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.     

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.     

ADSORPTION ISOTHERMS AND HEATS OF IMMERSION IN THE ADSORPTION OF BINARY MIXTURES ON ACTIVATED CARBON

The surface excess and the heat of immersion in the adsorption from binary mixtures on the active carbon surface were calculated in terms of the concentrations of adsorbed phase, the adsorption capacity ratios and the heats of immersion of pure compounds. The surface concentrations of binary mixtures were obtained from the thermodynamic model incorporating the intermolecular interactions between the surface and bulk molecules, and a model for surface activity coefficient considering the orientational states of adsorbed molecules, and the UNIQUAC equation. The calculated adsorption isotherms and heats of immersion were fair agreement with experiments of various binary isotherms.     

MODIFIED PLANTAIN PEEL AS CELLULOSE-BASED LOW-COST ADSORBENT FOR THE REMOVAL OF 2,6-DICHLOROPHENOL FROM AQUEOUS SOLUTION: ADSORPTION ISOTHERMS,KINETIC MODELING,AND THERMODYNAMIC STUDIES

In this study, the feasibility of using modified plantain peel to remove 2,6-dichlorophenol from iaqueous solutions was investigated under batch mode. The effects of physical factors such as initial 2,6-dichlorophenol concentration, contact time, biosorbent particle size, biosorbent dosage and temperature on the removal process were evaluated. The results showed that biosorption of 2,6-dichlorophenol was dependent on these factors. The equilibrium biosorption data were analyzed by the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) adsorption isotherm models. The four tested isotherm models provided good fits to the experimental data obtained at 30°C; however, the Freundlich isotherm model provided the best correlation (R² = 0.9874) of the experimental data. The maximum monolayer biosorption capacity (Q _max ) was found to be 14.25 mg/g. The biosorption kinetics data of 2,6-dichlorophenol were analyzed by pseudo-first-order, pseudo-second-order, Elovich, intraparticle diffusion, and liquid film diffusion models. The five kinetic models fitted well to the biosorption kinetic data; however, the pseudo-second-order kinetic model gave the best fit when the biosorption mechanism was controlled by film diffusion. Thermodynamic quantities such as standard Gibbs free energy (ΔG°), standard enthalpy (ΔH°), standard entropy change of biosorption (ΔS°), and activation energy (E_a) were evaluated, and it was found that the biosorption process was spontaneous, feasible, endothermic in nature and of dual nature, physisorption and chemisorption; however, the physisorption process was dominant. Therefore, modified plantain peel has potential for application as an effective bioadsorbent for removal of 2,6-dichlorophenol from aqueous solution.     

TAURINE AS A GREEN CORROSION INHIBITOR FOR AISI 4130 STEEL ALLOY IN HYDROCHLORIC ACID SOLUTION

The inhibition ability of 2-aminoethanesulfonic acid (taurine) against the corrosion of AISI steel 4130 in 1 M HCl solution was evaluated by polarization, impedance (EIS), and chronoamperometry. Polarization studies indicated that taurine retards both cathodic and anodic reactions through chemical adsorption and blocking the active corrosion sites. The adsorption of this compound obeyed the modified Langmuir adsorption isotherm. EIS data shows that as the inhibitor concentration increased, the charge transfer resistance of steel increased, while double layer capacitance decreased. Kinetic and thermodynamic parameters such as activation energy, enthalpy, entropy, and free energy of activation and adsorption were calculated. Gibbs free energy indicated that the adsorption process is spontaneous. Atomic force microscopy (AFM) and optical microscopy were used to study the steel surface. Surface studies show that the surface of a sample in solution with inhibitor molecules looks more uniform, with less roughness, than that in the uninhibited solution. Results obtained from quantum chemical studies show excellent correlations between quantum chemical parameters and experimental inhibition efficiencies using density functional theory (DFT).     

NEW ARYLAZODYES AS CORROSION INHIBITORS FOR MILD STEEL IN HCl SOLUTION

Five arylazocyanoacetamide derivatives were investigated as corrosion inhibitors of mild steel in 2 M HCl solution using weight loss and galvanostatic polarization techniques. The inhibiting properties were found to depend on the concentration, the temperature, and the molecular structure of the compounds. Enhancement in inhibition efficiency of these compounds was observed on addition of KSCN due to synergism. The inhibitive action may be attributed to adsorption of inhibitor molecules on the active sites of the metal surface following the Frumkin adsorption isotherm. Thermodynamic parameters for the corrosion of mild steel in the presence and absence of the arylazocyanoacetamide derivatives have been calculated. Polarization curves indicate that these compounds act as mixed-type inhibitors. The correlation between inhibition efficiency and quantum chemical parameters has been investigated by PM3 quantum chemical calculation.     

