Multi element analysis using LIBS

Multi element analysis using LIBS
Multi element analysis using LIBS

The Laser Induced Breakdown Spectroscopy (LIBS) establishes new possibilities for a true real-time analysis of any material without time-consuming sample preparation. The evaporation of solid samples by means of a focused laser beam together with a simultaneous spectral analysis of the formed microplasma permits a chemical analysis of microscopic tiny areas.

The Echelle spectrometer / Echelle spectrograph of the ESA 4000 series is well suited for measurements of ultrashort plasma discharges and enables a simultaneous multi-element analysis. The evaluation of the emitted spectral line emission allows detection of main and trace elements at the same time and therefore a real-time analysis of the atomic composition of materials.

The Echelle spectrometer / Echelle spectrograph ESA 4000 is a compact measuring device with high spectral resolution, capable to control most commonly used laser sources. Applications of the ESA 4000 system are for instance the LIBS-analysis of material composition of technical glasses or micro analytical evaluation of tool steel.

Analysis of glass

Analysis of glass by ESA 4000
Analysis of glass by ESA 4000

Due to its high transparency, small inhomogeneities in glass are immediately visible for the human eye. Easy identification of glass imperfections poses high requests on the glass production. In case product faults or cords occur during production, the fault source has to be identified quickly. With a laser microscope and a connected Echelle spectrometer ESA 4000 it is possible to localise such faults. Usually a simple half quantitative analysis is sufficient. This is possible by a simple comparison between the plasma spectra of the fault and the plasma spectra of the fault surrounding.

Application example

The figures show a local fault in a tumbler. A micro defect analysis was performed along the indicated line to identify the fault source. Measurements were performed with a diode pumped Nd:YAG-laser at an excitation wave length of 266 nm. In the second figure the absolute intensities of the silicium, calcium and aluminium lines are displayed as function of the location.

In comparison with the surrounding glass matrix, the line scan showed a strong increase of Al content inside the defect, whereas the Ca content decreased; the concentration of Si varied slightly. Such defects are typical for corrosion with an Al2O3-containing ore, featuring a high melting point.

Glass fault in a tumbler - microscope pictureChange of element composition at a glass defect (punctiform defect) in a tumbler – line scan

Analysis of metal alloys

Echelle spectrum of a steel sample (LIBS measurement, Nd:YAG-Laser, 1064 nm)
Echelle spectrum of a steel sample (LIBS measurement, Nd:YAG-Laser, 1064 nm)

The Echelle spectrometer ESA 4000 in combination with an external laser is used for various purposes. Through the integrated analysis of all relevant Echelle optic lines in the spectral range from 200 nm to 800 nm measured simultaneously with a resolution of a few pm, and thus almost all chemical elements are detected in a single measurement. The detection limits range down to the ppm range. The performance of the Echelle spectrometer is reflected in selected applications, such as the analysis of steel, carbide, aluminum or precious metal alloys.

The good focusing ability of laser light and the use of very short wavelength radiation in the ultraviolet spectral range enables the investigation of smallest amounts of material within dimensions of serveral microns.The quasi-selective vaporization option allows a simple and rapid detection of local inhomogeneities along the sample surface and the recording depth of profiles.

Application example

Micro analytical evaluation of tool steel

The wear of tempered cutting edges poses high demands on the physical material properties. Properties like hardness, abrasion and temperature resistance are substantially determined by the microscopic structure. Local analysis of the chemical composition of tiny material areas can therefore deliver important information regarding the causes of diminished resistance.

For the characterisation of material inhomogeneities an exact quantitative analysis is not strictly required.
A determination of the failure nature is possible by comparison of the elements composition between base material and the „defect“. A quasi punctiform excitation permits a targeted shoot on microscopic small changes. Analysis of the intensity proportions of element specific spectral lines from the plasma radiation permits an easy half quantitative analysis.

The microscope image shows the cutting edge of a tool steel. It is a tool with a soldered small carbide metal plate. The transition area tool carrier – solder – carbide metal before and after the plasma analysis is shown. The line scan was performed vertical to the soldering edge. Based on the recorded spectra an immediate qualitative analysis of the elemental composition is possible. By selection of suitable analysis lines a suitable measurement program for the automatic metal analysis was set up. The program permits a direct print out of measurement protocol with the selected spectral range and the identified line intensities or line proportions respectively.

Microscope pictures of a tool steel - area of transition basic material, (solder) carbid metal,
(a) before and (b) after LIBS analysis (linescan, 90 µm step width, 1064 nm excitation)

Microscope picture of tool steel before LIBS analysis Microscope picture of tool steel after LIBS analysis

The analysis of the carbid metal showed W, Ti, and Co as main components, characterising abrasion and temperature resistance. Ta, Si, and traces of Cu, Fe and Cr were found with low concentration. The basic material for the tool is a steel alloy with Mn and Si and a small amount of Cu and Cr. The measured line intensities along the performed line scan show the change of the composition for the transition area basic material – solder – carbid metal. The spatial resolved measurements vertical to the solder edge indicated the diffusion processes of several elements, e.g. Si and Fe into the Cu solder.

Modification of the element composition (line scan) along the basic material (solder) carbid maetal transition in tool steel

Modification element composition