Change of Electrical Resistivity of Graphite Powder During Heating in Air

Abstract

The electrical resistivity of the powder of high purity artificial graphite was measured from room temperature up to 600°C. The change of the resistivity during heating in air was classified to several steps; i) between 200° and 300°C, the resistivity decreases slightly with time, ii) between 300° and 330°C, the resistivity decreases abruptly and temporarily, iii) between 340° and 360°C, the resistivity increases slightly, iv) above 400°C, the resistivity decreases abruptly, and v) at about 600°C, the resistivity increases abruptly. From comparison of these changes shown in argon, in vacuo, and at reheating, and with thermogravimetric changes at same C41ditions, these changes of resistivity could be connected with the following changes of surface state, respectively; i) formation of unstable surface oxide (Cf*-+C*(0)), ii) decomposition of unstable surface oxide (C*(0)-Cf), iii) formation of stable surface oxide (Cf-+C(0)), iv) decomposition of stable surface oxide (C(0)→Cl), and v) regeneration of active surface site (Cf-Cf*). Then the contribution of the surface state to the electrical resistivity of graphite powder can be expressed asPc r. P C. (0) Pcf and Pc (o) Pc, where pc, . means the specific resistivity of powder aggregate of the graphite which has Cr* surface state, and so on.