Boundary Lubrication Properties Research Articles

Evaluation of Boundary Lubrication Properties of Fatty Acids Using a Lateral Force-Controlled Tribometer

Evaluation of Boundary Lubrication Properties of Fatty Acids Using a Lateral Force-Controlled Tribometer

Grease lubricity in the fretting contact: Are ionic liquids the solution?

A statistical, energy-based approach is employed to experimentally characterize the ability of different greases to reduce friction when a point contact is subjected to repeated reciprocal displacements of smaller magnitude than the contact diameter. This approach allows the assessment of lubricant fretting performance with respect to its ability to remain within the contact and also its boundary lubrication properties. The results indicate that composition-dependent boundary lubrication properties of greases loaded with non-halogenated ionic liquids containing bis(oxalato)borate ([BOB]) and bis(mandelato)borate ([BMB]) anions can result in no detectable wear and low friction, even under conditions of moderately high pressures and where the original contact area is never fully uncovered. This discovery paves the way for the development of anti-fretting ionic greases.

Construction and Tribological Properties of Biomimetic Cartilage-Lubricating Hydrogels.

Articular cartilage provides ultralow friction to maintain the physiological function of the knee joint, which arises from the hierarchical complex composed of hyaluronic acid, phospholipids, and lubricin, covering the cartilage surface as boundary lubrication layers. Cartilage-lubricating polymers (HA/PA and HA/PM) mimicking this complex have been demonstrated to restore the lubrication of cartilage via hydration lubrication, thus contributing to the treatment of early osteoarthritis (OA) in vivo. Here, biomimetic cartilage-lubricating hydrogels (HPX/PVA) were constructed by blending HA/PA and HA/PM (HPX) with polyvinyl alcohol (PVA) to improve the boundary lubrication and wear properties, so that the obtained hydrogels may offer a solution to the main drawbacks of PVA hydrogels used as cartilage implants. The HPX/PVA hydrogels exhibited good physicochemical and mechanical properties through hydrogen-bonding interactions, and showed lower friction and wear under the boundary lubrication and fluid film lubrication mechanisms, which remained when the hydrogels were rehydrated. Our strategy may provide new insights into exploring cartilage-inspired lubricating hydrogels.

Esterification of Hydrogenated Hydroxyl-Terminated Polybutadiene as a High-Performance Lubricating Oil

Lubricating oils have been widely used to reduce the friction and energy consumption in mechanical drive systems. Here, a novel high-performance lubricating oil was developed by the esterification of the hydrogenated hydroxyl-terminated polybutadiene (HHTPB). Owing to the unique chemical structure, it possessed the advantages of both the poly-α-olefins (PAOs) such as high chemical stability, low pour point, high viscosity index, and low evaporation loss and the synthetic esters such as good film formation property and excellent boundary lubrication properties. As a lubricating oil without any additive, the HHTPB isooctanoate exhibited ultralow friction and excellent wear-reduction performance, making it a promising candidate for practical applications.

Effect of SiC nanoparticles on the tribological properties of rice bran oil-based lubricant

The environmental impact of petroleum products has forced the industry to search for alternative bio-products. Vegetable oils can be considered as an alternative to these petroleum products due to the high viscosity index and excellent boundary lubrication properties. In this work, rice bran oil (RBO) is selected as a base-stock for developing bio-lubricants. The silicon carbide (SiC) nanoparticles were added to RBO in different proportions (0.01 to 0.05 wt. %). The tribological properties were evaluated for different samples using a standard four-ball tribo-tester. The weight percentage of SiC in RBO was optimised based on the tribological results. The optimum concentration of SiC nanoparticles in RBO was found to be 0.03 wt. %. The experimental study also evaluated the tribological properties of chemically modified RBO (MRBO) with 0.03% SiC nanoparticles. It was noted that the tribological properties are better for MRBO with 0.03% SiC nanoparticles.

Lubricity, Tribological and Rheological Properties of Green Ester Oil Prepared from Bio-Based Azelaic Acid

