Effect of Graphene and MoS₂ Flakes in Industrial Oils to Enhance Lubrication

Abstract

Tribological studies of the 2D nanoadditives such as MoS2 and graphene are mostly performed in base oils such as SN500, SN150, or paraffin. We have focused on their effect in lubrication properties of industrial oils (e.g., axle, transmission, and compressor oils) along with SN500 oil employing a four-ball tester. Two types of graphene powders (GpowA with fewer defects than GpowC), MoS2 powder, and their physical mixtures are chosen as nanoadditives. The tribology performance for 0.05 wt% of additives in various industrial oils is evaluated by monitoring the coefficient of friction (COF) during rubbing and wear scar diameter (WSD) of the steel balls after rubbing. Elemental analysis and electron microscopy have been performed on the wear surfaces for evidence of any tribofilm formation. GpowA favors antifriction for axle and transmission oils with 40% reduction in axle oil, whereas it improved antiwear properties in most of the oils. GpowC shows a COF decrement by 12% only for compressor oil, but contribute to wear reduction in all oils. The observed COF reduction is attributed to the compatibility of nonfunctionalized GpowA with nonpolar axle oil and functionalized GpowC with polar compressor oil. MoS2 shows a decrease in the COF and WSD in most industrial oils; the best being 60% COF and 7% WSD reduction in axle oil. For additives in oils that favor antiwear, flakes or particles are observed on the wear surface supported by the higher elemental contribution of the constituents from the wear region. The mixtures of GpowA or C with MoS2, however, does not seem to favor improvement in the COF or WSD in industrial oils. With assistance from oleylamine surfactants, the lubrication properties of most additives are improved, particularly for the mixtures with 12–15% COF reduction and 4–7% WSD reduction in compressor oil. The study indicates that a large sheet size of high-quality graphene aids antifriction and addition of surfactant molecules facilitates a co-operative effect between MoS2 and graphene for improved tribology.

Structural-Defect-Mediated Grafting of Alkylamine on Few-Layer MoS2 and Its Potential for Enhancement of Tribological Properties

“…However, in the presence of MoS 2 –ODA, the coefficient of friction gradually decreased for the initial 10 min and then stabilized with no further changes (Figure b). Over the recent past, MoS 2 in variable shapes, viz ., nanosheets, nanoparticles, and nanovesicles, was demonstrated as an additive to different lube oils such as SN-500 mineral oil, liquid paraffin, and rapeseed oil for enhancement of tribological properties. − These dispersions (0.05–2 wt %) reduced the friction between the steel tribo-pair in the range of 15–45% (Table ). Herein, a minute dose of MoS 2 –ODA (0.01 wt %) decreased the friction by 48%, a significantly improved frictional property than the reported performance of MoS 2 . − The dangling sulfur atoms at outer layers of MoS 2 showed good affinity with the iron surface and formed a MoS 2 -derived tribo-chemical thin film .…”

In Situ Study of Structure–Activity Relationship between Structure and Tribological Properties of Bulk Layered Materials by Four-Ball Friction Tester

“…Among these wear scars, those of h-BN and WS 2 exhibit a deeper and wider wear region (Figure B,C) than those of graphite and MoS 2 (Figure A,D). For MoS 2 , the abundant active elements such as Mo and S play an important role in reducing the wear and increasing the load capacity. , However, the worn surface of graphite shows smaller wear, which is ascribed to the flexible layered graphite filling the worn grooves by exfoliating off few graphene nanosheets and forming stable transfer films on the worn surface. − Therefore, it can be inferred that the relationship between the structural evolution and friction performance can be revealed by studying the materials before and after ball-milling.…”

“…The two-dimensional (2D) layered materials as lubricant additives were capable of forming protective films or sliding layers on the contact surface, which were very effective in reducing friction and wear . Lately, the bulk layered materials (e.g., graphite, MoS 2 , WS 2 , and h-BN) have extensively been used as lubrication additives to improve the friction and wear properties of lubricants. , Due to the intrinsically low friction properties of the 2D layered nanosheet structures, they were desirable in many engineering applications, where friction coefficients were reduced to 0.07–0.27. − The proposed mechanism of the friction-reducing performance, which has been revealed to be a result of a durable boundary film on the rubbing surfaces to prevent metal-to-metal contact, relied on sliding between the layers because of weak van der Waals forces. − Consequently, the structure of 2D layered nanosheets played an intriguing role in the lubrication properties, , thus accounting for an unknown relationship between the structure and friction properties. , …”

MoS2‐Functionalized Graphene Composites—Potential Replacement for Lubricant Friction Modifier and Anti‐Wear Additives

“…The highest reduction in WSD with the addition of GpowA‐MoS 2 in SN500 oil was 55%, and there was no improvement in WSD reduction with the GpowA–MoS 2 in compressor oil. [ 8 ] Gong et al reported that at room temperature (50 N load) the average wear reduction of 50% was obtained by adding 0.5 wt% MoS 2 /Gr to the pure oil. [ 9 ] Addition of rGO‐MoS 2 at optimum 2.0 wt% with applied load 10 N can reduce the friction to μ ~ 0.2, [ 10 ] and an extremely high reduction of friction by 80% also can be observed with MoS 2 /rGO under applied load of 5 N. [ 11 ]…”