Comparison of LIBS and μ-XRF measurements on bronze alloys for monitoring plasma effects

Abstract

The laser-induced breakdown spectroscopy (LIBS) technique is often used as atomic spectroscopic technique for elemental analysis of materials. However, it presents some drawbacks that make an accurate quantitative analysis difficult. Since the plasma properties, such as spatial inhomogeneity and plume stoichiometry strongly depend on the experimental conditions, the measurements are less reproducible. In order to evaluate the measurement fluctuations, we propose to use the more established micro X-Ray fluorescence (μ-XRF) technique for validating LIBS data. In particular, the quantitative data, obtained by varying the laser fluence, the shot numbers and the temporal acquisition parameters, were compared with those obtained by μ-XRF on laboratory made samples of binary, ternary and quaternary bronze alloys. For LIBS measurements a mobile double pulse laser instrument equipped with an high resolution Echelle type monochromator coupled to an intensified CCD camera was used. μ-XRF analyses were performed with a portable instrument that uses a micro collimated X-Ray beam and it is equipped with an high resolution detector. The LIBS results show a strong dependence both on the instrumental set up and the chemical-physical properties of the sample. With our findings we could identify the most suitable parameters to be used in the investigation of the different bronze alloys. The possibility to carry out a quantitative analysis by using the LIBS technique was checked through the comparison with related μ-XRF data. In particular in this paper we identified a set of reliable LIBS parameters for the quantitative analysis of copper, tin and zinc. Further analyses will be necessary to reach this goal also for the minor constituents as lead.