Effective Performance Modifications for a Composite Rocket Propellant via Coagglomerates of Cyclic Nitramines

The new combustion modifier cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-<i>d</i>]-imidazole (BCHMX) was tested on an aluminum HMX/HTPB/AP propellant. Monitored were the changes in the propellant characteristics, when the 10, 20, and 30 wt % ammonium perchlorate (AP) were substituted by pure 1,3,5,7-tetranitro-1,3,5.7-tetrazocane (HMX), mechanical mixture HMX/BCHMX (PM), and coagglomerate of HMX/BCHMX (CACs), the latter two in a weight ratio of 8:1. By means of the powder X-ray diffraction and FTIR and Raman spectroscopies, it was confirmed that CACs are a mixture of cocrystal β-HMX/BCHMX with excess β-HMX. The relationships were discovered between the burning rate of the prepared samples and the heat of combustion (<i>Q</i> _c), ignition temperature, specific rate constant of thermal decomposition, impact sensitivity, hardness, and specific impulse. Correspondingly, relationships between <i>Q</i> _c and ignition temperature, as well as the impact and friction sensitivities, were investigated. It was found that increasing the amount of CACs in the propellant reduces the pressure exponent, while pure HMX and PM have the opposite effect. The significantly positive effect of CACs on the burning rate, especially at 20 wt % substitution of AP by these microcrystals, is another noteworthy finding.