Lubricant Additives Research Articles

Sulfur-Containing Carbon Nanospheres as Lubricant Additives for Antiwear and Friction Reduction

Sulfur-Containing Carbon Nanospheres as Lubricant Additives for Antiwear and Friction Reduction

Effect of texture shapes and additives in lubricants on the dynamic characteristics of the hydrodynamic journal bearing

PurposeThis study aims to understand how the texture shape, number of textures and addition of nanoparticle additives in lubricants impact the dynamic characteristics of journal bearing by comparing six different texture shapes like triangle, chevron, arc, circle, rectangle and elliptical applied in pressure-increasing region under various geometrical and operating conditions.Design/methodology/approachThe finite element method approach has been employed to solve governing Reynold’s equation, assuming iso-viscous Newtonian fluid, for computation of performance parameters like stiffness and damping coefficient, threshold speed, etc. By using a regression model, the impact of adding nanoparticles Al2O3 and CuO to the base lubricant on viscosity variation is calculated for selected temperature ranges and weight fractions of nanoparticles.FindingsThe arc-shaped texture with an area density of 28.27%, eccentricity ratio of 0.2 and texture depth of 0.6 exhibited 35.22% higher direct stiffness and 41.4% higher damping coefficient compared to the lowest value in the circle-shaped texture. Increasing the number of arc-shaped textures on the bearing surface with low area density led to declining stiffness and damping parameters. However, with nanoparticle additives, the arc-shaped texture further showed 10.75% and 8.11% improvement in stiffness and 9.99% and 4.87% enhancement in damping coefficient for Al2O3 and CuO, respectively, at 90 °C temperature and 0.5% weight fraction.Originality/valueBy understanding the influence of texture shapes on the dynamic characteristics, engineers can design bearings that exhibit improved stability and enhance overall performance.

TiO2 Nanoparticles Coated with Nitrogen-Doped Amorphous Carbon as Lubricant Additives in Engine Oil

TiO₂ Nanoparticles Coated with Nitrogen-Doped Amorphous Carbon as Lubricant Additives in Engine Oil

Mechanisms of friction and wear reduction by nanosilver additives to base oil: Molecular dynamics simulation and experimental study

Although nanosilver particles are commonly used as oil lubrication additives, their mechanism for improving lubrication at the atomic scale remains unclear. This article explains how the performance of a pentaerythritol oleate lubrication system can be improved using silver nanoparticles through molecular dynamics simulation. Additionally, tribological tests were conducted using a reciprocating friction and wear testing machine. The relative concentrations and simulated shear conformation revealed that silver nanoparticles underwent deformation under shear stress and fractured at the interlayer slip. This resulted in the formation of a deposited film that spread over both the top and bottom Fe layers. We characterized the interaction between pentaerythritol oleate molecular chains and Fe layers by analyzing interfacial interaction energies, mean square displacements, and self-diffusion coefficients. Our findings indicate that the presence of silver nanoparticles improves both the adsorption of pentaerythritol oleate molecular chains onto the Fe layer and their diffusion behavior. The results of tribological tests indicate that adding silver nanoparticles significantly reduces friction coefficient and frictional wear across various lubrication conditions. The addition of silver nanoparticles at different loads and temperatures resulted in varying reductions in the coefficient of friction and wear. At a load of 20 N and a temperature of 298 K, the coefficient of friction decreased by 9%, and wear decreased by 31%. When the load was reduced to 2 N while maintaining a temperature of 298 K, the coefficient of friction decreased by 8% and wear decreased significantly by 84%. Finally, at a load of 20 N but with an increased temperature to 373 K, there was a larger reduction in the coefficient of friction (23%) compared to wear (50%). The film-formation mechanism of improved lubrication by silver nanoparticles was verified through tribological tests and simulations.

Tribological Evaluation of Vegetable Oil/MoS2 Nanotube-Based Lubrication of Laser-Textured Stainless Steel.

In the present work, the functionalisation of austenitic stainless steel, AISI 316L surfaces via nanosecond Nd:YAG laser texturing in order to modify the surface morphology with crosshatch and dimple patterns is presented. A tribological analysis under lubrication with sunflower and jojoba oil with and without the addition of a solid lubricant, MoS2 nanotubes, was performed. In conjunction with friction/wear response laser-textured surface wettability, oil spreadability and oil retention capacity were also analysed. It was shown that the crosshatch pattern generally exhibited lower friction than the dimple pattern, with the addition of MoS2 nanotubes not having any significant effect on the coefficient of friction under the investigated contact conditions. This was found in addition to the better oil spreadability and oil retention capacity results of the crosshatch-textured surface. Furthermore, texturing reduced the wear of the stainless-steel surfaces but led to an approximately one order of magnitude larger wear rate of the steel counter-body, primarily due to the presence of hard bulges around the textured patterns. Overall, the crosshatch pattern showed better oil retention capacity and lower friction in combination with different vegetable oils, thus making it a promising choice for improving tribological performance in various environmentally friendly applications.

