Coupling in-situ synchrotron X-ray radiography and FT-IR spectroscopy reveal thermally-induced subsurface microstructure evolution of solid propellants

The evolution information of the condensed phase of solid propellants during combustion is crucial to mastering the behavior of solid propellants and obtaining desired characteristics. However, insight into condensed-phase microstructure and gaseous production evolution and their correlations achieved via in-situ characterization are still lacking due to the phase opacity and violent deformation of the condensed-phase region during operating conditions. Consequently, ex-situ quenched surface study has dominated this field for several decades. Herein, we demonstrate our initial work, where the subsurface condensed-phase evolution characterization is achieved via in-situ synchrotron X-ray radiography and FT-IR spec-troscopy. The obtained images show the evolution of component-specific microstructure due to the con-version of solid ingredients to gas during the thermal decomposition process. Comparatively, in-situ FT-IR spectroscopy tracks the evolved gas products. For the first time, we directly observed different evolved behaviors of the condensed-phase microstructure of two typical solid propellants using inert and en-ergetics binders, respectively, via the in-situ image technique. Such microstructure transformations are further quantitatively evaluated based on a series of imaging processing and subsequently their corre-lations with the chemical structure of different binders are also investigated via analyzing the gaseous product during degradation. Therefore, the combination of the above techniques helped study the con-densed phase of solid propellant, especially for microstructural changes under reaction conditions. We expect this methodology would be beneficial for directly understanding the subsurface microstructure evolution properties linked with related chemical reactions.(c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.