In this study, the tribological behavior of both liquid (oil) and semi-liquid (grease) lubricants enhanced by multilayer graphene nano platelets and titanium dioxide nano powder was evaluated using ball-on-disk and shaft-on-plate tribo-meters. Oil samples for both 2D graphene nano platelets (GNP) and titanium nanopowders (TiNP) were prepared at three concentrations of 0.01 %w/w, 0.05 %w/w and 0.1 %w/w. In addition, 0.05% w/w mixtures of GNP and TiNP were prepared with three different ratios to analyze collective effects of both nano additives on friction and wear properties. For semi-liquid lubricants, 0.5% w/w concentrations were prepared for both nano additives for shaft-on-plate tests. Viscosity and oxidation stability tests were conducted on the liquid-base lubricants. Nano powders of both additive and substrate were analyzed using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). In addition, Raman spectroscopy was conducted to characterize the graphene and titanium dioxide. The study shows that adding graphene and titanium dioxide individually sacrifices either the wear or friction of lubricants. However, use of both additives together can enhance friction resistance and wear preventive properties of a liquid lubricant significantly. For a semi-liquid lubricant, the use of both additives together and individually reduces friction compared to base grease.
In this study, the tribological effects of three different forms of reduced graphene oxide (rGO)-2D nano-additives in base oil were investigated. Reduced graphene oxide nanoplatelets were manufactured using a modified Hummers’ method. However, different filtration methods were used to obtain rGO nanoplatelets at three different bulk densities. After adding nano-additives to the base oil at 0.01%w/w concentration, physical and chemical characterization tests were performed such as viscosity test, four-ball wear test, rotating pressure vessel oxidation test (RPVOT), resistivity test and friction coefficient test. The presented results show that material-1 with the lowest bulk density and less lattice defect can perform better by reducing wear of the material by 10.63% as well as the coefficient of friction (COF) by 6.3% with respect to the base oil and under test conditions. The presented results show the promising effect of rGO as nano-additives to fluid lubricants on wear preventive properties without compromising the physical and chemical characteristics of the lubricants.
In this study, reduced graphene oxide (rGO) nano platelets were used as an additive to enhance friction and wear properties of oil-based lubricants by preparing three samples at 0.01% w/w, 0.05% w/w, and 0.1% w/w concentrations. To analyze the direct effect of rGO nano platelets on tribological properties, 99.9% pure oil was used as a liquid lubricant. A comparative tribological study was done by performing a ball-on-disk wear test in situ under harsh conditions, which was further analyzed using a non-contact 3D optical profilometer. Morphological evaluation of the scar was done using transmission and scanning electron microscopy (TEM, SEM) at micro and nano levels. The lubricants' physical properties, such as viscosity and oxidation number, were evaluated and compared for all samples including pure oil (control sample) as per ASTM standards. Findings of all these tests show that adding rGO nano platelets at 0.05% w/w showed significant reduction in friction at high speed and in wear up to 51.85%, which is very promising for increasing the life span of moving surfaces in machinery. Oxidation and viscosity tests also proved that adding rGO nano platelets to all samples does not sacrifice the physical properties of the lubricant, while it improves friction and wear properties.Due to their widespread use in different fields, a great deal of research has been conducted to improve the manufacturing capabilities of carbon-based nanomaterials on wide-ranging characteristics that can be tuned for different applications. These characteristics are directly related to factors such as defects in crystalline structures, morphology and surface area, electrical and thermal conductivity, optical behavior, molecular specification, number of layers, and uniformity of the carbon-based nanomaterials [6].Graphene, one of the emerging carbon allotropes, has been shown to possess excellent mechanical, thermal, electrical, and optical properties. As a result, it has been used for numerous applications such as storing energy, electronics, opto-electronics, sensing applications, and many more [7][8][9][10][11][12][13][14]. Previous studies show that graphene particles can mitigate metal-to-metal contact and enhance wear behaviors of moving and mating parts. Graphene nano platelets with high surface areas have only a few layers (two to ten layers), and the weak van der Waals forces between these layers generate material lubricity, which can shear under the loading conditions [15]. However, low dispersibility of graphene in liquid-based lubricants is considered a main challenge. Because of their high surface area, graphene nano platelets can start conglomerating in the lubricant shortly after mixing with the liquid lubricants [16]. This problem can be resolved by using different surface modifications of the graphene particles; however, these modifications have high environmental and ecological costs.Graphene oxide (GO) is another carbon allotrope that has recently found more applications in different sectors including lubrications and tribo...
Graphene is one of the strongest allotropes in carbon family. Applications of graphene are found in many industries such as coating, sensors, electronics, light processing, energy, and environmental sectors. Myriad studies have proven that graphene has excellent tribological capabilities. In fact, multilayer structure of graphene allows layers to shear between the mating surfaces to reduce friction. In addition, its extensive mechanical properties allow graphene particles to work as nano bearings to mitigate metal-to-metal contact and reduce wear. In this study, graphene nano particles were evaluated at 1%w/w concentration using the lithium-base general purpose grease (NL-1), the water proof general purpose grease (NL-2) and the extreme pressure grease (NL-3). To characterize graphitic defects and topography of graphene platelets, micro-Raman spectroscopy and transmission electron microscopy (TEM) were utilized at high magnification. For tribological evaluation, shaft-on-plate tribometer was used to test grease at different loads and rotating speeds. The results show that all three nano greases have lower average friction coefficient (AFC) in comparison with control sample (pure grease). Among them, the water resistive grease (NL-2) has the best performance followed by the extreme pressure grease (NL-3) and the lithium based grease (NL-1) respectively.
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