Estudo teórico das propriedades termodinâmicas e cinéticas nas reações de combustão do diborano como combustível de foguete

Abstract

A study was carried out on the thermodynamic and kinetic properties of the combustion reactions of diborane as rocket fuel. To this end, it aims to understand the characteristics and thermodynamic and kinetic properties of the thermal decomposition of high energy materials in order to develop a mechanism of chemical combustion reactions. From the methodological point of view, the geometrization of the molecules was modeled using the Gaussian9 software, considering the bonds of each molecule of interest B-B, B-H, B-О, О-О, Н-H, O-H, mentioned in the isodesmic reactions. It is evident that the optimizations of the equilibrium molecules in the ground state were performed using the functional B3LYP model of DFT for the geometries of the molecules. It is stated that the calculations of the reactions were computed at different temperatures of 100K, 298K, 500K, and 1000K, thus it was possible to extract from the Gaussian output file, the thermodynamic properties such as enthalpy variation, Gibbs free energy, and equilibrium constant. The equilibrium constants Keq were computed from the thermodynamic properties of the reactants and products as a function of temperature, and the enthalpy variation (AH) was calculated based on the difference between the enthalpies of the products and reactants. It reinforces that in the Density Functional Theory (B3LYP) the base set cc-pVTZ (Triple Zeta) was used to determine the enthalpy of formation of neutral and critical species in thermal decomposition. The presentation of the computational data of the molecular geometries was presented in the form of tables and graphs. It was concluded that the isodesmic reaction technique is very successful in determining the types of combustion reactions, and helped us to clarify which of the reactions are involved in the absorption of the heat produced during the process. It was observed that reactions I, II and III are reactions with a high value of the Gibbs energy variation (negative) and that release a high value of energy to the medium