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In this investigation, a porous oxide coating has been formed on aluminium using direct current anodising technique, sensitised in stannous ion followed by colouring in dilute silver ion at different concentrations and durations to produce pleasing colours ranging from yellow to brown and black. The metallically coloured surface has been analysed using EDAX, atomic force microscopy, X-ray diffraction and ultraviolet-visible-infrared spectrophotometer, and a suitable mechanism has been proposed.

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Nanocrystalline nickel phosphorus (NC-NiP) deposits from sulphate/glycine bath using a simple electroless deposition process is demonstrated. In the present investigation, nanoporous alumina films are formed on the aluminium surface by anodization process followed by deposition of nickel onto the pores by electroless plating method. Anodic aluminium oxide surface was first sensitized and activated by using palladium chloride solution before immersing into the electroless nickel bath. Electroless nickel plating was carried out from the optimized bath by changing the deposition time from 20 to 1800 s at a constant temperature of 80 • C and a pH of 4•0. Surface morphology, elemental composition, structure and reflectance of the deposits have been analysed by using scanning electron microscopy, atomic force microscopy, energy dispersive X-ray analysis, X-ray diffractometry and UV-visible spectroscopic studies, respectively. Electroless nickel deposits formed at an early stage produces dense uniform nanocrystals containing higher percentage of atomic phosphorus with cubic Ni (111) structure. As the deposition time increased, nanocrystalline sharp peak became amorphous and dimension of the crystal size varied from 54 to 72 nm.