The Diffusion of Deterrents into Propellants Observed by FTIR microspectroscopy - Quantification of the diffusion process

The interior ballistic performance of propellants can be significantly improved by the application of deterrents. However the diffusion of the deterrents from the surface into the propellant grains during long‐time storage may significantly reduce the propellants shelf life. The diffusion of different types of deterrents into single‐ and double‐base propellants was investigated by Fourier Transform Infrared (FTIR) Microspectroscopy. The observed diffusion phenomena were explained sufficiently well by the 2nd Fickian diffusion equation. The determined diffusion coefficient values ranged between 10−17 m2/s and 10−14 m2/s at 71 °C. Polymeric deterrents were found to diffuse about one order of magnitude slower than deterrents of small molecular weight in the same propellant matrix. The diffusion velocities of the deterrents investigated increased by about 2 orders of magnitude between single and double base propellants. The changes in the interior ballistic behaviour caused by long‐time storage could be correlated with the obtained deterrent diffusion coefficient values. The results of this study are in good agreement with the very few data about the solventless diffusion process of deterrents published before.