Experimental Investigation of the Decomposition Preceding Cookoff in a Composite Propellant

The decomposition preceding autoignition of an ammonium-perchlorate-based composite propellant was experimentally investigated. Autoignition temperature is measured for a selected heating rate. At that same heating rate, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and hot-stage microscopy are employed to study the propellant behavior leading to reaction. These experiments are conducted on both cured composite propellant and individual ingredients, including neat ammonium perchlorate and a cured binder. For a heating rate of , it is determined using thermogravimetric analysis/Fourier transform infrared that ammonium perchlorate and the binder begin to react together near 150°C, whereas differential scanning calorimetry shows initial exothermic behavior after the orthorhombic-to-cubic phase transition near 240°C. This disparity is discussed and further investigated using larger-scale cubes of propellant heated in ovens at the same heating rate of . It is found that the larger-scale testing is consistent with the findings of the thermogravimetric analysis/Fourier transform infrared. Changes in the gas phase composition are observed when ammonium perchlorate, the binder, and propellant are slowly heated. Implications of these experimental observations are discussed.