Nanolubricants E-Book
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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
NANOLUBRICANTS Through the dissemination of the latest advancements in nanolubrication science, this volume addresses the pressing concerns surrounding their economic feasibility, environmental acceptability, sustainability, and overall viability. Lubrication is the lifeblood of machinery and the key to its smooth operation. In the world of mechanics and engineering, the role of lubricants cannot be overstated. They are the unsung heroes that reduce friction between surfaces in contact, thus preventing excessive heat generation during motion. Beyond this primary function, lubricants find their application in diverse areas, including power transmission, foreign object transportation, and the regulation of surface temperature. In recent times, the world has shifted towards sustainable and environmentally-friendly practices, prompting a transition from conventional lubricants to more efficient and eco-conscious alternatives. Among these emerging solutions, nanolubricants have emerged as formidable contenders, reshaping the landscape of lubrication technology. Their adoption not only promises enhanced performance but also carries the added benefit of environmental responsibility through biodegradability. This book delves into the multifaceted realm of nanolubricants, exploring their characterization and application across various domains. From vegetable oil-based lubricants to those incorporating metal and non-metal oxide components, this comprehensive work encompasses nine meticulously curated chapters. A particular focus is placed on the intriguing synergy between nano-dimensionality and the incorporation of metals and metal oxides into vegetable oil-based biodegradable lubricants. The book explores the environmental advantages, progress, and challenges associated with this innovative approach. Furthermore, it delves into the integration of functionalized nanostructured semi-metal-based compounds as lubricant additives in non-edible vegetable oils, paving the way for improved tribological properties. Audience The book is extremely important to industrial practitioners working in mechanical engineering, tribology, wear, tear, friction and lubrication behavior of machinery. Researchers in nanoscience, nanotechnology, materials science, and sustainability subjects, will find this book useful.
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Veröffentlichungsjahr: 2024
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Table of Contents
Cover
Table of Contents
Series Page
Title Page
Copyright Page
Preface
1 An Insight into Nanolubrication and Nanolubricants
1.1 Introduction
1.2 Advantages of Nanolubricants
1.3 Preparation of Nanolubricants
1.4 Lubrication Mechanism
1.5 Tribological and Thermophysical Properties of Nanolubricants
1.6 Conclusion and Future Directions
References
2 Nanolubrication Chemistry and Its Application
2.1 Introduction
2.2 Nanolubrication and Its Requirements
2.3 Synthesis of Nanoparticles
2.4 Preparation of Nanofluids/Nanolubricants
2.5 Mechanism of Nanolubrication
2.6 Nanoparticle Properties Necessary for Nanolubrication
2.7 Advantages of Nanolubricants
2.8 Nanoparticles Ability to Boost Grease Performance
2.9 Tribological Performance of Nanolubricants
2.10 Nanolubricants and Base Oils
2.11 Various Types of Nanoparticles as Lubricant Additives
2.12 Recent Advancement in Nanolubrication
2.13 Conclusion and Future Outlook
References
3 Characterization Techniques for Nanolubricants Using Different Approaches
3.1 Introduction
3.2 Nanoparticles as an Additive to Nanolubricants
3.3 Application of Nanolubricants
3.4 Preparation of Nanolubricants
3.5 Characterization Factors of Nanolubricants
3.6 Characterization Techniques Used for Nanolubricants
3.7 Conclusion
References
4 Metal-Based Nanolubricants: Current and Future Perspectives
4.1 Introduction
4.2 Synthesis Mechanism of NPs
4.3 NPs as Potential Candidate for Lubricant Additive
4.4 Methods to Enhance Dispersion Stability of Nanolubricants
4.6 Conclusion
References
5 Transition Metal-Based Catalysts for Preparing Biomass-Based Lubricating Oils
5.1 Introduction
5.2 Synthesis of Biolubricants
5.3 Catalysts for Biolubricant Synthesis
5.4 Conclusions
References
6 Effect of Integration of Nanostructured Semimetals on Lubrication Performance of Non-Edible Vegetable Oil-Based Biolubricants
6.1 Introduction
6.2 Lubrication and Lubricating Materials
6.3 Inedible Vegetable Oils-Based Biolubricants
6.4 Nanoparticle Additives to Enhance Tribological Performance of Non-Edible Vegetable Oil Lubricants
6.5 Tribological Mechanisms of Nanoparticles
6.6 Conclusion
References
7 Zinc Oxide Nanomaterials—Synthesis, Characterization, and Applications Focused on Lubricating Behavior
7.1 Introduction
7.2 Preparations
7.3 Characterization
7.4 Applications
References
8 Improvement in the Properties of Biodegradable Nanolubricants
8.1 Introduction
8.2 Nanoparticles for Lubricants
8.3 Types of Biodegradable Nanolubricants
8.4 Conclusion and Outlook
References
9 Nanodimensional Metal-/Metal Oxide-Incorporated Vegetable Oil-Based Biodegradable Lubricants: Environmental Benefits, Progress, and Challenges
9.1 Introduction
9.2 Concept of Lubrication and Characteristics of a Lubricant
9.3 Vegetable Oil-Based Biolubricants
9.4 Nanolubricants
9.5 Challenges for Sustainable Bio-Nanolubrication
9.6 Conclusion
References
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Types of nanolubricant based on additives, with examples and uses....
Chapter 2
Table 2.1 Physical methods for synthesis of nanolubricants.
Table 2.2 Chemical methods for synthesis of nanolubricants.
Table 2.3 Biological methods for synthesis of nanolubricants.
Table 2.4 Different mechanism of nanolubrication.
Table 2.5 Nanoparticles in reducing wear scar diameter and friction coeffici...
Table 2.6 Base oil category as per its quality.
Chapter 4
Table 4.1 Base oil categorized by the American Petroleum Institute [51–53]....
Table 4.2 List of nanoparticles added, dispersion method, test parameters, a...
