Study of graphene nanolubricant using thermogravimetric analysis
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Rashmi Walvekar Energy Research Division, Taylor’s University, Subang Jaya, Selangor 47500, Malaysia
Thummalapalli Chandra Sekhara Manikyam Gupta Apar Industries Limited, Chembur, Mumbai 400071, India
Andrew Chan Environmental Research Division, Faculty of Engineering, University of Nottingham Malaysia Campus, Semenyih, Selangor 43500, Malaysia (Received 25 August 2015; accepted 30 October 2015)
Thermal degradation of graphene based mineral oil lubricants was studied using thermogravimetric analysis (TGA). As-synthesized graphene sheets of 8, 12, and 60 nm thick and engine oil formulations 20W50 SN/CF and 20W50 SJ/CF were used for synthesizing various test samples. UV-Vis spectrophotometry, zeta potential, field emission scanning electron microscopy, and energy-dispersive x-ray spectroscopy were used to characterize the graphene sheets and the nanolubricants. TGA revealed that the onset temperature of oxidation for the SN/CF oil could be delayed by 13–17 °C in the presence of graphene. Moreover the rate of oxidation when the weight loss of oil in the presence of graphene reaches 40–20% could be delayed by more than 30 °C. Resistance to oil degradation depends strongly on the graphene nanoparticle size and concentration. TGA kinetics studies show that the base oils have higher activation energy (Ea) and the addition of graphene significantly reduces Ea.
I. INTRODUCTION
Improving lubricant properties has been an indispensable area of research for many decades. Several additives were introduced to enhance thermal and lubricating properties of the lubricants nevertheless the efficiency is still compromised. Recently, it was shown that the addition of nanometer sized (1–100 nm) particles to liquids including base oils could significantly enhance various properties of base fluids. Such nanoparticle suspensions are widely known as nanofluids or nanolubricants.1 Carbon nanotubes based nanofluids were found superior to most of the metallic and oxide nanofluids1,2 in terms of enhanced thermal conductivity. Nonetheless, the discovery of graphene nanoflakes3 made it possible to synthesize nanofluids with even better efficiency. Graphene nanoflakes are made of one layer of atomic carbon with theoretical specific surface area up to 2600 m2/g.4 In addition, it has excellent in-plane thermal
Contributing Editor: Mohd Fadzli Bin Abdollah a) Address all correspondence to this author. e-mail: [email protected] A previous error in this article has been corrected, see 10.1557/jmr.2016.236. DOI: 10.1557/jmr.2015.359
conductivity which can be as high as 5200 W/mK.5 Moreover, 0.2 mg/L graphene (Graphene Laboratories Inc., Calverton, New York) added as an additive to the base oil will only cost approximately US$ 0.0005. This makes graphene one of the cheapest additives available in the market. As the bulk production techniques for graphene are getting efficient, the cost is expected to further decrease drastically. Furthermore, the nano size of graphene makes it possible to enter small contact regions and also pass through oil fil
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