Thermal conductivity of CVD diamond fibres and diamond fibre-reinforced epoxy composites

Diamond fibres were fabricated using hot filament chemical vapour deposition (CVD) with tungsten wire of varying diameters as the cores. A steady-state technique was used to measure the thermal conductivity along the length of the individual fibres over a distance of 6 cm. The room temperature thermal conductivity of the fibres ranged between 750 and 1088 W m−1 K−1. This is lower than values measured for CVD diamond thin films by other groups, due to the fact that the measurements were made perpendicular to the growth direction, and hence involved traversing a large number of grain boundaries. Epoxy composites containing the fibres were produced. The thermal conductivity of these composites was compared to metal bars of the same dimensions for both heating and cooling cycles. It was found that diamond composites are more efficient heat conductors than metal rods and can combine good lengthwise heat transfer with low heat transfer to the surroundings, as well as high electrical insulation. This makes them suitable for applications such as 'heat pipes' in electrical circuits.