Raman spectrometer. The temperature rise in the heated area of
the test fiber causes a down-shift of Raman peak. In the experiment,
a Linkam model THMS600 heating and cooling microscope
stage is used to keep the sample at different constant temperatures
for measuring the temperature dependence of shifted Raman peak
frequency. The slope of the shifted Raman frequency versus temperature
graph will be used later for calculating the local temperature
of the test fiber.
The PAN-based carbon fibers measured in the experiment are
provided by Chinese Institute of Coal Chemistry. During a typical
manufacturing process, a continuous filament is derived from
polyacrylonitrile and becomes the molecular backbone. Then the
polymeric filament is heated in an oxidation oven from 200 C to
300 C when the oxygen molecules are combined with the polymeric
molecules. After that, the filament is heated in specially designed
furnaces for carbonization. The processing temperature is
progressively increased up to 2900 C and the most non-carbon
molecules are removed. The annealed carbon fibers have optimized
crystallization of carbon molecules and contain more than 90%
carbon.