Nanocarbon materials are being considered for applications in a wide range of fields with highly controllable microstructures. Fullerenes, carbon nanotubes, and graphene, which are based on graphite structures, are expected to have low-friction properties,besides functional nanosized shape worked at narrow friction interface. In this review, the inherent lubrication property of carbon-based nanomaterials will be introduced. As a case study, graphene oxide, which has revealed a new friction mechanism, will be discussed regarding the functional frictional motions at the friction interface, such as when added to lubricating oil.

Since 2000, advancements in nanoparticle production have led to increased research on the effects of adding various nanoparticles to lubricants, such as metals, oxides, nitrides, sulfides, carbides, nanodiamonds, graphene, and fullerenes. These studies highlight the benefits of reduced friction and improved wear resistance. Unlike DLC coatings, which only cover specific parts, nanoparticles work across all lubricated components, offering broader impact. This report examines the mechanisms of friction reduction by carbon-based nanoparticles under mixed lubrication conditions. Key requirements include the generation and detachment cycles of functional groups on nanoparticles, appropriate lubrication conditions, and the maintenance of nanoparticle dispersion. Experiments have confirmed that these factors are crucial for effective friction reduction.

Tribological behavior of graphene and modified graphene systems are analyzed by molecular simulations. First, the origin of kinetic friction in atomistic level is briefly explained. The mechanism of low friction of graphite is explained by thermal escape motion of graphene transfer layer. Then the friction simulation of graphene as solid lubricant vertically buried into iron contact surface is introduced. As an application, molecular simulation of solid lubricants of combined graphene and iron nanoparticles is then introduced. Finaly, the shear simulation of graphene oxide is introduced. In each case, low friction mechanism is explained by the dynamics of hole sheet, surface coverage, and the atomistic contact such as commensurate and incommensurate contact.

Recently, cellulose nanofibers (CNFs) have been developed as biomass industrial materials. CNFs have already been applied to applications such as sensor technology, cosmetics, catalysis, energy production, water remediation, near-paper industry, petroleum industry and applications, and medicine. This interpretive article focuses on the research trends of concentrated CNF moldings,which are CNF-rich gel and plastic materials. In this interpretive article, the author especially shows the recent research topics related to concentrated CNF moldings in tribological fields.

Cellulose nanofibers (CNFs) are attracting as an eco-friendly new material. One of the functions of CNFs as an aqueous additive is rheology controlling with the network structure. CNFs can stabilize fine particles and form sprayable gels. CNFs has also emulsifying ability. CNFs can form oil in water emulsion (Pickering emulsion) by absorbing onto the surface of oil droplets thermodynamically. Third, CNFs can disperse hydrophobic particles in water. CNFs improve wettability and dispersibility of the particles by adsorbing its surface. CNFs are already applied to various fields, such as cosmetics, paints, inks, and ceramics with these unique properties.

Since carbon coating on inorganic particles by the vapor-phase coating method is difficult due to particle agglomeration, liquid-phase coating for uniform coating has been desired. Considering uniform carbon coating on inorganic particles by liquid-phase method, it was needed to be mixed in a state where the particles are well dispersed in the solvent and the nanocarbon material is dissolved in the solvent. However, nanocarbon materials are inherently insoluble, and it was needed to create nanocarbon materials that could be soluble in solvents. By studying the carbonization of various oxygen-containing compounds, we found that the carbon materials synthesized from phloroglucinol could be soluble in organic solvents. Uniform carbon coating on inorganic particles was achieved by liquid-phase carbon coating using soluble carbon materials. This liquid-phase carbon coating could improve lubricity and wear inhibition to the silica particles, and fluidity to the stainless-steel particles. The addition of various functions to inorganic particles by liquid-phase carbon coating is expected to be applied in various fields.

New bearing units having lubricant supply structure were devised for realizing longer lifetime and better performance of rotation mechanisms of space machineries. The spacer sandwiched by two bearings was filled with grease and porous body was established between grease and the bearing for both preventing thickener transferred into bearings and supplying only oil for bearings. The oil supply function was verified by friction tests and bearing tests using fluorescent agent. The contribution for long lifetime of the oil supply system was confirmed by the lifetime tests under a vacuum which showed stable rotation for 2×10⁸ revolutions at a room temperature and 1×10⁹ revolutions at a temperature of 60℃. Moreover, large size bearing units with the oil supply structure were evaluated under high rotation speed for utilized in larger spacecraft requiring larger attitude control torque and observation systems requiring agile attitude control. Using larger size bearings and rotating with higher speed would cause to promote oil scattering by centrifugal force and oil evaporation by temperature rise, whereas the oil supply structure was conducted the feasibility to realize both larger size bearings, higher rotation speed, longer lifetime and low torque.