Laser-induced breakdown spectroscopy (LIBS) on geological samples : compositional differentiation and relative hardness quantification

Abstract

This master’s thesis is focused on the LIBS technique for compositional differentiation and relative hardness quantification of selected geological samples. The experimental part of this thesis was conducted at the National Institute of Laser Enhanced Sciences (NILES) in Cairo, Egypt where a simple LIBS system was constructed. In parallel to the experimental work, the literature review was surveyed with the aim to give a thorough view of the history, fundamentals and all the factors related to LIBS. LIBS is a developing analytical technique, which is used to perform qualitative and semi-quantitative elemental analysis of materials (solid, liquid and gas). The fast data collection and the lack of sample preparation made LIBS be an attractive technique to be used for geological samples. This study was done to improve analytical methods for geochemical analysis of samples during different exploration phases (Mining, filed analysis, etc.), as a real-time analysis method to save money and time spent in labs. For a generation of laser induced plasma, a Q-switched Nd: YAG laser operated at 10 Hz and wavelength of 1064 nm was employed on the surface of the samples. A spectrometer fitted with an intensified charge-coupled device (ICCD) was used to disperse and detect the spectrum; then fed to a computer for recording and further processing of the data. The sample set was compiled from samples collected from different areas (South Africa and Namibia). Using principal component analysis (PCA), it was found that LIBS was able to differentiate between the samples even those of the same area. The results from the LIBS technique were correlated with subsequent analysis of the same samples by Particle-induced X-ray emission (PIXE). The feasibility of relative hardness estimation using LIBS was done by measuring the plasma excitation temperature for different samples. LIBS with its advantages as an elemental analysis technique made it possible to estimate the hardness of geological samples. Based on theory and results, an analytical technique for compositional differentiation and quantification of relative hardness of geological samples is proposed.