A Cleaning Method for Aged Architectural Titanium

摘要

The built of the Guggenheim-Museum at Bilbao meant a milestone in the use of titanium for architectural purposes. After a few years of atmospheric exposure the rectangular titanium panels began to show a change in the surface characteristics that was labelled as a "soiling" problem, unable to be eliminated by common cleaning procedures. The problem was identified by INASMET as a "colouring" or "tarnishing" phenomenon, occurred in the surface of the titanium panels due to an increase of the titanium oxide natural protective film. Several factors influenced the size and morphology of the undesirable "colouring". These factors were analysed by a carefully inspection of the specific exposure conditions and by the study of the metallurgical characteristics and surface condition of the titanium material used in the construction. The major objective was to develop a method to clean in situ the affected surface without altering the surface characteristics. The most appropriate form of treatment seemed to be what is known as selective passive stripping, with the application of acid followed by water-jet rinsing.