Low Explosives Research Articles

Composition of the combustion products from pyroxylin at atmospheric pressure

Temperature measurements have shown there to be four modes of combustion in low explosives as the pressure increases. Of the four, the cold-flame state (0.1-2.0 MPa) and the two-flame state (1.2-5.5 MPa) have equilibrium values attained for the maximum temperature and the composition of the combustion products. Little is known of the composition of the combustion products from a cold-flame reaction. The authors have examined the combustion products of pyroxylin, which is composed of 96.5% nitrocellulose, with the remainder made up of solvent, binder, water, etc. The experiments were performed in a quartz reaction vessel provided with external filament heating. Mass spectroscopy was used as a preliminary analysis, followed by chromatographic analysis, revealing the hydrocarbon, nitrogen, and nitrogen composition of the combustion products. The maximum cold-flame temperature measurements were compared to the calculated temperatures and their agreement indicates that the experimental data correspond to the calculated chemical composition.

Convective-combustion propagation in porous low and high explosives

Convective-combustion propagation in porous low and high explosives

Shock initiation of granular explosives pressed to low density

The dependence of the shock initiation of pressed granular explosives on density of the pressing, interstitial gas in the pressing, grain size of the explosive, and characteristics of the initiating shock is discussed. The validity of applying the hydrodynamic equations for a homogeneous material to an inhomogeneous assembly of particles is examined. Various mechanisms for the initiation of granular explosives are compared in terms of current knowledge. Initiation of low density explosives is not satisfactorily explained by uniform shock heating of the pressing nor by shock heating of the interstitial gas, as has long been thought. It appears that initiation is dependent on minute shock interactions and resulting spalling and jetting, with initiation occurring in the fine particles of the spall or when the products of spalling or jetting are stagnated at the surface of an intact grain. Several experiments are suggested with plane wave constant pressure shocks replacing the complicated geometry of the usual gap sensitivity test. Other experiments are suggested for studying small scale details of proposed mechanisms of initiation.

Hot spots and the initiation of explosion

Thermally dissipated energy from periodic mechanical action can lead to the creation of areas of intense, localized heating in heterogeneous composite materials, called hot spots. Measurements of hot spots have been performed in shock, impact, and friction studies of energetic materials, amongst others. In this work, high-frequency contact loading allows for the controlled development of hot spots near explosive crystals embedded in polymer with temperature gradients suitable for shadowgraph visualization. Heat dissipation initiated the delamination of crystal-binder interfaces, which led to increased heating from interfacial motion and further delamination propagation. A variety of explosives were considered. Low melting point explosives were driven to reaction despite a hypothesized reduction in interfacial friction upon melting, and crystals with controlled surface morphology still experienced damage. Shadowgraphy allows nonintrusive access to internally developing hot spots which, in turn, enables the identification of heat generation mechanisms to inform our understanding of explosive initiation.