In Situ Raman Observations of the Formation of MoDTC-Derived Tribofilms at Steel/Steel Contact Under Boundary Lubrication

Ōkubo, H.; Yonehara, Misa; Sasaki, Shinya

doi:10.1080/10402004.2018.1462421

Cited by 30 publications

(20 citation statements)

References 19 publications

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“…The characteristic Raman analyses of the tribofilm obtained at 100°C under standard conditions with MoDTC 1 are presented in Figure 5. The two MoS2 characteristic Raman shifts 1 and 1 at 373 cm -1 and 405 cm -1 , respectively, are detected, in agreement with Raman analyses of MoDTC tribofilms [10,14,25]. The presence of amorphous MoS3 compound [26] could explain the background shape near 2 1 and 1 .…”

Section: S2psupporting

confidence: 82%

“…Several solutions have been developed, in particular Transition Metal Dichalcogenides (TMDs), like MoS2, have been known as efficient solid lubricants for more than fifty years [2][3][4]. MoS2 is used in tribological contacts as coating but it can also be formed in situ through tribochemical reactions from molecular lubricant additives [5][6][7][8][9][10]. Among molecular lubricant additives effective under boundary lubrication for steel-steel contacts, the "all-in-one" types of molecules, that is the ones which provide the molybdenum and the sulfur atoms within a single molecule, are commonly used.…”

Section: Introductionmentioning

confidence: 99%

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Mo(VI) dithiocarbamate with no pre-existing Mo–S–Mo core as an active lubricant additive

Kharboutly

Veryasov

Gaval

et al. 2021

Tribology International

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MoDTC molecular additives reduce friction in boundary lubricated steel-steel contacts through formation of MoS2 sheets. The chemical pathway from MoDTC to MoS2 is investigated for optimizing MoS2 formation. Our experiments show that a MoDTC molecule containing sulfur only in its thiocarbamate ligands forms MoS2 sheets during friction, demonstrating that the presence of peripheral thiocarbamate ligands can be sufficient to provide the required sulfur source. This molecule is not only competitive with MoDTC containing sulfur in the core of the molecule but also more efficient at high contact pressures. Mechanistic investigations on the chemical transformation of MoDTC to MoS2 reveal that thermal activation alone is not sufficient thus suggesting that pressure and/or shear are necessary for MoS2 generation in this system.

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Section: S2psupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Mo(VI) dithiocarbamate with no pre-existing Mo–S–Mo core as an active lubricant additive

Kharboutly

Veryasov

Gaval

et al. 2021

Tribology International

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“…Note that the accumulation of MoS 2 does not affect the rate of friction reduction or the steady state friction coefficient. asperities, which then gets redistributed around the surface by mechanical processes) 14,17,25,26 . Some features are exaggerated for clarity.…”

Section: The Accumulation Of Mos 2 Outside Of Contact Tracksmentioning

confidence: 99%

Temperature dependence of molybdenum dialkyl dithiocarbamate (MoDTC) tribofilms via time-resolved Raman spectroscopy

Garcia

Ueda

Spikes

et al. 2021

Sci Rep

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Molybdenum dialkyl dithiocarbamate (MoDTC) is a friction reducing additive commonly used in lubricants. MoDTC works by forming a low-friction molybdenum disulphide (MoS2) film (tribofilm) on rubbed surfaces. MoDTC-induced MoS2 tribofilms have been studied extensively ex-situ; however, there is no consensus on the chemical mechanism of its formation process. By combining Raman spectroscopy with a tribometer, effects of temperature and shear stress on MoS2 tribofilm formation in steel-steel contacts were examined. Time-resolved Raman spectra of the tribofilm were acquired, together with the instantaneous friction coefficient. The tribofilm is constantly being formed and removed mechanically during rubbing. Increasing shear stress promotes MoS2 formation. The nature of the tribofilm is temperature-dependent, with high-temperature tribofilms giving a higher friction than lower temperature films. Below a critical temperature Tc, a small amount of MoS2 gives significant friction reduction. Above Tc, a patchy film with more MoS2, together with a substantial amount of amorphous carbon attributed to base oil degradation, forms. The composition of this tribofilm evolves during rubbing and a temporal correlation is found between carbon signal intensity and friction. Our results highlight the mechanochemical nature of tribofilm formation process and the role of oil degradation in the effectiveness of friction modifier MoDTC.

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“…Therefore, it is difficult for the UHV-based analytical techniques to evaluate the chemical characterization of the tribofilms without contamination and their timedependence characterization changes during the friction test. This is why in situ or in-contact analytical approaches are effective for studying tribofilms, as they can easily classify the tribofilm characterization and the time-dependence properties of the tribofilms without washing the samples and removing them from the test rigs [5,[21][22][23][24][25][26][27]. Spikes et al [5,[21][22][23] revealed the tribofilm formation process using a mini traction machinespace layer imaging method (MTM-SLIM), which is a useful tool for monitoring the film thickness of tribofilms on a worn surface.…”

Section: Introductionmentioning

confidence: 99%

“…The SLIM technique can evaluate the thickness of the boundary (tribofilms) and EHD films by using a silica spacer layer-coated glass disk through analyzing interference fringes of the contacts between the glass disk and the steel ball [21][22][23]. On the other hand, we have recently reported that a lab-built in situ Raman tribometer can monitor the time-dependence chemical composition change of the tribofilms on the worn surface without washing the samples and removing them from the test rigs [24][25][26][27]. Chemical characterization and film thickness are important factors for analyzing the tribofilm formation process, as both are strongly related [5].…”

Section: Introductionmentioning

confidence: 99%

<i>In Situ</i> Raman-SLIM Monitoring for the Formation Processes of MoDTC and ZDDP Tribofilms at Steel/Steel Contacts under Boundary Lubrication

2020

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In this study, the formation processes of molybdenum dithiocarbamate (MoDTC) and zinc diallyldithiophosphate (ZDDP) tribofilms were investigated using an in situ Raman-space layer imaging method (SLIM) tribometer under boundary lubrication. According to the results, the ratio of the PO x and P-O-P bonds in the tribofilms was almost the same as the film thickness behavior calculated from the SLIM images. Hence, the the time-dependence chemical composition change of the tribofilms of phosphate related bonds in the tribofilms is considered a factor in the growth of ZDDP tribofilms. Moreover, the presence of MoDTC in the ZDDP solution contributed to the formation of phosphate compounds with a relatively high ratio of P-O-P links, such as ultra-phosphate glasses. This mechanism is attributable to the friction-reduction effects of MoS 2 on the tribofilm, which can contribute to maintaining a suitable condition for the formation of relatively high P-O-P-link-ratio tribofilms.

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In Situ Raman Observations of the Formation of MoDTC-Derived Tribofilms at Steel/Steel Contact Under Boundary Lubrication

Cited by 30 publications

References 19 publications

Mo(VI) dithiocarbamate with no pre-existing Mo–S–Mo core as an active lubricant additive

Mo(VI) dithiocarbamate with no pre-existing Mo–S–Mo core as an active lubricant additive

Temperature dependence of molybdenum dialkyl dithiocarbamate (MoDTC) tribofilms via time-resolved Raman spectroscopy

<i>In Situ</i> Raman-SLIM Monitoring for the Formation Processes of MoDTC and ZDDP Tribofilms at Steel/Steel Contacts under Boundary Lubrication

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