Fabrication of lanthanum-silane film by electrochemically assisted sol–gel method for enhanced corrosion resistance of sintered NdFeB

Abstract

The surface of sintered NdFeB was coated with a lanthanum-silane film using an electrochemically assisted sol–gel method to improve its protective performance. The electrochemically assisted deposition mechanism is localized alkali catalysis at the surface with an applied cathodic potential, which promotes the condensation reaction of hydrolyzed silanol groups on the sintered NdFeB substrate surface and the production of lanthanum oxide/hydroxide in the silane film as well. Contact angle test results indicated that the hydrophobicity of the lanthanum-silane film was considerably enhanced compared to the bare sintered NdFeB substrate, and the water contact angle was above 150°. Meanwhile, electrochemical measurements suggested that the lanthanum-doped silane film significantly reduced the corrosion rate of the sintered NdFeB magnet in a 3.5 wt% NaCl solution with an I_corr value of 5.26 × 10⁻⁷ A cm⁻², and the protection efficiency reached 92.5 %. Furthermore, the magnetic properties of the lanthanum-silane film-coated sintered NdFeB sample were also evaluated and the effect was negligible.