Research

14 pages, 5529 KiB

Open AccessArticle

Mechano-Chemical Properties and Tribological Performance of Thin Perfluoropolyether (PFPE) Lubricant Film under Environmental Contaminants

by Yeonjin Jung and Changdong Yeo

Lubricants 2023, 11(7), 306; https://doi.org/10.3390/lubricants11070306 - 21 Jul 2023

Cited by 1 | Viewed by 1092

Abstract

Through molecular dynamics (MD) simulations with ReaxFF potential, the effects of chemical contaminants on the mechano-chemical properties and tribological performance of perfluoropolyether (PFPE) lubricants were investigated. For the two types of contaminants, i.e., silicon dioxide (SiO₂) nanoparticles and water (H₂ [...] Read more.

Through molecular dynamics (MD) simulations with ReaxFF potential, the effects of chemical contaminants on the mechano-chemical properties and tribological performance of perfluoropolyether (PFPE) lubricants were investigated. For the two types of contaminants, i.e., silicon dioxide (SiO₂) nanoparticles and water (H₂O), their molecular interactions with the two different PFPE lubricants, i.e., Ztetraol and ZTMD, were evaluated at the two different temperatures, i.e., 300 K and 700 K. Contaminants were adsorbed onto the PFPE lubricants at a controlled temperature. Then, air shear simulations were conducted to examine the mechano-chemical behaviors of the contaminated lubricants. Sliding contact simulations were performed to further investigate the tribological performance of the contaminated lubricants, from which the resulting friction and surface contamination were quantified. Lastly, chemical reactions between PFPE lubricants and contaminants were studied to investigate the degradation of PFPE lubricants. It was observed that SiO₂ nanoparticles stiffened the PFPE lubricant, which decreased its shear displacement and increased friction. In the case of the H₂O contaminant, it weakened and decreased the PFPE lubricant’s viscosity, increasing its shear displacement and lowering friction. However, the decreased viscosity by H₂O contaminants can weaken the lubricity of the PFPE lubricant, leading to a higher chance of direct solid-to-solid contact under high contact force conditions. Full article

(This article belongs to the Special Issue Nanolubrication and Superlubrication)

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13 pages, 4901 KiB

Open AccessArticle

Viscosity Variations and Tribological Performances of Oleylamine-Modified Fe₃O₄ Nanoparticles as Mineral Oil Additives

by Xiaoyu Wang, Huanchen Liu, Qilong Zhao, Xiaobo Wang and Wenjing Lou

Lubricants 2023, 11(3), 149; https://doi.org/10.3390/lubricants11030149 - 20 Mar 2023

Cited by 4 | Viewed by 1699

Abstract

In order to improve the flowabilities and anti-friction and anti-wear properties of lubricants, the viscosity variations and tribological performances of oleylamine-modified Fe₃O₄ nanoparticles as mineral oil additives were systematically investigated via rotational parallel plate rheometer, ball–disc reciprocating tribometer, non-contact three-dimensional [...] Read more.

In order to improve the flowabilities and anti-friction and anti-wear properties of lubricants, the viscosity variations and tribological performances of oleylamine-modified Fe₃O₄ nanoparticles as mineral oil additives were systematically investigated via rotational parallel plate rheometer, ball–disc reciprocating tribometer, non-contact three-dimensional surface profiler, scanning electron microscope, energy dispersive X-ray spectrometer and X-ray photoelectron spectroscopy. Spherical monodisperse Fe₃O₄ nanoparticles were synthesized and dispersed into mineral oils to obtain lubricants with mass fractions of 1%, 3%, 5%, 8%, 10% and 20%, respectively. These lubricants have excellent stabilities within 12 months. Interestingly, the dynamic viscosity and kinematic viscosity of the lubricants first decrease and then increase with the increase in Fe₃O₄ content, and the lubricants’ viscosity is at a minimum when the mass concentration is 5%. The tensile curves also show that with the mass fraction increase, the lubricants’ tackiness and adhesion have the same change law, and both reach the lowest point when the mass concentration is 5%. Meanwhile, Fe₃O₄ nanoparticles can improve the tribological properties of the base oils. It is worth noting that the maximum reduction in the wear volume at 25 °C is up to 93.8% compared with base oils when the additive concentration of the Fe₃O₄ nanoparticles is 5 wt%. Full article

(This article belongs to the Special Issue Nanolubrication and Superlubrication)

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16 pages, 5868 KiB

Open AccessArticle

Study on the Dispersion and Lubrication Properties of LDH in Lubricating Oil

by Yong Li, Qiang Zhang, Weidong Zhou, Yongwang Huang and Jingbin Han

Lubricants 2023, 11(3), 147; https://doi.org/10.3390/lubricants11030147 - 19 Mar 2023

Cited by 1 | Viewed by 1704

Abstract

The dispersion of nanomaterials in lubricating oil plays an important role in the lubrication and wear-resistance properties. In this work, supramolecular layered double hydroxides (LDHs) were prepared and added to lubricating oil with different dispersants. The content of key elements in the samples [...] Read more.

