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Graphene-based materials have great potential for tribological applications. Graphene's unique properties such as low shear resistance, high stiffness, and thermal conductivity make it an attractive material for improving the properties of lubricants in a wide range of industrial applications, from vehicles to house refrigerators and industrial machinery such as gearboxes, large compressors, etc. The current review aims to give an engineering perspective, attributing more importance to commercially available graphene and fully formulated lubricants instead of laboratory-scaled produced graphene and base oils without additives. The use of lubricants with graphene-based additives has produced e.g., an increase in mechanical efficiency, consequently reducing energy consumption and CO2 emissions by up to 20% for domestic refrigerators and up to 6% for ICE vehicles. Potential effects, other than purely friction reduction, contributing to such benefits are also briefly covered and discussed. [ABSTRACT FROM AUTHOR]

Grease‐lubricated sealing systems have an increased risk of starved lubrication. For this work, the lubricity of 23 greases in a rotary shaft sealing system was evaluated with a new test and evaluation method. The lubricity was then correlated with rheological and other grease properties. These grease properties are either available by the data sheet or can be measured with low effort. The results of the correlation allow a preselection of greases which are expected to lubricate rotary shaft seals well. This can support manufacturers and users in considering the lubrication of the sealing system early in the development process. [ABSTRACT FROM AUTHOR]

The review deals with the development of lubricants taking into account the requirements associated with the operation of modern electric vehicles and determined by the design features of both the vehicles themselves and their separate units. The scientific and technical literature concerning the development of lubricants for electric vehicles is analyzed. The base oils and functional additives that are used most frequently are indicated, and their advantages and drawbacks are discussed. Problems associated with the further development of basic and applied aspects of the modern lubricating materials science as applied to electric vehicles are considered. [ABSTRACT FROM AUTHOR]

The major trends in the development of grease products are described in an analysis of the relevant research and patent literature, including research on superalkaline calcium greases for heavilyloaded friction units and possible applications of nanoparticle additives to multifunctional greases. Developments in lowtemperature greases derived from biodegradable polyester bases and lubricants for electric car friction units are also examined. [ABSTRACT FROM AUTHOR]

The influence of polymer additive (polytetrafluoroethylene) in grease based on paraffin oil on the resistance to fatigue wear (pitting) was investigated of rolling contact. The research results revealed that grease containing a polymer caused an increase in resistance to fatigue. It was examined whether the additive affects the properties of the grease, including rheological (investigated with the use of rheometer operated in the cone/plate configuration) and thermal (determined using the Differential Scanning Calorimetry) to check their relationship with a resistance to fatigue. A scanning electron microscope equipped with an energy dispersive spectrometer was used to determine if a polymer was present on wear trace. Then the sources of chemical elements were analysed with the use of X‐ray photoelectron spectroscopy to explain the improvement of resistance to fatigue. The relation between rheological properties and resistance to fatigue was shown, and the presence of polymer in friction contact was observed. [ABSTRACT FROM AUTHOR]

The properties of lubricating grease fillers such as molybdenum disulfide, tungsten disulfide and graphite are described. Their influence on the tribotechnical properties of polyurea greases prepared with various dipersion media studied using a Brugger tribometer in accordance with DIN 513471:20000; an SRV-3 tribometer, in accordance with ASTM D5707. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to evaluate the influence of nanoparticles as an additive on the tribological properties of calcium grease. Design/methodology/approach: The nano additives in this research are with different concentration of multi carbon nanotubes (MWCNTs) and Talc powder (1, 2, 3, 3 and 5 per cent). The ratio of MWCNTs to Talc powder is 1:1. The tribological properties of hyper MWCNTs/Talc powder to calcium grease were evaluated using a pin-on-disk wear testing. The results show that the nano additives MWCNTs/Talc to calcium grease exhibit good performance in anti-wear and friction reduction. The action mechanism was estimated through analysis of the worm surface with x-ray diffraction and transmission electron microscope. Findings: The result indicates that boundary film mainly composed of MWCNT and Talc powder, and other organic compound was formed on the worm surface during the friction test. In addition, the wear rate and coefficient of friction of nanogreases have shown excellent improvement about 80.62 and 63.44 per cent, respectively, at 4 Wt.% of MWCNTs/Talc powder. Moreover, the thermal conductivity of nanogrease increased about 51.72 per cent. Originality/value: This study describes the inexpensive and simple fabrication of nanogrease for improving properties of lubricants, which improve power efficiency and extend lifetimes of mechanical equipment. [ABSTRACT FROM AUTHOR]

