Theoretical study of corrosion inhibition of amides and thiosemicarbazones

An examination of quantum chemical and corrosion inhibition studies were carried out to investigate whether any clear links exist between the results of quantum chemical calculations and the experimental efficiencies of urea (U), thiourea (TU), acetamide (A), thioacetamide (TA), semicarbazide (SC), thiosemicarbazide (TSC), methoxybenzaldehydethiosemicarbazone (MBTSC), 2-acetylpyridine-(4phenyl) thiosemicarbazone (2AP4PTSC), 2-acetylpyridine-(4-methyl) thiosemicarbazone (2AP4MTSC), benzointhiosemicarbazone (BZOTSC) and benzilthiosemicarbazone (BZITSC) being corrosion inhibitors. The quantum chemical calculations have been performed by using DFT, ab-initio molecular orbital and semi-empirical methods for some amides and thiosemicarbozone derivatives being corrosion inhibitors. The highest occupied molecular orbital energy (E_HOMO), lowest unoccupied molecular orbital energy (E_LUMO), the energy gap between E_HOMO and E_LUMO (ΔE_HOMO-LUMO), dipole moments (μ), charges on the C, O, N, S atoms, the total energies of the molecules and the polarizabilities 〈α〉, the coefficients of the development of the MO over the atomic orbital (AO) corresponding to the between atoms which a new bond is established have been calculated.The results of quantum chemical calculations and experimental efficiencies of inhibitors were subjected to correlation analysis. We have reached the conclusion that the synthesis of better corrosion inhibitors can be achieved by controlling all electronic properties and parameters of a selected group of molecules.     

Electronic structure of some conjugated polymers for electron transport

The chemical and electronic structure of three different, strictly alternating copolymers, poly(2,5-diheptyl-1,4-phenylene-alt-1,4-naphthylene) (P14NHP), poly(2,5-diheptyl-1,4-phenylene-alt-2,6-naphthylene) (P26NHP) and poly(2,5-diheptyl-1,4-phenylene-alt-9,10-anthrylene) (P910AHP), have been studied by photoelectron spectroscopy and optical absorption spectroscopy. The experimental results have been analyzed using the results of quantum chemical calculations. In the geometrical structure of all three of the polymers there are large torsion angles between the phenylene unit and the naphthylene or anthrylene units. These large torsion angles lead to localization of the π-electron wave functions, and minimal conjugation along the polymer backbone. For all three polymers, the highest occupied molecular orbital is completely localized to the naphthylene or anthrylene unit. The frontier molecular orbital wave functions are very reminiscent of the highest occupied orbitals of the isolated naphthalene or anthracene molecules. The optical absorption spectra of all three polymers verify the existence of large optical band gaps, consistent with the large torsion angels. The first several optical transitions in the polymers are also very reminiscent of the transitions in single naphthalene and anthracene molecules.     

Corrosion inhibition of mild steel by plant extract in dilute HCl medium

The inhibition effect of Zenthoxylum alatum plant extract on the corrosion of mild steel in 5% and 15% aqueous hydrochloric acid solution has been investigated by weight loss and electrochemical impedance spectroscopy (EIS). The corrosion inhibition efficiency increases on increasing plant extract concentration till 2400 ppm. The effect of temperature on the corrosion behaviour of mild steel in 5% and 15% HCl with addition of plant extract was studied in the temperature range 50-80 °C. Surface analysis (SEM, XPS and FT-IR) was also carried out to establish the corrosion inhibitive property of this plant extract in HCl solution. Plant extract is able to reduce the corrosion of steel more effectively in 5% HCl than in 15% HCl. The adsorption of this plant extract on the mild steel surface obeys the Langmuir adsorption isotherm.     

Quantum chemical studies on corrosion inhibition of some lactones on mild steel in acid media

Study of the efficacy of some lactones to counter iron corrosion in 1 M hydrochloric acid using ab initio quantum chemical deductions and its comparison with the available experimental data forms a part of this research. It is believed that the inhibition efficiency has lucid correlation with the charge of oxygen atoms of inhibitor molecules. Furthermore, thermo-chemical calculations for oxepan-2-one (L3) on iron cluster result in adsorption energies close to experimental values. However, the interaction energies of L3 and iron cluster with the natural bond orbital are also reported. Furthermore, interaction energy of hydrogen ion and inhibitor with iron surface is investigated.     

