SciELO - Scientific Electronic Library Online

 
vol.8 issue2A study of Pr-Fe-B magnets produced by a low-cost powder method and the hydrogen decrepitation processElectrochemical behavior of steel-FeNbC composites used in the production of oxygen author indexsubject indexarticles search
Home Pagealphabetic serial listing  

Services on Demand

Journal

Article

Indicators

Related links

Share


Materials Research

Print version ISSN 1516-1439On-line version ISSN 1980-5373

Abstract

SALIBA-SILVA, Adonis Marcelo; OLIVEIRA, Mara Cristina Lopes de  and  COSTA, Isolda. Effect of molybdate on phosphating of Nd-Fe-B magnets for corrosion protection. Mat. Res. [online]. 2005, vol.8, n.2, pp.147-150. ISSN 1516-1439.  http://dx.doi.org/10.1590/S1516-14392005000200009.

Nd-Fe-B magnets are highly susceptible to corrosion and need protection against environment attack. The use of organic coatings is one of the main methods of corrosion protection of these materials. Data related to the effect of conversion coatings, such as phosphating, on corrosion performance of these magnets is still scarce. Studies about the effect of phosphating on the corrosion resistance of a commercial Nd-Fe-B sintered magnet indicated that it increases the corrosion resistance of these magnets, compared to non-phosphated magnets. In this study, the solution chemistry of a phosphating bath was altered with the addition of molybdate and its effect on the corrosion resistance of magnets investigated. Sintered magnet specimens were phosphated in solutions of 10 g/L NaH2PO4 (pH 3.8), either with or without molybdate [10-3 M MoO42-], to improve their corrosion resistance. The effect of phosphating time was also evaluated, and specimens were phosphated for 4 and 18 hours. To evaluate the corrosion performance of phosphated and unphosphated specimens, a corrosion test based on monitoring hydrogen evolution on the surface of the magnets was used. This technique revealed that the addition of molybdate to the phosphating solution improved the corrosion resistance of the magnets phosphated by immersion for short periods but had no beneficial effect if phosphated by immersion for longer periods.

Keywords : corrosion; Nd-Fe-B magnets; phosphating; molybdate.

        · text in English     · English ( pdf )

 

Creative Commons License All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License