The dispersion of nanomaterials in lubricating oil plays an important role in the lubrication and wear-resistance properties. In this work, supramolecular layered double hydroxides (LDHs) were prepared and added to lubricating oil with different dispersants. The content of key elements in the samples was measured by an oil element analyzer, and the dispersion properties of different samples were studied. The friction coefficient of the samples was measured by high-frequency linear vibration (SRV), and the morphology and composition were characterized by SEM to study the antiwear performance and action mechanism of LDH. The oxidation induction time of the samples was measured by RBOT to study the antioxygenic properties of LDH in lubricating oil. The results show that LDH can be well-dispersed in lubricating oil with the action of specific dispersants. After adding LDH, the antiwear performance of lubricating oil was improved, as a uniform and dense protective film was formed on the friction surface. Full article

(This article belongs to the Special Issue Nanolubrication and Superlubrication)

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18 pages, 2531 KiB

Open AccessArticle

Extensive Stability Assessment of TiO₂/Polyvinyl Ether Nanolubricant with Physical Homogenization

by Mohd Farid Ismail, Wan Hamzah Azmi, Rizalman Mamat, Korada Viswanatha Sharma and Hafiz Muhammad Ali

Lubricants 2023, 11(2), 67; https://doi.org/10.3390/lubricants11020067 - 08 Feb 2023

Viewed by 1080

Abstract

Proper preparation and stability evaluation of the nanolubricant shall be established when applying the nanoparticle dispersion technique in a two-phase system. The stability of the nanolubricant ensures the maximum benefit gained from the dispersion of nanoparticles in specified Polyvinyl ether (PVE). In this [...] Read more.

Proper preparation and stability evaluation of the nanolubricant shall be established when applying the nanoparticle dispersion technique in a two-phase system. The stability of the nanolubricant ensures the maximum benefit gained from the dispersion of nanoparticles in specified Polyvinyl ether (PVE). In this study, TiO₂/PVE nanolubricant was prepared using two methods of physical homogenization: high-speed homogenizer (HSH) and ultrasonication bath. The HSH used a preparation time of up to 300 s in the stability assessment. Meanwhile, the ultrasonication bath had a preparation time of 1, 3, 5, and 7 h. The stability condition of the nanolubricant was evaluated using photo capturing, ultraviolet-visible (UV-Vis) spectrophotometer, zeta potential, and zeta sizer. A sample with 180 s of preparation time shows the best stability condition from HSH. The nanolubricant with ultrasonication offers excellent stability at 5 h of homogenizing time with a concentration ratio of more than 90% for up to 30 days of observation. In conclusion, ultrasonication homogenizing methods show better results than HSH with a zeta potential of more than 60 mV. In addition, HSH can be recommended as an optional method to produce nanolubricant with a low preparation time for immediate use. Full article

(This article belongs to the Special Issue Nanolubrication and Superlubrication)

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22 pages, 8084 KiB

Open AccessArticle

Experimental Investigation on the Wear Performance of Nano-Additives on Degraded Gear Lubricant

by Harish Hirani, Dharmender Jangra and Kishan Nath Sidh

Lubricants 2023, 11(2), 51; https://doi.org/10.3390/lubricants11020051 - 30 Jan 2023

Cited by 7 | Viewed by 1783

Abstract

This study investigates the degradation of a commercially available gear lubricant and the potential of nano-additives to mitigate such degradation. Initially, we performed an experimental study on the chemical degradation of commercially available API GL-4 EP90 gear lubricant by mixing the different concentrations [...] Read more.

This study investigates the degradation of a commercially available gear lubricant and the potential of nano-additives to mitigate such degradation. Initially, we performed an experimental study on the chemical degradation of commercially available API GL-4 EP90 gear lubricant by mixing the different concentrations of aqueous hydrochloric acid (aqueous HCl) varying from 0.0005% v/v up to 0.0025% v/v, while maintaining overall water content in the oil below the prescribed limits. The degradation was monitored using the pH value, total acid number (TAN) value, and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) analysis. The experiments were performed on a developed gear test rig using conventional gear oil as well as chemically aged gear oil, and the corresponding results of pH value and wear debris were recorded. Based on the results, an empirical regression model between the concentration of aqueous HCl and lubricant aging time has been established. Under chemically aged lubricant, severe wear of gear was observed, which motivated us to explore suitable nano-additive to minimize the gear wear. Initially, three nano-additives—graphite, graphene, and “graphene oxide functionalized with silicon oxide (GO@SiO₂)”—were chosen. A series of tests were conducted using the design of experiments method (L8 and L16 orthogonal array) to investigate the effect of nano-additives and to find the optimum additive for wear performance. Finally, experiments were conducted on gear setup using the degraded lubricant optimized with nano-additive. Overall results indicate a very significant contribution of nano-additives in decreasing gear wear. Full article

