Abstract
The inhibition effect of halide ions such as iodide, bromide and chloride ions on the corrosion of iron in 0.5 mol L-1 H2SO4 and the adsorption behaviour of these ions on the electrode surface have been studied by polarization and impedance methods. It has been found that the inhibition of nearly 90% has been observed for iodide ions at 2.5 <FONT FACE=Symbol>´</FONT> 10-3 mol L-1, for bromide ions at 10 <FONT FACE=Symbol>´</FONT> 10-3 mol L-1 and 80% for chloride ions at 2.5 <FONT FACE=Symbol>´</FONT> 10-3 mol L-1. The inhibition effect is increased with increase of halide ions concentration in the case of I- and Br- ions, whereas it has decreased in the case of Cl- ion at concentrations higher than 5 <FONT FACE=Symbol>´</FONT> 10-3 mol L-1. The double layer capacitance values have decreased considerably in the presence of halide ions which indicate that these anions are adsorbed on iron at the corrosion potential.
Highlights
Adsorption of anions over metal surfaces leading to the inhibitive or stimulation effects on metallic corrosion have been reported by earlier researchers.[1,2,3,4,5,6] It is well known that the dissolution of iron in H SO solutions occurs in four different states viz. active, passive, transpassive and brightening states as determined by the nature and kinetics of reaction involved, which depend on the potential and electrolyte composition
From the table it is clear that the addition of iodide ions in the concentration range 0.5 × 10-3 to 5 × 10-3 mol L-1 markably reduces the dissolution rate of iron in 0.5 mol
It is observed that the icorr values are decreased to 90 μA cm-2 for 5.0 ×10-3 mol L-1 of KCl corresponding to an inhibition efficiency of 78% and after that a sharp rise in corrosion current density is observed with further increase in concentration of chloride ions
Summary
Adsorption of anions over metal surfaces leading to the inhibitive or stimulation effects on metallic corrosion have been reported by earlier researchers.[1,2,3,4,5,6] It is well known that the dissolution of iron in H SO solutions occurs in four different states viz. active, passive, transpassive and brightening states as determined by the nature and kinetics of reaction involved, which depend on the potential and electrolyte composition. Adsorption of anions over metal surfaces leading to the inhibitive or stimulation effects on metallic corrosion have been reported by earlier researchers.[1,2,3,4,5,6] It is well known that the dissolution of iron in H SO solutions occurs in four different states viz. For Tafel polarization method, ct the corrosion inhibition efficiency was evaluated from the measured icorr values using the relationship where icorr and icorr’ are the corrosion current densities without and with the addition of halide ions. The inhibition efficiency was evaluated from the measured charge transfer resistance Rct values as where R and R ’ are the charge transfer resistance values ct ct in the absence and presence of halide ions. From the measured double layer capacitance Cdl, the surface coverage θ of inhibitor is given by since Cdls
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