Synergistic lubricating effect of graphene/ionic liquid composite material used as an additive
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Synergistic lubricating effect of graphene/ionic liquid composite material used as an additive 1
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Lincong LIU ，Ming ZHOU , Youtang MO , Pengpeng BAI , Qilin WEI , Long JIN , Shengli YOU , Mingyue 1 1 1 4 2 WANG , Liangchuan LI , Xin CHEN , Xiao LI , Yu TIAN 1
School of Mechanical and Transportation Engineering, Guangxi University of Science and Technology, Liuzhou 545006, China State Key laboratory of Tribology, Tsinghua University, Beijing 100084, China 3 Department of Electromechain and Automotive Engineering, Liuzhou City Vocational College, Liuzhou 535006, China 4 Chengdu Carbon Co., Ltd., Chengdu 610100, China 2
Received: 20 May 2020 / Revised: 28 July 2020 / Accepted: 10 August 2020
© The author(s) 2020. Abstract: We prepared a graphene/ionic liquid (G/IL) composite material by the hybridization of G and an IL for use as a lubricating oil additive. The friction coefficient and wear volume of a base oil containing 0.04 wt% of the G/IL composite was reduced by 45% and 90%, respectively. Furthermore, the base oil containing the G/IL composite exhibited better lubricating properties than the base oil containing G, IL, or a mixture of IL and G at the same mass fraction. A synergistic lubrication mechanism was also revealed. The G/IL composite was adsorbed and deposited on the wear surface, forming a more ordered protective film and a unique tribochemical reaction film during rubbing. Therefore, the G/IL composite exhibited the synergistic lubricating effects of G and IL, which significantly improved the lubricating performance of the base oil. This study also suggested a way to limit the out-of-plane puckering of G at the macroscale. Keywords: grapheme (G); ionic liquid (IL); synergistic lubrication; protective films; out-of-plane puckering mechanism
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Introduction
Excessive wear directly degrades the stability, safety, and reliability of mechanical equipment [1]. The use of lubricants is an effective method of controlling friction and wear in mechanical equipment. Various additives (e.g., zinc dialkyldithiophosphate and metallo-organic compounds) are used to improve the lubricating performance of lubricants to meet the stricter requirements of modern industry. However, these additives contain toxic substances such as sulfur and phosphorus, which can seriously affect the environment. Green additives such as molybdenum disulfide (MoS2) and nanocarbon materials are increasingly being developed [2−5]. Graphene (G) is a type of 2D material with a *Corresponding author: Ming ZHOU, E-mail: [email protected]
hexagonal honeycomb 2D grid structure; it consists of single-layer carbon atoms exhibiting sp2 hybridization. Monolayer G is currently the thinnest nanomaterial [6]. Owing to its excellent electrical and optical properties, atomic thickness, good mechanical properties, and layered structure with low shear strength, G can be used in a wide range of applications, such as solar cells, supercapacitors, catalysts, sensors, and lubricants [7−10]. For
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