Carbon black (CB) is used in lubrication research as a surrogate for soot, often with apparently contradicting findings, which may be explained by differences in particle characteristics. Here, three commercial carbon blacks (MogulL, Monarch 430, and Vulcan XC-72R) were extensively characterised. Particle sizes were measured using transmission electron microscopy, 3D reconstructions were obtained by electron tomography, microstructures were probed by fringe analysis, and chemical compositions were evaluated by X-ray photoelectron spectroscopy. Additionally, a high-frequency reciprocating rig tribometer was used to assess wear, friction, and boundary film coverage of CB-doped lubricating oils (0. 05-2. 5wt. %). Significant differences in primary particle size were observed, with Vulcan exhibiting larger particles (up to 60 nm) and a more diverse morphology than the other samples (10-40 nm). The pronounced graphitic nature of Vulcan, with the longest and flattest carbon lamellae, was confirmed by fringe analysis. Comparable carbon content (>96%) was found in all samples, with traces of surface oxygen (1wt. %). Variations in surface-to-volume ratio, 3D circularity, and carbon organization suggest different oxidation tendencies. Tribological tests revealed that wear, which always increased with CB concentration, varied significantly between CBs, with Mogul showing the least wear, followed by Vulcan and Monarch. The differences in wear outcomes could be attributed to 3D morphology and surface roughness of the three CBs. Monarch 430 appears to have rigid abrasive globular shape aggregates, while Vulcan XC-72R's branched structures could enhance oil entrainment, reducing abrasiveness. The small-scale roughness of Mogul L aggregates seems to allow for an effective oil film stability and reduced wear volumes. • Three carbon blacks used as a soot surrogate in tribological studies have been investigated. • TEM analysis showed particle sizes from 10-60 nm, with Vulcan being most diverse. • Vulcan exhibited higher graphitic character and larger particles than other samples. • Tribological tests revealed wear increased with carbon black concentration. • Mogul showed the least wear, followed by Vulcan; Monarch had the most wear.
Pacino et al. (Fri,) studied this question.