(This article belongs to the Special Issue Nanolubrication and Superlubrication)

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14 pages, 7411 KiB

Open AccessArticle

Enhanced Tribological Behaviour of Hybrid MoS₂@Ti₃C₂ MXene as an Effective Anti-Friction Additive in Gasoline Engine Oil

by Kalaimani Markandan, Thachnatharen Nagarajan, Rashmi Walvekar, Vishal Chaudhary and Mohammad Khalid

Lubricants 2023, 11(2), 47; https://doi.org/10.3390/lubricants11020047 - 29 Jan 2023

Cited by 9 | Viewed by 2027

Abstract

Hybrid molybdenum disulfide (MoS₂)-MXene (Ti₃C₂) was added as an additive in SAE 5W-40-based engine oil in an attempt to reduce interfacial friction between contact surfaces. It was found that the coefficient of friction (COF) and wear scar [...] Read more.

Hybrid molybdenum disulfide (MoS₂)-MXene (Ti₃C₂) was added as an additive in SAE 5W-40-based engine oil in an attempt to reduce interfacial friction between contact surfaces. It was found that the coefficient of friction (COF) and wear scar diameter (WSD) were reduced by 13.9% and 23.8%, respectively, with the addition of 0.05 wt.% MoS₂-Ti₃C₂ compared to base engine oil due to the interlaminar shear susceptibility of MXene. However, we postulate that the high surface energy and presence of -OH, -O and -F functional groups on the surfaces limited the dispersibility and stability of MXene in base oil, while high activity of MoS₂ nanoparticles due to large surface area and vigorous Brownian motion prompted fast settling of nanoparticles due to gravitational force. As such, in the present study, hybrid MoS₂-Ti₃C₂ were amine-functionalized to attain stability in SAE 5W-40-based engine oil. Experimental findings indicate that amine-functionalized 0.05 wt.% MoS₂-Ti₃C₂ exhibited higher COF and WSD, i.e., 12.8% and 12.3%, respectively, compared to base oil added with 0.05 wt.% unfunctionalized MoS₂-Ti₃C₂. Similarly, Noack oil volatility was reduced by 24.6% compared to base oil, indicating reduced oil consumption rate, maximal fuel efficiency and enhanced engine performance for a longer duration. Full article

(This article belongs to the Special Issue Nanolubrication and Superlubrication)

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17 pages, 4103 KiB

Open AccessArticle

Impact of Thermal and Activation Energies on Glauert Wall Jet (WJ) Heat and Mass Transfer Flows Induced by ZnO-SAE50 Nano Lubricants with Chemical Reaction: The Case of Brinkman-Extended Darcy Model

by Umair Khan, Aurang Zaib and Anuar Ishak

Lubricants 2023, 11(1), 22; https://doi.org/10.3390/lubricants11010022 - 07 Jan 2023

Cited by 4 | Viewed by 1142

Abstract

Heat transfer machinery or technology is rapidly expanding due to the need for effective cooling and heating systems in the requisite automotive, chemical, and aerospace industries. This study aims to provide a numerical solution to wall jet (WJ) flow with mass and heat [...] Read more.

Heat transfer machinery or technology is rapidly expanding due to the need for effective cooling and heating systems in the requisite automotive, chemical, and aerospace industries. This study aims to provide a numerical solution to wall jet (WJ) flow with mass and heat transport phenomenon comprising of the colloidal mixture of SAE50 and zinc oxide nanoparticles immersed in a Brinkman-extended Darcy model. The idea of WJ flow suggested by Glauert is further discussed along with the impact of the activation energy, thermal radiation, and binary chemical reaction. The leading equations are transformed into ordinary differential equations through proper similarity variables and then worked out numerically by employing a very efficient bvp4c method. The importance of pertaining quantities is illustrated and well explained through several tables and graphs. The major results suggest that the velocity profiles decline while the temperature and concentration augment due to the higher impact of nanoparticles volume fraction. In addition, the shear stress and heat transfer rate are accelerated by rising the volume fraction of nanoparticles while the Sherwood number declines with bigger impacts of nanoparticle volume fraction. In addition, the radiation factor progresses the quantitative outcomes of the heat transfer rate. Full article

