Lubricants with Nanoparticle-Improved Functionalities

Lubricating oils can greatly benefit from nano-additives, which help to reduce friction and wear. It is however crucial, that nano-additives such as nanoparticles, graphene monolayers or core-shell nanospheres are uniformly and single-dispersed in the lubricant. Ultrasonic dispersion has been proven as reliable and efficient mixing method, providing homogeneous nanoparticle distribution and preventing aggregation.

How to Disperse Nano-Additives in Lubricating Fluids? – With Ultrasonics!

Using nano-additives in lubricants is considered as one of the most effective methods to improve tribological characteristics reducing friction and wear. Such tribological improvement greatly enhances energy conservation, emission reduction, thereby lowering environmental impact.
The challenge of nano-improved lubricants lies in the mixing: Nanomaterials such as nanoparticles or crystalline nano cellulose require focused high-shear mixers that disperse and disentangle the nano-materials uniformly into single particles. Creating unique energy-dense fields, ultrasonication using high-power ultrasound probes has been proven superiority in nanomaterial processing and is thereby the established method for nano-dispersions.
Ultrasonic disperser can be used in batch and continuous flow mode for mixing nanofillers into varishes.Molseh et al. (2009) showed that the dispersion stability of three different nanoparticles (molybdenum disulfide (MoS2), tungsten disulfide (WS2), and hexagonal boron nitride (hBN)) in CIMFLO 20 with ultrasonic treatment was better than that with mechanical shaking and stirring. As ultrasonic cavitation creates unique energy-dense conditions, probe-type ultrasonication excels conventional dispersion techniques in effectiveness and efficiency.
Nanoparticles characteristics such as size, shape, and concentration are influencing their tribological properties. Whilst ideal nano-size varies in dependence of the material, most nanoparticles show highest functionalities in the range of ten to hundred nanometers. Ideal concentration of nano-additives in lube oil is mostly between 0.1–5.0% .
Oxide nanoparticles such as Al2O3, CuO or ZnO are widely used as nanoparticles improving the tribological performance of lubricants. Other additives include ashless additives, ionic liquids, borate esters, inorganic nanomaterials, carbon-derived nanostructures like carbon nanotubes (CNTs), graphite and graphene. Specific additives are used in order to improve specific properties of lube oils. For instance, wear preventative lubricants contain extreme pressure additives such as molybdenum disulfide, graphite, sulfurized olefins and dialkyldithiocarbamate complexes or antiwear additives such as triarylphosphates and zinc dialkyldithiophosphate.
Ultrasonic probe-type homogenizers are reliable mixers and are used for the formulation of high-performance lubricants. Renown as superior when it comes to the preparation of nano-sized suspensions, sonication is highly efficient for the industrial manufacturing of lube oils.

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High-performance ultrasonicators are reliable and highly efficient inline mixing systems for the production of nano-lubricants.

Industrial ultrasonic mixing system for the high-throughput dispersion of nanoparticles into lubricating oils.

The video shows the ultrasonic mixing and dispersing of Graphite in 250mL of Epoxy Resin (Toolcraft L), using an ultrasonic homogenizer (UP400St, Hielscher Ultrasonics). Hielscher Ultrasonics makes equipment to disperse graphite, graphene, carbon-nanotubes, nanowires or fillers in the lab or in high volume production processes. Typical applications are the dispersing nano materials and micro materials during the functionalization process or for dispersing into resins or polymers.

Mix Epoxy Resin with Graphite Filler using Ultrasonic Homogenizer UP400St (400 Watts)

Ultrasonic Lubrication Manufacturing

  • improved tribological performance
  • uniform nano-additive incorporation
  • vegetable-oil-based lubricants
  • preparation of tribofilm
  • sheet metal forming fluids
  • nanofluids for improved cooling efficacy
  • ionic liquids in aqueous or oil-based lube
  • broaching fluids
Aluminium oxide is dispersed in lubricants using power-ultrasonication.

Ultrasonic dispersion of Aluminium oxide (Al2O3) results in a significant particle size reduction and uniform dispersion.

Manufacturing of Lubricants with Nano-Additives

For the production of nano-reinforced lubricating oils, adequate nano-material and a powerful, efficient dispersion technique are crucial. Without reliable and long-term stable nano-dispersion, there cannot be manufactured a high-performance lubricant.
Ultrasonic mixing and dispersing is an established method for the production of high-performance lubricants. The base oil of lubricants is reinforced with additives such as nanomaterials, polymers, corrosion inhibitors, antioxidants and other fine aggregates. Ultrasonic shear forces are highly efficient in providing a very fine particle size distribution. Ultrasonic (sonomechanical) forces are capable to mill even primary particles and are applied to functionalize particles, so that the resulting nanoparticles offer superior characteristics (e.g. surface modification, core-shell NPs, doped NPs).
Ultrasonic high-shear mixers can greatly help to manufacture high-performance lubricants efficiently!

Ultrasonic dispersing is highly efficient for the distribution of nano-additives such as nanoparticles, anti-corrosion agents and anti-wear protective additives into lubricating oils.

