U.J. Ekpe

Inhibitory action of methyl and phenyl thiosemicarbazone derivatives on the corrosion of mild steel in hydrochloric acid

Abstract The inhibition of corrosion of mild steel (98% Fe) in hydrochloric acid (HCl) by derivatives of thiosemicarbazones has been studied using weight loss and hydrogen evolution techniques. The thiosemicarbazone derivatives used as corrosion inhibitors were 2-acetylpyridine-(4-phenylthiosemicarbazone) (2AP4PTSC) and 2-acetylpyridine-(4-methylthiosemicarbazone) (2AP4MTSC). 2AP4PTSC exhibited a higher maximum inhibition efficiency (80.67%) than 2AP4MTSC (74.59%). Generally, inhibition was found to increase with increasing inhibitor concentration and decreasing temperature. A first-order type of mechanism has been deduced from the kinetic treatment of the results, and the process of inhibition was attributed to physisorption. The difference in the inhibition behaviour of the two compounds is explained in terms of the difference in their molecular structures.

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 ...

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.

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...