Lithium Based Red Colorants in Environmentally Friendly Pyrotechnical Illuminants

Dr. Thomas Klapoetke | Ludwig Maximilian University of Munich

WP19-1287

Objective

Replacing perchlorate oxidizers and banning chlorine donors in general from currently used pyrotechnic products has become the focus of interest of international researchers in this field. While perchlorates are highly persistent in water and the perchlorate anion blocks the uptake of iodine into the thyroid gland due to its similar ionic radius, mixtures of chlorine donors and organic compounds or chlorinated organic materials combust to form highly carcinogenic polychlorinated aromatics such as polychlorinated dibenzo-p-dioxins, biphenyls and dibenzofurans. When it comes to pyrotechnics with a red flame color, so far strontium-based compounds are the colorants of choice. However, strontium (Sr) has been detected at levels of concern in 7% of the public water systems in the United States of America and has been proved to replace calcium in the bone resulting in reduced bone strength. Therefore, the United States Environmental Protection Agency (EPA) is considering to regulate the amount of strontium in drinking water. Regarding the versatile applications of pyrotechnics in both the military sector, e.g. for signaling, as well as the civil sector, e.g. for firework displays on national holidays, and the frequency of their use, the enormously large part of the population exposed to the remaining smoke clouds and the severe impact on health and environment become obvious. This gives reason for research on environmentally benign red-burning pyrotechnic formulations that omit any chlorine source and strontium.

The objective of this project is to find a novel pyrotechnic system that will significantly reduce the environmental impact of pyrotechnics. It will aim to:

  • Develop new lithium (Li) based pyrotechnical compositions as red illuminates
  • Synthesize high-nitrogen Li-salts which are new or as described in literature
  • Focus on simple reactions with a low number of reaction steps for potential scale-up and industrial adaption.
  • Develop completely Sr/chlorine and perchlorate-free formulations which are nonpolluting.
  • Increase the intensity of lithium containing formulations
  • Investigate also lithium-based strobe formulations.

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Technical Approach

The waiver of strontium can be accomplished by employing lithium salts as red coloring agents. In this way, the use of halogenated materials is circumvented since the metastable light-emitting species in this case is atomic lithium. Synthesizing the lithium salts of high-nitrogen compounds and further investigating the literature-known compounds seems to be a good starting point as nitrogen will be the main combustion product and the amount of smoke produced will be reduced. Salts with a high lithium content might additionally yield luminous intensities superior to those of published lithium-containing formulations. Among those, salts accessible by a low number of reaction steps will be preferred in order to address economic needs. To ensure environmental friendliness and health safety, the lithium salts will be tested for their toxicity by the luminescent bacteria inhibition test, quantitative structure-activity relationship models, and the Ames test. The most promising candidates will then be blended into small-scale illuminant configurations and qualitatively evaluated concerning the desired red signature upon combustion at ARDEC before they will be consolidated into the full-sized hand-held signal form factor and quantitatively characterized with respect to burning time, dominant wavelength, spectral purity, and luminous intensity.

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Benefits

The developed new formulations will be completely chlorine-/heavy metal-/strontium-free, meeting potential U.S. EPA future regulations regarding strontium. This could avoid future health problems for all people related to pyrotechnical applications worldwide.

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Points of Contact

Principal Investigator

Dr. Thomas Klapoetke

Ludwig Maximilian University of Munich

Phone: 0014915201581378

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