Colloidal stability of greases is one of the most important physicochemical parameters, which characterizes their working capacity and affects the mechanical strength and tribological properties. An integrated study of the colloidal stability of greases based on synthetic base oils with organic thickening agents demonstrated that the stability depends to a noticeable extent on quite a number of factors, such as the nature of a base oil and a thickening agent, presence of fillers, synthesis conditions, etc. A combination of these factors makes it possible to obtain greases with required colloidal stability. [ABSTRACT FROM AUTHOR]

A review of grease degradation mechanisms and existing grease models is presented, followed by a detailed thermodynamic analysis of grease degradation. Fundamental formulations are derived from thermodynamic laws and applied to instantaneous nonlinear response of grease to loading. The resulting model of grease degradation relates grease shear stress response to mechanical work, temperatures and environmental effects via the irreversible entropy generated by these dissipative interactions. The model is experimentally verified, and a universally consistent grease characterization methodology is described. A near 100% agreement between the grease model and nonlinear data from uncontrolled experimental measurements is achieved. The model also gives rise to new material and process parameters to characterize grease for performance and hence, system optimization. Image 1 • Fundamental irreversible thermodynamics is applied to grease degradation. • Degradation-Entropy Generation theorem is reviewed and further developed. • Instantaneous shear stress-based grease characterization model is formulated. • Methodology is demonstrated and experimental verified using nonlinear shearing. • Perfect fit between theoretical model and experimental data is observed ( R 2 = 1). [ABSTRACT FROM AUTHOR]

• Both ILs improved the antiwear performance of the anhydrous calcium-based grease. • [P 6,6,6,14 ][TCM] improved the friction reduction performance of both greases. • [P 6,6,6,14 ][TCM] improved the oxidation stability of both greases. • The ferrometric and the surface roughness results confirmed the wear results. Two phosphonium-derived ionic liquids: trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate (IL1) and trihexyltetradecylphosphonium tricyanomethanide (IL2) were used as additives in lithium complex- (G1) and anhydrous calcium-based (G2) greases at 5 wt%. Friction torque and wear tests were performed using a modified four-ball machine for testing rolling bearings in order to determine the friction and wear reducing properties of these grease samples in a real component. The IL2 improved the friction reduction performance of both greases, especially G1. Both ILs improved the antiwear behaviour of grease G2. Grease G2 showed higher oxidation and thermal ageing levels than G1, but the addition of the ILs, IL2 in particular, improved this issue. [ABSTRACT FROM AUTHOR]

This work investigates the effects on thermal transport and tribological performance of incorporating silicate particles – emulating pollutants – within various greases: lithium thickened (MB), soap complex thickened (SB) and silica thickened (UB). Silicate particles (200–300 µm) were homogeneously dispersed, by a mechanical method, within the selected greases in concentrations of 1.5 g/10 ml. For tribological evaluation a four-ball tribotester was employed according to ASTM D2266 standard test method for wear preventive characteristics of lubricating greases. For the silica thickened grease (UB) the WSD increased by ~15%; for the lithium soap and the complex soap thickened greases, the changes were almost negligible due to the behavior of their soap thickener and base oil. For the thermal transport evaluation, a guarded hot-plate method-based apparatus was used to characterize the thermal conductivity of greases with and without silicate particles, showing an enhancement range of 25–70% in thermal conductivity with the addition of 1.5 g/10 ml of silicate particles. Thermal conductivity measurements offer an accuracy of ~5%. It was shown that MB and SB greases have a positive impact on the thermal conductivity as silicates are added; UB reflected a negative effect on the thermal conductivity as silicates were mixed within the grease. These results show that silicate contaminants may be able to thermal properties of greases while not affecting significantly their tribological performance. • Silicates affect greases' performance by increasing frictional torque, wear and surfaces in contact and relative movement. • Roughness increased in all greases with the addition of silicate contaminant; 23, 60 and 94% for MB, SB and UB, respectively, compared to base greases. • For the MB grease, the addition of silicates increases the WSD by 13%, similar to the UB grease, which increased by 12%. • Results demonstrate that silicates have a detrimental effect on wear characteristics of greases due to their high hardness. • Thermal conductivity is affected by silicate particles within the greases. However, UB grease showed a reduction in performance due to heat percolation threshold not achieved due to a low silicate concentration. [ABSTRACT FROM AUTHOR]