Chapter 5
Table 5.1 Catalyst performance for transesterification reaction between meth...
Table 5.2 Catalytic performance of complexes in the methanolysis of various ...
Table 5.3 Effect of chiral ligands on hydrogenation of β-enamino esters (Rea...
Chapter 7
Table 7.1 Crystallite size and lattice strain values of ZnO nanoparticles de...
Chapter 8
Table 8.1 Lubricants (vegetable oil) with industry applications [28].
Table 8.2 Popular lubricant additives and their impact on lubricants.
Chapter 9
Table 9.1 The reaction condition involved in the
in situ
synthesis of differ...
List of Illustrations
Chapter 1
Figure 1.1 One-step and two-step preparation methods for nanolubricants.
Figure 1.2 (a) Surfactant-free method, (b) surfactant addition method, and (c)...
Chapter 2
Figure 2.1 An overview of nanolubrication components.
Figure 2.2 Synthesis of nanolubricant using two-step method.
Chapter 3
Figure 3.1 Schematic diagram of the main components in a UV-visible spectropho...
Chapter 4
Figure 4.1 Schematic representation of the electrospinning setup.
Figure 4.2 Schematic representation of the MoS
2
synthesis using sputtering tec...
Figure 4.3 Schematic illustration of a pulsed laser deposition (PLD) setup.
Figure 4.4 Schematic diagram of the hydrothermal method.
Figure 4.5 Graphical representation of different mechanisms involved with a na...
Figure 4.6 (a) Ball rolling mechanism by NPs-based lubricant; (b) protective f...
Figure 4.7 (a) AFM images of friction surface before sliding (surface roughnes...
Figure 4.8 Model structures and morphology of thiol-modified Ag NPs. NP-TBBT-1...
Figure 4.9 Schematics of (a) a sharp tip pushing a particle in a single-partic...
Figure 4.10 Optical micrographs showing the adhered material onto the ball sur...
Figure 4.11 Comparison of friction coefficient traces (left) and wear volumes ...
Figure 4.12 Friction torque graphs of base oil SAE 10 and oils with nano-addit...
Figure 4.13 Crystal structures of archetypal layered structures: graphite and ...
Figure 4.14 Crystal structure of TMDCs. Reprinted with permission from Kuc
et
...
Figure 4.15 Possible mechanisms of 2D nanosheets to reduce friction and wear: ...
Chapter 6
Figure 6.1 (a) Mechanical properties of a tribological system and (b) types of...
Figure 6.2 Interaction mechanism of (a) natural esters of vegetable oils and (...
Figure 6.3 Tribological mechanisms of nanoparticles: (a) ball-bearing effect; ...
Figure 6.4 Schematic representation of the effect of size on the lubrication m...
Figure 6.5 Effect of silica nanoparticles on the lubrication properties (frict...
Chapter 7
Figure 7.1 Crystal structure of ZnO hexagonal wurtzite.
Figure 7.2 Pulsed laser ablation process.
Figure 7.3 Chemical vapor deposition.
Figure 7.4 Anodization process.
Figure 7.5 Electrophoretic decomposition technique.
Figure 7.6 Hydrothermal method.
Figure 7.7 Electrochemical deposition method.
Figure 7.8 Sol–gel method for the ZnO thin film.
Figure 7.9 Thermal decomposition method.
Figure 7.10 Synthesis of ZnO by combustion method.
Figure 7.11 Microwave-assisted combustion method.
Figure 7.12 Synthesis of ZnO by co-precipitation method.
Figure 7.13 Preparation of ZnO powder with
Calotropis Gigantea
plant.
Figure 7.14 X-ray diffraction patterns of ZnO nanoparticles.
Figure 7.15 SEM images of ZnO thin films.
Figure 7.16 AFM represents the surface morphology of ZnO thin film.
Figure 7.17 Optical transmission spectra of ZnO thin films.
Figure 7.18 Plot of (αhν)2 vs. photon energy (hν) of ZnO film with different s...
Figure 7.19 Photoluminescence spectrum of ZnO.
Figure 7.20 Applications of ZnO.
Chapter 8
Figure 8.1 Synthesis of biodegradable nanolubricants.
Figure 8.2 Rolling effect and protective film formation by using nanoparticles...
Figure 8.3 Micelle formation due to surfactants.
Figure 8.4 A pie chart of different additives used over the last decade.
Chapter 9
Figure 9.1 Different configurations used in commercial tribometers with normal...
Figure 9.2 An illustration of different lubricating regimes and its relation t...
Figure 9.3 Types of base oils for lubricant formulation.
Figure 9.4 The triboemission/process taking place along with the physical and ...
Figure 9.5 (a) Bond dissociation energies of C–H bond and structure and (b) at...
Figure 9.6 Reaction steps involved in auto-oxidation: (a) initiation process o...
Figure 9.7 Different mechanisms involved in the nanolubrication process.
Figure 9.8 Reaction steps involved in
in situ
synthesis of Cu nanoparticles in...
Figure 9.9 Four ball tester for analysis of lubrication properties.
Figure 9.10 The variation of coefficient of friction MO and PO samples modifie...
Figure 9.11 Illustrations of (a) an experiment used for the
in situ
synthesis ...
Guide
Cover Page
Table of Contents
Series Page
Title Page
Copyright Page
Begin Reading
Index
WILEY END USER LICENSE AGREEMENT
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Scrivener Publishing
100 Cummings Center, Suite 541JBeverly, MA 01915-6106
Publishers at ScrivenerMartin Scrivener ([email protected])Phillip Carmical ([email protected])
Nanolubricants
Generation and Applications
Edited by
Mohd Yusuf
School of Life & Natural Sciences, The Glocal University, Saharanpur, India
Lalit Prasad
School of Basic Sciences, Galgotias University, Greater Noida, India
and
Shafat Ahmad Khan
Department of Chemistry, Galgotias University, Greater Noida, India
This edition first published 2024 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA© 2024 Scrivener Publishing LLCFor more information about Scrivener publications please visit www.scrivenerpublishing.com.
