ORIGINAL IN-SITU METHOD TO QUANTIFY THE SIC ACTIVE CORROSION RATE AND ACTIVE/PASSIVE TRANSITION IN Ar/O_2 AND Ar/H_2O GAS MIXTURES AT VERY HIGH TEMPERATURES

摘要

Oxidation behavior of silicon carbide under Ar/O_2 and Ar/H_2O gas mixtures was investigated at very high temperatures (>1700°C) in order to further understand both active oxidation kinetics as well as transition between active and passive oxidation modes. Experiments were conducted by Joule heating TEXTRON SCS-6 fiber samples inside an airtight vessel under different Ar/O_2 or Ar/H_2O environments. Temperature was regulated by means of a computer-assisted control loop consisting of a two-color pyrometer and a power supply delivering electrical current through the sample. Recordings of the variation of the electrical data relative to Joule heating were used to deduce in-situ information on the samples. All experimental results were compared to theoretical results obtained with a 3D finite volume simulation of transport phenomena inside the vessel. Active oxidation rates were found to increase linearly with P_(O2), and to be independent of gas flow rate and of temperature up to 2100°C. Experimental results were in good agreement with simulation results and suggested that oxidation kinetics are limited by species transport through a free convection boundary layer. Active/passive transition results show good agreement with results from the literature obtained at lower temperature.