【作者】 邱舒；

【导师】 李长生；

【作者基本信息】 江苏大学 ， 材料科学与工程， 2024， 博士

【摘要】 普遍存在的摩擦磨损现象会导致机械部件的损坏及能量的损耗,从而引发不可估量的经济损失。润滑油作为缓解摩擦磨损的有效材料,已在行业内广泛采用。然而,单纯使用润滑油无法满足日益增长的润滑需求,润滑油添加剂的引入便显得尤为重要。润滑油添加剂可通过特定的化学或物理手段,显著减少磨损,进一步提升润滑油的性能。二维纳米材料具有低剪切强度,高比表面积、较好的平面内固体强度和优异的表界面稳定性,可用于制备高性能润滑油添加剂,在摩擦学领域受到了重点关注。如何在保持二维纳米材料原有性能的前提下,通过合理配比二维纳米材料与其他纳米材料,协同构筑新型功能材料来提升润滑性能、拓宽应用范围,使之高效地应用于机械、新能源及新材料等领域,受到研究者的重点关注。本文以绿色环保菜籽油为基础油,以几种典型的二维纳米材料,如高强韧的氧化石墨烯（GO）、优异自润滑性的二硫化钼（Mo S₂）以及新兴润滑添加剂二维金属有机框架（2D MOFs）等,为研究对象,通过在二维纳米材料表面可控制备出二维纳米杂化材料,研究其化学组成、微观结构和协同润滑机制,取得如下结论:首先,以具有高强度、卓越的柔韧性和高比表面积的GO纳米片为研究对象,通过简单的溶剂热方法,将具有良好承载性和润滑性的Ce O₂纳米颗粒原位锚定在GO纳米片表面,构建GO/Ce O₂纳米杂化材料,研究其对菜籽油的摩擦学机制。结果表明,GO为Ce O₂纳米颗粒提供了理想吸附平台,Ce O₂纳米颗粒能彼此隔离且边界清晰吸附着在GO纳米片表面,且所制备GO/Ce O₂纳米杂化材料能在菜籽油中保持良好分散稳定性。同时,添加0.1wt.%GO/Ce O₂纳米杂化材料后摩擦系数降低36.5%,磨损率降低62.4%。这主要是由于GO纳米片表面存在的大量的官能团为Ce O₂纳米颗粒提供了分散平稳的锚定点,且均匀分布的Ce O₂纳米颗粒与GO纳米片通过调节粘度增加了菜籽油的承载能力。随着GO纳米片在滑动过程中不断碎片化形成润滑膜,促使Ce O₂纳米颗粒在滑动表面上释放,促进形成更稳定的摩擦膜,从而提高GO/Ce O₂二维纳米杂化材料在菜籽油中的摩擦学性能。其次,选择具有优异自润滑性能的二维纳米材料Mo S₂纳米片为研究对象,通过多巴胺（DA）在其表面氧化自聚合提供大量活性位点,再利用水热法在其表面构筑粒径在2-4nm Ce O₂超细纳米颗粒,成功构筑Ce O₂/PDA/Mo S₂杂化纳米材料,并研究了其对菜籽油的摩擦学性能增强机制。结果表明,Ce O₂/PDA/Mo S₂纳米杂化材料在润滑油中具有较好的分散稳定性。当添加0.5 wt.%的Ce O₂/PDA/Mo S₂纳米杂化材料到菜籽油中时,摩擦系数降低30.5%,磨损率降低78.03%。磨痕深度降低57.2%,磨痕宽度降低38.0%。由于Mo S₂纳米片为Ce O₂纳米颗粒提供了平稳的支撑平台,有效约束Ce O₂超细纳米颗粒因为表面能过大造成的团聚或分散不均现象。此外,Ce O₂超细纳米颗粒填充在摩擦表面的犁沟处,对磨损表面进行有效地补充修复,随着摩擦的持续进行,最终在摩擦接触面上形成含有Mo、Fe和Ce等多种元素构成的摩擦膜,从而改善和提高润滑油的摩擦学性能。再次,在前期研究基础上,进一步采用温和条件下的水热反应,构筑一种由Ce O₂纳米片与Mo S₂纳米片形成的2D/2D纳米杂化材料,并研究了其微观结构、化学组成以及润滑机制。结果显示,Ce O₂纳米片嵌入Mo S₂纳米片表面,在可以防止Ce O₂纳米材料的聚集的同时充分利用Ce O₂纳米片的高承载能力和Mo S₂纳米片的高润滑能力,协同增强油菜籽油的润滑性能。Mo S₂/Ce O₂纳米杂化材料的摩擦系数减小42.71%,磨损率减小70.14%。Mo S₂和Ce O₂之间的协同效应以及在磨损界面形成的稳定摩擦膜是摩擦性能增强的主要原因。具体为:Mo S₂纳米片能防止磨损表面的直接接触,并促使沉积膜的形成以减少磨损。Mo S₂纳米片的存在作为Ce O₂片的锚定空间,增强了Ce O₂在菜籽油中的分散性。“硬”的Ce O₂纳米片为“软”Mo S₂纳米片提供支撑,延长Mo S₂在摩擦过程中发生断裂和变形的时间,从而增强Mo S₂/Ce O₂纳米杂化材料的承载能力和极限压力。Mo S₂/Ce O₂纳米杂化材料在摩擦界面受到摩擦力的作用下发生变形和断裂,Ce O₂纳米片对摩擦表面的粗糙接触点进行抛光,形成了相对光滑的摩擦表面。由于外部压力和摩擦热,在光滑的界面上形成了包含Mo O₃、Mo S₂、Ce O₂、Fe₂O₃、Fe SO₄和Fe Cr O₄的稳定摩擦转移和化学反应膜。最后,鉴于2D MOFs具有超薄厚度、低密度、高孔隙率和机械柔性等特征,我们对这种新型功能型材料在润滑领域中的应用开展初步研究。通过有机分子（ODA）改性和二维杂化改性（Ni-MOF/GO）两种不同方法对Ni-MOF纳米片进行改性。研究发现改性后Ni-MOF纳米片在菜籽油中均展现良好的分散稳定性,提升了菜籽油的摩擦学性能。结果表明,ODA-Ni-MOF纳米杂化材料和Ni-MOF/GO纳米杂化材料的COF分别降低29.62%和25.75%,磨损率分别降低89.18%和93.60%。通过对磨损表面的分析揭示了润滑机制,ODA分子从Ni-MOF表面分离,释放出的有机表面改性剂和高化学活性的Ni可以吸附到滑动钢表面,产生边界润滑膜,从而提高耐磨性;而GO纳米片可防止摩擦表面之间的直接接触以减少磨损,为Ni-MOF提供了支撑平面,有效改善Ni-MOF纳米片在菜籽油中团聚问题。随着磨损过程的进行,Ni-MOF纳米片的填充作用降低了滑动界面的表面粗糙度,从而形成相对光滑的摩擦表面。同时在外部压力和摩擦热的作用下,形成含有更高比例的铁和镍元素的摩擦膜。更多还原

【Abstract】 The common phenomenon of friction and wear can lead to damage to mechanical components and energy loss,resulting in incalculable economic losses.Lubricating oil,as an effective material for alleviating friction and wear,has been widely used in modern industries.However,the use of lubricating oil alone cannot meet the growing actual demands,making the introduction of lubricating oil additives particularly important.Lubricant additives can further enhance the performance of lubricating oil and significantly reduce wear through specific chemical or physical means.Two-dimensional（2D）nanomaterials,with low shear strength,high specific surface area,good in-plane solid strength,and excellent interfacial stability,have great potential in reducing friction and relieve wear,and can be used to prepare high-performance lubricant additives,attracting significant attention in the field of tribology.While maintaining the inherent properties of 2D nanomaterials,synergistically constructing