A tribological comparison was conducted among micro-MoS2 (m-MoS2), platelet-like nano-MoS2, and spherical nano-MoS2 in lithium grease, lithium-calcium grease, and polyurea grease, respectively. Micro-MoS2 slightly improved the lubrication of the 3 greases. The 2 nano-MoS2 samples had obvious superiority over m-MoS2. The tribofilms produced by nano-MoS2 contained MoS2 and MoO3. However, the tribofilms with m-MoS2 did not contain Mo, or Mo only existed in the form of MoO3. The absence of MoS2 in tribofilms was the main reason for the poor lubrication of m-MoS2 greases. Moreover, the improved lubrication of the spherical nano-MoS2 greases than the platelet-like nano-MoS2 ones was ascribed to the lubricating superiority of the spherical structure to the platelet-like one. [ABSTRACT FROM AUTHOR]

Dispersions of microfibrillated cellulose (MFC) in triethyl citrate have been considered as biodegradable lubricants containing 1–7 % MFC. Due to the presence of microfibril entanglements, these dispersions exhibit shear-thinning and shear-thickening behaviors, as well as viscoelastic properties of gels, which makes them typical greases. Moreover, the dispersions maintain their ability to flow at temperatures as low as −50 °C, being potentially applicable as low-temperature lubricants. Microfibrils reduce friction and wear of steel surfaces in two ways. Microfibrils in low concentrations fill irregularities of friction surfaces and decrease their wear, while microfibrils in high concentrations create a smooth chromium-enriched tribological film on the wear surfaces and largely reduce their friction. [Display omitted] • Cellulose microfibrils form entanglements in oil dispersions being shear thinning. • Entanglement network gives dispersions a yield stress and viscoelasticity of greases. • Microfibrils significantly reduce the dependence of oil viscosity on temperature. • Microfibrils in low concentrations fill irregularities in surfaces and cut their wear. • Microfibrils in high concentrations produce a smooth tribofilm with low friction. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to fabricate composite nanogrease for tribological applications. Multi-walled carbon nanotubes (MWCNTs) with a size 10 nm average diameter and 5 μm in length were used as additives to calcium grease.Design/methodology/approach The tribological four-ball machine was used to evaluate calcium grease with carbon nanotubes (CNTs) as an additive. The interaction between CNT and calcium grease (nanogrease) were studied by transmission electron microscopy and X-ray diffraction.Findings MWCNTs composite nanogrease was manufactured for tribological applications. The effectiveness of the fabricated grease in improving the tribological performance at different concentrations and under different loads was tested. The results are summarized as follows. CNT nanoparticle additive dispersed in calcium grease significantly improve its anti-wear performance, reducing friction, increasing load-carrying capacity and extreme pressure (EP) property. The friction is reduced by about 50 per cent, the wear scar diameter (WSD) decreased to 32 per cent and the EP properties increases about 38 per cent, with only 3 wt.%. The modified grease with CNTs additives of 3 wt.% showed the most favorable results. Energy dispersive x-ray (EDX) analysis shows that C was present on the worn scar surface, with atomic concentration of about 22 per cent. The presence of C suggests that a lubricating film is likely formed because of the presence of CNTs and very likely prevented the steel-to-steel direct contact.Originality/value The results indicated that a 3 wt.% of MWCNT nanogrease is an excellent antiwear, with EP and low friction coefficient. It was also found that the friction coefficient was reduced to about 50 per cent, the WSD decreased by about 32 per cent and the EP properties increased about 38 per cent. The mating surfaces were investigated with scanning electron microscopy and EDX. The results show that a boundary film mainly composed of CNTs, Cr and Fe was formed on the rubbed surfaces. [ABSTRACT FROM AUTHOR]

