P.C. Okafor

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...

Inhibitive action of Carica papaya extracts on the corrosion of mild steel in acidic media and their adsorption characteristics

Purpose – To evaluate the effect of different parts of Carica papaya (leaves (LV), seeds (SD), heart wood (HW) and bark (BK)) as eco‐friendly and non‐toxic mild‐steel corrosion inhibitors in H2SO4 at 30 to 60 oC.Design/methodology/approach – Acid extracts of the different parts of Carica papaya were used as inhibitors in various corrosion tests. Gravimetric and gasometric techniques were used to characterise the mechanism of inhibition.Findings – The LV, SD, HW and BK extracts were found to inhibit mild steel corrosion in H2SO4. The inhibition efficiencies of the plants part extracts follow the trend: LV > SD > HW > BK. Inhibition efficiency increased with extracts concentration but decreased with temperature. Physical adsorption of the phytochemical components of the plant on the metal surface is proposed as the mechanism of inhibition. The experimental data fits well into the Langmuir and Temkin adsorption isotherms.Practical implications – The plant extracts can be used in chemical cleaning and pickin...

Eco‐friendly corrosion inhibitors: inhibitive action of ethanol extracts of Garcinia kola for the corrosion of mild steel in H2SO4 solutions

– This paper aims to investigate the inhibitive effect of ethanol extracts of Garcinia kola (EXG) for the corrosion of mild steel in H2SO4 solutions. The study is another trial to find a cheap and environmentally safe inhibitor for mild steel corrosion., – The inhibition efficiency has been evaluated using the hydrogen evolution technique at 30‐60°C. The mechanism of adsorption inhibition and type of adsorption isotherm were proposed based on the trend of inhibition efficiency and kinetic data., – The results obtained indicate that EXG inhibits the corrosion of mild steel in acidic medium and that the inhibition efficiency increases with an increase in the concentration of ethanol extracts and decreasing temperature. The inhibition efficiency increased on addition of potassium iodide to EXG, indicating synergism. The experimental data obeyed the Langmuir adsorption isotherm as well as the El‐Awady et al. thermodynamic‐kinetic model. The activation energy of inhibition of 6.8508 KJ/mol calculated for the corrosion process suggests that the EXG molecules are physically adsorbed on the metal surface., – Further investigations involving electrochemical studies such as polarization method will provide further enlightenment on the mechanistic aspect of the corrosion inhibition., – This paper provides new information on the possible application of EXG as an environmentally friendly corrosion inhibitor under the specified conditions. This environmentally friendly inhibitor could find possible applications in metal surface anodizing and surface coatings.

Corrosion inhibition and adsorption behaviour of Ocimum basilicum extract on aluminium

Purpose – To appraise the inhibiting effect of Ocimum basilicum extract on aluminium corrosion in 2 M HCl and 2 M KOH solutions, respectively, at 30 and 60°C.Design/methodology/approach – Corrosion rates were determined using the gas‐volumetric technique and the values obtained in absence and presence of extract was used in calculation of the inhibition efficiency. The mechanism of inhibition was estimated from the trend of inhibition efficiency with temperature.Findings – Ocimum basilicum extract was found to inhibit aluminium corrosion in the acidic and alkaline environments. Inhibition efficiency increased with extract concentration but decreased with rise in temperature, suggesting physical adsorption of the organic matter on the metal surface. These results were corroborated by kinetic and activation parameters for corrosion and adsorption processes evaluated from the experimental data at the temperatures studied. Halide additives synergistically improved the inhibition efficiency of the extract.Orig...

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...

Studies on the inhibition of aluminium corrosion by 2-acetylphenothiazine in chloroacetic acids

The inhibition of corrosion of aluminium in chloroacetic acids namely monochloroacetic acid (MCA), dichloroacetic acid (DCA) and trichloroacetic acid (TCA) solution using 2-acetylphenothiazine (2APTZ) at 303 K and 313 K at concentrations 1 x 10 - 3 M, 1 x 10 - 4 M, 7.5 x 10 - 5 M, 5 x 10 - 5 M and 1 x 10 - 5 M was studied using the weight loss and hydrogen evolution techniques. The order of % inhibition efficiency of 2APTZ in MCA is 1 x 10 - 3 M (60.24%) > 1 x 10 - 4 M (44.58%) > 7.5 x 10 M (35.54%) > 5 x 10 - 5 M (32.14%) > 1 x 10 - 5 M (27.71%) at 303 K. Similar trend was observed at 313 K and lower values were observed for DCA and TCA. 86.16% inhibition efficiency was obtained at the highest concentration studied using the hydrogen evolution technique. The two techniques used however reveal that 2APTZ inhibits corrosion reaction. The mechanism of physical adsorption is proposed from the obtained average. E a values of 76.05 KJmol - 1 for MCA, 70. 75 KJmol - 1 for DCA and and 68.52 KJmol - 1 for TCA. 2APTZ was also found to obey the Freundlish adsorption isotherm equation at the concentration studied. The two techniques employed revealed a first order kinetics.

