Ignition and combustion of AlH3-nanoparticles: A molecular dynamics study

Abstract

AlH3 has tremendous potential for hydrogen energy storage and energetic applications. The structure and thermodynamic properties of core-shell AHNP with different oxidation degrees from ignition to combustion are studied using ReaxFF molecular dynamics simulations. Two models covered by different alumina shells are built. Results indicate that the thinner shell is ready to form an Al-rich environment, which is crucial for accelerating ignition and subsequent combustion processes. In ignition period, the influence of shell is investigated by comparing surface oxygen adsorption rates, oxidation degree of Al and H atoms, and stress evolution of AHNP. AHNP with thinner shell exhibits a higher O adsorption rate to form an O-rich environment, which accelerates the oxidation process of Al atoms. A thicker shell significantly inhibits the thermal diffusion of core Al and H atoms, while H atoms are still able to penetrate it with a low diffusion rate. Stress analysis shows the thickness of the shell directly affect the thermal diffusion rate of Al atoms. The combustion of AHNP can be divided into three stages: rapid, slow, and self-sustaining combustion. The combustion process is controlled by the particle and external O atoms diffusion behaviors. A detailed structural evolution process during AHNP combustion has also been clarified through the displacement analysis. The findings provide a theoretical foundation for the diffusion-dominated combustion mechanism of AHNP from an atomic view. Novelty and Significance StatementAlH3 has tremendous potential for hydrogen energy storage and energetic applications. At present, the combustion mechanism of AlH3-nanoparticles (AHNP) is still not well understood, and the atomic-scale evolution process and reaction mechanism are also poorly studied, which is difficult to obtain in experiments. In this study, the ignition and combustion mechanisms of AHNP is revealed based on the ReaxFF molecular dynamics simulations, and the influence of oxidation degree on the ignition and combustion of AHNP is also clarified, which can provide theoretical guidance for the application of AHNP as a clean fuel and preparing for the combustion research of AHNP coated with different materials.