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MITC 2013 2013. 11. 9

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

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MITC 2013 2013. 11. 9

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  1. MITC 20132013. 11. 9 Mt. Iwate Morioka Boundary Lubrication as Surface Chemistry １．Surface chemistry ２．Chemical Analyses of BL ３．Tribochemical Reaction ４．Conclusions Iwate University Shigeyuki Mori Photo by Obara Tribology and Surface Chemistry

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

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

  4. Friction of clean metals and influence of adsorbed gases F. P. Bowden and T. P. Hughes, Proc. Roy. Soc., A172 (1939) 263. Glass chamber Hg diffusion pump metal wire metal slider There is no simple methodof determining the nature or the amount of any impurity which may remain on a metal surface. Study on boundary lubrication under vacuum

  5. Chemical Processes of Solid Surfaces 0 s 10 s 20 s 30 s Time 2007 Nobel prize 100 μm 2D Pt CO + 1/2O2→ CO2 CO Chemical composition Prof. Gerhard Ertl O2 Fe N2 + 3H2→　2NH3 Haber-Bosch method(1913) PEEM

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

  7. Chemistry TOF-SIMS S bonding TEM-EELS FTIR Raman Chemical resolution XPS XANES composition S FeS2 FeSO4 FeSR RSSR AES element EPMA AFM Mechanical properties Size mm Spatial resolution nm μ m Time Surface analytical tools Where ? What? When? Sulfur compounds Chemical structure

  8. Ion gun Detector TOF-SIMS m/e is estimated by time of flight of secondary ions Sample m = (2eU/L2) t2 • Advantages of TOF-SIMS • High sensitivity less than monolayer • High mass resolution chemical characterization • High 2D resolution 1 μm Ｘ線光電子分光装置 Principle of Time of Flight Secondary Ion Mass Spectroscopy

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

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

  11. what？ where？ Chemical analysis of tribo-films by TOF-SIMS Chemical image Distribution of tribo-film 2D 1μm Thickness less than 1 nm Mass spectrum Chem. structure Mass spectrum Chemical images of boundary layer from PTFE in PEEK-PTFE composite

  12. PTFE = (CF2CF2)n CF2 = 50 1000 300 Mass number TOF-SIMS mass spectrum of material surface

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

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

  15. Chemical images of PTFE and steel components on bearing material ①6MPa ②18MPa ③6→18→6MPa PTFE （CF+) Steel （Fe+) Removal and recovering of tribofilm

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

  17. Observation of tribochemical degradation of nano-lubricant film on hard disks Lubricant oil (1 nm) Hard disk DLC (3 nm) Magnetic layer detected by TOF-SIMS Head HOCH2CHCH2OCH2-CF2O(CF2CF2O)m-(CF2O)nCF2-CH2OCHCH2OH OH HO Perfluoropolyether (PFPE) oil

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

  19. Analyzing position coating：Al2O3 ，TiN，DLC，c-BN 0.5μｍ 50μｍ Si tip 10 mm slider 1.8 inch magnetic disk Fomblin Z-dol Conditions load ： 0.2～0.8 mN velocity ： 8 rpm(0.01m/s) Friction tester of a hard disk in the main chamber of TOF-SIMS

  20. Mass spectrum of hard disk 2.5 C+ Intensity， 106counts CF+ 2.0 C2F5+ 1.5 CFO+ CF3+ C2F4+ CF2+ 1.0 0.5 Mass (amu) 0 Chemical image of friction track Friction track 20 µm Original surface 0 50 100 150 200 What? and Where? CF+ Al2O3

  21. 40000 20000 0 -20000 -40000 0 50 100 150 200 Chemical image of friction track ? C+ Component in friction track 27 Intensity， counts CF+ CF2+ CF3+ In original surface CFO+ C2F4+ C2F5+ Mass number (amu) Subtracted mass spectrum of TOF-SIMS Al2O3 slider，0.8mN，friction repeated100

  22. Al+ 250 600 20 µm 200 400 150 100 200 50 0 0 26.6 26.6 26.8 26.8 27.0 27.0 27.2 27.2 27.4 27.4 102.6 102.8 103.0 103.2 103.4 AlF4- 800 (c) track （negative ion) 600 400 200 mass 0 （a）　track C2H3+ Al+ TOF-SIMS analysis Ion intensity, cps （b）　original surface sapphire(Al2O3) Sapphire(Al2O3) C2H3+ Disk Disk Material transfer of Al on disk surface Al species　⇒　where？ Chemical wear Al2O3 + (CF2O) AlF3+ CO2

  23. CF+ (a)CF+ chemical image 20 15 10 5 0 20 40 60 80 100 120 0 (b) Profile of ion intensity CF＋intensity，Counts lubricant loss Position，μｍ

  24. 60 40 20 0 TiN DLC ｃ‐BN Fragment ion：　C2F4+ Lubricant loss， Counts×μm Lewis acid Al2O3 Slider materials Effect of slider material on lubricant loss load ： 0.8 mN, speed ： 8 rpm, friction repeated ： 400 lubricant ： FOMBLINZDOL

  25. Long life of head-disk interface(HDI) Al2O3・TiC DLC hard Chemically stable lubricant(1 nm) DLC Long lige TOF-SIMS analysis 3Danalysis of chemical structure at friction truck To develop a new tribo-system for HDI A better combination of lubricant and material

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

  27. Lubrication of nitrides with ethyl alcohol CH3CH2OH CD3CD2OH TiN or CrN? TiN CrN Friction coefficient CrN Time, s Wear track Outside Surface product analyzed by TOF-SIMS Y. Enomoto, S. Mori, et al.,(2010)

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

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

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

  31. Ion gauge Variable leak valve Friction force To TM pump ball load disk Lub. oil Q-mass Magnetic rotating assembly Fig.6 Experimental apparatus with Q-mass Table 1 Conditions Table 2 Test piece

  32. + H2 Au Au stop start 12 10 adsorption desorption m/e = 82 8 6 Intensity,10-9 A m/e = 78 4 0.6 m/e = 84 0.4 0.2 40 0 20 80 60 100 Time, s Gold becomes to be active chemically by scratching Catalytic dehydrogenation and hydrogenation of olefin by nascent surface of Au

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

  34. H2, CH4・・・ Hydrocarbon oil Load Active sites on nascent surface Organic contaminant Catalytic effect ball Metal oxide Steel disk Frictional heat friction Tribochemical decomposition of hydrocarbon oil

  35. Rate of gas formation Decomposition of hydrocarbon oil Rd=C2(P2-P)/kT=C2ΔP/kT sliding Gas evolution during lubrication (MAC, 2cm/s, 8N, 4km) MAC: multi-alkylated cyclohexane

  36. Conclusions Boundary lubrication from the viewpoint of surface chemistry • 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 Al2O3and 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.

  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

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