A study on interfacial behaviors of epoxy/graphene oxide derived from pitch-based graphite fibers

Graphene oxide (GO) is a versatile material with inherent unique properties that can be used in a wide range of applications. GO is produced from graphitic materials including graphite, and its properties can depend on the nature of stacking in the graphene structures. In this study, GO was prepared from pitch-based graphite fibers via the modified Hummer’s method and subsequently incorporated into an epoxy matrix to obtain graphene-loaded nanocomposites (EP/GO). Presented experimental results revealed that the addition of 0.6 wt% GO yielded an ∼110% increase in the fracture toughness. The corresponding fracture energies as well as the flexural strengths and flexural modulus exhibited similar trends to the fracture toughness. The thermophysical properties of the EP/GO, to further demonstrate the reinforcing effectiveness of GO, were also observed. Collectively, these results indicate that GO investigated in the study can be a viable reinforcement candidate to develop next-generation nanocomposites with multifunctional properties.

Analysis of roller designs for sintering and firing machines

The article analyzes the known constructions of roller units of carts for the manufacture of agglomerate and pellets on conveyor lines. The article points out the advantages and disadvantages of roller designs, the lack of standard technical solutions for the design of roller assemblies, as well as reliable methods for calculating their parts for strength and durability. To increase the life of the rollers, the authors, after successful industrial tests, offer innovative technical solutions: seals in the form of stuffing boxes made of expanded graphite fibers reinforced with steel thread; bearing antifriction filler made from polytetrafluoroethylene, carbon fiber and graphite. The article shows that due to axial loads during the operation of the bogies, it is impractical to use ball bearings in the ball, they should be replaced with roller bearings. The authors propose an approximate method for calculating the durability of bearings, which additionally takes into account the elastic deformation of the material of the bogies during their thermal expansion and the gaps in the nodes of the bogies. The authors use the calculation of experimental results on the size of the gaps in the nodes of the bogies, the curvature of the body of the heated bogies on the conveyor line and their movement on three rollers instead of four, take into account the change in the coefficient of linear expansion of the material of the bogie depending on the increase in the heating temperature of the case.

Impact of Microstructure on the Electrochemical Performance of Round-Shaped Pitch-Based Graphite Fibers

In this study, three kinds of round-shaped pitch-based graphite fiber with different microstructural features (crystallinity and carbon layer orientation) were fabricated by melt-spinning, preoxidation, carbonization and graphitization. The morphology, crystalline size and carbon layer orientation of carbon fibers from different pitch precursors and spinning rates were characterized through X-ray diffraction, scanning electron microscopy and transmission electron analyses. The correlation of the electrochemical performance and microstructure of graphite fibers as anode materials for lithium-ion batteries was investigated. The results suggest that large-diameter anisotropic graphite fibers (L-AF3000) with a radial texture of the transverse section are more favorable for lithium intercalation storage. The discharge capacity of L-AF3000 is 319.1 mAh∙g−1 at 0.1 C (current density). Nevertheless, the capacity drops to 209.9 mAh∙g−1 at a high current density of 1 C, and the capacity retention is only 82.2% over 100 cycles at 0.1 C. Small-diameter anisotropic graphite fibers (S-AF3000) with a spiral-shaped wrinkle texture of the transverse section possess discharge capacities of 284.1 mAh∙g−1 at 0.1 C and 260.2 mAh∙g−1 at a high current density of 1 C. Meanwhile, the best capacity retention of the fibers is 101.6% over 100 cycles at 0.1 C. The results suggest that the disordered carbon layers in S-AF3000 can retain the structural integrity of fibers as anode material for lithium-ion batteries and thus obtain excellent cycle stability. In addition, larger crystalline sizes of fibers correspond to higher discharge capacity, and a smaller diameter is beneficial to the fast insertion and extraction of lithium-ion in fibers.