Abstract: A rare earth-iron-boron permanent magnet such as neodymium—iron—boron permanent magnet can be imparted with high corrosion resistance by forming a corrosion-resistant coating layer on the surface comprising an alkali silicate, e.g., sodium silicate or lithium silicate, and a thermosetting resin such as melamine, epoxy and acrylic resins in uniform admixture.

Abstract: A rare earth-based permanent magnet such as a neodymium-iron-boron permanent magnet, which is disadvantageous in respect of the low corrosion resistance, can be imparted with high corrosion resistance by providing the surface with a protective coating film of vitrified alkali metal silicate, e.g., sodium silicate, of which the SiO.sub.2 :(alkali metal oxide) molar ratio is in the range from 1.5 to 20. The vitrified alkali metal silicate-based protective coating film can be formed by coating the surface of the magnet with an aqueous coating solution containing sodium silicate to form a coating layer which is dried and subjected to a heat treatment at 50.degree. to 450.degree. C. to effect vitrification of the alkali metal silicate. The thickness of the thus formed protective coating film should be in the range from 5 nm to 10 .mu.m.