Graphene and graphene-based materials are relatively novel 2D materials with great tribological potential. Graphene is inherently low-friction, very high stiffness, and its thermal conductivity may reduce friction and wear.
Terms * | Definitions * |
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Graphene Graphene layer Single-layer graphene Monolayer graphene |
A single layer of carbon atoms with each atom bound to three neighbors in a honeycomb structure. Can be abbreviated as 1LG to distinguish from bilayer graphene (2LG) and few-layer graphene (FLG). It has edges and can have defects and grain boundaries where the bonding is disrupted. |
Bilayer graphene 2LG |
Two-dimensional material consisting of two well-defined stacked graphene layers. |
Few-layer graphene FLG |
Two-dimensional material consisting of three to ten well-defined stacked graphene layers. |
Graphene nanoplate Graphene nanoplatelet GNP |
Nanoplate consisting of graphene layers. Typically have thicknesses of between 1 nm and 3 nm and lateral dimensions ranging from approximately 100 nm to 100 µm. |
Graphene oxide GO |
Chemically modified graphene prepared by oxidation and exfoliation of graphite, causing extensive oxidative modification of the basal plane. Graphene oxide is a single-layer material with a high oxygen content, typically characterized by C/O atomic ratios of approximately 2, depending on the method of synthesis. The functional groups found include hydroxyl (OH), carboxyl (COOH), and epoxide (COC). ** |
Reduced graphene oxide rGO |
Reduced oxygen content for graphene oxide. If graphene oxide was fully reduced, then graphene would be the product. However, in practice, some oxygen-containing functional groups remain and not all sp3 bonds will return back to the sp2 configuration. Different reducing agents will lead to different carbon-to-oxygen ratios and different chemical compositions in reduced graphene oxide. It can take the form of several morphological variations such as platelets and worm-like structures. |
Carbon NanoTubes (CNTs) | Carbon with a diameter of nanometers and a length of micrometers (where the length-to-diameter ratio exceeds 1000) |
Lubricant | Graphene Type | Graphene Concentration | Dispersion/Surfactant | Benefit | Prop. Mechanism | Ref. |
---|---|---|---|---|---|---|
PAO4 | 3 GnP: 300, 600 and 750 m2/g (<2 nm, 1–2 µm lateral size) | 0.5 wt% | none | Increased wear resistance and thermal conductivity, especially in electric conditions | [26] | |
SAE 5W-30 | Graphene nanosheets | 0.03, 0.20, 0.40 and 0.6 wt% | Oleic acid | Lower friction and wear. Significant fuel saving | Tribofilm (self-healing) | [27] |
SAE 5W-30 | Powder (1.3 nm thick) and graphene nanoplates | 0.03 to 0.15 wt% | N-dimethylformamide | 15% lower wear, 35% lower friction. 77% higher TC, 30% viscosity | tribofilm | [28] |
HDD CH-4 20W-50 | Commercial N002-PDR | 0.5 to 3.0% | Lipophilic polymer, WinSperse 6020 | 20% higher TC | thermal | [29] |
SN-500 base oil | GO nanosheets | 0.02, 0.04, 0.06, 0.8 wt% | none | Reduced friction and wear on four-ball | Protective film | [30] |
SN-150 base oil | GO functionalized with DtBHBA | 0.2 to 0.8 mg/mL | none | 40% lower CoF, 17% lower wear under rolling conditions | tribofilm | [9] |
PAO 06 | GN and fluorinated graphene (FGN) | 0.005 to 0.020 wt% | T161 | Reduced friction | tribofilm | [31] |
Engine oil | Graphene and GO | 0.02 to 0.06 mg/mL | none | Reduced friction | Mending and tribofilm | [32] |
20W-50 | MWCNT, Graphene Nanosheets, C nanoballs, and Fullerene Nanoparticles (C60) | 0.1 and 0.2% | 10% higher TC with C nanoballs | thermal | [33] | |
Mineral oil | GNS (grade C-750, 900, 407 Sigma Aldrich (St. Louis, MO, USA), <2 µm size) | 0.1, 0.5, 1.0 wt% | not informed | Reduced wear | [34] | |
GL-4EP90 (degraded) | Graphite, Graphene and [34] | Respectively 0.5, 0.5, 0.15 wt% | SiO2 for the GO, No dispersants | 16% lower wear | tribofilm | [35] |
500N base oil | Expanded graphite and Potassium Borate | 0.03, 0.05, 0.10 wt% | - | 30% lower CoF, 36% lower wear | TC and Tribofilm | [36] |
