New Triazole and Isoxazole Compounds as Corrosion Inhibitors for Cu-Ni (90/10) Alloy and Galvanized Steel Substrates

Three organic compounds containing azole rings 1-benzyl-4-phenyl-1H-1,2,3-triazole (I₁), 5-phenyl-3-propylisoxazole (I₂), and 3,5-diphenylisoxazole (I₃) were synthesized and characterized as corrosion inhibitors on galvanized steel and copper-nickel (Cu-Ni, 90/10) substrates. The three tested azole inhibitors acted as corrosion inhibitors on galvanized steel in the presence of real cooling water used as electrolyte. Electrochemical performance indicated that the presence of heteroatoms, such as N and O, with free pair electrons, the chain length, and the aromatic ring plays an important role in the capacity to inhibit corrosion of galvanized steel. 3,5-diphenylisoxazole (I₃) has the best inhibition activity with j_corr of 2.04 × 10⁻⁷ (5 ppm), 7.57 × 10⁻⁸ (10 ppm), and 1.73 × 10⁻⁸ (20 ppm) A cm⁻², followed by compounds I₁ and I₂. The synthesized compounds are comparable or even higher than the electrochemical performance of commercial inhibitor tolyltriazole (TTA, j_corr = 3.06 × 10⁻⁸ A cm⁻²). Conversely, for Cu-Ni (90/10) substrates, commercial TTA with 20 ppm displayed the lowest corrosion current densities (j_corr = 3.20 × 10⁻⁸ A cm⁻²) through a characteristic anodic pseudo-passivation; however, pits were observed after ~550 mV_Ag/AgCl. In contrast, the synthesized compounds tended to suppress anodic copper dissolution at positive potentials but, in the best case, displayed greater corrosion rates I₃ (1.463 mils per year (MPY)), I₂ (1.515 MPY), and I₁ (0.677 MPY) in comparison with TTA (0.091 MPY). The low inhibition efficiency (IE) of synthesized compounds is correlated to the weak absorption on the copper surface.