Behaviour of anodised aluminium in very long-term atmospheric exposure

This communication analyses the behaviour of anodised aluminium specimens, with different degrees of sealing in deionised water and acetate solutions, exposed for 25 years to the Madrid atmosphere. Changes in physical–chemical properties as a function of ageing are assessed using traditional standard quality control tests, electrochemical impedance spectroscopy (EIS) and optical and electron microscopy, and durability is estimated on the basis of gravimetric data. The results allow, for atmospheres of moderate aggressivity, such as the case of the CENIM in the University City of Madrid, service lifetimes of 100 years or more to be predicted for the usual anodic film thicknesses in architectural applications. If the localised corrosion process is not initiated, the quality of anodic films improves with ageing, in contrast to what happens with the rest of protective coatings.