Structural evolution during combustion of carbon nanoparticles generated by spark discharge

Abstract

The oxidation behaviour of carbon nanoparticles generated by electrical discharge between two graphite electrodes (commonly referred to as spark discharge soot, SDS) is investigated and compared to that of nanoparticles originating from the incomplete combustion of organic fuels. Soot generated via a Combustion Aerosol Standard (CAST) soot generator and carbon black (CB) samples are taken as reference materials for the latter. By changing the carrier gas composition of the spark generator, carbon particles with varying reactivity and nanostructure can be obtained. SDS nanoparticles are considerably smaller, have much higher specific surface areas, and display a distinct nanostructure arrangement compared to CAST soot and CB. The evolution of the surface area with the extent of oxidation is tracked, showing that the surface area development of SDS is fundamentally different from that of CAST soot and CB. While the latter shows an extreme increase in the specific surface area during combustion, in comparison, the specific surface area increase of SDS is marginal. This information is crucial for anticipating the specific surface area gain achievable through partial oxidation, based on the initial morphology of the carbonaceous particles. The reactivity was found to correlate with Raman features. When analysing the evolution of the Raman spectra with oxidation, more reactive SDS showed a substantial increase in nanostructure order compared to the less reactive SDS and CAST soot.