Open Access Research Article Issue
Classification and spectrum optimization method of grease based on infrared spectrum
Friction 2024, 12 (6): 1154-1164
Published: 05 December 2023

The 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.

Open Access Research Article Issue
Conductivity and tribological properties of IL-PANI/WS2 composite material in lithium complex grease
Friction 2023, 11 (6): 977-991
Published: 08 September 2022

An ionic liquid-polyaniline/tungsten disulfide (IL-PANI/WS2) composite was synthesized in 1-butyl-3-methylimidazole tetrafluoroborate (LB104) aqueous solution by in-situ polymerization and characterized by Fourier transform infrared spectroscopy. A current-carrying friction and wear tester was used to study the tribological properties of steel–steel and copper–copper friction pairs lubricated by an IL-PANI/WS2 lithium complex grease (LCG). After the experiment, scanning electron microscope was used to observe the surface morphology of the wear scar on the steel and copper plates, and X-ray photoelectron spectrometer was used to analyze the elemental composition of the wear scar surface. The results show that compared with greases containing IL-PANI and WS2, greases containing IL-PANI/WS2 exhibit better antiwear performance when lubricating steel–steel friction pairs and better tribological performance and electrical conductivity when lubricating copper–copper friction pairs. Therefore, it can be concluded that WS2 and IL-PANI have a synergistic effect.

Open Access Research Article Issue
Conductive and tribological properties of TiN-Ag composite coatings under grease lubrication
Friction 2021, 9 (4): 774-788
Published: 28 August 2020

TiN-Ag composite coatings were prepared by pulsed bias arc ion plating. X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) were applied to analyze the compositions of the coatings. Tribological properties of the coatings were studied using an MFT-R4000 ball-on-disk friction tester in the presence of lubricating greases containing multilayer graphene. Scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used to analyze the worn surface compositions of the lubricating films. The results show that with the decrease in Ag in the film, hardness increased but electrical conductivity decreased. The coating with 10 at% Ag content shows the best friction-reducing and anti-wear properties, which can be attributed to the moderate content of Ag embedded in the TiN crystal gap that enhanced the grain bonding force to improve the anti-wear and self-lubricating ability. Graphene can be adsorbed on the coating as a solid lubricant.

Open Access Research Article Issue
A synergetic strategy based on laser surface texturing and lubricating grease for improving the tribological and electrical properties of Ag coating under current-carrying friction
Friction 2021, 9 (5): 978-989
Published: 26 August 2020

Herein, a series of Ag coatings with different micro-dimples were fabricated on copper surfaces by laser surface texturing (LST) and magnetron sputtering. Multilayer graphene lubricating grease (MGLG) was prepared using multilayer graphene as an additive. The textured Ag coatings and MGLG were characterized. Moreover, the tribological and electrical performances of the textured Ag coatings under MGLG lubrication were investigated in detail. Results demonstrated that the textured Ag coating with an appropriate dimple diameter could exhibit improved tribological and electrical properties when compared to the non-textured Ag coating under MGLG lubrication. The characterization and analysis of the worn surfaces suggest that the synergetic effect of LST and MGLG contributes to these excellent tribological and electrical properties.

Open Access Research Article Issue
Tribological application and mechanism of epicuticular wax
Friction 2019, 7 (1): 44-58
Published: 20 April 2018

The plant cuticle is a complex mixture of omnipresent, commonly monofunctional, fatty acid derivatives and taxon-specific, generally bifunctional, specialty compounds. This study explored expanded applications for these substances. Four types of plant cuticles were distilled from leaves and the resulting lipid mixtures were analyzed using gas chromatography-mass spectrometry. These were then used as additives for a synthetic ester lubricant. A reciprocating friction and wear testing machine was utilized to investigate the resulting tribological properties. The worn surfaces of the lower discs were observed and analyzed using optical microscopy and time-of-flight secondary ion mass spectrometry. The results reveal that cuticular waxes can modify the friction properties of the base oil. Furthermore, cuticular waxes demonstrate better performance when compared to the commercially available additive molybdenum dithiocarbamates. A protective adsorption film was identified as the reason for the improved friction reduction and anti-wear properties of the lubricant on the friction pair. This study provides a reference for the study of new types of non-sulfur, phosphorus, and other active element additives and demonstrates considerable potential for the economical utilization of plant leaf waxes.

Open Access Research Article Issue
Nano-montmorillonite-doped lubricating grease exhibiting excellent insulating and tribological properties
Friction 2017, 5 (2): 219-230
Published: 12 May 2017

Three types of nano-montmorillonite were doped as additives to afford lubricating greases. The physicochemical, insulating, and tribological performances of the obtained lubricating greases were investigated in detail. Furthermore, the tribological action mechanisms were analyzed by high magnification optical microscope, Raman spectroscopy, and energy dispersive X-ray spectroscope (EDS). The results show that the inorganic modification montmorillonite (IOMMT) can significantly increase the number of electron traps in the base grease, leading to excellent insulating performances. Moreover, IOMMT as a novel lubricant additive (1.5 wt% in grease) significantly enhances the friction reducing and anti-wear abilities for steel/steel contact that comprises a unique layered structure to prevent friction between the contact pairs and the protective tribofilm generated by physical adsorption and chemical reaction.

Erratum Issue
Erratum to: Conductive grease synthesized using nanometer ATO as an additive
Friction 2015, 3 (4): 352
Published: 23 October 2015
Open Access Research Article Issue
Conductive grease synthesized using nanometer ATO as an additive
Friction 2015, 3 (1): 56-64
Published: 13 February 2015

A new conductive grease was synthesized using a nanometer powder, i.e., Sb doped SnO2 (ATO), as an additive. The typical properties of this new conductive grease were investigated in detail. The results indicate that ATO can dramatically improve the dropping point and reduce contact resistance. The tribological properties of the new conductive grease were investigated using the MFT-R4000 reciprocating friction and wear tester. The tribol-test results indicate that ATO can dramatically improve the tribological properties of the grease. When the ATO concentration is 0.1wt%, the grease demonstrates the best friction reduction properties; when the concentration is 0.5wt%, the grease demonstrates the best anti-wear properties. The worn surfaces were observed and analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy, and the friction mechanisms for the new conductive grease are proposed. The excellent tribological properties of the new conductive grease are attributed to the mechanical effect of ATO, and the film formed by Sn and Sb elements or metallic oxide deposited on worn surfaces during the friction process.

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