Carboxylic Acids as Corrosion Inhibitors for Cu, Zn and Brasses in Simulated Urban Rain

Carboxylic acids (hexanoic, decanoic, myristic and stearic) were studied as corrosion inhibitors for Cu, Zn, Cu10Zn and Cu40Zn in simulated urban rain, using electrochemical measurements. The surfaces of Cu, Zn and brasses were modified by immersion in ethanol solutions of carboxylic acids of various molarities (0.01 M to 0.1 M). Times of immersion were between 1 min and 6 days. The effect of surface etching was also studied. All carboxylic acids formed hydrophobic, self-assembled layers with a contact angle over 90°. Carboxylic acids with longer carbon chains were better corrosion inhibitors. The formation of self-assembled layers was a rapid process, high values of inhibition effectiveness being observed after only one minute of immersion. Myristic and, particularly, stearic acids are good inhibitors of Cu and brasses, providing protection of >95 %, even at low molarities. Both acids were less effective for Zn with up to 60 % effectiveness.