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Library of Congress Cataloging-in-Publication Data
ISBN 978-1-119-86510-0
Cover image: Pixabay.ComCover design by Russell Richardson
Preface
Lubrication is the lifeblood of machinery and the key to its smooth operation. In the world of mechanics and engineering, the role of lubricants cannot be overstated. They are the unsung heroes that reduce friction between surfaces in contact, thus preventing excessive heat generation during motion. Beyond this primary function, lubricants find their application in diverse areas, including power transmission, foreign object transportation, and the regulation of surface temperature.
In recent times, our collective consciousness has shifted towards sustainable and environmentally friendly practices, prompting a transition from conventional lubricants to more efficient and eco-conscious alternatives. Among these emerging solutions, nanolubricants have emerged as formidable contenders, reshaping the landscape of lubrication technology. Their adoption not only promises enhanced performance but also carries the added benefit of environmental responsibility through biodegradability.
This book delves into the multifaceted realm of nanolubricants, exploring their characterization and application across various domains. From vegetable oil-based lubricants to those incorporating metal and non-metal oxide components, this comprehensive work encompasses nine meticulously curated chapters.
A particular focus is placed on the intriguing synergy between nano-dimensionality and the incorporation of metals and metal oxides into vegetable oil-based biodegradable lubricants. The book explores the environmental advantages, progress, and challenges associated with this innovative approach. Furthermore, it delves into the integration of functionalized nanostructured semi-metal-based compounds as lubricant additives in non-edible vegetable oils, paving the way for improved tribological properties. We anticipate that this book will serve as a catalyst for stimulating the interests of scholars and researchers within the academic sphere, igniting a new wave of exploration and inquiry into the realm of nanolubricants. Through the dissemination of the latest advancements in lubrication science, this volume aims to address pressing concerns surrounding economic feasibility, environmental acceptability, sustainability, and overall viability.
We extend our gratitude to the contributors who have shared their expertise, and we invite all readers to join us on this enlightening expedition into the world of nanolubricants. We acknowledge the great efforts of the eminent authors without whom this book would have been unimaginable. We also appreciate the interest shown and the support given by the dedicated team at Scrivener Publishing, especially Martin Scrivener, which allowed us to compile this handbook.
Dr. Mohd Yusuf
Dr. Lalit Prasad
Dr. Shafat Ahmad KhanFebruary 2024
1An Insight into Nanolubrication and Nanolubricants
Deepshikha Singh1,2, Wasim Khan1†and Mohd Yusuf3*
1Department of Petroleum Engineering, School of Science and Technology, Glocal University, Mirzapur Pole, Saharanpur, Uttar Pradesh, India
2Department of Chemical Engineering, Madan Mohan Malaviya University of Technology, Gorakhpur, Uttar Pradesh, India
3Department of Natural and Applied Sciences, School of Science and Technology, Glocal University, Mirzapur Pole, Saharanpur, Uttar Pradesh, India
Abstract
Over the last decade, nanomaterials and nanotechnology have been increasingly used in lubrication to prepare anti-friction mediums in industry-relevant tribological applications. Various nanolubricants are being developed as viable replacements for standard lubricants containing chlorine, phosphorus and sulfur, which pollute the environment when discarded. This chapter provides an overview of recent advances in nanolubricants, focusing on using nanoadditives in lubricant preparation. Finally, the applications of nanolubricants are summarized, along with future research directions.
Keywords: Nanomaterials, anti-friction medium, nanoadditives, tribological applications
1.1 Introduction
The use of nanotechnology in lubrication refers to nanolubrication, one of the most recent innovative technologies used in lubrication science, to provide an appropriate solution for energy loss. When moving materials come into contact, friction and wear occur, and studying these phenomena is critical in many applied sciences [1, 2]. It is now critical to develop lubricants that can be used in harsh environments, prompting research into the use of nanoparticles as lubricant additives. In terms of development, nanoparticles are the most recent lubricant additives. Base oil (lubricant), nanoadditives, and surfactants are the three main components of nanobased lubricants. Nanoparticles are colloidal solid particles in lubricating oil [3–6]. Efforts have been proposed to incorporate various nanoadditives into base lubricants to develop suitable nanolubricants to improve lubricant friction, wear resistance, and extreme pressure properties [7–11]. Nanolubricants have a wide range of applications, including industrial, automotive, aerospace, and biomedical. In the automotive industry, nanolubricants can be used to improve fuel efficiency, reduce emissions, and extend the life of engine components. In the aerospace industry, nanolubricants are used to improve the performance of aircraft engines and other critical components. Nanolubricants are a growing field, with continued research and development to improve their properties and expand their applications. The development of nanolubricants is driven by the need for more sustainable and energy-efficient lubrication solutions and the increasing demand for high-performance lubricants in various industries.
Nanoscale particles in lubricants have shown great promise in improving tribological properties and as a result, energy conservation. This chapter aims to provide the information needed to comprehend the fundamentals of nanolubrication, the mechanisms involved, and the forces at the nanoscale. Nonetheless, rising demand and resource depletion force us to take the steps necessary to preserve and conserve energy. This chapter investigates recent advances and developments in nanolubricants that may serve as a responsive outlook for future research directions.
1.2 Advantages of Nanolubricants
Nanolubricants are used widely because they have many advantages over traditional lubricants. These advantages include the following:
Nanoparticle-laden lubricants have higher surface-to-volume ratios and better stability than lubricants dispersed with microsized particles because the added nanoparticles become more chemically reactive due to the presence of a large number of surface atoms, which aids in surface modification of the nanoparticles for stable dispersion in conventional lubricants.
