Flory Huggins Isotherm Research Articles

Adsorption of tetramethylthiourea in concentrated NaClO4 solutions

Tetramethylthiourea electrosorption behaviour on the mercury electrode in 2, 3 and 4 mol l–1 NaClO4 was determined by means of double-layer differential capacity measurements. The relative surface excess Γ′ of the adsorbate calculated from the surface pressures depended on the NaClO4 concentration. A clear influence of NaClO4 concentration appeared in the changes of interaction parameter A obtained from the Flory–Huggins isotherm and in the permittivity parameter of the inner layer.

Corrosion inhibition of mild steel in sulfamic acid solution by S-containing amino acids

Rp, potentiodynamic polarization curves and EIS techniques were applied to study the effect of five S-containing amino acids on the corrosion of mild steel in 5% sulfamic acid solution at 40 °C. The compounds are effective inhibitors and the inhibition efficiency follow the order: N-acetylcysteine (ACC) > cysteine (RSH) > S-benzylcysteine (BzC) > cystine (RSSR) ≅ methionine (CH3SR). The inhibitors affect the anodic dissolution of steel by blocking the anodic sites of the surface. EIS measurements indicated that charge transfer is the rate determining step in the absence and presence of the inhibitors and the steel/solution interface can be represented by the equivalent circuit Rs(RctQdl). Adsorption of RSH, CH3SR and RSSR follows the Langmuir model while the Temkin isotherm describes the adsorption of ACC and BzC. From the application of the Flory–Huggins isotherm, the number of water molecules displaced by the adsorbing inhibitor molecules was estimated. The potential of zero charge pzc of mild steel without and with the inhibitors is calculated and the mechanism of corrosion inhibition is discussed in the light of the molecular structure.

Synthesis of some ferromagnetic composite resins and their metal removal characteristics in aqueous solutions

In this study, a procedure for synthesis of new organic-inorganic magnetic composite resins was established. The procedure was based upon immobilization of magnetite (Mag) as a ferromagnetic material within the polymer poly(acrylic acid acrylonitrile) P(AA-AN) and the ion exchange resin (Amberlite IR120). The produced magnetic resins, IR120-PAN-Mag (R1) and P(AA-AN)-Mag (R2) were assessed as sorbents for Cr(VI). Various factors influencing the sorption of Cr(VI), e.g., pH, equilibrium time, initial concentration and temperature were studied. The sorption process was very fast initially and maximum sorption was achieved within 3 h and pH 5.1. The kinetic of the system has been evaluated with pseudo first order model, second order model, Elovich model, intra-particle diffusion model and liquid film diffusion model. Chromium interaction with composite particles followed second-order kinetics with a correlation coefficient extremely high and closer to unity and rate constant ( k s) has the values 1.68 × 10 −4 and 1.9 × 10 −4 g (mg −1 min −1) for R1 and R2, respectively. The values of equilibrium sorption capacity ( q e) are consistent with the modeled data and attain the range 893–951 mg g −1. Kinetically, both pore diffusion and film diffusion are participating in ruling the diffusion of Cr(VI) ions. The sorption data gave good fits with Temkin and Flory–Huggins isotherm models. The isotherm parameters related to the heat of sorption are in the range 8–16 kJ mol −1 which is the range of bonding energy for ion exchange interactions and so suggest an ion exchange mechanism for removal of Cr(VI) by the composite sorbents. The adsorption process was exothermic with Δ H in the range of −73 to −97 kJ mol −1. The negative values of Gibbs free energy confirm the feasibility and the spontaneous nature of Cr(VI) removal with these novel composites.

