Study on the spontaneous ignition mechanism of nitric esters (I)

Abstract

The spontaneous ignition mechanism of cellulose nitrate (NC) was analyzed in terms of the pressure change and the thermal behavior during isothermal storage at 393 K. During storage of the NC, atmospheric O 2 was consumed during an exothermic reaction. The heat release behavior as well as the O 2 decreasing behavior could be fitted to a first-order reaction. The rate constant ( K) and the induction period ( t indc) for the heat release behavior almost coincided with those for the O 2 decreasing behavior (O 2 decreasing behavior: K = 7.7 × 10 −5 s −1, t indc = 10 h; heat release behavior: K = 8.1 × 10 −5 s −1, t indc = 9.2 h). The reaction heat did not increase even if the initial amount of NC increased under a limited O 2 condition. These results would suggest that NC released reaction heat due to autoxidation which was propagation involving O 2 and radical species generated from NC. Even in a 4.7 vol.% NO 2/air atmosphere, the amount of reaction heat did not significantly change from those in dry air. The reaction order was also not affected by the partial pressure of NO 2. On the one hand, the K was slightly higher, and the t indc was shorter in the 4.7 vol.% NO 2/air ( K = 1.8 × 10 −4 s −1; t indc = 3.4 h) than those in dry air. These results would indicate that NC accumulated reaction heat due to autoxidation by atmospheric O 2, and NO 2 contributed to the initiation process before the autoxidation occurred.