Further carbonization of anisotropic and isotropic pitch-based carbons by microwave irradiation

Abstract

Isotropic (PFO) and anisotropic (NMP) pitch-based carbon powders thermally carbonized above 600°C were carbonized further by microwave irradiation under inert gases, Ar and N 2. The temperature of the carbon powder during microwave irradiation was measured by an Inconel sheathed thermocouple. The sample under Ar gas showed higher temperature than that under N 2 gas before exhibition of the Ar arc discharge. The temperature increased in the early stage and decreased when the irradiation was continued. The irradiation increased the L c(002) value and electric conductivity with no significant differences in values between isotropic and anisotropic pitch-based carbons. The results were explained on the basis of the mechanism of inductive heating from the material’s resistance to electron movement leading to similar morphological structure with lapse of irradiation time. However, the morphological structural differences between the isotropic and anisotropic carbons reflect on the variations of L c(002) and d (002) values with irradiation time. d (002) of anisotropic carbon showed minimum and maximum behaviors with the increase in L c(002) value indicating stacking in advance and subsequently reduction in d (002) values of the uniformly ordered crystallites. On the other hand, d (002) values of isotropic carbons decreased monotonically with increasing L c(002) values, reflecting the wide distributions of the crystallite sizes in the isotropic carbon. Microwave irradiation for 30 min effectively increased the L c(002) value comparable with the value of NMP-based carbon thermally heat treated at 1500°C for 1 h.