Effect of cationic surfactant and inorganic anions on the electrochemical behavior of carbon steel in formation water

Corrosion behavior of carbon steel in formation water associated crude oil from Egyptian western desert was studied at various concentrations of dodecyl dimethyl ammonium chloride (CS) as a cationic surfactant. Polarization curves indicate that CS has a good inhibition efficiency for carbon steel in formation water and behaves as cathodic inhibitor. The inhibition efficiency was found to increase with increase in CS concentration until reaches a maximum constant value corresponding to the critical micelle concentration of CS and decrease with increase in solution temperature. The adsorption of CS follows the kinetic thermodynamic model and Flory–Huggins isotherm. Thermodynamic parameters obtained indicate that that the presence of the CS increases the activation energy. Polarization and Impedance measurements indicate that the addition of KI has a significant synergistic effect with CS and results in increase the inhibition efficiency of CS in formation water.

Interfacial adsorption with molecular reorientation

Abstract This work presents the results of a theoretical study of semi-infinite linear diffusion of single geometrically anisotropic molecular species to a stationary planar interface and monolayer adsorption at the interface assuming reorientation of the initially flat adsorbed molecules to perpendicular position. A modified Flory–Huggins isotherm including lateral molecular interaction was used in the study of adsorption kinetics with different models of molecular reorientation. The connection between the structural changes of the adsorbed monolayer induced by reorientation of the initially flatly adsorbed molecules and the corresponding subtle, but the experimentally accessible changes in the fractional electrode coverage is established and investigated. It is shown that depending on the rate constants of the reorientation process, the change in the fractional interface coverage can range from barely noticeable to a very pronounced, manifested as a pit in the fractional coverage curve. The possible implications for the experimental detection of reorientation are discussed. The presented theoretical predictions are compliant with the recent experimental findings.

Berberine as a natural source inhibitor for mild steel in 1 M H 2SO 4

Berberine was abstracted from coptis chinensis and its inhibition efficiency on corrosion of mild steel in 1 M H 2SO 4 was investigated through weight loss experiment, electrochemical techniques and scanning electronic microscope (SEM) with energy disperse spectrometer (EDS). The weight loss results showed that berberine is an excellent corrosion inhibitor for mild steel immersed in 1 M H 2SO 4. Potentiodynamic curves suggested that berberine suppressed both cathodic and anodic processes for its concentrations higher than 1.0 × 10 −4 M and mainly cathodic reaction was suppressed for lower concentrations. The Nyquist diagrams of impedance for mild steel in 1 M H 2SO 4 containing berberine with different concentrations showed one capacitive loop, and the polarization resistance increased with the inhibitor concentration rising. A good fit to Flory–Huggins isotherm was obtained between surface coverage degree and inhibitor concentration. The surface morphology and EDS analysis for mild steel specimens in sulfuric acid in the absence and presence of the inhibitor also proved the results obtained by the weight loss and electrochemical experiments. The correlation of inhibition effect and molecular structure of berberine was then discussed by quantum chemistry study.

Influence of halide ions on the inhibitive effect of congo red dye on the corrosion of mild steel in sulphuric acid solution

The inhibitive effect of congo red dye (CR) on mild steel corrosion in sulphuric acid solution was studied at different temperatures using gravimetric techniques. The influence of halide additives namely: KCl, KBr and KI on the inhibition efficiency of CR was also investigated. Inhibition efficiency increased with CR concentration but decreased with rise in temperature. Corrosion activation energies of 82.98 and 96.92kJmol−1 were observed in the absence and presence of CR, respectively. The observed corrosion data suggest that inhibition of mild steel corrosion is due to physical adsorption of the CR molecules on the metal surface, which follow Flory–Huggins isotherm. Inhibition antagonism and synergism were respectively observed at 30 and 60°C on addition of halide salts to inhibited systems containing CR. The inhibition efficiency of CR in the presence of halides increased with rise in temperature and corrosion activation energy in these systems decreased to 40.63kJmol−1. These observations indicate a chemical adsorption mechanism, thus suggesting that the halide ions reversed the mechanism of CR adsorption within the concentration range studied. The calculated values of heat of adsorption confirm physisorption and chemisorption mechanisms respectively for CR adsorption in the absence and presence of halides.

