Simulation of heat flow curves from microcalorimetry-What has been achieved already

Abstract. With isothermal heat flow microcalorimetry (HFMC) one measures the net heat flow of the sample, which can be in total endothermal or exothermal or changes over time the characteristic. In detail the heat flow is determined by the reaction heats or reaction enthalpies of the underlying chemical reactions in the sample. But some so-called physical effects can contribute also, for example relaxation effects of the sample container, evaporation or melting of the sample. In lucky cases with a pure substance only one dominant chemical reaction may occur, and the simulation of the resulting heat flow curve is quite straight forward. One must know the enthalpies of formation from the starting substance and the ones from the decomposition products to determine the reaction enthalpy with the corresponding reaction rate equation. Reaction enthalpies and reaction rate constants are needed to simulate the heat flow curve. More complicated, but in principle the same procedure, is the prediction of heat flow curves of a stabilized NC-based propellant. The complexity is increased by a lot of reaction rate equations: (1) decomposition of NC, (2) reaction of decomposition products with NC, (3) the reaction of NOX with the stabilizer (4) consecutive reaction products from stabilizer and their reactions. An example is presented with a DPA stabilized ball powder. The NC reactions are discussed as well as the stabilizer reactions. For all of them reaction enthalpies and the reaction rate constants are necessary to know. The next step is to establish the complete reaction scheme for the heat flow with all relevant reactions und to solve it with respect to the measured heat flow curve. This can be done by so-called Runge-Kutta-Fehlberg procedures. The actual or targeted objective is to find out the underlying reactions of the stabilizer. This is a step further to assess its stabilizing quality.