Measurement of the extinction angle about laminar pyrocarbons by image analysis in reflection polarized light

A new technique, including optical imaging and data processing, was presented for measuring of the extinction angle of pyrocarbons deposited around carbon fibers. The experiment was performed using a rotating analyzer in the reflection polarized light microscope coupled with a digital imaging camera. The special specifications for adjusting each part in the optical arrangement were detailed. The principle of the proposed method was discussed from the crystal grain distribution of pyrocarbons and the extinction property of graphite. The researched C/C composites respectively contain smooth laminar, rough laminar and dark laminar pyrocarbons. The digital images were captured at intervals of 1°. The extinction curves were plotted by fitting the sampled pixel values, and the extinction angles were obtained corresponding to the lowest point of these curves. The correlation between the experimental results and the observation by eyes in PLM is consistent with Bourrat's conclusion.