The risks and toxicity caused by adding additives to increase lubricant qualities are largely minimized by employing environmentally safe nanoparticles (NP).
Nanoparticles included in lubricants may enter the gap between the tribo-pair in action, causing wear to be reduced.
Nanolubricants have improved thermophysical characteristics (particularly thermal conductivity), which help in the extraction of heat created by excessive friction and wear.
1.3 Preparation of Nanolubricants
Nanolubricants are prepared by one- and two-step methods, as shown in Figure 1.1. The one-step method for the preparation of nanolubricants involves the direct addition of nanoparticles to the base oil. This simple method can achieve a high concentration of nanoparticles in the lubricant. The one-step method is often favored for its ease of preparation, quick results, and reduced cost. The nanoparticles used in this method can be directly dispersed in the base oil through ultrasonication or mechanical stirring. However, this method can result in poor dispersion and aggregation of the nanoparticles, leading to reduced lubrication performance. Techniques in the one-step method include microwave irradiation [12], chemical reduction [13], laser ablation [14], polyol process [15], physical vapor condensation method [16], plasma discharging technique [17], and submerged arc nanoparticles (NP) synthesis system [18].
Figure 1.1 One-step and two-step preparation methods for nanolubricants.
The two-step method for preparing nanolubricants involves synthesizing the nanoparticles and adding them to the base oil. This method results in a more uniform nanoparticle distribution and higher purity than the one-step method. In the first step, the nanoparticles are synthesized through methods such as precipitation, co-precipitation, sol–gel, and hydrothermal synthesis. In the second step, the synthesized nanoparticles are added to the base oil and dispersed using ultrasonication or mechanical stirring techniques. This method results in better distribution and stability of the nanoparticles in the lubricant, leading to improved tribological properties.
1.3.1 Methods of Nanolubricant Preparation
There are several methods for the preparation of nanolubricants [19–21]; some of the common ones are
Chemical reduction method:
This involves reducing metal ions to form metal nanoparticles, which can then be used as lubricant additives. The most commonly used metal nanoparticles are silver, copper and gold.
Mechanical milling method:
This method involves grinding the lubricant base oil and the nanoparticle additive together using a ball mill, attritor mill, or other similar equipment. This method allows for the homogeneous dispersion of the nanoparticles in the base oil.
Sol–gel method:
This method involves the synthesis of nanoparticles through the gelation of a precursor solution. The gel is then dried, and the resulting material is ground to obtain the desired particle size.
Sonication method:
This method involves the dispersion of the nanoparticles in the lubricant base oil using ultrasonic energy. This method results in the homogeneous dispersion of the nanoparticles in the base oil.
Microemulsion method:
This method involves the preparation of a microemulsion of the lubricant base oil and the nanoparticle additive. The microemulsion is then stabilized to prevent the separation of the two phases.
The preparation of nanolubricants can also be performed using various other methods, including the surfactant-free method, the surfactant addition method, and the surfactant-modified method. The surfactant-free method involves the direct addition of nanoparticles to the base oil without the use of surfactants (Figure 1.2). This method is simple, but it may result in poor dispersion and aggregation of the nanoparticles, leading to reduced lubrication performance. The surfactant addition method involves the addition of surfactants to the base oil to help disperse the nanoparticles. The surfactants reduce the surface tension between the base oil and the nanoparticles, improving the distribution and stability of the nanoparticles in the lubricant. This method can result in improved tribological properties, but using surfactants can lead to additional costs and environmental concerns. The surfactant-modified method involves the modification of the surface of the nanoparticles with surfactants to improve their dispersion in the base oil. This method results in improved stability and distribution of the nanoparticles in the lubricant, leading to improved tribological properties. However, this method requires additional steps in synthesizing the nanoparticles and can be more complex and costly than other methods.
Figure 1.2 (a) Surfactant-free method, (b) surfactant addition method, and (c) surfactant-modified method.
1.3.2 Types of Nanolubricants Based on Additives’ Characteristics
A literature review on the types of nanolubricants based on their additives’ characteristics can provide an understanding of the various nanolubricant properties. Nanolubricants contain nanoparticles, which can improve their tribological properties such as reducing friction and wear. There are several types of nanolubricants based on the type of nanoparticle used as an additive. Carbon nanotubes, nanodiamonds, metal oxides, and graphene are some of the most commonly used nanoparticles in nanolubricants as shown in Table 1.1.
Carbon nanotube (CNT)-based nanolubricants:
Carbon nanotubes are commonly used as additives in nanolubricants due to their high mechanical strength, high thermal conductivity and excellent wear resistance. These properties make CNTs suitable for reducing friction and wear in various industrial applications. A study by Ma
et al
. [
22
] found that adding multi-walled carbon nanotubes (MWCNTs) to a base oil significantly reduced friction and wear, compared to the base oil alone. Another study by Bhowmick
et al
. [
23
] found that adding single-walled carbon nanotubes (SWCNTs) to a base oil improved its tribological properties, reducing friction and wear.
Nanodiamond-based nanolubricants:
Nanodiamonds are another type of nanoparticle commonly used as an additive in nanolubricants. They have high wear resistance, high thermal stability, and a low friction coefficient, making them suitable for improving the tribological properties of lubricants. A study by He
et al
. [
24
] found that adding nanodiamonds to a base oil significantly improved its tribological properties, reducing friction and wear. Another study by Vasudevan
et al
. [
25
] found that adding nanodiamonds to a base oil improved its anti-wear properties, which can be useful in applications requiring high wear resistance.
Metal oxide-based nanolubricants:
Metal oxides, such as titanium dioxide (TiO
2
) and zinc oxide (ZnO), are also commonly used as additives in nanolubricants. These metal oxides have good chemical stability, high thermal stability and low friction coefficients, making them suitable for improving the tribological properties of lubricants. A study by Li
et al
. [
26
] found that adding TiO
2
nanoparticles to a base oil significantly improved its tribological properties, reducing friction and wear. Another study by Jang
et al
. [
27
] found that adding ZnO nanoparticles to a base oil improved its anti-wear properties, which can be useful in applications requiring high wear resistance.
