6533b834fe1ef96bd129decb

RESEARCH PRODUCT

Initial reaction steps in the condensed-phase decomposition of propellants

subject

description

Understanding the reaction mechanisms for the decomposition of NO2-containing energetic materialsin the condensed phase is critical to our development of detailed kinetic models of these energetic materials in propellant combustion. To date, the reaction mechanisms in the condensed phase have been represented by global reactions. The detailed elementary reactions subsequent to the initial NO2 bond scissioning are not known. Using quantum chemical calculations, we have investigated the possible early steps in the decomposition of energetic materials that can occur in the condensed phase. We have used methylnitrate, methylnitramine, and nitroethane as prototypes for O−NO2, N−NO2 and C−NO2 nitro compounds. We find the energetic radials formed from the initial NO2 bond scissioning can be converted to unsaturated non-radical intermediates as an alternative to the unzipping of the energetic radical. This reaction pathway is caused by the cage effect, which prevents the NO2 molecule from diffusing away before it can react with the energetic radical to form HONO. We propose a new, prompt oxidation mechanism in which the HONO, while still trapped within the cage, can add back onto the energetic molecule. This produces oxidation products in the condensed phase that normally would not be produced until much later in the flame. We propose that this prompt oxidation mechanism may be a general feature of both nitramines and nitrate esters. The resulting HONO formed by the H-atom abstraction will be strongly influenced by the physical properties of the condensed phase. The applicability of this mechanism is demonstrated for decomposition of ethylnitrate, illustrating the importance of the cage effect in enabling this mechanism to occur at low temperatures.