Tribo-chemistry How to investigate mechanism of additives

November 10, 2011 Tribology Days Seminar on Automotive Tribology Tribo-chemistry How to investigate mechanism of additives Ichiro MINAMI Luleå Tekn...
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November 10, 2011

Tribology Days Seminar on Automotive Tribology

Tribo-chemistry How to investigate mechanism of additives

Ichiro MINAMI Luleå Tekniska Universitet, Sverige Iwate University, Japan

Outline D

D

D

D

Introduction D

Tribo-chemistry and lubricant chemistry

D

Targets of tribo-chemistry

Role of over-based calcium sulfonates D

Background – belt CVT lubricants

D

Dependence of Ca contents in boundary film on friction

Interaction of organic friction modifiers with rubbing surfaces D

Background – DLC coatings for engine elements

D

Stable isotopic tracers

Strategy of surface analysis for tribo-chemistry

Lubricant chemistry D

Definition Scientific study of substances that reduce any disadvantages caused by friction, thereby improve quality of machine operation.

D

Appearance of lubricant D

Liquids (oils)

D

Semi-liquids (greases)

D

Solids (as additives or as coatings)

Liquid lubricants: base oil(s) + additives (5-20 mass%)

Stabilizers or sustainers

Tribo-improvers

Rheoimprovers

Tribo-chemistry D

Definition Science and technology of substances at rubbing contact. Mechanochemistry is closely related, however tribo-chemistry regards mostly lubrication.

D

D

Objectives D

Investigating how substances behave at rubbing contact.

D

Developing task-specific lubricants

Major targets: Tribo-improving additives D

Friction modifiers

D

Anti-wear agents

D

Load carrying additives (Extreme pressure additives)

Belt CVT system

Low friction in bearings for better fuel economy

High friction between belt-pulley for efficient power transmission

Courtesy of Idemitsu Kosan Co., Ltd.

Challenging model Additive formulation

Tribo-material Tribological energy

Tribo-material

Over-based calcium sulfonates

D

Inorganic salts dispersed in hydrocarbon SO

oils by surfactants

SO3

3

SO

CaCO3

3

Mainly used as “detergents” to neutralize

SO

D

3

SO3

D

Exhibit certain AW/EP properties H.Hong,A.T.Riga,J.M.Cahoon,J.N.Vinci: Lubrication Engineering, 49(1), 19-24 (1993).

How do they reduce friction? Can we control friction?

SO

3

SO3

SO3

acid contaminants

Tribo-test: Rotating-cylinder & flat type 0.16

Base oil & others

Friction coefficient,-

0.14 0.12 0.10

Ca-Sul

0.08 0.06 0.04

C

C+I

C+Z

C+I+Z

I

Z

Z+I

B

0.02 0.00

0

200

C : Ca-sul, I : imide, Z:ZnDTP

400

600

Load, N

800

1000

1200

Chemical mapping: TOF-SIMS Sample

Fe+

Ca+

O-

S-

C

C+I

worn surface

worn surface

I

worn surface

C : Ca-sul, I : imide

worn surface higher lower

INTENSITY

Chemical mapping: TOF-SIMS Sample

Ca+

Fe+

O-

S-

C

Zn+

higher lower

P-

INTENSITY

C+Z worn surface

Z worn surface

C:Ca-sul, Z:ZnDTP

worn surface

worn surface

worn surface

worn surface

Qualitative depth profile: XPS Ca 348.3eV 347.2eV

Depth CaO

Ca(OH)2 5 nm

Quantitative depth profile: XPS 50

Concentration, wt%

45

Fe:out of wear track

40

Fe:worn surface

35 30 25

Ca:worn surface

20 15 10

Ca:out of wear track

5 0

0

10

20

30

Depth, nm

40

50

Quantitative depth profile: XPS

Concentration of Ca, wt%

35 30 25

Sample C (Ca-Snl) 20 15

Sample C+Z (Ca-Sul+ZnDTP)

