Study of the ratio of fuel to oxidant on the kinetic of ignition reaction of Mg/Ba(NO3)(2) and Mg/Sr(NO3)(2) pyrotechnics by non-isothermal TG/DSC technique

摘要

The effect of mass ratio of fuel to oxidant in pyrotechnic compositions of Mg/Ba(NO3)(2) and Mg/Sr(NO3)(2) was studied using the non-isothermal thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques. The mass ratios 10:90, 25:75 and 50:50 of Mg powder to oxidant (nitrate salt) were used for preparation of pyrotechnic compositions. The kinetic parameters of thermal ignition reactions of pyrotechnics were obtained by using TG/DSC curves under nitrogen atmosphere at heating rates of 20, 25 and 30 A degrees C min(-1). The DSC curves showed that the 25:75 weight ratio of fuel to oxidant resulted in a complete ignition reaction and showed the highest enthalpy of the reaction. Also, this mass ratio was not indicated a mass gain after the combustion step in the TG curves. The model-free methods of Kissinger, Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS) were used for calculation of activation energy (E (a)) of ignition reactions of pyrotechnics. The E (a) values 130.5 and 146.3 by Kissinger, 138.3 and 153.2 by OFW and 132.2 +/- 2.4 and 146.3 +/- 1.7 kJ mol(-1) by KAS methods, respectively, were obtained for Mg/Ba(NO3)(2) and Mg/Sr(NO3)(2) pyrotechnics. Also, the nonlinear model-fitting method was used to determine the pre-exponential factor (A) and kinetic model function. The sigmoidal shapes were resulted from the curves of conversion factor (alpha) versus T. The model of A (3/2) with the functions of g(alpha) = [- ln(1 - alpha)](2/3) and f(alpha) = 3/2(1 - alpha)[- ln(1 - alpha)](1/3) as a nucleation reaction model was proved by using the model-fitting method for the ignition reaction of both pyrotechnic compositions. The ln A values 8.1 and 7.6 min(-1) were obtained, respectively, for the ignition reaction of magnesium powder with Ba(NO3)(2) and Sr(NO3)(2).