Surface temperature jump beyond active oxidation of carbon/silicon carbide composites in extreme aerothermal conditions

The behavior of carbon/silicon carbide composites at very high temperatures is investigated in an inductively-coupled plasma generator that simulates atmospheric re-entry aerothermal conditions for space vehicles. Samples exposed to heat fluxes exceeding 1.2 MW/m2 and low pressures of 2000-6000 Pa show a spontaneous jump in surface temperature near 2100 K, rapidly leading to temperatures above 2400 K. Under these conditions the silicon carbide coating at the samples' surface is entirely eroded and the bare carbon fibers of the substrate are left exposed to the incoming flow. The material loses nearly half of its mass and is no longer reusable. The temperature jump phenomenon is described by means of infrared temperature measurements and real time visible recordings of the surface. Space- and time-resolved optical emission spectroscopy and scanning electron microscopy analysis of the samples are used to discuss and explain the chemical processes occurring at the surface. Jump conditions are compared to the passive and active oxidation regimes for carbon/silicon carbides, showing that such a sudden temperature increase occurs at conditions beyond active oxidation and cannot be attributed to the passive/active transition itself.

Publication year:2014

Keywords:oxidation, ceramic matrix composite, gas-surface interaction