Decomposition mechanisms in thermally-aged thin-film explosives

摘要

The isothermal decomposition of nitrocellulose (NC) has been examined using two substantially different experimental techniques, involving both confined and unconfined samples. The confined isothermal aging technique involved confined thin-film samples heated to temperatures of 150 to 170(degrees)C, for 1 to 72 hours. Condensed-phase chemistry was monitored real-time using FTIR. Results indicated that the first step in decomposition was scission of the O-NO(sub 2) bond and subsequent formation of carbonyl and hydroxyl products. Scission of the O-NO(sub 2) bond appeared to occur by a first-order reaction. The Arrhenius expression for the first-order reaction rate constant was evaluated from the experimental data. The unconfined rapid isothermal decomposition technique involved both high speed-photography and time-of-flight mass spectrometry (TOFMS). Mass spectra obtained from experiments at 420(degrees)C indicated that NO(sub 2) formation and, therefore, scission of the O-NO(sub 2) bond occurred by a first order reaction, the rate constant for which was evaluated from the experimental data. The rate constant for global pseudo-first order decomposition of NC at 450(degrees)C was also estimated from high speed photography results. Rate constants at 420 and 450(degrees)C were predicted using the Arrhenius expression developed from the confined isothermal aging results and were in good agreement with the rate constants obtained at those temperatures in the unconfined rapid decomposition experiments using TOFMS and high-speed photography. Results from these substantially different measurements gave consistent results over a temperature range of about 300(degrees)C, in which reaction rates vary by nine orders of magnitude, and indicate that the two experimental techniques being developed have good potential for studying condensed-phase decomposition of energetic materials. (ERA citation 19:033801)