CORROSION INHIBITION AND ADSORPTION BEHAVIOR OF MALACHITE GREEN DYE ON ALUMINUM CORROSION

Malachite green dye (MG) was studied as a corrosion inhibitor for aluminum in 1.0 mol dm^?3 HCl and 0.5 mol dm^?3 KOH using the gravimetric technique. The results revealed an inhibiting effect of MG, which was highly restrained in 0.5 M KOH and pronounced in 1.0 M HCl. MG inhibited the corrosion reaction in the acidic medium by adsorption on the metal/solution interface following the Flory-Huggins isotherm. Inhibition efficiency increased with MG concentration and synergistically increased in the presence of iodide ions, but decreased with a rise in temperature. The local reactivity of the MG molecule was analyzed theoretically using the density functional theory to explain the adsorption characteristics, while molecular dynamics simulations were performed to illustrate the adsorption structure of MG at a molecular level. The theoretical predictions showed good agreement with experimental results.     

CORROSION INHIBITION OF CARBON STEEL IN ACIDIC MEDIA BY BIFURCARIA BIFURCATA EXTRACT

The effect of extract of brown alga Bifurcaria bifurcata (Bb) on the corrosion of steel in 1 M HCl solution was studied using weight loss, potentiodynamic, and polarization resistance measurements. Experimental data revealed that Bb extract acted as an inhibitor in the acid environment. The extract was a mixed-type inhibitor, predominating as an anodic inhibitor at higher concentration. It was found that the inhibition efficiency increased with an increase in Bb extract concentration. The corrosion inhibition of Bb extract on carbon steel in 1 M HCl solution was also investigated by infrared and UV-visible spectrophotometry to obtain information on bonding mechanism between the metallic surface and the inhibitor. The process of inhibition is attributed to the adsorption of the extract molecules, the precipitation of Fe-chelates, and/or formation of complex at the electrode surface.     

INHIBITING EFFECT OF CRYSTAL VIOLET DYE ON ALUMINUM CORROSION IN ACIDIC AND ALKALINE MEDIA

Crystal violet dye (CV) was studied as a corrosion inhibitor for aluminum in hydrochloric acid (1 mol dm^?3) and potassium hydroxide (0.5 mol dm^?3) solutions in the temperature range 30°–60°C using the gravimetric technique. The effect of iodide ions on the inhibiting efficacy of CV was also assessed. CV was found to inhibit Al corrosion in both aggressive media, exhibiting greater inhibition efficiency in 1 M HCl (83.6%) than in 0.5 M KOH (23.0%). Inhibition efficiency in 0.5 M KOH was, however, synergistically increased in the presence of iodide ions to attain values up to 85.3%. Inhibition efficiency in the acidic and alkaline solutions increased with CV concentration but decreased with rise in temperature, suggesting physical adsorption of CV on the Al surface. The calculated values of activation energy (E_a), free energy of adsorption (ΔG_ads), and heat of adsorption (Q_ads) confirm the physisorption mechanism. The inhibitor adsorption characteristics were approximated by the Freundlich adsorption isotherm.     

SURFACE ANALYSIS OF INHIBITOR FILMS FORMED BY N-(2-HYDROXYBENZILIDENE) THIOSEMICARBAZIDE ON CARBON STEEL IN ACIDIC MEDIA

The corrosion and behavior of carbon steel in 2 M HCl in the presence of N-(2-hydroxybenzilidene) thiosemicarbazide (HBTC) was investigated using weight loss and electrochemical studies. The morphology of carbon steel surface was investigated using scanning electron microscopy (SEM) and Mössbauer spectrometry. The corrosion current was determined using Tafel polarization. The inhibition efficiency increased with HBTC concentration; the experimental results suggest that the presence of HBTC in the solution increases the surface coverage (θ); a decrease in the corrosion spot with the increase of the HBTC concentration indicates good adsorbability of HBTC on the metal surface. The adsorption of this compound on the metal surface is found to obey Langmuir's adsorption isotherm. Mössbauer spectroscopy showed at this stage the main product of corrosion is a non-stoichiometric amorphous Fe³⁺ oxyhydroxide, consisting of a mixture of α, β, and γ-FeOOH, where γ-FeOOH is the main phase.     

pH值和氯离子浓度对碳钢在酸溶液中的腐蚀电化学行为的影响

本文研究了溶液pH值和Cl~-浓度对碳钢在酸溶液中的腐蚀电化学行为的影响。结果表明,OH~-和Cl~-都参与了碳钢的阳极溶解过程,反应级数分别为0.3和0.5;b_α和b_κ分别为55mV和115mV。提出了碳钢在含Cl~-的酸溶液中阳极溶解反应的动力学式及阴极析氢反应的动力学式。实验结果还证明,在pH值与Cl~-浓度两者对碳钢的腐蚀电位φ_c和腐蚀电流密度i_c的影响之间没有交互效应。     

