Mechanical activation of graphite in air: A way to advanced carbon nanomaterials

A high-energy planetary mill AGO-2 was used for mechanical activation of synthetic graphite with the particle size of 25–30 μm and specific surface area S_BET = 3.0 m²/g in air for 1–60 min at a 100 g acceleration of milling bodies. The X-ray diffraction, Raman spectroscopy and electron microscopy studies showed that the 60 min mechanical activation of graphite decreases the number of graphene layers in graphite crystallites to 8–12 and induces their turbostratic disorder. The size of graphite particles decreases to 6.9 μm after 30 min of mechanical activation and increases to 12.1 μm when the time of mechanical activation is extended to 60 min. Similar changes are observed for the true density of graphite: after 60 min of mechanical activation it becomes equal to 2.48 ⋅ 10³ kg/m³, which is by 10% higher than the true density of graphite not subjected to such treatment. The specific adsorption surface of graphite (S_BET) reaches its maximum values, 427–460 m²/g, after 7–12 min of mechanical activation. A further increase in the activation time to 30–60 min decreases S_BET of graphite to 230–250 m²/g. Due to attrition of steel milling bodies caused by mechanical activation, iron is accumulated in the samples and its content exceeds 5%. Iron is distributed uniformly in the graphite as the 30–100 and 3–5 nm particles of hematite and iron carbide. The IR spectroscopy study revealed the formation of 0.8 mEq/g of the hydroxyl, phenolic, lactone and carbonyl groups on the graphite surface in the course of mechanical activation. - Highlights: • Graphite was mechanically activated in air at a 100 g acceleration of milling bodies. • The amount of graphenes in graphite crystallites decreases to 8–12. • Graphite transforms into a nanocrystalline X-ray amorphous state. • A metal–graphite composite with the 30–100 and 3–5 nm iron particles is formed. • Oxygen-containing groups in the amount of 0.8 mEq/g are present on the graphite surface