Amino acids and their derivatives as corrosion inhibitors for metals and alloys

The influence of 2,6-bis-(hydroxy)-pyridine (P1), 2,6-bis-(chloro)-pyridine (P2) and diethyl 1,1’-(pyridine-2,6-diyl)bis(5-methyl-1H-pyrazol2-3-carboxylate ( P3) on the corrosion of steel in 1 N HCl solution has been studied by weight loss measurements, potentiodynamic and impedance spectroscopy methods. The inhibiting action increases with the concentration of these compounds to attain 91,5% at 10 -3 M for P3. We note good agreement between gravimetric and electrochemical methods. The polarisation measurements show also that the pyridines act essentially as mixed inhibitors and the cathodic curves indicate that the reduction of proton at the steel surface happens with an activating mechanism. The temperature effect on the corrosion behaviour of iron in 1 M HCl without and with these inhibitors at different concentrations was studied in the temperature range from 313 to 353 K , and allows deducing the apparent activation energy, enthalpy and entropy of the dissolution process and the free energy were determined and discussed. The inhibitors were adsorbed on the iron surface according to the Langmuir adsorption isotherm model at different temperatures and some thermodynamic data for the adsorption process are calculated. The experimental study has been finished by quantum theoretical study; the quantum chemical calculations, based on DFT methods at B3LYP/6-31G** level of theory, were performed, by means of the GAUSSIAN 03 set of programs. Structural parameters, such as the frontier molecular orbital energies ( EHOMO

Quantum Chemical Studies and Corrosion Inhibitive Properties of Mild Steel by Some Pyridine Derivatives in 1 N HCl Solution

This work reports results from potentiodynamic polarisation and impedance investigation, with a rotating disc electrode, of inhibition of corrosion of A106 steel in aerated, unstirred 3.0 % NaCl solutions using di-n-butyl bis(thiophene-2-carboxylato-O,O′)tin(IV) as inhibitor. These studies showed that it is a mixed-type inhibitor. Inhibition efficiency increased with increasing di-n-butyl bis(thiophene-2-carboxylato-O,O′)tin(IV) concentration and decreases with increasing solution temperature. Maximum efficiency of inhibition of the inhibitor of approximately 78 % is observed at a concentration at 10−2 M. The inhibition process was attributed to formation of an adsorbed film on the metal surface that protects the metal against corrosive agents. The adsorption isotherm confirms the applicability of Langmuir equation to describe the adsorption process. Thermodynamic functions for the adsorption process were determined. The efficiency of corrosion inhibitors and global chemical reactivity depend on such properties as energy of the highest occupied molecular orbital (E
 HOMO), energy of the lowest unoccupied molecular orbital (E
 LUMO), energy gap (ΔE), which were calculated. All calculation was been performed by density functional theory (DFT) using the Gaussian03W suite of software. Calculated results were usually in agreement with the experimental data.

Theoretical investigation of inhibition of the corrosion of A106 steel in NaCl solution by di- n -butyl bis(thiophene-2-carboxylato- O , O ′)tin(IV)

Influence of Anions on the Corrosion Inhibition Effect of Imidazolium Based Ionic Liquids for Copper in 3.5 % NaCl Solution

L'etude experimentale de l'inhibition de la corrosion du cuivre dans le milieu nitrique par des acides amines tels que l'arginine (Arg), la cysteine (Cys), la glycine (Gly), la lysine (Lys) et la valine (Val) a ete completee par une approche theorique des equilibres de dissociation protoniques de ces acides amines a l'aide d'une methode semi- empirique: Austin Model one (AMl). Le site le plus favorable a la protonation de ces composes est l'atome d'azote du groupement amine. Une correlation lineaire entre l'efficacite inhibitrice obtenue experimentale-ment et la difference d'energie ΔE entre les orbitales moleculaires frontieres a savoir la plus haute occupee (EHOMO) et le plus basse vacante (ELUMO) a ete determinee. Cet examen a permis de constater que la cysteine est le meilleur inhibiteur de la serie des acides amines testes. En outre, le calcul des affinites protoniques et les charges atomiques nettes de la cysteine permet de mettre en evidence les groupements fonctionnels de la Cysteine (NH3+, SH, COOH) qui participent aux phenomenes de complexation Cu (II)/Cys a la surface du cuivre.

Khadija Barouni

Papers

Etude théorique de l´effet inhibiteur de certains acides aminés sur la corrosion du cuivre en milieu nitrique