ].…”