EIS investigation of the corrosion resistance of uncoated and coated Nd-Fe-B magnets in PBS solution

Journal of the Brazilian Chemical Society

CNEN, São Paulo, Brazil¹  Costa, Isolda¹  Martins, Emerson A¹  Melo, Hercílio G. de¹  Rossi, Jesualdo L¹  Oliveira, Mara C. L¹  USP, São Paulo, Brazil¹ 

关键词: corrosion;    Nd-Fe-B magnets;    EIS;    dentistry;    porous electrode behaviour;   

DOI  :  10.1590/S0103-50532011000200011

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

The aim of this work is to investigate the corrosion behavior of powder metallurgy produced Nd-Fe-B magnets and to evaluate the corrosion protection afforded by two different surface treatments: a phosphate conversion and a non-functional silane (BTSE) layer. The electrochemical tests were performed in a phosphate buffered solution (PBS) at neutral pH, which ionic concentration coincides with that of the human body. The corrosion behavior was monitored by means of electrochemical impedance spectroscopy (EIS) and anodic potentiodynamic polarization curves, and SEM-EDS analyses were used to monitor coating deposition. EIS response has evidenced a porous electrode behavior for the Nd-Fe-B magnets according to the de Levie theory. The results also indicated a good performance of the phosphate layer, whereas the BTSE layer did not improve the corrosion resistance of the magnets. The good anticorrosion performance of the phosphate layer was explained on the basis of the formation of an insoluble phosphate layer both on the electrode surface (identified by interference colors) and on the pore walls. Precipitation of insoluble Nd phosphate on the Nd-rich phase also contributes to the superior corrosion protection afforded by this coating.

【 授权许可】

Unknown