On the Relationship between Shock and Thermal Initiating Conditions for Various Reactive Powder Mixtures

The critical conditions for initiation of reaction by shock loading in various compositions that produce little or no gas upon reaction were investigated. Shock recovery experiments using Mn+S were first carried out in two different apparatus geometries and for two different initial sample densities. In one geometry, the sample was subjected to a planar shock followed by interactions with the confining walls. In the other geometry, a curved shock free of wall interactions was delivered to the sample. The low-density (55?% TMD) Mn+S was found to be significantly more sensitive to the curved shock than to the planar shock with wall interactions. For high-density (90?% TMD) Mn+S samples however, shock sensitivity was the same in both apparatuses. Next, the reaction onset temperature and the critical initiating shock pressure were determined for a number of powder mixtures using DTA and shock recovery (in the geometry producing planar shocks with interactions with the confinement walls), respectively. For the majority of the mixtures tested, the minimum shock energy required to cause the entire sample mixture to react was found to be much less than the enthalpy of the sample at its reaction onset temperature, with no significant correlation between these two parameters. The process of arrested ball-milling, which results in a reduction of the reaction onset temperature of a mixture, may lead to an increase in shock sensitivity. Additionally, thermal sensitivity in the particular mixtures considered was not increased when they were first shock-compacted by sub-critical shocks.