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The feasibility of CuP as a multifunctional additive in lithium grease was evaluated for the first time. The experimental results indicated that the CuP significantly enhanced the friction reduction, antiwear properties, extreme pressure capabilities, and antimicrobial characteristics of lithium greases. The SRV test results suggested that the optimal tribological properties were obtained by adding 3 wt% of CuP to lithium greases, resulting in a decrease of the friction coefficient and wear volume by 28.25% and 34.98%, respectively. The four-ball results confirmed that the extreme pressure performance of the lithium grease with 3 wt% CuP was enhanced by a factor of 3.17. The bacterial inhibition rate of lithium grease with 3 wt% CuP was higher than 99.98%. The lubrication mechanism and antimicrobial mechanism was explained.

At extreme deep-sea pressure, the assessment of the electroacoustic conversion performance of transducers is a major problem, particularly in the acoustic exploration of seabed sediment in 11,000-m abysses. To address this problem, an online measurement method was proposed for the electroacoustic performance under extreme pressure. The method utilized the 11,000-m transceiver with the high-frequency and narrow-beam characteristics. In the full-depth pressure profile, the transceiver signal was measured online by an extreme pressure simulation device. At different extreme pressure sites, characteristics of the transceiver signal were analyzed using the transceiver signal at atmospheric pressure as the reference. The characteristics included amplitude response characteristics, frequency response characteristics and time-frequency characteristics. The 11,000-m transceiver has verified the stability and reliability of its electro-acoustic conversion performance. It was also analysed the effect of the transducer on the calculation of seabed sediment parameters in a pressure environment. [ABSTRACT FROM AUTHOR]

Extreme Pressure (EP) additives are commonly used in lubricants to reduce wear and prevent seizures at high temperatures and pressure. In terms of their mechanism, these build up a film on the surface with chemisorption. This film efficiently prevents metal-metal adhesion. Industrial statistics show that extreme pressure additives are mostly used in metalworking fluids, lubricating greases and engine oils. Sulfurized vegetable oils can be used as EP additives of lubricants. This type of EP additive is ashless, derived from renewable sources and has a lesser negative effect on the environment compared to those that are not derived from vegetable sources. Several technologies for the preparation of additives have been developed, of which the dark sulfurization process has been studied. Several physical and lubricating properties of the obtained additives have been investigated, based on which, it is possible to produce additives with favourable viscosity values and low copper corrosion grade. [ABSTRACT FROM AUTHOR]

The performance loss in industrial equipment due to friction and wear is one of the critical concerns among researchers. This drives the need to develop lubrication fluids that reduce friction to provide extended performance. The global sustainability movement drives the research towards novel bio-based oils to aid in lubrication. This study analyses the dispersion stability, tribological behaviour and antiwear properties of zinc oxide (ZnO), titanium dioxide (TiO2) and molybdenum di sulphide (MoS2) nanoparticles as an additive in hazelnut and sunflower oils. The viscosity index and flash point of the prepared nano lubricants were analyzed. The tribological test conducted on four ball tester resulted in a 12.6% and 35.8% reduction in coefficient of friction (COF) for 0.5% ZnO in hazelnut oil and 1% MoS2 in sunflower oil. The corresponding wear scar images were analysed. The extreme pressure (EP) test resulted that 1% MoS2 in sunflower oil exhibiting improved performance as it sustained a 1800N load. The kinematic viscosity of the 0.5% ZnO in hazelnut oil and 1% MoS2 in sunflower oil had an improvement against others. Therefore, infusion of nano additives in bio-oils offers enhanced tribological properties foreseeing sustainability in applications.

Abstract Lubricating approaches involving nanoparticles have a significant role in reducing friction and wear. Reducing friction is crucial for preserving energy, minimizing emissions, and protecting the environment. The present experimental study investigates green nano-lubricants prepared by dispersing various concentrations of CaCO3 nanoparticles in jojoba oil. The aim of the study is to assess the usability of a bio-sourced alternative nanolubricant to depleting conventional lubricants. The role of nanoparticle concentration and thermo-physical properties in improving the lubrication properties of jojoba oil was thoroughly investigated in the present study. The anti-wear and extreme-pressure behavior of jojoba oil dispersed with CaCO3 nanoparticles were evaluated as per the ASTM D4172 and ASTM D2783 test standards. The coefficient of friction, wear scar diameter, last non-seizure load, initial seizure load, weld point load, and load wear index of each sample were assessed. Compared with pure jojoba oil, the addition of CaCO3 nanoparticles in jojoba oil revealed remarkable anti-wear and extreme-pressure properties with significant improvements in the last non-seizure load, initial seizure load, weld point load, and load wear index, the average friction coefficient and the average wear scar diameter of the steel balls decreased by as much as 34.1% and 40.2%, respectively.