10

Sample C+I (Ca-Sul+Imid)

5 0

0

10

20

30

Depth, nm

40

50

Process of boundary film formation Calcium alkylsulfonate Calcium carbonate

Heat (1) Adsorption

(2) Pyrolysis of the inorganic salt CaCO3 → CaO

Press

(3) Film formation

Boundary film model: results of additive interactions Over based Ca- Sulfonates (Precursor)

Over based Ca- Sulfonates (Precursor) +Imide or ZnDTP (Controller)

Depth

:CaO

:FexOy

The periodic table of elements Group

Period

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

1

H

He

2

Li

Be

B

C

N

O

F

Ne

3

Na

Mg

Al

Si

P

S

Cl

Ar

4

K

Ca

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Ga

Ge

As

Se

Br

Kr

5

Rb

Sr

Y

Zr

Nb

Mo

Tc

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te

I

Xe

6

Cs

Ba

La

Hf

Ta

W

Re

Os

Ir

Pt

Au

Hg

Tl

Pb

Bi

Po

At

Rn

7

Fr

Ra

Ac

Rf

Db

Sg

Bh

Hs

Mt

Ds

Rg

Cn

La

La

Ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Ac

Ac

Th

Pa

U

Np

Pu

Am

Cm

Bk

Cf

Es

Fm

Md

No

Lr

Trends of environmentally friendly engine oils Rheological

Chemical

Low viscosity base oils

Reduce heteroatom contents

Wear protection

Low wear materials

AW additives

On going projects

HCO-additives

Achievement by Nissan Motor Friction coefficient, -

O O

0.15

GMO

0.10

OH OH

Mechanism?

0.05 0.00 steel-steel

steel-DLC

5W-30GF-3

steel-DLC

steel-DLC

5W-30 + MoDTC

5W-30 + GMO

Material and lubricant Tribology Letters, Vol. 18(2), 245-251 (2005).

How to detect HC-compounds? H CH

H CH

H CH

CH3 CH H H CH2 H H H C H C H C H C H H C H C H C H C H H H H

H H C C H H C H

Boundary film

CH3 H H H H C H C H C H C H C H H C H C H C H C H C H H H H H

D (2H)

13C

Hydrocarbon moieties can be distinguished

Samples

O C

O

OH OH

c-GMO

O O

g-GMO

C

C

C

OH

where C means 13C

OH

Results of GMO in PAO Steel cylinder

0.15

O

C O

O

Similar 0.10 friction reduction by the isotope derivatives

O C OH

GMO

c-GMO

Additive

C

OH

0.00 Additive-free (PAO)

C

OH

0.05

OH

Friction coefficient, -

DLC flat

g-GMO

The fragmentation of GMO (positive)

O O

OH OH

m = 265 for GMO and g-GMO, m = 266 for c-GMO

m = 339 for GMO, m = 340 for c-GMO, m = 342 for g-GMO

Mass spectrum of un-rubbed surfaces (positive) T o t al C o u n t s (0 .1 8 am u bin )

Integral: 10906

11UNSAVED + Ions 173µm 1061768 cts

200 265

m/z 265

207

150

GMO 337

239

100 219

211

50

202

m/z 339

281

231

321

253

225

0 200

250

300

350

T o t al C o u n t s (0 .1 8 am u bin )

Integral: 25439

12UNSAVED + Ions 173µm 1195215 cts

500 340

400

m/z 266

300

c-GMO

m/z 340

266

2 0 0 202

207

219

239

279

231

215

313

226

100 0 200

250

322

300

350

T o t al C o u n t s (0 .1 8 am u bin )

Integral: 65323

14UNSAVED + Ions 173µm 3251920 cts

1000 265

m/z 265

m/z 342

800

342

g-GMO

600 4 0 0 202

207

337

221 215

239 227

372 253

200 0 200

250

300

350

388

Mass spectrum of rubbed surfaces (positive) T o t a l C o u n t s (0 .1 8 a m u b i n )

