Impact of laser-induced breakdown spectroscopy implementation for the quantification of carbon content distribution in archaeological ferrous metals

Abstract

The presence of carbon content is a key enabling factor in archaeological ferrous material studies because it can provide technological and temporal information on its fabrication. A strong relationship exists between the composition, the metallographic structure, and the mechanical properties of metals. Laser-induced breakdown spectroscopy (LIBS) is one of the techniques that can be used in situ to access the carbon content of samples.This paper presents a thorough investigation of the influence of key experimental parameters on the analytical implementation of LIBS, proposes a suitable protocol for carbon quantification, and discusses its limitations. We demonstrate that the global carbon concentration can be obtained with the help of a large laser spot, but this is not sufficient to separate all steel phases. To overcome this problem of spatial distribution and to achieve quantitative measurements, a smaller laser spot has been used and a specific analytical procedure has been developed. As a result, a smaller spot is needed for detecting the different steel phases and to show the metallographic structure. On a macro-scale, a preliminary sampling can be performed with a larger laser spot on the objects in situ in order to locate the high carbon content, such as cementite (Fe3C), for further analysis. On a micro-scale, the different phases of steel and their distribution in the object should be precisely and locally determined with a smaller laser spot, even on nonequilibrium structures. This opens up prospects for researchers to quantify the presence of different phases within the steel matrix and correlate such findings with the technological background behind steel making in historical times.