Plant oil derived compounds have been used as the raw material for the synthesis of green biolubricant. Azelaic acid derived from oleic acid is one of the interesting compounds. The synthesis of azelate esters oil based synthetic green biolubricants was carried out. The esterification process of azelaic acid with variety type of alcohols was catalyzed by concentrated H2SO4. The yields percentages of azelate esters oil produced were varied depending their overall molecular structure. The azelate esters oil properties were evaluated for their suitability as a biolubricant. The results showed that the linear azelate esters oil showed high pour point values in a range of 15 to 5 ºC for di-decyl azelate, di-octyl azelate and di-hexyl azelate respectively. On the other hands, the branch azelate esters oil showed very low pour point of -70, -58 and -50 ºC for di-2-butyloctyl azelate, di-2-ethylhexanol azelate and di-2-ethylbutyl azelate, respectively. Moreover, the linear azelate esters oil gave high values of flash point, viscosity index and oxidative stability, and they were slightly affected by branching molecule structure. The tribological and rheological properties of high molecular azelate esters oil were also performed. Subsequently, most of them were classified as non-Newtonian fluids and having boundary lubrication properties with low friction coefficient. The branch azelate esters oil is plausible to be used as green biolubricants in many applications including automotive, marine engine oils, compressor oils, hydraulic fluids, gear oils and industrial biolubricants.

Dry mouth diagnosis and saliva substitutes-A review from a textural perspective.

The aim of this review is to assess the objective and subjective diagnosis, as well as symptomatic topical treatment of dry mouth conditions with a clear focus on textural perspective. We critically examine both the current practices as well as outline emerging possibilities in dry mouth diagnosis and treatment, including a patent scan for saliva substitutes. For diagnosis, salivary flow rates and patient-completed questionnaires have proven to be useful tools in clinical practice. To date, objective measurements of changes in mechanical properties of saliva via rheological, adsorption, and tribological measurements and biochemical properties of saliva such as assessing protein, mucins (MUC5B) are seldom incorporated into clinical diagnostics; these robust diagnostic tools have been largely restricted to application in non-clinical settings. As for symptomatic treatments of dry mouth, four key agents including lubricating, thickening, adhesive, and moisturizing agents have been identified covering the overall landscape of commercial saliva substitutes. Although thickening agents such as modified celluloses, polysaccharide gum, polyethylene glycol, and so forth are most commonly employed saliva substitutes, they offer short-lived relief from dry mouth and generally do not provide boundary lubrication properties of real human saliva. Innovative technologies such as self-assembly, emulsion, liposomes, and microgels are emerging as novel saliva substitutes hold promise for alternative approaches for efficient moistening and lubrication of the oral mucosa. Their adoption into clinical practice will depend on their efficacies, duration of relief, and ease of application by the practitioners and patient compliance.

Synergistic nano-tribological interaction between zinc dialkyldithiophosphate (ZDDP) and methyl oleate for biodiesel-fueled engines

In biodiesel-fueled compression-ignition (CI) engines, dilution by unburned biodiesel has been found to have adverse effects on the boundary lubrication properties of additives in fully formulated engine lubricants. Such dilution of engine lubricants could be even more pronounced for CI engines running on higher blend concentrations of biodiesel. Given the nanoscopic nature of the interaction, this study seeks to determine the nano-tribological properties of an engine lubricant additive (e.g., zinc dialkyldithiophosphate (ZDDP)) when diluted with a fatty acid methyl ester (e.g., methyl oleate). Using lateral force microscopy (LFM) together with a fluid imaging technique, the lowest nanoscopic friction forces and coefficient of friction values (0.068–0.085) were measured for ZDDP when diluted with 70 vol% of methyl oleate. These values are also observed to be lower than those measured for neat ZDDP and neat methyl oleate, respectively, under similar conditions. Subsequently, interpreting the data with the Eyring thermal activation energy approach, it could then be elucidated that the lower frictional losses observed for the contact lubricated with this volumetric mixture are a result of the lower potential energy barrier and activation energy required to initiate sliding. These energy values are approximated to be 2.6% and 28.9% (respectively) lower than that of the contact lubricated with neat ZDDP. It was also found that the mixture, at this volumetric concentration, possesses the highest possible pressure activation energy (load-carrying capacity) along with the lowest possible shear activation energy (shearing), potentially indicating optimum tribological conditions for boundary lubrication. Thus, the findings of this study suggest that an optimum concentration threshold exists in which a synergistic nano-tribological interaction between additives and fatty acid methyl esters can be attained, potentially reducing boundary frictional losses of lubricated conjunctions. Such findings could prove to be essential in effectively formulating synergistic additive concentrations for engine lubricants used in biodiesel-fueled CI engines.

