The carbon fibres are coated and the exposure time to elevated temperatures was 8 hrs. Then the fibres left to cool off and subsequently were subjected to the XRD test.
Annealing at 300 degC has produced a small change in microstructure (degree of graphitization??) evident from the slight difference in line broadening.
Thank you for your answer. Is it possible to speculate that the change in grain size and the degree of graphitization to increase the brittleness of the fibre?