Lithium Grease Research Articles

Investigating the effects of base oil type on microstructure and tribological properties of polyurea grease

The soaring prices and physiological toxicity of lithium-based grease make polyurea grease a promising alternative due to its balanced cost and performance. Employing preformed thickeners to avoid toxic raw materials has become a preferred method for eco-friendly preparation of polyurea grease. However, the underlying mechanism of base oil modulates the microstructure of polyurea greases prepared with preformed thickeners, subsequently influencing their macroscopic performance remains unclear. Herein, three polyurea greases were synthesized by regulating the base oil types ((poly(α-olefin) oil (PAO40), alkyl naphthalene oil (AN30), and polyether oil (OSP320)) with the same preformed thickener. The real-time polarizing microscope observation of the grease structure evolution process revealed that the preformed thickeners gradually expanded in the base oil and formed a fiber structure. An increased polarity disparity between thickener and base oil leads to a reduced swelling rate and increased fiber length. As a result, compared with high polarity OSP320 and low polarity AN30, non-polar PAO40 induces a more interconnected 3D network composed of long fiber in obtained grease (PG). Low field nuclear magnetic resonance characterization and molecular simulations reveal this network exhibits significant binding ability towards base oil, reducing the movement ability of the base oil, endowing PG with the highest structural strength, achieving effective lubrication and low noise performance. These in-depth understandings will help promote the research and development of polyurea greases.

Study of low-toxicity copper pyrithione as a multifunctional additive for lithium grease

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.

Quantitative analysis for the microstructure of lithium-based grease: Methodology and application

The advancement of image processing technology has introduced novel approaches for material structural analysis. This study develops a quantitative analysis method for the microstructure of lithium-based greases utilizing ImageJ. The SEM images of grease fibers are firstly pre-processed in order to enhance the accuracy of calculation. Then the void fraction in the fiber network is obtained through threshold and area calculation. The average fiber diameter and length are calculated via local thickness analysis and skeleton analysis, respectively. Additionally, this method was applied to assess the microstructural changes in lithium grease under conditions of intense mechanical shearing and high temperature. The possible reasons for the deterioration of grease performance are also discussed.

Effect of structure of ZnO and SiO2 core-shell composite nanoparticles as lubricant additive on tribological properties of greases

Nano-additives can enhance the tribological properties of greases. In particular, core-shell composite nanoparticles, which combine multiple nanoparticles, have been the subject of recent research due to their superior properties. In this study, based on the friction pairs material, GCr15, by choosing ZnO with low hardness and SiO2 with high hardness, core-shell composite nanoparticles with soft shell hard core SiO2@ZnO and hard shell soft core ZnO@SiO2 were prepared by chemical deposition and calcination methods. The impact of different structural forms of these composite nanoparticles as grease additives were investigated for the first time by adding them into lithium grease. The results show that ZnO@SiO2 have good tribological properties under light load, reducing the COF by 18 % and decreasing the WSD by 22 %. SiO2@ZnO exhibit the best anti-friction effect under heavy load conditions, reducing the COF by 15 % and decreasing the WSD by 28 %. The GCr15-ZnO-SiO2 surface composite film structure is the key to improve the performance of grease in the two composite nanoparticles. It not only has good wear resistance, but also can increase the bearing capacity of the oil film. The two core-shell structure nano-additives provide a new idea for the design of lubricants under special conditions.

TiO2 and CeO2 nanoparticles as lithium complex grease additives for enhanced lubricity