new functional materials by properly combining2D nanomaterials with other nanoparticles can enhance lubrication performance,expand application scope,and efficiently apply them in fields such as machinery and new energy.Based on environmentally-friendly rapeseed oil as the base oil,this thesis investigated several typical two-dimensional nanomaterials,including high strength and toughness graphene oxide（GO）,self-lubricating molybdenum disulfide（Mo S₂）,and the emerging lubrication additive two-dimensional metal-organic frameworks（2D MOFs）.By controllably preparing two-dimensional nano-hybrid materials on the surface of these nanomaterials,we studied their chemical composition,microstructure,and synergistic lubrication mechanism,and the following conclusions:Firstly,taking GO nanosheets with high strength,excellent flexibility,and high specific surface area as the object,Ce O₂ nanoparticles with good load-bearing and lubrication properties were anchored in situ on the surface of GO nanosheets through a simple solvent thermal method to construct GO/Ce O₂ nanohybrid and study their tribological mechanism on rapeseed oil.The results indicate that GO nanosheets provide an ideal platform for the uniform adsorption of Ce O₂nanoparticles.The Ce O₂ nanoparticles are isolated from each other and adhere clearly to the surface of GO nanosheets,and the prepared GO/Ce O₂ nanohybrid can maintain good dispersion and stability in rapeseed oil.Meanwhile,after adding 0.1 wt.%GO/Ce O₂ nanohybrid,the friction coefficient（COF）decreases by 36.5%,and the wear rate decreases by 62.4%.This is mainly because the abundant functional groups on the surface of GO nanosheets provide stable anchoring points for Ce O₂ nanoparticles.The uniformly distributed Ce O₂ nanoparticles and GO nanosheets can increase the carrying capacity of rapeseed oil by adjusting viscosity.As the GO nanosheets continuously fragmentize during sliding to form a lubricating film,it prompts the release of Ce O₂nanoparticles on the sliding surface,promoting the formation of a more stable transfer film,thereby improving the tribological performance of GO/Ce O₂ nanohybrid in rapeseed oil.Secondly,taking the 2D Mo S₂ nanosheets with excellent self-lubricating performance as the target,abundant active sites were provided by dopamine（DA）oxidation self-polymerization on its surface.Subsequently,Ce O₂ ultrafine nanoparticles with a particle size of 2-4 nm were constructed on its surface using a hydrothermal method.Ce O₂/PDA/Mo S₂nanohybrid was successfully constructed,and their enhancement mechanism on the tribological performance of rapeseed oil was studied.Ce O₂/PDA/Mo S₂ nanohybrid exhibited good dispersion and stability in rapeseed oil.When adding 0.5 wt.%Ce O₂/PDA/Mo S₂ nanohybrid,the friction coefficient of rapeseed oil decreased by 30.5%,and the wear rate decreased by 78.03%.The depth of worn surface decreased by 57.2%,and the width decreased by 38.0%.Mo S₂ nanosheets provided a stable support platform for Ce O₂ nanoparticles,effectively restraining the aggregation or uneven dispersion of Ce O₂ ultrafine nanoparticles caused by excessive surface energy.Ce O₂ ultrafine nanoparticles filled in the furrows on the worn surface,effectively filling and repairing the worn surface.As friction continues,a friction transfer film composed of multiple elements such as Mo,Fe,and Ce was eventually formed on the friction contact surface,thereby improving and enhancing the