Effect of additional nickel on crystallization degree evolution of expanded graphite during ball-milling and annealing

Expanded graphite (EG) and a mixture of EG and nickel (EG–Ni system) were ball-milled and subsequently annealed, respectively. The products were characterized by X-ray diffraction (XRD), Raman spectra and transmission electron microscopy (TEM). After 100 h milling, the average crystallite thickness (Lc) of EG and EG–Ni system deceases from 14.5 to 8.0 and 9.6 nm, respectively, while the interlayer spacing (d0 0 2) increases from 0.3341 to 0.3371 and 0.3348 nm, respectively. It can be concluded that ball-milling decreases the crystallization degree of EG, while the additional nickel restrains this process. For the samples ball-milled for 80 h, the disorder parameter ID/(ID + IG) ratio of EG and EG–Ni system is in the range of 20.7–55.8% and 31.7–45.8%, respectively, implying that the presence of nickel is beneficial to more homogeneous ball-milling of EG. When the samples after ball-milling for 80 h were annealed for 4 h, the average crystallite thickness of EG and EG–Ni system increases from 8.5 to 9.0 nm and from 11.8 to 15.5 nm, respectively. It is deduced that annealing improves the crystallization degree of ball-milled EG, and the additional nickel is helpful for this process.