MITC 2013 2013. 11. 9
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MITC 2013 2013. 11. 9
Boundary Lubrication as Surface Chemistry
Photo by Obara
Shigeyuki Mori
Tribology and Surface Chemistry
Iwate University
1. Surface chemistry2. Chemical Analyses of BL3. Tribochemical Reaction4. Conclusions
Mt. IwateMorioka
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1. Surface chemistry2. Chemical Analyses of BL3. Tribochemical Reaction4. Conclusions
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Space station
Tribology and Surface Chemistry
shear
Oil moleculeBall
Disk
Complicated phenomena
Lubricating contact
Simplification
Components
Contact conditions Materials
Atmosphere
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M
S
C R
F
I
YO
X
Q
M
S
C R
F
I
YO
X
Q
Friction of clean metals and influence of adsorbed gases
F. P. Bowden and T. P. Hughes, Proc. Roy. Soc., A172 (1939) 263.
Hg diffusion pump
There is no simple method of determining the nature or the amount of any impurity which may remain on a metal surface.
Glass chamber
metal slider metal wire
Study on boundary lubrication under vacuum
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Prof. Gerhard Ertl
Chemical Processes of Solid Surfaces
PEEM
N2 + 3H2 → 2NH3
Haber-Bosch method(1913)
Fe
2007 Nobel prize
Chemical composition
CO
O2
0 s 10 s 20 s 30 s Time
CO + 1/2O2 → CO2
Pt
2D100 μm
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1. Surface chemistry2. Chemical Analyses of BL3. Tribochemical Reaction4. Conclusions
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Time
FTIR
AES
XPS
EPMAelement
bonding
Sizeμm nm
ChemistryTOF-SIMS
TEM-EELS
mm
composition
AFM
Raman
XANES
Spatial resolution
Ch
emic
al r
eso
luti
on
Surface analytical tools
S
FeS2
FeSO4
FeSR
RSSR
S
Sulfur compounds
Mechanical properties
Chemical structure
Where ? What? When?
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Principle of Time of Flight Secondary Ion Mass Spectroscopy
TOF-SIMS
Advantages of TOF-SIMS1.High sensitivity less than monolayer2.High mass resolution chemical characterization3.High 2D resolution 1 μm
Ion gun
Sample
Detector
m = (2eU/L2) t2
m/e is estimated by time of flight of secondary ions
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Chemical analysis of boundary films formed from PTFE in PEEK
PTFE
PEEK
Boundary film
Bearing composite
Steel ring
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PEEK + PTFE0.5 to 6 wt%
Contact pressure 2 to 12 MPaSliding speed 2 m/sLubricant oil 40 ℃
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Mass spectrum
Chem. structure
Chemical image
Distribution of tribo-film
2D 1μm
Thickness less than 1 nm
Chemical analysis of tribo-films by TOF-SIMS
what ?
where ?
Chemical images of boundary layer from PTFE in PEEK-PTFE composite
Massspectrum
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TOF-SIMS mass spectrum of material surface
300 1000Mass number
CF2 = 50
PTFE = (CF2CF2)n
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Chemical images of CF+ from PTFE on composite material after tribo-tests at different contact pressures
Contact pressure
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Effect of contact pressure on surface coverage of PTFE
0
20
40
60
80
100
120
0 5 10 15 20 25 30
MPa面圧 ( )
P
TF
E被
覆率
(%)
Seizure
Seizure was occurred at 20% of the coverage of PTFE-tribofilm.
PTFE Coverage = constant×
Contact pressure (MPa)
PT
FE
Cov
erag
e (%
)
PTFE intensity
Fe intensity
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PTFE
( CF+)
Steel
( Fe+)
③6→18→6MPa②18MPa①6MPa
Removal and recovering of tribofilm
Chemical images of PTFE and steel components on bearing material
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Formation model of tribofilm from PTFE-PEEK composite
Removal of tribofilm
High contact pressure
Recovery of tribofilm
Low contact pressureLow contact pressure
Formation of tribofilm
steel
PEEK + PTFE
Summary
Contact Pressure
Time
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Observation of tribochemical degradation of nano-lubricant film on hard disks
Magnetic layer
DLC (3 nm)
Lubricant oil (1 nm)Hard disk
Head
HOCH2CHCH2OCH2-CF2O(CF2CF2O)m-(CF2O)nCF2-CH2OCHCH2OH
OHHO
Perfluoropolyether (PFPE) oil
detected by TOF-SIMS
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Tribo-tester installed in TOF-SIMS
Rotating assembly
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Friction tester of a hard disk in the main chamber of TOF-SIMS
1.8 inch magnetic disk
slider
load : 0.2 ~ 0.8 mNvelocity : 8 rpm (0.01m/s)
Conditions
Analyzing position
coating : Al2O3 , TiN , DLC , c-BN
0.5μ m
50μ m
Si tip
10 mm
Fomblin Z-dol
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Mass (amu)
0 50 100 150 200
Inte
nsi
ty,
10
6
counts
0
0.5
1.0
2.0
1.5
2.5
C+
CF+
CF2+
CF3+CFO+
C2F4+
C2F5+
Mass spectrum of hard disk
What? and Where?
20 µm
Chemical image of friction track
Friction track
Original surface
CF+
Al2O3
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Subtracted mass spectrum of TOF-SIMS
0 50 100 150 200
CF2+ CF3
+
CFO+
C2F4+
C2F5+
C+
CF+
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0
20000
40000
-20000
-40000
Component in friction track
In original surfaceInte
nsity
, c
ount
s
Mass number (amu)
Al2O3 slider , 0.8mN , friction repeated 100
Chemical image of friction track
?
