Preparation And Electrochemical Characterization Of The Inhibitive Films On The Surface Of Brass

Corrosion inhibition of brass has become an important research subject. From the aspect of corrosion inhibition of metals, it is very necessary to deposit the appropriate inhibitive films on the surface of brass.The technique of deposition is practically and theoretically advantageous in the protection of metals.The purposes of our research are to prepare La-conversion coatings and self-assembled silane film on brass surface and to investigate the formation and inhibition mechanism.The main results of this dissertation can be summarized as the following:(1) La(NO3)3and BTAH had an excellent synergistic effect on the corrosion inhibition of brass. A remarkable enhancement of the brass’s corrosion protection was obtained by the formation of La-conversion coatings, which acted as a barrier to the release of metal ions and inhibited the diffusion of oxygen. La-conversion coatings on brass is sensitive to SO42-and Cl-in the artificial rainwater and the corrosion process was affected by the deposition of corrosion product.(2)The La2O3nanoparticles incorporation and electrodeposition were used together to prepare the La-conversion coatings on brass surface. A critical nanoparticulate La2O3content and a critical deposition potential were observed, under which the conversion coatings had the highest protective properties. Increased electrodeposition time improves the quality of conversion coatings.The La-conversion coatings could provide important protection against brass corrosion with a trend of first increase and then decrease and the corrosion process was controlled by the reaction of anodic dissolution.(3)Self-assembled silane films of PropS-SH, DTMS and CPTMS suppress corrosion of brass as mixed inhibitors and the inhibition efficiency follows the sequence of PropS-SH> CPTMS> DTMS. Inhibitive action of the PropS-SH and DTMS can be explained by chemisorption which obeys the Langmuir adsorption isotherm.The functional groups on alkoxyl carbon-based chain change the overall reactivity of the silane molecules. Among the four silanes, PropS-SH molecules has the smallest energy gap and the highest reactivity. So the PropS-SH molecules can adsorb on the brass surface and form a higher inhibition efficiency of self-assembled silane film.The conclusions of quantum chemical calculations explained the results of electrochemical experiments well.(4) Nano-La2O3particles were added to the self-assembled silane films of PropS-SH coated onto the brass substrates. The results show that nano-La2O3particles change the surface morphology and thermostability of silane films, but not affect the molecular structure and the electrochemical reaction of electrode. Silane films containing La2O3nanoparticles present improved barrier properties because nano-La2O3particles can fill the holes of coating, improve the coating density and enhance the barrier properties of silane-metal interface. Further, nano-La2O3particles can change to be LaOOH by hydrolysis reaction and the hydrated lanthanum cover on the cathode area.(5)Corrosion resistance of brass was improved by inhibitive films in natural seawater, and the self-assembled silane films of PropS-SH doped by nano-La2O3particles has the best effect of corrosion inhibition.