G. Nicolas

Modelling of temperature evolution on metals during laser hardening process

Abstract To achieve a precise and controlled laser process, an exhaustive analysis of the thermal behaviour of the material is necessary. In the present paper, a numerical simulation of the laser hardening process has been developed using both analytical solutions and the finite element code ANSYS™ to solve the heat transfer equation inside the treated material. The knowledge of the thermal cycles has enabled suitable processing parameters to be ascertained thus improving surface properties when metallic alloys have been irradiated. A simpler analytical method is also used to determine the mentioned parameters more quickly. This general purpose method has been applied to a specific experimental situation, namely the treatment of cylindrical pieces used in a multistage pump rotary jacket.

Spectrochemical study for the in situ detection of oil spill residues using laser-induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy (LIBS) has been used to identify the differences or similarities between crude oil and fuel residues. Firstly, a man portable LIBS analyzer was used for the on-site environmental control and analysis of the oil spill from The Prestige. An exhaustive analysis of crude oil and oil spill residues (collected during the field campaign in the Galician Coast) was performed in the laboratory. Characteristics elements in petroleum such as C, H, N, O, Mg, Na, Fe and V were detected. In addition, contributions from Ca, Si and Al in the composition of residues have been found. The use of intensity ratios of line and band emissions in the original fuel (crude oil) and in the aged residues allowed a better characterization of the samples than the simple use of peak intensities. The chemical composition between the crude oil and the fuel residues was found completely different. As well, a statistical method was employed in order to discriminate residues. Although significant differences were observed, no conclusions in terms of age and provenance could be reached due to the unknowledgment in the origin of the samples.

Laser-Induced Breakdown Spectroscopy for Chemical Mapping of Materials

Abstract: Analytical techniques able to perform spatially resolved analysis are highly demanded in the surface analysis and material science fields. Compared to other analytical techniques usually employed, laser-induced breakdown spectroscopy (LIBS) offers several advantages, such as simplicity and robustness of instrumentation, which permit on-line and in situ measurements. No or minimal sample preparation is required, and the analysis of any sample without restrictions on the shape, size, or conductive nature can be performed under atmospheric conditions in a matter of seconds. In this work, a review of the different instrumental approaches employed in the generation of compositional maps as well as a detailed discussion of the different applications that involve the use of LIBS to obtain two-dimensional or even three-dimensional chemical maps is presented.

3D chemical maps of non-flat surfaces by laser-induced breakdown spectroscopy

In this work, the possibility of performing 3D multielemental chemical maps of non-flat samples by laser-induced breakdown spectroscopy (LIBS) is demonstrated for the first time. In a first step, information of surface morphology of the area to be analyzed is obtained and digitized by a simple experimental arrangement. Using this information, a point-to-point map is generated by the LIBS technique preserving, for every position in the analyzed area, a constant distance between sample surface and both focusing and collection systems. Finally, morphological and spectral information are associated by a homemade computer application which allows plotting the compositional maps in different formats. 3D (X, Y and Z-depth) multielemental chemical images of samples presenting different nature and contour will be shown and the feasibility of this approach will be demonstrated.

UV laser surface processing of metallic alloys: comparison of experimental and numerical results

The modifications resulting from a laser irradiation and which occur in solid materials are located mainly in the near surface region. An examination of the exposed areas and cross-sections allows to determine the influence of such a treatment. For most of materials, a molten layer is formed during the interaction processes and its depth depends on the irradiation conditions. The thickness of this layer can be measured experimentally but can also predicted by a numerical modelling which provides an analysis of the thermal cycles developed into the sample. In the present study, a KrF laser radiation has been used to irradiate metallic alloys in air and experimental and numerical investigations have been performed in order to compare both results. The aim is to provide complementary information for a more complete understanding of the melt front into solid.

Provenance Characterization of Archaeological Ceramics by Laser Induced Plasma Spectroscopy

Archaeological ceramics Terra Sigillata manufactured in different production centres have been studied by “laser induced plasma spectroscopy” (LIPS). The aim of this work is to demonstrate the capability of LIPS for the classification of pottery shreds in function of their provenance. Characteristic emission spectra of different pottery groups were obtained and simple linear correlation methods were used for grouping samples. In addition, complementary scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDX) analysis were performed to obtain morphological features and to confirm chemical results