Methods and means for physico-chemical properties optimization of carbon-carbon composite materials of thermal protection purpose

Аuthors

Zubko A. A.^*, Kozhemyako А. S.^**, Nikitin P. V.^***, Sotnik E. V.^****

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: zbk.anna@mail.ru
**e-mail: sir.kozhemiacko@gmail.com
***e-mail: petrunecha@gmail.com
****e-mail: es2103s@gmail.com

Abstract

The article deals with creation of new heat-resistant and heat-proof carbon-based materials employed in thermal protection systems of high-speed apparatuses. The said properties of materials are being determined by their component composition, physico-chemical characteristics, structure, and stress state under intense thermal and gas dynamic effect. It was found that a simple set of individual components with high temperature resistance and necessary catalytic and radiative properties cannot reproduce these properties in the composition of a composite material. This means that it is necessary to search for their optimal compositions to develop composites with specified properties. For all their advantages, carbon-carbon composite materials (UCM) display two serious drawbacks. Firstly, the material is low-thermo-resistant (carbon is being oxidized at a temperature of T ~ 1000 K). Secondly, the UCM surface displays absolute catalytic activity to heterogeneous exothermic reactions of carbon compounds with oxygen and nitrogen atoms of the incoming flow. To eliminate these serious drawbacks, the authors proposed a technology for protecting the surface with a thin layer of heat-resistant composite ceramic coating. Such layers obtaining technology was developed at the MAI 204 department. Its main feature is being expressed in a scientifically based search for compositional structure. Further, micro- or nano-powders with addition of rare earth metals are produced from the materials of the selected composition. Then a supersonic, low-temperature heterogeneous flow is being generated in a special device, which forms a thin heat-resistant layer on the specially prepared surface of the sample, i.e. a barrier layer for oxygen and nitrogen atoms of the incoming dissociated flow. It was found that with the Si-Ti-Mo composition application as a barrier coating composition, the necessary catalytic activity of the surface is being ensured by the appearance of an amorphous film of oxides on the surface, such as SiO₂, TiO₃ and MoO₃. As additives, such materials should be employed which degree of blackness increases with temperature increase. It was found in the course of the experiment that the most optimal coatings from the viewpoint of heat resistance and catalyticity are Si-Ti-Mo-B-Y-Al and Si-Ti-Mo-B-Y-Hf.

Keywords:

chemically active boundary layer, thermal protection, heat-resistant coatings, carbon-ceramic composite materials, surface catalytic activity, heat-stressed structures, heterogene-ous supersonic flows, surface microhardness

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