A perfluoropolyether (PFPE) grease was exposed to 110 keV electron beam for fluence of 1 × 10 15 , 5 × 10 15 and 1 × 10 16 e/cm 2 in vacuum. The friction and wear behaviour of the electron irradiated grease-lubricated 2Cr13 steel in vacuum was investigated by using a pin-on-disk type tribometer. The morphologies of the worn surfaces for the irradiated grease-lubricated 2Cr13 steel were observed by a scanning electron microscope (SEM). Gaseous products from the PFPE grease during the electron irradiation were monitored with a quadrupole mass spectrometer (QMS). The compositions and chemical states of grease samples before and after electron irradiation were analysed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Results show that the irradiated grease-lubricated 2Cr13 steel sliding against the same material in vacuum presents a high friction and a high wear. The QMS, XPS and FTIR analyses reveal that COF 2 gas, low molecular weight perfluoroethers and acid fluoride groups are formed due to decomposition when the PFPE grease is exposed to 110 keV electron beam in vacuum. Moreover, the base oil content of the PFPE grease decreases with increasing the electron irradiation fluence, leading to the loss of lubricating ability of the PFPE grease. [ABSTRACT FROM AUTHOR]

Purpose – In order to meet the requests of exploring environmental-friendly and multifunctional lubricant additives, some novel dimercaptothiadiazole derivatives containing hydroxyl are prepared and used as antiwear (AW) and extreme-pressure (EP) additives in biodegradable lithium grease. The paper aims to discuss these issues. Design/methodology/approach – The tribological performances of the grease samples containing these derivatives are evaluated by using a four-ball tester. X-ray absorption near edge structure (XANES) spectroscopy is used to analyze the chemistry of tribofilms under AW/EP regime, and thermal films are also considered for comparison. Findings – The tribological tests show that these derivatives are all effective in reducing wear, especially at lower additive concentrations, but they are basically failed in reducing friction. They are also helpful in improving the EP characteristic of the base grease. The thermal films generated by these derivatives are composed of adsorbed organic sulfide and ferrous sulfate, though for short-chain derivatives, organic sulfide is the only component at 5.0 wt.%. Ferrous sulfide is the main component of the tribofilms formed by these derivatives at various additive concentrations. But for short-chain derivatives, these tribofilms consist of ferrous sulfide and ferrous disulfide at 5.0 wt.%, and the appearance of disulfide suggests that the interfacial temperature between the upper ball and three lower balls under these conditions is considerably low. The EP films generated by short-chain derivatives are all composed of organic sulfide and ferrous sulfide, while for long-chain derivatives, ferrous sulfide is the main component. Originality/value – These low-toxic and oil-soluble dimercaptothiadiazole derivatives are effective in improving the tribological characteristic of the biodegradable lithium grease, and these heterocyclic derivatives may be good substitutes for some harmful traditional additives. [ABSTRACT FROM AUTHOR]

Boron compounds are widely used in a range of tribological applications such as friction modifiers, antioxidants, antiwear additives, and in many cases as environmentally friendly lubricants. The chemical nature and structure of boron compounds provide multifunctionality. They are used as (1) solid lubricants such as boric acid and hexagonal boron nitride, (2) liquid lubricants such as ionic liquids, (3) lubricant additives such as borate derivatives of various organic and inorganic compounds, and (4) coatings such as cubic boron nitride and different metal borides. Boron is also one of the most favorable elements for coatings and thin films in biotribological and biomedical applications. This review outlines the growing role of boron in lubrication over the past several decades, summarizes the main findings, and identifies future challenges related to boron chemistry. [ABSTRACT FROM AUTHOR]