PurposeThis paper aims to improve the tribological properties of lithium complex greases using nanoparticles to investigate the tribological behavior of single additives (nano-TiO2 or nano-CeO2) and composite additives (nano-TiO2–CeO2) in lithium complex greases and to analyze the mechanism of their influence using a variety of characterization tools.Design/methodology/approachThe morphology and microstructure of the nanoparticles were characterized by scanning electron microscopy and an X-ray diffractometer. The tribological properties of different nanoparticles, as well as compounded nanoparticles as greases, were evaluated. Average friction coefficients and wear diameters were analyzed. Scanning electron microscopy and three-dimensional topography were used to analyze the surface topography of worn steel balls. The elements present on the worn steel balls’ surface were analyzed using energy-dispersive spectroscopy and X-ray photoelectron spectroscopy.FindingsThe results showed that the coefficient of friction (COF) of grease with all three nanoparticles added was low. The grease-containing composite nanoparticles exhibited a lower COF and superior anti-wear properties. The sample displayed its optimal tribological performance when the ratio of TiO2 to CeO2 was 6:4, resulting in a 30.5% reduction in the COF and a 29.2% decrease in wear spot diameter compared to the original grease. Additionally, the roughness of the worn spot surface and the maximum depth of the wear mark were significantly reduced.Originality/valueThe main innovation of this study is the first mixing of nano-TiO2 and nano-CeO2 with different sizes and properties as compound lithium grease additives to significantly enhance the anti-wear and friction reduction properties of this grease. The results of friction experiments with a single additive are used as a basis to explore the synergistic lubrication mechanism of the compounded nanoparticles. This innovative approach provides a new reference and direction for future research and development of grease additives.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2023-0291/

An approach of the internal friction-dependent temperature changes for conventional and pure biogenic lubricating greases

This work investigated the temperature changes inside the bulk of lubricating greases under controlled high-shear stress conditions (250–500 s−1). For this purpose, a newly developed temperature-measuring cell called Calidus was successfully tested. The temperature changes (ΔT) have been related to the greases’ components (thickener, base oil-type, and composition) and the structural degradation of the lubricating greases. Furthermore, a theoretical approach was proposed for calculating the internal temperature change of lubricating greases during shear stress. All greases showed an internal temperature profile characterised by a sudden rise in ΔT within the first 4 h from starting the test and subsequent ΔT decay until it reaches the steady state value. Furthermore, it was found that greases C1 and C5, formulated with lithium and calcium soap, respectively, with different soap content (16.1 wt% and 9.7 wt%, respectively), but the same base castor oil, showed the highest value of the maximum ΔT, c.a. 3.2 K, and the most drastic drop of ΔT. These greases showed both the highest specific densities and heat capacities. In addition, they showed the lowest ratio of expended energies (Rtee), which means more structural degradation in the stressed grease. On the contrary, the grease C3, with 13 wt% of Li-soap but the lowest base oil’s viscosity, showed the lowest maximum ΔT and the temperature profile was characterised by a moderate variation of ΔT along the test. The biogenic grease B3 developed a low-temperature change in the group of pure bio-genic greases close to grease C3.

Influence of MWCNTs, ZnO, and boric acid nanomaterial blend on the tribological and thermal properties of lithium grease

The roller/ball bearing plays a crucial role in the power transmission of high-speed machines used in industrial applications. The inadequate lubricant at the contacting surfaces may cause bearing failure and lead to financial misfortune. Effective lubrication at the contacting surface is the only criteria to obtain significant bearing performance and enhance the life of the bearing. Therefore, in this paper, efforts have been carried out to enhance the tribological and thermo-physical properties of lithium by adding nanomaterials. Multi-walled carbon nanotubes (MWCNTs), zinc oxide (ZnO), and nanoboric acid (nBA) nanomaterials were used as an additive. The 52100 steel ball specimens were considered in the four-ball tribometer to analyze the friction coefficient, lubricant film strength, wear scar diameter (WSD), wear volume, and frictional power loss parameters. In addition, the thermal conductivity of base grease and nanoparticles added grease was assessed using a KD2 Pro thermal analyzer. The findings of the experimental investigations demonstrated that the enhanced thermo-physical characteristics of lithium grease-containing nanomaterials led to a significant decrease in wear and friction at the contact surfaces of the steel ball specimen. An optimum concentration of 0.75% MWCNTs was observed which resulted in 22.75% and 37.5% reduction in friction coefficient and WSD. Also, the surface roughness and wear volume were reduced 59% and 84.7% with MWCNTs blended grease in comparison with base grease.

