Synthesis of a fullerene/expanded graphite composite and its lubricating properties

A fullerene/expanded graphite composite, in which fullerene crystals were incorporated into the expanded graphite interspaces, was prepared by chemical and thermal treatments and its lubricating properties in commercial grease were investigated. Expanded graphite, which was synthesized from graphite by oxidizing by KMnO₄ in 98% H₂SO₄ containing NaNO₃ and by heating at 400 °C for 3 min, and fullerene were placed in a stainless steel tube, and were heated in a furnace under vacuum at 600 °C for 2 weeks. The fullerene/expanded graphite composite obtained was characterized by X-ray diffraction analysis (XRD), Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM). XRD and FT-IR analyses showed that crystalline fullerene was present in the material and SEM images confirmed that it existed in the expanded graphite interspaces. The composite was blended with a commercial grease, and its lubricating properties were investigated using a four-ball lubricant tester. These properties were evaluated by measuring the wear scar diameter and wear volume loss of the test ball. The combination of composite and grease provided a better lubricating performance than that of pure graphite and grease.