Fireworks: Composition and Chemistry Through Raman Spectroscopy and SEM-EDS Imaging
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VOL. 24 NO. 3 (2012) ARTICLE Fireworks: composition and chemistry through Raman spectroscopy and SEM-EDS imaging Kepa Castro, Silvia Fdez-Ortiz de Vallejuelo and Juan Manuel Madariaga University of the Basque Country, Faculty of Science and Technology, Department of Analytical Chemistry, PO Box 644, 48080 Bilbao, Spain. E-mail: [email protected] Introduction other nitrates. Metallic particles (alumin- Great efforts have been expended in Fireworks are widely used to entertain ium, titanium) can also be present the detection of high explosives such as audiences at events such as music to produce brilliant effects, as well as trinitrotoluene (TNT), octogen (HMX), concerts, theatre and street perfor - organic matter used as a fuel or propel- cyclonite/hexogen (RDX) and penta- mances, local and popular festivals, lant for the combustion of the firework. erythritol tetranitrate (PETN) 2–5 and New Year’s Eve celebrations, during The skills of the firework manufac- rapid and direct analytical protocols for sports events (for example, Olympic turer in mixing all these chemicals, as the detection of explosives have been Games, American Super Bowl, European well as in the design of the way they are developed for security and counter- Football League) etc. and have become distributed within the firework, produces terrorism issues, even being imple - a very important part of these celebra- the enthralling, entrancing and marvel- mented in airports, customs and seaport tions in our life. Anyone who has seen lous light, colour and sound effects. offices.6 From the forensic point of view, a firework display will admit that for To the average onlooker, any firework very interesting analytical methodologies impressive grandeur, colour effects and which rises into the air is a rocket; in have been described for establishing contrasts of light and shade, pyrotechny contrast, there are many different types criminal evidence7,8 and it is now possi- is unapproachable. In fact, almost no of fireworks: lanterns, rockets, Catherine ble to determine explosive residues even other form of amusement is capable of wheels/pinwheels, jumping crackers, after explosions.9,10 In contrast, it seems giving enjoyment to so many people of squibs and even liquid fireworks for that low explosives and pyrotechnic arte- all classes and tastes at any one time.1 indoor use.1 facts have been scientifically ignored. As in many aspects of our life, chem- However, fireworks have also Consequently, in order to support accu- istry is also linked with fireworks and the been used during riots, in street satory evidence, appropriate analytical fireworks industry. In fact, fireworks are demonstrations, inside football stadia etc. forensic studies are required. a mixture of different chemicals that, by violent protest and extremist groups It is also well known that in many of after burning in the proper way, produce and hooligans and they can be used to these artefacts, non-allowable hazard- the well-known light, colour and sound cause aerial disasters and severe injuries ous and risky substances for human effects. In addition to sulfur, saltpetre etc. Every year, tons of indoor pyrotech- beings are employed. For instance, (potassium nitrate) and charcoal, fire - nics are confiscated by police and local Croteau et al.11 found evidence for works often contain different salts and authorities in almost every country. It unalloyed Mg, which is banned from fuels. For example, copper salts produce must be taken into account that fireworks consumer fireworks in the USA. In the blue flames, whereas lithium salts are considered to be low explosives and, European Union, the REACH (Regulation, produce red flames, barium salts are subsequently, they are subjected to strict Evaluation, Authorisation and Restriction responsible for the green colour, calcium legislation in all countries; the manufac- of Chemicals) Regulation 12 covers a for the orange colour and sodium for the turing process, storage, transport and sale process for which those substances that yellow colour. Saltpetre is used as an are strictly regulated and restricted. Police are considered to pose an unacceptably oxidiser, but other compounds are possi- forces fight against the illegal commerce, high risk to human health and the envi- ble, such as chlorates, perchlorates and business and storage of such substances. ronment may be removed from the 6 SPECTROSCOPYEUROPE www.spectroscopyeurope.com smarter FT-IR Never before has a research grade FT-IR provided more information, in less time and more easily. The revolutionary design of the Thermo Scientific Nicolet iS50 FT-IR Spectrometer allows any user to move from one experiment to another with the push of a single button—integrating ATR, Raman and NIR. Hyphenated techniques are part of its versatility. TGA-IR and GC-IR functionality are coupled with powerful automated data analysis tools to extract information quickly and consistently, eliminating