INHIBITION OF MILD STEEL CORROSION IN H2SO4 USING EXUDATE GUM FROM PACHYLOBUS EDULIS AND SYNERGISTIC POTASSIUM HALIDE ADDITIVES

The corrosion inhibitive effects of Pachylobus edulis exudate gum for mild steel in 2 M H₂SO₄ and influence of potassium halide additives on the inhibition efficiency were investigated using hydrogen evolution and thermometric methods at 30°–60°C. Inhibition efficiency was determined by comparing the corrosion rates in the absence and presence of additives. The trend of inhibition efficiency with temperature was used to propose the mechanism of inhibition. It was found that the exudate gum acts as an inhibitor for acid-induced corrosion of mild steel. Inhibition efficiency (%I) of the exudate gum increased with an increase in concentration of the exudate gum and synergistically increased on addition of potassium halides but decreased with increase in temperature. Inhibitor adsorption characteristics were approximated by Temkin adsorption isotherm at all the concentrations and temperatures studied. The phenomenon of physical adsorption is proposed from the activation parameters obtained.     

THE ROLE OF PHOSPHONATE DERIVATIVES ON THE CORROSION INHIBITION OF STEEL IN HCL MEDIA

The inhibition of corrosion of steel by two P-containing compounds, sodium methyldodecyl phosphonate and sodium methyl (11-smethacryloyloxyundecyl) phosphonate, in hydrochloric acid has been investigated at various temperatures using electrochemical techniques (impedance spectroscopy (EIS), potentiodynamic polarization) and weight loss measurements. Inhibition efficiency (E%) increased with phosphonate concentration. Adsorption of inhibitors on the steel surface in 1 M HCl follows the Langmuir isotherm model. EIS measurements showed that the dissolution process of steel occurred under activation control. Polarization curves indicated that inhibitors tested acted as cathodic inhibitors. The temperature effect on the corrosion behavior of steel in 1 M HCl without and with the inhibitor was studied in the temperature range from 313 to 353 K. The adsorption free energy and activation parameters for the steel dissolution reaction in the presence of phosphonates were determined.     

THE ROLE OF PHOSPHONATE DERIVATIVES ON THE CORROSION INHIBITION OF STEEL IN HCL MEDIA

The inhibition of corrosion of steel by two P-containing compounds, sodium methyldodecyl phosphonate and sodium methyl (11-smethacryloyloxyundecyl) phosphonate, in hydrochloric acid has been investigated at various temperatures using electrochemical techniques (impedance spectroscopy (EIS), potentiodynamic polarization) and weight loss measurements. Inhibition efficiency (E%) increased with phosphonate concentration. Adsorption of inhibitors on the steel surface in 1 M HCl follows the Langmuir isotherm model. EIS measurements showed that the dissolution process of steel occurred under activation control. Polarization curves indicated that inhibitors tested acted as cathodic inhibitors. The temperature effect on the corrosion behavior of steel in 1 M HCl without and with the inhibitor was studied in the temperature range from 313 to 353 K. The adsorption free energy and activation parameters for the steel dissolution reaction in the presence of phosphonates were determined.     

SYNERGISTIC EFFECT OF N,N-BIS(PHOSPHONOMETHYL) GLYCINE AND ZINC IONS IN CORROSION CONTROL OF CARBON STEEL IN COOLING WATER SYSTEMS

A protective film has been developed on the surface of carbon steel in low chloride aqueous environment using a synergistic mixture of an environmentally friendly phosphonic acid, N,N-bis(phosphonomethyl) glycine (BPMG), and zinc ions. Impedance studies of the metal/solution interface indicated that the surface film is highly protective against the corrosion of carbon steel in the chosen environment. Potentiodynamic polarization studies showed that the inhibitor is a mixed inhibitor. X-ray photoelectron spectroscopic analysis (XPS) of the film showed the presence of the elements iron, phosphorus, nitrogen, oxygen, carbon, and zinc. Deconvolution spectra of these elements in the surface film showed the presence of oxides/hydroxides of iron(III), Zn(OH)₂, and [Zn(II)-BPMG] complex. This inference is further supported by the reflection absorption Fourier transform infrared spectrum of the surface film. Analysis by SEM is presented for both the corroded and protected metal surfaces. Based on all these results, a plausible mechanism of corrosion inhibition is proposed.     

INVESTIGATION OF ADSORPTION AND INHIBITIVE PROPERTIES OF SOME DIAMINE COMPOUNDS ON MILD STEEL CORROSION IN HYDROCHLORIC ACID SOLUTION

In this work, the adsorption and corrosion inhibition effect of two new synthesized compounds on mild steel in 6 M hydrochloric acid was studied by electrochemical impedance spectroscopy, Tafel polarization, weight loss, quantum, and atomic force microscopy methods. The obtained results show that these compounds are efficient corrosion inhibitors for mild steel in hydrochloric acid media. Electrochemical impedance spectroscopy shows that inhibition efficiency increases with increase of concentration of both inhibitors. These molecules obey the Langmuir adsorption isotherm. Some samples of mild steel were examined by atomic force microscopy. Quantum chemical calculations were further applied to reveal the adsorption structure and explain the experimental results.     

