Mechanism of catalytic additive effects on diethylnitramine dinitrate combustion rates

Abstract

Burning of DINA (diethylnitramine dinitrate, (O 2NOCH 2CH 2) 2NNO 2) at atmospheric pressure has been investigated. The burning rate is shown to be determined by the rate of heat evolution in the reaction zone of the condensed phase (the C-phase) as well as by the heat flux from the gas phase. Two groups of additives are differentiated: (1) compounds such as ammonium persulfate, hydrazine sulfate, and hydroxylamine sulfate, which increase the burning rate through the intensification of heat evolution in the C-phase and (2) compounds of hexavalent chromium and composite additives, including soot and lead and copper compounds, which accelerate burning as a result of additional heat flux from incandescent condensed particles formed on the burning surface and heated to a temperature of 1000–1200°C by the heat from heterogeneous catalytic reactions. In the case of the chromium compounds, the active substance responsible for the effect is found to be Cr 2O 3 formed in a combustion wave as a result of oxidation-reduction processes and thermal decomposition of initial additives. The second mechanism of the action of additives is shown to be widely spread. In particular, incandescent particles on a burning surface occur when chromium containing additives is introduced into picric acid, RDX, nitrocellulose, and double-base propellant, as well as in a mixture of ammonium perchlorate or ammonium nitrate with combustible components. It has been proved experimentally that fast-burning picrates are formed in the reaction zone of the C-phase when picric acid burns with salts of chromium acids as additives. The increase in the burning rate with these additives is found to be caused by the joint action of picrates and chromic oxide formed in the combustion process; however, the contribution of the latter is far greater.