The present study reports the tribological performance of a novel hybrid nano-lubricant for bronze/AISI 4340 alloy-steel tribopair. The hybrid nano-additive used in the present study helps to improve the lubricity and can sustain under extreme conditions. Initially, friction and wear properties are recorded by varying concentrations of Al2O3 (0.5, 0.8, 1.0, and 1.5 wt. %) and GNP (0.05, 0.1, 0.2, and 0.5 wt. %). Based on the results, an optimum hybrid concentration (OHC) is prepared by adding 0.8 wt. % of Al2O3 and 0.2 wt. % of GNP which resulted in 83.84% and 79.75% reductions in coefficient of friction (COF) in comparison to optimum Al2O3-based and GNP-based lubricants, respectively. However, the wear volume (WV) for OHC lubricant indicated 98.28% and 75% reduction in comparison to the above-mentioned lubricants, correspondingly. Extreme pressure (EP) tests were carried out and OHC lubricant reported improved weld point for hybrid nano additive-based lubricant. [ABSTRACT FROM AUTHOR]

The performance loss in industrial equipment due to friction and wear is one of the critical concerns among researchers. This drives the need to develop lubrication fluids that reduce friction to provide extended performance. The global sustainability movement drives the research towards novel bio-based oils to aid in lubrication. This study analyses the dispersion stability, tribological behaviour and antiwear properties of zinc oxide (ZnO), titanium dioxide (TiO2) and molybdenum di sulphide (MoS2) nanoparticles as an additive in hazelnut and sunflower oils. The viscosity index and flash point of the prepared nano lubricants were analyzed. The tribological test conducted on four ball tester resulted in a 12.6% and 35.8% reduction in coefficient of friction (COF) for 0.5% ZnO in hazelnut oil and 1% MoS2 in sunflower oil. The corresponding wear scar images were analysed. The extreme pressure (EP) test resulted that 1% MoS2 in sunflower oil exhibiting improved performance as it sustained a 1800N load. The kinematic viscosity of the 0.5% ZnO in hazelnut oil and 1% MoS2 in sunflower oil had an improvement against others. Therefore, infusion of nano additives in bio-oils offers enhanced tribological properties foreseeing sustainability in applications. [ABSTRACT FROM AUTHOR]

Ammonia is a prospective zero-carbon-emission fuel for use in large marine diesel engines. Current research focuses on several technical aspects, such as injection strategies or exhaust gas aftertreatment options, but investigations regarding the impact of ammonia on engine oil degradation are largely absent from the literature. This study provides a methodology with which to evaluate this phenomenon via artificial oil alteration. By using an admixture of various contaminations to air, such as ammonia and its partial combustion product nitrogen dioxide, their respective impacts on chemical oil degradation were assessed. Subsequently, the lubricating performance of altered oils was investigated, with a focus on corrosion properties, deposit formation, and load-bearing capability. Although the application of a stoichiometric ammonia–air mixture resulted in less pronounced thermo-oxidative degradation compared to alteration with neat air, static and dynamic deposit formation as well as corrosion properties and load-bearing capability were severely impacted by the presence of ammonia. On the contrary, nitrogen dioxide contamination resulted in higher oxidation and acidification of the oil, but altered samples performed considerably better than ammonia-altered aliquots in terms of coking tendencies, corrosivity, and load bearing. [ABSTRACT FROM AUTHOR]

