Application of small-angle neutron scattering to the study of porosity in energetic materials

Small-angle neutron scattering (SANS) and the method of contrast variation were used to measure porosity and crystallite surface area in the energetic system octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and to gauge the effects of mechanical deformation on the pore-size distribution and cr ystallite surface area. The crystallite surface area and the presence of vo ids (pores) in a high explosive system are known to affect its behavior and overall performance. Measures of these two quantities after an insult, res ulting from various process and accident scenarios, can be used to predict the performance of an explosive system after process- and accident-related mechanical deformation. The contrast variation technique allows us to discr iminate between internal pores and features that are on or contiguous with the crystallite surface. Measurements were conducted on loose powders of HM X (261 and 10 mu m, volume averaged mean particle diameters) and pellets ma de by uniaxial consolidation to 7 and 10 vol% porosity, respectively. Analy sis of the SANS data indicates significant alteration of the intragranular pore structure and systematic shifts in the surface area that are dependent upon mechanical deformation.