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A new ceramic–carbon nanostructured hybrid (86vol.% ceramics, 14vol.% 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 (d 001 31.5Å) 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 (50vol.% fibers, 33vol.% carbon matrix, 5vol.% hybrid and 12% porosity) exhibiting flexural strength 290MPa, modulus 55GPa and toughness 2.9MPa 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 50vol.%, 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 Ωcm, flexural strength 180MPa, modulus 69GPa, but low ductility. [ABSTRACT FROM AUTHOR]

Abstract: Since copper does not wet graphite foams (GFs), a method for the synthesis of Mo2C coatings throughout the GFs was developed for improving the wetting between GFs and copper and for the preparation of GF/copper composites. The coatings were formed on the GFs in a reaction medium consisting of ammonium paramolybdate, which decomposed to fine MoO3, in a mixture of molten NaCl–KCl salts. The formation mechanism and microstructure of the Mo2C coatings on GFs were investigated. Then the microstructure, thermal conductivity and thermal expansion behavior of the obtained GF/copper composites were studied. Results indicated the formation of Mo2C coatings occurred in two steps, namely, the reduction of MoO3 to MoO2 and the reduction of MoO2 to Mo2C. Copper was infiltrated into the Mo2C-coated GFs without external pressure and the nearly pore-free GF/copper composites were obtained. The thermal conductivity of the composite with a density of 5.76g/cm3 reached 268.4W/mK. Significant reduction in coefficient of thermal expansion of the composite compared with that of copper (8.91 versus 18.59ppm/K) was obtained. [Copyright &y& Elsevier]

Abstract: Mesophase pitch based graphite foams with different thermal properties and cell structures were infiltrated with glass by pressureless infiltration to prepare potential alternative composites for cooling electronics. Microstructure, thermal diffusivity and coefficient of thermal expansion (CTE) of the obtained composites were investigated. It was demonstrated that there was excellent wettability of the graphite foam by molten glass, and the foam framework was retained well after infiltration, which could facilitate good heat transfer throughout the composites. The highest thermal diffusivity of the composites reached 202.80mm2/s with a density of 3.81g/cm3. And its CTE value was 4.53ppm/K, much lower than the corresponding calculated result (7.46ppm/K) based on a simple “rule of mixtures” without considering the space limitations of the graphite foams. Thus, the mechanical interlocking within the space limitations of the graphite network played a crucial role in limiting the thermal expansion of the glass. The CTEs of the graphite foam/glass composites varied from 4.53 to 7.40ppm/K depending on the graphite foam density which varied from 0.82 to 0.48g/cm3. The CTEs were a good match to those of semiconductor chips and packaging materials. [ABSTRACT FROM AUTHOR]