(This article belongs to the Special Issue Nanolubrication and Superlubrication)

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20 pages, 4486 KiB

Open AccessArticle

Tribology Performance of Polyol-Ester Based TiO₂, SiO₂, and Their Hybrid Nanolubricants

by Abdul Hamid Hamisa, Wan Hamzah Azmi, Mohd Farid Ismail, Rosminazuin Ab Rahim and Hafiz Muhammad Ali

Lubricants 2023, 11(1), 18; https://doi.org/10.3390/lubricants11010018 - 05 Jan 2023

Cited by 12 | Viewed by 1423

Abstract

The tribology properties of TiO₂/POE, SiO₂/POE and TiO₂-SiO₂/POE nanolubricants were investigated for an automotive air-conditioning system with an electrically-driven compressor (EDC). A two-step preparation method was used in dispersing TiO₂ and SiO₂ nanoparticles [...] Read more.

The tribology properties of TiO₂/POE, SiO₂/POE and TiO₂-SiO₂/POE nanolubricants were investigated for an automotive air-conditioning system with an electrically-driven compressor (EDC). A two-step preparation method was used in dispersing TiO₂ and SiO₂ nanoparticles into Polyol-ester (POE)-based lubricant at different volume concentrations of 0.01 to 0.1%. The coefficient of friction (COF) and wear scar diameter (WSD) were investigated using a Koehler four-ball tribo tester and microscopes. For the TiO₂/POE, SiO₂/POE and TiO₂-SiO₂/POE nanolubricants, respectively, the lowest COFs with maximum reduction were attained at 37.5%, 33.5% and 31.6% each at volume concentrations of 0.05%, 0.01% and 0.03%. The highest WSD reduction for the TiO₂/POE and SiO₂/POE mono nanolubricants were attained at 12.5% and 26.4%, respectively, at the same volume concentration of 0.01%. Meanwhile, the maximum reduction of WSD for the TiO₂-SiO₂/POE hybrid nanolubricant was reached at 12.4% at 0.03% volume concentration. As a conclusion, mono and hybrid nanolubricants with volume concentrations of less than 0.05% are suggested for use in air-conditioning systems with EDC because of their outstanding tribology performances. Further performance investigation of nanolubricants in the air-conditioning system is required to extend the present work. Full article

(This article belongs to the Special Issue Nanolubrication and Superlubrication)

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18 pages, 3515 KiB

Open AccessArticle

Stability and Thermal Conductivity of Mono and Hybrid Nanoparticles Dispersion in Double-End Capped PAG Lubricant

by Mohd Zaki Sharif, Wan Hamzah Azmi, Mohd Fairusham Ghazali, Nurul Nadia Mohd Zawawi and Tri Yuni Hendrawati

Lubricants 2023, 11(1), 1; https://doi.org/10.3390/lubricants11010001 - 20 Dec 2022

Cited by 1 | Viewed by 1271

Abstract

Stable nanolubricant mixtures are interrelated with thermal conductivity enhancement, thus improving heat transfer performance in automotive air conditioning (AAC) systems. This paper studies the stability and thermal conductivity of double-end capped polyalkylene glycol (PAG)-based nanolubricants specially designed for R1234yf refrigerant. Mono nanolubricants (Al [...] Read more.

Stable nanolubricant mixtures are interrelated with thermal conductivity enhancement, thus improving heat transfer performance in automotive air conditioning (AAC) systems. This paper studies the stability and thermal conductivity of double-end capped polyalkylene glycol (PAG)-based nanolubricants specially designed for R1234yf refrigerant. Mono nanolubricants (Al₂O₃/PAG and SiO₂/PAG) and hybrid nanolubricants (Al₂O₃–SiO₂/PAG) were prepared using a two-step preparation method at different volume concentrations of 0.01 to 0.05%. The stability of these nanolubricants was observed by visual, UV-Vis spectrophotometer, and zeta potential. Thermal conductivity (k) was measured from 30 to 70 °C using a C-Therm thermal properties analyser. The results from the stability analysis show that all nanolubricants were confirmed in excellent stability conditions for more than six months with minimum visual sedimentation, more than 70% concentration ratio, and zeta potentials greater than 60 mV. The Al₂O₃–SiO₂/PAG samples recorded the highest values of thermal conductivity increment, followed by the Al₂O₃/PAG and SiO₂/PAG samples with 2.0%, 1.7%, and 1.5% enhancement. Hybrid nanolubricants have been shown to have greater potential in the AAC system because of their excellent stability and better property enhancement in thermal conductivity. Full article

(This article belongs to the Special Issue Nanolubrication and Superlubrication)

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