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A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (13 March 2024) | Viewed by 13684

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Prof. Dr. Jiusheng Li

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Laboratory of Advanced Lubricating Materials, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, China
Interests: organic synthesis; lubricating additive; lube oil; grease; nanomaterials; tribological test; tribochemistry; surface & interface chemistry; tribological mechanism; surface characterization; molecular simulation; biomaterials

Special Issue Information

Dear Colleagues,

During the past decade, both education and economic development have reached a new level, and a series of breakthroughs have been made in lubricating materials. The current Special Issue will present the state of the art on functional lubricating materials. It aims to display a number of recent representative advances in basic and application research on lubricating base oil, lubricant additives, liquid lubricating materials, solid lubricating materials, polymer-based lubricating materials, intelligent lubricating materials, nanostructured functional polymers and functional metal matrix composites. Scientists and engineers from academia and industry are invited to contribute articles on experimental and theoretical research.

Prof. Dr. Jiusheng Li
Guest Editor

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Lubricants is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

lubricating base oil
lubricant additive
liquid lubricating material
solid lubricating material

Published Papers (11 papers)

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Research

14 pages, 2254 KiB

Open AccessArticle

Effect of Copper Nanoparticles Surface-Capped by Dialkyl Dithiophosphate on Different Base Oil Viscosity

by Xufei Wang, Shuguang Fan, Ningning Song, Laigui Yu, Yujuan Zhang and Shengmao Zhang

Lubricants 2024, 12(4), 137; https://doi.org/10.3390/lubricants12040137 - 18 Apr 2024

Viewed by 460

Abstract

In order to more accurately characterize the effects of nanoparticles on lubricant viscosity, the effects of copper dialkyl dithiophosphate (HDDP)-modified (CuDDP) nanoparticles on the dynamic viscosity of mineral oils 150N, alkylated naphthalene (AN5), diisooctyl sebacate (DIOS), and polyalphaolefins (PAO4, PAO6, PAO10, PAO40, and PAO100) were investigated at an experimental temperature of 40 °C and additive mass fraction ranging from 0.5% to 2.5%. CuDDP exhibits a viscosity-reducing effect on higher-viscosity base oils, such as PAO40 and PAO100, and a viscosity-increasing effect on lower-viscosity base oils, namely, 150N, AN5, DIOS, PAO4, PAO6, and PAO10. These effects can be attributed to the interfacial slip effect and the shear resistance of the nanoparticles. The experimental dynamic viscosity of the eight base oils containing CuDDP was compared with that calculated by the three classical formulae of nanofluid viscosity, The predicted viscosity values of the formulae deviated greatly from the experimental viscosity values, with the maximum deviation being 7.9%. On this basis, the interface slip effect was introduced into Einstein’s formula, the interface effect was quantified with the aniline point of the base oil, and a new equation was established to reflect the influence of CuDDP nanoparticles on lubricating oil viscosity. It can better reflect the influence of CuDDP on the viscosity of various base oils, and the deviation from the experimental data is less than 1.7%. Full article

(This article belongs to the Special Issue Functional Lubricating Materials)

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15 pages, 12640 KiB

Open AccessArticle

Preparation and Tribological Behavior of Nitrogen-Doped Willow Catkins/MoS₂ Nanocomposites as Lubricant Additives in Liquid Paraffin

by Yaping Xing, Ebo Liu, Bailin Ren, Lisha Liu, Zhiguo Liu, Bocheng Zhu, Xiaotian Wang, Zhengfeng Jia, Weifang Han and Yungang Bai

Lubricants 2023, 11(12), 524; https://doi.org/10.3390/lubricants11120524 - 10 Dec 2023