INHIBITION OF MILD STEEL CORROSION IN SULFURIC ACID MEDIUM BY HYDROXYETHYL CELLULOSE

The inhibitive effect of hydroxyethyl cellulose (HEC) on mild steel corrosion in aerated 0.5 M H₂SO₄ solution was studied using gravimetric and electrochemical techniques. The effect of temperature on corrosion and inhibition was also investigated. The results show that hydroxyethyl cellulose functioned as a good inhibitor in the studied environment and inhibition efficiency increased with concentration of inhibitor. Potentiodynamic polarization measurements revealed that HEC inhibited both the cathodic and anodic partial reactions of the corrosion processes. Impedance results clearly show that HEC inhibited the corrosion reaction by adsorption onto the metal/solution interface by significantly decreasing the double layer capacitance (C _dl ). This result was greatly pronounced in the presence of the inhibitor system (HEC + KI) that contains halide additive. Temperature studies revealed an increase in inhibition efficiency with rise in temperature. The adsorption behavior was found to obey the Freundlich isotherm. The values of activation energy, heat of adsorption, and standard free energy suggest that there was transition from physical to chemical adsorption mechanism of HEC on the mild steel surface. Quantum chemical calculations using the density functional theory (DFT) was employed to determine the relationship between molecular structure and inhibition efficiency.     

STUDIES ON THE ADSORPTION OF FURFURAL FROM AQUEOUS SOLUTION ONTO LOW-COST BAGASSE FLY ASH

The present study deals with the sorptive removal of furfural from aqueous solution by carbon-rich bagasse fly ash (BFA). Batch studies were performed to evaluate the influence of various experimental parameters, namely, initial pH (pH₀), adsorbent dose, contact time, initial concentration, and temperature on the removal of furfural. Optimum conditions for furfural removal were found to be pH₀ ≈ 5.5, adsorbent dose ≈4 g/L of solution, and equilibrium time ≈4 h. The adsorption followed pseudo-second-order kinetics. The effective diffusion coefficient of furfural is of the order of 10^-13 m²/s. Equilibrium adsorption data on BFA was analyzed by Freundlich, Langmuir, Dubnin-Radushkevich, Redlich-Peterson, and Temkin isotherm equations using regression and error analysis. The Redlich-Peterson isotherm was found to best represent the data for furfural adsorption onto BFA. Adsorption of furfural on BFA is favorably influenced by a decrease in the temperature of the operation. Values of the change in entropy (ΔS⁰) and heat of adsorption (ΔH⁰) for furfural adsorption on BFA were negative. The high negative value of change in Gibbs free energy (ΔG⁰) indicates the feasible and spontaneous adsorption of furfural on BFA.     

STUDIES ON THE ADSORPTION OF FURFURAL FROM AQUEOUS SOLUTION ONTO LOW-COST BAGASSE FLY ASH

The present study deals with the sorptive removal of furfural from aqueous solution by carbon-rich bagasse fly ash (BFA). Batch studies were performed to evaluate the influence of various experimental parameters, namely, initial pH (p H ₀), adsorbent dose, contact time, initial concentration, and temperature on the removal of furfural. Optimum conditions for furfural removal were found to be p H ₀ ≈ 5.5, adsorbent dose ≈4 g/L of solution, and equilibrium time ≈4 h. The adsorption followed pseudo-second-order kinetics. The effective diffusion coefficient of furfural is of the order of 10^?13 m²/s. Equilibrium adsorption data on BFA was analyzed by Freundlich, Langmuir, Dubnin-Radushkevich, Redlich-Peterson, and Temkin isotherm equations using regression and error analysis. The Redlich-Peterson isotherm was found to best represent the data for furfural adsorption onto BFA. Adsorption of furfural on BFA is favorably influenced by a decrease in the temperature of the operation. Values of the change in entropy (ΔS ⁰) and heat of adsorption (ΔH ⁰) for furfural adsorption on BFA were negative. The high negative value of change in Gibbs free energy (ΔG ⁰) indicates the feasible and spontaneous adsorption of furfural on BFA.     

CORROSION INHIBITION AND ADSORPTION BEHAVIOR OF SOME AZO DYE DERIVATIVES ON CARBON STEEL IN ACIDIC MEDIUM: SYNERGISTIC EFFECT OF HALIDE IONS

Corrosion inhibition of carbon steel in HCl by azo dye derivatives (ADD) was investigated using chemical and electrochemical techniques. Results obtained indicate that ADD inhibited the corrosion of carbon steel in the acid medium. Inhibition efficiency increases with increase in ADD concentration and is synergistically enhanced on addition of iodide and bromide ions. By fitting the obtained experimental data with the Langmuir adsorption model and the Arrhenius equation, some thermodynamic and kinetic parameters for the corrosion process were estimated, and the values support the results obtained. Some quantum chemical parameters and the Mulliken charge densities for ADD were calculated by the MNDO semi-empirical method to provide further insight into the mechanism of inhibition of the corrosion process.     

ON THE ASYMMETRY OF ADSORPTION AND DESORPTION IN MICROPOROUS SOLIDS

We have presented in this paper a theory to explain the asymmetry of the adsorption curve and the desorption curve in microporous solids by taking into account the surface mass action process at the pore mouth of the micropore. Effects of concentration and temperature are particularly investigated. The difference between the activation energy for desorption and that for micropore diffusion has been found to have a strong effect on this asymmetry.     