A potential, sustainable, and economical eco-friendly alternative to harmful petroleum-based lubricants is a big challenge for the 21st-century lubricant industry. The present study explores, for the very first time, polysaccharide gums like gum acacia (GA) and guar gum (GG) as additives (0.5–10 %w/w) to enhance the extreme-pressure (EP) performance of greases (based on vegetable oil and organoclay). The greases are evaluated on a four-ball tester for the standard EP test (ASTM D2596). Adding GA or GG to greases enhances EP performance significantly. The performance ameliorates with the gum's concentration showing impressive results at higher concentrations (up to ≈ 60% better than a commercial grease). The superior performance is attributed to an in-situ formed polymer-layered silicate nanocomposite tribofilm at the interface via chemisorption (for GA) or physisorption (for GG). The formulated greases are a possible replacement for existing mineral oil-based commercial greases. [Display omitted] [ABSTRACT FROM AUTHOR]

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Extreme pressure (EP) and antiwear (AW) additives are necessary for boundary lubrication. However, their mechanisms and physical and chemical properties remain unclear. EP and AW additives were reviewed to fill gaps in theoretical and industrial applications. Compounds containing chlorine, sulfur, and phosphorus elements were first used in boundary lubrication because of thermal reaction with metal to form film characteristics. First, the mechanisms of traditional EP and AW additives were analyzed, the physical and chemical properties were compared, and properties affecting factors were studied. Traditional EP and AW additives are not environmentally friendly, but nanoparticle EP and AW additives are excellent substitutes. The mechanisms of nanoparticle EP and AW additives were summarized. The influence of nanoparticle structure parameters, concentration, and media polarity on properties was studied. Second, the influence law of non-polar chain length on traditional EP and AW additives was revealed. The improvement interval of traditional EP and AW additives on the performance of the base fluid was determined. The structural advantage of low crystallinity onion-like and multilayer sheet-like low wrinkle effect of nanoparticles was explained. The particle size design principle attached to the surface roughness and size-dependent melting inhibition mechanism was established. The influence of concentration and media polarity on nanoparticle properties was obtained. Finally, the research of minimum amount matching database and mathematical selection model for traditional EP and AW additives and the molecular dynamics analysis of surface-modified nanoparticles and the development of green general-purpose additives based on molecular design are prospected. [ABSTRACT FROM AUTHOR]

To prepare the diethanolamine borate (DEAB) and ricinoleic acid triethanolamine salt (RTAS) as water-based emulsion additives.The structures were analyzed and confirmed by hydrogen nuclear magnetic resonance spectroscopy (1H NMR) and mass spectrometry. The extreme pressure and anti-rust properties of DEAB, RTAS and their complex aqueous solutions were studied.The results showed that: The extreme pressure of DEAB aqueous solution is less than 98 N,the extreme pressure performance of RTAS is poor, but it can significantly improve the extreme pressure performance of RTAS. Under the condition of 646.8 N load, the spot diameter decreases by 10.17% when 0.5% DEAB is added to 0.5% RTAS aqueous solution.The anti-rust effect of DEAB aqueous solution is better than that of RTAS aqueous solution, but the combined solution of DEAB and RTAS shows better anti-rust performance.When 0.8% DEAB is added to 0.5% RTAS aqueous solution, the synergistic corrosion inhibition rate reaches 92.70%.The combination of DEAB and RTAS is more conducive to develop water-based emulsion with excellent extreme pressure and anti-rust performance. [ABSTRACT FROM AUTHOR]

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present work focused on the extreme pressure characteristics of different grades of polyalphaolefins (i.e., PAO 4, PAO 6, PAO 40, and PAO 100) with LaF3 nanoparticles as an additive. The LaF3 nanoparticles were synthesized by the sol-gel method and modified with oleic acid. The synthesized nanoparticles were characterized with various analytical tools, viz. X-ray diffractometry (XRD), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Varying doses (0.025–0.15 wt%) of synthesized nanoparticles were blended in all PAOs to prepare nanolubricants. The extreme pressure (EP) properties of nanolubricants were measured using a four-ball tester as per ASTM D2783 to find the last nonseizure load (LNSL), initial seizure load (ISL), just before weld load (JBWL), weld load (WL), and load wear index (LWI). The results revealed that the incorporation of LaF3 nanoparticles efficiently enhanced the EP properties of all PAOs. However, 0.15 wt% of additive was the optimum dose in all PAOs, demonstrating the best EP behavior; that is, the highest LWI and lowest wear scar diameter (WSD) at ISL and JBWL. Numerous characterization techniques such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and scan probe microscopy (SPM) were adopted to investigate the probabilistic rationale for the improvement in EP properties. [ABSTRACT FROM AUTHOR]