Graphene-based nanolubricants:
Graphene is another material used as an additive in nanolubricants due to its high mechanical strength, high thermal conductivity and low friction coefficient. A study by Li
et al
. [
28
] found that adding graphene to a base oil significantly improved its tribological properties, reducing friction and wear. Another study by Song
et al
. [
29
] found that adding graphene to a base oil improved its anti-wear properties, which can be helpful in applications requiring high wear resistance.
Table 1.1 Types of nanolubricant based on additives, with examples and uses.
Type of nanolubricant
Additives
Particle size
Examples
Uses
Carbon-based
Carbon nanotubes (CNTs), graphene
1–10 nm
Multi-walled carbon nanotubes (MWCNTs), single-walled carbon nanotubes (SWCNTs), graphene/oil
Low friction, high wear resistance, high thermal stability
Metal oxide-based
Titanium dioxide (TiO
2
), zinc oxide (ZnO)
5–50 nm
TiO
2
/oil, ZnO/oil, aluminum oxide (Al
2
O
3
/oil)
Improved anti-wear properties, high thermal stability, improved oxidation resistance
Diamond-based
Nanodiamonds
2–10 nm
Nanodiamond/ oil, cubic boron nitride (cBN)/oil
High wear resistance, high thermal stability, low friction
Hybrid
Combination of different types of additives
Varies
Graphene/ TiO
2
/oil, CNTs/ZnO/ oil
Improved wear resistance, reduced friction, high thermal stability
Silica-based
Silica (SiO
2
)
10–50 nm
SiO
2
/oil
Improved antiwear properties, improved oxidation resistance, high thermal stability
Metal-based
Metal nanoparticles
10–50 nm
Au/oil, Ag/oil
Improved anti-wear properties, high thermal stability, improved oxidation resistance
1.4 Lubrication Mechanism
Lubrication is a crucial process in mechanical systems that helps to reduce friction and wear between moving surfaces, thus extending the lifespan and improving the efficiency of the machinery. Nanoparticles are added to the lubricant to improve its tribological properties via two lubricating mechanisms: direct and indirect lubrication mechanisms. Ball-bearing and protective/tribofilm mechanisms are direct lubrication mechanisms, whereas mending and polishing mechanisms are indirect lubrication mechanisms. Several lubrication mechanisms reduce friction and wear, including boundary, mixed, and full-film lubrication [30–37]. The following are the different mechanisms of nanoparticle lubrication:
Boundary lubrication:
This type of lubrication occurs when the surfaces in contact are separated by a thin film of lubricant that is insufficient to separate the surfaces. The friction and wear in this regime are dominated by direct metal-to-metal contact between the surfaces. To improve boundary lubrication, additives such as extreme pressure agents are added to the lubricant to enhance its wear protection properties.
Mixed lubrication:
This is a combination of boundary and full-film lubrication, where a thin layer of lubricant separates the surfaces, but the lubricant film is not thick enough to completely separate the surfaces. In this regime, both metal-to-metal contact and hydrodynamic forces play a role in determining the friction and wear between the surfaces.
Full-film lubrication:
This type of lubrication occurs when a thick lubricant film completely separates the surfaces in contact, preventing any direct metal-to-metal contact. Hydrodynamic forces, such as pressure gradients, shear forces, and lubricant viscosity, determine this regime’s friction and wear.
Physical interlocking:
In this mechanism, the nanoparticles interlock physically with the asperities on the surfaces, reducing the contact area between the surfaces and thus reducing friction.
Chemical interlocking:
This mechanism involves the formation of chemical bonds between the nanoparticles and the surfaces, which locks the nanoparticles in place and reduces the possibility of metal-to-metal contact.
Load transfer:
The small size of the nanoparticles enables them to transfer the load from one surface to another, reducing the pressure on any one surface, and thereby reducing friction and wear.
Surface modification:
Nanoparticles can also modify the surface properties of the surfaces in contact, reducing the friction and wear between them.
Film formation:
The presence of nanoparticles can alter the rheological properties of the lubricant, leading to the formation of a more robust and stable lubricant film that separates the surfaces and reduces friction and wear.
1.5 Tribological and Thermophysical Properties of Nanolubricants
Tribology is the science and engineering of interacting surfaces in relative motion, including friction, wear, and lubrication. Nanolubricants, which are lubricants containing nanoparticles, have been developed in recent years to improve the tribological properties of conventional lubricants. The following are the tribological and thermophysical properties of nanolubricants [38, 39]:
1.5.1 Tribological Properties
Friction reduction:
Nanolubricants have been proven to dramatically reduce friction compared to traditional lubricants due to the tiny size of the nanoparticles, which allows them to penetrate the interface between moving surfaces and minimize the contact area. Friction reduction can contribute to higher efficiency, longer mechanical component lifespan, and lower energy usage. Non-polar functional group-containing hybrid and mono-nanoparticle-based nanolubricants showed improved friction and wear resistance. Due to the increased antioxidant nature of the nanolubricant, oleic acid and oleylamine-based-modified nanostructures have a synergistic impact on friction and wear reduction. Friction and wear reduction in non-polar (metal, carbon)-based nanolubricants are greater than metal oxide-based nanolubricants due to the increasing polar (Al-O, Ni-O, Ti-O, O-H) function group in nanolubricants. Nanoparticles having a larger surface-to-volume ratio and a lower concentration have a superior tribological impact. Carbon nanostructures, in particular, have exceptional tribological characteristics due to their conducting, semiconducting, and insulating nature [
39
].
