Tribochemical Study of Hydrogenated Carbon Coatings With Different Hydrogen Content Levels in Ultra High Vacuum

Yun, Xianghe; Bogy, David B.; Bhatia, Charanjit S.

doi:10.1115/1.2833514

Cited by 20 publications

(5 citation statements)

References 15 publications

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“…Our final comment regards the influence of oxide functionalities present on CHx carbon surfaces on the chemical degradation of PFPE lubricants. Yun et al have reported that PFPE degradation on amorphous hydrogenated carbon surfaces is dependent on the amount of hydrogen incorporated into the carbon film . Since Wang et al have reported that the level of surface oxidation of CHx is inversely dependent on the hydrogen level present in the carbon film, one questions the role (if any) of the carbon active sites in determining the propensity of the PFPE to catalytically degrade.…”

Section: Discussionmentioning

confidence: 99%

“…While it is known that metal oxide surfaces can catalyze the degradation of PFPE lubricants, which severely limits their use in numerous applications, for example, lubrication in jet engines, the question as to the ability of an oxidized carbon surface to effect lubricant degradation has not been thoroughly investigated. If a significant interaction between the PFPE lubricant and the carbon surface were to develop, then a reduction in the overall chemical stability of the PFPE under disk-drive operating conditions might result. , …”

Section: Introductionmentioning

confidence: 99%

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Computer-Modeling Study of the Interactions of Zdol with Amorphous Carbon Surfaces

1999

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The formation of a tribologically reliable interface between the magnetic recording disk and the magnetic recording head in hard-disk drives is predicated upon the presence of a molecularly thin perfluoropolyether (PFPE) lubricant film. The molecular interactions that develop between the PFPE lubricant and the underlying amorphous carbon overcoat of the magnetic recording disk govern the adhesion, physical coverage, thermal stability, and mobility of the lubricant on the carbon surface and hence are of paramount importance in defining the tribological performance of the drive. In this work, information pertaining to the interfacial interactions between the hydroxyl-terminated PFPE lubricant Zdol and amorphous carbon surfaces is obtained via ab initio calculations. The small fluorinated ether molecules CF3OCF2CH2OH (ZD) and CF3OCF3 (PFDME) were used as computationally tractable models for the PFPE lubricants. A population analysis is performed on the ZD model lubricant and the various chemical functionalities known to exist on amorphous carbon surfaces. In the case of an amorphous, hydrogenated carbon surface, CHx, the adhesive interactions of the PFPE backbone with the nonpolar component of the carbon surface were modeled by the interaction of ZD with simple hydrocarbons. The attractive van der Waals interactions that result are comparatively weak and insufficient at room temperature to overcome the associated decrease in entropy. As a consequence, these interactions will not contribute significantly to the adhesion of PFPE's to the carbon surfaces under disk-drive operating conditions. The primary source of adhesion in the Zdol−CHx system stems from hydrogen bonding of the hydroxyl end groups of the Zdol lubricant with the carboxylic acid and ketone functionalities on the CHx surface. The computed binding energies of the ZD + ketone and ZD + carboxylic acid interactions are −11 and −15 kcal/mol, respectively. These interaction strengths are large enough to compensate for the entropy decrease and hence result in a net decrease in the free energy. In addition to these thermodynamically stable adhesive interactions, the computed binding energy of the cohesive hydrogen-bonding interactions between ZD molecules is significant. The formation of a highly associated, two-dimensional structure is therefore possible for molecularly thin Zdol films on carbon surfaces. Amorphous nitrogenated carbon, CNx, can also provide strong physisorption sites for Zdol. The interaction of ZD with imine and nitrile functionalities were studied. The interactions of the hydroxyl end group with imine centers is strongly attractive, leading to the formation of a hydrogen bond with a strength of −16 kcal/mol. Interactions with nitrile sites are somewhat less favorable with a computed binding energy of −10 kcal/mol. The nitrogen centers on CNx are negatively charged, and hence repulsive interactions with the negatively charged perfluoroalkyl ether backbone are expected. The modeling results are then used to interpret previous experimental resu...

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Computer-Modeling Study of the Interactions of Zdol with Amorphous Carbon Surfaces

1999

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“…This mechanism occurs during the run-in period observed for many DLC materials, when the friction is initially high, but is reduced as graphitization and transfer film formation generally occur over hundreds to thousands of cycles. Hydrogenated DLC films, however, perform well in ultrahigh vacuum and other inert environments (77,78), so long as some fraction of the self-contained supply of hydrogen distributed throughout the coating is present in the near-surface region (79,80). Performance of a:CH films often degrades in the presence of humidity or other vapors, owing to surface coverage with oxygen or hydroxyl ions, resulting in increased adhesive forces in the friction contact (73).…”

Section: Extrinsic Solid Lubricantsmentioning

confidence: 99%

Chameleon Coatings: Adaptive Surfaces to Reduce Friction and Wear in Extreme Environments

Muratore

Voevodin

2009

Annu. Rev. Mater. Res.

