The effect of the mechanical activation dose on the defective structure of artificial graphite

Abstract

Energy parameters (dose D and the work of surface formation) have been determined for the for mation of a defective structure as a result of mechanical activation of graphite. Graphite activation has been shown to be a two stage process: at low doses (D ≤ 20 kJ/g), the disruption and shift of graphite particles are the main processes, which are accompanied by a reduction in particle size, formation of meso and micropores, and a rise in the BET specific surface area to 450-550 m 2 /g predominantly due to the develop ment of a slitlike mesoporosity. At the same time, the crystalline structure of graphite is transformed into a turbostrate one with a concomitant increase in the lattice parameter and a decrease in the sizes of coherent scattering regions. The shape of diffraction lines can be described under the assumption that several fractions with greatly different degrees of defectiveness coexist in graphite. At higher doses, turbostrate graphite is transformed into X ray amorphous carbon with a concomitant decrease in the specific surface area and meso and microporosity. The defects resulting from the mechanical activation cannot be completely annealed at 2800°C. The main parameter of mechanical activation is the dose of supplied energy D = J g t (J g is the specific power consumption, and t is the duration of the activation). The curves describing accumulation of different defects can be represented in the form of a unified dependence on the dose for the J g and, accordingly, t values varied by more than an order of magnitude (J g = 1.7-22 W/g).

Characteristics of local atomic configurations in ball‐milled fullerenes

“…Unfortunately, the specific energy transferred to samples during ball‐milling is not indicated in most cases, except for Ref. and it complicates the interpretation of the results from different authors. However, a comparative analysis can be performed using X‐ray diffraction data.…”

“…The initial and intermediate stages of decomposition of the molecular crystal C 60 were reported [13]. A further increase of milling time resulted in the destruction of the C 60 molecules (energy input~120 kJ g -1 ) and, respectively, the formation of amorphous carbon similar to ball-milled graphite [22,32].…”

Introducing Students to Energy-Efficient Mechanochemistry of Biopolymers

“…However, the lack of fundamental knowledge about the physicochemical processes occurring upon mechanochemical treatment of complexly organized polymeric molecules impedes the larger-scale use of mechanochemical methods in education and science. , The lack of knowledge about the energetic effects during mechanochemical processes is particularly noticeable. − The mechanical stress relaxation pathways known in solid-state chemistry (formation of a new surface, amorphization of crystallites, or the rupture of covalent bonds) through which the energy supplied to the activated substance is expended still remain unclear. There are only sparse studies where it has been demonstrated using model inorganic materials that only 3–5% of the all the supplied energy is expended for mechanochemical processes to occur. − Almost no similar fundamental studies addressing polymeric objects are available thus far.…”