Electrochemical and quantum chemical studies of 3,4-dihydropyrimidin-2(1H)-ones as corrosion inhibitors for mild steel in hydrochloric acid solution

The inhibition effect of 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) on the corrosion of mild steel in hydrochloric acid medium has been investigated using weight loss measurements, electrochemical impedance spectroscopy, potentiodynamic polarization and quantum chemical study. Among the compounds studied, DHPM-3 exhibited the best inhibition efficiency η (%) 99% at 10 mg L⁻¹ at 308 K. Polarization measurements indicate that all the examined compounds are of mixed-type inhibitor. The adsorption of studied compounds obeyed the Langmuir’s adsorption isotherm. The electronic properties obtained using quantum chemical approach, were correlated with the experimental inhibition efficiencies.     

The electronic structure of poly(3,4-ethylene-dioxythiophene): studied by XPS and UPS

The electronic structure of poly(3,4-ethylene-dioxythiophene) (PEDOT) has been investigated by X-ray and ultraviolet photoelectron spectroscopies as well as quantum chemical calculations. Significant differences have been observed in the photoelectron spectra between as-prepared chemically neutralized and anion-doped PEDOT thin films. The electronic structures of as-prepared neutral and doped PEDOT obtained from the photoelectron spectra are in good agreement with the results of new quantum chemical electronic structure calculations. No significant thermal-induced effects have been detected for either as-prepared neutral or doped PEDOT films. The concentration of anions on the polymer surface depends upon the size of the anion, with large anions, like polystyrene sulfonate (PSS⁻) base, being much more likely to cover the surface of a PEDOT film than small anion, such as tosylate(p-methyl benzyl sulfonate). This surface concentration effect probably makes the large-anion-doped polymer a more suitable candidate as an electrode in polymer light-emitting diodes (LEDs) than the small-anion-doped polymer.     

Molecules with enhanced negative third order vibrational polarizabilities: polymethine dyes and their vibrational spectra

In this paper, we present a theoretical study, based on quantum chemical “ab initio” calculations, on the structural requirements necessary for obtaining large and negative third order molecular polarizabilities (γ). In particular, we focus on polymethine dyes (H₂N–(CH₂)_n–NH₂) of various chain lengths. We show how it is possible to obtain the desired structural data from the frequency and intensity analysis of the vibrational spectra (infrared and Raman). Moreover, the vibrational method allows to calculate the vibrational contributions to molecular polarizabilities and thus permits an estimate of the non-linear optical (n.l.o.) response of the molecules considered. The conclusion that can be drawn is that in order to optimize the results attention must be paid not only to the intrinsic molecular property but also to the mutual arrangement of the molecules in any condensed phase.Our study is completed by the synthesis of one of the molecules studied chosen as a representative of the whole class. In this way, we could experimentally verify the conclusion derived from the theoretical calculations.     

Vibrational spectra of functionalized fullerenes containing amide

The set of three new hydrogen bonding functionalized fullerenes containing amide (PCB-t-BA, PCB-n-BA, and MPCB-t-BA) was investigated using the infrared absorption and Raman scattering spectroscopies. Additionally, the quantum chemical calculations of the equilibrium geometry and normal mode vibrations of the molecules were performed. Role of hydrogen bonds (HB) in the investigated samples was under our particular attention. Bifurcated HB was suggested.     

A theoretical study of some hydroxamic acids as corrosion inhibitors for carbon steel

The corrosion inhibition characteristics of two hydroxamic acids, i.e., oxalyl-dihydroxamic acid (C2) and pimeloyl-1,5-di-hydroxamic acid (C7), on carbon steel has been studied using density functional theory (DFT). Quantum chemical parameters such as highest occupied molecular orbital energy (E_HOMO), lowest unoccupied molecular orbital energy (E_LUMO), and energy gap (ΔE) have been calculated using B3LYP/6-31 + G∗∗ basis set. The relationship between the inhibition efficiency and quantum chemical parameters has been discussed in order to elucidate the inhibition mechanism of these compounds.     

Conformation-dependent molecular optical nonlinearities in bisnaphthol derivatives

The ‘vibrational technique’ has been applied to measure first-order and second-order molecular nonlinearities β and γ of bisnaphthol derivatives constrained in a non-coplanar conformation and containing electron donor and acceptor groups. The vibrational chemical shifts observed in the IR spectra of model molecules show that in solution a conformational equilibrium exists with only one conformer favouring electron injection by the oxygen lone pair into the aromatic ring, with the consequent increase of the weight of a quinoid structure. It follows that the hyperpolarizabilities are conformationally dependent and may show temperature dependence. The same spectroscopic approach to the bisnaphthol derivatives shows that the conformationally dependent role of the electron injecting property of the oxygen is more relevant than the inter-ring electron hopping between p_z orbitals.     

