Analysis of catalytic properties of siliconized heat-shielding coatings

The catalytic properties of heat-shielding coatings ($\beta$-cristobalite and $\mathrm{SiC}$) used on space vehicles are analyzed on the basis of the microscopic approach with consideration of the molecular structure of the near-surface layer. The heterogeneous recombination coefficient of oxygen atoms and the recombination energy accommodation coefficient are determined. The energy distribution by internal degrees of freedom is calculated. In particular, it is found that, when the energy of collision of atoms with the surface is small, the oxygen atom heterogeneous recombination is more efficient for $\mathrm{SiC}$ coatings, whereas this recombination is more efficient in the case of $\beta$-cristobalite if the collision energy is large. Nevertheless, the heat-transfer coefficient is greater for $\mathrm{SiC}$ coatings in the studied range of collision energy variations, since the recombination energy accommodation is larger.