Full automation of a laser-induced breakdown spectrometer for quality assessment in the steel industry with sample handling, surface preparation and quantitative analysis capabilities

Abstract

An instrument capable of reducing the quality assessment time in stainless steel-factories by a factor of 25 was built and evaluated. The instrument performs quantitative analysis based on laser-induced breakdown spectrometry (LIBS) to check for the occurrence of accidental mixing during steel production which may lead to incorrect shipping of the final products ("mix-up"). A number of developments, findings and achievements underlying the instrument itself allowed many of the variables traditionally associated with LIBS to be fixed. A laser-to-fiber robust interface was developed, which permitted safe and reliable transmission of the laser beam without gradual degradation of the fiber optic. As an additional benefit, the laser beam at the output of the fiber optics presented a homogeneous transverse profile, which allowed very flat craters to be produced. A depth profile study of stainless-steel components was used to obtain reproducible analytical results on stainless-steel samples with different surface finishes. Enhanced off-axis light collection resulted in better signal-to-background ratios without significant signal drift. Multivariate calibration for elemental analysis with LIBS proved to be a valuable tool for the correction of matrix effects and spectral interferences in certain cases. The assessment of "mix-up" was accomplished with a success rate of 100% in all the tests carried out with real samples.