Viewed by 1448

Abstract

In this study, willow catkins/MoS₂ nanoparticles (denoted as WCMSs) have been prepared using a hydrothermal method. The WCMSs were modified with oleic acid (OA) to improve dispersion in base oil. The friction and wear properties of WCMSs in liquid paraffin (LP) for steel balls were investigated using a four-ball wear tester. The results have shown that at a high reaction temperature, willow catkins (being used as a template) and urea (being used as a nitrogen resource) can effectively decrease the wear scar diameters (WSDs) and coefficients of friction (COFs). At a concentration of 0.5 wt.%, the WSD and COF of steel balls, when lubricated using LP containing modified WCMS with urea, decreased from 0.65 mm and 0.175 of pure LP to 0.46 mm and 0.09, respectively. The addition of urea and hydroxylated catkins can generate a significant number of loose nano-sheets and even graphene-like sheets. The weak van der Waals forces, decreasing the shear forces that the steel balls must overcome, provide effective lubrication during rotation. On the other hand, the tribo-films containing MoS₂, FeS, azide, metal oxides and other compounds play important roles in reducing friction and facilitating anti-wear properties. Full article

(This article belongs to the Special Issue Functional Lubricating Materials)

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16 pages, 7959 KiB

Open AccessArticle

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

by Can Zhu, Zhongyi He, Liping Xiong, Jiusheng Li, Yinglei Wu and Lili Li

Lubricants 2023, 11(12), 517; https://doi.org/10.3390/lubricants11120517 - 08 Dec 2023

Viewed by 1302

Abstract

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. Full article

(This article belongs to the Special Issue Functional Lubricating Materials)

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7 pages, 5243 KiB

Open AccessCommunication

Tribological Property of Al₃BC₃ Ceramic: A Lightweight Material

by Jinjun Lu, Rong Qu, Fuyan Liu, Tao Wang, Qinglun Che, Yanan Qiao and Ruiqing Yao

Lubricants 2023, 11(11), 492; https://doi.org/10.3390/lubricants11110492 - 14 Nov 2023

Viewed by 1116

Abstract

Lightweight materials with a density less than 3 g/cm³ as potential tribo-materials for tribological applications (e.g., space tribology) are always desired. Al₃BC₃ ceramic, a kind of ternary material, is one of the lightweight materials. In this study, dense Al₃BC₃ ceramic is prepared via a reactive hot-pressing process in a vacuum furnace. Its tribological properties are investigated in two unlubricated conditions (one is at elevated temperature up to 700 °C in air, and another is in a vacuum chamber of back pressures from 10⁵ Pa to 10⁻² Pa at room temperature) and lubricated conditions (i.e., water and ethanol as low-viscosity fluids). At 400 °C and lower temperatures in air, as well as in vacuum, the tribological property of Al₃BC₃ ceramic is poor due to the fracture of grains and formation of a mechanically mixed layer. The beneficial influence of adsorbed gas species on reducing friction is very limited. Due to the formation of lubricious tribo-oxide at 600 °C and 700 °C, the friction coefficient is reduced from ca. 0.9 at room temperature and 400 °C to ca. 0.4. In the presence of low-viscosity fluids, a high friction coefficient and wear but a polished surface are observed in water, while a low friction coefficient and wear occur in ethanol. A lubricious carbide-derived carbon (CDC) coating on top of Al₃BC₃ ceramic through high-temperature chlorination can be fabricated and the wear resistance of CDC can be improved by adjusting the chlorination parameters. The above results suggest that Al₃BC₃ ceramic is a potential lubricating material for some tribological applications. Full article

(This article belongs to the Special Issue Functional Lubricating Materials)

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14 pages, 7076 KiB

Open AccessArticle

Preparation and Tribological Behavior of Nitrogen-Doped Carbon Nanotube/Ag Nanocomposites as Lubricant Additives

by Shaokun Jia, Jiahuan Zhao, Guangzhen Hao, Jifeng Feng, Chuanbo Zhang, Zhihui Wang, Zhengfeng Jia and Yungang Bai

Lubricants 2023, 11(10), 443; https://doi.org/10.3390/lubricants11100443 - 13 Oct 2023

