First report of fumed alumina incorporation in carbon–carbon composite and the consequent improvement of the oxidation resistance and mechanical properties

Abstract The first report of fumed alumina incorporation in carbon–carbon (C/C) composite is provided. Fumed alumina (0.5 vol.% solid alumina in the C/C, 15-nm average pore size, 100–200-nm squishable/conformable aggregates of nanoparticles) as a filler in unidirectional C/C (44 vol.% fibers, fabricated by 1000 °C 21-MPa hot-press mesophase-pitch carbonization) is as effective as one-cycle densification for decreasing the porosity (from 16% to 14%) and increasing the flexural modulus (from 52 to 68 GPa) and longitudinal hardness (from 2.7 to 5.5 GPa), and more effective than one-cycle densification for improving the flexural strength (to 330 vs. 280 MPa), longitudinal compressive modulus (to 38 vs. 30 GPa) and oxidation resistance. The positive mechanical/thermal effects of fumed alumina incorporation suggest pore structure refinement, due to the nanostructure and conformability of fumed alumina. Thus, a quality C/C is obtained at a low density (1.54 g/cm 3 ). Fumed alumina is more effective than organobentonite (3.3. vol.%, previously shown to serve unusually as both filler and binder) for improving the oxidation resistance and as effective as organobentonite for increasing the flexural strength/modulus, in spite of the higher porosity of its C/C (14% versus 12%). However, fumed alumina is inferior to organobentonite for increasing the toughness or longitudinal compressive modulus.