Verfahren zum Herstellen eines Mn-Bi-Magnetkoerpers

摘要

A Mn-Bi magnet formed by compacting Mn-Bi powder, is polished in a rotating drum with polishing elements e.g. steel, ceramic and carborundum in an anhydrous medium such as petrol or kerosene and then coated with a metal layer such as Cu or Ni at least 25 microns thick from an aqueous solution of the metal salt either electrolytically or by chemical reduction. Before coating the polished compact may be dipped in a dilute HCl solution. For electrolytic deposition of Ni the aqueous solution may contain 300 g/l of nickel sulphamate, 30 g/l nickel chloride, 30 g/l boric acid and have a pH of 4.5-5. For the chemical deposition of Cu the aqueous solution contains 110 g/l copper pyrophosphate, 380 g/l potassium pyrophosphate, 25 g/l potassium citrate and 10 mls/l ammonia and have a pH of 8.2.