Rail lubrication is vital in determines the friction, wear and noise level in the wheel and rail contacts. In general, the primary function of a rail curve grease is to minimize friction between the contact as well as to protect side wear of rails on a curved track. In this study, three commercially applied railway greases were identified and the wear and friction behavior, as well as the load-carrying ability, were investigated. Before that, the grease's physiochemical properties in terms of the consistency and drop point, as well as the element content, were also examined. The tribological investigation of the greases was also carried out using four-ball wear tester. In this test, the wear preventive (WP) and extreme pressure (EP) properties of the grease were measured under sliding actions between the balls, and the wear surface analysis was also carried out. The tests results explained that the rail curve greases are very soft in texture yet have stable structure over a high-temperature range. The greases also presenting low friction coefficient; ranges between 0.070 to 0.090, and acceptable wear scar diameter indicating the good anti-friction and anti-wear properties. High load-carrying ability up to 400 kg is also the significant properties for a rail curve grease to perform as the desired functions.

To investigate whether the dense Kondo compound CeB6 might evolve into a topological insulator under sufficient pressure, four-point electrical resistivity measurements have been carried out over the temperature range 1.3 K-295 K in a diamond anvil cell to 122 GPa. The temperature Tmax of the resistivity maximum initially increases slowly with pressure but disappears between 12 and 20 GPa. The marked changes observed under pressure suggest that a valence and/or structural transition may have occurred. Synchrotron x-ray diffraction measurements, however, fail to detect any change in crystal structure to 85 GPa. Although a transition into an insulating phase is not observed, this dense Kondo system is completely suppressed at 43 GPa, leaving behind what appears to be a conventional Fermi liquid metal.

Four 10-undecenoic acid-based Schiff bases were synthesized by condensation of methyl 11-(2-aminoethylthio) undecanoate with various aromatic aldehydes. Synthesized compounds were characterized by spectral techniques and evaluated for their tribological and antioxidant performances in biolubricant base oil, namely epoxy 2-ethyl hexyl esters of karanja fatty acids. The tribological test results indicate that all the synthesized thioethers containing Schiff bases act as good antiwear and extreme pressure additives. A significant reduction in wear scar diameter was observed at a very low concentration (0.6 wt%), whereas, at 1 wt% concentration, weld point enhancement observed from 160 to 230 kg. Quantum chemical calculations based on density functional theory for the interactions of Schiff bases with surfaces correlated with experimental wear data. Overall, the dimethoxy-substituted phenyl ring containing Schiff base was more effective in enhancing the antiwear and extreme pressure performance of base oil, whereas dihydroxy-substituted phenyl ring containing Schiff base exhibited good antioxidant property. [ABSTRACT FROM AUTHOR]

The paper aims to study the antiwear (AW) and extreme pressure (EP) properties of avocado oil mixed with zinc dialkyl dithiophosphate (ZDDP) in concentrations of 1% to 3% by weight for lubrication purposes. The AW and EP tests are conducted as per ASTM-4172 and ASTM-2783 standards respectively. Further, the rheological behavior of avocado oil mixed with ZDDP is determined for varying shear rates of 50 – 2000 s−1. The maximum improvement in the wear properties for avocado oil is equal to 39.8% at 1 wt.%. The load wear index of pure avocado oil increases from 32.6 to 80.3 at 3 wt.% ZDDP whereas, the weld point increases to 252 kgf at 3 wt.% ZDDP. The improvement in the antiwear and extreme pressure properties are attributed to the protective film formation on the tribopairs as characterized by SEM and EDX analysis. Also, the addition of ZDDP increases the viscosity of the oil at all concentrations and maintains the Newtonian behavior of oil. [ABSTRACT FROM AUTHOR]

A research has been done to investigate the tribological performance of palm kernel oil (PKO) with addition of different percentage of pour point depressant, PPD (5w%, 10wt%, 20wt% and 30wt%) according to ASTM D2783. The main analyses that have been done in this research are low temperature performance ability of blended PKO, coefficient of friction (COF), wear scar diameter (WSD) and surface profile. The result of the experiment has shown that for low temperature performance, PKO with 20wt%PPD (A2-20%) and 30wt%PPD (A2-30%) show great performance in withstanding lower temperature (15℃). Under extreme pressure test, it can be seen that PKO can only withstand lower load (110kg) compared to mineral oil (140 kg). The sample 10wt%PPD (A2-10%) shows good lubricity performance in terms of COF as compared to other sample. 5wt%PPD (A2-5%) and 10wt%PPD show good lubricity performance in terms of anti-wear behaviour (A2-10%) by producing the lowest WSD when compared to other samples. From overall view, PPD is considered as successful in improving low temperature performance of PKO, but in terms of lubricity performance, adding PPD will slightly reduce the lubricity performance under extreme pressure if compared to pure PKO.

