Micro-scale Experimental Investigation of Carbon Oxidation

The morphology characteristics and ablation behavior of a highly porous carbon ber preform will be studied. First, the morphological characterization of the three-dimensional structure of the material will be performed by hard X-rays synchrotron micro-tomography. The resulting micro-tomography voxels will be used to compute geometrical properties of the carbon preform, like porosity, specic surface area and tortuosity, that are otherwise indirectly measured through experimental techniques. The reconstructed volumes are used to build a computational grid for numerical simulations of the bers' ablation. By modeling the diusion of oxygen through the porous medium using Lagrangian methods, and the oxidation at the carbon bers? surface using a reactivity model, the ablation of the carbon bers will be simulated for a range of Thiele numbers. Next, the oxidation at high Knudsen number of FiberForm, the matrix material of NASA's Phenolic Impregnated Carbon Ablator, will also be investigated experimentally at the NASA Flow Tube facility. The mass loss and recession of carbon preform samples will be measured at temperatures between 700 and 1300 K and pressures around 2000 Pa. Using the parametric data obtained by the 3D reconstruction, numerical simulation of that experiment will be performed and compared to the experimental results.