Multifunctional nanofluids with 2D nanosheets for thermal and tribological management J. Taha-Tijerina a,n,1 , L. Pen ˜ a-Paras b,1 , T.N. Narayanan a,1 , L. Garza b , C. Lapray b , J. Gonzalez b , E. Palacios b , D. Molina b , A. Garcı ´a b , D. Maldonado b , P.M. Ajayan a a Department of Mechanical Engineering and Materials Science, Rice University, Houston, TX 77005, USA b Universidad de Monterrey, Av. Morones Prieto 4500 Pte. San Pedro Garza Garcı ´a, N.L. 66238, Me´xico article info Article history: Received 16 October 2012 Received in revised form 29 November 2012 Accepted 10 December 2012 Keywords: Hexagonal boron nitride (h-BN) Graphene 2-D nanosheets Tribology Friction abstract Development of multifunctional nanofluids for applications such as thermal management and lubrication is very essential for the advancement of many energy efficient modern industries. Here, we demonstrate the tribological improvement of two dimensional (2D) atomic sheets, such as hexagonal boron nitride (h-BN) and graphene (G), reinforced mineral oils over bare mineral oil, which was proven earlier by its better thermal performance. Latter, thermal and tribological properties of dielectric and metal-cutting lubricants reinforced with h-BN and G were investigated with a detailed study on their viscosity variation with temperature and nanofiller concentration. Two different tribological tests were performed for coefficient of friction and wear studies, namely ITEePib Polish method, and ASTM D5183. Results from these methods are compared and they show in agreement with each other. Tribological tests showed that the addition of nanofillers, even in small filler fraction, resulted in to a significant decrease in the wear scar and friction coefficient along with a huge enhancement in thermal performance. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Energy management is becoming more crucial for meeting the rising needs of mankind [1]. Nowadays, with increasing pressure of globalized markets and companies’ profit race, a dramatic search for materials having high energy efficient performance is being intensified. The advent of nanomaterials motivated scientist to address this, and to design various energy efficient systems, where these ultra-fine materials can play a seminal role in the energy management with lower amount of materials. A revolution in the field of nanofluids (NFs) was happened with the advent of thermal management fluids, a concept intro- duced by Choi in 1990s [2]. NFs contain smaller nanoparticles (ultra-fine particles) stabilized in a carrier fluid, and are attracted the attention of researchers to use them for thermal and electrical management and also for tribology. Friction plays a key role in diverse processes such as drilling, cutting, working pair components and mechanisms, among others; becoming more relevant in today’s life. Wear is the major cause of material and energy loss in mechanical processes, as components are in constant friction. Lubricants can be used to minimize contact friction between components, resulting into considerable energy and tooling savings [3]. However, frictional heat generated, when two or more moving surfaces are in contact can degrade lubricants or oxidize them; thus, this heat generated should be dissipated rapidly. Recently, diverse nanoparticles were tested as reinforcements in common lubricants and metal-cutting fluids for their enhanced tribological properties [4–9]. Some of these studies show that the addition of nanoparticles to conventional lubricants can enhance the supporting force during loading and sliding movement, thus decreasing tribological issues such as friction and wear. Nano- particles could be deposited on the rubbing surface and improve the tribological properties of conventional lubricants and metal- cutting fluids, showing the contribution of friction and wear reduction by dispersed nanoparticles The addition of nanoparticles or nanoadditives to NFs has shown excellent results in tribological tests reducing wear and the frictional coefficient, also improving load carrying capacity [8–13]. Herna ´ ndez- Battez et al. [9] studied the friction behavior of NiCrBSi coatings lubricated by CuO nanoparticles suspended in poly-alphaolephin (PAO6). Block-on-ring tests showed a decrease of up to 100% in the friction coefficient with 2 wt% CuO. Similarly, Yu et al. [11] reported improved lubricating properties by adding 0.2 wt% Cu nanoparticles to lubricant oil; in their study Cu formed a soft film by friction- shearing and high pressure reducing the coefficient of friction up to 20%. Wu et al. [13] examined the tribological properties of nanofluids Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/wear Wear 0043-1648/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.wear.2012.12.010 n Corresponding author. Tel.: þ1 7133485904. E-mail addresses: jaime_taha@hotmail.com, jjt3@rice.edu (J. Taha-Tijerina). 1 Contributed equally to this work. Please cite this article as: J. Taha-Tijerina, et al., Multifunctional nanofluids with 2D nanosheets for thermal and tribological management, Wear (2013), http://dx.doi.org/10.1016/j.wear.2012.12.010i Wear ] (]]]]) ]]]–]]]