Study of the Effect of Continuous Thermal Effects on the Shear Stability of Magnetorheological Grease

Magnetorheological dampers in the service of the medium in a project experience continuous thermal effects, frequent reciprocating shear and other complex conditions. Shear stability is an important indicator of the reliability of a magnetorheological media service. Magnetorheological grease (MRG) was prepared using hydroxy iron powder with a mass fraction of 30% and lithium grease of different consistency grades as a continuous phase. The results of magnetic and rheological properties analysis were combined to investigate the mechanism of the continuous thermal effect on the shear stability of MRG. The results show that changes in the temperature field and magnetic field cause significant changes in the magnetic and rheological properties of MRG. At low temperatures and low magnetic fields, the soap fiber structure unique to MRG can effectively inhibit the movement of magnetic particles, with slight changes in the rheological properties and excellent shear stability. When the temperature increases to 80 °C, 00#MRG is damaged by the high temperature. The soap fiber structure is fractured and reorganized, and the rheological properties change significantly. However, the rheological properties of 1#MRG remain largely unchanged during the magnetic field enhancement to saturation, showing better shear stability. The higher consistency continuous phase has excellent heat resistance and better shear performance stability in the face of thermomagnetic coupling conditions, but the fiber breakage caused by continuous reciprocating shear poses a challenge to the service stability of MRG.

Study on the Influence of the MoS2 Addition Method on the Tribological and Corrosion Properties of Greases

MoS2 lithium-based grease is suitable for lubrication protection between bearings at high temperatures and loads due to its excellent tribological properties. However, there is little research on the influence of different addition methods of MoS2 additive on its tribology and corrosion properties. In this work, eco-friendly vegetable oil was selected as the base oil, with MoS2 powder as the additive to synthesize lithium-based grease. The effects of different adding modes of MoS2 on the tribology and corrosion properties of the grease were studied. The experimental results showed that adding 0.01 wt% MoS2 before thickening (Method D) was more conducive to improving the tribological properties of lithium grease. The average friction coefficient was reduced by 26.1%, and the average wear scar diameter was reduced by 0.16 mm. After grinding and adding (Method B) 0.01 wt% MoS2, the corrosion inhibition efficiency of the steel sheet was as high as 96.97%. The reason was that the tribochemical reaction of MoS2 evenly distributed throughout the grease during friction, forming a thin friction film, reducing friction and wear. The protective film formed by MoS2 and GCr15-bearing steel improved the corrosion inhibition performance of the grease.

Classification and spectrum optimization method of grease based on infrared spectrum

AbstractThe infrared (IR) absorption spectral data of 63 kinds of lubricating greases containing six different types of thickeners were obtained using the IR spectroscopy. The Kohonen neural network algorithm was used to identify the type of the lubricating grease. The results show that this machine learning method can effectively eliminate the interference fringes in the IR spectrum, and complete the feature selection and dimensionality reduction of the high-dimensional spectral data. The 63 kinds of greases exhibit spatial clustering under certain IR spectrum recognition spectral bands, which are linked to characteristic peaks of lubricating greases and improve the recognition accuracy of these greases. The model achieved recognition accuracy of 100.00%, 96.08%, 94.87%, 100.00%, and 87.50% for polyurea grease, calcium sulfonate composite grease, aluminum (Al)-based grease, bentonite grease, and lithium-based grease, respectively. Based on the different IR absorption spectrum bands produced by each kind of lubricating grease, the three-dimensional spatial distribution map of the lubricating grease drawn also verifies the accuracy of classification while recognizing the accuracy. This paper demonstrates fast recognition speed and high accuracy, proving that the Kohonen neural network algorithm has an efficient recognition ability for identifying the types of the lubricating grease.

Development of environmentally friendly lubricant using natural resources: Layered double hydroxide gels

The development of a sustainable and environmentally friendly alternative to petroleum-based lubricants is a major challenge. In this study, layered double hydroxide (LDH) vegetable oil gels were prepared from stearic-acid-intercalated LDH (LDH-SA) and vegetable oil. The effects of content of LDH-SA and types of vegetable oils on the rheological properties of the gels were studied. The effects of several plant-derived antioxidants on the oxidative stability of LDH-SA gels were also investigated. Further, the tribological properties of LDH-SA gels were studied and compared with those of a lithium grease under the same conditions. The results showed that LDH-SA gels exhibit the typical rheological properties of grease, such as viscoelasticity, shear thinning, and structural thixotropy. Tocopherols, tea polyphenol, gallic acid, and their combinations can enhance the oxidative stability of LDH-SA gels. The tribological experiments showed that LDH-SA gels maintained the inherent excellent tribological properties of their corresponding vegetable oil. LDH-SA gels provide a new idea for the development of environmentally friendly lubricants.

