PHOTOACOUSTIC FT-IR SPECTROSCOPY OF NATURAL COPPER PATINA

Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) has proved to be a useful tool for nondestructive testing of copper corros ion layer (patina) formed in the atmosphere. The samples cut from a pi ece of the roof of the Stockholm City Hall were examined without any a dditional pretreatment. The components of the patina-brochantite Cu-4( OH)(6)SO4, antlerite Cu-3(OH)(4)SO4, and basic cupric carbonate Cu2CO3 (OH)(6) . H2O-as well as some other minerals were identified. The phot othermal beam deflection (PBD) method was used for independent photoac oustic characterization of the samples. The depth profiling capability of FT-IR/PAS was used to determine the degree of photoacoustic satura tion of the spectral bands and to evaluate the depth distribution of t he main patina components. The technique thus compares favorably with more common approaches of patina examination which are more expensive and require special sample preparation.