7.2 Carbonization of PET
115
materials [36]. Furthermore, the inorganic impurities can act as the oxidation catalyst, promoting the thermal degradation, and decreasing the oxidation temperature
of carbon materials [37–39].
Further information can be obtained from the SEM morphology of the carbon
materials shown in Fig. 7.3b–d. The carbon material produced at 620 °C (Fig. 7.3b)
comprises of large particles up to several hundred micrometers with irregular shapes
and sharp edges. Moreover, despite the fact that the material has been heated in air, the
SEM micrograph does not show any sign of oxidation, indicating the high oxidation
resistance of the carbon material. The C:O atomic ratio of the sample was recorded
to be 5.2 by EDX analysis, which is considerably greater than that of crystallized
PET (1.8). Nevertheless, the oxygen content of the sample is still remarkable, and
this can be a barrier toward further graphitization of the carbon material.
Overall, the carbon material produced at 850 °C (Fig. 7.3c, d) possesses approximately the same morphological features as that of the carbon material produced at
620 °C. The presence of irregular-shaped large particles is evident from the micrograph. Furthermore, small surface pitting holes can also be observed from the higher
magnification of Fig. 7.3d, which is an indication of the initial stage of oxidation. It
was observed that the carbon material is completely oxidized into gaseous species at
the higher heat treatment temperature of 1100 °C. Nevertheless, the thermal analysis
results presented in Fig. 7.2 and SEM micrographs of Fig. 7.3 demonstrate that the
amorphous carbon driven from PET has a very high oxidation resistance up to temperatures as high as 900 °C. This characteristic can be assigned to the large particle
sizes, high purity, low porosity and the low density of surface defects in PET-derived
amorphous carbon materials [24].
As discussed, the endothermic peak observed at 791.2 °C in the DSC thermogram
of Fig. 7.2 is attributed to the onset of the graphitization occurred in the PET-derived
turbostratic carbon. Gutiérrez-Pardo et al. [40] have reported the development of
graphitic structures upon pyrolysis of wood impregnated with FeCl 3 at temperatures
as high as 1000–1600 °C. For this, wood samples were impregnated with 3 M FeCl 3
solution in isopropanol in vacuum for 2 h to ensure the complete filling of the pores.
The pyrolysis process took place by heating of impregnated samples in a flow of
nitrogen to a maximum temperature in the range 1000–1600 °C. After pyrolysis, the
residual iron was removed by stirring in concentrated HNO 3 [40]. Figures 7.4a and b
show the SEM and TEM micrographs of the sample produced at 1600 °C, respectively, representing a porous carbon structure with a BET surface area of about
167 m
2 g
−1 . Figure 7.4c shows the heat flow versus temperature during pyrolysis of
the impregnated wood, and also that without impregnation with FeCl 3 (black line).
The DSC curve of the impregnated sample shows a pronounced endothermic peak at
718 °C, which is related to the onset of the graphitization process. This peak could
only be detected in the FeCl 3 impregnated sample, demonstrating the effect of FeCl 3
on the graphitization process. Figure 7.4.d shows the Raman spectra of the samples produced at different temperatures. The progress of the graphitization is evident
based on the increase of the relative intensity of the G band.
In this research, the graphitization occurred was related to the catalytic effect
of Fe leading to the formation of Fe X C Y droplets from which graphitic structures
115
materials [36]. Furthermore, the inorganic impurities can act as the oxidation catalyst, promoting the thermal degradation, and decreasing the oxidation temperature
of carbon materials [37–39].
Further information can be obtained from the SEM morphology of the carbon
materials shown in Fig. 7.3b–d. The carbon material produced at 620 °C (Fig. 7.3b)
comprises of large particles up to several hundred micrometers with irregular shapes
and sharp edges. Moreover, despite the fact that the material has been heated in air, the
SEM micrograph does not show any sign of oxidation, indicating the high oxidation
resistance of the carbon material. The C:O atomic ratio of the sample was recorded
to be 5.2 by EDX analysis, which is considerably greater than that of crystallized
PET (1.8). Nevertheless, the oxygen content of the sample is still remarkable, and
this can be a barrier toward further graphitization of the carbon material.
Overall, the carbon material produced at 850 °C (Fig. 7.3c, d) possesses approximately the same morphological features as that of the carbon material produced at
620 °C. The presence of irregular-shaped large particles is evident from the micrograph. Furthermore, small surface pitting holes can also be observed from the higher
magnification of Fig. 7.3d, which is an indication of the initial stage of oxidation. It
was observed that the carbon material is completely oxidized into gaseous species at
the higher heat treatment temperature of 1100 °C. Nevertheless, the thermal analysis
results presented in Fig. 7.2 and SEM micrographs of Fig. 7.3 demonstrate that the
amorphous carbon driven from PET has a very high oxidation resistance up to temperatures as high as 900 °C. This characteristic can be assigned to the large particle
sizes, high purity, low porosity and the low density of surface defects in PET-derived
amorphous carbon materials [24].
As discussed, the endothermic peak observed at 791.2 °C in the DSC thermogram
of Fig. 7.2 is attributed to the onset of the graphitization occurred in the PET-derived
turbostratic carbon. Gutiérrez-Pardo et al. [40] have reported the development of
graphitic structures upon pyrolysis of wood impregnated with FeCl 3 at temperatures
as high as 1000–1600 °C. For this, wood samples were impregnated with 3 M FeCl 3
solution in isopropanol in vacuum for 2 h to ensure the complete filling of the pores.
The pyrolysis process took place by heating of impregnated samples in a flow of
nitrogen to a maximum temperature in the range 1000–1600 °C. After pyrolysis, the
residual iron was removed by stirring in concentrated HNO 3 [40]. Figures 7.4a and b
show the SEM and TEM micrographs of the sample produced at 1600 °C, respectively, representing a porous carbon structure with a BET surface area of about
167 m
2 g
−1 . Figure 7.4c shows the heat flow versus temperature during pyrolysis of
the impregnated wood, and also that without impregnation with FeCl 3 (black line).
The DSC curve of the impregnated sample shows a pronounced endothermic peak at
718 °C, which is related to the onset of the graphitization process. This peak could
only be detected in the FeCl 3 impregnated sample, demonstrating the effect of FeCl 3
on the graphitization process. Figure 7.4.d shows the Raman spectra of the samples produced at different temperatures. The progress of the graphitization is evident
based on the increase of the relative intensity of the G band.
In this research, the graphitization occurred was related to the catalytic effect
of Fe leading to the formation of Fe X C Y droplets from which graphitic structures