【作者】 高传平；

【导师】 王燕民；

【作者基本信息】 华南理工大学 ， 材料学， 2014， 博士

【摘要】 纳米颗粒材料由于自身的物理和化学特性（即，大比表面积、高扩散性、易烧结、低熔点、高硬度等），不仅使其能在摩擦副表面形成低剪切应力膜、降低摩擦系数，且对摩擦表面具有填补和修复作用，因而，其作为润滑添加剂具有优良的抗磨减摩性能。本论文主要对磁性Fe3O4纳米颗粒、纳米高岭土和纳米伊/蒙粘土作为润滑添加剂添加在#40润滑油中的摩擦学性能进行了研究。首先，采用四球摩擦磨损试验机所获得的平均摩擦系数、磨斑直径、磨损量以及润滑油最大无卡咬负荷（PB）等指标评价和研究了不同的纳米颗粒（即，磁性Fe3O4纳米颗粒、纳米高岭土和纳米伊/蒙粘土）添加在#40润滑油中的抗摩擦性能；同时，考察了纳米颗粒的微观形貌（主要针对磁性Fe3O4纳米颗粒的六方片状、八面体状和不规则状）、添加量和摩擦时间等参数对纳米颗粒在#40润滑油中抗摩擦性能的影响。结果表明：不同的纳米颗粒（即，磁性Fe3O4纳米颗粒、纳米高岭土和纳米伊/蒙粘土）在#40润滑油中均表现出良好的抗摩擦磨损性能；当分别地添加的纳米颗粒含量为最优时（即，磁性Fe3O4纳米颗粒为1.5wt%；纳米高岭土为1.0wt%；纳米伊/蒙粘土为2.0wt%），可使摩擦副的平均摩擦系数和磨斑直径最小、摩擦接触面最光滑平整、犁沟和划痕最浅，与当使用纯润滑油时的摩擦效果相比，含六方片状、八面体状和不规则状磁性纳米颗粒的润滑油的平均摩擦系数和磨斑直径分别降低58.16%、47.96%、34.69%和13.87%、11.17%和10.18%；含纳米高岭土的润滑油的摩擦系数和磨斑直径分别降低24.21%和16.43%；含纳米伊/蒙粘土的润滑油的摩擦系数降低60%。另外，对不同形貌的磁性Fe3O4纳米颗粒而言，其微观形貌是影响其在润滑油中抗摩擦性能的主要因素之一。由于六方片状磁性Fe3O4纳米颗粒薄片所接触的表面积比其它两种形貌的大得多，对摩擦副表面的覆盖更完全，摩擦化学反应形成的保护膜更均一完整；且层片之间以滑动摩擦为主（其它两种形貌的滚动和类滚动摩擦为主），因此，其抗摩擦磨损性能优于其它两种形貌的磁性纳米颗粒。其次，通过分析摩擦前后片状磁性Fe3O4纳米颗粒、纳米高岭土和纳米伊/蒙粘土的相组成、化学元素组成、非晶化程度、晶面间距、平均晶粒尺寸、磁性能和氧化转变温度等研究了润滑油中与摩擦副表面接触的纳米颗粒和与之相关的润滑油和摩擦副表面的摩擦化学性能；同时，探索了不同纳米颗粒添加剂在#40润滑油中的抗摩擦机理，重点分析和讨论了动态抗摩擦保护膜的形成和组分及其抗摩擦作用，并比较和分析了它们的抗摩擦性能特点。结果表明：与摩擦前片状磁性Fe3O4纳米颗粒、纳米高岭土和纳米伊/蒙粘土的性质相比，摩擦后纳米颗粒的非晶化程度和氧化转变温度均增大，而晶面间距和平均晶粒尺寸减小；磁性Fe3O4纳米颗粒性质经摩擦后的相组成和化学元素组成等均比摩擦前丰富。与摩擦前的纯润滑油相比，含片状磁性Fe3O4纳米颗粒的润滑油摩擦后其性质变化不明显。由于纳米高岭土和纳米伊/蒙粘土层片间含有结晶水，因此，摩擦后的润滑油中含有少量的水分。改性纳米颗粒的表面作用（即，纳米颗粒的尺寸效应、范德华力、改性形成的表面有机链和磁性Fe3O4纳米颗粒剩磁作用（Mr）产生的磁吸引力等）促使其在摩擦开始前粘附在摩擦副表面，并对其进行有效的补充修复；摩擦副持续、激烈的高速旋转摩擦形成的高速剪切力诱导磁性Fe3O4纳米颗粒、纳米高岭土和纳米伊/蒙粘土分别与摩擦副发生摩擦化学反应，最终在摩擦接触面上生成具有自修复能力、富含元素Fe、C、O和纳米颗粒特征元素（即，磁性Fe3O4纳米颗粒中的Fe元素；纳米高岭土和纳米伊/蒙粘土中的Al和Si元素）的化合物的动态抗摩擦保护膜，阻碍摩擦副间的直接接触，从而降低摩擦、减少磨损、改善和提高润滑油的摩擦学性能。另外，对比片状磁性Fe3O4纳米颗粒、纳米高岭土和纳米伊/蒙粘土在#40润滑油中的抗摩擦性能特点可知：三种纳米润滑添加剂在润滑油（#40润滑油）中均表现出良好的摩擦学性能；且纳米颗粒的微观层片结构有利于其在摩擦副表面的粘附和完全覆盖，从而有助于摩擦接触面上性能均一、覆盖完全的抗摩擦保护膜的生成；摩擦后润滑油的性质变化虽不明显，但纳米颗粒的性质（如：相组成、非晶化程度、晶面间距、平均晶粒尺寸、磁性能、氧化转变温度等）与摩擦前有较大变化。同时，三种片状润滑添加剂在摩擦表面的粘附作用方式和摩擦化学略有不同：摩擦开始时，除了纳米颗粒的尺寸效应、范德华力和改性形成的表面有机链外，磁性Fe3O4纳米颗粒还依靠剩磁作用（Mr）产生的磁力粘附在摩擦副表面；而纳米粘土薄片表面积较大，易对摩擦副表面形成完全覆盖，且在摩擦过程中更易碎裂成颗粒尺寸和薄片面积更小的碎小薄片，出现大量的不饱和键（如Si-O、Si-O-Si、-OH等），这不仅有利于其在摩擦副表面的粘附，也增强了O2的释放能力，促进摩擦副表面上摩擦化学的发生，加快表面自修复膜的生成速度，从而更好地改善摩擦副的抗摩擦性能。另外，纳米粘土在摩擦过程中还有脱水现象。再次，采用数值方法对不含和含1.5wt%含量的片状磁性Fe3O4纳米颗粒的润滑油在汽油机曲轴和连杆间形成油膜的膜厚度及其压力分布进行了模拟计算和分析。结果表明，与纯润滑油相比，片状磁性Fe3O4纳米颗粒（含量为1.5wt%）的加入对润滑过程中的油膜膜厚影响较小，甚至轴承某些位置的膜厚有所减小；但其油膜的承载压力显著提高，这与磁性纳米颗粒加入后所引起的润滑油的最大无卡咬负荷（PB）提高的实验结果一致。最后，利用汽油发动机检验和评价了片状磁性Fe3O4纳米颗粒作为润滑添加剂在#40润滑油中的实际抗磨减摩效果。结果表明：当含有1.5wt%片状磁性Fe3O4纳米颗粒的润滑油加入汽油发动机时，摩擦后的连杆表面更平整光滑、犁沟更浅，表面粗糙度比采用纯润滑油时降低约25%；且表面元素分布更均匀；同时，汽油机的时平均耗油量比采用纯润滑油时降低约10%；经检测，摩擦过程中所生成的抗摩擦自修复保护膜的厚度为40～50nm。更多还原

【Abstract】 As lubricating additives, inorganic nanoparticles (NPs) have superior anti-wear andanti-friction properties due to their distinctive physical and chemical characterizations (i.e.,great specific surface area, superior diffusivity, low sintering temperature, low fusion and highhardness, etc.). The multilayer films with a lower shearing are formed on the friction pairsurfaces in the presence of NPs in lubricating oil, resulting in the reduction of the averagefriction coefficient, and the filling and reparation of the friction pair surfaces. This dissertationwas thus to investigate the tribological properties of the magnetic Fe3O4NPs, kaolin clay NPsand Iillite/Smectite (I/S) clay NPs in#40lubricating oil as lubricating additives.Firstly, the anti-friction properties of various NPs (i.e., magnetic Fe3O4NPs, kaolin clayNPs and I/S clay NPs) were evaluated by average friction