Enhancing the corrosion inhibition of copper sheets in oil-in-water (O/W) emulsions by combining two organic heterocyclic derivatives.

Copper sheets corrode easily when exposed to oil-in-water (O/W) emulsions during metal-forming processes. The quest for identifying novel, high-efficiency copper inhibitors and realizing the effective protection of copper surfaces from emulsion corrosion has gradually attracted considerable attention. In this study, two organic heterocyclic derivatives, N,N-bis(2-ethylhexyl)-4-methyl-1H-benzotriazol-1-methanamine (NBTAH) and 2,5-bis(octyldithio)-1,3,4-thiadiazole (BTDA), were introduced as copper inhibitors into O/W emulsions. Their corrosion inhibition performance was investigated in-depth using electrochemical measurements, surface characterization, adsorption isotherms and wetting techniques. The results indicated that both inhibitors generated anodic passive films on the copper surface, and thus enhanced the corrosion resistance. The maximum corrosion inhibition efficiency achieved was 94.0% with combination of 5 mM NBTAH and 8 mM BTDA. From the surface analysis, it was confirmed that the composite inhibitors could successfully adsorb onto the copper surface via the polar atoms of the benzene, azole, and thiazole rings. The adsorption formed multilayer inhibitor films comprised of Cu-NBTAH and Cu-BTDA chelates. In addition, these films significantly reduced the wettability of the O/W emulsions on the copper surface, thus isolating copper from the corrosive medium. The anti-corrosion mechanism for adsorption and shielding of the composite inhibitors on the copper surface is preliminarily proposed.