Inhibitory Action of Artemisia annua Extracts and Artemisinin on the Corrosion of Mild Steel in H2SO4 Solution

The action of ethanol (EEAA), acid (AEAA), and toluene (TEAA) extracts from Artemisia annua and Artemisinin (ATS) on mild steel corrosion in H2SO4 solutions was investigated using gravimetric and gasometric techniques. The extracts and ATS functioned as good inhibitors, and their inhibition efficiencies (%IE) followed the trend: EEAA > AEAA > TEAA > ATS. %IE increased with increase in inhibitors concentration and decreased with increase in temperature. The enhanced %IE values of the extracts were attributed to synergistic effect of the components of the plant extracts with ATS. The adsorption of the inhibitors was consistent with Langmuir isotherm. Physisorption is proposed as the mechanism of inhibition.

Combretum bracteosum extracts as eco‐friendly corrosion inhibitor for mild steel in acidic medium

Purpose – The purpose of this paper is to investigate the corrosion inhibitive properties of extracts from mature leaves of Combretum bracteosum for the corrosion of mild steel in H2SO4.Design/methodology/approach – Acid extracts from mature leaves of Combretum bracteosum are used as mild steel corrosion inhibitors in various tests at 30‐60°C. The gravimetric and hydrogen evolution (via the gasometric assembly) measurements are conducted.Findings – The mature leaves of Combretum bracteosum extracts inhibit the corrosion of mild steel in H2SO4 to reasonable extent. Inhibition efficiency increases with the plant extracts concentration and decreases with temperature. Phenomenon of physical adsorption is proposed as the mechanism of inhibition and the Frumkin adsorption isotherm obeyed. Kinetic parameters for the dissolution of mild steel in H2SO4 solutions are calculated.Practical implications – Mature leaves extract from Combretum bracteosum can be used in chemical cleaning and pickling processes.Originalit...

3-[(4-amino-2- methyl-5-pyrimidinyl) methyl]-5- (2-hydroxyethyl)-4-methyl thiazolium chloride hydrochloride as green corrosion inhibitor of copper in HNO3 solution and its adsorption characteristics

Abstract The inhibitory effect of 3-[(4-amino-2-methyl-5-pyrimidinyl) methyl]-5-(2-hydroxyethyl)-4-methyl thiazolium chloride hydrochloride (thiamine hydrochloride) or vitamin B1 hydrochloride on acid corrosion of copper in 2.5 M nitric acid (HNO3) solution was investigated using a weight loss method. Thiamine hydrochloride inhibited the corrosion of copper in 2.5 M HNO3 solutions. The inhibition efficiency increased with increasing concentration of thiamine hydrochloride but decreased with increasing exposure. Adsorption of thiamine hydrochloride molecules on copper surface was found to obey Langmuir adsorption isotherm with standard free energy of adsorption (Δ ) –30.55 kJ mol−1. The inhibition mechanism was characterized from trends of inhibition efficiency, thermodynamic, and kinetic parameters.

THE INHIBITORY EFFECT OF SOME BIPYRIDINE DERIVATIVES ON THE CORROSION BEHAVIOR OF N80 CARBON STEEL IN SULPHURIC ACID SOLUTIONS

The corrosion inhibition characteristics of 2,2′-bipyridine (BIPY) and 2,2′-bipyridine-3,3′-dicarboxylic acid (BIDA), on carbon steel in sulphuric acid solutions was studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques at 20°C, 30°C and 40°C. The results indicate that the organic compounds inhibit the corrosion of mild steel in H2SO4 solutions and the extent of inhibition increases with inhibitor concentration and decreases with temperature. A mixed-inhibition mechanism is proposed for the inhibitive effects of the compounds. The order of inhibition efficiency obtained was BIDA>BIPY. There is a good correlation between the quantum chemical parameters and experimentally determined inhibition efficiency of the inhibitors. The adsorption characteristics of the inhibitor were approximated by Temkin isotherm. Morphological study of the carbon steel electrode surface was undertaken by scanning electron microscope (SEM) and the interfacial species formed on the surface in the presence of inhibitors analyzed by Infrared spectroscopy.