Activated carbons are commonly used for adsorption/depollution applications, but only a few studies are related to their lubricating properties. In order to investigate a new family of friction reducers, the tribological properties of biochars and derived activated carbons obtained from sugar cane bagasse are investigated. Activated carbons are obtained from either a physical (steam water) or chemical (with phosphoric acid) activation process. The tribological tests show that the activated carbons present very low friction coefficients, close to 0.08. The correlation of textural and tribological investigations shows that the specific surface area of the compounds as well as the microporous and mesoporous domain extensions are key parameters to optimize the friction reduction properties of activated carbons. The friction properties of the compounds are improved if the mesoporous domain extension is above 40% of the total porous volume. This study shows that local biomass waste valorization is possible and that sugar cane bagasse-derived activated carbons appear as interesting new friction reduction additives for lubricants.

This article focused on the effects of the presence of liquid on tribological performances of graphite and hexagonal boron nitride (hBN) particles at ambient atmosphere. Two tribological tests conditions have been evaluated with AISI 52100 steel materials. In dry conditions for lubrication tests with pure particles and liquid conditions a drop of liquid is added before or during the friction tests. In dry conditions, graphite and hBN have two different tribological performances, while whatever was the type of liquid in liquid conditions, they are similar: μpure graphite ≈ 0.09 and μpure hBN ≈ 0.42, while μgraphite+liquid ≈ μhBN+liquid ≈ 0.06. Raman spectroscopy and scanning electron microscopy (SEM) investigations bring out weak influence of sliding mechanical constraints for tribofilms built in the presence of the liquid. Different hypotheses have been investigated; tribo-intercalation, influence of adsorption, lubrication by hydrogen, and action of the liquid. The simultaneous presence of liquid and particles induces friction mechanism inside the tribofilm reducing friction due to its nanostructuration.