114
7 Molten Salt Conversion of Plastics into Highly Conductive …
d (002) toward higher values in comparison to that of graphite. This indicates the
poorly crystalline nature of these carbon materials [29–31].
The turbostratic carbon has been identified as a variant graphite with hexagonal
structure, in which the (002) carbon layers may randomly translate to each other
and rotate about the normal of the layers [28]. Ramakrishnan et al. [30] observed
the position of the (002) XRD reflection in a turbostratic nanocarbon at 2θ –23°.
Figure 7.3a shows the XRD pattern of PET pyrolyzed at 850 °C. In this pattern,
the diffraction peaks arisen from the (002) planes and the (100)/(101) overlapping
can be observed at the 2θ values with the maximum of 25.2°, corresponding to an
interlayer spacing value of 3.54 Å, and 43.2°, respectively. As can be observed, in
comparison with the carbon material produced at 620 °C, the carbon sample obtained
at 850 °C possesses a more intense (002) diffraction peak. Moreover, this peak has
shifted toward a larger value. These observations indicate that the sample obtained
at 850 °C has a greater degree of crystallinity. Therefore, the endothermic peak
observed at 791.2 °C corresponds to the graphitization onset.
Ruz et al. [29] produced a turbostratic carbon using sucrose and zeolite template
at 700 °C, and detected the (002) and (101) diffraction peaks of the carbon material in
the corresponding XRD pattern at 2θ values of around 20° and 44°, respectively. In
their work, by increasing the processing temperature to 900 °C, the diffraction peaks
became more intense and shifted toward higher angles. This was attributed to the
increased translational ordering in the carbon sample produced at higher temperatures
[29].
Turbostratic carbons might find interesting applications in the future such as electrode materials for sodium ion [32] or vanadium redox flow batteries [33]. However,
currently, graphitized nanostructured carbon materials are candidates for a number
of applications in energy and environmental fields, as will be discussed later in this
chapter.
As discussed, the endothermic peak observed in Fig. 7.2 at 791.2 °C can be
attributed to the onset of the graphitization of the turbostratic carbon [24]. Moreover,
from the TGA micrograph of Fig. 7.2, it can be realized that about 10% of the PET
material, which is around 40% of the total solid carbon still remained at 900 °C in
air atmosphere, where the thermal analysis was terminated. It demonstrates that the
amorphous carbon material obtained by the carbonization of PET has a high thermal
stability and resistance against thermal oxidation in air.
It should be mentioned that usually at temperatures above 500 °C, the intensive
oxidation of carbon materials in air occurs. The oxidation temperature is a function
of the carbon properties including its crystallinity or degree of graphitization, flake
size, porosity and purity [34]. With this in mind, the thermal oxidation of highly
oriented pyrolytic graphite (HOPG) has been reported to occur at 550–950 °C [35].
At temperatures lower than 875 °C, The oxidation process mainly proceeds by the
formation of pits at defect sites. At higher temperature, however, the oxidation event
takes place on both defects, and also carbon basal planes. On the other hand, the oxidation rate of amorphous carbons is known to be greater than that of graphitic carbon
7 Molten Salt Conversion of Plastics into Highly Conductive …
d (002) toward higher values in comparison to that of graphite. This indicates the
poorly crystalline nature of these carbon materials [29–31].
The turbostratic carbon has been identified as a variant graphite with hexagonal
structure, in which the (002) carbon layers may randomly translate to each other
and rotate about the normal of the layers [28]. Ramakrishnan et al. [30] observed
the position of the (002) XRD reflection in a turbostratic nanocarbon at 2θ –23°.
Figure 7.3a shows the XRD pattern of PET pyrolyzed at 850 °C. In this pattern,
the diffraction peaks arisen from the (002) planes and the (100)/(101) overlapping
can be observed at the 2θ values with the maximum of 25.2°, corresponding to an
interlayer spacing value of 3.54 Å, and 43.2°, respectively. As can be observed, in
comparison with the carbon material produced at 620 °C, the carbon sample obtained
at 850 °C possesses a more intense (002) diffraction peak. Moreover, this peak has
shifted toward a larger value. These observations indicate that the sample obtained
at 850 °C has a greater degree of crystallinity. Therefore, the endothermic peak
observed at 791.2 °C corresponds to the graphitization onset.
Ruz et al. [29] produced a turbostratic carbon using sucrose and zeolite template
at 700 °C, and detected the (002) and (101) diffraction peaks of the carbon material in
the corresponding XRD pattern at 2θ values of around 20° and 44°, respectively. In
their work, by increasing the processing temperature to 900 °C, the diffraction peaks
became more intense and shifted toward higher angles. This was attributed to the
increased translational ordering in the carbon sample produced at higher temperatures
[29].
Turbostratic carbons might find interesting applications in the future such as electrode materials for sodium ion [32] or vanadium redox flow batteries [33]. However,
currently, graphitized nanostructured carbon materials are candidates for a number
of applications in energy and environmental fields, as will be discussed later in this
chapter.
As discussed, the endothermic peak observed in Fig. 7.2 at 791.2 °C can be
attributed to the onset of the graphitization of the turbostratic carbon [24]. Moreover,
from the TGA micrograph of Fig. 7.2, it can be realized that about 10% of the PET
material, which is around 40% of the total solid carbon still remained at 900 °C in
air atmosphere, where the thermal analysis was terminated. It demonstrates that the
amorphous carbon material obtained by the carbonization of PET has a high thermal
stability and resistance against thermal oxidation in air.
It should be mentioned that usually at temperatures above 500 °C, the intensive
oxidation of carbon materials in air occurs. The oxidation temperature is a function
of the carbon properties including its crystallinity or degree of graphitization, flake
size, porosity and purity [34]. With this in mind, the thermal oxidation of highly
oriented pyrolytic graphite (HOPG) has been reported to occur at 550–950 °C [35].
At temperatures lower than 875 °C, The oxidation process mainly proceeds by the
formation of pits at defect sites. At higher temperature, however, the oxidation event
takes place on both defects, and also carbon basal planes. On the other hand, the oxidation rate of amorphous carbons is known to be greater than that of graphitic carbon