The synthesis of Graphene is critical to achieving its functions in practical applications. Different methods have been used to synthesis graphene, but graphite exfoliation is considered the simplest way to produce graphene and graphene oxide. In general, controlling the synthesis conditions to achieving the optimum yield, keeping the pristine structure to realize on-demand properties, minimum layers with the smallest lateral size, and minimum oxygen content are the most obstacles experienced by researchers. Each application requires a specific graphene model, graphene oxides GO, or even graphene intercalated compounds (GIC) depending on synthesis conditions and approach. This paper reviewed and summarized the most researches in this field and focusing on exfoliation methods.
A facile method is proposed to use a computer controlled Arc discharge gap between graphite electrodes together with an yttrianickel catalyst to synthesize carbon nanotubes under an Ar-H 2 gases mixture atmosphere by applying different DC currents and pressure. This produces carbon nanotubes with decreased diameters and increased length. XRD evidence indicated a shift toward higher crystallinity nanotubes. Yields of the CNTs after purification were also enhanced.
Squeeze casting is a pressure casting process in which molten metal is solidified under the direct action of a pressure. In squeeze casting, the relationship between the process parameters and the quality of the squeeze cast components is not fully understood; thus the need for more studies in this area of technology for better understanding of the process. The present work encompasses studying the effect of direct squeeze casting process parameters on the production of (3 and 20٪) volume fraction carbon fibers (CF) reinforced Al-Si matrix composites. The evaluated process parameters are squeeze pressure in the range (7.5-53) MPa, die preheating temperature (100,200,300)°C, pouring temperature (700,780)°C, squeeze time (30 sec.), and delay time (5 sec.). The results show a good distribution of the matrix between the carbon fibers when using higher casting pressures of (38 and 53MPa), lower pouring temperature of (700°C) and lower die temperatures of (100 and 200°C). Increasing the carbon fibers volume fraction had led to increasing the tensile strength. The using of higher pressure (53MPa), lower pouring temperature (700°C), and lower die temperature (200°C) have increased the ultimate tensile strength of the CF/Al-Si composites to (183MPa) when compared to that of the nonreinforced alloy which was (168MPa) because of the increased bonding, decreased shrinkage defects and fibers degradation based on the results.
In this study, continuous wave CO2 laser with 1.7 and 2 kW were used to deposit clad layers of premixed powders of either Ni-10 wt% Al or Ni-30 wt% Al onto inconel 617 substrate. Different cladding traverse speeds in the range 1 to 35 mm/s were used for premixed clad powder of Ni-10 wt% Al and 1.65 to 11.2 mm/s for premixed clad powder of Ni-30 wt% Al. Two powder feeding rates were used, 10 and 8.9 gm/min for premixed clad powders of Ni-10 wt% Al and Ni-30 wt% Al respectively. The other laser independent variables were selected to be constant. The results showed that different percentages of area dilution were found ranging from 3.7 to 78.3% for premixed clad powder of Ni-10 wt% Al and 6.9 to 41 % for premixed clad powder of Ni-30 wt% Al depending on the laser cladding independent variables used. Furthermore, dilution was affected mainly by cladding traverse speeds.
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