Saviour A. Umoren

Gum arabic as a potential corrosion inhibitor for aluminium in alkaline medium and its adsorption characteristics

Purpose – To investigate the inhibitive effect of gum arabic (GA) for the corrosion of aluminium in alkaline (NaOH) medium and determine its adsorption characteristics. The present work is another trial to find a cheap and environmentally safe inhibitor for aluminium corrosion.Design/methodology/approach – The inhibition efficiency (%I) has been evaluated using the hydrogen evolution (via the gasometric assembly) and the thermometric methods at 30 and 40°C. The concentrations of GA (inhibitor) used were 0.1‐0.5 g/l and the concentrations of NaOH (the corrodent) were 0.1‐2.5 M. The mechanism of adsorption inhibition and type of adsorption isotherms were proposed from the trend of inhibition efficiency with temperature, Ea, ΔGads and Qads values.Findings – GA inhibited the corrosion of aluminium in NaOH solutions. The inhibition efficiency increased with increase in GA concentration and with increase in temperature. Phenomenon of chemical adsorption is proposed for the inhibition and the process followed th...

Effect of halide ions on the corrosion inhibition of mild steel in acidic medium using polyvinyl alcohol

Purpose – To investigate the effect of halide ions on the corrosion inhibition of mild steel using polyvinyl alcohol (PVA) in H2SO4 at 30‐60°C and to study the mechanism of action.Design/methodology/approach – The corrosion rates were determined using the gravimetric (weight loss) and gasometric (hydrogen evolution) techniques. The results obtained in the absence and presence of PVA, halides, PVA – halides combination were used to calculate the inhibition efficiency (%I), degree of surface coverage and to propose the mechanism of inhibition and type of adsorption.Findings – Results obtained showed that inhibition efficiency (%I) increased with the increase in concentration of PVA, on the addition of halides and with the increase in temperature. Phenomenon of chemical adsorption was proposed and PVA was found to obey Langmuir, Flory‐Huggins and Freundlich adsorption isotherms. The synergism parameter, S1, evaluated was found to be greater than unity and the values of Ea, ΔH°, ΔS° and ΔG° obtained revealed ...

Application of carbohydrate polymers as corrosion inhibitors for metal substrates in different media: A review

Naturally occurring polysaccharides are biopolymers existing as products of biochemical processes in living systems. A wide variety of them have been employed for various material applications; as binders, coatings, drug delivery, corrosion inhibitors etc. This review describes the application of some green and benign carbohydrate biopolymers and their derivatives for inhibition of metal corrosion. Their modes and mechanisms of protection have also been described as directly related to their macromolecular weights, chemical composition and their unique molecular and electronic structures. For instance, cellulose and chitosan possess free amine and hydroxyl groups capable of metal ion chelation and their lone pairs of electrons are readily utilized for coordinate bonding at the metal/solution interface. Some of the carbohydrate polymers reviewed in this work are either pure or modified forms; their grafted systems and nanoparticle composites with multitude potentials for metal protection applications have also been highlighted. Few inhibitors grafted to introduce more compact structures with polar groups capable of increasing the total energy of the surface have also been mentioned. Exudate gums, carboxymethyl and hydroxyethyl cellulose, starch, pectin and pectates, substituted/modified chitosans, carrageenan, dextrin/cyclodextrins and alginates have been elaborately reviewed, including the effects of halide additives on their anticorrosion performances. Aspects of computational/theoretical approach to corrosion monitoring have been recommended for future studies. This non-experimental approach to corrosion could foster a better understanding of the corrosion inhibition processes by correlating actual inhibition mechanisms with molecular structures of these carbohydrate polymers.

Studies of the anti‐corrosive effect of Raphia hookeri exudate gum‐halide mixtures for aluminium corrosion in acidic medium

Purpose – The purpose of this paper is to investigate the effect of Raphia hookeri exudate gum and halide ions on the corrosion inhibition of aluminium in HCl solutions at 30‐60°C and to study the mechanism of action.Design/methodology/approach – The corrosion rates were determined using the gravimetric (weight loss), gasometric (hydrogen evolution) and thermometric techniques. The results obtained in the absence and presence of Raphia hookeri, halides and Raphia hookeri – halides combination were used to calculate the inhibition efficiency (%I), degree of surface coverage and to propose the mechanism of inhibition and type of adsorption.Findings – Results obtained showed that the Raphia hookeri exudates gum acted as an inhibitor for aluminium corrosion in acidic environment. Inhibition efficiency (%I) increased with increase in concentration of the Raphia hookeri exudates gum and synergistically increased to a considerable extent on the addition of halide ions. The increase in inhibition efficiency (%I) ...