Wear reduction:
The presence of nanoparticles in the lubricant can also reduce wear by reducing the friction between the surfaces and preventing metal-to-metal contact. The small size of the nanoparticles enables them to physically interlock with the asperities on the surfaces, reducing the contact area and thus reducing wear.
Load-carrying capacity:
Nanolubricants have been shown to have improved load-carrying capacity compared to conventional lubricants due to the ability of the nanoparticles to transfer the load from one surface to another. This reduces the pressure on any one surface and improves the overall performance of the lubricant.
Thermal stability:
The thermal stability of nanolubricants can be improved compared to conventional lubricants due to the presence of nanoparticles. The nanoparticles can act as heat sinks, absorbing heat from the system and reducing the temperature of the lubricant, reducing the degradation of the lubricant and improving its overall performance. A nanolubricant with higher surface-to-volume ratio and optimum concentrations of nanoparticle exhibits excellent stability. Oleic acid and oleylamine-based non-polar surfactant show better stability in lubricant medium due to reduced agglomeration (intermolecular forces) between the nanoparticles. Specifically, carbon-based nanostructures showed better stability than other nanostructures due to similar functional groups.
1.5.2 Thermophysical Properties
1. Viscosity
The viscosity of nanolubricants can be modified compared to conventional lubricants, depending on the type and size of the nanoparticles used. Viscosity can be increased or decreased based on working temperature and nanostructures concentration, which can affect the ability of the lubricant to flow and the thickness of the lubricant film that separates the surfaces. Stable aggregation or mono-nanoparticles help to enhance lubricant viscosity. Specifically, the non-polar functional group with better surface area contained nanoparticles that helps to improve the viscosity index in the base lubricant.
2. Surface tension
The surface tension of nanolubricants can be modified compared to conventional lubricants due to the presence of the nanoparticles. Surface tension can be increased or decreased, which can affect the ability of the lubricant to wet the surfaces and form a stable lubricant film. One important consideration in understanding the surface tension of nanolubricants is the interfacial behavior of the particles themselves. Due to their small size, nanolubricant particles have a large surface area-to-volume ratio, which can make them highly reactive and prone to aggregation. To stabilize the particles and prevent them from clumping together, surface modifiers and dispersants are often used. Another factor that can affect the surface tension of nanolubricants is the presence of surface-active agents, which are compounds that can adsorb to the surface of the particles and alter their interfacial behavior. These agents can reduce the surface tension of the nanolubricant, making it easier for the lubricant to spread and form a thin film on the surface on which it is applied [40].
3. Density
The density of a nanolubricant is an important physical property that affects its flow behavior, lubrication efficiency, and storage requirements. The density can be increased or decreased compared to conventional lubricants, depending on the type and size of the nanoparticles used, which can affect the ability of the lubricant to flow and its overall performance. For example, metal nanoparticles are generally denser than most base fluids, and their addition to the fluid can increase the overall density of the nanolubricant. Conversely, carbon nanotubes have a lower density than most base fluids, and their addition can decrease the overall density of the nanolubricant.
4. Thermal conductivity
The thermal conductivity of nanolubricants increases with temperature. High interparticle spacing between nanoparticles is a symptom of poor thermal conductivity. Metal, metal oxide, carbon (conducting nanostructures), and hybrid nanoparticles have higher thermal conductivities and a higher surface-to-volume ratio, making them ideal for use as a nanolubricant. Discrete nanostructures with high surface area or stable aggregation boost thermal conduction processes even further. Nanolubricants offer better thermal conductivity due to more frequent nanoparticle aggregation and improved suspension characteristics although there is no association between enhancing thermal conductivity and other lubricant properties such as friction/wear, kinematic viscosity, flash point, and pour point.
5. Flash point
The flash point of nanolubricants refers to the temperature at which the lubricant will ignite when exposed to a flame or spark. Nanolubricants can have different flash points than traditional lubricants due to their unique chemical properties and composition. The addition of nanoparticles can increase the flash point of lubricants, making them safer to use in high-temperature applications. The improved thermal stability of nanolubricants is attributed to the ability of nanoparticles to act as heat sinks and reduce the chances of the lubricant reaching its ignition temperature. Flashpoint is higher for non-polar than polar nanoparticles and increases with the concentration of nanoparticles.
6. Pour point
The pour point of a nanolubricant is a critical property that influences its ability to flow and lubricate under low-temperature conditions. The pour point of a nanolubricant is determined by the base fluid and the type and concentration of nanomaterials used. Nanomaterials can modify the base fluid’s pour point by adsorbing onto the fluid’s surface and altering its physical properties. For example, metal nanoparticles can increase the viscosity of the base fluid, which can lead to an increase in the pour point. However, carbon nanotubes can decrease the pour point by forming a stable network within the fluid that prevents the formation of ice crystals. Non-polar (C–H, C=C=C, C=C, C≡C) functional group containing carbon nanostructures shows a higher pour point [41].
1.6 Conclusion and Future Directions
The actual behavior of a lubrication system can be complex and can vary based on many factors, including the geometry of the surfaces, the speed and load conditions, the temperature and pressure of the system, and the properties of the lubricant itself. The actual performance of nanoparticle lubrication can be influenced by several factors, including the size and shape of the nanoparticles, the properties of the surfaces, the temperature and pressure of the system, and the properties of the lubricant. In conclusion, nanolubricants have been shown to have improved tribological and thermophysical properties compared to conventional lubricants. The small size of the nanoparticles enables them to penetrate the interface between moving surfaces and reduce friction, wear, and temperature. The tribological and thermophysical properties of nanolubricants can be tailored to suit the specific needs of a particular application by selecting the type and size of the nanoparticles used.