Palm oil olein and palm oil ester is well-known potential candidate in plant-based oil to replace the conventional mineral oil. Harvested all year round, the advantages and benefits initiate the palm oil to be used in varieties of application. In this paper, palm oil olein was tested on its capability as a lubricant to replace the mineral oil. To enrich the performance of this oil, different types of nanoparticles additives were added. Previous studies proved that by adding small size of additives into lubricating oil can lessen the friction and improve anti-wear properties. The adjustment of the lubricating oil with nanoparticle additives will reduce the friction between two contact surfaces and produce less heat. In his study, three type material of solid additives namely nanoclay and carbon nanotubes were used. Four ball tester following ASTM D4072-94 was conducted to determine the optimum concentration of each additives and its tribological properties under boundary lubrication (metal to metal contact). Result obtained shows that the addition of 0.04 wt% of carbon nanotubes recorded the lowest coefficient of friction with a 10.8% improvement compared to the pure palm oil. The additive also contributed to better wear scar diameters and possessed good anti-wear properties for palm oil. This thus shows the significant potential of carbon nanotubes as the wear preventive additive for palm oil olein. It is also discovered that 0.04 wt% of nanoclays additive is the optimum concentration of the mixture with coefficient of friction reduced 22.16% compared to mineral oil.

Stepped spillways have been increasingly used to handle flood releases from large dams associated with hydropower plants, and it is important to evaluate the fluctuating pressure field on the steps. Hydraulic model investigations were conducted on three 53° (1V:0.75H) sloping and relatively large-stepped chutes to characterize the mean, fluctuating, and extreme pressures acting on the most critical regions of the step faces, near their outer edges. The pressure development along the chutes is presented, generally indicating an increase of the modulus of pressure coefficients up to the vicinity of the point of inception of air entrainment, and a decrease further downstream. The extreme pressure coefficients along the spillway are fitted by an empirical formula, and the critical conditions potentially leading to cavitation on prototypes are calculated. The correlation between the cavitation index and the friction factor is also applied for predicting the onset of cavitation on prototypes, and the results are compared with the pressure data-based method. Generally, the results obtained from those methods yield typical values for the cavitation index in the vicinity of the point of inception, varying approximately from 0.8 to 0.6, respectively. In light of these results, maximum unit discharges of about 15–20 m2/s are considered advisable on 53° sloping large-stepped spillways without artificial aeration, for step heights ranging from 0.6 to 1.2 m. For much higher unit discharges, a considerable reach of the spillway may potentially be prone to the risk of cavitation damage.

Eu-doped WO3 (WO3:Eu3+) nanoparticles were prepared by Pechini method under different pH values (pH 1, 3, 5, and 7). The prepared nano-powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The results showed that the average external diameter of the prepared nano-WO3:Eu3+ powders is the smallest and reaches 50 nm at pH 5. Structural transformation matrix contained different crystals of anorthic and orthorhombic structures. Eu3+ ions are located at the center of the non-inversion symmetry of WO3:Eu3+. The tribological properties of the WO3:Eu3+ as extreme pressure and wear resistance agents in water-based lubricant were investigated by a four-ball machine. The results showed that WO3:Eu3+ displays excellent load-carrying capacity, wear resistance, and friction-reducing properties in water-based lubricant, particularly in the best concentration of WO3:Eu3+ was 0.6 wt%. WSD was reduced from 0.62 to 0.35 mm and COF was decreased from 0.083 to 0.055. This was due to the formation of tribofilms with a few tens of nanometers thick, which prevented no actual metal-to-metal contact. [ABSTRACT FROM AUTHOR]

The lubricity of sweet almond oil (Prunus amygdalus var. Dulcis) was evaluated through Anti Wear (AW) properties and Extreme Pressure (EP) performance in a four-ball tribometer. The results were compared to those obtained with two mineral oils of contrasting viscosity, namely technical white mineral oil and delta 360 plasticizer, neither of them containing additives. Sweet almond oil was found to have greater lubricity than the mineral oils, as the spheres it lubricated had lower average wear track diameter and friction coefficient. In addition, sweet almond oil showed better performance under extreme pressure conditions and a greater weld point than mineral oils. Finally, an FT-IR spectroscopic analysis allowed determining that under the conditions of the current assays almond oil does not oxidize.

