Barriers of Oxidation ans Ageing of Space Shuttle Material
During the atmospheric re-entry phase, the thermal protection of a spacecraft vehicle is submitted to air plasma. The transfer of the kinetic energy of the gases to the surface leads to an important heating of the nose cap and leading edges. The energy released from the recombination of oxygen atoms on the surface produces an additional amount of heat, increasing further the temperature. This excess of heat can damage the protection materials. This last mechanism leads to the oxidation of the surface and an accelerated ageing of the material. The oxidation produces a new surface layer of oxide such as SiO2 (Passive oxidation) and leads to the ablation of the material by the formation of CO, CO2, SiO and to the diffusion of oxygen in the bulk creating micro-cracks in the material (Active oxidation). Thus the composition of the surface and consequently the protection material properties are modified. The atmospheric re-entry conditions are created with a non equilibrium low pressure RF plasma chemical reactor. The ageing of the material and the diffusion of oxygen are studied by mass spectrometry analysis of 18O isotope for temperatures ranging from 300 – 1000 K. Silicon Carbide targets are covered with two different coatings, Chromium oxide, and Chromium oxide/ Silica. Oxygen diffusion in the material bulk for the targets was followed by Secondary Ion Mass Spectroscopy (SIMS).Mass Spectrometry shows the formation of CO and CO2 pointing out the process of ablation. This ablation is much lower in the case of polluted sample (with Chromium oxide). SIMS analyses show that Cr2O3 acts like a barrier in the oxidation of the material by limiting the diffusion of oxygen in the bulk.
T. Chandra, N. Wanderka, W. Reimers , M. Ionescu
G. Da Rold et al., "Barriers of Oxidation ans Ageing of Space Shuttle Material", Advanced Materials Research, Vols. 89-91, pp. 136-141, 2010