The nonlinear chemical reaction kinetics of NH4ClO4+Mg+K2Cr2O7 system I. Experimental phenomenon of solid-phase oscillatory combustion

Under normal circumstances the reaction system of NH4ClO4 + Mg + K2Cr2O7 do es not burn at a constant velocity, it bums oscillatorily. The nonlinear ch emical properties of the system are studied in the present paper. New formu las for the solid-phase oscillatory combustion are introduced. In these for mulas, the ratio of composition is changed in order to obtain the new oscil latory combustion phenomenon. The experimental results are recorded by X-Y digit-at recorder and Kodak EM 1020 high speed movement analysis apparatus. The waveforms show that the formula in this study can produce oscillatory combustion. From the experimental study, it can be seen that with the incre asing of NH4CLO4 and Mg contents, the frequency increases: Moreover, the ch ange of the K2Cr2O7 content greatly affects the oscillation frequency. The experiment results and reaction mechanisms are analyzed by the methods of the nonlinear chemical reaction kinetics. It can be seen that oscillator y combustion occurs mainly as a result of the competing reactions among the three phases of Mg with oxygen. 1. Solid-phase Mg(s) reacts with oxygen and releases energy. In open system s, if the energy cannot maintain the temperature of the system, the reactio n will stop and combustion ceases. When Mg(s) is at the vapor temperature, if the heat released from phases ch ange of Mg is equal to the heat required for heating the mixture, the tempe rature is steady, and then the reaction occurs at a smouldering sate. If more heat is generated during the heat production than that consumed, th e reaction rate will increase. At this moment there are two states: one is that the production rate of Mg(g) is slower than the consumption rate, and deflagration will not appear; the other is that the production rate of Mg(g ) is greater than that of consumed and deflagration appears, or in the vapo r state and the temperature is high. From the experiment, it can be seen th at, the deflagration time of the reaction is longer than the smouldering ti me with the increasing of the Mg content. The formulas of this work make th e reaction in a middle state between deflagration and smouldering, it is sh own that the concentration of Ma controls the reaction process. 2. At the smouldering stage, the major reaction is part of Mg(s) reacting w ith oxidant gas. At the deflagration stage, the major reaction is the gas-g as reaction of Mg(g) and oxidant gas. There are two different reaction mech anisms replacing each other that result in the pulse oscillatory combustion . 3. Because the vaporizing rate and vapor concentration of Mg(s) have remark able influence on the frequency of smouldering and deflagration, the endoth ermic materials generated in the reaction can greatly regulate the vapor ra te of Mg(s) and effectively control the pulse frequency of pyrotechnics. Th e frequency-modulating; species K2Cr2O7 can control the vapor of Mg by form ing the condensed phase layer at smouldering stage, and it is an essential condition for an oscillatory combustion to occur.