Thermal conductivity, specific heat capacity, and emissivity of ceramic matrix composities at high temperatures

Ceramic matrix composites (CMCs) with low porosity are obtained in one cycle via the well established liquid silicon infiltration (LSI) process, which is characterised by short processing times and fairly low manufacturing costs. Apart from aerospace applications, such as hot structures for re-entry vehicles, more and more applications beyond this classic field of CMCs are of increasing interest, eg brake discs, zero-expansion materials, high-temperature heat exchangers, heat-sink materials, etc. By applying special process parameters the microstructure as well as the physical properties can be tailor-designed to match specific requirements. The thermophysical properties of C/C-SiC, especially specific heat capacity, thermal conductivity as well as total and spectral emissivity were investigated in order to find out how the selection of fibres and pretreatment of the material affect them. Thermal conductivity of carbon fibres and therefore also of the composite considerably increases with increasing pyrolysis and graphitisation temperature.