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.     

羟基铁交联累托石吸附重金属离子Cr6+的研究

研究羟基铁交联累托石的制备及其对Cr6+的吸附性能.当溶液pH值为3左右,羟基铁交联累托石(以下简称CLR)～的用量为13.2g/LH20时,常温振荡吸附60min,Cr6+的去除率可达到98%,残留Cr6+浓度可降至0.5mg/L以下.     

工业纯铁/盐酸体系中聚丙烯酸的缓蚀作用机理

利用稳态极化曲线测量和恒电位方波测极化阻力Rp 的方法研究了聚丙烯酸 (PAAC)在工业纯铁 / 0 .5mol·L-1HCl中的缓蚀行为及其吸附特征 .结果表明 ,PAAC作为阻滞剂参与并阻滞了铁在盐酸溶液中的阳极溶解过程 ,但对阴极过程几乎无作用 .推导了PAAC参与并阻滞铁的阳极溶解过程的动力学方程 ,提出了相应的缓蚀机理 .     

活性炭的改性及其对苯酚吸附行为的研究

通过正交试验的方法,优化活性炭的改性条件;并以活性炭为载体,氢氧化钠溶液为改性剂,在最优条件下制备改性活性炭;测定了改性前后活性炭的比表面积及表面酸性官能团的含量;考察了改性前后活性炭对苯酚的吸附行为。结果表明,在NaOH溶液浓度为0．1mol／l,浸渍时间为3h,活化时间为3h,活化温度为400℃的情况下,改性活性炭吸附效果最佳,苯酚吸附量为149．05mg／g,比未改性活性炭的吸附量提高了61．97％;NaOH-改性活性炭的比表面积为1046．10m2／g,比未改性活性炭的比表面积增加了12．42％,改性后表面的酸性基团含量降低,碱性增强;Freundlich和Langmuir二种等温线模型均能较好的反应活性炭对苯酚的吸附行为,其中Freundlich模型更为理想。     

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.     

ADSORPTION,KINETICS, AND EQUILIBRIUM STUDIES ON REMOVAL OF 4,4-DDT FROM AQUEOUS SOLUTIONS USING LOW-COST ADSORBENTS

The removal of a chlorinated pesticide (4,4-DDT) from aqueous solutions by a batch adsorption technique using different low-cost adsorbents was investigated. Two adsorbents, wood sawdust (A) and cork wastes (B), were used to determine adsorption efficiency. The influence of the adsorbent particle size and the organic matter of water (humic acids) on the removal process was studied. The obtained results were compared to those obtained with a commercial powdered activated carbon (PAC, F400, Chemviron) (C). Kinetic studies were performed to understand the mechanistic steps of the adsorption process. The rate of the adsorption kinetics of 4,4-DDT on the low-cost adsorbents was found best fitted with a pseudo-second-order kinetic model. This is in contrast to the rate of the adsorption kinetics of the PAC F400, which was best fitted with the Lagergren model. The application of the Morris-Weber equation showed that the adsorption process of 4,4-DDT on these adsorbents was complex. Both the adsorption on the surface and the intraparticle diffusion were the rate-controlling mechanisms. Langmuir and Freundlich adsorption isotherms were applicable to the adsorption process and their constants were evaluated. The adsorption capacity (q_m) calculated from the Langmuir isotherm (69.44 mg·g^?1, 19.08 mg·g^?1, and 163.90 mg·g^?1, respectively, for A, B, and C) showed that the process is highly particle size dependent, that the organic matter influenced the adsorption process negatively, and that wood sawdust is the most effective adsorbent for the removal of 4,4-DDT from aqueous solutions. The adsorbents studied exhibited a possible application in water decontamination, as well as in treatment of industrial and agricultural waste waters.     

碘化钾水溶液中碘在活性炭上的吸附等温线

测定了碘化钾水溶液中碘在活性炭上的吸附平衡数据，证明碘在液固两相中的平衡关系可用Ｆｒｅｕｎｄｌｉｃｈ方程式拟合，其平衡方程式为：ｘ／ｍ＝０．３８１Ｃ     

INHIBITION OF THE CORROSION OF NICKEL AND ITS ALLOYS BY NATURAL CLOVE OIL

The corrosion behavior of nickel, Inconel 600, and Inconel 690 in different concentrations of HCl solutions and its inhibition by clove oil was studied using potentiostatic polarization measurements. As the acid concentration increases, the rate of corrosion increases, indicating that HCl accelerates the dissolution of nickel and its alloys. The inhibition efficiency of the clove oil was found to increase with increase of its concentration. The inhibitive action of this oil was discussed in view of adsorption onto the metal surface. The adsorbed layer acts as a barrier between the metal surface and aggressive solution, leading to a decrease in corrosion rate. The adsorption process follows Langmuir adsorption isotherms. It was found that the clove oil provides good protection to nickel and its alloys against pitting corrosion in chloride-containing solution using potentiodynamic anodic polarization techniques.