literally hours of data analysis. Smarter spectroscopy, exemplified. easily do more • discover easy versatility • thermoscientific.com/iS50 iS50 Raman Module Mapping and well-plate screening in sample compartment mounted module iS50 ATR Module Leaves main sample compartment free for other analyses iS50 NIR Module Develop QC methods for bulk samples © 2012 Thermo Fisher Scientific Inc. All rights reserved. FASTLINK / ENTER 004 FOR FURTHER INFORMATION VOL. 24 NO. 3 (2012) ARTICLE market unless there is a justifiable need tra17,18 as well as against our own collec- powder appearance, together with for them to remain in use. Thus, a control tion of spectra. some grey fibres. SEM-EDS analysis of these kinds of artefacts should be A scanning electron microscope (Carl showed the presence of N, O, C and recommended and it is another reason Zeiss) coupled to an energy- dispersive Ti. A more detailed mapping of the for the development of analytical proto- X-ray spectrometer (Oxford Instruments) elements in different areas revealed cols for their analysis. was used for electron image acquisitions a high coincidence among the distri- and elemental composition determina- bution maps of N, O and C, whereas Samples tion. The elemental analysis was carried Ti appeared concentrated in spots of Several cracker fireworks were sent to our out using an 8.5 mm working distance around 100 µm in size. EDS spectra of laboratory in order to find out whether and an acceleration voltage of 20 kV. the Ti particles did not present any other they really were recreational fireworks and EDS distribution maps of the elements element (EDS spectrum in Figure 1). to determine the chemical composition as well as EDS false-colour images were However, the match among the elemen- of all of them. The (cardboard) cartridge obtained for a better interpretation of the tal mapping for C, N and O revealed the of each artefact was opened to obtain data. As the samples may contain carbon presence of an organic compound. Figure the solid powders that were the object compounds, they were not covered with 1 shows a false colour image (Cameo of the analysis. No other pre- treatment graphite to avoid interference. option in Oxford software) obtained was performed on the samples except after EDS mapping where the red colour those appropriate to each analytical tech- Results and discussion represents the energies of N, C and O nique. In addition, several liquids/gels, The analytical procedure consisted first and the blue colour represents the ener- putatively used as indoor (theatre) fire- of an SEM-EDS analysis in order to deter- gies of Ti. These kinds of representations, works, were also analysed to determine mine the elemental composition of together with the single distribution of their chemical composition and identify the samples and the distribution of the the elements along the mapped area, potential firework materials used in their elements, followed by a Raman spectro- are of great value at the time of interpret- manufacture. scopic analysis to obtain the molecular ing experimental data, and give valuable composition. The elemental chemical clues for the interpretation of the Raman Analytical approach information was used to help in the data. Raman spectroscopy is a very valu- interpretation of the molecular data. To After SEM-EDS analysis, a Raman study able tool for explosives detection, 6,13 illustrate this approach, several examples was carried out. In this case, Raman thanks to its non-invasiveness and the are discussed below. spectra only showed the bands due to non- destructiveness of the samples, One of the samples analysed nitrocellulose (bands at 146, 209, 406, a critical characteristic when irreplace- in our laboratory presented a grey 561, 627, 696, 844, 921, 1001, 1062, able samples or evidences have to be analysed. However, the interpretation of the Raman spectra is not trivial and care must be taken. Unfortunately, not all the compounds present in fireworks are Raman active, thus, complementary techniques are needed, such as Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) etc.14–16 In the present work, a combina- tion of Raman spectroscopy and SEM-EDS is proposed. Sample prepa - ration is described in the literature.15,16 Raman analysis was performed using a Renishaw InVia Raman spectrometer joined to a Leica DMLM microscope. The system is equipped with two lasers, 514 nm (ion–argon laser) and 785 nm (diode laser). Laser power was reduced in order to avoid sample photo- decomposition and possible explosions. Figure 1. False-colour image after EDS mapping showing the nitrocellulose fibres (in red) and The obtained Raman spectra were titanium particles (in blue); EDS analysis of a titanium particle (inset: top, left) and Raman compared with several database spec- Figure spectrum 1. ofFalse-colour nitrocellulose image fibres after(inset: EDS bottom, mapping right). showing the nitrocellulose fibres (in red) and titanium particles (in blue); EDS analysis of a titanium particle (inset: top, left) and Raman spectrum of nitrocellulose fibres (inset: bottom, right).