Venkatachari, G. (1983) Investigations on the mechanism of corrosion and its inhibition. PhD thesis, Madurai-Kamaraj University.

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Abstract

The mechanism of corrosion of iron in HCl in the presence of quinoline, iodide and hexamine, the inhibition of corrosion of iron in HCl by quinoline, iodide and hexamine, the mechanism of zinc corrosion in HCl and the inhibition of zinc corrosion in HCl by quinoline, iodide and hexamine have been studied by galvanostatic method, potentiodynamic method and impedance method. The scope of Faradic distortion method for measuring corrosion rate and Tafel slopes at corrosion potential has also been examined. The mechanism of corrosion of pure iron in HCl is found to occur through the iron hydroxyl chloride complex (FeClOH) with rds as (FeClOH-)rds ---> FeClOH + e. The presence of quinoline, iodide and hexamine does not alter the mechanism of dissolution since the Tafel slopes are not altered. However, the rate of formation of the intermediate (FeClOH)- is decreased in the presence of inhibitors since these inhibitors are found to decrease the reaction orders with respect to (H+) or (Cl-). Besides, these inhibitors reduce the available area of reaction by (1-θ) through coverage. The amount of inhibition of iron dissolution by quinoline and hexamine is found to be dependent on coverage. The inhibitor efficiency is found to decrease with decrease of (H+) ion concentration and (Cl-) ion concentration. This indicates that these inhibitors adsorb through the cationic form. These inhibitors are found to obey Temkin adsorption isotherm. In the case, Iodide also the inhibitor efficiency decreases with decrease of (H+) ion concentration and the effect of chloride ion is not significant. The dissolution of zinc in HCl is found to be accelerated by both (H+) ions and (Cl-) ions. The mechanism of corrosion of zinc in HCl can be explained in terms of rds as (ZnClrds) + H+ ---> (Zn Cl H+). The inhibitor efficiency of quinoline and hexamine for zinc dissolution in HCl is found to be dependent on the surface coverage. The inhibitor efficiency of quinoline does not vary with (H+) ion concentration, while it increases with increase of (Cl-) ion concentration due to synergistic effect of chloride ions. For iodide and hexamine, the inhibitor efficiencies do not vary in a regular manner with (H+). But inhibitor efficiencies are found to increase with decrease of chloride ion concentration. The Faradic distortion method is found to be useful for measuring ba, bc and Icorr at corrosion potential. Various systems such as iron in 1.0 N HCl, steel in 1.0 N, HCl and zinc in 1.0 N HCl have been examined. The corrosion currents and Tafel slopes obtained by this method are in good agreement with the values obtained by polarisation method. Besides, the corrosion current values obtained from the individual harmonic current values are found to agree each other.

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	Corrosion inhibition
Subjects:	Corrosion Science and Engineering
Divisions:	UNSPECIFIED
Depositing User:	Dr. N Meyyappan
Date Deposited:	12 Jun 2012 06:03
Last Modified:	12 Jun 2012 06:03
URI:	http://cecri.csircentral.net/id/eprint/2802

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