Using Simultaneous Time-Resolved SHG and XRD Diagnostics to Examine Phase Transitions of HMX and TATB

Abstract

Simultaneous SHG (second harmonic generation) and XRD (x‐ray diffraction) diagnostics have been applied to examine the phase behavior of energetic materials, HMX (octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine) and TATB (1,3,5‐triamino‐2,4,6 trinitrobenzene). This unique capability provides information about both volume and surface effects that occur during the solid‐solid transformation process. This paper reports XRD results for HMX and TATB at elevated temperatures and on simultaneous SHG and XRD experiments on HMX at fixed temperature. Our results do not indicate that a solid‐solid phase transformation occurs for TATB even at temperatures up to 340°C. XRD results on HMX held at 165°C and 1 bar, indicate that the β to δ transformation is incomplete after a period of 4.5 hours which do not temporally correlate with SHG. Overall information indicates that the observed SHG intensities from surface effects can, in some cases, dominate over volume generated SHG contributions. Finally, we have run in situ AFM scans of HMX at 180°C and 184°C that show HMX surface area increases by many orders of magnitude after the δ‐phase transformation is completed.