coefficient (c f), wear scar diameter(WSD), wear weight and maximum non-seizure load (PB) of lubricating oil, etc., which wereobtained in a four-ball tribo-tester, respectively. The effects of micro-morphologies of Fe3O4NPs (i.e., hexagonal, octahedral and irregular morphologies), NPs concentration in thelubricating oil and friction duration on the anti-friction properties in#40lubricating oil werealso investigated. The results show that all the NPs additives (i.e., magnetic Fe3O4NPs, kaolinclay NPs and I/S clay NPs) have superior anti-friction properties. The optimum concentrationsfor Fe3O4NPs, kaolin clay NPs and I/S clay NPs as an additive in lubricating oil are1.5,1.0and2.0wt%, respectively. The low values of averagec fand WSD of the friction pairsurfaces are obtained at each optimum concentration. Compared to the pure lubricating oil,the WSD was reduced by13.87,11.17, and10.18%and thec fwas reduced by58.16,47.96,and34.69%in the case of the oils containing Fe3O4NPs with hexagonal, octahedral, andirregular morphologies, respectively, at the concentration of1.5wt%. In the case of the oilscontaining kaolin clay NPs at the concentration of1.0wt%, the WSD andc fwere reducedby16.43%and24.21%, respectively. In the case of the oils containing I/S clay NPs at theconcentration of2.0wt%, thec fwas reduced by60%. The friction pair surfaces appear smooth and the furrows are shallow after the friction in the oils with NPs. In addition, thehexagonal morphology of Fe3O4NPs has a positive effect on the anti-friction properties ratherthan the octahedral and irregular morphologies due to its sliding friction mechanism, resultingin the more whole coverage for the friction pair surfaces and the more uniform protectivefilm.Secondly, the tribochemical behaviors of the NPs on the friction surfaces in thelubricating oil were investigated via the analysis of the properties of NPs (i.e., magnetic Fe3O4NPs with hexagonal morphology, kaolin clay NPs and I/S clay NPs), such as phasecomposition, chemical elemental composition, non-crystallizing degree, interplanar spacing,average grain size, magnetic characterization and transition temperature of oxidation, etc..The tribochemical properties of the lubricating oil and the friction pair surfaces related to theNPs were also analyzed. Moreover, the anti-friction mechanism of various NPs in lubricatingoil as additives were discussed, particularly for the formation, chemical composition andanti-friction properties of the dynamic self-repairing film, and the tribological properties ofvarious NPs (i.e., magnetic Fe3O4NPs with hexagonal morphology, kaolin clay NPs and I/Sclay NPs). The results show that, compared to the properties of the original NPs (beforefriction), the non-crystallizing degree and transition temperature of oxidation are reduced forall the NPs after friction. The phase composition and chemical composition on the frictionpair surfaces lubricated with the lubricating oil containing Fe3O4NPs with hexagonalmorphology at a concentration of1.5wt%are most abundant among all the NPs. Theproperties of the lubricating oil containing Fe3O4NPs with hexagonal morphology after48-dfriction does not change. There exists crystal water in the lubricating oil when kaolin clay NPsand I/S NPs are used. It is indicated that the adhesion between the NPs (i.e., Fe3O4NPs withhexagonal morphology, kaolin clay NPs and I/S clay NPs) and the friction pair surfaces canbe enhanced due