Towards Direct Synthesis of Alane: A Predicted Defect-Mediated Pathway Confirmed Experimentally

The rapid H2 release from AlH3 dehydrogenation forming porous layer in AlH3/hydroxyl-terminated polybutadiene (HTPB) fuels during combustion

Although the motivation of AlH₃ enhancing combustion were recognized in many research, the promotion mechanism have been rarely explored. Herein, a previously unreported porous layer mechanism when combustion were determined in HTPB/AlH₃ fuels by SEM, thermo-analysis and a new simplified calculation method, owing to rapidly released gas phase H₂ from AlH₃ dehydrogenation exposing in melting layer. 5/10% 40-80 μm and 10% 80-200 μm AlH₃-HTPB formulas show the regression rate increase by, 25.7%, 29.0% and 43.0% at Gox = 350 kg/m²·s, while by 57.2%, 42.0% and 44.2% enhancement at Gox = 150 kg/m²·s. The low AlH₃ content (≤ 10%) promotes the regression rate obviously, while excess AlH₃ content (≥ 20%) promotes slightly as a result of comprehensive factors combined by energy release, a certain porous layer mechanism, aggregated Al₂O₃ attached on the burning surface and the blocking effect of the gaseous released H₂. A new model predicting the overlapping process of AlH₃ dehydrogenation and Al oxidation in air atmosphere was developed by superimposing AlH₃ dehydrogenation simulation and corresponding separated Al oxidation simulation. A 1.5th Avrami-Erofeev (A-E) simulation was proposed for Al passivation weight gain between 420 and 520 K with an activation energy of 124.92 kJ/mol and the pre-exponential of 10^12.35.