Bearings, as a key part of a vehicle transmission system, were extensively studied to improve their abrasion resistance and fatigue life. Mixtures of hard ceramic particles, namely, molybdenum disulphide (MoS2) and graphite particles (PC), were sprayed with a high-pressure inert gas onto the surface of AISI52100 bearing steel, forming the lubricant film. The morphology and phase composition of the protective layer were examined using confocal laser scanning microscopy, surface roughness tester, X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The changes in surface microhardness were evaluated with a microhardness tester. The friction factor and anti-wear properties of the lubricant layer were assessed with an SRV-IV microvibration tester. The solid lubricant is shown to effectively reduce the friction factor. The surface modification gave a twofold increase in extreme pressure 14% reduction in the friction factor, and 20% enhancement in microhardness. This study offers a practical method to enhance the bearing surface strength for a vehicle transmission system. [ABSTRACT FROM AUTHOR]

Abstract To enhance the lubricating and extreme pressure (EP) performance of base oils, two types of oil-soluble ionic liquids (ILs) with similar anion albeit dissimilar cations were synthesized. The physical properties of the prepared ILs were measured. The anticorrosion properties of ILs were assessed by conducting corrosion tests on steel discs and copper strips, which revealed the remarkable anticorrosion properties of the ILs in comparison with those of the commercial additive zinc dialkyldithiophosphate (ZDDP). The tribological properties of the two ILs as additives for poly-α-olefin-10 (PAO10) with various mass concentrations were investigated. The tribological test results indicate that these ILs as additives are capable of reducing friction and wear of sliding contacts remarkably as well as enhance the EP performance of blank PAO10. Under similar test conditions, these IL additives exhibit higher lubricating and anti-wear (AW) performances than those of ZDDP based additive package in PAO10. Subsequently, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometer (EDS) were conducted to study the lubricating mechanism of the two ILs. The results indicate that the formation of tribochemical film plays the most crucial role in enhancing the lubricating and AW behavior of the mixture lubricants.

Vegetable oils were one of the main sources of lubricating oils before the appearance of oil. Currently, due to low thermal stability and oxidation, they are not used with the same frequency in the industrial sector. However, the different fatty acids that make up vegetable oils can significantly reduce the coefficient of friction. To optimize the lubrication, vegetable oils can be mixed with additives. In this research, a comparative study of the lubricating power of sesame oil with polyethylene wax and paraffin as additives was carried out. This property was evaluated by preventative wear tests and extreme pressure in a four-ball tribometer. The experimental results showed that for the preventive wear test the mixture with polyethylene wax has the smallest average diameter of the fingerprint, while for the extreme pressure test the mixture with paraffin gave a greater resistance to the applied load, obtaining a welding point to 32 Kg-F (314N) being greater than for pure oil and with polyethylene wax (24 Kg- F (235N)). In relation to the coefficient of friction the results obtained show that there is no difference between the oil and the mixtures with the different additives. From these results it can be concluded that the yield of sesame oil as a lubricant can be improved by mixing it with paraffin and polyethylene wax; however, the percentages added must be determined correctly. [ABSTRACT FROM AUTHOR]

A nano-copper suspension solution with an average particle diameter of about 139 nm was prepared by chemical reduction method. The surface modification of the nano-copper suspension solution using one buffer and a pair of non-ionic surfactants was carried out to study its suspension stability in 220# mining lubricant oil. And the tribological properties of the nano-copper lubricants were studied by MFT-R4000 high-speed reciprocating friction and wear tester and AW lubricant antiwear tester. The results show that when the usage of the buffer, Tween-80 and Span-80 are 233%,2% and 2% in the nano-copper suspension solution, respectively, and the amount of nano-copper modified is 0.3% in the lubricating oil, the suspension stability of the nano-copper in 220# lubricating oil is the best, and the friction coefficient is reduced by 67.07%, 15.79% and 43.40% compared with original oil under the load of 5,10 and 20 N, respectively. Meanwhile, the extreme pressure and wear resistance are improved over 20.0% and 63.9%, respectively. [ABSTRACT FROM AUTHOR]

