Adsorption Studies of the Effect of Thiosemicarbazides on the Corrosion of Steel in Phosphoric Acid

Abstract

ABSTRACT:The corrosion inhibition of steel in phosphoric acid by thiosemicarbazide derivatives has been studied using different chemical and electrochemical techniques. The observed order of increasing inhibition efficiency was correlated with changes in the molecular structures of the inhibitors. Potentiodynamic polarization curves indicate that the compounds are mixed-type inhibitors. Electrochemical impedance spectroscopy has been used successfully to evaluate the performance of the inhibitors. AC measurements showed that the dissolution process was activation-controlled. The kinetic-thermodynamic model and the Flory-Huggins adsorption isotherm described the experimental findings well. The number of active sites, binding constant and change in free energy were computed for all the inhibitors studied. It was found that the inhibitor molecule was adsorbed through more than one active centre and occupied more than one active site on the steel surface.

Corrosion Inhibitive Effect and Adsorption Behaviour of Hibiscus Sabdariffa Extract on Mild Steel in Acidic Media

“…Fig. 4 shows the adsorption curves of the extracts on to mild steel from 1 M H 2 SO 4 and 2 M HCl, illustrating the relationship between surface coverage and concentration [1]. Adsorption of the extract is further substantiated by the fit of the experimental data to the Langmuir adsorption isotherms (Fig.…”

“…These inhibitors have also found useful application in the formulation of primers and anti-corrosive coatings, but a major disadvantage is their toxicity and as such their use has come under severe criticism. Among the alternative corrosion inhibitors, organic substances containing polar functions with nitrogen, sulphur, and/or oxygen in the conjugated system have been reported to exhibit good inhibiting properties [1][2][3][4]. The inhibitive characteristics of such compounds derive from the adsorption ability of their molecules, with the polar group acting as the reaction centre for the adsorption process.…”

Inhibitive Effect of<i> Costus afer</i> Extracts on Mild Steel Corrosion in Acidic Medium

“…where f ( , x) is the configuration factor whose functional form depends on the physical model adopted and assumptions made in deriving the isotherm, is the degree of surface coverage, x is known as the size ratio which gives the number of water molecule replaced by the inhibitor molecule, is a molecular interaction parameter whose value depends on the type of molecular interactions in the adsorption layer and the degree of homogeneity of the surface, C is the inhibitor concentration while k is the adsorption equilibrium constant which is temperature dependent according to the relation [4,25,26]. The correlation coefficients obtained (r 2 = 0.993) indicate that the adsorption of extracts of Costus afer onto the mild steel surface was best described by Langmuir adsorption isotherm (Figures 4 -5).…”

Inhibition of Corrosion of Aluminum Alloy AA8011 in Alkaline Medium Using<i> Palisota hirsute</i> Extract

“…where f ( , x) is the configuration factor whose functional form depends on the physical model adopted and assumptions made in deriving the isotherm, is the degree of surface coverage, x is known as the size ratio which gives the number of water molecule replaced by the inhibitor molecule, is a molecular interaction parameter whose value depends on the type of molecular interactions in the adsorption layer and the degree of homogeneity of the surface, C is the inhibitor concentration while k is the adsorption equilibrium constant which is temperature dependent according to the relation [21,29,30]. The Langmuir and Temkin Isotherms were tested using the experimental data and the Langmuir isotherm gave the best fit.…”