Understanding how microscopic defects trigger explosive initiation remains a challenge in energetic materials science. Hotspot formation, which results from localized energy concentration under shock loading, is widely recognized as the first step toward ignition and detonation. A recent study in Energetic Materials Frontiers presents a multiscale investigation of vacancy- and void-controlled hotspot formation in RDX, revealing how coupled defect structures regulate chemical activation and thermal localization across multiple length scales.
“Traditional hotspot theories primarily focus on void collapse as the dominant mechanism for energy localization,” explains corresponding author Yi-feng Dong from Institute of Advanced Structure Technology at Beijing Institute of Technology, “However, energetic crystals also contain molecular-scale defects such as vacancies that may significantly influence decomposition chemistry.”
The researchers integrated AIMD and RMD simulations to bridge atomic-scale reaction kinetics with mesoscale shock responses, providing a unified description of defect-mediated hotspot formation.
“The coupled void-vacancy defect structures create a more sensitive local environment for hotspot initiation,” says Dong. “Vacancy-rich regions can accelerate local reaction onset and promote stronger thermochemical activity during shock loading.”
Vacancies Accelerate Early Decomposition
Using AIMD simulations, the researchers then investigated the thermal decomposition behavior of RDX crystals containing molecular vacancies. “We found that vacancies significantly shorten reaction initiation times and reduce decomposition barriers,” shares Dong.
Compared with defect-free crystals, vacancy-containing systems exhibit earlier formation of key intermediates including NO₂ and HNO₂, accelerating the initial decomposition process and enhancing chemical reactivity. Molecular vacancies effectively create energetically favorable sites that facilitate bond rupture and promote reaction propagation.
“These findings indicate that even a small concentration of molecular defects can substantially influence the early-stage chemistry of energetic materials, says Dong.
Coupled Vacancies and Voids Promote Hotspot Formation
To investigate shock-induced hotspot formation, the researchers constructed RDX supercells containing nanoscale voids surrounded by vacancy-rich regions and subjected them to shock loading at different particle velocities.
“At relatively low shock strengths (particle velocities of 2.0–2.5 km·s⁻¹), vacancy-containing systems generated significantly larger hotspot regions than vacancy-free systems, reveals Dong. “Under a particle velocity of 2.5 km·s⁻¹, the hotspot area exceeding 2000 K reached 655.79 nm² in the vacancy-containing crystal, approximately 2.5 times larger than the corresponding vacancy-free system (268.44 nm²).”
Temperature contour maps further revealed that localized high-temperature regions emerge rapidly near collapsing voids when vacancies were present. “These hotspots grow more quickly and reach higher temperatures than those observed in perfect crystals,” adds Dong. “The simulations also show enhanced NO₂ production, indicating stronger chemical activation and heat release.”
The results demonstrated that molecular vacancies amplify energy localization during void collapse, leading to accelerated hotspot growth and increased shock sensitivity.
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Contact the author:
Institute of Advanced Structure Technology, Beijing Institute of Technology, Beijing, 100081, China. E-mail addresses: dongyifeng@bit.edu.cn (Y.-f. Dong), bitliying@bit.edu.cn (Y. Li)
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Energetic Materials Frontiers
Multiscale AIMD-RMD study of vacancy and void-controlled hotspot formation in RDX
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.