Microstructure and thermophysical properties of graphite foam/glass composites

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 202.80 mm2/s with a density of 3.81 g/cm3. And its CTE value was 4.53 ppm/K, much lower than the corresponding calculated result (7.46 ppm/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 7.40 ppm/K depending on the graphite foam density which varied from 0.82 to 0.48 g/cm3. The CTEs were a good match to those of semiconductor chips and packaging materials.