Tribological properties of lithium potassium titanate (PT), molybdenum disulphide, and tungsten disulphide-dispersed mineral oil (MO) were investigated. The sample containing 2 wt.% WS2 exhibited the lowest coefficient of friction. However, the wear scar diameters of the additivated samples were very narrow. Extreme pressure properties of mineral oil were enhanced with the addition of additives. The rolling contact fatigue results exhibited better fatigue life of the balls in MoS2 and PT-dispersed MO. Surface characterization of the balls indicated more pitting on the balls of the MO and WS2-dispersed MO as compared to MoS2 and PT, indicating a stable film in the case of MoS2 and PT, which was confirmed by the presence of additives on ball surfaces by Raman spectrograph. The results of extended rolling contact fatigue tests proved that PT-added mineral oil provided the highest life cycles of the tested balls, followed by MoS2 and WS2-added mineral oil; thus, indicating PT as a plausible alternative to MoS2 and WS2.

The pressure-viscosity coefficient, α, is a measure of the pressure dependence of the viscosity of the liquid in elastohydrodynamic lubrication (EHL). There seems to be confusion around the understanding of the pressure-viscosity response in the inlet zone. In this paper the values of α were obtained from measurements of viscosity as a function of pressure and offers a understanding on the piezoviscous effect at various inlet pressures for those liquids. Moreover, the viscosities of several commercial engine oils and laboratory blends of mineral and synthetic base oils with polymer additives were measured at pressures up to 1 GPa and at temperatures of 40°, 75°, and 100°C. It was observed in some of these materials The significant changes within viscosity are temperature- and pressure-dependent. Analysis of the experimental results indicated that the solidification (significant increase viscosity) is due to liquid-solid phase transitions occurring in the lubricant's polymer additives. Thus, this paper gives evidence on the role of molecular weight and concentration of polymer and its influence on the pressure and temperature-dependent onset of the phase transitions. This transition has not been discussed in the open literature and is not accounted for in current bearing design using the Barus equation or the modified Yasatomi equation and may be the cause of some bearing damage modes.

Orientation: Exchange market pressure (EMP) is the selling pressure of domestic currency or excess demand needed for foreign currency. Research purpose: The purpose of this study was to analyse EMP using extreme value theory (EVT) and to compare two commonly used EVT methods. Motivation for the study: To determine whether the EMP of two African countries can be modelled with EVT, and if so, which method would be best suited. To determine periods of extreme pressure or currency crisis by using these methods. Lastly, to study the individual components of the EMP index during these periods of stress of crises. Research design/approach and method: The monthly data of the three components of the EMP index for two African countries (Republic of South Africa [RSA] and Kenya) were studied for a period of 19 years (1999–2017). The data were modelled using the generalised Pareto distribution (GPD) with the peak over threshold (POT) method using maximum likelihood estimation. Moreover, the data were also modelled using the non-parametric Hill estimate. Appropriate estimated and empirical quantiles are reported in order to determine periods of extreme pressure or crises. The components of the EMP RSA data set were modelled with appropriate autoregressive moving averages and/or autoregressive conditional heteroscedasticity/generalised autoregressive conditional heteroscedasticity (ARMA/ARCH/GARCH) processes to ensure independent and identically distributed variables. Main findings: Reliable and accurate estimates were obtained for the scale and shape parameter using the GPD POT method for both countries. Positive shape parameters confirmed generalised extreme value distributions with heavy tails of the Frechet type. Similarly, accurate and reliable shape estimates were computed using the non-parametric Hill estimator for both countries. Practical/managerial implications: The GPD POT method more closely reflected estimates to the empirical qauntiles compared to the Hill method. It is feasible to model the EMP data of two African countries with EVT using both POT estimation methods. However, the GPD method using maximum likelihood estimation was more accurate compared to the non-parametric Hill estimate. Contribution/value-add: It is feasible to model the EMP data of two African countries using EVT using both POT methods. As a consequence periods of extreme pressure could be identified. Therefore the individual components of the EMP at those periods of extreme pressure could be studied more closely.

