Slide 1

On Nanoparticles’ Tribology;

Reducing the Real Area of

Contact to Reduce Friction and

Control Wear

Hamed Ghaednia PhD Candidate

Dr. Robert Jackson Associate Professor

Multi-Scale Tribology Laboratory

Department of Mechanical Engineering

Samuel Ginn College of Engineering

Auburn University

Slide 2

Agenda

• Introduction

• Motivations and Challenges

• Experimental investigations

• Nanoparticle Contact Model

• Nanoparticles in Dry Contact

• Conclusion

Slide 3

Introduction

Nano-Technology Nanotechnology is the understanding and control of matter at dimensions of roughly 1 to 100 nanometers, where unique phenomena enable novel applications. Encompassing nanoscale science, engineering and technology, nanotechnology involves imaging, measuring, modeling, and manipulating matter at this length scale. US National Nanotechnology Initiative

Nanotechnology-based consumer products inventory (as of March 10, 2011).

http://www.nanotechproject.org/inventories/consumer

There is a small set of materials explicitly referenced in nanotechnology consumer products.

Silver (313 products) Carbon(91) Titanium (and titanium dioxide) (59) Silica (43) Zinc (and oxide) (31) Gold (28).

Slide 4

Introduction

Nano-Lubricants •Nanoparticles are metallic or non-metallic particle smaller than 100 nm (1 nm = 10-9 m)

•Nanoparticles are clusters/arrangements of atom/molecules and not individual ones.

•Particle additives are historically known as "Solid Lubricant Additives”

•Components of a nano-lubricant

Main Lubricant

Dispersant agent

Nanoparticles

http://angiebiotech.com/

Slide 5

Introduction

Why nanoparticles as lubricant additives?

• Small enough to penetrate contact

• Scale dependent properties

• Versatility of characteristics

• Numerous combinations

Challenges and Disadvantages

• Stability of the suspensions

• Reclamation of particles

• Environmental issues

• Often expensive

• Unknown Mechanisms

Nowak, Mook, Minor, Gerberich, Carter, 2007

Slide 6

Motivation for Nanoparticle Lubrication

Vehicle Industry for Example…

• Reducing engine friction will improve fuel economy.

• 20% to 30% of the energy produced by a modern combustion engine is lost to friction.

• The DOE finds that merely a 5% reduction of engine energy losses would cut the consumption of oil by approximately 100 million barrels.

• This approach could allow for improved friction in not only new vehicles but vehicles currently on the road.

Holmberg, K., Andersson, P., and Erdemir, A., 2012, "Global Energy Consumption Due to

Friction in Passenger Cars," Tribology International, 47(0), pp. 221-234.

Slide 7

Experimental investigations of nanoparticle lubricants

Slide 8

• Proposed nanoparticle lubrication enhancement mechanisms:

(1) the particles affect viscosity

(2) the particles affect the thermal properties and thermal stability

(3) the particles could roll between the surfaces as “nano ball bearings”

(4) the particles could mend worn surfaces by adhering to them, “Transfer Films”.

(5) Particle could reduce the real area of contact

2. Rolling

1. Transfer films

3. Reducing the real area of contact

What to look for?

Tao, Jiazheng, Kang (1996) and Liu et al. (2004)

Slide 9

• Base lubricants

- Mineral 600HC Heavy Base Oils

- Mineral 100HC light Base Oils

• Nano Particles

Copper Oxide Particles of size 5 - 15 nm.

Sodium Oleate as surfactant.

CuO Nano-Lubricant

Clary, D. R., and Mills, G., 2011, "Preparation and Thermal Properties of Cuo

Particles," The Journal of Physical Chemistry C.

100HC

50% vol

600HC

50% Vol

Base oil

Dodecane

10.0 % wt

CuO/SOA

particles

Slide 10

Friction Results

Normal Load: 0.0 N ~ 450 N

Rotational Speed: 570 rpm

• Nanoparticles appear to be more influential

farther into boundary lubrication regime

Friction Results

Slide 11

Ball

Disk

Stylus tip

Stylus Profilometry

Slide 12

(b)

(c)

Surfaces Analysis

(a) Surface tested with control

EDX Analysis SEM Analysis

Slide 13

Surfaces Analysis

Surface tested with 1.0%wt

nano-lubricant

EDX Analysis

SEM Analysis Distribution of Cu

Slide 14

Wear Analysis

Slide 15

Silver Nano-lubricant

polyethylene glycol (PEG)

MW of 600 g/mol

Nano-Lubricant

Nanoparticle

Surfactant/

Coating Agent

Lubricant

polyvinyl pyrollidone (PVP)

MW of 10K g/mol

metallic silver particles

Average size 7 nm

0.75 – 4.5 mM Ag

1.5 mM PVP

Remaining is PEG

Stable for 6 months

Control lubricant

1.5 mM PVP

Remaining is

PEG

100 nm

Slide 16

Friction and Wear Tests

Pin-On-Disk Friction test

• 10 mm sphere

• AISI 52100 chromium steel

• Rotating disk

• AISI 1080 carbon steel

• Submerged samples

• Contact suspension

• Feedback controlled normal force

• ECR sensor to detect contact

• The setup is capable of conducting carefully controlled experiments

Slide 17

Wear Analysis

0.025

0.03

0.035

0.04

0.045

0.05

0.055

0.04

0.05

0.06

0.07

0.08

0 1 2 3 4 5

Wea

r V

olu

me

(mm

3)

CO

F

Particle Concentration (mM)

COF Wear

• Wear was measured using the

profilometry method.

