Corrosion Inhibition And Quantitative Structure Activity Relationship Study Of Nicotinic Acid, Acridine, And Berberine For Hot Dipping Coated Steels In Diluted HC1 Solutions

For purpose of finding chromate-substituting inhibitor in finishing process of hot dip coated steels, inhibition effects and quantitative structure activity relationship of environment-friendly inhibitors—nicotinic acid, acridine, and berberine, for hot dipping Zn, 5%Al-Zn, and 55%Al-Zn coated steels in diluted HCl solution was investigated using quantum chemical calculation method, weight loss test, electrochemical measurement, and scanning electronic microscope analysis.Quantum chemistry calculation results showed that these three heterocyclic compounds had planar structure with a number of active centers. The populations of the Mulliken charge, the highest occupied molecular orbital (HOMO) energy, and the lowest unoccupied molecular orbital (LUMO) energy were showed that the active centers were mainly focused around oxygen, nitrogen atoms, and the heterocyclic. The corrosion inhibition of hot dip coatings was discussed in terms of blocking the electrode reaction by adsorption of the molecules at the active centers on the electrode surface. And frontier orbital of the three compounds could interact with the frontier orbital of Zn atom of coating surface; thus they might form an adsorption barrier film on the coating surface to decrease the corrosion rate of zinc.Weight loss test and electrochemical measurement results indicated that nicotinic acid, acridine, and berberine were effective and environmental friendly corrosion inhibitors for the three hot dip coatings in HCl solutions, and the highest inhibition efficiency was up to 99%. Among the three inhibitors, berberine showed the best performance with inhibition efficiency up to 80% when at a relatively lower concentration of 1.0×10-4 mol/L. It also was found that the adsorption of the three compounds on coating surface followed Langmuir adsorption isotherm with single molecular layer, and molecules adsorbed on the coating surface probably by chemisorption. The surface morphology also showed that the surface corrosion of hot dipped coatings could decrease remarkably after these three inhibitors added in hydrochloric acid. The inhibition efficiency obtained using different techniques showed a good agreement with each other, and both confirmed the presumption from the quantum chemical calculation.Moreover, the inhibition mechanism of nicotinic acid, acridine, and berberine for the hot dip coating steels in hydrochloric acid was studied by coulostat method and quantitative structure–activity relationship (QSAR). The coulostat method confirmed the results of the weight loss test and electrochemical measurement that nicotinic acid, acridine, and berberine were mixed-type inhibitors. And they adsorbed on the coating surface through active centers adsorption style to suppress both anodic and cathodic processes. The results of QSAR showed that the inhibition efficiency increased with the increasing values of EHOMO of inhibitor, and increased with theΔE decreasing. And these three inhibitors acted as inhibition effect by electron donating to Zn atom of the coating surface.Finally, the effects of removing corrosion products for hot dip coating steels by inhibited hydrochloric acid were contrasted with the chromic acid. The results showed that the finishing method of inhibited hydrochloric acid could perform as a chromate-substituting method of removing corrosion products and efficient environment-friendly finishing method for hot dip coated steels in finishing process.