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Dithio‐oxamide as inhibitor of Copper corrosion in chloride solutions at various ph values
Author(s) -
Monticelli C.,
Brunoro G.,
Frignani A.
Publication year - 1991
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.19910420806
Subject(s) - corrosion , chloride , copper , dielectric spectroscopy , dissolution , electrochemistry , chemistry , erosion corrosion of copper water tubes , corrosion inhibitor , inorganic chemistry , polarization (electrochemistry) , electrolyte , sodium , nuclear chemistry , electrode , organic chemistry
This paper investigates the inhibiting properties of dithiooxamide (DTOA) towards copper corrosion in chloride media at different pH values. The aggressive solutions were prepared by dissolving 0.1 M sodium chloride in a Britton Robinson buffer, adjusted at the pH values of 3, 5, 7 and 9. The inhibitor was tested at the concentration of 10 −3 M. The inhibiting efficiency of DTOA was evaluated after 20 days of immersion in the solutions at the temperature of 30°C. Both dc (polarization curves and voltammetric tests) and ac (electrochemical impedance spectroscopy, EIS) electrochemical tests were performed to elucidate the inhibition process. The results indicate that DTOA affords its best inhibiting efficiency at pH 5 and 7, but even at pH 3 it can retard the corrosion process. On the contrary, at pH 9 it stimulates the corrosion process. Between pH 3 and 7, the additive is reputed to form a protective film of Cu(II)DTOA salt, which is formed through a two step oxidative process, probably involving Cu(I)DTOA as an intermediate. The EIS analysis indicates that in chloride solutions copper fits a model of a partially blocked electrode. This analysis suggests that at pH 3 and 7 the film produced on copper by DTOA has a lower porosity than that of the oxide or cuprous chloride films formed in non inhibited solutions, thus hindering the mass transport through the layer.