An XPS and AES study of the ageing of a Co–20%Ni metal‐evaporated tape

The initial oxidation behaviour of a Co–20%Ni alloy exposed to air and the longer term oxidation of a metalevaporated magnetic recording tape (MET) of the same composition have been studied using XPS and AES. Air exposure of the alloy for 24 h showed the formation of a mixed hydroxide/carbonate layer over a relatively small amount of oxide. The hydroxide‐containing layer was composed of both Co(OH) 2 and Ni(OH) 2 , with the outer surface enriched in Co(OH) 2 . The carbonates are believed to originate from the hydration of carbides present in the alloy. Analysis of MET showed the presence of the oxides Co 3 O 4 and NiO in addition to the hydroxides and carbonates. An Auger depth profile through MET indicated the presence of significant oxygen below the surface oxide, which increased in concentration towards the metal/polymer interface. This is explained by penetration of oxygen/water vapour into both voids and cracks formed during the manufacturing process.