Use of Functionalized Graphene-Based Materials on Grease

The growing awareness of reduced friction losses and new demands for electrical powertrains demand improved lubricants. Due to their unique properties, such as high thermal and electrical conductivity, graphene and its derivatives have been investigated for tribological applications, especially as lubricant additives. In this work, we investigated three commercially available graphene variants, one comprising a few layers and the other two comprising nanoplates, after functionalization as additives to lithium soap grease. The grease temperature dropping point increased by approximately 6 °C. Additionally, during the reciprocating friction test, friction increased with the test duration for the baseline grease, whereas it decreased for the ones containing graphene-based additives. On the test end, friction was reduced by 8% compared to the baseline grease. On a four-ball tribometer, the wear scar was reduced from 10 to 18% compared to the baseline grease. In general, no significant difference was seen between the three graphene-based variants. The promising results found with graphene nanoplates, a less expensive material than a few graphene layers, creates opportunities for a cost-competitive additive to commercial greases.

Study on the Sliding Tribological Behavior of Oleic Acid-Modified MoS2 under Boundary Lubrication.

The effects of MoS2 and MoS2 modified by adding oleic acid (OA) on the friction properties of lithium-based grease under boundary lubrication conditions are studied by molecular dynamics (MD) simulation and experiment. A rough wall boundary lubrication MD model with peaks and grooves is established to simulate the mechanical properties and lubrication effects of three lubrication systems on rough walls for the relative shear velocity between the two solid walls of 5 m/s at 500 MPa. The stress, wear amount, friction force, normal pressure, and friction heat of the friction surface are quantitively calculated. Simultaneously, a Retc friction and wear testing machine is used to measure the friction coefficient under different concentrations of additives and different pressures. The results show that the grease added with MoS2 can reduce friction, wear, and the temperature between friction pairs. However, under high pressure and shear, MoS2 can easily agglomerate and accumulate in the pits, reducing the lubricating effect. At the same time, since OA-modified MoS2 can reduce agglomeration, the modified MoS2 is adsorbed on the metal wall surface, forming a stable lubricant film. The main contributions of this article can be found in combining MD simulation and experimentation, establishing the connection between micronano structures and macroscopic properties, exploring the mechanism of the influence of wall roughness and particle size on the friction performance of lubricating oil, and providing a theory for predicting and developing high-performance new lubricating grease.

Effects of Contamination on Selected Rheological and Tribological Properties of Lubricating Greases Working in Underground Mines

This study examines the effect of mining pollutants and wear products on the rheological and tribological properties of a lubricating grease working in the microclimate of the Polkowice-Sieroszowice mine belonging to the KGHM Polska Miedź Group (Polkowice, Poland). The material under investigation is a commercial lubricating grease thickened with complex lithium soap, based on mineral oil with a molybdenum disulfide (MoS2) addition. A sample of the grease was taken from one of the friction junctions of a self-propelled drilling jumbo operated in the mine. Comparative tests of the fresh grease and the spent grease were carried out. For the two greases, rheological tests, i.e., dynamic oscillation tests and tests in steady flow conditions, were carried out at a constant shear rate. The rheological tests were conducted using a rotational rheometer. Moreover, the tribological characteristics of the tested greases under different friction junction loads were carried out using a ball-on-disc tribometer. Besides friction resistance, the lubrication ability of the two greases was also evaluated through an analysis of the wear of the steel disks after the friction process. Contour and topographic maps of the wear traces of the discs together with their wear profiles were compared.

