Abstract: The working surfaces of nickel-coated substrates for rigid magnetic discs are polished in a single-step process that employs a polishing composition comprising an aqueous suspension of unlubricated aluminum oxide powder having a hexagonal crystal shape and a nominal particle size of 1 to 10 microns, and colloidal aluminum oxide.

Abstract: Metal surfaces such as the working surfaces of nickel plated blanks for rigid memory discs are polished in a two-stage process of rough and finish polishing by a combination of mechanical and chemical mechanisms. Each stage involves a plurality of cycles in which the surface is polished using a rotating polishing pad with an aqueous suspension of aluminum oxide containing a lubricant-surfactant and a chlorine-containing oxidizing agent present at the surface-pad interface followed by the addition of an aqueous colloidal aluminum oxide sol to the oxidizing agent-containing suspension at the interface which frees the chlorine in the oxidizing agent to exert a chemical polishing action on the surface.