Thermodynamical analysis of the hydrogel state in poly(2-hydroxyethyl acrylate)

The thermodynamical properties of water and polymer in a hydrogel are analyzed from experimental equilibrium sorption isotherms at different temperatures in the case of poly(2-hydroxyethyl acrylate). The equations of the thermodynamics of mixtures allow to calculate the specific partial thermodynamical properties of water and polymer in the hydrogel as a function of its water content. Partial volume of water in the gel at low activities is slightly lower than the specific volume of water in the liquid state. The partial enthalpy and entropy differ significantly from those of pure water at the lowest water contents, and tend to those of pure water for activities close to one. The mutual interaction between the gel's components is discussed through the residual part of the mixing free energy. This function is positive for all gel compositions, suggesting that, on the average, the water–polymer interactions are not stronger than the water–water or polymer–polymer interactions, and that the affinity of water to mix homogeneously with the polymer has a combinatorial origin. The composition dependence of the Flory–Huggins interaction parameter is calculated and explained in terms on the residual free energy. This parameter is compared with the apparent interaction parameter, obtained fitting point by point the experimental sorption isotherm to the Flory–Huggins isotherm. The difference often found between the sorption capacity of an hydrogel when equilibrated in saturated water vapour and in liquid water is discussed.

Effect of octylphenol polyethylene oxide on the corrosion inhibition of steel in 0.5M H2SO4

A non-ionic surfactant, octylphenol polyethylene oxide (OPPEO), was evaluated as an inhibitor for corrosion of low-carbon steel in 0.5 M H 2 SO 4 . Potentiodynamic and potentiostatic methods and scanning electron microscopy were used to study the inhibition effectiveness of the surfactant. The inhibition efficiency was found to increase with the inhibitor concentration and decrease with temperature. OPPEO showed higher constant protection efficiency near its critical micelle concentration. The activation energy of corrosion was found to be higher in presence than in absence of the inhibitor. The experimental data were fitted with the Flory–Huggins isotherm at a molecular ratio of 5:1. The Gibbs energy of adsorption decreases with the temperature. The inhibitor has relatively lower inhibition efficiencies at ambient and higher temperature. This was attributed to the molecular structure of the inhibitor.

Effect of octylphenol polyethylene oxide on the corrosion inhibition of steel in 0.5 M H 2SO 4

A non-ionic surfactant, octylphenol polyethylene oxide (OPPEO), was evaluated as an inhibitor for corrosion of low-carbon steel in 0.5 M H 2SO 4. Potentiodynamic and potentiostatic methods and scanning electron microscopy were used to study the inhibition effectiveness of the surfactant. The inhibition efficiency was found to increase with the inhibitor concentration and decrease with temperature. OPPEO showed higher constant protection efficiency near its critical micelle concentration. The activation energy of corrosion was found to be higher in presence than in absence of the inhibitor. The experimental data were fitted with the Flory–Huggins isotherm at a molecular ratio of 5:1. The Gibbs energy of adsorption decreases with the temperature. The inhibitor has relatively lower inhibition efficiencies at ambient and higher temperature. This was attributed to the molecular structure of the inhibitor.

Adsorption of 1,1,3,3-tetramethyl-2-thiourea on the mercury electrode: dependence on the concentration of the base electrolyte

Adsorption of 1,1,3,3-tetramethyl-2-thiourea (TMTU) on a mercury electrode from 1, 0.5, and 0.1 M NaClO 4 is described by means of the adsorption isotherms constants calculated from the surface pressure as a function of electrode charge density and adsorbate bulk concentration. The adsorption parameters for the double-layer were calculated based on the data from the differential capacity–potential curves. The values of the relative surface excess increase with an increase in the concentration of NaClO 4. In each system studied, significantly smaller values of Γ S for σ M<0 were obtained, compared with the corresponding values for σ M≥0. At positive values of σ M, the values of Δ G° obtained from either the Frumkin or the Flory–Huggins isotherm are similar. However, the values of the parameter A obtained from the Flory–Huggins isotherm are lower. The dependence of Φ M−2 on the relative surface excess at a constant charge density is nonlinear. The rectilinear segments of these dependences obtained for smaller values of Γ′ were analyzed in order to calculate the electrostatic parameters of the inner layer.