Evaluation of the tribological properties and oxidative stability of epoxidized and ring opened products of pure rice bran oil

Vegetable oils constitute a potential base stock for bio-lubricants, which has good biodegradability, high flash point, high viscosity index and excellent boundary lubrication properties. They also possess some limitations like low thermal and oxidation stability, poor low temperature properties and narrow range of viscosities. These limitations can be altered by modifying the vegetable oils chemically or by providing additives into the oils. This research work focused on the chemical modification of pure rice bran oil by epoxidation process using 30% hydrogen peroxide and glacial acetic acid. The epoxidized rice bran oil was then subjected to ring opening process using butanoic acid. The epoxidation process was optimized with four factors (Temperature, Time, Weight % of Catalyst, Hydrogen Peroxide molar ratio), each factors having four levels. The lubricant properties of pure rice bran oil (RBO), epoxidized rice bran oil (ERBO) and ring opened rice bran oil (RRBO) were studied. It was noted that the lubricant properties of ERBO and RRBO were better compared to pure RBO.

Boundary Lubrication Properties of Maleic Dithiophosphate Derivatives

Boundary Lubrication Properties of Maleic Dithiophosphate Derivatives

Boundary lubrication properties and contact mechanism of carbon/MoS2 based nanolubricants under steel/steel contact

Lubrication mechanism of some carbon-based nanoparticles is unresolved and needs proper attention. In this work, friction and wear properties of carbon/MoS2 solid lubricants are tested in the boundary lubrication regime and further compared with oil-based binary and ternary nanolubricants. Results show that MWCNT and fullerene have high values of friction coefficient and wear rate in a dry medium. However, in lubricated medium with fomblin oil, they comply with the boundary lubrication mechanism and provide low friction and wear. The binary and ternary nanolubricants of oil-graphene, oil-MoS2, and oil-graphene-MoS2, oil-graphene-fullerene have provided enhanced wear and friction performance due to a build-up of a tribofilm between the contact zones. The interfacial contact mechanism depends on aggregation and particle rolling for dry and lubrication contact, respectively.

Nano-tribological characterisation of palm oil-based trimethylolpropane ester for application as boundary lubricant

Abstract To isolate shearing of boundary film from direct surface-to-surface asperity interactions, the study determines boundary lubrication properties of palm oil-based TMPE (PTMPE) using Lateral Force Microscopy coupled with fluid imaging. PTMPE is produced through a series of 3-step transesterification processes, converting palm oil (PO) into palm methyl ester (PME) and finally into PTMPE. It is shown that PME generates the lowest friction. However, using Eyring thermal activation energy approach, PME is shown to possess less desirable load bearing property, portraying a form of stiction or adhesive nature. Even though friction is higher, PTMPE exhibits better load bearing ability, demonstrating the onset of lubricant laminar flow due to increased hydrodynamic effect, which is not observed for the PO and PME measurements.

Study on Boundary Lubrication Properties and Lubrication Mechanism in Combined Condition of MoP and ZnDTP

Study on Boundary Lubrication Properties and Lubrication Mechanism in Combined Condition of MoP and ZnDTP

Suitability of ethyl cellulose as multifunctional additive for blends of vegetable oil-based lubricants

In a previous study, ethyl cellulose was successfully blended with castor oil and the results demonstrated its suitability to be used as additive to expand the range of operating conditions under which fluid film lubrication is sustained, mainly at high temperature. However, apparent solubility problems were detected when mixed with other vegetable oils with lower polarity than castor oil. In this work, a suitable combination of ethyl cellulose (EC) with both high oleic sunflower (HOSO) and castor (CO) oils was found able to reach stable and non gel-like blends with viscosities at 40 °C ranging between 62 and 493 cSt, and viscosity indexes fitting into group III (VI ≥ 120) of API classification of base fluids. The ternary HOSO/CO/EC blend showed an important reduction in friction coefficient at low entrainment speed, and generated a stable EHD-film at 100 °C of around 20 nm, which suggests better boundary properties than HOSO/EC or CO/EC blends. On the other hand, ethyl cellulose hindered wax crystallization process of these vegetable oil-based lubricants at 5 °C, yielding comparable results to those obtained with standard polymethacrylate backbone additives. Therefore, the suitable combination of both castor and HOSO with EC as multifunctional additive allow a set of eco-friendly base fluids to be formulated with a wide kinematic viscosity range, better viscosity-temperature dependence than many mineral or synthetic oils lubricants and excellent boundary lubrication properties, making them suitable for many lubricant applications.

冷間圧延における水溶性ポリマーの潤滑性の向上

The application of water-solution lubricants to cold rolling processes is attractive because they have the potentialto conserve clean environments around rolling mills, and are also superior because of their easy maintenance and long life for circulated use. Polyalkylene glycols (PAGs) are representative components of metalworking solution lubricants. However, their application to industrial use is difficult because of their poor lubricity. In this study, conditions for the improvement of lubricity are investigated, especially for the high-speed cold rolling conditions of steel strips. It is found that the lubricant solutions can be improved to the level of oil-in-water emulsions if the amount of plated-out lubricant on the steel surface is sufficiently large by increasing the polymer concentrations in water and the surface temperature of the strip. Also, it is concluded that further investigations on additives are necessary to improve boundary lubrication properties in order to apply the lubricant solutions to industrial cold rolling processes.

