Papers by Author: M.C.E. Bandeira

Abstract: Nd-Fe-B magnets present outstanding magnetic properties. However, due to their low corrosion resistance, their applications are limited to non-corrosive environments. Nowadays, significant efforts are underway to increase the corrosion resistance of these materials, through the use of coatings. Herein are presented the results of a study on the corrosion resistance of Nd-Fe-B magnets coated with polypyrrole (PPY). The electrochemical behavior of coated and uncoated magnets has been studied by Electrochemical Impedance spectroscopy (EIS) in synthetic saliva. The results were compared to previous investigations, which were carried out under similar conditions, in Na2SO4 and NaCl solutions. In sulphate solution, the corrosion resistance of the PPY-coated magnet was 3 times larger (1600
.cm2) than that of uncoated magnet (500
.cm2). In NaCl solution, however, the corrosion resistance of coated and uncoated magnets were very similar (250
.cm2). In synthetic saliva, both the uncoated and coated magnets presented good corrosion performance (1940
.cm2). Such behavior can be attributed to the phosphate ions in saliva, which play a role as corrosion inhibitor, producing phosphating, at least partially, of the magnet surface. The PPY-coated magnets presented a strong diffusional control from moderate to low frequencies, caused by the polypyrrole film. The thicker PPY film increased the corrosion resistance of the magnet in synthetic saliva.

Abstract: The characterization of poly-{trans-[RuCl2(vpy)4]}films, deposited on Nd-Fe-B magnets and on Pt, Au and Glassy Carbon (GC) electrodes, produced in the present work were carried out by several in situ and extra situ techniques, aiming by the understanding of film structure improve its use as corrosion protection coating and/or electrocatalyst. Cyclic Voltammetry (CV) was used to estimate the surface coverage, film stability and the surface redox potential of films produced at different conditions. By Chronocoulometry films diffusion coefficient (Dct) were evaluated. Film morphology was studied by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Chemical composition analyses were carried out by Energy Dispersive Spectroscopy (EDS), X-ray Photonelectron Spectroscopy (XPS) and Raman Spectroscopy. The results indicated that the film structure is similar to the Ru complex in solution. Films Dct is limited by the electron transfer rate between Ru metallic centers. Films on Nd-Fe-B were composed by Ru3+ whereas on Pt by Ru2+.