Inhibition of mild steel corrosion in sulphuric acid using indigo dye and synergistic halide additives

Gravimetric method was used to study the inhibitory properties of indigo dye during corrosion of mild steel in aerated sulphuric acid solutions at 30–50 °C. The effect of addition of halide salts KCl, KBr and KI was also investigated. The corrosion rates in all systems studied increased with rise in temperature. The inhibition efficiency of indigo dye increased with concentration and synergistically increased on addition of halide salts. Temperature studies revealed increased inhibition efficiency at higher temperatures, which is suggestive of chemisorption mechanism. The inhibitor adsorption characteristics were approximated by Frumkins isotherm and Flory–Huggins isotherm. Activation energy for Fe dissolution in sulphuric acid was observed to reduce from 54.6 kJ mol −1 in the uninhibited system to 34.9 kJ mol −1 in the inhibited system.

Corrosion inhibition of steel in crude oil storage tanks

AbstractThe corrosion behavior of steel in water from certain oil fields with various organic inhibitors was studied by applying potentiodynamic technique at pH 5.9. The inhibitors which were used include 2‐methylbenzimidazole (I), 2‐mercaptobenzimidazole (II), 2‐mercapto‐5‐methylbenzimidazole (III), and 2‐mercaptothiazole (IV). The inhibiting efficiency of the different additives was evaluated from their anodic and cathodic polarization curves at different temperatures.A comparative study of curve fitting procedures using the kinetic thermodynamic model and those utilizing well‐known adsorption isotherms was undertaken. Three types of isotherms were used, Langmuir, Frumkin and Flory‐Huggins isotherm. The results show that the kinetic‐thermodynamic model and Flory‐Huggins isotherms are more suitable to fit the data for the four inhibitors, at all applied temperatures. From the values of binding constants, K, the order of inhibitor efficiency is:III &gt; IV &gt; II &gt; Iand thus 2‐mercapto‐5‐methylbenzimidazole was the most effective inhibitor. The thermodynamic parameters obtained for all the compounds used showed low values of Hads, which indicates that the action of these inhibitors is physically adsorptive in nature.

The effect of propargylic alcohol on the corrosion inhibition of low alloy CrMo steel in sulphuric acid

The effect of propargylic alcohol (PA) on the corrosion inhibition of low alloy CrMo steel in sulphuric acid at the open circuit potential Eoc was investigated by DC-polarization and AC-impedance spectroscopy measurements, respectively. It was found that the addition of PA induced the positive shift of Eoc and the decreasing of cathodic currents. The anomalous Tafel cathodic slopes were explained using a modified adsorption–interaction model. The inhibition process was treated as the substitutional adsorption process. The adsorption of PA was fitted well by means of Flory–Huggins isotherm. The standard free energy of adsorption of PA was calculated (−15 kJmol−1).

N,N-Dipropynoxy methyl amine trimethyl phosphonate as corrosion inhibitor for iron in sulfuric acid

The corrosion inhibition of iron in 0.5 M sulfuric acid by N, N-dipropynoxy methyl amine trimethyl phosphonate has been investigated by means of the potentiodynamic polarization and electrochemical impedance spectrum (E.I.S) techniques. N,N-dipropynoxy methyl amine trimethyl phosphonate was studied in concentrations from 40 ppm to 320 ppm at a temperature of 298 K. The results show that the inhibition mechanism of N,N-dipropynoxy methyl amine trimethyl phosphonate is mixed controlled. It is also found that this inhibitor obeys the Frumkin adsorption isotherm and Flory-Huggins isotherm based on a substitutional adsorption process.