A research has been done to investigate the tribological performance of palm kernel oil (PKO) with addition of different percentage of pour point depressant, PPD (5w%, 10wt%, 20wt% and 30wt%) according to ASTM D2783. The main analyses that have been done in this research are low temperature performance ability of blended PKO, coefficient of friction (COF), wear scar diameter (WSD) and surface profile. The result of the experiment has shown that for low temperature performance, PKO with 20wt%PPD (A2-20%) and 30wt%PPD (A2-30%) show great performance in withstanding lower temperature (15°C). Under extreme pressure test, it can be seen that PKO can only withstand lower load (110kg) compared to mineral oil (140 kg). The sample 10wt%PPD (A2-10%) shows good lubricity performance in terms of COF as compared to other sample. 5wt%PPD (A2-5%) and 10wt%PPD show good lubricity performance in terms of anti-wear behaviour (A2-10%) by producing the lowest WSD when compared to other samples. From overall view, PPD is considered as successful in improving low temperature performance of PKO, but in terms of lubricity performance, adding PPD will slightly reduce the lubricity performance under extreme pressure if compared to pure PKO. [ABSTRACT FROM AUTHOR]

Enzymatic synthesis of six esters of α-lipoic acid with different fatty alcohols and diols was carried out to produce novel compounds with lubricant additive properties. The synthetic route was mild and efficient with good yields. The synthesized compounds were characterized by IR, NMR, and mass spectral studies and screened for their thermal stability, antiwear (AW), extreme pressure (EP), and antioxidant (AO) properties. The tribo tests in a synthetic base fluid indicated that all the synthesized compounds act as antiwear and extreme pressure additives. All the prepared esters exhibited very good thermal stability and excellent antioxidant properties with better performance compared to commercial antioxidant BHT as determined by differential scanning calorimetry. [ABSTRACT FROM AUTHOR]

To enhance the lubricating and extreme pressure (EP) performance of base oils, two types of oil-soluble ionic liquids (ILs) with similar anion albeit dissimilar cations were synthesized. The physical properties of the prepared ILs were measured. The anticorrosion properties of ILs were assessed by conducting corrosion tests on steel discs and copper strips, which revealed the remarkable anticorrosion properties of the ILs in comparison with those of the commercial additive zinc dialkyldithiophosphate (ZDDP). The tribological properties of the two ILs as additives for poly-α-olefin-10 (PAO10) with various mass concentrations were investigated. The tribological test results indicate that these ILs as additives are capable of reducing friction and wear of sliding contacts remarkably as well as enhance the EP performance of blank PAO10. Under similar test conditions, these IL additives exhibit higher lubricating and anti-wear (AW) performances than those of ZDDP based additive package in PAO10. Subsequently, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometer (EDS) were conducted to study the lubricating mechanism of the two ILs. The results indicate that the formation of tribochemical film plays the most crucial role in enhancing the lubricating and AW behavior of the mixture lubricants. [ABSTRACT FROM AUTHOR]

The lamellar structure of MoS2 provides very good protecting layer that can be easily sheared under the application of extreme pressures and thus enhance the antiwear performance of the chromium steel bearing aircraft grade E52100. ASTM standard 2266 uses 4-ball testing by keeping the load at 393 Newton wherein the grease is heated to 75°C and the test is conducted at a rotational speed of 1200 min-1 for 1 hour and the wear scar is measured at the end of the period. While this method is useful under fixed conditions it is not always representative of the fields where variable loads and speeds and different break in periods play a role and could change the results tremendously. The goal of this study was to examine the loads and speeds conditions with and without break in period of 30 second at the start of the test and every 7.5 minutes thereafter. This will help explain their influences on the wear properties of lithium base grease under fixed 2% MoS2 concentrations. Results indicated that wear was largely dependent on the loading condition during specific break in period at a higher rotational speed. It is believed that MoS2 greases perform better under moderate loading when break in period is used as was optimized by Design Expert analysis (DOE). MoS2 is sufficient to improve the wear characteristics at different break in period for different speeds and loads for extreme pressure applications. [ABSTRACT FROM AUTHOR]