Persulfate salt as an oxidizer for biocidal energetic nano-thermites

Abstract

Nanoscale potassium persulfate (K₂S₂O₈) was evaluated as an alternative to other peroxy salts, such as periodates (KIO₄), in aluminum-fueled energetic nano-composite formulations. High speed imaging coupled with temperature jump (T-jump) ignition found the nano-Al/K₂S₂O₈ reaction to have an ignition temperature of 600 °C which is comparable to nano-Al/KIO₄ and lower than nano-Al/K₂SO₄. The results from constant-volume pressure cell experiments further show that nano-Al/K₂S₂O₈ releases more gas and has a longer burn time than nano-Al/KIO₄. Thermal analyses at low heating rates (10 °C min⁻¹) by coupled differential scanning calorimetry (DSC), thermal gravimetric analysis (TG) and mass spectrometry (MS) show that there are three main steps of thermal decomposition for nano-K₂S₂O₈, with initial exothermic decomposition to release O₂ at 270 °C, and following endothermic decomposition to release both O₂ and SO₂ at higher temperatures. The heat of formation of K₂S₂O₈ was measured to be −1844.5 kJ mol⁻¹ based on the DSC results. Experiments performed at ultrafast heating rates (∼10⁵ °C s⁻¹) using temperature-jump time-of-flight (T-jump/TOF) MS show that the low O₂ generation temperature of nano-K₂S₂O₈ contributes to its high reactivity in nano-thermite compositions. An ignition mechanism involving gaseous oxygen was proposed for nano-thermite compositions containing reactive oxysalts such as nano-K₂S₂O₈. In contrast, a condense phase ignition mechanism was proposed for nano-thermites involving less reactive oxysalts such as nano-K₂SO₄. Given that the nano-Al/K₂S₂O₈ system is highly exothermic in addition to generating a considerable amount of SO₂, it may be a candidate for use in energetic biocidal applications.