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Al species ⇒ where ?
102.6 102.8 103.0 103.2 103.40
50
100
150
200
250
mass
AlF4-
(c) track( negative ion)
Al+C2H3
+
26.6 26.8
27.0 27.2 27.40
200
400
600
26.6 26.8 27.0
27.2 27.40
200
400
600
800
C2H3+
( a ) track
( b ) original surface
Ion
inte
nsity
, cp
s
Chemical wearAl2O3 + (CF2O)
AlF3 + CO2
Material transfer of Al on disk surface
Sapphire(Al2O3)
Disk
20 µm
Al+
sapphire(Al2O3)
Disk
TOF-SIMS analysis
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(a) CF+ chemical image
CF+
0 20 40 60 80 100 120
Position , μ m
0
5
10
15
20
CF
+in
tensi
ty,
Counts
(b) Profile of ion intensity
lubricant loss
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0
20
40
60
Al2O3 DLC c‐ BNTiN
Slider materials
Lubr
ican
t lo
ss
,C
ount
s×μ
m
Effect of slider material on lubricant loss
lubricant : FOMBLIN ZDOL
load : 0.8 mN, speed : 8 rpm, friction repeated : 400
Fragment ion :C2F4
+
Lewis acid
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Long life of head-disk interface(HDI)
3D analysis of chemical structure at friction truck
lubricant(1 nm)DLC
Al2O3 ・TiChard
Chemically stableDLC
TOF-SIMS analysis
Long lige
To develop a new tribo-system for HDI
A better combination of lubricant and material
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Organic additives Organic contaminants
C, H, O
2H(D), 13C, 18O
Stable isotope as a tracer
Tracer method using stable isotopes
Analysis with TOF-SIMS
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Lubrication of nitrides with ethyl alcohol
Y. Enomoto, S. Mori, et al.,(2010)
Surface product analyzed by TOF-SIMS
Wear track Outside
CrN
CD3CD2OHTiN or CrN?
CH3CH2OH
TiN
CrNFric
tion
coef
ficie
nt
Time, s
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1. Surface chemistry2. Chemical Analyses of BL3. Tribochemical Reaction4. Conclusions
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・ ・ ・・ ・・ ・ ・・ ・
Causes of tribochemical reaction
Ball
Space station
Tribology and Surface Chemistry
DiskBase oil additive
Reaction Conditions Surface Activities
High temp. + high pressure nascent surfacedefectradical site・・・・・・
Mechanical Energy
Boundary films are formed through tribochemical reactions.
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Metal oxide
Organic contaminant
Nascent surface
adsorption desorption
Monitoring the chemical process on nascent surface
Surface defects
Monitor with Q-mass
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Sliding speed 2, 3, 4, 5, 6 cm/s
Load 2, 4, 8, 12, 16 N
Temp. R.T.
Vacuum less than 2×10-4 Pa
Table 1 Conditions
To TM pump
Q-mass
Fig.6 Experimental apparatus with Q-mass
Magnetic rotating assembly
Lub. oil disk
ballload
Ion gauge
Ball Disk
Material 52100
Diameter
6.25mm 20mm
Table 2 Test piece
Friction force
Variable leak valve
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Time, s
m/e = 84
m/e = 78
Inte
nsi
ty, 1
0-
9 A
m/e = 82
20 40 60 80 1000
10
8
6
4
0.6
0.40.2
12Austopstart
Gold becomes to be active chemically by scratching
Catalytic dehydrogenation and hydrogenation of olefin by nascent surface of Au
+ H2
Au
adsorption
desorption
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Metal oxide
Organic contaminant
Nascent surface
adsorption desorption
Monitoring the chemical process on nascent surface
Surface defects
Monitor with Q-mass
(RO)3P=OPolar compd.
RSSRNon-polar compd.
Additives are effective under
severe condition Mild condition
EP additives
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Load
Metal oxide
ball
friction
Organic contaminant
Steel disk
Active sites on nascent surface
Catalytic effect
Hydrocarbon oilH2, CH4
・・・
Frictional heat
Tribochemical decomposition of hydrocarbon oil
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Gas evolution during lubrication (MAC, 2cm/s, 8N, 4km)
Rd=C2(P2-P)/kT=C2ΔP/kT sliding
Rate of gas formation
MAC: multi-alkylated cyclohexane
Decomposition of hydrocarbon oil
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Conclusions
1. Chemical analyses of boundary layers TOF-SIMS is a powerful tool to analyze boundary films and
tribochemical reactions. TOF-SIMS analyses revealed that very thin layer of PTFE was
removed at higher contact pressure and was recovered under the sliding condition of low contact pressure.
It was found that thin layer of PFPE oil was decomposed catalytically by Al2O3 and TiN as a slider material, but the decomposition was deactivated by DLC and c-BN coating. Chemically inert coatings such as DLC make a longer life of HDI.
Stable isotopes such as D(2H), 13C and 18O can be used as a tracer to detect boundary film without the effect of organic contamination.
Boundary lubrication from the viewpoint of surface chemistry
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2. Nascent surfaces of metals as a active source of tribochemical reactions are characterized by our method.
Even gold becomes to be active chemically and benzene decompsed on nascent gold surface.
Sulfide is more active on nascent steel surface than phosphate.EP additives should be selected depending on lubricating conditions;Sulfides and phosphates are effective under severe and mild conditions, respectively. It was found that hydrocarbon oil was decomposed by the effect of nascent surface and temperature rise at mechanical contact. Phosphate is more effective to reduce the decomposition than sulfide.
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Thank you for your attention
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