Interaction of porcine gastric mucin with various polycations and its influence on the boundary lubrication properties

Abstract The interaction of porcine gastric mucin (PGM) with polycations possessing amine functional groups, including polyallylamine hydrochloride (PAH), poly- l -lysine (PLL) and polyethylenimine (PEI), was examined from a tribological standpoint at a self-mated polydimethylsiloxane (PDMS) interface. In all cases, PGM interacted with the cationic polymers, leading to a smaller size of the aggregates compared to PGM, surface charge compensation, and distortion of the PGM protein conformation. But, a synergistic lubrication effect was clearly observed only from the 1/1 (w/w) mixture of PGM with branched PEI (B-PEI) where the friction coefficient was reduced by two orders of magnitude compared to neat PGM or B-PEI in the speed range of 0.25–100 mm/s. This was attributed to the smallest hydrodynamic size and “sphere-like” conformation of B-PEI due to high degree of branching, which favors tenacious complexation with PGM, fast surface adsorption, and continuous reformation of the lubricating layer under cyclic tribostress in pin-on-disc tribometry.

Friction properties of surface-modified polished chemical-vapor-deposited diamond films under boundary lubrication with water and poly-alpha olefin

To reduce the friction coefficient of chemical-vapor-deposited diamond films, the films were surface modified by fluorination, oxidation, or nitrogen ion implantation. Surface modification of diamond surface structures (especially of the N+-implanted diamond film) was confirmed by Raman spectroscopy. Fluorinated diamond film demonstrated the lowest surface free energy, whereas the nanoindentation hardness and nanowear resistance were lowest in the N+-implanted diamond film. Boundary lubrication properties were evaluated by an oscillating friction test. The friction coefficient and surface damage of the oxidized and N+-implanted diamond films (with high surface free energies) were effectively reduced by boundary lubrication. Fluorinated and untreated diamond films exhibited low-friction and little damage under dry and boundary lubrication.

平滑ダイヤモンド膜とCF4プラズマ処理したダイヤモンド膜の表面特性と各種水溶液による境界潤滑特性

平滑ダイヤモンド膜とCF₄プラズマ処理したダイヤモンド膜の表面特性と各種水溶液による境界潤滑特性

Improvement in Boundary Lubrication Characteristics of SAE20W40 Oil Using Aluminum Oxide Nanoparticles

The present work includes the study of boundary lubrication properties of SAE20W40 lubricating oil added with aluminum oxide nanoparticles. Pin-on-disk tribometer is employed to study the effects of nanoparticles in different sizes (40–80 nm) and concentrations (0–1% by weight) on the friction coefficient. The experimental design consists of L18 orthogonal array involving six levels for nanoparticles concentration and three levels for nanoparticles size, sliding speed, and normal load. The presence of nanoparticles has significantly improved the lubrication properties of oil. Minimum friction coefficient is recorded at 1200 rpm rotational speed and 160 N normal load for 0.8% concentration of 60 nm sized nanoparticles. Scanning electron microscopy (SEM) and electron diffraction spectrometry (XRD) are employed to understand the friction reduction mechanism.

Boundary lubrication by adsorption film

AbstractA complete understanding of the mechanism of boundary lubrication is a goal that scientists have been striving to achieve over the past century. Although this complicated process has been far from fully revealed, a general picture and its influencing factors have been elucidated, not only at the macroscopic scale but also at the nanoscale, which is sufficiently clear to provide effective instructions for a lubrication design in engineering and even to efficiently control the boundary lubrication properties. Herein, we provide a review on the main advances, especially the breakthroughs in uncovering the mysterious but useful process of boundary lubrication by adsorption film. Despite the existence of an enormous amount of knowledge, albeit unsystematic, acquired in this area, in the present review, an effort was made to clarify the mainline of leading perspectives and methodologies in revealing the fundamental problems inherent to boundary lubrication. The main content of this review includes the formation of boundary film, the effects of boundary film on the adhesion and friction of rough surfaces, the behavior of adsorption film in boundary lubrication, boundary lubrication at the nanoscale, and the active control of boundary lubrication, generally sequenced based on the real history of our understanding of this process over the past century, incorporated by related modern concepts and prospects.