抄録
Investigations have been made on the thermal expansion behavior in the c-direction of pyrolytic graphite bromine residual compounds (PG (Br), 0.9∼5.5 weight percent bromine) within the temperature range of 20∼1000°C. The thermal expansion consists of three stages: the first stage below about 120°C, the second stage 120∼300°C, and the third stage above about 300°C. The thermal expansion coefficient in the third stage increases linearly with the amount of bromine. The expansion under heating-cooling cycles shows a thermal hysteresis which relates to the existence of bromine. The observed behavior is explained, using a model which considers the bromine to be ionically bonded to carbon near room temperature (1st stage) and to vaporize with increasing temperatures to make gaseous bubbles within the lamellar structure of the graphite crystal (2nd stage). After 2nd stage PG(Br) expands according to the ideal gas law (3rd stage). The calculation of the thermal expansion coefficients is based on the Griffith's crack model employed by Martin and Brocklehurst. The experimental results are in good agreement with the calculated values.
