Investigate the Corrosion Inhibition of Mild Steel in Sulfuric Acid Solution by Thiosemicarbazide

Corrosion inhibition of mild steel in 0.5 mol/L H2SO4 was investigated in the absence and presence of different concentrations of thiosemicarbazide. The inhibition efficiency of thiosemicarbazide was studied by electrochemical impedance methods, potentiodynamic polarization and scanning electron microscopy at different inhibitor concentrations. Inhibition efficiency, corrosion rate and surface coverage were evaluated at different concentrations of thiosemicarbazide. Electrochemical impedance plots indicated that the presence of the inhibitors increased the charge transfer resistance of the corrosion process, increasing the inhibition efficiency. Polarization curves showed that this compound acted as mixed type inhibitor. The results of the investigation showed that this compound had good inhibiting properties for mild steel corrosion in 0.5 M sulfuric acid. The adsorption isotherm studies showed that Thiosemicarbazide adsorbed chemisorbed and formed a stable surface complex on the mild steel surface. And Langmuir obeyed the adsorption isotherm. Scanning electron microscopy analysis shows that, the surface morphology of the polished mild steel in the presence of thiosemicarbazide as inhibitor is smoother surface as compared with polished mild steel specimen in the absence of inhibitor.

DFT Calculations for Corrosion Inhibition of Ferrous Alloys by Pyrazolopyrimidine Derivatives

The inhibition performance of 5-tolyl-2-phenylpyrazolo[1,5-c] pyrimidine-7(6H)thione (Tolyl), 5-tolyl-2-pheenylpyrazolo?[1,5-c]pyrimidine-7(6H)one (Inon) was?investigated as corrosion inhibitors using density functional theory (DFT) at the B3LYP/6-31?+?G(d,p) level of theory. The calculated quantum chemical parameters correlated to the inhibition efficiency are:?the?highest occupied molecular orbital energy(EHOMO),?the?lowest unoccupied molecular orbital energy (ELUMO), the energy gap (ΔEL-H), dipole moment (μ), ionization energy (Ι), electron affinity?(Α), absolute electronegativity (χ), absolute hardness (η), absolute softness (σ), the fraction of electron transferred (ΔN), and the total energy (Etot)?which?were calculated. The local reactivity has been analyzed through the Fukui function and local softness indices in order to compare the possible sites for nucleophilic and electrophilic attacks. The success of DFT calculations in predicting the inhibition efficiency?was?assessed.

Inhibition Mechanism of Pitting Corrosion of Nickel in Aqueous Medium by Some Macrocyclic Compounds

Anodic polarization of nickel was studied by potentiostatic technique in neutral media in presence of two macrocyclic ligands. Pit initiation was detected by measuring pitting potential, Ep and the charge transfer, Q during the anodic polarization. Initiation of pitting and Q were found to be dependent on the structure and concentrations of inhibitors. Under steady state conditions, the inhibition efficiency was in the order 1, 4, 8, 11 tetraazacyclotetradecane (cyclam) > N, N’-bis (2-aminoethyl) 1, 3-propandiamine (2,3,2-tet) due to macrocyclic effect. These findings were confirmed by fitting the data to different adsorption isotherms. Adsorption on nickel surface was obeyed kinetic-thermodynamic model for the two inhibitors. Influence of [Cl–] on corrosion behavior of nickel in sulphate solution containing inhibitors was investigated. A mechanism involving three competitive equilibria of dissolution of nickel in presence and absence of the inhibitors was proposed. Empirical and theoretical kinetic equations were compared and discussed. There is a good agreement between the calculated and observed rate constants.