REACTIVITY OF CARBON MATERIALS AGAINST METALLIC SODIUM

摘要

Several kinds of carbon samples prepared from needle-like petroleum cokes with different graphitization degree were allowed to react with sodium. X-ray diffraction, electrical resistivity and electron spin resonance (ESR) measurements were carried out. The 001 diffraction lines of carbon shifted towards lower angle of 16 along with the reaction with sodium, indicating the expansion of the carbon-carbon interlayer distance due to the intercalation of sodium into the interlayer space of carbon. The carbon samples with heat-treatment temperature of 1500℃ and 1750℃ (hereafter designated as HTT-1500 [or -1750] carbon) accepted large amounts of sodium compared to fairly well graphitized ones such as HTT-2200 and -2400 carbons. The electrical resistivity of HTT-1500 carbon block slightly decreased at early stages of reaction with sodium and then increased along with further reaction. Finally, it reached a larger value than that of the original carbon. On the contrary, the resistivity of carbon blocks with HTT higher than 1750℃ decreased monotonically along with the reaction. Therefore, the degradation of carbon due to the attack of metallic sodium was considered to be remarkable if HTT was below 1500℃. For HTT-2400 carbon the absolute value at saturation reached about 1/7 of that of the host carbon. It showed metallic temperature dependence with characteristic hysteresis during heating-cooling cycles between 77 and 400 K. Electron spin resonance of the products prepared from HTT-2200 and -2400 carbons gave signals due to conduction electron with g-value of around 2.002, corresponding to the characteristic value usually observed for many graphite intercalation compounds, while almost no signal was observed for the reaction products of HTT-1500 and -1750 carbons.