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Extended Reaction Network for RDX and HMX

Extended Reaction Network for RDX and HMX. D.Chakraborty, R. P. Muller, S. Dasgupta, J. Sheppard and W. A. Goddard III ASCI-ASAP Review Oct-5,6-99. Starting Points. GRI nitromethane mechanism

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Extended Reaction Network for RDX and HMX

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  1. Extended Reaction Network for RDX and HMX D.Chakraborty, R. P. Muller, S. Dasgupta, J. Sheppard and W. A. Goddard III ASCI-ASAP Review Oct-5,6-99

  2. Starting Points GRI nitromethane mechanism right physics for small [C,H,N,O] system, but not include RDX/HMX primary and secondary decomposition reactions 49 species 300 reactions Melius nitromethane mechanism 27 species 130 reactions Yetter RDX mechanism Comb. Sci. Tech., 1997, 124, pp 25-82. 48 species 240 reactions

  3. Extension • New decomposition scheme for RDX, HMX based on ab initio DFT calculation • DFT-B3LYP/6-31G* level of theory • Structure for all reactants, intermediates, transition states and products • Analytical frequency for all species • Incorporation of detailed reaction kinetics for early stage C, H, N, O reactions related to RDX/HMX combustion • CH2N reactions with NOx, N2O, OH etc. • Decomposition of CH2NNO2, CH2NNO etc.

  4. Concerted Ring Opening of RDX DFT-B3LYP(6-31G*) TS1

  5. N-NO2 Homolysis Pathway of RDX DFT-B3LYP(6-31G*) TS2

  6. HONO Elimination Mechanism of RDX DFT-B3LYP(6-31G*) TS10 TS13 3

  7. N-NO2 Homolysis Pathway of HMX DFT-B3LYP(6-31G*) TS1

  8. HONO Elimination Mechanism of HMX DFT-B3LYP(6-31G*)

  9. Overall Scheme • Modified Mechanism • Includes all new reactions related to RDX/HMX decomposition • 85 Species • 461 Reactions • Thermochemical data for all new species • Based on DFT-B3LYP/6-31G* level of calculation • Theoretical rate constants for all new reactions • RRKM/TST calculation of reaction rate constsnts

  10. Some New Species in reaction mechanism RDX RDXR RDXRO triazine Tetrazine HMXR HMXRO HMX N3 CH2N2 HNNO2 CH2NOH CH2NHNO2

  11. Fit Thermochemical Data to NASA Form • B3LPY/6-31G* calculation • Compute Cv, H, S from 300-6000 K • Fit to 14-term NASA form • HMX, HMXR, HMXRO • RDX, RDXR, RDXRO Entropy Temperature Cv Enthalpy

  12. Rate constants Unimolecular decomposition of RDX k1a RDX RDXR + NO2 (1a) k1c TS1 3MN (1b) TS10 k1b INT175 + HONO (1c) Bimolecular rate constant for CH2N + NO2 reaction ln k (s-1) 1000/T (k)

  13. Key Species in HMX Detonation Concentration (M) Time (s)

  14. Validation: Nitromethane Shock Data Induction Time (sec) Bars: Experiment Dots: Theory Temperature (K)

  15. Detailed Modeling of HE Detonation Provide a detailed reaction mechanism: 85 Species 461 Reactions Ultimately reduce (Eckett) Understand detonation on a reaction by reaction basis Understand how additional species (binder, aging, etc.) alters detonation properties. HMX HMXR HMXRO CO

  16. Use More Accurate EOS with Chemkin • Ideal gas law is poor approximation • Underestimates volume • Overestimates reaction rates by factor of ~15 • Constant Volume Mode uses Ideal Gas EOS • Cannot describe high P,T • Chemkin Real Gas Program (Iowa State) • BKW, vdW, Peng-Robinson • BKW EOS:

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