# Effect of Fuel Composition on Carbon Black Formation Pathways
## 3 Results and Discussion
### Carbon Black Formation--Dependence upon Fuel Compositional Differences
#### 3.5.2 FCC-CB  
FCC decant oil consists of higher paraffinic content such as branched compounds, alkylated aromatics, and waxes. The lower aromatic concentration delays inception by fuel-carried aromatic radical condensation. A contributing factor is radical capping by the saturate derived H-atoms and alkyl radicals plus radical termination by H-abstraction reactions from saturates. By this combination of physical dilution and radical termination reactions, particle inception and growth are delayed by the time required to reach sufficient aromatic concentrations for particle inception and growth. The kinetic time delay (\(\tau\)) for pyrolysis reactions and subsequent aromatic buildup allows turbulence induced mixing to lower the feed concentration (by mixing with surrounding post-combustion gases) while simultaneously increasing the temperature. The net result is that smaller species (e.g., acetylene) contribute to early particle growth under higher temperature conditions than the aforementioned processes (early growth) of reactive coalescence and surface condensation of PAHs as for CT. More ordered lamellae form--beginning upon particle inception. A higher sp\({}^{2}\)/sp\({}^{3}\) ratio results. More consistent chemical (aka growth species) and temperature environment produces primary particles with greater radial uniformity of nanostructure--as seen in Figures 2 and 3. Primary particles exhibit a single nucleus--as observed in Figures 2 and 3.  
Nanostructure Inferences Reconciled Using Oxidative Thermal Treatment on CT- and FCC-Carbon Black Nanostructure  
CT- and FCC-CB were treated isothermally at 500 \({}^{\circ}\)C in a TGA until a 50% weight loss was observed. Trends of weight loss and its derivative curve smoothed with respect to time are shown in Figure 6.  
Figure 6: TGA (**A**) weight and (**B**) derivative weight analysis for CT- and FCC-CB.  
TGA weight loss under isothermal (500 \({}^{\circ}\)C) conditions in air shows the CT-CB to lose more mass relative to the FCC-CB. This is better illustrated in their derivative plots, where the percent mass lost by CT-CB increases with heat treatment time and percent burn-out. This agrees with the disordered nanostructure of CT-CB resulting in lamellae break up, creation of edge sites, and material lost to oxidation, while the longer peripheral lamellae in FCC-CB resist thermal oxidation relative to CT-CB. TEM for both partially oxidized samples supports this interpretation.  
Figure 7 shows overview TEM micrographs of the two carbon blacks and Figure 8 shows HRTEM micrographs with arrows pointing towards crumbling particles in Figure 8A,B for CT-CB, while Figure 8C,D show hollowed out intact shells of FCC-CB black.  
The prevalent radial disorder within the particles of CT-CB black results in the lamellae reacting with the available oxygen. The preferential and faster oxidation is consistent with disordered, shorter lamellae comprising the particle perimeter. Such lamellae expose reactive edge sites. Without stable lamellae to support the shell, particle breakup results. On the other hand, FCC-CB shows a hollowed-out interior with a stable shell at the prevalent temperature. The more reactive carbon within the particle's core has preferentially oxidized, while the more stable carbon lamellae at the perimeter have partially annealed. This behavior has previously been observed for carbon blacks isothermally oxidized at temperatures of \(\sim\)500 \({}^{\circ}\)C [39] and indicates a significant difference in the C-C bonding chemistry between the CT- and FCC-CB blacks.  
Figure 7: TEM micrographs showing an aggregate of (**A**) CT- and (**B**) FCC-CB black after isothermal treatment in a TGA.