188

113

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Adaptive nanocomposite coating materials that automatically and reversibly adjust their surface composition and morphology via multiple mechanisms are a promising development for the reduction of friction and wear over broad ranges of ambient conditions encountered in aerospace applications, such as cycling of temperature and atmospheric composition. Materials selection for these composites is based on extensive study of interactions occurring between solid lubricants and their surroundings, especially with novel in situ surface characterization techniques used to identify adaptive behavior on size scales ranging from 10 −10 to 10 −4 m. Recent insights on operative solid-lubricant mechanisms and their dependency upon the ambient environment are reviewed as a basis for a discussion of the state of the art in solid-lubricant materials. 297 Click here for quick links to Annual Reviews content online, including: • Other articles in this volume • Top cited articles • Top downloaded articles • Our comprehensive search Further ANNUAL REVIEWS Tribology: the study of surfaces in relative motion, from the Greek word tribos, meaning rubbing Friction coefficient: the ratio of tangential force to applied normal force, or the ratio of shear strength to pressure if both forces are divided by contact area Abrasive wear: the plowing away of softer material by harder particles at contact interfaces Adhesive wear: asperities from both surfaces in contact adhere, and material from the softer surface is sheared away as the counterface moves Fatigue wear: the removal of material due to crack growth and propagation over repeated load cycles Wear rate: the rate of material loss from a surface due to sliding contact, often reported in units of volume lost per unit sliding distance per unit of applied normal force (e.g., mm 3 m −1 N −1) FUNDAMENTALS OF SOLID LUBRICATION IN DIVERSE ENVIRONMENTS A spray of liquid lubricant from a can available at the hardware store solves most familiar friction and wear problems on Earth under ordinary conditions of ambient pressure, humidity, and temperature. When any one of those operating parameters reaches the limits of advanced engineering materials, however, the availability of suitable lubricants is diminished significantly. Moreover, if operation throughout a broad range of any one of these environmental factors is desired, the number of choices becomes exactly zero; tribologists have found that no single surface can lubricate effectively outside a narrow span of ambient humidity or temperature (1-3). In fact, one of the primary technological barriers for the development of new jet engines for sustained highmach-number (>5) flights and other key aerospace advances is the ability to lubricate mechanical assemblies from ambient temperature to >1000 • C. Only recently have discoveries of self-adaptive mechanisms and subsequent developments in tribological coatings, made possible with modern instrumentation and pioneering efforts to observe phenomena at atomic through microscopic size scales at contact ...

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“…In the hard disk drive of a magnetic recording device, the head is newly coated by a diamond like carbon (DLC) film as to avoid the decomposition of the perfluoropolyether lubricating oil by the head material Al2O3-TiC, which possess strong catalytic action. However, even if the catalytic action is masked by the DLC film coating, the lubricant decomposition was not eliminated [18].…”

Section: Introductionmentioning

confidence: 99%

Characteristics and Pattern of Plasma Generated at Sliding Contact

Nakayama

Nevshupa

2003

Journal of Tribology

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To verify the tribo-microplasma concept proposed by Nakayama, who suggested that a microplasma is generated in the gap of a sliding contact due to electrical discharge of the ambient gas in the electric field caused by tribo-charging, we challenged to observe directly the tribo-microplasma and to measure spectral characteristics of the emitted photons. In experiments to observe plasma image (with a diamond hemispherical pin sliding on a sapphire disk) it was found that the plasma was generated in the several micrometer gap of the sliding contact. The plasma had a shape of an ellipse with a tail, surrounding the contact and spread to the rear of the sliding contact. The plasma image observed through the UV transmittable filter (UV image) had a horseshoe pattern, while the IR image had a shape of a ring on the ellipse. The strongest UV emission was observed in the center of the horseshoe pattern outside the sliding contact, while the IR photon image showed that the most intense emission occurred at the sliding contact. The electrical discharge origin of the photon triboemission was proved by comparing spectra of tribophotons with spectra of photons emitted from plasma by electrical discharge in parallel electrodes in various gases. The results showed that the spectra of photons emitted from the sliding contact and those of gas-discharge completely coincided for all gases tested, i.e., dry air, N2,O2,H2, He, CH4,C2H4 and C3H8, except peaks originated from the excited atoms of the sliding surfaces. It was concluded that microplasma is produced by electrical breakdown of ambient gas at sliding contact. These results corroborate the tribomicroplasma concept.

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Tribochemical Study of Hydrogenated Carbon Coatings With Different Hydrogen Content Levels in Ultra High Vacuum

Cited by 20 publications

References 15 publications

Computer-Modeling Study of the Interactions of Zdol with Amorphous Carbon Surfaces

Computer-Modeling Study of the Interactions of Zdol with Amorphous Carbon Surfaces

Chameleon Coatings: Adaptive Surfaces to Reduce Friction and Wear in Extreme Environments

Characteristics and Pattern of Plasma Generated at Sliding Contact

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