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Spheroidal carbon particles are touted as excellent additives in lubricants for reduction in friction and wear. Herein 50–100 nm-sized spheroidal carbon soot particles with heliocentric graphitic layers are prepared by controlled decomposition of wasted rubber and subsequent heat-treatment of wasted rubber derived soot. Thermogravimetric analysis showed that the on-set degradation temperature of the soot particles was representative of a material constituted by amorphous and crystalline phases complementing well with x-ray diffraction studies. The soot particles are dispersed in an additive-free base oil (BO), and the soot particles added oil was used as a lubricant. At room temperature, a reduction in coefficient of friction (CoF) and wear scar diameter (WSD) of ~9% and 16.55% were recorded. At a higher temperature of 70 °C, a reduction in CoF and WSD of as high as 48.93% and 28.12% were recorded. Based on the observations, it is theorized that the soot particles acted like nano-bearings between the contacting surfaces producing a rolling effect that efficiently reduced friction and wear concerning the contacting surfaces. Also, the dispersion of soot particles improved the viscosity retention of BO at higher temperatures indicating its multifunctional ability. [Display omitted] • 50–100 nm-sized carbon soot particles with sphere-like morphology are prepared from wasted rubber. • Heliocentric graphitic layers constituted the soot particles. • The carbon soot particles had a mixture of crystalline and amorphous characteristics. • The carbon soot particles are dispersed in an additive-free Group-2 dewaxed lubricating oil. • Carbon soot particles are an excellent additive in lubricating oil for considerable friction and wear reduction. [ABSTRACT FROM AUTHOR]

The prime objective of this study was to extend the application of graphene additive in oil solution via investigating the frictional interaction of graphene and ZDDP composite additives in point contact lubrication. Accordingly, 0.05 wt% graphene, 1 wt% ZDDP and their mixtures as additives were added into PAO4 base oil. The ball-on-disk reciprocating experiments were carried out under the load of 30 N, 80 N, 155 N and 310 N. The tribological performance of the single system containing graphene and ZDDP were evaluated separately to compare the tribological property of the composite system containing graphene + ZDDP. The result revealed that the friction coefficient of the graphene/ZDDP composite system was slightly higher compared to PAO4 oil under high load. Whereas the composite system exhibited excellent wear resistance under all loads, reducing the wear rate by 77% in comparison to that of PAO4 oil under a load of 30 N. The reduction in wear is attributed to the formation of the graphene tribofilm and the protective polyphosphate film, which avoided the direct contact with the sliding surface and effectively inhibited the wear of steel materials. [Display omitted] • Graphene/ZDDP composite system shows excellent antiwear performance as a lubricant additive. • The composite system reduces the wear rate by around 77%. • The wear resistance of the composite system is superior to that of the single system under high contact stress. • The introduction of graphene exhibits no positive response to improve the high friction coefficient of ZDDP. [ABSTRACT FROM AUTHOR]