4-Aminoantipyrine as an inhibitor of mild steel corrosion in HCl solution

4-aminoantipyrine (AAP) was tested as a corrosion inhibitor for mild steel in 2 M HCl solution using different techniques: weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that AAP is an inhibitor for mild steel in this medium. The inhibition was assumed to occur via adsorption of the inhibitor molecule on the metal surface. In the 20 to 60 ∘C temperature range, the AAP adsorption follows the Flory–Huggins isotherm and/or the El-Awady et al. kinetic-thermodynamic model. The protection efficiency increases with increasing inhibitor concentration (in the range 10−310−2 M) but decreases with increasing temperature. The thermodynamic functions of dissolution and adsorption processes were calculated.

The effect of some ethoxylated fatty acids on corrosion of aluminium in hydrochloric acid solutions

The inhibitive effect of some ethoxylated fatty acids St(EO) 80, OL(EO) 20, OL(EO) 40 and OL(EO) 80 on the corrosion of two types of aluminium, Al(1) and Al(2), has been studied in 1 M hydrochloric acid solution by weight loss method. The effect of inhibitor concentration, temperature and time of immersion have been investigated. The inhibitive effect of these fatty acids is due to their adsorption on aluminium surfaces. The inhibitive efficiency depends on both the type and concentration of additives. Increasing the ethylene oxide units in the molecules and the presence of the double bond in oleate structure will enhance the inhibition efficiency. The activation energy and the thermodynamic parameters for the corrosion process in the absence and presence of the inhibitors were determined. By fitting the corrosion data, it is found that the results agree with Langmiur, Frumkin, Flory-Huggins isotherm and the kinetic thermodynamic model.

Sorption and transport of ethanol and water in poly(ethylene-co-vinyl acetate) membranes

The ability to control the fluxes and the relative composition of multiple species permeating across a membrane would be invaluable to the design of controlled release systems. The counter-diffusion of ethanol and water across poly(ethylene-co-vinyl acetate) [P(E-co-VAc)] membranes was investigated as a case study. Ethanol and water fluxes across these membranes were measured from the changes of the refractive indices in the donor and receiver solutions. Ethanol and water solubilities in the membranes were determined by a sorption and desorption method. Ethanol absorption followed a Flory-Huggins isotherm, whereas water absorption exhibited a maximum due to opposing factors between the plasticization of the membrane by ethanol and the driving force of water. Ethanol and water diffusivities in the membranes were calculated from the flux and solubility data. In a 37% vinyl acetate P(E-co-VAc) membrane, ethanol permeability was found to increase exponentially with ethanol activity in the membrane; whereas water permeability decreased with water activity in the membrane. Transport models were developed to estimate ethanol and water fluxes across a 37% vinyl acetate P (E-co-VAc) membrane, given any set of compositions in the donor and receiver solutions. The counterdiffusing fluxes of ethanol and water across this membrane were found to be approximately linearly dependent. Additionally, the model suggested that a 37% P (E-co-VAc) membrane slightly favors water over ethanol, in separating ethanol and water by pervaporation.

Digital Simulation of Normal Pulse Polarographic Adsorption Waves of Methyl Viologen

Abstract Digital simulations of the normal pulse polarographic adsorption waves of the nernstian redox species obeying the Frumkin type Flory–Huggins isotherm interpret the unusual electrochemical behavior of methyl viologen. An orientation change of the adsorbed reductant causes a marked positive shift of adsorption waves.

Generalized Flory–Huggins isotherms for adsorption from solution

A new approach to the study of solutions composed of two kinds of molecules differing in size and shape has been developed on the basis of the lattice statistical model of athermal solutions. The results have been used for determination of the adsorption isotherms of organic compounds adsorbed from solution onto homogeneous surfaces. It is shown that the resulting isotherms are generalized forms of the Flory–Huggins isotherm, to which they are reduced by Flory's approximation. The possible ways of introducing the interactions between adsorbed molecules have also been examined. Finally, a critical examination of the validity of the isotherms is made by comparison with experimental data.