Improved lubrication performance of MoS2-Al2O3 nanofluid through interfacial tribochemistry

Enhanced Stability, Superior Anti-Corrosive, and Tribological Performance of Al2O3 Water-based Nanofluid Lubricants with Tannic Acid and Carboxymethyl Cellulose over SDBS as Surfactant

In this research work, the stability, tribological, and corrosion properties of a water-based Al2O3 nanofluid (0.5 wt%) formulated with tannin acid (TA) and carboxymethyl cellulose (CMC) as dispersants or surfactants were investigated. For comparative purposes, sodium dodecylbenzene sulfonate (SDBS) was also incorporated. The stability of the nanofluid was assessed through zeta potential measurements and photo-capturing, revealing the effectiveness of TA and CMC in preventing nanoparticle agglomeration. Tribological properties were examined using a pin-on-disk apparatus, highlighting the tribofilm of Al2O3 that enhanced lubricating properties of the nanofluid by the SEM, resulting in reduced friction and wear of the contacting surfaces. Sample with the addition of both TA and CMC exhibited the best tribological performance, with a ~ 20% reduction in the friction coefficient and a 59% improvement in wear rate compared to neat nanofluid without TA and CMC. Additionally, the corrosion resistance of the nanofluids were evaluated via weight loss and electrochemical impedance spectroscopy. The nanofluid sample containing both TA and CMC exhibited the lowest corrosion rate, with 97.6% improvement compared to sample without them. This study provides valuable insights into the potential applications of TA and CMC-based Al2O3 nanofluids as effective and environmentally friendly solutions for coolant or lubrication in cutting processes.

Tribological Behavior of Reduced Graphene Oxide-Al2O3 Nanofluid: Interaction among Testing Force, Rotational Speed and Nanoparticle Concentration

The tribological properties of nanofluids are influenced by multiple factors, and the interrelationships among the factors are deserving of further attention. In this paper, response surface methodology (RSM) was used to study the tribological behavior of reduced graphene oxide-Al₂O₃ (rGO-Al₂O₃) nanofluid. The interaction effects of testing force, rotational speed and nanoparticle concentration on the friction coefficient (μ), wear rate (W_r) and surface roughness (R_a) of steel disks were investigated via the analysis of variance. It was confirmed that all the three input variables were significant for μ and W_r values, while testing force, nanoparticle concentration and its interaction with testing force and rotational speed were identified as significant parameters for R_a value. According to regression quadratic models, the optimized response values were 0.088, 2.35 × 10^-7 mm³·N^-1·m^-1 and 0.832 μm for μ, W_r and R_a, which were in good agreement with the actual validation experiment values. The tribological results show that 0.20% was the optimum mass concentration which exhibited excellent lubrication performance. Compared to the base fluid, μ, W_r and R_a values had a reduction of approximately 45.6%, 90.3% and 56.0%. Tribochemical reactions occurred during the friction process, and a tribofilm with a thickness of approximately 20 nm was generated on the worn surface, consisting of nanoparticle fragments (rGO and Al₂O₃) and metal oxides (Fe₂O₃ and FeO) with self-lubrication properties.

Effects of an Electrical Double Layer and Tribo-Induced Electric Field on the Penetration and Lubrication of Water-Based Lubricants

Understanding the effects of electrical double layers (EDL) and tribo-induced electric fields on the electroosmotic behaviors of lubricants is important for developing high-performance water-based lubricants. In this study, EDL conductivities of aqueous lubricants containing a surfactant of 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS) or cetyltrimethylammonium bromide (CTAB) were analyzed. The interfacial zeta potentials of the synthesized lubricants and Al2O3 ceramic-alloy steel contacts were measured, and frictional potentials of ceramic and steel surfaces were determined using a modified ball-on-disc configuration. The distribution characteristics of the tribo-induced electric field of the ceramic-steel sliding contact were numerically analyzed. The electroosmotic behaviors of the lubricants were investigated using a four-ball configuration. It was found that an EDL and tribo-induced electric field was a crucial enabler in stimulating the electroosmosis of lubricants. Through altering EDL structures, CHAPS enhanced the electroosmosis and penetration of the water-based lubricant, thus resulting in improved lubrication.

Study on the Tribological Behaviour of Nanolubricants during Micro Rolling of Copper Foils

Water-based lubricants with different fractions of TiO₂ nanoparticles ranging from 1.0 to 9.0 wt.% were utilized to study the lubrication mechanisms during micro rolling tests and the tribological behaviour of nanolubricants during the micro rolling of copper foils. The results indicate that the application of TiO₂ nanolubricants remarkably improves the surface quality of rolled copper foils during rolling processes. For lubricants with inadequate TiO₂ nanoparticles, it is found that few TiO₂ nanoparticles enter the contact regions between the rolls and foils, causing insufficient lubrication during rolling processes. Instead, for lubricants with excessive TiO₂ nanoparticles, obvious agglomeration occurs at the contact regions and promotes the generation of voids on the surface of the rolled foils, thereby deteriorating the surface quality of the rolled copper foils. In addition, it is found that the surface quality of rolled foils is improved by utilizing a large reduction ratio. Overall, the fraction of 3.0 wt.% TiO₂ nanolubricants is optimal to improve the lubrication conditions at the contact regions, thereby improving the surface quality of the rolled copper foils.