Diphenolic Schiff bases as corrosion inhibitors for aluminium in 0.1 M HCl: Potentiodynamic polarisation and EQCM investigations

The effects of novel synthesised two Schiff bases on the corrosion of aluminium in 0.1 M HCl were investigated using potentiodynamic polarisation and electrochemical quartz crystal microbalance measurements. Results show that inhibition efficiencies increase with increase in inhibitor concentration. This reveals that the inhibition occurs through adsorption of the inhibitor molecules on the metal surface. Adsorption of these inhibitors follows Temkin adsorption isotherm. The correlation between the inhibitor performances and their molecular structures has been investigated using quantum chemical parameters obtained by MNDO (modified neglect of diatomic overlap) semi-empirical method. Calculated quantum chemical parameters indicate that Schiff bases adsorbed on aluminium surface by chemical mechanism.     

The synergistic inhibitive effect and some quantum chemical parameters of 2,3-diaminonaphthalene and iodide ions on the hydrochloric acid corrosion of aluminium

The effect of iodide ions on the inhibitive performance of 2,3-diaminonaphthalene (2,3-DAN) in 1 M HCl for aluminium corrosion has been studied using hydrogen evolution (gasometry) measurements at 30 and 40 °C. Results obtained showed that the presence of 2,3-DAN molecules in the corrosive medium (1 M HCl solution) inhibits the corrosion process of aluminium and as the concentration of 2,3-DAN increases the inhibition efficiency also increased at the studied temperatures. A synergistic effect was observed between KI and 2,3-DAN. The experimental results suggest that the presence of iodide ions in the solutions stabilized the adsorption of 2,3-DAN molecules on the metal surfaces and, therefore improve the inhibition efficiency of 2,3-DAN. Phenomenon of physical adsorption is proposed for the inhibition and the process followed the Freundlich adsorption isotherm. The activation energy (E_a), heat of adsorption (Q_ads) and free energy of adsorption for the corrosion process (ΔG_ads) have been evaluated at the different temperatures and the values support the results obtained. Some quantum chemical parameters and the Mulliken charge densities for 2,3-diaminonaphthalene were calculated by the AM1 Semi-empirical method to provide further insight into the mechanism of inhibition of the corrosion process.     

Corrosion inhibition of mild steel in hydrochloric acid solution by some double Schiff bases

The inhibition effect of four double Schiff bases on the corrosion of mild steel in 2 M HCl has been studied by polarization, electrochemical impedance spectroscopy (EIS) and weight loss measurements. The inhibitors were adsorbed on the steel surface according to the Langmuir adsorption isotherm model. From the adsorption isotherm, some thermodynamic data for the adsorption process were calculated and discussed. Kinetic parameters activation such as E_a, ΔH∗, ΔS∗ were evaluated from the effect of temperature on corrosion and inhibition processes. Quantum chemical calculations have been performed and several quantum chemical indices were calculated and correlated with the corresponding inhibition efficiencies.     

The electron irradiation induced corrosion of silicon

The electron irradiation induced aqueous corrosion of silicon has been studied, in situ, in a million volt electron microscope. At temperatures below — 20°C ionization damage causes silicon to react with water to produce colloidal silica in the form of blisters and bubbles on the silicon surface. These are internally pressurized by hydrogen produced in the chemical reaction. The observations are consistent with a reaction model involving the passage of water molecules through the silica film and reacting, in the presence of the electron beam, with the silicon surface.     

Electrochemical and theoretical investigation of triazole derivatives on corrosion inhibition behavior of copper in hydrochloric acid medium

The inhibition effect of three triazole derivatives namely 4-amino-4H-1,2,4-triazole-3thiol (ATT), 4-amino-5-methyl-4H-1,2,4-triazole-3thiol (AMTT) and 4-amino-5-ethyl-4H-1,2,4-triazole-3thiol (AETT) have been investigated against the corrosion of copper in 0.5 M HCl solution. The investigations were analyzed using potentiodynamic polarization, electrochemical impedance, weight loss methods and quantum chemical studies. Potentiodynamic polarization measurements indicate that all three examined compounds are cathodic type inhibitors. Among the studied compounds, 4-amino-5-ethyl-4H-1,2,4-triazole-3thiol exhibited the best inhibition efficiency 96.09% at 2.58 mM. The adsorption of these compounds obeyed the Langmuir adsorption isotherm. The electronic properties obtained using quantum chemical approach, were correlated with the experimental results.     

