Reinforced combustion of the ZrH2-HMX-CMDB propellant: the critical role of hydrogen

Metal hydrides, which are capable of producing H-2 and release much energy efficiently via combustion, are regarded as promising high-energy fuels for future advanced solid propellants. Here, we report our first attempt on the application of a high-density hydride ZrH2 in CMDB propellants containing the high-energy explosive HMX and the revelation of the combustion mechanism of ZrH2 in HMX-CMDB propellants. ZrH2 was found to be capable of enhancing the combustion of HMX-CMDB propellants effectively. Especially, hydrogen in ZrH2 was determined to play a critical role during both its intrinsic combustion and the combustion in propellants. Upon ignition, ZrH2 dehydrogenates to produce Zr and H-2, followed by combustion of the decomposition products. Interestingly, H-2 release results in particle fragmentation either, promoting the combustion of hydride. As for the combustion of propellant with ZrH2, in the condensed phases, the H delta+-H delta- interaction promotes the thermal decomposition of HMX, leading to enhanced reaction rates. The ZrH2 combustion in propellant also starts with the hydrogen-release process, followed by melting and combusting of the newly generated metallic Zr on the burning surface. Thus, the heat feedback is greatly reinforced and the reactions in the condensed phases are further speeded up. The other dehydrogenation product, H-2, participates in the gaseous combustion reactions. The insights into the effects of metal hydrides on propellant combustion are believed to be of great importance for developing novel hydride fuels for solid propellants.