Nir-flare compositions basing on hot water band emission

NIR-Flares are widely used in military clandestine night operations, but they often show a lot of unwanted visible light due to excited metal lines or soot production. For this purpose suitable NIR emitters are needed emitting little or no visible radiation. Therefore, water is a potential molecule, because it shows several strong bands in the NIR and no bands in the visible range and additionally, it is formed as a main product in almost every hydrocarbon combustion reaction. So the idea is to produce hot water (bands) by a pyrotechnic reaction without the emission of visible light excluding most metal- and chlorine-containing compounds. Ammonium dinitramide (ADN), as a metal- and chlorine-free high-energy oxidizer, in combination with a suitable fuel was investigated in this regard. To determine the fuel/oxidizer mixing ratios providing highest degree of water formation, calculations were performed using the ICT-Thermodynamic Code. Paraffin, polyethylene, cellulose, and benzoic acid were chosen as fuels and ADN was the oxidizer. For different concentration ratios, the reaction temperature and the amount of formed water were calculated. Combustion temperatures of 2600 to 2800 K and water concentrations of 40 to 42% were found near the stoichiometric point. Based on these calculations, four mixtures were prepared and burned. The samples containing benzoic acid, cellulose and polyethylene could easily be ignited and burned with a self-sustaining flame. The flames of benzoic acid and polyethylene show high soot production in the visible spectral range, while those with cellulose were almost invisible. The sample with paraffin pyrolizes producing a lot of smoke. The measured NIR-spectra of all samples show strong emission of water, but only the sample with cellulose shows no soot production. In case of the sample with ADN and cellulose a mixture is found, which shows intense and distinct water bands in the NIR range, while it is nearly invisible in the visible range.