to the presence of van der Waals force, organic chain introduced by surfacemodification, and magnetic force from the remanent magnetization (Mr) of Fe3O4NPs. Thetribochemical reactions between the NPs and the friction pairs surface occur in the drasticfriction, finally resulting in the formation of a mono-or multi-layer self-repairing film with various phases containing the elements Fe, C, O and the characteristic elements (i.e., elementFe for Fe3O4NPs and elements Al and Si for kaolin clay NPs and I/S clay NPs, respectively.)on the friction surfaces. The film could prevent the direct contact between friction pairsurfaces and decrease the friction and wear for the improvement of the tribological propertiesof the lubricating oil.In addition, compared to the anti-friction properties of various NPs (i.e., Fe3O4NPs withhexagonal morphology, kaolin clay NPs and I/S clay NPs) in lubricating oil, all the NPsadditives have superior tribological properties, and the adhesion and coverage of various NPson the friction pair surfaces are enhanced due to the layered structure, resulting in theformation of the uniform and whole coverage self-repairing film on the friction pair surfaces.It is indicated that the chemical composition of the lubricating oil containing various NPsafter48-h friction does not change. However，the physical and chemical properties of the NPsafter friction (i.e., phase composition, crystallizing degree, interplanar spacing, average grainsize, magnetic properties and transition temperature of oxidation, etc.) do vary. Besides thesize effect, van der Waals force, organic chain introduced by surface modification, theadhesion between Fe3O4NPs with hexagonal morphology and the friction pair surfaces can beenhanced due to the presence of magnetic force from the remanent magnetization (Mr). Thefriction pair surfaces can be entirely coverd by kaolin clay NPs and I/S clay NPs due to theirlarge surface areas and the unsaturated bonds (like Si-O、Si-O-Si、-OH). The release of O2from the clay NPs during friction results in the tribochemical reactions and the formation ofthe self-repairing film on the friction pair surface to improve the anti-friction properties of thefriction pairs.Thirdly, the thickness and pressure distribution of the oil film without and with Fe3O4NPs with hexagonal morphology at a concertration of1.5wt%between the crankshaft andconnecting rod of a gasoline engine were analyzed by a numerical method. The results showthat, compared to those of the lubricating oil, Fe3O4NPs with hexagonal morphology have aslight impact on the thickness of the oil film, even less in some positions on the journalbearing. However, the load carrying capacity of the oil film can be improved, which is in accordance with the PBresults of lubricating oil containing Fe3O4NPs.Finally, the effect of Fe3O4NPs with hexagonal morphology in#40lubricating oil on theanti-friction performance in a gasoline engine was evaluated. The results show that theconnecting rod surface appears smooth, the furrows are shallow and the chemical elementsdistribution on friction surface are uniform after friction in the lubricating oils containingFe3O4NPs with hexagonal morphology. The surface roughness and the average gasolineconsumption are reduced by approximately25%and10%, respectively. Moreover, thethickness of self-repairing film on the friction surface determined by X-ray photoelectronspectroscopy (XPS) is40～50nm.更多还原