ИСТИНА

Heterogeneous processes play a key role in determining the heat fluxes to the surface of reusable space vehicles during their entry into the atmosphere. Revealing the mechanisms of these processes and determining their main kinetic characteristics are decisive importance for the effective design of modern heat-shielding systems. The relevance of research into the properties of heat-shielding coatings is increasing due to the development of new materials for advanced reusable space vehicles that need effective heat shielding at surface temperatures about 2000 K. A closed kinetic model of the interaction of dissociated air with the surface of heat-shielding material SiO2 (β-cristobalite) has been developed. To describe heterogeneous processes, a cluster approach was used, in which the surface of a material with a crystal structure was modeled by a cluster that conveys the stoichiometry of the crystal and the valence states of the atoms lying on the surface. The potential energy surface was calculated using the electron density functional theory (DFT) method with an extended hybrid functional combined with Lee–Yang–Parr correlation functional (X3LYP) [1]. The correlation-consistent polarized triple-zeta valence basis set cc-pVTZ was used as the basis functions. The rate constants of the elementary stages (adsorption/desorption, associative and impact recombination) are obtained according to the transition state theory adapted to surface reactions [2]. The calculated rate constants of the processes under consideration were approximated in the generalized Arrhenius form in the temperature range 500–2200 K and compared with the phenomenological models available in the literature and numerical calculations by other authors. Some results for oxygen adsorption and impact recombination are demonstrated on the Fig. 1.