Superb enhancement of thermal decomposition of ammonium perchlorate in the presence of methyl viologen salts: A TG-DSC/MS and kinetic study

Different salts of 1,1′-dimethyl-4,4′-bipyridinium which known as methyl viologen compounds (MVX₂) (where X= iodide (I‾, MVI₂), perchlorate (ClO₄‾, MVC₂) and tetraphenylborate anion (BPh₄‾, MVT₂)) were prepared and characterized using ¹H NMR, ¹³C NMR, elemental analysis and mass spectroscopy. The impact of these viologen salts on the thermal decomposition of ammonium perchlorate was investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and mass spectroscopy. The obtained results revealed that the high-temperature decomposition (HTD) temperature of MVX₂:AP mixtures (5:100 (w/w)) significantly decreases by 121 ^◦C, 151 ^◦C and 112 ^◦C compared to pure AP in MVC₂, MCI₂ and MVT₂, respectively. Moreover, the apparent released heat of AP decomposition in these mixtures grows up from 574.2 J g⁻¹ for the pure AP to 2108, 1965 and 1564 J g⁻¹ for MVC₂, MCI₂ and MVT₂, respectively. Furthermore, the calculation of the kinetic parameters confirms that the activation energy of HTD of AP was significantly decreased from 142.9 to 124.9, 138.9 and 131.2 KJ mol⁻¹, upon mixing with MVC₂, MVI₂ and MVT₂ respectively. The rate constant of AP decomposition at the peak temperatures of these mixtures was higher than that at the peak temperature of pure AP. The evolved gas analysis using mass spectrometry shows that the decomposition of pure AP mainly results in ClO_3, ClO_2, HClO_4, ClO_, Cl_2, HCl, N₂O and O₂, while the major gaseous products of the 5:100 (w/w) mixture of MVX₂ salts with AP were detected as N₂, NO, N₂O, O₂, Cl₂, ClO, ClO₂, ClO₃, HClO₄, HCl and 4, 4′-Bipyridine (Bpy). The amounts of Bpy in decomposition products of AP/MVX₂ mixtures follow the order of MVC₂>MVI₂>MVT₂, which surprisingly is in accordance with the catalytic activity of these compounds.