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Research Papers: Micro-Nano Tribology

Development of Nanocomposite Grease: Microstructure, Flow, and Tribological Studies

[+] Author and Article Information
Jayant Singh, Naresh Tandon

Industrial Tribology, Machine Dynamics and
Maintenance Engineering Centre (ITMMEC),
Indian Institute of Technology Delhi,
New Delhi 110016, India

Deepak Kumar

Industrial Tribology, Machine Dynamics and
Maintenance Engineering Centre (ITMMEC),
Indian Institute of Technology Delhi,
New Delhi 110016, India
e-mail: dkumar@itmmec.iitd.ernet.in

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received August 20, 2016; final manuscript received December 28, 2016; published online May 26, 2017. Assoc. Editor: Ning Ren.

J. Tribol 139(5), 052001 (May 26, 2017) (9 pages) Paper No: TRIB-16-1273; doi: 10.1115/1.4035775 History: Received August 20, 2016; Revised December 28, 2016

Greases are widely used for variety of applications at extreme pressures, temperatures, and speeds with obligation of high bearing and shaft life with low noise. The present study deals with the development of nanocomposite greases and records their flow and frictional characteristics. The commercial grease is modified, by dispersing nanoparticles, to get the nanocomposite greases. Reduced graphene oxide (rGO), calcium carbonate (CaCO3), and alpha-alumina (α-Al2O3) are used as nano-additives. The microstructure of newly developed greases is examined using high-resolution transmission electron microscopy (HRTEM), and the presence of different chemical functional groups is explored using Fourier transform infrared spectroscopy (FTIR). Further, the new greases are investigated for rheological, consistency, and tribological behavior using Visco Tester, penetrometer, and elastohydrodynamic (EHD) rig, respectively. The flow properties reveal the shear-thinning, yielding, and thixotropic nature of lubricating greases. The study shows that there is an optimality in concentration of different nano-additives above which grease's flow and tribological performance degrades. Up to 35%, 27%, and 10% reduction in coefficient of friction is recorded for optimum concentration of rGO nanosheets, CaCO3, and α-Al2O3 nanoparticles, respectively. The difference in the performance of nanocomposite greases can be attributed to the appearance of different friction mechanisms for different nano-additives.

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Figures

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Fig. 1

Process flow diagram showing methodology for the preparation of nanocomposite grease

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Fig. 2

Schematic representation of disk–ball arrangement in EHD rig

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Fig. 3

X-ray powder diffraction pattern of (a) nano-rGO sheets, (b) nano-CaCO3 particles, and (c) nano-α-Al2O3 particles

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Fig. 4

HRTEM image of (a) rGO nanosheets, (b) CaCO3 nanoparticles, and (c) α-Al2O3 nanoparticles

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Fig. 5

Size distribution of dispersed (a) nano-rGO sheets, (b) nano-CaCO3 particles, and (c) nano-α-Al2O3 particles in toluene

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Fig. 6

HRTEM images of (a) bare grease (BG), (b) processed bare grease (P-BG) as per the process flow diagram shown in Fig. 1, (c) BG + rGO nanosheets, (d) BG + CaCO3 nanoparticles, and (e) BG + α-Al2O3 nanoparticles. The images (c)–(e) represent nanoparticles' dispersion in lithium hydroxystearate (soap) fiber structure after removing the oil.

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Fig. 7

Penetration depth (1/10) mm of bare grease and different nanocomposite greases

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Fig. 8

IR spectra of (a) nanopowders, (b) bare grease (BG), processed bare grease (P-BG), and various formulated nanocomposite greases

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Fig. 9

Variation of dynamic viscosity with shearing time of bare and nanocomposite greases at a constant shear of 100 s−1

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Fig. 10

Shear decay curves with shearing time of bare and nanocomposite greases at a constant shear of 100 s−1

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Fig. 11

Shear stress versus shear rate relationship of bare and nanocomposite greases with Herschel–Bulkley curve fitted for optimum concentration of different nanoparticles in bare grease

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Fig. 12

Variation of dynamic viscosity with shear strain for bare and nanocomposite greases for optimum concentration of nanoparticles

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Fig. 13

Variation of coefficient of friction with rolling speed (1–1000 mm/s) at (a) SRR = 0% and (b) SRR = 50% at constant load of 30 N (pH = 0.9 GPa) at a temperature of 25 °C for bare and nanocomposite greases

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Fig. 14

Schematic representation for explaining the effect of optimum concentration of nano-additives in composite greases (a) at lower concentration and (b) at higher concentration

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