Effect of molybdate on phosphating of Nd-Fe-B magnets for corrosion protection

Materials Research

Adonis Marcelo Saliba-silva¹  Mara Cristina Lopes De Oliveira¹  Isolda Costa¹ 

[1] ,Centro de Ciência e Tecnologia de Materiais Instituto de Pesquisas Energéticas e Nucleares São Paulo,Brazil

关键词: corrosion;    Nd-Fe-B magnets;    phosphating;    molybdate;   

DOI  :  10.1590/S1516-14392005000200009

来源: SciELO

【 摘 要 】

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 MoO4(2-)], 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.

【 授权许可】

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