Viewed by 1019

Abstract

In this study, nitrogen-doped carbon nanotube/Ag nanocomposites (denoted as N-C/Ag) have been synthesized in a urea solution using a hydrothermal method. The carbon nanotubes, AgNO₃ solution, urea and poly-dopamine (PDA) served as carbon, silver, nitrogen and carbon sources, respectively. The results show that the diameter of the carbon tubes was about 30 nm, and the Ag nanoparticles, with a diameter of ca. 10 nm, dispersed on the carbon tube surface. The Ag particle size decreased with a lower degree of crystallinity at a high temperature in the presence of urea. The friction and wear behavior of the oil acid (OA) modified N-C/Ag (OAN-C/Ag) as an additive in liquid paraffin (LP) were studied using a four-ball friction and wear tester. The results have shown that the coefficients of friction (COFs) and wear scar diameters (WSDs) of steel balls lubricated with LP-OAN-C/Ag decreased by 27.3% and 25.3%, respectively, relative to pure LP. Tribofilms containing Ag, carbon and nitride were formed on the worn steel ball surfaces. Details, the carbon, Fe₂O₃, azides and nitride, Ag and alloy and other compounds on the wear scars may improve tribological properties. The synergistic effect of carbon, Ag and urea plays a critical role during sliding. Full article

(This article belongs to the Special Issue Functional Lubricating Materials)

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16 pages, 8312 KiB

Open AccessArticle

Tribological Performance of Steel/W-DLC and W-DLC/W-DLC in a Solid–Liquid Lubrication System Additivated with Ultrathin MoS₂ Nanosheets

by Meirong Yi, Taoping Wang, Zizheng Liu, Jin Lei, Jiaxun Qiu and Wenhu Xu

Lubricants 2023, 11(10), 433; https://doi.org/10.3390/lubricants11100433 - 07 Oct 2023

Cited by 1 | Viewed by 965

Abstract

In this paper, MoS₂ nanosheets with an ultrathin structure were fabricated using a solvothermal method and further added into PAO oil, which was further combined with W-DLC coating to constitute a solid–liquid lubricating state. The influences of MoS₂ concentration, applied load and counter surfaces on the lubricating of the solid–liquid hybrid lubricating system were explored through a ball-on-disk tribometer. The friction results indicated that the steel/W-DLC and W-DLC/W-DLC tribopairs lubricated with ultrathin MoS₂ possessed better friction reduction and wear resistance behaviors in comparison to pure PAO oil. However, compared to the steel/steel couple case, the prepared MoS₂ nanosheets exhibited a more efficient lubricating effect for the W-DLC/W-DLC couple. The beneficial boundary lubricating impact of MoS₂ nanosheets on self-mated W-DLC coated rubbing surfaces could be attributed to the tribochemical reaction between MoS₂ and doping W element in DLC, resulting in a formation of a thin tribofilm at both counterparts. Meanwhile, the extent of graphitization of W-DLC film induced by friction was alleviated because of the lubrication and protection from the formation of MoS₂-based tribofilm at both counterparts. Full article

(This article belongs to the Special Issue Functional Lubricating Materials)

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16 pages, 11894 KiB

Open AccessArticle

An Evaluation of the Tribological Characteristics of Diaphragm Plates for High-Pressure Hydrogen Gas Compressor Applications

by Sung-Jun Lee, Yoonchul Sohn, Dawit Zenebe Segu and Chang-Lae Kim

Lubricants 2023, 11(9), 411; https://doi.org/10.3390/lubricants11090411 - 20 Sep 2023

