Protection of Nd2Fe14B-based melt-spun ribbons using nanoscale sol-gel derived films of SiO2 and Al2O3

We have coated NdFeB melt-spun powders used for the production of bonded magnets with SiO2 and Al2O3 using the sol-gel technique. Highly accelerated stress tests were conducted to compare the corrosion properties of the powders by measuring the weight change. The composition and microstructure of the powders and surface layers were determined using Auger-electron spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, secondary-electron spectroscopy and electron-diffraction spectroscopy. The magnetic properties were compared using a vibrating-sample magnetometer. Both the SiO2 and Al2O3 coatings resulted in a superior corrosion resistance and better magnetic properties.