Abstract: Nanocarbon-coated α-Al₂O₃ composite powders were synthesized by high-energy ball milling using expanded graphite and α-Al₂O₃ as raw materials. The effects of milling time and speed on phase composition and microstructure of the composite powders were investigated. X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) were employed to characterize the phase composition, morphology and microstructure of the composite powders. The results show that nanocarbon with a size of 20–50 nm coated on the α-Al₂O₃ particles when the expanded graphite and α-Al₂O₃ with a weight ratio of 1:2 were milled for 5 h at a speed of 600 r/min. By increasing the milling time, the (002) diffraction peak of graphite gradually disappeared, and nano-graphite sheets desquamated from expanded graphite and then chaped to nanocarbon particles. Milling for the same time, higher milling speed was beneficial to synthesize nanocarbon particles, but when milling speed reached certain value, the size of nanocarbon cannot become smaller again. Nanocarbon-coated α-Al₂O₃ composite powders cannot be synthesized using a milling speed of 480 r/min even milled for 5 h. The morphology and microstructure of the composite powders were basically the same when the composite powders were milled at 600 and 700 r/min for 5 h.

Key words: high-energy ball milling, expanded graphite, nanocarbon-coated, α-Al₂O₃