Synthesis And Performance Study Of8-hydroxyquinoline Azole Derivatives As Self-assembled Films On Magnesium Alloy

Magnesium alloys have attracted extensive attention for their application in fields such as aerospace, communication, military, attributing to their high thermal and electrical conductivity, dimensional stability, good electromagnetic shielding effect, machinability and recoverability. In particular, they can function as raw materials for auto parts and the shell of electronic products. Actions to expand the scope of their applications not only have a directly bearing on the industrialization of abundant magnesium resources in our country, but also have critical implications for materials science and development of the society. However, the corrosion resistance of magnesium alloys is poor, and the alloy need to be surface-modified before it can be used in wet environment or solutions. To achieve this purpose, researchers have come up with a variety of surface treatment technology, among which self-assembled films come into people’s minds as an effective method recently. This process occurs in situ and forms a film that is thermodynamically stable, tightly and orderly arranged and not affected by the shape of the alloy.8-hydroxyquinoline(8-HQ) presented corrosion inhibition efficiency on normal metals such as copper, iron and aluminium, owing to its possession of atom N and O with lone electron pair as well as a conjugated system. It can form a complex with magnesium, but the inhibition effect is not that excellent. We employed benzimidazole derivatives to modify it, designed and synthesized four novel coumpounds ID, BD, BTD and MD, then investigated the corrosion inhibition efficiency of their self-assembled films on the magnesium alloy.This essay includes the following three sections:(1) Explored the synthetic methods of ID, BD, BTD, MD and characterized their structures with the approaches of NMR, IR and MS.(2) Prepared the self-assembled films of these four compounds on the surface of magnesium alloy, studied their anti-corrosion properties through electrochemical impedance spectroscopy and potentiodynamic polarization tests. We found the synergistic effect of two functional groups in the molecule improved the original inhibition efficiency of8-HQ by more than20%. Then we investigated the effect of concentration and assembling time and obtained the best assembling concentration was12g/L, the best assembling time was24h. By proposing two appropriate equivalent circuit, we saught for the mechanism of the films. Identified the surface properties of MD modifying film with FT-IR, XPS and SEM, and proved that the combination occurred between the atom O of8-HQ and the surface of magnesium alloy.(3) According to the characteristics of their containment of electron-rich atoms in addition to the protection of magnesium alloy, extended the use of ID, BD and BTD to corrosion inhibitors of mild steel in1.0mol/L HCl solution and reached a best efficiency of 97.11%. Then inspected the adsorption behavior of these molecules, found that it obeyed Langmuir’s adsorption isotherm, and calculated the corresponding dynamic parameters.