Inhibitive effect of chloride on copper corrosion in dilute nitric acid

The effect of chloride on the corrosion mechansim of copper in deaerated, 0.1 M HNO 3 was studied by electrochemistry, atomic force microscopy, and scanning electron microscopy. Nitrate reduction, the first cathodic step in the corrosion pathway, was completely inhibited in the presence of ppm levels of chloride, thereby shutting down the corrosion sequence of the system involving solution reactions by copper ions and the subsequent reduction of NO 2 – . Nitrite reduction was minimally affected, suggesting that the two reduction steps differ substantially in their sensitivity to the surface state during corrosion. Our results support that the key step for the inhibitive effect of chloride is the adsorption of chloride to form an adlayer on the surface. Nitrate reduction on copper appears to be inhibited by chloride in the presence of corrosion accelerators NO 2 – and Cu + /Cu 2+ , which suggests that the chloride adlayer remains intact under more aggressive conditions and lowers the rate of corrosion from nitrate reduction in the presence of other oxidants. • Cl – inhibits copper corrosion in deaerated, 0.1 M HNO 3 ( IC 50% = 0.58 wt. ppm) • The first cathodic step in the corrosion mechanism is inhibited (NO 3 – reduction) • The second cathodic step is unaffected (NO 2 – reduction) • NO 3 – reduction remains inhibited in the presence of NO 2 – and Cu + /Cu 2+ • The mechanism of inhibition is proposed to be Cl – adsorption