Alkylamine-Grafted Molybdenum Disulfide Nanosheets for Enhanced Dispersion Stability and Lubricity Properties.

The unique structure and ultralow interlayer shear strength give molybdenum disulfide (MoS2) materials a broad prospect for energy savings, economic benefits, and extended operating life of lubrication systems. Herein, we prepared an effective integration strategy to prepare novel small-sized and chemically grafted MoS2 to solve the problems of poor dispersibility and easy agglomeration of MoS2. The MoS2 powder was stripped and oxidized to generate active centers using acid oxidation and high-speed ultrasonic crushing to obtain two different types of alkylamine chemically, covalently grafted, oxidized MoS2 nanosheets as lubricant additives to achieve friction reduction and antiwear. The chemical changes and structural characteristics of different types of alkylamine molecules upon covalent interaction with oxidized MoS2 were investigated in detail by FTIR, XPS, TGA, XRD, and TEM analyses. The results showed that the alkylamine-grafted MoS2 oxide nanosheets had good dispersion in 15# industrial white oil, and friction experiments confirmed that the alkylamine-grafted MoS2 oxide (MoS2-O-OLA) nanosheets exhibited better friction and wear resistance such that, compared with pure 15# industrial white oil, the 0.02 wt % MoS2-O-OLA nanosheets could significantly reduce friction (36.2%) and wear (22.4%). The field-emission scanning electron microscopy (FESEM) and EDS analyses of the wear surface showed that MoS2-O-OLA nanosheets play an important role in improving tribological properties by generating interlayer slippage at the steel ball contact interface, thereby forming surface protection and a uniform oil film.

Tribological Behavior of 1,8-Diazabicyclo[5.4.0]Undecane-7-Ene–Organophosphoric Acid-Based Protic Ionic Liquids as Lubricant Additives

Tribological Behavior of 1,8-Diazabicyclo[5.4.0]Undecane-7-Ene–Organophosphoric Acid-Based Protic Ionic Liquids as Lubricant Additives

Tribochemical insights into the carbon film formation induced by metallic species derived from layered double hydroxide nanoadditives

Layered double hydroxides (LDHs) have demonstrated excellent tribological performance in various studies. However, there remains a fundamental knowledge gap concerning the chemical composition of tribofilms across the cross-section. In this study, we seek to elucidate this question by tribologically testing various binary LDHs. It was found that five out of eight LDHs, denoted as CoAl-, CoFe-, MgAl-, NiFe-, and ZnAl-LDHs could induce hierarchical protective tribofilms due to the formation of rigid oxide layers and in situ carbon-based films. The five tribofilms helped to reduce wear loss and friction by approximately 90% and 20%, respectively. Remarkably, the Co-based tribofilms showed the best antiwear performance because of the thick carbon tribofilm formation and the strong bonding at the metallic/tribo-oxide interfaces. The formation mechanisms of the carbon tribofilm and its characteristic nature were evaluated and revealed by scanning transmission electron microscopy and electron energy loss spectroscopy. Meanwhile, the intriguing nano-scale mechanical properties, i.e., the hardness and reduced elastic modulus of different tribofilms, were well-demonstrated by nanoindentation and nanoscratch experiments. The correlation between chemical structures and mechanical properties of the tribofilms derived from LDH lubricant additives was first conducted and discussed, unveiling the tribochemical and lubrication mechanisms between the LDHs and sliding surfaces.

One-step fabrication of amorphous/ITO-CNTs coating by plasma electrolytic oxidation with particle addition for excellent wear resistance

