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Research Papers: Lubricants

Novel Tribological Behavior of Hybrid MWCNTs/MLNGPs as an Additive on Lithium Grease

[+] Author and Article Information
M. E. Ashour, A. B. Elshalakny

Production Engineering and
Printing Technology Department,
Akhbar El Yom Academy,
Giza 12655, Egypt;
Mechanical Design and
Production Engineering Department,
Cairo University,
Giza 12655, Egypt

T. A. Osman, A. Khattab

Mechanical Design and
Production Engineering Department,
Cairo University,
Giza 12613, Egypt

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received February 6, 2016; final manuscript received November 22, 2016; published online April 4, 2017. Assoc. Editor: Ning Ren.

J. Tribol 139(4), 041801 (Apr 04, 2017) (7 pages) Paper No: TRIB-16-1050; doi: 10.1115/1.4035345 History: Received February 06, 2016; Revised November 22, 2017

The goal of this paper is to investigate tribological characteristics of nanographene platelets and hybridized nanocomposite of multiwalled carbon nanotubes (MWCNTs)/multilayer nanographene platelets (MLNGPs)/lithium based-grease. Characterization is done through high resolution transmission electron microscopy (TEM) and X-ray diffraction. While grease properties were tested using Falex four-ball testing machine. Scanning electron microscopy (SEM) and energy dispersive X-ray diffraction (EDX) were utilized to characterize the lubrication mechanism and the worn surface. The results showed that 1% of MLNGPs is the optimum concentration. Wear scar diameter (WSD) was reduced by 66%, friction coefficient was reduced by 91%, while maximum nonseizer load was increased by 90 kg over ordinary lithium grease. Hybrid MWCNTs\MLNGPs were studied, and the optimum ratio of MLNGPs to MWCNTs was found to be 4:1.

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References

Figures

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Fig. 1

HRTEM images of the MWCNTs

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Fig. 2

HRTEM images of the MLNGPs

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Fig. 3

Electron diffraction of MLNGPs

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Fig. 4

X-ray diffraction of MWCNTs

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Fig. 5

X-ray diffraction of MLNGPs

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Fig. 6

TEM images of the dispersed MLNGPs in grease with different concentrations (a) 0.5%, (b) 1%, (c) 1.5%, and (d) 2 wt.%

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Fig. 7

Wear scar diameter versus load at different MLNGPs concentration 1200 rpm, 60 mins running time

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Fig. 8

Coefficient of friction versus load at different MLNGPs concentration 1200 rpm, 60 mins running time

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Fig. 9

TEM images of the hybrid MWCNTs\MLNGPs grease formed at different concentrations: (a) 100% MLNGPs, (b) 80% MLNGPs-20% MWCNTs, (c) 60% MLNGPs-40% MWCNTs, (d) 40% MLNGPs-60% MWCNTs, (e) 20% MLNGPs-80% MWCNTs, and (f) 50% MLNGPs-50% MWCNTs

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Fig. 10

Wear scar diameter versus load at different hybrid MWCNTs/MLNGPs concentrations 1200 rpm, 60 mins running time

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Fig. 11

Coefficient of friction versus load at different hybrid MWCNTs/MLNGPs concentrations 1200 rpm, 60 mins running time

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Fig. 12

SEM images of the worn surfaces of the balls lubricated by (a) lithium grease only, (b) sample 1: MLNGPs, and (c) sample 2: hybrid MWCNTs/MLNGPs

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Fig. 13

EDX of the worn surfaces of the balls: (a) lithium grease only, (b) MLNGPs, and (c) hybrid MWCNTs/MLNGPs

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Fig. 14

SEM images of the worn surfaces after the friction process

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Fig. 15

WSD (mm) versus load (kg) for MWCNT, MLNGP, and MLNGP/MWCNT

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