Phase Transformation Mechanism of Graphite-Turbostratic Graphite in the Course of Mechanical Grinding

The transformation from graphite to turbostratic graphite by means of the treatment with high energy ball milling was investigated by X ray powder diffraction method. It is believed that the size effect of nano crystal leads to this transformation. A possible transformation mechanism is proposed from the change of the eletronic structure of the hexagonal plane of the carbon atoms.

High-performance solid-solution potassium-ion intercalation mechanism of multilayered turbostratic graphene nanosheets

The solid-solution reaction between an alkali cation and an active host material is known as a singlephase redox mechanism,and it is typically accompanied by a continuous voltage change.It is distinct from the typical alkali cation intercalation reaction at an equivalent site of the active host material,which exhibits a voltage plateau.Herein,we report an unusual solid-solution potassium-ion intercalation mechanism with a low-voltage plateau capacity on multilayered turbostratic graphene nanosheets(T-GNSs).Despite the disordered graphitic structure with a broad range of d-spacings(3.65–4.18À),the T-GNSs showed a reversible plateau capacity of~200 m A h g^(-1),which is higher than that of a well-ordered graphite nanoplate(~120 m A h g^(-1)).In addition,a sloping capacity of~220 m A h g^(-1)was delivered with the plateau capacity,and higher rate capabilities,better reversibility,and a more stable cycling performance were confirmed on the turbostratic microstructure.First-principles calculations suggest that the multitudinous lattice domains of the T-GNSs contain diverse intercalation sites with strong binding energies,which could be the origin of the high-performance solid-solution potassium-ion intercalation behavior when the turbostratic graphene stacks have a d-spacing smaller than that of equilibrium potassium–graphite intercalation compounds(5.35À).

Tribological behaviour of sintered iron based self-lubricating composites

This work is a review of previous works,presenting and discussing the most important results obtained by an ongoing research program towards the development of innovative,low-cost,self-lubricating composites with a low friction coefficient and high mechanical strength and wear resistance.Special emphasis is given to uniaxial die pressing of solid lubricant particles mixed with matrix powders and to metal injection moulding associated with in situ generation of solid lubricant particles.Initially,a microstructural model/processing route (powder injection moulding followed by plasma-assisted debinding and sintering) produced a homogeneous dispersion of in situ generated solid lubricant particles.Micrometric nodules of graphite with diameter smaller than 20 μm were formed,constituting a nanostructured stacking of graphite foils with nanometric thickness.Micro Raman analysis indicated that the graphite nodules were composed of turbostratic 2D graphite having highly misaligned graphene planes separated by large interlamellae distance.Large interplanar distance between the graphene foils and misalignment of these foils were confirmed by transmission electron microscopy and were,probably,the origin of the outstandingly low dry friction coefficient (0.04).The effect of sintering temperature,precursor content,metallic matrix composition and surface finish is also reported.Furthermore,the influence of a double-pressing/double-sintering (DPDS) technique on the tribological performance of self-lubricating uniaxially die-pressed hBN + graphite-Fe-Si-C-Mo composite is also investigated.Moreover,the tribological behaviour of die-pressed Fe-Si-C matrix composites containing 5,7.5 and 10 wt％ solid lubricants (hBN and graphite) added during the mixing step is analysed in terms of mechanical properties and wear mechanisms.Finally,the synergy between solid lubricant particles dispersed in a metallic matrix and fluid lubricants in a cooperative mixed lubrication regime is presented.

Raman analysis of epitaxial graphene on 6H-SiC(000) substrates under low pressure environment

This article investigates the formation mechanism of epitaxial graphene on 6H-SiC （0001） substrates under low pressure of 2 mbar environment. It is shown that the growth temperature dramatically affects the formation and quality of epitaxial graphene. The higher growing temperature is of great benefit to the quality of epitaxial graphene and also can reduce the impact of the substrate for graphene. By analyzing Raman data, we conclude that epitaxial graphene grown at 1600 ℃ has a turbostratic graphite structure. The test from scanning electron microscopy （SEM） indicates that the epitaxial graphene has a route for fabricating larger size of epitaxial graphene on SiC size of 10μm. This research will provide a feasible substrate.