This paper investigates the inhibiting properties of 1 mM dithio-oxamide (DTOA) towards copper corrosion in 0.1 M NaCl media at different buffered (3; 5; 7; 9) pH values. The inhibiting efficiency of DTOA was evaluated after 20 day immersion in the solutions at 30 °C. Both dc (polarization curves and voltammetric tests) and ac (electrochemical impedance spectroscopy, EIS) techniques were applied 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 indicate 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.
Dithio-oxamide as inhibitor of copper corrosion in chloride solutions at various pH values
MONTICELLI, Cecilia;BRUNORO, Giancarlo;FRIGNANI, Alessandro
1991
Abstract
This paper investigates the inhibiting properties of 1 mM dithio-oxamide (DTOA) towards copper corrosion in 0.1 M NaCl media at different buffered (3; 5; 7; 9) pH values. The inhibiting efficiency of DTOA was evaluated after 20 day immersion in the solutions at 30 °C. Both dc (polarization curves and voltammetric tests) and ac (electrochemical impedance spectroscopy, EIS) techniques were applied 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 indicate 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.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
