Thermally induced polymorphic transformation of Hexanitrohexaazaisowurtzitane (CL-20)

To investigate the polymorphic transformation and crystal morphology changes of epsilon-CL-20 under different thermal stimuli, isothermal and non-isothermal experiments were conducted using a hot stage microscope and in situ X-ray powder diffraction. It was found that the epsilon-and gamma-phases coexisted at 120 degrees C (9.727 wt% gamma-CL-20), and the epsilon ->gamma phase transformation occurred between 115 and 120 degrees C and reached completion at 130 degrees C. The epsilon-CL-20 expanded isotropically in the temperature range of 25 to 115 degrees C. About a quarter of the epsilon-CL-20 transformed after being heated at 120 degrees C for 12 h, whereas almost all of epsilon-CL-20 transformed after being heated at 150 degrees C for 12 h. Under the microscope, the expansion of crystal volume, changes of crystal morphology, and phenomena of decomposition were observed during heating. Molecular dynamics simulation and Rietveld refine-ment were conducted to verify the experimental results. A solid-solid phase transition mechanism is presented. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

The experimental results show that epsilon-CL-20 undergoes phase transformation at 120 degrees Celsius and complete transformation at 150 degrees Celsius. Additionally, changes in crystal morphology and decomposition phenomena were observed during the experiments.