As moving machine parts, aluminum alloys suffer from poor wear resistance, however, the combination of amorphous materials and anti-friction lubricant phases has rarely been investigated to improve tribological performance. The amorphous coatings were fabricated by one-step plasma electrolytic oxidation (PEO) with ITO and CNTs addition, of which CNTs were used as lubricant additives to enhance the anti-friction properties of aluminum alloy. It is found that the amorphous phases in the coatings increase with ITO concentration in the electrolyte. As well as, when the concentration of ITO in the electrolyte reaches 40 g/L, XRD cannot detect Al2O3 phase, but only ITO and amorphous phase. The formation of the amorphous coating is due to the fact that In3+ can be used as a network modifier to improve the glass-forming ability of molten oxides and the rapid cooling after discharge. Further, the amorphous coating exhibits a higher hardness (1472 HV0.5) compared to single Al2O3 coatings (267 HV0.5) and its main wear mechanism is adhesive wear with a high friction coefficient (∼0.68). In contrast, with the incorporation of CNTs, the amorphous coating exhibits slight abrasive wear after 6000 sliding cycles under dry friction conditions, with a stable frictional coefficient of around 0.14. Of which, the amorphous coating (1704 HV0.5) serves as a load-bearing and CNT acts as a lubricant phase during friction and wear. Hence, through the synergistic effect of the CNTs additive and the amorphous coating, the tribological properties of aluminum alloy are significantly improved, with a low friction coefficient and shallow wear trace.

Late-model N, B, and P-co-doped carbon dots as additives for friction-reduction and anti-wear

Carbon dots (CDs), a kind of burgeoning carbon-based nanomaterial, were widely used as high-efficiency lubricant additives for promoting the friction-reduction and anti-wear behaviors of green PEG-based lubricating oils. Undoubtedly, advances in CDs-based lubricant additives play a crucial role in enhancing their application prospect and utility value. Recent studies suggest that doping CDs with heteroatoms, especially multiple heteroatoms could remarkably promote their tribological performance. Therefore, the state-of-the-art N, B, and P-co-doped CDs (N,B,P-CDs) with a diameter of approximately 3.8 nm and composed of amorphous structures were synthesized by conveniently “one-step” pyrolyzing the corresponding carbon sources and dopants. Noticeably, the synthetic procedures of N,B,P-CDs were uninvolved in any pre-processing and post-processing techniques, showing favorable large-scale preparation potential. Adding suitable concentrations of N,B,P-CDs, the friction-reduction, anti-wear, and load-supporting functions of PEG200 base oil can be maximally increased by 38.1 %, 86.2 %, and 66.7 %, respectively, showing outstanding tribological performances. In addition, the tribological behaviors of N,B,P-CDs are evidently better than that of N,B-CDs and P-CDs under identical test conditions, exhibiting a multiatomic synergistic lubrication effect. According to the wear track surface analysis results and previous reports, the excellent tribological performance of N,B,P-CDs attributes to their favorable film-forming ability and nano-lubrication effect in the different friction stages.

Development and performance evaluation of self-lubricating cemented carbide

Nowadays, there is a trend in the industry to reduce or even eliminate the use of cutting fluid in machining operations. The high costs of purchasing, using, and disposing of fluids and problems related to environmental pollution and operator health favor the dry-cutting technique. However, in some machining processes, lubrication is required. In this cases, solid lubrication may be a solution. The present study investigated the development of self-lubricating cutting tool materials by adding graphite in WC – 10 wt% Co cemented carbide and how this graphite affects the sample's mechanical properties and wear behavior. The WC - 10 wt% Co cemented carbide was prepared by spark plasma sintering (SPS), and solid graphite lubricant was added at different concentrations. The samples were mixed in a high-energy ball mill and sintered at 1200 °C under 40 MPa. Microstructure, hardness, fracture toughness, and wear analyses were performed on the samples to understand the effect of graphite addition on sintered material properties. The chemical composition of the samples was analyzed by XRD and Raman spectroscopy. The wear measurement was performed by analyzing the volume of material lost by the samples during the pin-on-disk tests. Profilometry analyzes of the samples before and after the tests made it possible to measure the volume of lost material, allowing to verify the influence of the addition of solid lubricant on the wear rate of the samples. The results of the mechanical tests show that the highest hardness and the modulus of elasticity were 1578 HV and 870 GPa, respectively. The wear presented by the samples with 1% of graphite was up to 9 times less than the standard samples. The wear mechanisms are micro-cracking and fragmentation of WC grains; however, the presence of a solid lubricant avoids the steel counterpart material transfer for the pin surface. Also, it was observed the formation of a graphite and oxide tribolayer on the worn disc surface during the tests, thus avoiding excessive wear.

Assessing the Influence of Micro Lubricant Additives on Worm Gearbox Power Consumption: A Tribological Investigation Utilizing Hazelnut Oil-Based Lubricants

As technology progresses, lubricant additives are becoming more prevalent and expanding the application areas of modern tribology. This study aimed to investigate the tribological properties of recently used additive particles and their impact on worm gearbox power consumption. To achieve this, hazelnut oil was chosen as the base oil, and graphite, boric acid (BA), and hexagonal boron nitride (hBN) particles were added in certain proportions. The effect of each additive on the coefficient of friction and wear was investigated under different operating speeds and loads using a pin-on-disc tester. Optimal additive ratios for worm gearbox oils were utilized based on the previous studies, and oils using hazelnut oil as the base were prepared accordingly. The efficacy of the additives was evaluated using a worm gearbox test system.

