Avaliação do efeito de tratamentos superficiais na resistência à corrosão de magnetos de Nd-Fe-B / Assessment of the effect of surface treatments on the corrosion resistance of Nd-Fe-B Magnets.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

Nd-Fe-B magnets produced by powder metallurgy are highly susceptible to corrosion due to their complex microstructure and intrinsic porosity due to their fabrication process. Moreover, these magnets have excellent magnetic properties and find many applications. In the nuclear area, permanent magnets based on rare earth transition-iron-boron (Ne-Fe-B) are used in the manufacture of magnetic media (magnetic levitation) for ultra-centrifuges used for isotopic enrichment of uranium employed in nuclear reactors. In dentistry these types of magnets are used to fix total and partial prostheses on implants; in orthodontics to correct dental malocclusion and make moves; in buco-maxillo-facial surgery for setting facial prostheses of large defects of the face. In electronic equipment, they are used in scales, locks, electric motors and particularly in the manufacturing of hard drives of computers. The objective of this study is to evaluate the corrosion resistance of the magnet tested and surface treatments that could replace chromating that generates toxic residues and present high cost of processing waste with treatments that are environmentally friendly. The evaluation of the corrosion resistance was carried out through the analysis potentiodynamic polarization curves, electrochemical impedance spectroscopy, monitoring of corrosion potential as a function of test time and scanning electron microscopy to try to correlate the magnet microstructure with its corrosion resistance. The results show that these magnets are highly susceptible to corrosion that occurs preferentially in the Nd-rich phase, located in the boundaries of the magnetic matrix phase (). Treatment with silane, cerium, sam, Cr 6+, tricationic phosphate followed by bath of chromium trioxide and in NaH2PO4 solution for 24 hours followed by bath of zinc sulphate did not improve the corrosion resistance of the magnet. Among the treatments used, immersion in NaH2PO4 solution for 24 hours pH=3.8 was the one that provided the best corrosion protection against corrosion, when compared with the other types of tested treatments.

ASSUNTO(S)

magnetos de nd-fe-b magnetos de nd-fe-b corrosão odontologia. corrosão odontologia.

ACESSO AO ARTIGO

Documentos Relacionados