Kinetic constants for decomposition of nitrocellulose in the 50 °C to 500°C range are analyzed. At T < 100°C, three processes (depolymerization, peroxide formation, and hydrolysis) are consistent with the reported kinetics. For T = 100°C–200°C, 28 of 30 previously reported kinetic measurements can be organized clearly into two categories by the use of the kinetic compensation effect. These two groups fit the first‐order and autocatalytic processes. Conflicting interpretations are reconciled by this approach. At T > 200°C, the kinetics are consistent with the existence of the first‐order step and desorption of the products as two parallel processes which, together, control the rate. Time‐to‐exotherm and mass burning rate kinetics are compared as temperature‐dependent reaction‐desorption events.
During the combustion of solid propellants, explosives, or pyrotechnics, the condensed phase experiences heating rates that may exceed 20,000 K/s. At such high heating rates, the thermal decomposition behavior of the energetic material could be affected by its rate of decomposition. To simulate the high heating rate environment, the T-jump experiment was developed for use with Fourier-transform infrared spectroscopy. The T-jump experiment utilizes electrical resistance heating of a thin Pt filament on which a small amount of the energetic test sample is placed. This work describes a heat transfer model of the filament and sample, a model of the current's control circuit, and global decomposition and heat release mechanisms of Cyclotrimethylenetrinitramine (RDX), which is an energetic ingredient .used in propellants and explosives. Comparisons of model calculations with experimental data reveal an excellent agreement. Similarly, the predicted time to rapid heat release for the highly energetic RDX sample also shows a good agreement with experimental results. Thus the use of the developed model in conjunction with experiments should be a useful tool in studying the thermal decomposition behavior of energetic materials under combustion-like conditions.
NomenclatureA = pre-exponential factor A f = cross-sectional area of filament c, c p -specific heat E -activation energy gi, 82 = gains of electronic circuit h = heat transfer coefficient h g = enthalpy of gas = current = thermal conductivity = length of sample ' -mass = number of species = Nusselt number = heat transfer = Rayleigh number = universal gas constant = temperature -time time constants of electronic circuit = internal energy = voltage drop across filament -width of filament = axial coordinate = species mass fraction = thermal diffusivity or coefficient of electrical resistivity = thermal expansion coefficient = heat of formation i k L s m Af Nu q Ra R u T t *d u V w x Y a t c2 = A/i/ e = emissivity v = kinematic viscosity p e = resistivity of filament p f = density of filament p s = density of sample cr = Stefan-Boltzmann constant aj" = species production Subscripts av = average cond = conduction conv = convection e = electrical ex = time to explosion / = filament g = gas i = ith species in = initial / = liquid Ig = liquid to gas max = maximum rad = radiation ref = reference quantity s = sample set = set or prescribed condition sur = surroundings 0 = sample location Superscripts ' = per unit length ± = left (-) or right (+) side at x = L s
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