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Notes
*
Corresponding author
:
*
Corresponding author
:
2Nanolubrication Chemistry and Its Application
Smrita Singh1*, Ashutosh Singh Chauhan2and Lalit Prasad3†
1Creative Bioinformatics and Science, Morna, Bijnor, Uttar Pradesh, India
2Archaeological Survey of India, Agra Fort, Agra, Uttar Pradesh, India
3Galgotias University, Greater Noida, Uttar Pradesh, India
Abstract
Lubrication is a method to reduce friction in moving machinelike parts. However, rising demand and ongoing resource depletion urge us to take essential steps to save and conserve energy. Nanolubrication is a viable option for reducing energy consumption. Nanolubricant films must be resistant to adhesives, cohesiveness, and stresses in order to be effective. The way these films is organized, whether they are single molecules or mixed species, has a big impact on how well they perform. A film’s most essential property is its ability to adhere to a surface. Physical or chemical adsorption is how molecules adhere to a surface. Major factors in affecting molecular weight molecules are bond strength, nature of the bonds, the number of bonds per molecule, molecular orientation, and packing density per unit area. Molecular adhesion to a surface can be homogenous and equally distributed on an ideal surface. The crystalline orientations and phases present at the surface of silicon have an impact on its chemical reactivity and mechanical capabilities. Dangling bonds are formed when the surface is mechanically damaged or thermally stimulated, producing high-energy active sites for adsorption and contact. Surface layers of silicon nitride and silicon carbide can be produced on silicon using gas phases in a vacuum. Nickel and diamond-like carbon are the other two materials commonly used in microsystems. With magnetic lubrication of hard drives, the hard drive is protected by a monolayer of perfluoropolyether (PFPE). Commonly used PFPE has two OH functional groups at the ends of molecules. Colloid physics and chemistry offer exciting opportunities for research to reduce friction and wear in various metallurgical contexts. Different chemical methods have been developed to produce nanoparticles, permitting the development of an oil-stable dispersion of selected efficient tribochemical film precursors.
Keywords: Perfluoropolyether, tribochemical film, packing density, molecular orientation, colloid, nanoparticles
2.1 Introduction
One of the most effective ways to reduce energy use and increase the productivity of machinery used in various industries has been thought to be lubrication. By introducing a lubricant or lubricating agent between two surfaces that are moving in close proximity to one another, lubrication is described as the process or technique used to reduce friction and wear [1]. A slippery film is created when a lubricant is present, significantly reducing friction, wear, and tears between mating surfaces. In addition to reducing friction and wear, lubricants also enhance cooling and heat transfer, reduce vibration and noise, remove dirt and pollutants on their own, and, in some situations, prevent leaks. Lubricants should have properties like high boiling point, acceptable viscosity, low freezing point, high thermal stability, and resistance to oxidation and corrosion in order to fulfill these functions. The tribological characteristics of the lubricating media are crucial for effective machine lubrication. Mineral oils have been historically used to lubricate tribo-pairs effectively on the global market. The various chemical modifications, sometimes referred to as additives, improve the tribological effectiveness of the lubricants. The additives function as viscosity index enhancers [2], anti-wear agents, extreme pressure agents, anti-corrosion agents, and friction modifiers. High temperatures and pressures have been observed to cause the standard additives to fail. These additives also have a number of technical flaws, including inherent toxicity, non-biodegradability, high reactivity, ineffectiveness at low temperatures, and slow speeds, among others [3]. This has created a need for environmentally friendly lubricants that will improve tribo-pair performance while being less harmful to the environment. With the development of nanotechnology, a wide range of different types of tailored materials are now readily available, making the answer simple. Different kinds of nanoparticles are perfect lubricant additions because they do not have the drawbacks of traditional lubricants listed above. Therefore, adding extremely modest amounts of nanoparticles to lubricants may improve their tribological qualities. Generally speaking, such tailored fluids with nanoparticle dispersions are referred to as nanofluids [4–7]. However, “nanolubricants” have been used frequently in the literature [2, 8–12] to refer to nanofluids used as lubricating media. More specifically, nanolubricants are stable colloidal suspensions of nanosized materials (such as nanofibers, nanotubes, nanowires, nanorods, and nanosheets) that are added in extremely small amounts (<1 wt%) to traditional lubricants to improve their tribological properties.
2.2 Nanolubrication and Its Requirements
Controlling and maintaining the surface energy state—defined by electrostatic charges, defects, and active sites—is necessary to safeguard the surface. Due to the lack of regulated contact geometry and insufficient molecules to produce such films, the load is unlikely to be maintained at the nanoscale by the macroscale squeezed-film mechanism. Since it is challenging to continually provide the molecules to replace the film, and because it is challenging to dispose of the degradation products, the nano-sacrificial film method is likewise not very likely. Therefore, a new lubricating principle is required. Tenacious, long-lasting surface coatings will be required to lubricate surfaces at the nanoscale. With the limited supply of lubricants, the film’s effectiveness in reducing shear stress is very important as only one or two layers of molecules are available for the duration of the device’s lifetime. The ability of the film to withstand repeated contact over a long period of time is also critical. Earlier, it was proved that a monolayer of fatty acids on glass surfaces reduces friction as proved by experiments of Bowden and Tabor [2]. Due to repeated sliding, these monolayer films did not last long and the film failed as some of the molecules were removed from the surface by mechanical rubbing. The effectiveness of solid lubricant films such as MoS2, graphite, and Teflon, should be checked before using them, as any severe abrasive wear can be caused by inorganic degradation products such as MoOx or carbon particles. Micro/nanoscale devices need to be operated in a clean environment. If there are outlets and scraping devices for the degradation products, such as roller bearings, these foils could be effective. Any organic film that can function effectively is able to repair and refill, and remains intact when impacted or damaged. An important characteristic of a lubricant is self-repair mechanism due to the migration of molecules when lubricant molecules are removed from one site, due to contact, oxidation, or evaporation. Temperatures can rise at typically high speed contacts; therefore, in order to overcome this effect, these molecules must withstand thermal decomposition and oxidation. Low vapour pressure, volatility and high resistance to oxidation and decomposition is required for these lubricants. Perfluoropolyether (PFPE) is used as a lubricant in magnetic secdisk with a thickness of 1 and 2 nm. The main characteristics of PFPE are resistance to oxidation, low volatility (106 torr), and adherence to the surface by hydrogen bonding to withstand the high centrifugal force of disk rotation.
