Thermal reaction and combustion mechanism of AlH3 with different particle sizes

In recent years, aluminum hydride (AlH3) has been extensively researched as a new metal fuel for solid propellants. Using thermogravimetric analysis, differential scanning calorimetry, and a laser ignition test system, the present study investigates the dehydrogenation and oxidation characteristics of AlH3 with different particle sizes under low (thermogravimetric) and high (laser heating) heating rates. The reaction residues were then analyzed using scanning electron microscopy. The thermogravimetric results show that AlH3 forms a porous structure on the surface during the dehydrogenation process, while also forming flaky aluminum. Defects on the sample surface decrease the onset and peak dehydrogenation temperatures while increasing the final dehydrogenation amount. Under air, the reaction exhibits one weight-loss and two weight-gain stages. The samples with different particle sizes show similar degrees of oxidation at 1000 °C but different amounts and rates of the reaction during the three weight-change stages. A diffusive oxidation reaction is inferred. The laser ignition results show that under argon, hydrogen released from the sample carries the particles above the platform, forming a mushroom-shaped particle stream. Under air, hydrogen is released and burns before the AlH3 particles ignite. Particles above the hydrogen flame then begin to burn. A two-flame phenomenon was observed during the flame development stage. Microscopic images reveal high dispersion and low agglomeration of the AlH3 particles during combustion. The combusting particles exhibit gas jetting and explosion phenomena. Both gas- and liquid-phase combustion is observed. Surface defects contribute little to the reaction under laser heating, and the combustion performance improves with decreasing particle size. The combustion residue includes spherical, lamellar, and polyhedral solid forms.