Surface heterogeneity study of some reference Cu-Ag alloys using laser-induced breakdown spectroscopy

Abstract

Investigation of the chemical composition, surface structure, metallurgical features, corrosion mechanism, and surface modification techniques of archeological metallic artifacts from Romans and pre-Roman times aimed to simulate the most commonly used Cu-based and Ag-based alloys. These simulated reference alloys will be used as sacrificial materials to study the most appropriate conservation materials and procedures. In the present work, laser-induced breakdown spectroscopy (LIBS) is introduced as a new validated surface mapping technique to study the micro-chemical distribution of elements in binary reference copper–silver alloy samples. Using different techniques for surface and bulk analysis, such as SEM coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction, it has been proven that LIBS is a simple, sensitive, and direct technique in the determination of heterogeneity of the sample's surface. By changing the laser wavelength (λ/nm) and focal length of the used focusing lens (f/cm), different spot sizes can be obtained. It was possible to control the spatial resolution in mapping the investigated samples' surface and to achieve local chemical information. In the present work, Q-switched neodymium-doped yttrium aluminum garnet laser has been used at its fundamental wavelength 1064 nm and its second harmonic 532 nm. The studied samples were specially manufactured heterogeneous copper–silver alloys with known grain size as studied via SEM investigation. The obtained LIBS results are in good agreement with those by other analytical techniques and extend the applicability of the surface techniques to study metallic ancient objects. Copyright © 2015 John Wiley & Sons, Ltd.