In summary, nanoscale lubrication (control of adhesion, stiction, and friction) requires lubricant molecules that should have the following important properties:
non-volatile,
resistant to oxidation,
thermal degradation,
good adhesion and cohesion with the surface, and
self-repairing or regenerating.
A nanolubricant consists of three components (Figure 2.1) [13]:
base oils: mineral oil, synthetic oil, and vegetable oil;
additives: chemical additives and nano-additives; and
surfactants.
Mineral oils, synthetic oils, and vegetable oils are the three types of base oils. Chemical additives and nano-additives are two more categories of additives that improve the fundamental tribological characteristics of oil [14]. Surfactants stabilize the nanolubrication system.
Figure 2.1 An overview of nanolubrication components.
2.3 Synthesis of Nanoparticles
There has been a variety of evolved nanoparticles, including metals, metal oxides, and sulfides (tungsten disulfide, molybdenum disulfide, and copper monosulfide), carbon-based nanoparticles (diamond, graphene, and fullerene), and nanocomposites (Cu/SiO2, Cu/graphene oxide, Al2O3/ SiO2, Al2O3/TiO2, and serpentine/La(OH)3). Examples of metal nanoparticles are iron, silver, copper, gold, and zinc. ZnO, TiO2, SiO2, CuO, Fe3O4, ZrO2, and Al2O3 are metal oxide nanoparticles. There are three methods for nanoparticle synthesis [1]:
physical methods,
chemical methods, and
biosynthetic methods.
2.3.1 Physical Method
In order to create nanoparticles, the physical process of nanoparticle creation employs the use of mechanical, compressive, thermal, and electrical radiation. Ball milling, inert gas condensation, electrospray, pulsed evaporation, melt mixing, laser pyrolysis, flash spray pyrolysis, and other physical techniques are among them (Table 2.1) [1, 15].
Table 2.1 Physical methods for synthesis of nanolubricants.
S. no.
Physical method
Material used
Nanoparticle
Size (nm)
Reference
1
Ball milling
Graphite SiO
2
Si
5-500
[
19
]
Graphite/Nitrogen
Nitrogen doped Carbon
210
[
20
]
Iron powder
Magnetite
12-20
[
21
]
2
High energy ball milling
Iron sulphur
FeS
2
10
[
22
]
3
Inert condensation
------
Au Pd
1-5
[
23
]
Manganese granules
Mn
2-20
[
24
]
4
PVD
HOPG, gold
Au
2-15
[
25
]
5
PVD Laser ablation
Zinc
ZnO
2
5-19
[
26
]
6
PVD/Sputtering
------
Cu-Au
Less than 7
[
27
]
7
Laser pyrolysis
Iron compound
Fe-FeO
2
14
[
28
]
Titanium chloridepyTolyss (FeCo
5
)
TiO
2
/Fe-TiO
2
[
29
]
8
Spray pyrolysis
Magnesium nitrate/Hexa methylene tetramine
MgO
9
[
30
]
Source: Adopted from Shafi WK, Charoo M. Nanolubrication systems: an overview. Mater Today: Proc. 2018;5(9):20621–20630.
2.3.2 Chemical Methods
This is the most popular and straightforward method for creating nanoparticles. Through a chemical reaction involving several precursors and solvents, the creation of nanoparticles involves their breakdown into atoms, followed by their aggregation into clusters [16]. Precursor concentration, pH, calcination temperature, and other factors all affect the size, shape, and stability [17]. Simple precipitation method, sol–gel method, hydrothermal, solvothermal, chemical vapor deposition, and polyol synthesis among others, are a few of the different chemical processes used to create nanoparticles. Table 2.2 provides a collection of several research publications on chemical synthesis techniques [1].
2.3.3 Biological Methods
The safest, least poisonous, and most environmentally responsible approach to creating nanoparticles is through biological processes. For the synthesis of nanoparticles, biosynthetic processes use plant extracts, bacteria, viruses, and fungi [18]. Research on the biosynthetic processes are depicted in Figures 2.1 and 2.2 (Table 2.3).
Table 2.2 Chemical methods for synthesis of nanolubricants.
S. no.
Chemical method
Precursor/Solvent
Nanoparticle
Size (nm)
Reference
1
Hydrothermal
Zirconia /NaOH
ZrO
2
15-30
[
31
]
Zinc nitrate/ NaOH, DI water
ZnO
50
[
32
]
2
Solvothermal
Nickel/acetyl acetone/2-Butanone
NiO
5.5-6.5
[
33
]
3
Simple aqueous route
Zinc chloride/ Distilled water
ZnO
8-30
[
34
]
TiOSO
4
, /H
2
0
2
:
TiO
2
28-50
[
35
]
4
Sol-gel
Zirconium-n-Propoxide /n-Propanol, Water/Ammonia
ZrO
2
30-100
[
36
]
Titanium- iso-Propoxide isopropyl alcohol, water, NaOH, Pluronic (F-127)
TiO
2
10-12
[
37
]
5
Polyol
Silver nitrate ethelene glycol,
Silver
30-60
[
38
]
PVP, NaCI
Palladiunm
2
[
39
]
Source: Adopted from Shafi WK, Charoo M. Nanolubrication systems: an overview. Mater Today: Proc. 2018;5(9):20621–20630.
Figure 2.2 Synthesis of nanolubricant using two-step method.
Table 2.3 Biological methods for synthesis of nanolubricants.
Biological method
Material used
