A ceramic-carbon hybrid as a high-temperature structural monolith and reinforcing filler and binder for carbon/carbon composites

A new ceramic-carbon nanostructured hybrid (86 vol.% ceramics, 14 vol.% carbon) formed from organoclay during pyrolysis is reported. It functions as a reinforcing filler and a binder for carbon/carbon (C/C) composites. Alone, it can also serve as a high-temperature structural monolith. During pyrolysis, the ordered montmorillonite clay (d₀₀₁ 31.5 Å) is transformed to mullite, cristobalite and disordered clay, allowing the clay part of the organoclay to serve as both binder and reinforcement. The organic part serves as a binder. Thus, a unidirectional C/C composite (50 vol.% fibers, 33 vol.% carbon matrix, 5 vol.% hybrid and 12% porosity) exhibiting flexural strength 290 MPa, modulus 55 GPa and toughness 2.9 MPa is obtained by 1000 °C 21-MPa hot-press pyrolysis in the presence of mesophase pitch powder, which serves as an additional binder, without densification after the pyrolysis. With the hybrid incorporation, the fiber content decreases from 53 to 50 vol.%, but the flexural strength and modulus are increased by 46% and 14% respectively, relative to the composite without the hybrid but with densification. Hot pressing the organoclay alone forms a black monolithic sheet with high thermal stability, electrical resistivity 6 × 10⁶ Ω cm, flexural strength 180 MPa, modulus 69 GPa, but low ductility.