Oxidation of ZrB2-SiC Ultrahigh-Temperature Ceramic Composites in Dissociated Air

High-enthalpy test environments, flow modeling and in situ diagnostics for characterizing ultra-high temperature ceramics

“…Such test environments are provided by arc-jet or inductively coupled plasma (ICP) wind tunnels which expose test articles to high-enthalpy reactive gas flows. Tests of UHTC materials in arc-jet facilities have been reported in the scientific literature by Kaufman, 3 Metcalfe et al, 8 Wuchina and Opeka, 9 Opila et al, 10 Gasch et al, 11 Chamberlain et al, 12 Savino et al, 13 Monteverde and Savino, 14 and Zhang et al 15 Tests of UHTC materials in ICP facilities have been reported by Ito et al, 16 Marschall et al, 17 and Playez et al 18 In this paper we discuss the test environments provided by these two types of plasma wind tunnel facilities. We highlight the coupling between the high-enthalpy reactive flow stream and the test specimen in determining UHTC material response to these environments.…”

“…In practice, it is not straightforward to choose the "correct" value of emittance for a UHTC component at high temperature. 17 As an illustrative example of the process described above, we show some results obtained for a recent series of stagnation point oxidation tests performed in the VKI Plasmatron on UHTC specimens of a hot-pressed ZrB 2 material containing 30 volume percent SiC (termed ZrB 2 -30SiC). 17 Tests were performed at static chamber pressures of 10 4 Pa with an air mass flow rate of 16 g s −1 over a range of Plasmatron powers from 150 to 210 kW.…”

“…Both values of emittance are reasonable estimates for oxidized ZrB 2 -SiC composites. 14,17,43 Without an in situ method for determining the high-temperature emittance during testing, such a level of uncertainty (∼15%) in emittance is unavoidable. Note that the hot wall heat fluxes are only about half of the corresponding cold wall heat fluxes, which suggests that the surface catalytic efficiencies of the oxidized UHTC surface must be low.…”

“…17 The CFD codes used for this procedure are the VKI Boundary Layer Code 24,30 and the VKI ICP Code, 31,32 both of which use the PEGASE library to perform thermodynamic and transport property calculations. 33 The ICP code solves the time-averaged magneto-hydrodynamic equation at low Mach and low magnetic Reynolds numbers, assuming axisymmetric flow and local thermodynamic equilibrium, to simulate the flow inside the plasma torch and around the test article in the vacuum chamber.…”

“…2 shows the cold wall heat flux measured by a calibration probe and the steady-state UHTC sample surface temperature measured using a two-color pyrometer during each test run. Both the cold wall heat flux and the 17 The cold wall heat flux is measured by a calibration probe and the sample surface temperature is measured by a two-color pyrometer during each test run. The hot wall heat fluxes are estimated from q hw = εσT 4 s with ε = 0.90 and ε = 0.75, assuming q cond ≈ 0. specimen surface temperature increase with Plasmatron power as expected.…”