The Tribological Mechanism of Cerium Oxide Nanoparticles as Lubricant Additive of Poly-Alpha Olefin
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ORIGINAL PAPER
The Tribological Mechanism of Cerium Oxide Nanoparticles as Lubricant Additive of Poly‑Alpha Olefin Lili Wu1 · Xue Lei1 · Yujuan Zhang1 · Shengmao Zhang1 · Guangbin Yang1 · Pingyu Zhang1 Received: 2 April 2020 / Accepted: 8 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Oleylamine (hereinafter referred to as OM)-modified CeO2 nanoparticles were synthesized by a one-pot pyrolysis method. The tribological properties of the as-prepared CeO2 nanoparticles as the lubricant additive in poly-alpha olefin (PAO) were investigated with a four-ball machine, and their lubricating mechanism was discussed in relation to worn surface analyses by SEM, EDS, and XPS. Findings indicate that these nanoparticles exhibit good dispersibility as well as excellent anti-wear ability in PAO. This is because OM-modified C eO2 nanoparticles can catalyze the oxidation of metallic Fe to form ferrite oxide-containing tribo-film. Under the condition of ASTM D2266-2001, the same lowest WDS was obtained at the concentration of 0.2 wt% and 1.8 wt%. When the concentration of C eO2 is 0.2 wt%, a compact catalytic oxidation tribo-film is formed, which has more outstanding long-term anti-wear ability. When 1.8 wt% CeO2 is added, the tribo-film formed is the combination of catalytic oxidation film and ceria deposition film, which has more significant bearing capacity. Keywords CeO2 nanoparticles · Lubricating mechanism · Anti-wear · Catalyze oxidation
1 Introduction In recent years, the use of nanomaterials as lubricant additives has become an important research area due to their potential excellent anti-wear and friction-reducing in tribology [1–9]. Along with soaring of environmental concern for lubricating oil products and enforcement of more strict environmental protection laws, the demand for green lubricating oil additives rises [10]. Among a variety of nanoparticles as potential lubricant additives, metal oxide nanoparticles have high thermal and chemical stability and exclude the environmental pollution elements such as sulfur, phosphorus, and chlorine that appeared widely in traditional extreme pressure (EP) and anti-wear agents [11–15]. CeO2 nanoparticles as an additive of lubricating oil or grease has high load-carrying capability, friction reduction, and outstanding wear resistance and is expected to become a widely used green EP and anti-wear agent. * Yujuan Zhang [email protected] * Shengmao Zhang [email protected] 1
Engineering Research Center for Nanomterials, Henan University, Kaifeng 475004, China
It was reported that C eO2 nanoparticles, as an EP agent of lubricating oil, showed excellent friction-reducing performance at a very low concentration (0.01wt%), but did not improve the bearing capacity [16, 17]. It was attributed to the polishing effect of C eO2 nanoparticles on the surface of friction pairs. The more common phenomenon has been found that CeO2 nanoparticles show significant anti-wear ability in a large concentration range (0.1–1.0 wt%), without a
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