Synergistic lubrication mechanism of core/shell C@MoS2 particles as lubricant additives

To unify the lubrication characteristics of carbon spheres (CS) with high load-bearing capacity and molybdenum disulfide (MoS2) with exceptional low-shear friction performance, CS wrapped with MoS2 (C@MoS2) were accomplished via an efficient and facile hydrothermal method based on the self-assembly principle. Then, 0.5 wt% C@MoS2 particles were dispersed into Poly Alpha Olefin 40 (PAO 40) for enhancing the anti-friction/wear abilities. Subsequently, 0.5 wt% of C@MoS2 particles were dispersed into Poly Alpha Olefin 40 (PAO 40) to enhance its anti-friction and wear-resistant capabilities. The excellent tribological properties of C@MoS2 particles were attributed to the synergistic lubrication between bearing and filling effect of CS as well as the superior antifriction capacity of MoS2 shell. Furthermore, the synergetic lubrication mechanism of C@MoS2 may be segmented into different stages: I. the shell crushing stage, corresponding to the rolling bearing effect of C@MoS2 particles at the friction interface; II. the core/shell separation stage, corresponding to the rolling bearing effect and self-repair effect of C@MoS2 particles; III. the core/shell recombination stage, corresponding to the construction and reinforcement of protective film and the great improvement of anti-friction/wear abilities performance.

Lubricating Ability of Protic Ionic Liquids as Additives to a Biodegradable Oil for Aluminum-Steel Contact: Effect of Alkyl Chain Length and Propensity to Hydrogen Bonding

Although aluminum alloys are widely used in the automotive and aerospace industries due to their excellent strength-to-weight ratio and good corrosion resistance, the poor tribological performance and low compatibility of these materials with lubricant anti-wear and anti-friction additives in conventional mineral oils are major limitations. In addition, environmental awareness has increased the need for more environmentally friendly lubricants. Ionic Liquids (ILs) have exhibited significant potential as lubricants and lubricant additives. One of the more interesting properties of ILs is that they can form physically-adsorbed or chemically-reacted layers that reduce friction and wear of the surfaces in contact. Among ILs, Protic Ionic Liquids (PILs) have received more attention recently because of their simple and economic synthesis route. Furthermore, the anions and cations of PILs can be selected to be considered environmentally benign. In this article, the tribological behavior of a family of six PILs are studied as additives to a biodegradable oil (BO), under aluminum-steel contact. Al2024 disks slid against AISI52100 steel balls under a normal load of 3 N and a frequency of 5 Hz at room temperature and using a ball-on-flat reciprocating tribometer. PILs used in this study, were synthesized using two strong acids, with short and long hydrocarbon chains, and three weak bases with different propensities to hydrogen bonds. Results show that, although adding just 1 wt.% of any PIL to BO reduced friction and wear, the alkyl chain length influenced the lubricating ability of these ordered fluids. Wear mechanisms and surface interaction are discussed on the basis of 3D profilometry, SEM-EDX and RAMAN spectroscopy.

Tribological performance for an Mg alloy subjected to sliding at elevated temperatures: A comparison between Al2O3 and MoS2 nano additives in silicone oil-based lubricant

Magnesium (Mg) and its alloys are crucial for energy-efficient vehicles due to their strong and lightweight properties, necessitating high-temperature fabrication and lubrication to reduce oxidation, friction, and wear. This paper investigated the tribological performance of lubricating oil using different particles to a Mg alloy subjected to contact sliding in an open system at high temperatures up to 250 °C. The overall experimental results showed improved tribological performances by using the two types of nanoparticles / nanoparticle-clusters (concentration ≥ 0.5 wt%) compared with the base silicone oil. The mechanisms by which the two types of nano lubricants improved the tribological performance are different. Al2O3 particles provided a more stable Al-rich anti-wear surface at higher temperatures in the range of 200–250 °C, while a tribo-chemical reaction film was formed with MoS2 additives, generating MoO3 and MgSO4. It is generally concluded that Al2O3 has more positive effect in terms of reduced coefficient of friction and wear rate as comparison to MoS2.