• Each test was repeated three times.

• Friction decreases monotonically

versus particle concentration.

• Ag particles reduce wear as well.

Slide 18

Discussion on Enhancing Mechanism

Transfer Films

Rolling

Reducing contact area

• CuO/SOA and Ag Nanoparticles added to base oil as an additive in the absence of any other additives.

• Friction coefficient decrease as the nanoparticles concentration increases.

•Wear volume has a maximum value for CuO nanoparticle weight fraction of 1% and a minimum value for 2%wt.

•Wear volume decreases versus nanoparticle concentration for softer Ag nanoparticles.

• Surface analyses and wear measurement results are consistent with nanoparticles reducing the real area of contact.

• The mechanism of reduction in the real area of contact needs further investigation and study to be fully proven.

Slide 19

Analytical multi-scale contact model for nano-lubricants

Slide 20

Overview of the Model

Model nanoparticle in contact between rough surfaces

• Assumptions - Nanoparticle are suspended in a stable colloidal suspension.

- Particles are distributed over a range of size.

- Both particles and the surface are deformable

- Other assumptions discussed later

• Goals

- Model should include scale dependent properties of particles.

- Model should consider different weight fractions of nano-lubricants.

- Model should investigate the effect of particles on the contact mechanics.

Slide 21

Proposed Multi-Scale methodology

- Multi-scale rough surface contact model

Handles the rough surface and micron size features of the surface

Models the asperities in contact

Average contact pressure and surfaces area of contact is modeled

- Statistical particle model to handle the nanoparticle deformation and size dependent properties

Models the effect of particles inside the rough surface contact region

Particles engage in the contact and alter rough surface area contact and contact force

Stack two models to account for different scales

• Classic friction and abrasive wear models are used to link the contact

mechanics data to the experimental data.

Slide 22

Predicting Friction and Wear

Friction and Wear Model

Friction coefficient directly relates to the real Area of contact

- Possible mechanism verified: Area decreases as particles

engage inside the contact region and reduce the area of

contact.

- This also explains why softer particle can reduce friction and

wear simultaneously.

Experiments- CuO particles

F

AA sppsrs

0 1 2 3 4 5 6 7 8 90.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8x 10

-6

Wo

rn V

olu

me

/ S

lid

ing

dis

tan

ce [

m2]

0 1 2 3 4 5 6 7 8 90.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0.11

Volume PercentC

OF

Particle Induced Wear

Coefficient of Friction

Nanoparticle Contact Model- Si particles

Rq = 0.05 um

Slide 23

Nanoparticle in Dry Contact

Slide 24

• The proposed mechanism suggests that the nanoparticles ONLY, could effectively alter contact behavior.

• What is the role of nanoparticles compared to the lubricant’s in the boundary lubrication regime?

• The CuO/SOA nanoparticle can be dispersed in Chloroform. Chloroform is highly volatile with a boiling point of 61 oC.

• The solution is applied on a disk with a syringe and chloroform is evaporated under a heating lamp leaving a coating of nanoparticles on the disk.

Heating Lamp

Pour CuO- Chloroform

solution on the disk

Let the sample dry under

heating lamp

Disk coated with

CuO particles Original disk

Nanoparticle Dry Friction Tests

Slide 25

Dry Nanoparticle Test Results

0 200 400 600 800 1000 12000.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Time (s)

CO

F

Dry Friction Test

Nanoparticle Dry Friction Test

Nano-Lubricant Friction Test

Lubricated Friction Test

Dry Friction Test

Lubricated Friction Test

Nanoparticle Dry Friction Tests

Nano-Lubricant Test

Nanoparticle Dry Test

The results not only prove that dry nanoparticles can reduce friction but also suggests that they can be very effective.

This is a work in progress…

Slide 26

Conclusions

•Nano-materials and nano-technology are offering new solutions in a wide verity of topics and currently finding their way to consumer products.

•Nanoparticle additives are one example. Nanoparticles can infiltrate the small gaps between surfaces in contact and alter friction and wear.

•Experimental investigations explored the effect of CuO and Ag nanoparticles on friction and wear. Surface analysis and electron microscopy were used to shed light on particle/surface interaction. Results were consistent with nanoparticles reducing the real area of contact.

•A model for contact between rough surfaces separated by nano-lubricants is developed. The reduction of the real area of contact is further verified as an important mechanism governing the contact mechanics of nano-lubricants

•Dry nanoparticle friction tests revealed promising potential for nanoparticles to be used as dry coatings to reduce friction.

Slide 27

Previous Industrial Collaborations at the Auburn Tribology Lab:

• Development and Application of Multi-scale Friction

Prediction Methods to Dynamic Actuator Systems, Siemens

AG

• A Study of Various Material Combinations on the Bolted

Contacts of Busbars, John Deere

• Feasibility Test of Solvay Bearings for Baking Applications,

Solvay Advanced Polymers

• Theoretical and Experimental Investigation on Fretting

Corrosion and Thermal Degradation for a High Power

Connector, LS Cable

Slide 28

• Acknowledgment

Appreciation is expressed to Mr. Mohammad Sharif and Dr. German Mills of Auburn University chemistry department for providing the colloids; Dr. Michael Bozack and Dr. Mike Miller of Auburn University for providing support and assistance with the surface analyses.

This material is based upon work supported by the US Department of Energy under Award Number DE-SC0002470.

• Thanks