Rapid sealing of an alumina nanoporous network grown by anodizing and dye-filled

Abstract

In the field of indoor decorative items, aluminium alloys are widely used since their surface may be coloured by adsorption of dyes within an anodic nanoporous network. This anodizing/colouring process is followed by a sealing step ensuring the protection of the treated surface without modifying its aesthetic appearance.In the present paper, water, nickel acetate and sodium silicate were used as sealing agents and implemented in rapid sealing processes dedicated to anodized then coloured aluminium surfaces. The morphological aspects were finely observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The elemental repartition was tracked by wavelength and dispersive spectrometry (WDS/EDS). The sealing efficiency was evaluated by electrochemical impedance spectroscopy (EIS) and a dye spot test. An optical characterization was performed by visible reflection spectrometry and gloss measurements.Both water and nickel salt lead to the precipitation of a few tens of nanometres hydroxide layer, providing an efficient sealing in a short time while maintaining optical properties. Best performances are obtained with nickel salt. In contrast, the high adsorption of silicates inhibits the formation of the sealing superficial sheets on the one hand and even makes the dye desorb from the nanoporous oxide layer.