Viewed by 1173

Abstract

Diaphragm plates, a key part of high-pressure hydrogen gas compressors, are easily cracked or broken due to repeated shape deformations caused by pressure, resulting in increasing difficulties in maintenance. This study aimed to improve the durability of diaphragm plates. This investigation focuses on the potential for friction and wear reduction through the application of surface polishing and Teflon coating on two diaphragm plate materials, namely stainless steel 301 and Inconel 718. To achieve this, various metal substrates with diverse surface morphologies were prepared and subjected to comprehensive assessments of their surface, mechanical, and tribological properties. Research findings revealed that the surface hardness and tensile strength of stainless steel 301 surpassed those of Inconel 718. Through friction and wear analysis, it was observed that Teflon-coated diaphragm plate material with a microstructure demonstrated superior friction performance. Furthermore, finite element analysis was employed to investigate the stress behavior of stainless steel 301 under different applied loads and conditions, offering valuable insights into the diaphragm’s performance. From the results of this study, the excellence of the Teflon coating applied to the surface of stainless steel 301—the material of the hydrogen compressor diaphragm plate—was confirmed. Full article

(This article belongs to the Special Issue Functional Lubricating Materials)

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17 pages, 10121 KiB

Open AccessArticle

Graphite Fluoride as a Novel Solider Lubricant Additive for Ultra-High-Molecular-Weight Polyethylene Composites with Excellent Tribological Properties

by Guodong Huang, Tao Zhang, Yi Chen, Fei Yang, Huadong Huang and Yongwu Zhao

Lubricants 2023, 11(9), 403; https://doi.org/10.3390/lubricants11090403 - 15 Sep 2023

Viewed by 1027

Abstract

The tribological properties of ultra-high-molecular-weight polyethylene (UHMW-PE) play a significant role in artificial joint materials. Graphite fluoride (GrF), a novel solid lubricant, was incorporated into ultra-high-molecular-weight polyethylene (UHMW-PE) at different concentrations via ball milling and heat pressing to prepare the GrF-UHMW-PE composites. The structure, hardness, and tribological behavior of the composites were investigated using X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectrometry, ball indentation hardness, and a reciprocating ball-on-plane friction tester, respectively. The results of FT-IR showed that hydrogen bonds (C-F···H-C) could be formed between GrF and UHMW-PE. The hardness of the composites was significantly enhanced by increasing the GrF concentrations. GrF in the composites displayed superior lubricant properties and the coefficient of friction (COF) of the composites was significantly decreased at lower concentrations of GrF viz. 0.1 and 0.5 wt%. The addition of GrF also significantly enhanced the anti-wear properties of the composites, which was a combined effect of lubrication as well as hardness provided by GrF. At 0.5 wt% GrF concentration, the COF and the wear rate were reduced by 34.76% and 47.72%, respectively, when compared to UHMW-PE. As the concentration of GrF increased, the wear modes of the composites transitioned from fatigue wear to abrasive wear. Our current work suggested that GrF-UHMW-PE composites could be a suitable candidate for artificial joint materials. Full article

(This article belongs to the Special Issue Functional Lubricating Materials)

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12 pages, 4824 KiB

Open AccessArticle

Tribological Behavior and Wear Protection Ability of Graphene Additives in Synthetic Hydrocarbon Base Stocks

by Ge Du, Hongmei Yang, Xiuli Sun and Yong Tang

Lubricants 2023, 11(5), 200; https://doi.org/10.3390/lubricants11050200 - 29 Apr 2023

Cited by 1 | Viewed by 1143

Abstract

Graphene carbon materials show good tribological properties due to their unique layered structures. In this work, the tribological properties of graphene (GN) and fluorinated graphene (FGN) were studied in two kinds of synthetic hydrocarbon base stocks at different working conditions. Firstly, the structures of GN and FGN were characterized comparatively using FT-IR, Raman, XRD, and TGA. Secondly, the tribological properties of GN and FGN as the lubrication additives both in PAO6 and CTL6 were studied on a four-ball tester. Finally, the surfaces of friction counterparts, before and after tribological tests, were analyzed to disclose the lubrication mechanism using UV, micro-Raman, and EDS. The results show that GN and FGN can be stably dispersed in the selected synthetic hydrocarbon base stocks with 1 wt.% T161 as the dispersant, and the optimal addition of graphene additive is 100 ppm, which shows better friction reducing and anti-wear properties. GN and FGN also show better tribological performance at a higher load (not less than 392 N), and their compatibility with PAO6 is better. The worn surface analysis shows that the graphene additive participates in the lubrication film formation during friction by frictional chemical reaction with friction counterparts, which could improve the stability and tribological performance, resulting in an increased application temperature of synthetic hydrocarbon base stock by at least 10 °C. Full article