Boron–Nitrogen Codoped Carbon Nanosheets as Oil-Based Lubricant Additives for Antioxidation, Antiwear, and Friction Reduction

Boron–Nitrogen Codoped Carbon Nanosheets as Oil-Based Lubricant Additives for Antioxidation, Antiwear, and Friction Reduction

Tribological performance and lubrication mechanism of carbon nitride nanosheets as novel and high-efficiency additives for water lubrication

Recently, water-based nano-additives have attracted more attention with the resurrection of water lubrication owing to the increasing awareness of environmental protection and energy-saving. Highly water-dispersible carbon nitride nanosheets (C3N4 nanosheets), obtained via a high-yield and low-cost hydrothermal approach, were first used as a novel and environmentally-friendly nano-additive for water-based lubrication. The tribotest results exhibited that the tribological performances of C3N4 nanosheets in the water-based lubricant are highly sensitive to their adding concentrations. It was found that a C3N4 nanosheet concentration of 0.2 wt% could decrease the friction and wear in steel-steel contacts by 49.0% and 54.2%, respectively. The lubrication performances of C3N4 nanosheets as additives were much better than those of C3N4, attributed to their regular shape, good water dispersibility, and high reactivity. In addition, C3N4 nanosheets as additives exhibited a long service life even under harsh lubrication conditions. In addition, the molecular dynamics (MD) simulation technique was first employed to study the lubrication performances and lubrication regimes of C3N4 nanosheets. By combining the results of MD simulations and wear track surface analyses, the formation of water-based lubricating film and tribochemical film (mainly composed of organic compounds, metal nitrides, iron oxides, metal carbonates, and C3N4 nanosheets) coupled with the interlayer sliding and polishing effects of C3N4 nanosheets were primarily responsible for the excellent tribological performances of C3N4 nanosheets.

Influence of single phase NiS nanoparticles as lubricant additive in microscale deformation of copper gear

ABSTRACT Demand for miniature gears is increasing daily due to huge development in MEMS and microdevices. As a result of this drive towards miniaturisation, microsystem technologies are becoming increasingly important. In this concern, researchers are interested in developing a micro forming process to manufacture highly accurate micro gears, improved operational and functional characteristics, capacity to perform in hazardous environmental conditions, and longer service life. Single-phase NiS nanospheres were developed using a high-temperature wet chemical method and were dispersed in engine oil (SAE 20 W-40) for further forming process. During plastic deformation (micro-scale), the combined grain size effects and NiS nanoparticle added lubricant on formability and interfacial friction of the micro gear are investigated. The grain size effect significantly impacts the micro gear’s formability during micro forming. The grain size and orientation significantly influence the microscale deformation process. Due to the size effect, the microhardness value at the centre and the tooth varies considerably. Due to the existence of NiS nano additive lubricant, the surface quality of micro gear improved significantly. The findings of this work help to comprehend the properties of nano additive lubricant and how it behaves tribologically throughout the micro-forming process.

Cobalt phosphate octahydrates nanoflowers as oil-base additives for enhanced tribological performance

Recently, nanomaterial lubricant additives have attracted the attention of tribologists. Herein, a novel cobalt phosphate octahydrates (CoP) nanoflower was synthesized, and as an oil-base additive, CoP exhibited extraordinary tribological performance for titanium alloy. Compared with the pure PAO8, the friction coefficient (COF) and wear rate (WR) has been reduced by 69.77% and 99.27% at a concentration of 10 wt% CoP. Besides, SEM, EDS, and XPS characterization confirmed that CoP could fill and repair the surface of titanium alloy to make the worn surface smoother, and be deposited on the surface to form a deposition layer to protect the titanium alloy from severe wear. The low shear force between CoP nanosheets in the deposition layer promotes lubrication, achieving low COF.

Dialkyl phosphonate with carboxylic acid as antiwear additives for ester-base lubricants

Ester-base oils are commonly used in environmentally adapted lubricants (EALs) because of their biodegradability. However, their antiwear performance is difficult to improve using the conventional lubricant additives developed for mineral-base oils. In this study, dialkyl phosphonates with various functional groups were designed as antiwear additives for ester-base oils. The antiwear performances of these phosphonates were evaluated using four-ball tests. The results suggest that dialkyl phosphonate with carboxylic acid (DAPA) has better antiwear performance in ester-base oils than that of other phosphonates and conventional phosphorus additives. Remarkably, DAPA exhibits better antiwear performance under severe test conditions in ester-base oils than in poly-alpha olefin. X-ray photoelectron spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy were used to study the chemical compositions of steel surfaces after friction and better understand the antiwear mechanism of DAPA, particularly in ester-base oils.