Active Corrosion Protection of Sintered Ndfeb Magnets by Silane Composites Embedded with Poly (Urea-Formaldehyde) Microspheres Containing Benzotriazole and Cerium (Iii) Nitrate Hexahydrate

Abstract

In this study, benzotriazole (BTA) (an organic corrosion inhibitor) and cerium (III) nitrate hexahydrate (an inorganic corrosion inhibitor) were successfully co-encapsulated in poly(urea-formaldehyde) (PUF) microspheres to fabricate a hydrophobic self-healing silane composite film by an electrochemically assisted deposition method for active corrosion protection of sintered NdFeB magnets. The prepared spherical PUF microspheres exhibited a high loading capacity of 14% for BTA and Ce (NO3)3 hybrid inhibitors. The PUF@BTA/Ce(NO3)3 microspheres were uniformly distributed in the fabricated silane composite film. The corrosion protection and self-healing performance of the fabricated hybrid silane film were investigated by potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS). The composite films with 10 g/L microspheres possessed an excellent self-healing performance and corrosion resistance. The low-frequency impedance modulus at 0.01 Hz of the films immersed in the 3.5 wt.% NaCl solution was 8.310×104 Ω·cm2, which was twice as much as that of the pure silane film and nearly 35 times as much as that of the substrate. The capacitive are showed an increasing trend for the first 2.0 h to 24.0 h. In addition, the loaded BTA and Ce3+ inhibitors can release from PUF microspheres to form insoluble Fe-BTA chelates and alkaline passivation layers at the defects, which suppressed the corrosion propagation and resulted in a good self-healing property of the prepared hybrid silane film. Then, tests by magnetic material analyzer showed that the film has very little effect on the magnetic properties of NdFeB.

Keywords: PUF microspheres, Cerium (III) nitrate, benzotriazole, Silane film, Self-healing