Abstract:

In order to obtain the low-temperature expandable graphite (LTEG) by means of a low pollution method, the natural flake graphite (NFG) was oxidized in the perchloric acid solution by means of the electrochemical method. Thus, the sulfur-free LTEG of a large exfoliated volume (EV) and a low initial exfoliating temperature was prepared. Then, the influences of the current density, the electrolysis time, the mass fraction of HClO4 in electrolyte and the exfoliating temperature on the EV were discussed, and the LTEG was characterized by means of FTIR, TGA and XRD. The results show that (1) the mass fraction of HClO4 in electrolyte can be as low as 50%, which dramatically decreases in comparison with the results of chemical oxidation methods; (2) recycling the electrolyte is easy, which helps to reduce environmental pollution; (3) the EV of the LTEG reaches up to 282 mL/g and 594 mL/g respectively at the exfoliating temperatures of 200 ℃ and 950 ℃, and the LTEG is high-rate, sulfur-free and expandable at low temperatures; (4) there exists  carbonyl and carboxyl on the surface of the LTEG, and there exists ClO4－ and HClO4 as intercalation compounds within the space between the graphite pieces; (5) the intensity of the characteristic diffraction peak at a 2θ of 25.76 º is very weak, and a broad peak appears at a 2θ of 9.41 º with an interlayer distance of 0.94 nm; and (6) the thermal weight loss of the LTEG occurs obviously between 60～330 ℃ with a thermal weight loss rate of about 28%, and the total thermal weight loss rate is about 35% between 60～800 ℃.

Key words: natural flake graphite, low-temperature expandable graphite, electrochemical method, intercalation reaction, initial exfoliating temperature, low-temperature exfoliated volume