Subramanyan, N. (1971) Electrochemical processes in corrosion the corrosion-inhibitive nature and electro capillary behaviour of some organic sulphur compounds in 1 N sulphuric acid. PhD thesis, Banaras Hindu University.

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The action of organic compounds as inhibitors of corrosion of metals has been explained in various ways. It has been suggested that the inhibition increases with increasing size and molecular weight. Another view that has been put forward is that the organic substances increase the hydrogen overvoltage at the cathodic sites and thereby bring down corrosion. It has been postulated that the corrosion inhibitors get adsorbed on the cathodic sites. However, it has subsequently been demonstrated that they get adsorbed on the anodic sites also. The formation of films of the compound formed by the inhibitors with the metal surface has also been put up as the cause of corrosion inhibition. Recently, attempts have been made to explain the adsorption of inhibitors in terms of the functionally reactive groups amine and sulphide and the effects of various attached groups on the functional groups. In addition, the role of conjugated double bond in promoting adsorption by bi-bonding of the organic molecule with the metal surface has been emphasized. Another approach has been to interpret the adsorption of corrosion inhibitors on the basis of charge on the metal surface. In view of reports that the electro capillary behaviour of substances bears a close correlation to their corrosion inhibitive properties, a study has been made of five organic sulphur compounds, viz. dimethyl sulphide, dimethyl sulphoxide, dibutyl sulphide, diphenyl sulphide and thiophene to test the validity of the interpretations of the action of organic compounds with respect to adsorption as how by their electrocapillary behaviour on mercury and their effectiveness in the inhibition of corrosion of steel in 1 N sulphuric acid. A radio-tracer investigation of the adsorption of dibutyl sulphide containing radioactive sulphur has also been included in the study. It has been found that there is relationship between the electrocapillary behaviour on mercury and corrosion inhibition of steel only in the case of some substances. The concept of adsorption increasing with decrease in solubility of organic compounds is not completely borne out. Dimethyl sulphide is adsorbed to a greater extent and is more corrosion inhibitive than dibutyl sulphide in spite of the former’s higher solubility in the acid solution. However, dimethyl sulphoxide which is freely misible with the acid solution is much less adsorbed and corrosion inhibitive than either dimethyl sulphide or dibutyl sulphide. Incidentally, it has been observed that dibutyl sulphide containing radioactive sulphur accelerates the corrosion of steel in 1 N sulphuric acid at concentrations of the compound less than full saturation. Then, aromatic rings are directly linked to sulphur as in dibutyl sulphide, the adsorption on mercury is of a low order and the corrosion inhibitive effect is not high. In the case of thiophene, though adsorption on mercury surface is indicated by its electrocapillary behaviour, it is very poor as inhibitor of corrosion of steel in sulphuric acid. In both these compounds, the effectiveness of the sulphur atom is brought down, because of resonance of the electrons of sulphur with those of the aromatic ring. It is concluded that various aspects of adsorption and interactions between the organic compound and the metal surface, between the solute and the solvent and between the functional group and the attached groups of the compound itself have to be taken into account in attempting to explain the adsorption behaviour and corrosion inhibitive properties of organic corrosion inhibitors.

Item Type: Thesis (PhD)
Uncontrolled Keywords: corrosion inhibition; electrocapillary behaviour
Subjects: Corrosion Science and Engineering
Depositing User: Dr. N Meyyappan
Date Deposited: 12 Jun 2012 06:00
Last Modified: 12 Jun 2012 06:00

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