Correctness of determination of energetic materials high temperature decomposition kinetics

The kinetic parameters of high temperature decomposition kinetics are widely used in evaluating the characteristics of thermal explosion, ignition and combustion of energetic materials. At present, the true and correct data on the high temperature kinetics of energetic materials condensed phase reactions are unknown and probably will remain unattainable in the nearest future. This is because of enormous technical difficulties to obtain such information and the absence of proper theoretical approaches for treatment of non-isothermal data. Evidently, with highly exothermic reactions it is impossible to conduct experiments at elevated temperatures using approaches of a low heating rate or isothermal ones. The improvement of characteristics of existing devices for thermal analysis is impeded by both technical complications and difficulties of performing experiments with ultrathin specimens of energetic material to ensure the conditions of uniform heat-up of the bulk of the substance. Based on the results of numerical simulation it is shown in this paper that the approach suggested 50 years ago by A.G. Merzhanov of using ignition delay data for deriving high temperature kinetics was not theoretically justified and can provide only very approximate values for such kinetics. The paper concludes on the today's relevance of the tasks on elaboration of mathematically justified techniques for determining kinetic parameters of global exothermic condensed-phase reaction, which will be based on the experiments on EMs ignition

Mechanism of hot spots formation in pentaerythritol tetranitrate under pulsed laser irradiation

The spectral, kinetic, spatial, and amplitude characteristics of emissions of pressed samples of PETN (pentaerythritole tetranitrate) by the first harmonic of a neodymium laser (1064 nm, 12 ns) are studied. It is found that at the moment of irradiation of PETN by laser pulses, hot spots are formed on the surface of the samples. The energy density of laser radiation varies in the range of 0.5-3 J/cm{2}. The characteristics of hot spots are determined by absorbing inhomogeneities and parameters of laser radiation. Multi-pulse excitation leads to the annealing of absorbing irregularities and increased threshold of optical breakdown. The received results are interpreted on the basis of ideas of the low-threshold optical breakdown as evolving within local (defective) regions of the PETN in the electric field of the light wave

Polyurethane–poly(2-hydroxyethyl methacrylate) semi- IPN–nanooxide composites

Two sets of hybrid polyurethane–poly(2-hydroxyethyl methacrylate) semi-interpenetrating polymer network–nanooxide composites with 0.25 or 3 wt% nanosilica or nanoalumina functionalised with OH, NH2 or CHLCH2 groups were prepared. A combination of atomic force microscopy, infrared spectroscopy, thermally stimulated depolarisation current measurement, differential scanning calorimetry and creep rate spectroscopy analysis of the nanostructure and properties of the composites was performed. The pronounced dynamic heterogeneity and the strong impact of oxide additives, basically suppression of the dynamics and temperature-dependent increasing modulus of elasticity, were observed. The effects correlated with either interfacial interactions (for silica) or the nanostructure (for alumina). A low oxide content strongly affected the matrix due to the formation of an unusual cross-linked, via double covalent hybridisation of three components, structure of the nanocomposites

Microwave resonator method of dynamic measurement of mass of the samples of gasifying solid fuel

The paper describes novel contactless method of determining instantaneous gasification rate of solid materials under intensive blowing the reacting (gasified) surface. Method is based on dynamic measurement of the mass of dielectric substance within specially designed microwave resonator. The attenuation of passing through the resonator signal is proportional to the actual value of the sample mass. Before firing experiments the setup is calibrated using samples of studied material with different channel radius. With the proper choice of data acquisition system one can achieve the web sample thickness resolution around few microns and time resolution higher than 1 kHz. The examples of preliminary tests with paraffin samples blown by air jets with temperatures of 350-1500 K and speeds of 375–700 m/s are presented