Efficient protection of sintered NdFeB enabled by incorporation of polyethyleneimine-grafted graphene oxide into silane films

Abstract

Polyethyleneimine modified graphene oxide (PEI-GO) was designed as an additive and subsequently co-deposited with bis-silane on sintered neodymium-iron-boron (NdFeB) magnets to prepare hydrophobic and anti-corrosive PEI-GO/silane composite films via an electrochemically assisted sol-gel method. Structural and compositional characterizations were carried out using fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and Raman spectroscopy. Results confirmed successful grafting of PEI onto GO. Silane coupling agents linked to the PEI-GO additives, as well as the sintered NdFeB substrate, through covalent bonds. The corrosion resistance of the fabricated composite films in a 3.5 wt.% NaCl solution was assessed through electrochemical impedance spectroscopy and potentiodynamic polarization tests. The corrosion current density of PEI-GO/silane film under optimal deposition conditions was 8.365×10 -8 A·cm -2 , which is two orders of magnitude smaller than that of the neat silane film. Enhanced anti-corrosion performance of PEI-GO/silane composite film can be primarily attributed to the grafted PEI, which significantly enhanced the barrier effect of GO by improving its dispersion within the sol-gel system. Meanwhile, the co-deposited PEI-GO remarkably reinforced the structural integrity and compactness of the composite film. Furthermore, the composite coating exhibits outstanding hydrophobicity, with a water contact angle reaching 148.5°, and simultaneously maintains the magnetic properties of the sintered NdFeB magnets without detectable compromise.