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According to the redox ability of dopamine in a weak alkaline environment, silver nanoparticles were uniformly loaded on the surface of polydopamine-modified graphene oxide (Ag/PGO). The results show that the base oil containing Ag/PGO nanoparticles exhibits a better tribological property than base oil. The maximum decrease in wear rate and friction coefficient at different temperatures amounted to 68% and 53.6%, respectively. The tribofilm containing C, O, N, and Ag exists and plays an important role in reducing friction and increasing wear resistance. Molecular dynamics simulations show that the microscopic oil film composed of Ag/PGO and n-hexadecane has low shear deformation during the shearing process, and the oil film has low interaction energy with the upper and lower shear walls. [ABSTRACT FROM AUTHOR]

Graphene has attracted attention in the field of lubrication based on its excellent properties. However, the difficulty of graphene dispersion in base oil hinders its development. In this paper, the effects of ionic liquid as additives on the dispersion and lubricating properties of graphene lubricants were investigated. Results showed that after adding ionic liquid, the graphene could be still stably dispersed in base oil even after 30 days. Molecular simulation study showed that ionic liquid tended to insert into graphene layers, and promoted the affinity of graphene and base oil. Then, the tribological friction behaviour of ionic liquid/graphene lubricants was investigated by concentration of ionic liquid, applied load and sliding velocity. Results showed that the friction and wear property was improved better after adding ionic liquid. This work provides a new method to enhance the stability of the graphene lubricating oil, and thus broaden the graphene in tribological application. [ABSTRACT FROM AUTHOR]

Abstract: The zinc perrhenate used as oil additive was synthesised via aqua‐solution method and was dispersed into pentaerythritol ester with the surface‐active agents. The tribological properties of lubricants were examined by 4‐ball tester and ball‐on‐disc testing machine. Additional investigations were performed using XRD, XPS, SEM‐EDS, and DTA/TG to probe the possible lubricating mechanism. Four‐ball test results showed compared to base oil, the friction coefficient and wear scar diameter of oil with zinc perrhenate additive were reduced by 14.9% and 16.6%, suggesting that zinc perrhenate additive could improve the lubricating property of base oil under 4‐ball test condition. Frictional tests under a wide temperature range indicated that oil with zinc perrhenate additive exhibited friction‐reducing performance during elevated temperature process because of its intrinsic shear susceptible property and could form a protective layer with native oxides of the disc sample at the interface, thus significantly minimised friction. [ABSTRACT FROM AUTHOR]

Barium perrhenate [Ba(ReO4)2], a compound used as an oil additive, was synthesized via the aqua-solution method. Its tribological properties were examined using the four-ball test and ball-on-disc tribotester in a wide temperature range and compared with those of oil that contained the additive molybdenum disulfide (MoS2) and calcium carbonate (CaCO3) compound. X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and differential thermal analysis/thermogravimetry were performed to determine the possible mechanism of the antifriction behavior of the lubricants. Results of the four-ball test showed that all of the additives can improve the extreme pressure property of the base oil and decrease the wear scar diameters of low-carbon steel balls. The results of the ball-on-disc test suggested that the MoS2 additive exhibited better lubrication property than the Ba(ReO4)2 and CaCO3 additives at below 450°C. The CaCO3 additive displayed moderate performance in friction reducing in the high-temperature period. The Ba(ReO4)2 additive exhibited preferable comprehensive antifriction performance in a wide temperature range because of its intrinsic shear-susceptible property and crystalline change with varied temperatures, which could form a protective layer with some native oxides of the disc sample and thus effectively prevented direct contact between rubbing parts. The detailed friction-reducing mechanism of the three additives is also discussed. [ABSTRACT FROM AUTHOR]

The perrhenates of calcium, copper and lead used as oil additive were synthesised by using the aqueous solution method. The tribological properties of these perrhenates were examined by using a ball-on-disc tribotester during a wide temperature range and a four-ball testing machine at room temperature. The four-ball test results showed that all synthesised perrhenates presented good extreme pressure property to a certain degree and demonstrated satisfactory wear resistance at room temperature. The ball-on-disc experiment results showed that the base oil with perrhenate additives significantly decreased friction and wear compared with pure base oil at elevated temperatures. An antifriction and low-shear layer was verified to form on sample surface after testing under high temperature. This layer effectively prevented the direct contact of sliding surfaces and decreased the friction coefficient. The antifriction behaviour of perrhenates implied that they could be developed as the candidate of oil additives for a hybrid lubricating mode. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Magnesium perrhenate used as a lubricating additive was prepared by an aqueous solution method in this paper, and was suspended in a base oil poly alpha olefin (PAO6) with the aid of surface active agents (SA). The thermal stability of the mixed oil with/without magnesium perrhenate and surface active agents was investigated by thermogravimetry testing. The influences of magnesium perrhenate as solid lubricating additive on the extreme pressure performance and the friction-reducing properties over a wide temperature range of the mixed lubricants were determined by four-ball tests and ball-on-disc frictional tests for the commercially available silicon nitride ball and a Ni-base superalloy frictional pair. The results revealed that the added magnesium perrhenate did not obviously affect the thermostability and oxidation resistance of the base oil. Meanwhile, it minimized the coefficients of friction and wear scar diameter to a certain extent in the four-ball experimental conditions. Ball-on-disc rubbing tests suggested the mixed oil had a similar lubricating performance to the base oil below the decomposition temperature point. The most significant advancement was the impressive antifriction improvement at the high temperature range, while the friction coefficients of the oil containing magnesium perrhenate compound were obviously below that of the base stock. This better tribological performance of the mixed lubricant was attributed to the native shear susceptible property and chemical stability of magnesium perrhenate under high temperature conditions, which could form an effective durable and stable antifriction layer with the oxides from the superalloy matrix, thereby decreasing the friction in the high-temperature environment. [ABSTRACT FROM AUTHOR]