Combustion, flame and explosion of hydrazine and ammonia I—The spontaneous ignition of pure gaseous hydrazine

Abstract

The spontaneous ignition of hydrazine has been investigated in the gaseous phase. The critical conditions of temperature and pressure for decomposition to become explosive and the effect on them of inert diluents have been measured; product analyses have been carried out to determine the stoichiometry and exothermicity, especially in the immediate region of the explosion limit. The critical limit is simple in form, conditions under which pure hydrazine explodes spontaneously varying from 6·6. cm Hg at 585°C to 5·9 mm Hg at 807°C in a silica vessel (volume 250 cm 3, surface 300 cm 2). Helium increases and argon diminishes the difficulty of ignition. As the limit is crossed, from just subcritical to just supercritical pressures, the stoichiometry changes. At 630°C: Slow reaction N 2H 4 → 1·13 NH 3+0·43 N 2+0·30 H 3 δ=−35·1 kcal mole −1 Explosive reaction N 2H 4 + 0·87 NH 3+0·57 N 2+O·72 H 2 δH=−32·3 kcal mole −1 The ignition satisfies qualitatively the criteria of thermal explosion: quantitatively, there are deviations from predicted behaviour. The deviations are thought to originate partly in interference from heterogeneous decomposition but principally in complexities of the homogeneous reaction. A thermal mechanism is in accord with the behaviour of closely related systems.