Nnabuk O. Eddy

Adsorption and quantum chemical studies on the inhibition potentials of some thiosemicarbazides for the corrosion of mild steel in acidic medium.

Three thiosemicarbazides, namely 2-(2-aminophenyl)-N phenylhydrazinecarbothioamide (AP4PT), N,2-diphenylhydrazinecarbothioamide (D4PT) and 2-(2-hydroxyphenyl)-N-phenyl hydrazinecarbothioamide (HP4PT), were investigated as corrosion inhibitors for mild steel in H2SO4 solution using gravimetric and gasometric methods. The results revealed that they all inhibit corrosion and their % inhibition efficiencies (%IE) follow the order: AP4PT > HP4PT > D4PT. The %IE obtained from the gravimetric and gasometric experiments were in good agreement. The thermodynamic parameters obtained support a physical adsorption mechanism and the adsorption followed the Langmuir adsorption isotherm. Some quantum chemical parameters were calculated using different methods and correlated with the experimental %IE. Quantitative structure activity relationship (QSAR) approach was used on a composite index of some quantum chemical parameters to characterize the inhibition performance of the studied molecules. The results showed that the %IE were closely related to some of the quantum chemical parameters, but with varying degrees. The calculated/theoretical %IE of the molecules were found to be close to their experimental %IE. The local reactivity has been studied through the Fukui and condensed softness indices in order to predict both the reactive centers and to know the possible sites of nucleophilic and electrophilic attacks.

Quantum chemical study of the inhibition of the corrosion of mild steel in H2SO4 by some antibiotics

The inhibition efficiency of some antibiotics against mild steel corrosion was studied using weight loss and quantum chemical techniques. Values of inhibition efficiency obtained from weight loss measurements correlated strongly with theoretical values obtained through semi empirical calculations. High correlation coefficients were also obtained between inhibition efficiency of the antibiotics and some quantum chemical parameters, including frontier orbital (EHOMO and ELUMO), dipole moment, log P, TNC and LSER parameters (critical volume and dipolar-polarisability factor), which indicated that these parameters affect the inhibition efficiency of the compounds. It was also found that quantitative structure activity relation can be used to adequately predict the inhibition effectiveness of these compounds.

Theoretical and experimental studies on the corrosion inhibition potentials of some purines for aluminum in 0.1 M HCl.

Experimental aspect of the corrosion inhibition potential of adenine (AD), guanine (GU) and, hypoxanthine (HYP) was carried out using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods while the theoretical aspect of the work was carried out by calculations of semi-empirical parameters (for AM1, MNDO, CNDO, PM3 and RM1 Hamiltonians), Fukui functions and inhibitor–metal interaction energies. Results obtained from the experimental studies were in good agreement and indicated that adenine (AD), guanine (GU) and hypoxanthine (HYP) are good adsorption inhibitors for the corrosion of aluminum in solutions of HCl. Data obtained from electrochemical experiment revealed that the studied purines functioned by adsorption on the aluminum/HCl interface and inhibited the cathodic half reaction to a greater extent and anodic half reaction to a lesser extent. The adsorption of the purines on the metal surface was found to be exothermic and spontaneous. Deviation of the adsorption characteristics of the studied purines from the Langmuir adsorption model was compensated by the fitness of Flory Huggins and El Awardy et al. adsorption models. Quantum chemical studies revealed that the experimental inhibition efficiencies of the studied purines are functions of some quantum chemical parameters including total energy of the molecules (TE), energy gap (EL–H), electronic energy of the molecule (EE), dipole moment and core–core repulsion energy (CCR). Fukui functions analysis through DFT and MP2 theories indicated slight complications and unphysical results. However, results obtained from calculated Huckel charges, molecular orbital and interaction energies, the adsorption of the inhibitors proceeded through the imine nitrogen (N5) in GU, emanine nitrogen (N7) in AD and the pyridine nitrogen (N5) in HPY.

QSAR, DFT and quantum chemical studies on the inhibition potentials of some carbozones for the corrosion of mild steel in HCl

Experimental aspects of the inhibition of the corrosion of mild steel in HCl solutions by some carbozones were studied using gravimetric, thermometric and gasometric methods, while a theoretical study was carried out using density functional theory, a quantitative structure–activity relation, and quantum chemical principles. The results obtained indicated that the studied carbozones are good adsorption inhibitors for the corrosion of mild steel in HCl. The inhibition efficiencies of the studied carbozones were found to increase with increasing concentration of the respective inhibitor. A strong correlation was found between the average inhibition efficiency and some quantum chemical parameters, and also between the experimental and theoretical inhibition efficiencies (obtained from the quantitative structure–activity relation).

Part 3. Theoretical study on some amino acids and their potential activity as corrosion inhibitors for mild steel in HCl

Quantum chemical parameters, namely energy of the highest occupied molecular orbital, energy of the lowest unoccupied molecular orbital, energy gap, dipole moment, total energy, total electronic energy, core–core repulsion, ionisation potential, cosmo area, cosmo volume and other quantum descriptors [calculated from PM6, PM3, AM1, RM1 and modified neglect of diatomic overlap (MNDO) Hamiltonians], have been used to predict the corrosion inhibition potential of asparagine, aspartic acid, glutamine and glutamic acid. The results obtained indicate that the trend for the variation of the inhibition efficiencies of the compound is in the order: glutamine>asparagine>aspartic acid>glutamic acid. There is a strong agreement between some quantum chemical parameters and the experimental inhibition efficiencies. In order to establish the sites for electrophilic and nucleophilic attacks, condensed Fukui function, condensed softness and relative nucleophilicity/electrophilicity were considered. The results reveal that the sites for nucleophilic attacks in aspartic acid and glutamine are at the nitrogen atom (N5) but at the carbon atom (C3) for asparagine and glutamic acid. The sites for electrophilic attacks are at the oxygen atom (O9, for aspartic acid), carbon atom (C6, for asparagine), oxygen atom (O10, for glutamic acid) and nitrogen atom (N9, for glutamine).