Integral: 11850

4UNSAVED + Ions 173µm 876417 cts

300 265

250

m/z 265

200

m/z 339

150

rubbed with GMO in PAO

339

239

1 0 0 202

211

279

207 219

50

225

243

0 200

335

253

250

300

350

T o t a l C o u n t s (0 .1 8 a m u b i n )

Integral: 22294

5UNSAVED + Ions 173µm 1033335 cts

GMO does exist on rubbed DLC surfaces

500

340

400

266

rubbed with c-GMO in PAO

m/z 340

m/z 266

300 200

239

202 207

215 219

279

226

0 200

250

380

336

252

100

300

350

T o t a l C o u n t s (0 .1 8 a m u b i n )

Integral: 133218

10UNSAVED + Ions 173µm 2244517 cts

1400 1200 1000

265

239

m/z 265

388

202

800

313 215

rubbed with g-GMO in PAO

m/z 342

370

219 227

252

342

279

600 400 200 0 200

250

300

350

Profile of surface analyses frequently found in tribology articles

Analytical area Method

Target

Results

Sensitivity

lattice

depth

Infrared spectroscopy (IR)

10 μm φ

1 μm

Mainly organic compounds

Functional group

depends on functional group

Electron probe micro analysis (EPMA,SEM-EDX)

1 μm φ

1 μm

Elements larger than Be

Elements

0.01 mass%

X-ray photoelectron spectroscopy (XPS,ESCA)

1 mm φ

5 nm

Elements larger than Li

chemical state of elements

0.1 atomic%

Auger electron spectroscopy (AES)

1 μm φ

1 nm

Elements larger than Li

Elements

0.1 atomic%

Secondary ion mass spectroscopy (SIMS)

1 μm φ

1 nm

All elements

partial structure

ppb

Principle of surface analysis

Input signal

Detect and analysis

Output signal

Target molecule

Outputs

1.2

Si (Elemental)

D

Spectrum Qualitative and quantitative analyses

Normalized intensity

1.0

0.8

0.6

Si (Oxide)

0.4 rubbed un-rubbed

0.2

94

96

98

100

102

104

106

108

110

112

114

0.0

Binding energy, eV

D

Chemical mapping

Wear track (0.6mm)

Distribution of target chemical species

Si

Analytical area: Example D

Size of rubbed surface (aluminum alloy) Width = 2.2 × 10-2 [mm] : calculated by Hertz’s equation 2

mm

Length = 12.7 [mm] Area of rubbed surface > 2.8 × 10-1 [mm2] =

2.8 × 105 [μm2]

D

Analytica area of EPMA and AES:

7.9 × 10-1 [μm2]

D

Size of molecule : =nm 1.3 2× 10-1 [nm2] = 1.3 × 10-7 [μm2]

D

Where should be spotlighted?

Lubrication mode for surface analysis

boundary film

Friction coefficient

boundary lubrication

hydrodynamic film

preferable surface anal. hydrodynamic lubrication

mixed lubrication

Parameter (V η/L)

Flow chart of surface analysis

Tribo-test repeatability yes

Literature database

morphology hypothesis analysis

unreasonable

consideration reasonable

Results

no

Strategy for successful surface analysis in tribo-chemistry D

D

D

Chemical resolution and sensitivity D

Chemical species of interest

D

Appropriate method for the chemical species

Spatial resolution and sensitivity D

Analytical size (lateral and deep)

D

Analytical point and/or area

Sample quality D

Surface roughness

D

Quantity of the target

D

Contamination

Review on stable isotopic tracers for tribo-chemistry

Ichiro Minami: “A Novel Tool for Mechanistic Investigation of Boundary Lubrication: Stable Isotopic Tracers” in New Tribological Ways, p425450, Edited by Taher Ghrib, InTech Publisher (April 2011), ISBN 978-953307-206-7. This is an open access book. Please visit at http://www.intechopen.com/articles/show/title/a-novel-tool-for-mechanistic-investigation-of-boundarylubrication-stable-isotopic-tracers

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