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