High-Temperature Oxidation of SSIC in Plasma Flows

Kurzfassung

Within the scope of this work high-temperature oxidation of SSIC was investigated in plasma wind tunnels at the Institute of Space Systems, University of Stuttgart. The tests were performed in both arc heated nitrogen/oxygen plasma flows and inductively heated oxygen plasma flows. In oxygen plasmas, passive-active transitions were determined for temperatures between 1801°C and 1869°C and for oxygen partial pressures between 812 and 3132 Pa. The tests were performed in supersonic and subsonic flows at velocities ranging from 390 to 6000 m/s. Passive-active transitions in nitrogen/oxygen started at temperatures from 1417°C up to 1839°C and oxygen partial pressures between 4 and 160 Pa. Active-passive transitions were determined for surface temperatures between 1831°C and 2145°C at oxygen partial pressures from 28 up to 2290 Pa. The pressures were estimated using mass spectrometer and Pitot probe measurements. The flow velocity was between 1570 and 6500 m/s. Analytical observations show, that reactions at the interface SiC-C-SiO₂ are responsible for the degradation of the silicon dioxide layer. The temperature jump during transition from passive to active oxidation in oxygen plasmas is attributed to the reaction of gaseous silicon and atomic oxygen, while the recombination of atomic nitrogen is mainly responsible for this phenomenon in nitrogen/oxygen plasma flows.