ISSN   1004-0595

CN  62-1224/O4

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DDP功能化UiO-66纳米颗粒的制备及其作为润滑油纳米添加剂的摩擦学性能研究

Preparation of DDP-Functionalized UiO-66 Nanoparticles and Tribological Properties as Lubricating Oil Additives

  • 摘要: 金属有机框架(Metal-organic frameworks, MOFs)材料具有良好的机械性能、可设计的组成结构以及可调的表面物化性质,在润滑油纳米添加剂方面表现出潜在的应用前景,然而,MOFs纳米颗粒与基础油之间差的相容性限制了其进一步的发展. 本文中选择具有良好化学、机械和热稳定性的UiO-66纳米颗粒作为润滑油添加剂,并通过将3种不同分子链长和结构的二烷基二硫代磷酸(DDP)分子在UiO-66上进行组装. 借助透射电子显微镜、X-射线衍射仪、傅里叶变换红外光谱仪、激光动态光散射和高频摩擦磨损试验机对DDP修饰前后UiO-66的微观形貌、物相组成、化学结构、粒径分布和摩擦学性能进行了研究,发现DDP分子可以通过配位相互作用组装在UiO-66纳米颗粒表面而不会破坏初始MOFs的形状尺寸和结晶性,DDP的修饰有效改善了UiO-66纳米颗粒在溶剂以及基础油中的分散稳定性,进一步将其作为润滑油纳米添加剂,可表现出良好的减摩抗磨性能,并能有效提高基础油的抗载能力以及综合摩擦学性能. 最后,通过X-射线光电子能谱仪对其摩擦机理进行了研究,结果表明:DDP分子修饰的UiO-66纳米颗粒通过DDP在摩擦副表面形成了摩擦反应膜以及Zr-MOFs的“滚珠轴承”效应,有效减少了摩擦副表面的摩擦磨损.

     

    Abstract: Nanoparticle additives have been widely researched and demonstrated to extensively improve the tribological performance of lubricating oil. Generally, the traditional nanoparticle as lubricating oil additives are mainly metals, metal oxides, sulfides, carbons, nanocomposites, rare earth compounds and so on. Compared with those traditional additives, metal-organic frameworks, as a category of novel organic-inorganic hybrid materials self-assembled from metal ions and organic ligands based on coordination bonds, have good mechanical properties, designable compositions and structures, as well as adjustable physicochemical properties, and thus have potential applications in lubricating oil. However, the feeble dispersity and compatibility between metal-organic frameworks and lubricating oils restricted their further development. In this research, we selected UiO-66 nanoparticles, a zirconium-based metal-organic framework with good chemical, mechanical and thermal stability, as a novel lubricating oil additives by combining them with dialkyldithiophosphoric acid (DDP) molecules with different molecular chain lengths and structures. We had characterized the nano-crystalline morphology, phase composition, chemical structure, hydrodynamic particle size and tribological properties of UiO-66@DDP-1/-2/-3 nanoparticles using transmission electron microscope (TEM), X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR), dynamic light scattering (DLS) and high-frequency friction and wear tester. Three kinds of DDP molecules were assembled in coordination on the surface of UiO-66 nanoparticles without destroying the morphology, size, and nano-crystallinity of the pristine metal-organic framework. After DDP functionalization, the dispersion stability of UiO-66 nanoparticles in organic solvent and based lubricating oil was greatly improved. Using as a novel lubrication oil additive, UiO-66@DDP nanoparticles made an excellent contribution to improving the friction reduction and anti-wear performance of the lubricating system at specific concentrations, as well as increasing the load-carrying capability and comprehensive tribological performance of the base lubricating oil. Specifically, the optimal concentration of UiO-66@DDP-1, UiO-66@DDP-2, and UiO-66@DDP-3 were 0.6%, 0.4%, and 0.6% (mass fraction), respectively. Compared to the based lubricating oil, the 0.4% UiO-66@DDP-2 additive demonstrated the best overall tribological performance with a friction coefficient of 0.108 and a wear volume of 27 996 μm3. Meanwhile, the tribological performance of the 0.4% UiO-66@DDP-2 additive in the variable load, temperature and frequency measurements was also outstanding, with the upper limits of 300 N, 70 ℃, and 45 Hz, respectively. The mechanism of UiO-66@DDP nanoparticles for friction and wear reduction was investigated by X-ray photoelectron spectroscopy (XPS), which showed that all three kinds of UiO-66@DDP nanoparticles formed a tribofilm and contributed to the “ball bearing” effect. Our work provided insights into the future functional lubricating oil additives to facilitate the rational design of high-performance metal-organic frameworks-based materials as lubricant additives.

     

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