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Laser Induced Breakdown Spectroscopy for identification of Aerospace Composites

Final Report Summary - LIBSAC (Laser Induced Breakdown Spectroscopy for identification of Aerospace Composites)

Executive Summary:
LIBS has shown to be able to identify a wide range of composites. We were able to distinguish all different raisins we got from Airbus. Also a miniature instrument was developed to measure in the field. The business case for aircraft recycling turns out to be too small to justify instrumentation development just for this market. The business case has to come from general recycling industry and aircraft recycling should try to benefit from this.
Project Context and Objectives:
In the next 25 years, it is predicted that approximately 10,000 aircraft will be retired from service [1]. Furthermore, there are currently around 3,000 commercial aircraft parked and awaiting dismantling and this number is expected to grow. The question of how to dispose of these aircraft is therefore both timely and important. Obviously, it is not desirable to send these aircraft or their constituents to landfill – the aircraft contain many complex yet environmentally hazardous materials and the latent value of each of these end-of-life aircrafts can be more than $10 million. Re-use and recycling of the aerospace components is both more environmentally and economically sound.

Some components, such as engines and avionics, can be re-used directly on other aircraft, but most of the aircraft is stripped and shredded. The shredded material, comprising diverse alloys, composites and other materials, should be reclaimed as efficiently as possible. The reclamation procedure requires accurate and rapid identification of the composition of each component in the waste stream for sorting and optimized recycling. Light material (fluff) is sucked away from the waste stream, ferrous metal is sorted by a magnet and non-ferrous metal can be sorted to some extent with an eddy-current device or similar. The State of the Art for material identification is X-Ray Fluorescence (XRF). XRF is an elemental analysis technique which can report on the atomic composition of materials, with limits of detection in the ppm range. XRF is also suitable for miniaturization, and consequently numerous handheld XRF instruments are commercially available and used in aerospace recycling.

However, despite the sensitivity and simplicity of XRF, there are a number of disadvantages to this technique when applied in an aerospace recycling environment. Firstly, XRF is not suitable for coated samples and hence requires additional preparation of the sample (e.g. sanding). Secondly, XRF is relatively expensive, with a handheld XRF instrument costing approximately €20,000. Limited profit margins for many components often militate against the use of such an expensive piece of equipment. Finally, and most crucially, XRF is not suitable for the identification of aerospace polymers and composites.

Thus the increasing complexity of the construction materials used in modern aircraft, and in particular the shift towards lightweight composites in place of alloys, necessitates the use of alternative analysis techniques for accurate sorting of waste streams. Currently, it is hard to identify composites unless their precise location in the aircraft is already known. Parts that cannot be identified end up in the non-recyclable waste stream, even though technology exists to regain carbon fibers for reuse, for example. Therefore, the next generation identification instruments must consist of fast, accurate, affordable, sensitive and portable techniques that are able to discriminate between different polymer composites, even in the case of coated samples. In addition, the technique should be able to identify aged or damaged components. The concept of this project is to use Raman spectroscopy to address this challenge. The innovations of the project are listed in Table 1:

number Description
Innov. 1 A miniaturized yet high-specification Raman spectrometer.
Innov. 2 The creation of a combined Raman and LIBS spectral database of polymer composite constituents.
Innov. 3 The development of an effective fluorescence removal technique, suitable for Raman spectroscopy of composites.
Innov. 4 Comparison of confocal Raman spectroscopy and spatially-offset Raman spectroscopy (SORS) for non-invasive identification of coated composites.
Table 1: List of Innovations described in the proposal
Although RASAC may be successful alone, we expect that their effectiveness will be further enhanced through combination with LIBS (potentially also extended to include their sister technique of Laser-Induced Fluorescence). The RASAC project is therefore strongly linked to the LIBSAC project – the two projects will be carried out in tandem and inform upon each other. In situations where one technique is ineffective, another complementary technique can sometimes solve the problem instead. Furthermore, the synergistic effect of combining the data from multiple spectroscopic techniques is an extremely powerful approach to extend the specificity and sensitivity of detection. Lastly, the ablating property of LIBS may aid Raman in the measurement of coated samples.

In this project, we will focus on combining the data from Raman and LIBS for enhanced analysis; combining the hardware is not a specific objective or deliverable of the project. However, TNO does have access to a combined Raman–LIBS spectrometer developed for another application and this instrument will be used and assessed for its suitability to this project/
Project Results:
The results can be found in the deliverable reports.
Potential Impact:
The following dissemination activities have been taken:
-J. Day, Aerospace polymer composite identification with optical spectroscopies, Photonics Event, Veldhoven, NL, 24th April 2013. Oral presentation.
-J. Day, Handheld identification of composites, AFRA Annual Meeting, Las Vegas 9-11th July 2013. Oral presentation.
-Aircraft Metal Recycling Workshop, Châteauroux Airport 36130 Déols, France, 2-3 July 2013. Workshop organized by CleanSky AiMeRe project. RASAC project was represented at the workshop by M. Sandtke.
-Technology demonstration at Airbus facility, 29-10-2013, Toulouse, France. Several aspects of the technology were shown on real aircraft parts.
-The LIBSAC project was presented a numerous times to potential customers and partners during the definition of the business case.

TNO is setting up a spin-off company that will commercialize the LIBS spectrometer developed within the LIBSAC project. Apart from the recycling market, other interesting markets have been identified. This company is likely to start Q2 if 2014.

List of Websites:
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