Changes in the Phase Composition and Structure of Al/Graphene Powder Mixture Particles and Evolution of the Graphene Structure during Processing in a Planetary Ball Mill in Dry and Liquid Media

Samples of a powder mixture of aluminum with graphene (0.5, 1, and 3 wt %) were ground in a planetary ball mill with a total processing time of 10 h in dry (with the addition of stearic acid) and liquid (in heptane) media. During the milling process, the spherical powder particles acquired a flaky shape and decreased in size to 50–100 μm. It was shown that after 10 h of treatment, the particle morphology and size do not depend on the presence of graphene and its quantity. As a result of aggregation of particles during grinding in heptane, their sizes are two or three times larger than when grinding in stearic acid. Using Raman spectroscopy, it was established that, as a result of structural changes in graphene during grinding, powders at different stages of processing contain a mixture of different forms of carbon. After 10 h of mechanosynthesis, the powder mixture contained nanocrystalline graphite or its mixture with graphene, depending on the initial amount of graphene. An X-ray diffraction study revealed a texture in the powders caused by stabilization of the defective face-centered cubic (fcc) structure of aluminum by graphene. The expression of texture, determined by the intensity ratio I200/I111 of the diffraction peaks of the aluminum fcc lattice, correlates with changes in the intensity ratio of the D and G bands in the Raman spectra, which characterize the defect density and disorder in the graphite structures.