tribological performance of the lubricant.Furthermore,based on previous research,we successfully constructed a 2D/2D nanohybrid composed of Ce O₂ nanosheets and Mo S₂ nanosheets through a hydrothermal reaction under mild conditions,and its microstructure,chemical composition,and tribological mechanism were investigated.The results show that Ce O₂ nanosheets are embedded on the surface of Mo S₂nanosheets,which can prevent the aggregation of Ce O₂ nanomaterials while fully utilizing the high load-bearing capacity of Ce O₂ nanosheets and the high lubrication ability of Mo S₂ nanosheets,synergistically enhancing the tribological performance of rapeseed oil.The COF of Mo S₂/Ce O₂nanohybrid decreased by 42.71%,and the wear rate decreased by 70.14%.The synergistic effect between Mo S₂ and Ce O₂ and the stable transfer film formed at the interface are the main reasons for the enhanced tribologocal performance.Specifically,Mo S₂ nanosheets prevent direct contact of the worn surface and promote the formation of deposition films to reduce wear.The presence of Mo S₂ nanosheets serves as anchoring space for Ce O₂nanosheets,thereby enhancing the dispersibility of Ce O₂ in rapeseed oil.The“hard”Ce O₂ provide support for the“soft”Mo S₂nanosheets,prolonging the time for fracture and deformation of Mo S₂ during sliding process,thereby enhancing the load-bearing capacity and ultimate pressure of Mo S₂/Ce O₂ nanohybrid.During sliding,Mo S₂/Ce O₂ nanohybrid undergo deformation and fracture at the friction interface under the action of frictional forces,and Ce O₂ nanosheets polish the rough contact points on the friction surface,forming a relatively smooth worn surface.Due to external pressure and frictional heat,a stable friction transfer and chemical reaction film containing Mo O₃,Mo S₂,Ce O₂,Fe₂O₃,Fe SO₄,and Fe Cr O₄ is formed on the smooth interface.Finally,due to their ultra-thin thickness,low density,high porosity and mechanical flexibility,we conducted preliminary research on the emerging functional material in lubricating additives,namely two-dimensional metal-organic frameworks（2D MOFs）.Ni-MOF nanosheets through two different methods were modified:organic molecule（ODA）modification and 2D nanohybrid modification（Ni-MOF/GO）.The research found that the modified Ni-MOF nanosheets exhibited excellent dispersion and stability in rapeseed oil and improved the tribological performance of rapeseed oil.The results indicate that the COF of ODA-Ni-MOF nanohybrid and Ni-MOF/GO nanohybrid decreased by 29.62%and 25.75%,respectively,and the wear rates decreased by 89.18%and 93.60%,respectively.Analysis of the worn surface revealed the tribological mechanism:ODA molecules separated from the surface of Ni-MOF,and the released organic surface modifier and highly chemically active Ni could adsorb onto the steel surface,forming a boundary lubricating film,thereby enhancing wear resistance.Meanwhile,GO nanosheets can prevent direct contact between the worn surfaces to relieve wear,provide a support plane for Ni-MOF,and effectively alleviate the aggregation problem of Ni-MOF nanosheets in rapeseed oil.As the sliding process progresses,the filling effect of Ni-MOF nanosheets reduces the surface roughness of the interface,thereby forming a more smooth worn surface.Simultaneously,under the influence of external pressure and frictional heat,a friction transfer film containing a higher proportion of iron and nickel elements is formed.更多还原