The reaction mechanisms of metal hydrides in the combustion of solid propellants are closely related to their effects on the energetic and combustion properties of propellants. Here, we report a first attempt to investigate the reaction mechanisms of ZrH 2 , a promising candidate for fuels, in the combustion of HTPB propellants using ammonium perchlorate (NH 4 ClO 4 , AP) as the oxidizer . ZrH 2 is determined to possess a good resistance to the direct oxidation by AP. Thus, it would dehydrogenate independently to generate H 2 and metallic Zr , which is believed to be very favorable for decreasing the gaseous molecular masses . On the other hand, due to the attachment of gaseous reactants to it, ZrH 2 was found to tune the decomposition behaviors of AP by enhancing the generation of NO in the high-temperature decomposition stage. More interestingly, the hydrogen released from ZrH 2 is evaluated to promote the combustion reactions in gaseous phases and be responsible for the two-stage combustion behaviors of the corresponding propellant, which are distinct from those when metallic Al is used as the fuel. The findings in this work validate the potential of ZrH 2 as a fuel for high-energy solid propellants.
The conventional carbothermal reduction method for preparing titanium carbide (TiC) from titanium dioxide (TiO 2 ) suffers from high reaction temperature and long processing time, necessitating development of novel reduction processes to reduce energy consumption and improve efficiency. This study utilizing a composite reducing agent of C+H 2 for reducing TiO 2 enables the efficient synthesis of titanium carbide, combining the advantages of both carbon and hydrogen. Herein, we systematically compare titanium carbide synthesis in TiO 2 -C and TiO 2 -C-H₂ systems to elucidate the mechanism of hydrogen enhancement. Thermodynamic calculations compare the preparation processes of titanium carbide in two different systems and reveal the dual role of hydrogen: participation in the reduction reaction and lowering of the oxygen potential. Experimental results demonstrate that the introduction of hydrogen not only significantly increases the carburizing rate from 36.09% to 92.46%, promoting the formation of TiC x O 1-x as the dominant phase, but also doubles the CO content in the exhaust gas compared to the hydrogen-free system. Integrated theoretical-experimental analysis reveals the triple role of hydrogen in accelerating the TiO 2 →TiC x O 1-x transformation through: (1) synergistic reduction with both C and CO, (2) effective lowering oxygen potential of the system, which enhances the thermodynamic driving force to accelerate both the TiO 2 →Ti 2 O 3 reduction and subsequent carbide formation, and (3) increased pore volume generation within the titanium oxide matrix due to the superior diffusivity and reducing capability of hydrogen, thereby facilitating enhanced gas diffusion pathways. This study provides fundamental mechanistic insights into the hydrogen-enhanced carbothermal reduction process for efficient TiC synthesis from TiO₂.
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