The properties and structure of the carbon fibre in carbon/carbon produced on the basis of carbon fibre reinforced phenolic resin

The properties of carbon fibre reinforced carbon produced on the polymer route by impregnation and subsequently hardening the resin, carbonisation and graphitization depend on many variables. During processing mainly the polymer matrix (and the interface) undergoes a strong change of its structure and properties. Depending on the type of fibre used, however, also large structural fibre changes can be found. This is demonstrated in the present investigation in which two types of fibres are used: a HT-fibre (HTA of AKZO company) and a HM-fibre (M40 J of Toray Company). The HT-fibre was found to be dimensionally and structurally unstable well below the maximum fibre processing temperature of 1400 °C. The fibre shrinks (the in-frozen processing stress relaxes) at temperatures as low as 850 °C. The shrinkage of the fibre bundle embedded in phenolic resin during the carbonisation process is influenced by matrix shrinkage stresses and pyrolysis products. Above 1000 °C the HTA carbon fibre in carbon/carbon bundles continuously changes its structure. After heat treatment at a temperature of 2800 °C the structure (lattice distance, orientation of the crystallites, crystallite size) is very similar to that of HM-fibres.