Study On The Performance And Interaction Between Components Of MTNP Composite Systems

The traditional TNT-based melt-cast explosive has the disadvantages of poor mechanical properties and unsatisfactory detonation performance,which can’t meet the current development requirements of high-energy insensitive ammunition.As an energetic nitrogen heterocyclic compound,MTNP has good thermodynamic stability and detonation performance.In addition,its melting point is 91.5℃,which is considered as a good candidate to replace TNT as a carrier of melt-cast explosives.However,the research and development of MTNP-based melt-cast explosives will inevitably involve the problem of multi-component formulations,and the complexity of component types and properties will inevitably affect its safety and reliability.Studying the intermolecular interaction of explosives is one of the important means to solve the physical and chemical problems among the components of explosives.Through quantitative calculation and molecular dynamics simulation,the interaction mechanism between MTNP and metal Al,high-energy component explosives（HMX and CL-20）and various properties of MTNP/HMX and MTNP/CL-20 composite system are studied in this paper,which provides ideas and theoretical basis for the application of MTNP in melt-cast explosives.The main research contents are as follows:（1）The adsorption and dissociation mechanism of MTNP on Al（111）surface was studied by using the first principal calculation based on density functional theory and generalized gradient approximation.By considering the adsorption sites on Al（111）surface and the molecular orientation of MTNP,17 initial configurations were constructed.After geometric optimization of these configurations,the adsorption energy,electron density difference,charge transfer and density of states were calculated and analyzed.Based on these results,we conclude that both dissociative and non-dissociative adsorption of MTNP on Al（111）is possible,which depends on the molecular orientation and the specific surface position involved.In the case of dissociative chemisorption,the adsorption of nitro O atoms in MTNP by Al surface atoms is determined as the main mechanism.The dissociated O atom forms a strong Al-O bond with the Al atom near the dissociation site.In addition,the free radical species obtained after the elimination of the O atom combine with the Al surface by forming the Al-N bonds or Al-O bonds.In addition,the process is accompanied by the transfer of electrons from Al surface to MTNP molecule.When the methyl group in MTNP is vertically above the Al plane,due to the mutual repulsion between methyl group and Al,MTNP undergoes physical adsorption.Therefore,the contact between MTNP and Al will lead to rapid oxidation reaction and form alumina coating on Al surface.When the thickness of oxide coating is large,its existence will seriously reduce the potential advantages of using Al particles.（2）The interaction between MTNP and two kinds of high-energy explosives（HMX and CL-20）was studied by using dispersion correction density functional theory.At the theoretical level of M062X-D3/def2-TZVP//B3LYP-D3/6-311+G（d,p）,the structural optimization and interaction energy calculation of MTNP/HMX and MTNP/CL-20 system were carried out.The type,strength,nature,and main contribution of the interaction in the system are analyzed in detail through the atomic theory in molecules,IGMH method,Symmetry-Adapted Perturbation theory and electrostatic potential.The results show that there are C-H···O type hydrogen bonds and C···O,O···O,N···O type van der Waals interaction,and reveals that the main contribution of the interaction comes from electrostatic and dispersion.Although the contribution of induced interaction is not as prominent as the former two,it can’t be ignored.The comparison of interaction energy shows that MTNP/HMX system has higher stability.In addition,the sensitivity change of high-energy component explosives is predicted by calculating the charge of its nitro before and after the formation of complex with MTNP.The results show that the sensitivity of high-energy component explosives decreases after the formation of complex.（3）The interface models of MTNP/HMX and MTNP/CL-20 mixed system with different mass ratios were constructed.The binding energy,radial distribution function,mechanical properties and detonation properties of the system were calculated by molecular dynamics simulation.The calculation results of binding energy show that the binding energy of MTNP/HMX is greater when the mass ratio is 45:50,MTNP/CL-20 is greater when the mass ratio is 40:60 and 50:50,and the system is more stable currently.The radial distribution function analysis shows that the interface between MTNP/HMX and MTNP/CL-20 system mainly forms hydrogen bonds through the H atom in MTNP and the O atom of nitro group in high-energy explosives,which is beneficial to the stability of the mixed system.MTNP/HMX（45:50）and MTNP/CL-20（50:50）mixed systems have smaller K,G,E and largerμ,C₁₂-C₄₄,K/G,currently,the system has less rigidity,enhanced flexibility,and better mechanical properties.The detonation performance calculated by Explo5 shows that the detonation performance of the composite system is lower than that of the pure high-energy components,but it is always better than MTNP.