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Peculiarities in the Behaviour of Thiourea as corrosion‐inhibitor
Author(s) -
El Din A. M. Shams,
El Hosary A. A.,
Saleh R. M.,
El Kader J. M. Abd
Publication year - 1977
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19770280107
Subject(s) - thiourea , sulfuric acid , dissolution , chemistry , inorganic chemistry , hydrogen sulfide , nitric acid , corrosion , adsorption , hydrogen peroxide , sulfide , metal , nuclear chemistry , sulfur , organic chemistry
The dissolution of Fe, cu, Zn and Al in nitric, hydrochlorid and sulfuric acids is retarded by low concentrations of thiourea, while higher thiourea concentrations may bring about a stimulation of corrosion. In nitric acid thiourea is probably oxidised (heat evolution); the dithioformamidine formed at first is then hydrolysed to give diaminocarbonyl disulfide which again is reduced to thiocarbamic acid at the cathodic sites of the surface. The depolarisation thus produced gives rise to accelerated dissolution. In non‐oxidising acids a monomolecular layer of thiourea is adsorbed at the metal at first; its subsequent reduction to sulfide and hydrogen sulfide again gives rise to an enhancement of corrosion. The critical concentration of the transition from inhibition to stimulation depends ont he type of the acid and its concentration.