Corrosion Inhibition of Aluminium Using Exudate Gum from Pachylobus edulis in the Presence of Halide Ions in HCl

The anti-corrosive effect of Pachylobus edulis exudate gum in combination with halides ions (Cl–, Br– and I–) for aluminium corrosion in HCl was studied at temperature range of 30-60°C using weight loss method. Results obtained showed that the naturally occurring exudate gum acts as an inhibitor for aluminium corrosion in acidic environment. Inhibition efficiency (%I) increases with increase in concentration of the exudate gum and synergistically increased to a considerable extent on the addition of the halide ions. The increase in inhibition efficiency (%I) and surface coverage (θ) in the presence of the halides was found to be in the order I– > Br– > Cl– which indicates that the radii as well as electronegativity of the halide ions play a significant role in the adsorption process. Pachylobus edulis exudate gum obeys Temkin adsorption isotherm. Phenomenon of physical adsorption is proposed from the values of kinetic and thermodynamic parameters obtained. The values of synergism parameter (S1) obtained for the halides are greater than unity suggesting that the enhanced inhibition efficiency of the P. edulis caused by the addition of the halide ions is only due to synergistic effect.

Performance evaluation of pectin as ecofriendly corrosion inhibitor for X60 pipeline steel in acid medium: experimental and theoretical approaches.

The corrosion inhibition effect of pectin (a biopolymer) for X60 pipeline steel in HCl medium was investigated using weight loss, electrochemical, water contact angle measurements, and scanning electron microscopy techniques. The results obtained show that pectin acts as a good corrosion inhibitor for X60 steel. Inhibition efficiency increased with increase in pectin concentration and temperature. Potentiodynamic polarization results reveal that pectin could be classified as a mixed-type corrosion inhibitor with predominant control of the cathodic reaction. The effective corrosion inhibition potential of pectin could be related to the adsorption of pectin molecules at the metal/solution interface which is found to accord with the Langmuir adsorption isotherm model and a protective film formation. Quantum chemical calculations provided insights into the active sites and reactivity parameters governing pectin activity as a good corrosion inhibitor for X60 steel.

POLYVINYLPYROLLIDONE AND POLYACRYLAMIDE AS CORROSION INHIBITORS FOR MILD STEEL IN ACIDIC MEDIUM

The corrosion inhibition of mild steel in 1 M H2SO4 in the presence of polyvinylpyrollidone (PVP) and polyacrylamide (PA) as inhibitors at 30–60°C was studied using gravimetric and gasometric techniques. The inhibition efficiency (1%) increased with increase in concentration of the inhibitors. Increase in temperature increased the corrosion rate in the absence and presence of inhibitors but decreased the inhibition efficiency. Both PVP and PA were found to obey Temkin adsorption isotherm and Kinetic-Thermodynamic Model of El-Awady at all the concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the activation parameters obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. PVP was found to be a better inhibitor than PA.

Water‐soluble polymers as corrosion inhibitors

Purpose – To determine the inhibition efficiency and adsorption characteristics of two water soluble polymers namely polyvinyl alcohol (PVA) and polyethyleneglycol (PGE) as corrosion inhibitors of mild steel in H2SO4.Design/methodology/approach – The inhibition efficiencies of PVA and PEG were evaluated using the weight loss and hydrogen evolution techniques at 30‐60°C.Findings – The inhibition efficiency (I per cent) of the inhibitors increased with increase in concentration and temperature. The inhibitors (PVA and PEG) were found to obey Temkin, Freundlich and Langmuir adsorption isotherms from the fit of the experimental data at all concentrations and temperatures studied. The phenomenon of chemical adsorption is proposed from the activation parameters obtained. PEG was found to be a better inhibitor than PVA.Research limitations/implications – The mechanistic aspect of the corrosion inhibition can be better understood using electrochemical studies such as polarization and AC impedance spectra.Practica...

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.

Leaves extract of Ananas sativum as green corrosion inhibitor for aluminium in hydrochloric acid solutions

Abstract The inhibition of corrosion of aluminum in hydrochloric acid solutions by the ethanolic extract of the leaves of Ananas sativum was studied using weight loss and hydrogen evolution methods. It was found that the plant extract retarded the acid induced corrosion of aluminum. Inhibition efficiency increased with increasing concentration of the extract and temperature. Adsorption studies revealed that Langmuir adsorption isotherm is the best adsorption model applicable to the adsorption of A. sativum on aluminum surface. Activation parameters such as activation energies (E a), activation enthalpy (ΔH o), and activation entropy (ΔS o) were evaluated from the effect of temperature on the corrosion and inhibition processes.