First-principles investigation of decomposition and adsorption properties of RDX on the surface of MgH2

- Microreaction mechanism of RDX molecule on MgH2 (1 1 0) surface is investigated.
- Chemical adsorption with high heat release occurs between RDX and MgH2 (1 1 0).
- RDX in the vertical configuration is more prone to decomposition on MgH2 (1 1 0).

Surface adsorption and decomposition mechanisms of cyclotrimethylenetrinitramine (RDX) molecules on the MgH2 (1 1 0) crystal face are investigated in this paper by employing the First-Principles. With the N-NO2 bond of RDX molecules as a reference, 12 adsorption sites are considered that are vertical (V1-V6) and parallel (P1-P6) to the MgH2 (1 1 0) surface. Results show that these 12 types of adsorption of RDX molecules on the MgH2 (1 1 0) crystal face are all chemical adsorption with high heat release, where the vertical Mg-top position (V1) is the most stable adsorption configuration. In all the 12 types of chemical adsorption, RDX molecules are decomposed, through 4 mechanisms including bis-nitro mono-N-O bond rupture, mono-nitro mono-N-O bond rupture, mono-nitro bis-N-O bond rupture and mono-N-O2 bond rupture, where the V-type adsorption is due to N-O bond rupture and the P-type adsorption is due to N-NO2 bond rupture, resulting in RDX decomposition. Secondly, in proximity to the Fermi level, the density of states of the RDX molecule highly coincides with that of the MgH2 (1 1 0) crystal face, which is prone to cause orbital hybridization and RDX decomposition. Also, the density of states in proximity to the Fermi level is mainly contributed by nitro O atoms and ring N atoms of RDX, as well as Mg atoms of the MgH2 (1 1 0) crystal face, and these 3 types of atoms are also active centers for chemical adsorption and decomposition reaction. Finally, an obvious phenomenon of charge transfer is present between Mg atoms in the first layer of the MgH2 (1 1 0) crystal face and O atoms in the nitro group of RDX. Also, the charge change in O and Mg atoms in the V configuration is greater than that in the P configuration, indicating that the V configuration has stronger interaction between RDX and the MgH2 (1 1 0) crystal face, and thus RDX in the V configuration is more prone to decomposition and the V configuration represents a better adsorption mode.