Research Of Molecules’ Influence On The Interface Of Rust Layers And Corrosion Resistance

In recent years, anti-corrosion maintenance of large devices plays an important role in industry. Traditional anti-corrosion needed complicated and thoroughly surface pretreatment, then was the brushing paint. But if the device rust again, then painted it again directly, it will be hard to achieve long-term anti-corrosion, so the residual rust coatings emerged at a historic moment. However, most traditional rust conversion solution contains the composition of tannic acid, phosphoric acid, and it’s difficult to control the acid amount, so an overdose of acid will induce the corrosion. And other rust conversion solution has an insufficient permeability, so the molecule couldn’t absolutely reach the bottom of the rust layer, that the rust conversion is not complete. More importantly, because of lacking of systematic knowledge of the relationship between the structure characteristics and performance abut the functional rust conversion ever before, when choosing proper rust-conversion molecule, it remains at trial level. In this paper, a series of special molecules with systematic chaging structures were synthesized and chosed and deposited on the rust surface to explore the rust conversion effect. The concrete content is as follow.Firstly, 1) 3 groups of molecules with different pendant chain length have been synthesized（A₃C（2, 6, 12, 18）, A₂C（2, 6, 12, 18）, A₁C（2, 6, 12, 18））, which were produced by melamine, 2-aminopyrimidine, 2-aminopyridine（A₃, A₂, A₁）, acetic acid（C₂）, caproic acid（C₆）, lauric acid(C₁₂) and stearic acid(C₁₈); 2) 3 kinds of heterocyclic compounds with different number of N atoms have been synthesized（A（3, 2, 1）KH560, they were prepared by A₃, A₂, A₁ and KH560; 3） molecules with different pendant groups have been selected: 2-Picolinic acid, 2-hydroxypyridine, 2-aminopyridine; 4) heterocyclic compounds with different heteroatoms have been selected: pyridine, furan, thiophene.Secondly, polarization curve, AC impedance technique, test of copper sulfate intravenous drip, molecular fragment method, scanning electron microscope（SEM） were used to research the influence on rust layer interface morphology and corrosion resistance by systematicly changing molecular structures, and the confirmations are as follows: 1) molecules(A（3, 2, 1）C₁₂) with proper chain length of pendant groups contribute more to anti-corrosion of rust layer than other molecules. A₁KH560 with 1 N atom on the ring can enhance the anti-corrosion ability of rust layer more than other molecules. The molecules 2-Picolinic acid pyridine and 2-Hydroxypyridine with functionalgroups-COOH and-OH made rust layer have stronger corrosion resistance than molecule 2-aminopyridine with functionalgroup –NH2. Pyridine and tetrol made rust layer have stronger corrosion resistance than thiophene. 2) Molecular fragment method predicted the close connection between hydrophobic parameter and corrosion inhibition performance of molecules, and the change rules are roughly the same as those in 1), and all those molecules can adsorb in the interface of rust layers to fill the cavities and change the growth shape of rust, and preferred functional molecules in 1) reacted with rust layer to produce denser film.Lastly, the final interaction effect of rust layer, functional molecule and film forming material is the most important aspect of evaluating coatings, A₃ steel treated by molecules with rusted surface was painted by self-prepared epoxy/PVB composite coatings, tested by corrosion resistance, the results show that: 1) the corrosion resistance of A₁C₁₂/ epoxy and A₂C₁₂/epoxy coatings was significantly better than that of the other coatings; 2) The A₁KH560/ epoxy coating has excellent corrosion resistance with respect to the A₂KH560/ epoxy and the A₃KH560/epoxy coatings; 3) the corrosion resistance of 2-/epoxy coating and 2-/epoxy coating was significantly better than that of 2-amino pyridine/epoxy coating; 4) the pyridine/epoxy and the epoxy/epoxy coatings have excellent corrosion resistance with respect to thiophene/epoxy coating; 5) basic performance test of coatings results also show that the comprehensive performance of A₁C₁₂/epoxy and A₂C₁₂/epoxy coatings, A₁KH560/epoxy coating, 2-formic acid pyridine/epoxy and 2-hydroxy pyridine/epoxy coatings, pyridine/epoxy and furan/epoxy coatings is excellent; the regular change of the corrosion resistance of coatings is consistent with the change of the corrosion resistance which is caused by the simple corrosion resistance of the small molecule and the rust layer.Above all, maintenance of bigger devices needs to think about long time anti-corrosion, so side chain length, number and type of heteroatom and functionalgroups should be systematicly concluded when choosing functional rust-conversion molecules. The content of this paper provides systematic, regular and effective basis for choosing the structure of functional rust-conversion molecules.