Experimental and theoretical studies on some amino acids and their potential activity as inhibitors for the corrosion of mild steel, part 2 ☆

Substituent constants and quantum chemical parameters were calculated from PM6, PM3, AM1, RM1 and MNDO. Hamiltonians were used to predict the corrosion inhibition potential of nine amino acids grouped under three skeletons. Skeleton I consisted of cysteine (CYS), serine (SER) and amino butyric acid (ABU). Those in skeleton II included threonine (THR), alanine (ALA) and valine (VAL) while those in skeleton III are aromatic amino acids, which included phenylalanine (PHE), tryptophan (TRP) and tyrosine (TYR). Trends obtained from substituent constants were not entirely useful in predicting the corrosion inhibition potentials of the studied amino acids. However, the results obtained from quantum chemical parameters indicated that the trends for the variation of corrosion inhibition potentials of the studied amino acids in skeletons I, II and III are CYS > SER > ABU, THR > ALA > VAL and TRP > TYR > PHE, respectively. Highest values of inhibition efficiency were obtained for inhibitors in skeleton III and are attributed to the presence of aromatic ring in the molecule while the corrosion inhibition potential of inhibitors in skeletons I and II are attributed to the presence of –SH and –OH functional groups, respectively. Analysis of data obtained from relative nucleophilicity/electrophilicity, condensed Fukui and softness functions indicated that the sites for electrophilic attacks for the amino acids in skeletons I and II are in the amine bonds but for those in skeleton III the sites were in their respective phenyl ring. The author proposed that quantum chemical parameters may be used to predict the corrosion inhibition potentials of amino acids.

Quantum chemical studies on the inhibition potentials of some Penicillin compounds for the corrosion of mild steel in 0.1 M HCl

AbstractInhibitive and adsorption properties of Penicillin G, Amoxicillin and Penicillin V potassium were studied using gravimetric, gasometric and quantum chemical methods. The results obtained indicate that these compounds are good adsorption inhibitors for the corrosion of mild steel in HCl solution. The adsorption of the inhibitors on mild steel surface is spontaneous, exothermic and supports the mechanism of physical adsorption. From DFT results, the sites for nucleophilic attacks in the inhibitors are the carboxylic acid functional group while the sites for electrophilic attacks are in the phenyl ring. There was a strong correlation between theoretical and experimental inhibition efficiencies. FigureResponse surface plot showing the variation of experimental inhibition efficiency with EHOMO and ELUMO (other variables held constant; ELUMO-HOMO=7.77e V, TE=- 3780 eV, EE=-30800 eV, C-C= 27500 eV, CosAr=348, CosVol=413, IP=8.75 eV and •=9.42 eV) obtained from PM6 model

Commiphora pedunculata gum as a green inhibitor for the corrosion of aluminium alloy in 0.1 M HCl

The effect of Commiphora pedunculata (CP) gum on the inhibition of the corrosion of aluminum alloy AA 3001) in solutions of HCl was investigated using gravimetric and thermometric methods of monitoring corrosion. The results obtained indicated that CP gum is a good adsorption inhibitor for the corrosion of aluminum in solutions of HCl. The inhibition efficiency of CP gum was found to increase with an increase in concentration but to decrease with increasing temperature. The adsorption of CP gum on the surface of aluminum was found to be endothermic, spontaneous and to support the mechanism of physical adsorption. The Langmuir adsorption model has been used to describe the adsorption characteristics of CP gum on aluminum surface.

Inhibitive, adsorption and synergistic studies on ethanol extract of Gnetum Africana as green corrosion inhibitor for mild steel in H2SO4

Abstract The inhibitive and adsorptive characteristics of ethanol extract of Gnetum Africana for the corrosion of mild steel in H2SO4 solutions have been studied using weight loss, gasometric, thermometric, and IR methods of monitoring corrosion. Ethanol extract of Gnetum Africana is a good adsorption inhibitor for the corrosion of mild steel in H2SO4. The inhibitive property of the extract is attributed to the presence of alkaloid, saponin, tannin, terpene, anthraquinone, cardiac glycoside, and alkaloid in the extract. The adsorption of the inhibitor on mild steel surface is exothermic, spontaneous and is consistent with the mechanism of physical adsorption. In addition, Langmuir and Temkin adsorption isotherms best described the adsorption characteristics of the inhibitor. Efforts to improve the adsorption of the inhibitor through synergistic combinations with halides indicated that only KCl may enhance the efficiency of the inhibitor. The study provides information on the use of ethanol extract of Gnetum Africana as a corrosion inhibitor for mild steel.

Corrosion inhibition and adsorption properties of ethanol extract of Gongronema latifolium on mild steel in H2SO4

Purpose – The purpose of this paper is to study the inhibitive and adsorptive characteristics of ethanol extract of Gongronema latifolium (GL) as a corrosion inhibitor for mild steel in H2SO4.Design/methodology/approach – The inhibition efficiencies were evaluated using thermometric and hydrogen evolution techniques.Findings – The inhibition efficiency of ethanol extract of GL vary with concentration of the extract, period of immersion and with temperature. The extract acts as an inhibitor because of its phytochemical and amino acid composition. The extract is adsorbed spontaneously on the surface of mild steel according to Langmuir adsorption isotherm. The mechanism of physical adsorption is proposed from the trend of the inhibition efficiency with temperature and the values of some kinetic and thermodynamic parameters obtained.Research limitations/implications – The study provides information on the use of ethanol extract of GL as a corrosion inhibitor. Electrochemical studies such as polarisation and a...