1. MITC 2013 2013. 11. 9 Boundary Lubrication as Surface Chemistry Photo by Obara Shigeyuki Mori Tribology and Surface Chemistry Iwate University １． Surface chemistry ２． Chemical Analyses of BL ３． Tribochemical Reaction ４． Conclusions Mt. Iwate Morioka

2. １． Surface chemistry ２． Chemical Analyses of BL ３． Tribochemical Reaction ４． Conclusions

3. Space station Tribology and Surface Chemistry shear Oil molecule Ball Disk Complicated phenomena Lubricating contact Simplification Components Contact conditions Materials Atmosphere 1

4. 2 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

5. Prof. Gerhard Ertl Chemical Processes of Solid Surfaces PEEM N 2 + 3H 2 → 2NH 3 Haber-Bosch method(1913) Fe 2007 Nobel prize Chemical composition CO O2O2 0 s 10 s 20 s 30 s Time CO + 1/2 O 2 → CO 2 Pt 2D 100 μm 3

6. １． Surface chemistry ２． Chemical Analyses of BL ３． Tribochemical Reaction ４． Conclusions

7. Time FTIR AES XPS EPMA element bonding Size μ m nm Chemistry TOF-SIMS TEM-EELS mm composition AFM Rama n XANES Spatial resolution Chemical resolution Surface analytical tools S FeS 2 FeSO 4 FeSR RSSR S Sulfur compounds Mechanical properties Chemical structure Where ? What? When? 4

8. Ｘ線光電子分光装置 Principle of Time of Flight Secondary Ion Mass Spectroscopy TOF-SIMS Advantages of TOF-SIMS 1.High sensitivity less than monolayer 2.High mass resolution chemical characterization 3.High 2D resolution 1 μm Ion gun Sample Detector m = (2eU/L 2 ) t 2 m/e is estimated by time of flight of secondary ions 5

9. Chemical analysis of boundary films formed from PTFE in PEEK PTFE PEEK Boundary film Bearing composite Steel ring 6

10. PEEK + PTFE 0.5 to 6 wt% Contact pressure 2 to 12 MPa Sliding speed 2 m/s Lubricant oil 40 ℃ 7

11. 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 Mass spectrum 8

12. TOF-SIMS mass spectrum of material surface 300 1000 Mass number CF 2 = 50 PTFE = (CF 2 CF 2 ) n 9

13. Chemical images of CF + from PTFE on composite material after tribo-tests at different contact pressures Contact pressure 10

14. Effect of contact pressure on surface coverage of PTFE Seizure Seizure was occurred at 20% of the coverage of PTFE-tribofilm. PTFE Coverage ＝ constant× Contact pressure (MPa) PTFE Coverage (%) PTFE intensity Fe intensity 11

15. PTFE （ CF+) Steel （ Fe+) ③ 6→18→6MPa ② 18MPa ① 6MPa Removal and recovering of tribofilm Chemical images of PTFE and steel components on bearing material 12

16. Formation model of tribofilm from PTFE-PEEK composite Removal of tribofilm High contact pressure Recovery of tribofilm Low contact pressure Formation of tribofilm steel PEEK + PTFE Summary Contact Pressure Time 13

17. Observation of tribochemical degradation of nano-lubricant film on hard disks Magnetic layer DLC (3 nm) Lubricant oil (1 nm) Hard disk Head HOCH 2 CHCH 2 OCH 2 - CF 2 O (CF 2 CF 2 O) m -(CF 2 O) n CF 2 -CH 2 OCHCH 2 OH OH HO Perfluoropolyether (PFPE) oil detected by TOF-SIMS 14

18. Tribo-tester installed in TOF- SIMS Rotating assembly 15

19. Friction tester of a hard disk in the main chamber of TOF-SIMS 1.8 inch magnetic disk slider load ： 0.2 ～ 0.8 mN velocity ： 8 rpm (0.01m/s) Conditions Analyzing position coating ： Al 2 O 3 ， TiN ， DLC ， c-BN 0.5μ ｍ 50μ ｍ Si tip 10 mm Fomblin Z-dol 16

20. Mass (amu) 050100150200 Intensity ， 10 6 counts 0 0.5 1.0 2.0 1.5 2.5 C+C+ CF + CF 2 + CF 3 + CFO + C2F4+C2F4+ C2F5+C2F5+ Mass spectrum of hard disk What? and Where? 20 µm Chemical image of friction track Friction track Original surface CF + Al 2 O 3 17

21. Subtracted mass spectrum of TOF-SIMS 050100150200 CF 2 + CF 3 + CFO + C2F4+C2F4+ C2F5+C2F5+ C+C+ CF + 27 0 20000 40000 -20000 -40000 Component in friction track In original surface Intensity ， counts Mass number (amu) Al 2 O 3 slider ， 0.8mN ， friction repeated 100 Chemical image of friction track ? 18