Change in the emission color and the quantum efficiency enhancement in urethane-substituted polythiophene/tris(8-hydroxyquinoline) aluminum double layer light-emitting devices

We have obtained bright red color from orange–red light emitting urethane-substituted polythiophene (PURET) by placing tris(8-hydroxyquinoline) aluminum (alq₃) between the PURET layer and the cathode. Rearrangement of PURET chains or alq₃ molecules at the interface induced by the interfacial interaction between PURET and alq₃ via hydrogen bond is suggested as a mechanism for the change in the emission color. Light output intensity increased with alq₃ film thickness but is insensitive to the PURET film thickness. Combination of the charge blocking effect and the doping induced quantum efficiency enhancement has been performed by annealing the double layer device. Annealing of the double layer device increased further the light output intensity and caused the EL spectrum to shift toward blue, resulting in bright greenish-yellow light emission. In situ absorption and photoluminescence measurements during the annealing process exhibit the diffusion of alq₃ molecules into the PURET layer and the formation of a doped region at the interface. Energy transfer from doped alq₃ molecules to PURET chains and the doping-induced deformation of PURET chains are examined to occur within the doped region. In this paper, we propose the annealing of polymer/organic double layers as an effective method to improve the quantum efficiency of polymer light-emitting devices.     

Corrosion inhibition of C38 steel in 1 M hydrochloric acid medium by alkaloids extract from Oxandra asbeckii plant

The inhibition effect of alkaloids extract from Oxandra asbeckii plant (OAPE) on the corrosion of C38 steel in 1 M hydrochloric acid solution has been investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The corrosion inhibition efficiency increases on increasing plant extracts concentration. Cathodic and anodic polarization curves show that OAPE is a mixed-type inhibitor. The effect of temperature on the corrosion behavior of C38 steel in 1 M HCl with and without addition of plant extract was studied in the temperature range 25–55 °C. The thermodynamic functions of dissolution and adsorption processes were calculated from experimental polarization data and the interpretation of the results are given. The adsorption of this plant extract on the C38 steel surface obeys the Langmuir adsorption isotherm. Surface analysis (Raman) was also carried out to establish the corrosion inhibitive property of this plant extract in HCl solution.     

Influence of substrate pre-treatments on the growth of SixNyHz thin films by plasma enhanced chemical vapor deposition

A two-step plasma enhanced chemical vapor deposition procedure has been developed to produce high quality Si_xN_yH_z films for quantum cascade laser applications. The procedure consists in exposing the GaAs substrate to a controlled N₂ plasma previous to the silicon nitride film deposition. The pre-treatment causes the formation of a thin GaN film that passivates the GaAs wafer. The method has been optimized varying RF power, N₂ flow rate and process time of the pre-treatments and monitoring their effects on the resulting chemical composition and dielectric properties of the nitride overlayers, by means of infrared spectroscopy, X-ray photoelectron spectroscopy and electric characterizations. A narrow window in the pre-treatment RF power, N₂ flux and time values, improves the composition, structural and dielectric properties of the silicon nitride overlayers. The best result has been found depositing the silicon nitride films on GaAs wafer after 2 min of N₂ plasma treatment with a power of 20 W and a 50 cm³/min flow rate.     

Adsorption and inhibitive properties of some new Mannich bases of Isatin derivatives on corrosion of mild steel in acidic media

Adsorption of four derivatives of piperidinylmethylindoline-2-one on mild steel surface in 1 M HCl solution and its corrosion inhibition properties has been studied by a series of techniques, such as polarization, electrochemical impedance spectroscopy (EIS), weight loss and quantum chemical calculation methods. The values of activation energy (E_a) for mild steel corrosion and various thermodynamic parameters were calculated and discussed. Potentiodynamic polarization measurements showed that all inhibitors are mixed type. The degree of surface coverage was determined by using weight loss measurements and it was found that adsorption process of studied inhibitors on mild steel surface obeys Langmuir adsorption isotherm.     

Inhibitive action of some plant extracts on the corrosion of steel in acidic media

The effect of extracts of Chamomile (Chamaemelum mixtum L.), Halfabar (Cymbopogon proximus), Black cumin (Nigella sativa L.), and Kidney bean (Phaseolus vulgaris L.) plants on the corrosion of steel in aqueous 1 M sulphuric acid were investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. EIS measurements showed that the dissolution process of steel occurs under activation control. Potentiodynamic polarization curves indicated that the plant extracts behave as mixed-type inhibitors. The corrosion rates of steel and the inhibition efficiencies of the extracts were calculated. The results obtained show that the extract solution of the plant could serve as an effective inhibitor for the corrosion of steel in sulphuric acid media. Inhibition was found to increase with increasing concentration of the plant extract up to a critical concentration. The inhibitive actions of plant extracts are discussed on the basis of adsorption of stable complex at the steel surface. Theoretical fitting of different isotherms, Langmuir, Flory-Huggins, and the kinetic-thermodynamic model, were tested to clarify the nature of adsorption.