JPS6421906A - Rare earth magnet having barrier film against hydrogen - Google Patents

Abstract

PURPOSE:To obtain a rare earth magnet, which can be used in an atmosphere including hydrogen atmosphere or hydrogen stably for a long time, by plating alloy including amorphous P, B or S as a lower layer on the surface of the rare earth magnet, and providing an amorphous film as an upper layer. CONSTITUTION:Alloy including amorphous P, B or S is applied on the surface of a rare earth magnet as a lower layer. An amorphous film is provided as an upper layer. For example, degreasing is performed by a spraying method using weak alkali degreasing liquid from the rare earth cobalt magnet. After washing with water, the magnet is immersed in aqueous solution of 0.1g/l of palladium chloride with pH of 5 at 50 deg.C. Then the magnet is washed with water. Amorphous plating is performed by an immersing method or an electrolytic method. In the case of Ni-P plating bath, the following materials are used: 30g/l of nickel sulfate, 10g/l of sodium hypophosphide, and 10g/l of sodium acetate. The value of pH is made to be 4.7. Thereafter, chromic acid anhydride, whose reduction rate is Cr<3+>/(Cr<3+>+Cr<6+>)=0.38, phosphoric acid and chromate liquid of polyacrylic acid are applied as a dried and applied film to a thickness of 0.5 g/m<2>. The film is heated to 100 deg.C and hardened. Thus a magnet is obtained.