(This article belongs to the Special Issue Functional Lubricating Materials)

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14 pages, 3978 KiB

Open AccessArticle

Enhanced Thermally Conductive Silicone Grease by Modified Boron Nitride

by Yumeng Wang, Ning Shi, Min Liu, Sheng Han and Jincan Yan

Lubricants 2023, 11(5), 198; https://doi.org/10.3390/lubricants11050198 - 29 Apr 2023

Cited by 3 | Viewed by 1651

Abstract

In this work, a chemical modification method was used to prepare silicone grease with high thermal conductivity. We report two preparation methods for thermal conductive fillers, which are hydroxylated boron nitride-grafted carboxylic silicone oil (h-BN-OH@CS) and amino boron nitride-grafted carboxylic silicone oil (h-BN-NH₂@CS). When h-BN-OH@CS and h-BN-NH₂@CS were filled with 30 wt% in the base grease, the thermal conductivity was 1.324 W m⁻¹ K⁻¹ and 0.982 W m⁻¹ K⁻¹, which is 6.04 and 4.48 times that of the base grease (0.219 W m⁻¹ K⁻¹), respectively. The interfacial thermal resistance is reduced from 11.699 °C W⁻¹ to 1.889 °C W⁻¹ and 2.514 °C W⁻¹, respectively. Inorganic filler h-BN and organic filler carboxylic silicone oil were chemically grafted to improve the compatibility between h-BN and the base grease. The covalent bond between functionalized h-BN and carboxylic silicone oil is stronger than the van der Waals force, which can reduce the viscosity of the silicone grease. Full article

(This article belongs to the Special Issue Functional Lubricating Materials)

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12 pages, 2265 KiB

Open AccessArticle

Halloysite Reinforced Natural Esters for Energy Applications

by Jose Jaime Taha-Tijerina, Karla Aviña, Victoria Padilla-Gainza and Aditya Akundi

Lubricants 2023, 11(2), 65; https://doi.org/10.3390/lubricants11020065 - 05 Feb 2023

Cited by 3 | Viewed by 1519

Abstract

Recently, environmentally friendly and sustainable materials are being developed, searching for biocompatible and efficient materials which could be incorporated into diverse industries and fields. Natural esters are investigated and have emerged as eco-friendly high-performance alternatives to mineral fluids. This research shows the evaluations on thermal transport and tribological properties of halloysite nanotubular structures (HNS) reinforcing natural ester lubricant at various filler fractions (0.01, 0.05, and 0.10 wt.%). Nanolubricant tribotestings were evaluated under two configurations, block-on-ring, and 4-balls, to obtain the coefficient of friction (COF) and wear scar diameter (WSD), respectively. Results indicated improvements, even at merely 0.01 wt.% HNS concentration, where COF and WSD were reduced by ~66% and 8%, respectively, when compared to pure natural ester. The maximum significant improvement was observed for the 0.05 wt.% concentration, which resulted in a reduction of 87% in COF and 37% in WSD. Thermal conductivity was analyzed under a temperature scan from room temperature up to 70 °C (343 K). Results indicate that thermal conductivity is improved as the HNS concentration and testing temperature are increased. Results revealed improvements for the nanolubricants in the range of 8–16% at 50 °C (323 K) and reached a maximum of 30% at 70 °C (343 K). Therefore, this research suggests that natural ester/HNS lubricants might be used in industrial applications as green lubricants. Full article

(This article belongs to the Special Issue Functional Lubricating Materials)

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