Complementarity of XRFS and LIBS for corrosion studies

A study of ancient coins with different corrosion degrees and the same or different composition has been carried out by using energy-dispersive X-ray fluorescence spectrometry (XRFS) and laser-induced break-down spectroscopy (LIBS). The results obtained show the complementarity of both techniques: XRFS provides information about the superficial composition which is used for the assignation of atomic lines in LIBS, and this provides in-depth and tomographic information. Thus, some very superficial impurities such as Ag, Cl, Au, Sr and Sb are only detected by XRFS, while highly corroded coins of iron-based alloy provided no iron signal by XRFS but increased concentration of this element up to constant composition by LIBS by increasing the shot number. The average of the same laser-shot number for all sampling positions of a sampling zone produces a significant improvement of the signal-to-noise ratio (SNR) in the detriment of punctual information as that obtained by single-position kinetic series.