Dry tribology and nanomechanics of gaseous flame soot in comparison with carbon black and diesel soot

Abstract

Ethylene gas is burnt and the carbon soot particles are thermophoretically collected using a home-built equipment where the fuel air injection and intervention into the 7.5-cm long flame are controlled using three small pneumatic cylinders and computer-driven controllers. The physical and mechanical properties and tribological performance of the collected soot are compared with those of carbon black and diesel soot. The crystalline structures of the nanometric particles generated in the flame, as revealed by high-resolution transmission electron studies, are shown to vary from the flame root to the exhaust. As the particle journeys upwards the flame, through a purely amorphous coagulated phase at the burner nozzle, it leads to a well-defined crystalline phase shell in the mid-flame zone and to a disordered phase consisting of randomly distributed short-range crystalline order at the exhaust. In the mid-flame region, a large shell of radial-columnar order surrounds a dense amorphous core. The hardness and wear resistance as well as friction coefficient of the soot extracted from this zone are low. The mechanical properties characteristics of this zone may be attributed to microcrystalline slip. Moving towards the exhaust, the slip is inhibited and there is an increase in hardness and friction compared to those in the mid-flame zone. This study of the comparison of flame soot to carbon black and diesel soot is further extended to suggest a rationale based on additional physico-chemical study using micro-Raman spectroscopy.

Exploring the internal structure of soot particles using nanoindentation: A reactive molecular dynamics study

“…The particles have a 7 nm diameter and varying degrees of crosslinking. The particles exhibit elastoplastic behaviour as in previous nanoindentation experiments [39,37,38]. It can be observed that the maximum load and the slope of the curves increases with the degree of crosslinking in the particle.…”

“…Nanocrystalline graphite is a noncrosslinked structure made of mobile graphene sheets, possessing very low hardness values (0.1-0.4 GPa) [36]. In contrast, soot shows hardness values of 2-8 GPa [37,38,39,40], values closer to a hard crosslinked structure such as charcoal (3-5 GPa) [41]. The wide range found for soot hardness suggests that particles collected at different residence times and produced in different combustion environments may be characterised by different structural properties.…”

Guest Editorial

“…The final paper in this special issue on Advanced Materials Engineering is entitled ''Dry tribology and nanomechanics of gaseous flame soot in comparison with carbon black and diesel soot'' [11]. It is from an Indian research group and deals with carbon soot particles that are collected thermophoretically from burning ethylene gas.…”