The explosive decomposition of azomethane

Abstract

The explosive decomposition of azomethane was studied experimentally in an apparatus which permits the simultaneous, time-resolved measurement of pressure, local gas temperature at the center of the spherical reaction vessel, and local gas temperature near the vessel wall. This is done by photographing the oscilloscope traces of the amplified output of variable-reluctance pressure transducers and of the emf of fine (0.001 in.) coated thermocouples. The explosion-limit pressure could be bracketed closely and the pre-explosion pressure and temperature rise, the maximum stable temperature rise, the length of the induction period, and the course of the fast but nonexplosive decomposition were measured at temperatures from 605° to 714°K and for some mixtures with added H 2 , He, N 2 , and NO. At temperatures between 636° and 687°K, the records indicate a thermal explosion, i.e., the temperature at the center rises exponentially just before the onset of explosion, and a large maximum temperature rise of 40° to 45°C is measured for the slow reaction just below the limit. From the temperature dependence of the limit, the maximum temperature rise, and the temperature rise well below the limit as function of initial concentration, an activation energy of 32 kcal/mole was obtained, in marked disagreement with the literature value of 51 kcal/mole from the slow, isothermal decomposition. Below 636°K, the induction periods are longer, the maximum temperature rise decreases, and the onset of explosion is abrupt, indicating at least partial branched-chain character. An oversimplified mechanism is proposed which accounts for several but not all of the observed features.