SYNTHESIS,CHARACTERIZATION, AND COMPARATIVE STUDY OF PYRIDINE DERIVATIVES AS CORROSION INHIBITORS OF MILD STEEL IN HCl MEDIUM

Radical catalysis has been used to achieve addition of dodecanethiol and mercaptoacetic acid to 4-vinylpyridine (4VP), giving 4-(dodecylthiaethyl)pyridine (DTEP) and 4-pyridylethylthia-acetic acid (PETAA). The purified monoadducts have been characterized using ¹H NMR and ¹³C NMR spectroscopy. Inhibition of the corrosion of mild steel in 1 M HCl by 4VP, DTEP, and PETAA has been investigated at 308 K using weight loss measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) methods. The results obtained show that PETAA is the best inhibitor and its inhibition efficiency (E %) increases with the inhibitor concentration, reaching up to 93% for DTEP at 10^?3 M. Potentiodynamic polarization studies clearly revealed that the inhibitors changed the mechanism of hydrogen evolution and that they acted as mixed inhibitors but most effectively in the cathodic range.     

几种活性炭表面酸性基团的测定及其对吸附性能的影响

考察了测定活性炭表面酸性基团方法的影响因素，测定了几种活性炭表面酸性基团的数量，初步研究了苯酚和苯甲酸在活性炭上的吸附与活性炭表面酸性基团的数量、种类之间的关系，结果表明：苯酚和苯甲酸在活性炭上的吸附在相当程度上受活性炭表面酸性基团的数量与种类的影响；苯酚的吸附量，随活性炭单位表面上酚羟基和羧基数量的增加而降低；而苯甲酸的吸附则与炭表面的酸性基团总量有关。     

BIOMASS EXTRACTS FOR MATERIALS PROTECTION: CORROSION INHIBITION OF MILD STEEL IN ACIDIC MEDIA BY Terminalia chebula EXTRACTS

The inhibiting action of the fruit extract of Terminalia chebula (TC) on mild steel corrosion in 1 M HCl solution was studied using gravimetric, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. The experimental results showed that TC functioned as an inhibitor in the acidic corrodent and that corrosion inhibition efficiency increased with extract concentration. Cathodic and anodic polarization curves show that TC functioned as a mixed-type inhibitor, while impedance results show that the extract organic matter was adsorbed at the metal/corrodent interphase. A computational study of the adsorption behavior of some of the organic constituents of the extracts was carried out using density functional theory (DFT). The computations were used to theoretically ascertain the individual contributions of the constituents to the observed corrosion-inhibiting effect of the extract.     

THE EFFECT OF ENVIRONMENTALLY BENIGN FRUIT EXTRACT OF SHAHJAN (MORINGA OLEIFERA) ON THE CORROSION OF MILD STEEL IN HYDROCHLORIC ACID SOLUTION

The inhibition of the corrosion of mild steel in hydrochloric acid solution by the fruit extract of shahjan (Moringa oleifera) was studied using weight loss, electrochemical impedance spectroscopy (EIS), linear polarization, and potentiodynamic polarization techniques (Tafel). Inhibition was found to increase with increasing concentration of the extract. The effect of temperature, immersion time, and acid concentration on the corrosion behavior of mild steel in hydrochloric acid solutions with addition of extract was also studied. The inhibition occurred via adsorption of the inhibitor molecules on the mild steel surface obeying the Langmuir adsorption isotherm. Thermodynamic activation parameters such as activation energy, enthalpy (ΔH*), and entropy (ΔS*) of activation for corrosion process were calculated and discussed. The results obtained show that both chemical and physical adsorption of inhibitor molecules occur simultaneously and the fruit extract of shahjan (Moringa oleifera) could serve as an effective inhibitor of the corrosion of mild steel in hydrochloric acid media.     

THERMODYNAMIC AND KINETIC STUDY OF ADSORPTION OF Ni(II) IONS ON CARBON ANODE DUST

In this study the use of carbon anode dust (CAD), which is the solid residue from aluminum production, as a low-cost adsorbent for the removal of Ni(II) ions from wastewater was investigated. A mechanism of adsorption kinetics and thermodynamics was proposed. In order to investigate the adsorption process of nickel ions on CAD three kinetic models were used: Lagergren's pseudo-first-order model, pseudo-second-order model, and the intra-particle diffusion model. Various thermodynamic parameters, such as the energy of activation (E_a), activation enthalpy (ΔH*), activation entropy (ΔS*), and free energy of activation (ΔG*), were evaluated. Observation of the value of the energy of activation suggests that the process uptake of Ni(II) ions can be described as activated chemisorption. The positive values of enthalpy of activation and free energy of activation, as well as negative values of entropy of activation, mean that the process of removal of Ni(II) ions is endothermic, non-spontaneous, and without structural changes in the solid carbon anode dust particles.