A previously unidentified amorphization mechanism of boron carbide yields insights into the failure of superhard materials.

Because of the excellent combination of high detonation and low sensitivity properties of the 1,1-diamino-2,2-dinitroethylene (FOX-7) energetic material (EM), it is useful to explore new energetic derivatives that start with the FOX-7 structure. However, most such derivatives are highly sensitive, making them unsuitable for EM applications. An exception is the new nitroenamine EM, 1,1-diamino-2-tetrazole-2-nitroethene (FOX-7-T) (synthesized by replacing a nitro group with a tetrazole ring), which exhibits good stability. Unfortunately, FOX-7-T shows an unexpected much lower detonation performance than FOX-7, despite its higher nitrogen content. To achieve an atomistic understanding of the insensitivity and detonation performance of FOX-7 and FOX-7-T, we carried out reactive molecular dynamics (RxMD) using the ReaxFF reactive force field and combined quantum mechanics MD (QM-MD). We found that the functional group plays a significant role in the initial decomposition reaction. For FOX-7, the initial decomposition involves only simple hydrogen transfer reactions at high temperature, whereas for FOX-7-T, the initial reaction begins at much lower temperature with a tetrazole ring breaking to form N₂, followed by many subsequent reactions. Our first-principles-based simulations predicted that FOX-7-T has 34% lower CJ pressure, 15% lower detonation velocity, and 45% lower CJ temperature than FOX-7. This is partly because a larger portion of the FOX-7-T mass gets trapped into condensed phase carbon clusters at the CJ point, suppressing generation of gaseous CO₂ and N₂ final products, leading to reduced energy delivery. Our findings suggest that the oxygen balance is an important factor to be considered in the design of the next generation of high-nitrogen-containing EMs.

Clathrate hydrates are ice-like crystalline substances in which small gas molecules are trapped inside the polyhedral cavities of water molecules. They are of great importance in both scientific research and the petroleum industry because of their applications in modern energy and environmental technologies. To achieve an atomistic-level understanding of the diffusion and decomposition of trapped molecules in clathrate hydrate, we used methane hydrates (MHs) as the prototype system and examined the methane diffusion and decomposition mechanism by employing quantum mechanics (QM) and quantum mechanics molecular dynamics (QMD) simulations. Our QMD simulations illustrated that the initial decomposition reaction in MHs initiates from hydrogen transfer among water molecules and attacks by fragments of O and OH on CH₄ molecules are responsible for the destruction of the methane molecules. Next, our QM simulations revealed that the methane molecule prefers to escape from the ice cage through the hexagonal face at low temperature. To suppress the methane diffusion, we demonstrated that the diffusion barrier is significantly enhanced by adding electron or hole carriers. This is because the extra electrons and holes enhance the electrostatic interaction between methane and water molecules, leading to an increased diffusion barrier. Thus, the clathrate hydrates could be stabilized by adding extra free electron or hole carriers.