Oil blend with zinc dialkyldithiophosphate (ZDDP) and surface modified PTFE nanoparticles (PHGM) after ultrasonic dispersion.
(Study and picture: Sharma et al., 2017)

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Novel Nano-Additives in Lubricating Oils

Novel nano-sized additives are developed to further improve functionalities and performance of lubricating oils and greases. For instance, cellulose nano-crystals (CNCs) are researches and tested for the formulation of green lubricants. Zakani et al. (2022) demonstrated that – in comparison to unsonicated lubricating suspensions – sonicated CNC lubricants could decrease COF (coefficient of friction) and wear by almost 25 and 30% respectively. Results of this study suggest that ultrasonication processing can significantly improve lubrication performance of CNC aqueous suspensions.

High-Performance Ultrasonic Dispersers for Lubricant Manufacturing

When nano-addititives are used in industrial manufacturing processes such as the production of lubricating oils, it is crucial that dry powders (i.e., nanomaterials) are homogeneously mixed into a liquid phase (lube oil). Nano-particle dispersion requires a reliable and effective mixing technique, which applies enough energy to break agglomerates in order to unleash the qualities of nano-scale particles. Ultrasonicators are well known as powerful and reliable dispersers, therefore used to deagglomerate and distribute various materials such as aluminium oxide, nanotubes, graphene, minerals and many other materials homogeneously into a liquid phase such as mineral, synthetic or vegetable oils. Hielscher Ultrasonics designs, manufactures and distributes high-performance ultrasonic dispersers for any kind of homogenization and deagglomeration applications.
Contact us now to learn more about ultrasonic dispersion of nano-additives in lubricants!

The table below gives you an indication of the approximate processing capacity of our ultrasonicators:

Batch Volume Flow Rate Recommended Devices
1 to 500mL 10 to 200mL/min UP100H
10 to 2000mL 20 to 400mL/min UP200Ht, UP400St
0.1 to 20L 0.2 to 4L/min UIP2000hdT
10 to 100L 2 to 10L/min UIP4000hdT
15 to 150L 3 to 15L/min UIP6000hdT
n.a. 10 to 100L/min UIP16000
n.a. larger cluster of UIP16000

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Ultrasonic high-shear homogenizers are used in lab, bench-top, pilot and industrial processing.

Hielscher Ultrasonics manufactures high-performance ultrasonic homogenizers for mixing applications, dispersion, emulsification and extraction on lab, pilot and industrial scale.



Ultrasonically dispersed PTFE nanolubricant shows good stability after sonication treatment.

PTFE nanolubricants after 7 days of preparation (A: base oil, B: PTFE nanolubricant with 1 hr ultrasonication, C: PTFE nanolubricant with 30 min. ultrasonication).
(Study and picture: © Kumar et al., 2013)

Ultrasonication produces uniformly distributed and highly stable aluminium nanoparticles in lubricating oils.

Effect of ultrasonication on the dispersion stability of Al2O3 in lubricants.
(Study and graphic: © Sharif et al., 2017)

Facts Worth Knowing

What are Lubricants?

The main use of lubricants or lube oils is to reduce friction and wear from mechanical contact as well as heat. Depending on their use and composition, lubricants are divided into engine oils, transmission fluids, hydraulic fluids, gear oils, and industrial lubricants.
Therefore, lubricants are widely used in motor vehicles as well as in industrial machinery. To provide good lubrication, lubricating oils typically contain 90% base oil (mostly petroleum fractions, i.e. mineral oils) and less than 10% additives. When mineral oils are avoided, vegetable oils or synthetic liquids such as hydrogenated polyolefins, esters, silicones, fluorocarbons and many others can used as alternative base oils. The main use of lubricants is to reduce friction and wear from mechanical contact as well as to lower frictional heat and energy losses. Therefore, lubricants are widely used in motor vehicles as well as in industrial machinery.
Antioxidative substances such as aminic andphenolic primary antioxidants, natural acids, peroxide decomposers and pyrazines extend the life cycle of lubricants by increasing the oxidative resistance. Thereby the the base oil is protected against heat degradation as thermo-oxidative breakdown occurs in reduced and delayed form.

Lubricant Types

Liquid lubricants: Liquid lubricants are generally based on one type of base oil. To this base oil often ofter substances are added in order improve functionality and performance. Typical additives include for example, water, mineral oil, lanolin, vegetable or natural oil, nano-additives etc.
The majority of lubricants are liquids, and they may be classified according to their origin into two groups:

  1. Mineral oils: Mineral oils are lubricating oils refined from crude oil.
  2. Synthetic oils: Synthetic oils are lubricating oils that are manufactured using compounds that are artificially modified or synthesised from modified petroleum.

Lubricating grease is a solid or semisolid lubricant which consist in a liquid lubricant, which is thickened by dispersing thickening agents into it. In order to produce lubrication grease, lubricating oils are used as base oils and are the main ingredient. Lubrication grease contains approx. 70% to 80% of lubricating oil.

Penetrating lubricants and dry lubricants are further types, which are applied mostly for niche applications.

Numerous types of nanoparticles have been successfully incorporated into lubricants using ultrasonic dispersers.

Nano-additives as listed exemplary above can be successfully mixed into lubricants using ultrasonic dispersers.


 

Literature / References


High performance ultrasonics! Hielscher's product range covers the full spectrum from the compact lab ultrasonicator over bench-top units to full-industrial ultrasonic systems.

Hielscher Ultrasonics manufactures high-performance ultrasonic homogenizers from lab to industrial size.