22. Al species ⇒ where ？ 102.6102.8103.0103.2103.4 0 50 100 150 200 250 mass AlF 4 - (c) track （ negative ion) Al + C2H3+C2H3+ 26.626. 8 27.027.227.4 0 200 400 600 26.626.827. 0 27.227.4 0 200 400 60 0 800 C2H3+C2H3+ （ a ） track （ b ） original surface Ion intensity, cps Chemical wear Al 2 O 3 + (CF 2 O) AlF 3 + CO 2 Material transfer of Al on disk surface Sapphire(Al 2 O 3 ) Disk 20 µ m Al + sapphire(Al 2 O 3 ) Disk TOF-SIMS analysis 19

23. (a) CF + chemical image CF + 020406080100120 Position ， μ ｍ 0 5 10 15 20 CF ＋ intensity ， Counts (b) Profile of ion intensity lubricant loss 20

24. 0 40 60 Al 2 O 3 DLC ｃ‐ BN TiN Slider materials Lubricant loss ， Counts×μm Effect of slider material on lubricant loss lubricant ： FOMBLIN ZDOL load ： 0.8 mN, speed ： 8 rpm, friction repeated ： 400 Fragment ion ： C 2 F 4 + Lewis acid 21

25. Long life of head-disk interface(HDI) 3D analysis of chemical structure at friction truck lubricant(1 nm) DLC Al 2 O 3 ・ TiC hard Chemically stable DLC TOF-SIMS analysis Long lige To develop a new tribo-system for HDI A better combination of lubricant and material 22

26. Organic additives Organic contaminants C, H, O 2 H(D), 13 C, 18 O Stable isotope as a tracer Tracer method using stable isotopes Analysis with TOF-SIMS 23

27. Lubrication of nitrides with ethyl alcohol Y. Enomoto, S. Mori, et al.,(2010) Surface product analyzed by TOF-SIMS Wear track Outside CrN CD 3 CD 2 OH TiN or CrN? CH 3 CH 2 OH TiN CrN Friction coefficient Time, s 24

28. １． Surface chemistry ２． Chemical Analyses of BL ３． Tribochemical Reaction ４． Conclusions

29. ・ ・ ・・ ・ Causes of tribochemical reaction Ball Space station Tribology and Surface Chemistry Disk Base oil additive Reaction Conditions Surface Activities High temp. + high pressure nascent surface defect radical site ・・・・・・ Mechanical Energy Boundary films are formed through tribochemical reactions. 25

30. Metal oxide Organic contaminant Nascent surface adsorption desorption Monitoring the chemical process on nascent surface Surface defects Monitor with Q-mass 26

31. Sliding speed2, 3, 4, 5, 6 cm/s Load2, 4, 8, 12, 16 N Temp.R.T. Vacuumless 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 ball load Ion gauge BallDisk Material52100 Diameter6.25mm20mm Table 2 Test piece Friction force Variable leak valve 27

32. Time, s m/e = 84 m/e = 78 Intensity, 10 -9 A m/e = 82 20 40 60 80 100 0 10 8 6 4 0.6 0.4 0.2 12 Au stop start Gold becomes to be active chemically by scratching Catalytic dehydrogenation and hydrogenation of olefin by nascent surface of Au + H 2 Au adsorption desorption 28

33. Metal oxide Organic contaminant Nascent surface adsorption desorption Monitoring the chemical process on nascent surface Surface defects Monitor with Q-mass (RO) 3 P=O Polar compd. RSSR Non-polar compd. Additives are effective under severe condition Mild condition EP additives 29

34. Load Metal oxide ball friction Organic contaminant Steel disk Active sites on nascent surface Catalytic effect Hydrocarbon oilH 2, CH 4 ・・・ Frictional heat Tribochemical decomposition of hydrocarbon oil 30

35. Gas evolution during lubrication (MAC, 2cm/s, 8N, 4km) R d =C 2 (P 2 -P)/kT=C 2 ΔP/kT RdC2kTRdC2kT Formation rate (molec./s) Conductance (m 3 /s) Boltzmann’s constant(1.38×10 -23 (J/K)) Temperature 度 (K) sliding Rate of gas formation MAC: multi-alkylated cyclohexane Decomposition of hydrocarbon oil 31

36. 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 Al 2 O 3 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( 2 H), 13 C and 18 O can be used as a tracer to detect boundary film without the effect of organic contamination. Boundary lubrication from the viewpoint of surface chemistry

37. 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.

38. Thank you for your attention Photo by Obara