Phase Transition and Thermal Expansion of Graphite Intercalation Compound with Nitric Acid

Abstract

Graphite-nitric acid-intercalation compounds with different stages (from 1 st to 5 th) were prepared by direct immersion into nitric acid with various concentrations. The temperature dependence of the identity period (I_C) was measured by X-ray diffraction over the temperature range +25 to -196°C.
The following results were obtained.
1) Anomalous expansion widths in I. due to the phase transition for the 1 st stage, 2 nd stage and 3 rd-5 th stage were O.025, O.031, and O.045 A, respectively. The phase transition temperature for the 1 st stage was about 10°C, but those for the higher stages and slightly. decomposed samples fell to 1328°C.
2) Another phase transition around 5°C was found from anomalous expansion and from the discrepancy between thermal expansion coefficients above and below 5°C.
3) Thermal expansion coefficients for the 2 nd stage to the 5 th stage at room temperature were a (2 nd) =49.9×10^-6/K, a (3 rd) =43.0 × 10^-6/K, a (4 th) =41.9 × 10^-6/K and r(5 th) =37.0× 10^-6/K.