A new approach to produce biodegradable low-temperature greases, based on cellulose acetate butyrate (CAB) that dissolves in the medium of acetyl tributyl citrate (ATBC) at high temperatures and produces a gel during cooling because of phase separation, is proposed. Rheological properties of CAB solutions and gels in a wide temperature range from −80 °C to 160 °C were investigated with characterization of their viscoelasticity and viscoplasticity that arise because of the sol-gel transition of CAB/ATBC systems at 55 °C. CAB gelation reduces the wear coefficient tenfold when using ATBC as a lubricant but leads to a noticeable increase in the friction coefficient. To improve tribological properties of gel greases, additives of various solid particles were used: hexagonal boron nitride, graphite, and polytetrafluoroethylene (PTFE). The introduction of 10% to 30% additives in a gel grease containing 10% CAB has shown the preference of PTFE at a concentration of 10% for improving grease tribological characteristics. • Cellulose acetate butyrate dissolves at high temperatures in acetyl tributyl citrate. • CAB/ATBC solution forms a gel upon cooling, becoming viscoelastic and viscoplastic. • CAB gelation greatly improves the antiwear properties of ATBC but increases friction. • Solid additives can reinforce the gel network or destroy it by creating their own net. • Polytetrafluoroethylene best improves the tribological properties of the gel grease. [ABSTRACT FROM AUTHOR]

Two kinds of new conductive lubricating greases were synthesized using 1-octyl-3-methylimidazolium hexafluorophosphate and 1-octyl-3-methylimidazolium tetrafluoroborate as base oil and the polytetrafluoroethylene as thickener. The conductivities of the new conductive lubricating greases are higher than the traditional conductive lubricating greases which contains conductive stuffing. In addition, the physical and tribological properties of the new lubricating greases were investigated in detail. The results show that the new lubricating grease show better friction reducing and anti-wear properties than the lubricating grease based on PAO10 at room temperature and 150 °C. The worn surfaces were observed and analyzed by scanning electron microscope and X-ray photoelectron spectroscope. Also, the possible friction mechanisms for the new lubricating greases are proposed. [ABSTRACT FROM AUTHOR]

Abstract: The friction torque and the operating temperatures in a thrust ball bearing were measured for seven different types of greases, including three biodegradable greases having low toxicity. These friction torque tests were performed using a modified Four-Ball machine. Rheological evaluations of the lubricating greases were made using a rheometer. Bleed oils were extracted from the greases and the dynamic viscosities were measured. In order to compare the performance of the lubricant greases in terms of friction, the grease characteristics were related to experimental results, showing that the interaction between thickener and base oil have strong influences in the bearing friction torque. [Copyright &y& Elsevier]

This paper describes experimental work on the frictional performance of a lithium grease lubricant filled with a combination of polytetrafluoroethylene (PTFE) and copper powders. The tribological testing was carried out in agreement with the prescriptions of the Polish standard PN-76/C-04147 using a fourball apparatus. The performance of the tested compositions was evaluated using three criteria: ball wear d, limiting wear load G, and seizure load Fz. Synergy between action of the powders of PTFE and copper in compositions with 6 wt.% of these fillers was found. Examinations of the chemical composition of the upper layer of the wear scars of the tested balls were carried out using an X-ray microanalysis method with dispersion of the radiation energy. The results of these analyses made it possible to confirm the author's notion that the synergy of PTFE with copper in the lithium grease tested was possible due to the thermal decomposition of PTFE and the consequent creation of new layers during a reaction of the decomposition products with the platering layer of copper. These new layers are, to a high degree of probability, complexes with copper, sulphur, and fluorine. [ABSTRACT FROM AUTHOR]

2Cr13 steel was modified by plasma nitriding. The microstructure, phase composition and microhardness of the nitrided samples were examined. The friction and wear behaviour of the nitrided and unnitrided samples sliding against self-mating under PFPE grease-lubricated conditions in vacuum was investigated on a pin-on-disk type tribometer, with the interactions among the nitrided layer and grease to be focused on. The morphologies of the worn surfaces were observed using a scanning electron microscope. The chemical states of several typical elements on the worn surfaces were examined by means of X-ray photoelectron spectroscopy. The chemical compositions of grease samples taken from the worn surfaces were analyzed by Fourier transform infrared spectroscopy (FTIR). Results show that the nitrided steel has better friction-reducing and anti-wear abilities than the unnitrided one under PFPE grease-lubricated conditions. In the former case, the wear of nitrided steel shows a transition from mild abrasive wear to fatigue one with increasing normal load. In the latter case, wear mechanism of unnitrided steel under all load applied is a combination of the severe abrasion and fatigue. [ABSTRACT FROM AUTHOR]

