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Research Papers: Lubricants

Tribological Behavior of Carbon Nanotubes as an Additive on Lithium Grease

[+] Author and Article Information
Alaa Mohamed

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

M. Zaki

Production Engineering and
Printing Technology Department,
Akhbar El Yom Academy,
Giza 12613, Egypt

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received June 29, 2013; final manuscript received June 6, 2014; published online August 27, 2014. Assoc. Editor: Zhong Min Jin.

J. Tribol 137(1), 011801 (Aug 27, 2014) (5 pages) Paper No: TRIB-13-1131; doi: 10.1115/1.4028225 History: Received June 29, 2013; Revised June 06, 2014

Carbon nanotubes (CNTs) with 10 nm average diameter and 5 μm in length were synthesized by electric arc discharge. The morphology and structure of CNTs were characterized by high resolution transmission electron microscopy (HRTEM) and X-ray powder diffraction. The tribological properties of CNTs as an additive on lithium grease were evaluated with a four ball tester. The results show that the grease with CNTs exhibit good performance in antiwear (AW) and decrease the wear scare diameter (WSD) about 63%, decrease friction reduction about 81.5%, and increase the extreme pressure (EP) properties and load carrying capacity about 52% with only 1% wt. of CNTs added to lithium grease. The action mechanism was estimated through analysis of the worn surface with a scanning electron microscope (SEM) and energy dispersive X-ray (EDX). The results indicate that a boundary film mainly composed of CNTs, Cr, iron oxide, and other organic compounds was formed on the worn surface during the friction process.

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References

Figures

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Fig. 1

XRD pattern of CNTs

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Fig. 2

HRTEM images of (a) CNTs (b) CNTs dispersed in lithium hydroxystearate (soap) fiber after removing the oil

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Fig. 3

Friction coefficient and WSD as a function of CNTs concentration (four ball, 1200 rpm, 300 N, and 30 min)

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Fig. 4

Friction coefficient as a function of applied load with the lubrication of lithium grease alone and that containing 1 wt.% CNTs (four ball, 1200 rpm, and 30 min)

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Fig. 5

WSD as a function of applied load with the lubrication of lithium grease alone and that containing 1 wt.% CNTs (four ball, 1200 rpm, and 30 min)

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Fig. 6

SEM morphologies of wear scar of steel balls lubricated by (a) lithium grease and (b) 1% CNTs at 300 N for 30 min

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Fig. 7

EDX of the worn scar of steel balls lubricated with base grease at 300 N for 30 min

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Fig. 8

EDX of the worn scar of steel balls lubricated with 1% CNTs at 300 N for 30 min

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