Group lll base oil | Functionalized graphene (AGO-C(n)) | 0.005, 0.01, 0.02 wt% | - | 22% lower CoF with 0.01 wt% | tribofilm | [37] |
5W-40 synthetic oil | RGO | 0.01 to 0.2 wt% | none | 5% lower CoF, 3% lower wear | tribofilm | [38] |
PAO and PAO + additives | GN (3–8 layers) | 1 and 5% | tribofilm | [39] | ||
HD-50 oil | Modified GNP | 0.005–0.1 wt% | Oleic acid and sodium dodecyl presulfate | Up to 35% lower wear | tribofilm | [40] |
20W50 SN/CF and SJ/CF | Graphene, thickness 8, 12, and 60 nm thick. | 0.01% | none | 70% higher Thermal conductivity, reduced wear | Thermal | [41] |
Maritime engine oil | GO MXene-Nitrogen-doped | 0.01% | none | 7% oil thermo conductivity increase and reduced viscosity. | Thermal and Hydrodynamic | [42] |
SN 150 oil | GO nanosheets | 0.1 wt% | polyisobutenyl succinic acid-polyamine ester | Friction and wear reduction on boundary, mixed, and EHL lubricant regimes | tribofilm | [43] |
oil | G, rGO, MoS2, hBN | 0.4 wt% each and 0.2, 0.4 | None, stability improved by mixing process | Up 80% lower wear, 42% lower CoF | Filling and mending | [44] |
pure paraffin liquid (PL) oil and with commercial additives | Graphene layered nanosheets | 0.1 wt% | mono-dispersed in silver (Ag) nanospheres | Reduction of Friction 40% and 36% on wear | Roller bearing and protective film | [45] |
SAE 10W-30 | Gr by liquid exfoliation | 0.05 to 0.20 wt% | 40% lower CoF and 36% lower wear | Protective tribo film | [46] | |
PAO 10 | GO, rGO, and graphene-like covalent-organic frameworks (GCF) nano-sheets | 0.002 to 0.08 wt% | [47] | |||
Lubricant film | Graphene sheets | 0.02–0.06 wt% | The friction coefficient and wear scar diameter were reduced by 17% and 14%, respectively | [48] |
Grease | Graphene Type | Graphene Concentration | Dispersion/Surfactant | Benefit | Prop. Mechanism | Ref. |
---|---|---|---|---|---|---|
Bentone Grease | Multilayer Graphene | ? | ethanol | Higher dropping point. Lower wear and friction | tribofilm | [49] |
Grease | Graphene (C 94%, O 6%) | 1 to 4% | none | CoF and wear reduction. 55% increase in Thermal conductivity | [50] | |
Calcium grease | MWCNT and G nanosheets | 0.5, 1, 3 wt% | Up to 30% higher dropping point, 60% lower CoF, 74% lower wear | [51] | ||
Cheavy-duty lithium grease | rGO, graphite, and MWCNT | 0.5, 1, 2, 3.5, 5 wt% | Increase in Timken test LCC, lower wear, friction, and temperature on rolling bearing tests. Increase in vibration damping. | [52] | ||
Base oil | Mixture of single and multilayer | poly isobutylene succinic imide (PIBSI) based | Reduced wear and friction | Tribofilm and thermal | [53] | |
Lithium grease | 3D hierarchical porous Graphene | 0.1, 0.3 and 0.5 wt% | none | 52% lower wear, 20% lower friction | tribofilm | [54] |
group II-III base oil | 3 variants of rGO | 0.01 wt% | Reduced wear and friction | [55] | ||
Grease (and also as dry lubrication) | Graphene platelets, 2, 6–8, 11–15 nm | 1 wt% | Reduced friction and wear | tribofilm | [56] | |
Ca and Li greases | CNT | 7.5 wt% | MoS2 was also added to the grease | Reduced friction and wear | tribofilm | [57] |
commercial lithium grease, mineral oil | rGO | 0.2, 0.4, 0.6 wt% | toluene | CoF lower 30% for rolling, 20% for sliding-induced-rolling | tribofilm | [58] |
Li Grease | GN and Graphite | 0.2 to 2.0% | tribofilm | [59] | ||
Li-based grease | GN | 0.2 to 2.0% | Friction and wear reduction | Tribofilm and enhancement of FeO2 and LiO2 tribofilms | [60] | |
Lithium complex Grease | FLG | 0.5, 1.0 and 2.0 wt% | 52% lower wear and 20% lower CoF | Tribofilm and ordered state of the graphene sheets (Hydro?) | [61] | |
Polyurea Grease | FLG | 0.5, 1.0 and 2.0 wt% | Reduced wear and friction. Improved rheology | Tribofilm | [62] | |
Lithium hydroxide monohydrate, mineral oil (KN4010) | GFL 0.5 to 1.5 nm thick | 0.1, 0.5, 1.0 and 2.0 wt% | none | Reduced wear and friction. 1.6x higher welding point | [63] | |
Li grease | NanoCarbon and GNPs | 0.2 wt% | Proprietary | Reduced friction and wear | [64] |
This entry is adapted from the peer-reviewed paper 10.3390/eng4040157