The biomaterials have gained the attention for utilization as sustainable alternatives for petroleum-derived products due to the rapid depletion of petroleum resources and environmental issues. Chitosan is an economical, renewable and abundant polysaccharide having unique molecular characteristics. Chitosan is derived by deacetylation of chitin, a natural polysaccharide existing in insects' exoskeleton, outer shells of crustaceans, and some fungi cell walls. Chitosan is widely used in numerous domains like agriculture, food, water treatment, medicine, cosmetics, fisheries, packaging, and chemical industry. This review aims to account for all the efforts made towards chitosan and its derivatives for utilization in the petroleum industry and related processes including exploration, extraction, refining, transporting oil spillages, and wastewater treatment. This review includes a compilation of various chemical modifications of chitosan to enhance the petroleum field's performance and applicability. [Display omitted] • Chitosan is a non-toxic, biodegradable, abundant, and versatile biopolymer. • It is susceptible towards derivatization for application in petroleum industry. • It is used as additive in bio-lubricant and as catalyst in bio-diesel production. • It is used as oil spill cleaner and in refinery waste waters treatment too. • Chitosan is appropriate feedstock for upstream chemicals due to sustainable nature. [ABSTRACT FROM AUTHOR]

In France, fatty residues considered as “non-ultimate” waste will not be accepted in landfill from 2002, in accordance with French legislation. Anaerobic digestion appears as an alternative process to mobilize and profitably use such fermentable waste. In this work, the effect of an alkaline pretreatment on the degradation of hexane extractible matter (HEM) and the production of volatile fatty acids (VFAs) was compared in reactors working at pH 6.5 and 8.5. The results obtained showed that 40% (±0.1) of HEM were degraded at pH 8.5 versus 10% (±0.3) at pH 6.5, regardless of the alkali agent used to saponify the greasy wastes. The highest performances of VFA production (8.45% ± 0.3) were obtained at pH 8.5 with greases saponified by potassium hydroxide, compared to results (4.25% ± 0.1) with greasy waste saponified by sodium hydroxide. This difference in VFA production might be attributable to biotoxic molecules generated during the saponification of greases by soda, limiting consequently the VFA production process. [Copyright &y& Elsevier]

Two greases formulated with lithium complex and anhydrous calcium thickeners were mixed with cation phosphonium-derived ionic liquids with the aim of studying their rheology, lubricant film forming properties, and the friction behaviour under different temperatures and speeds. The addition of the ionic liquids decreased viscosity, yield stress, storage modulus and loss modulus of the greases, with larger effect on anhydrous calcium-based grease. The use of the ILs as additive affected the lubricant film thickness at increasing temperature and mainly in the low speed region. The viscosity reduction led to lower friction results under both temperatures and range of speeds tested. The trihexyltetradecylphosphonium decanoate ionic liquid had the higher influence on the abovementioned properties, especially mixed with the anhydrous calcium-based grease. • The use of the ionic liquids reduced the rheological properties of the greases. • The viscosity reduction led to lower friction results under all test conditions. • The [P 6,6,6,14 ][DEC] had the higher influence on the above-mentioned properties. [ABSTRACT FROM AUTHOR]

This work focuses on presenting a new methodology, based on approach-retraction curves, to objectively and accurately measure adhesion and tackiness of industrial greases. The definitions of pull-off force and tackiness are redefined, explained and measured, whereas the effect of testing parameters such as retraction speed, grease film thickness, applied load and temperature is discussed. This work aims to point out that the adhesion and tackiness of greases are not just a single value, but that they strongly depend on the experimental conditions. Based on this proposed method, a mapping of the tackiness of greases with respect to the experimental or working conditions can be performed. [ABSTRACT FROM AUTHOR]

Industrial greases consist of mineral or synthetic oil, soaps, mainly calcium or lithium, and additives, including anti-corrosives, extreme pressure agents, copper deactivators, film and viscosity improvers, antiwear agents, water repellents, colorants, odor masks, and antioxidants, including diphenylamine (DPA) and phenyl-al-pha-naphthylamine (PAN). Greases contain sensitizers and are widely used, yet few cases of contact allergy have been reported, from DPA and PAN. PAN is a strong sensitizer in the guinea pig.