Carbon nanotubes as fast-thickening agents in polyalphaolefin greases: Partial crystallinity and intertube joints toward multifunctionality

Scalable and economic manufacturing of carbon nanotube (CNT) greases addresses the current challenges of nanofluids. The key problems remain the complex and non-obvious nature of nanotube-base fluid interactions with the diversity of nanotube morphological variants as the main aspect. Here, we prove that successful formation of stable and multifunctional CNT-polyalphaolefin (PAO) greases is possible only by employing two types of multi-wall CNTs (MWCNTs) as the thickening as well as thermo- and electro-active agents, i.e., (1) thin, entangled, less crystalline nanotubes and (2) thick nanotubes connected via few-mismatched-layer graphenoid joints. Using mechanical spectroscopy, SEM, TEM, Raman spectroscopy, inverse gas chromatography (IGC), and Hansen solubility parameters, we analyze the mechanisms governing fast-thickening behavior and CNT-PAO affinities, revealing a reversible formation of a 3D CNT-network which mimics a mesh of the conventional lithium soaps. Finally, we reveal the multifunctionality of the CNT-PAO greases, expressed in as high as 58%- and 700%-enhancements of thermal and alternating current conductivity, respectively, compared to PAO base fluid.

Experimental investigation to assess the effect of graphene blended lithium grease on friction, wear, and surface morphology of 52100 chrome alloy steel contacts

AbstractThe results of a research on the tribological behaviour of lithium grease with the addition of graphene nanoparticles are presented in current work. Using a four‐ball tribometer, the wear and friction coefficient of lithium grease and blended grease samples with graphene additions were assessed. The significance of graphene in enhancing the tribological properties of grease materials is evident from experimental results. In the experimental investigation, a considerable decrease in wear and friction co‐efficient values was also noted. One weight percent addition of graphene to base grease decreases friction by 23.73% and wear scar width by 19.51%.

Methyl Oleate-Alkylated Tetralin with Dual-Functional Groups as Base Oil with PAO to Improve the Performance of Lithium-Based Grease

Methyl Oleate-Alkylated Tetralin with Dual-Functional Groups as Base Oil with PAO to Improve the Performance of Lithium-Based Grease

Tribological Performance Evaluation of Greases on a Four-Ball Tester with Graphene Oxide Nanoparticles.

Conventional greases have an exceptional place in the field of lubrication. They are unique in the sense of their areas of application and are very difficult to replace with other lubricating substances for the same reason. The advancements in the field of nanoparticles and the results they provide as an additive in greases have great scientific interest as they improve the tribological properties of greases to a great extent. The current work's aim is to synthesize a nanogripe using graphene oxide (GO) nanoparticles to lithium grease (Li grease), which will increase the tribological properties of the plain Li grease. Steps were taken to investigate the impact of variation of load on the frictional and wear characteristics of nanogrease. Synthesis of nanogrease and tribological evaluation were performed with a magnetic stirrer with a hot plate and a four-ball tester. Results indicated that nanogrease exhibits better tribological properties. It is also found that the antiwear and frictional properties of grease are not proportional to the wt % of GO nanoparticles. It is also detected that with the increase in load, the tribological properties of nanogrease increase.

SYNTHESIS AND EVALUATION OF SULPHONYL BORATE ESTER AS GREASE ADDITIVE

This study includes synthesis and evaluation of an additive to improve the two main properties of lubricating grease which are; “increasing the dropping point and improving the extreme pressure (EP) properties” of Lithium grease without any negative effect on the other characteristics of lubricating grease. Increasing the dropping point and extreme pressure (EP) properties are the most important factors to widen the application of lubricating grease. The additive is synthesized via two-steps condensation reactions of polyethylene glycol 400 and Boric acid followed by reacting the product with Dodecyl-benzene sulfonic acid in the presence of Xylene as azeotropic solvent. The structure of the synthesized Sulphonyl-Borate ester SPB is confirmed by using FT-IR. Evaluation of the synthesized additive is conducted by blending it with laboratory prepared Lithium grease sample in different ratios. Analysis were carried out to study the effect of additive on the lubricating grease properties, especialy grease consistency ASTM D217, dropping point ASTM D2265, oil separation ASTM D6184, and Four–Ball test ASTM D2783. The results showed that synthesized additive increased the dropping point by 65 % and extreme pressure properties by 66 % of the prepared grease grease sample.

Impact of Multi-walled Carbon Nanotubes as an Additive in Lithium Grease to Enhance the Tribological and Dynamic Performance of Roller Bearing

Impact of Multi-walled Carbon Nanotubes as an Additive in Lithium Grease to Enhance the Tribological and Dynamic Performance of Roller Bearing